Commit message: tcp: make challenge acks less predictable

Yue Cao claims that current host rate limiting of challenge ACKS
(RFC 5961) could leak enough information to allow a patient attacker
to hijack TCP sessions. He will soon provide details in an academic
paper.

This patch increases the default limit from 100 to 1000, and adds
some randomization so that the attacker can no longer hijack
sessions without spending a considerable amount of probes.

Based on initial analysis and patch from Linus.

Note that we also have per socket rate limiting, so it is tempting
to remove the host limit in the future.

v2: randomize the count of challenge acks per second, not the period.

Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2")
Reported-by: Yue Cao <ycao009@ucr.edu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2016-5696
CWE: CWE-200
Vulnerability description: net/ipv4/tcp_input.c in the Linux kernel before 4.7 does not properly determine the rate of challenge ACK segments, which makes it easier for remote attackers to hijack TCP sessions via a blind in-window attack.

Project: net
File: tcp_input.c

void tcp_rcv_space_adjust(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int time;
	int copied;

	time = tcp_time_stamp - tp->rcvq_space.time;
	if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
		return;

	/* Number of bytes copied to user in last RTT */
	copied = tp->copied_seq - tp->rcvq_space.seq;
	if (copied <= tp->rcvq_space.space)
		goto new_measure;

	/* A bit of theory :
	 * copied = bytes received in previous RTT, our base window
	 * To cope with packet losses, we need a 2x factor
	 * To cope with slow start, and sender growing its cwin by 100 %
	 * every RTT, we need a 4x factor, because the ACK we are sending
	 * now is for the next RTT, not the current one :
	 * <prev RTT . ><current RTT .. ><next RTT .... >
	 */

	if (sysctl_tcp_moderate_rcvbuf &&
	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
		int rcvwin, rcvmem, rcvbuf;

		/* minimal window to cope with packet losses, assuming
		 * steady state. Add some cushion because of small variations.
		 */
		rcvwin = (copied << 1) + 16 * tp->advmss;

		/* If rate increased by 25%,
		 *	assume slow start, rcvwin = 3 * copied
		 * If rate increased by 50%,
		 *	assume sender can use 2x growth, rcvwin = 4 * copied
		 */
		if (copied >=
		    tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
			if (copied >=
			    tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
				rcvwin <<= 1;
			else
				rcvwin += (rcvwin >> 1);
		}

		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
		while (tcp_win_from_space(rcvmem) < tp->advmss)
			rcvmem += 128;

		rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
		if (rcvbuf > sk->sk_rcvbuf) {
			sk->sk_rcvbuf = rcvbuf;

			/* Make the window clamp follow along.  */
			tp->window_clamp = rcvwin;
		}
	}
	tp->rcvq_space.space = copied;

new_measure:
	tp->rcvq_space.seq = tp->copied_seq;
	tp->rcvq_space.time = tcp_time_stamp;
}

Project: net
File: tcp_input.c

static void tcp_add_reno_sack(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 prior_sacked = tp->sacked_out;

	tp->sacked_out++;
	tcp_check_reno_reordering(sk, 0);
	if (tp->sacked_out > prior_sacked)
		tp->delivered++; /* Some out-of-order packet is delivered */
	tcp_verify_left_out(tp);
}

Project: net
File: tcp_input.c

static void tcp_mtup_probe_success(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	/* FIXME: breaks with very large cwnd */
	tp->prior_ssthresh = tcp_current_ssthresh(sk);
	tp->snd_cwnd = tp->snd_cwnd *
		       tcp_mss_to_mtu(sk, tp->mss_cache) /
		       icsk->icsk_mtup.probe_size;
	tp->snd_cwnd_cnt = 0;
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->snd_ssthresh = tcp_current_ssthresh(sk);

	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
	icsk->icsk_mtup.probe_size = 0;
	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
}

Project: net
File: tcp_input.c

static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Check #1 */
	if (tp->rcv_ssthresh < tp->window_clamp &&
	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
	    !tcp_under_memory_pressure(sk)) {
		int incr;

		/* Check #2. Increase window, if skb with such overhead
		 * will fit to rcvbuf in future.
		 */
		if (tcp_win_from_space(skb->truesize) <= skb->len)
			incr = 2 * tp->advmss;
		else
			incr = __tcp_grow_window(sk, skb);

		if (incr) {
			incr = max_t(int, incr, 2 * skb->len);
			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
					       tp->window_clamp);
			inet_csk(sk)->icsk_ack.quick |= 1;
		}
	}
}

Project: net
File: tcp_input.c

static inline void tcp_end_cwnd_reduction(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
		tp->snd_cwnd = tp->snd_ssthresh;
		tp->snd_cwnd_stamp = tcp_time_stamp;
	}
	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
}

Project: net
File: tcp_input.c

void tcp_simple_retransmit(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	unsigned int mss = tcp_current_mss(sk);
	u32 prior_lost = tp->lost_out;

	tcp_for_write_queue(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;
		if (tcp_skb_seglen(skb) > mss &&
		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
				tp->retrans_out -= tcp_skb_pcount(skb);
			}
			tcp_skb_mark_lost_uncond_verify(tp, skb);
		}
	}

	tcp_clear_retrans_hints_partial(tp);

	if (prior_lost == tp->lost_out)
		return;

	if (tcp_is_reno(tp))
		tcp_limit_reno_sacked(tp);

	tcp_verify_left_out(tp);

	/* Don't muck with the congestion window here.
	 * Reason is that we do not increase amount of _data_
	 * in network, but units changed and effective
	 * cwnd/ssthresh really reduced now.
	 */
	if (icsk->icsk_ca_state != TCP_CA_Loss) {
		tp->high_seq = tp->snd_nxt;
		tp->snd_ssthresh = tcp_current_ssthresh(sk);
		tp->prior_ssthresh = 0;
		tp->undo_marker = 0;
		tcp_set_ca_state(sk, TCP_CA_Loss);
	}
	tcp_xmit_retransmit_queue(sk);
}

Project: net
File: tcp_input.c

static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb1;
	u32 seq, end_seq;

	tcp_ecn_check_ce(tp, skb);

	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
		tcp_drop(sk, skb);
		return;
	}

	/* Disable header prediction. */
	tp->pred_flags = 0;
	inet_csk_schedule_ack(sk);

	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);

	skb1 = skb_peek_tail(&tp->out_of_order_queue);
	if (!skb1) {
		/* Initial out of order segment, build 1 SACK. */
		if (tcp_is_sack(tp)) {
			tp->rx_opt.num_sacks = 1;
			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
			tp->selective_acks[0].end_seq =
						TCP_SKB_CB(skb)->end_seq;
		}
		__skb_queue_head(&tp->out_of_order_queue, skb);
		goto end;
	}

	seq = TCP_SKB_CB(skb)->seq;
	end_seq = TCP_SKB_CB(skb)->end_seq;

	if (seq == TCP_SKB_CB(skb1)->end_seq) {
		bool fragstolen;

		if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
		} else {
			tcp_grow_window(sk, skb);
			kfree_skb_partial(skb, fragstolen);
			skb = NULL;
		}

		if (!tp->rx_opt.num_sacks ||
		    tp->selective_acks[0].end_seq != seq)
			goto add_sack;

		/* Common case: data arrive in order after hole. */
		tp->selective_acks[0].end_seq = end_seq;
		goto end;
	}

	/* Find place to insert this segment. */
	while (1) {
		if (!after(TCP_SKB_CB(skb1)->seq, seq))
			break;
		if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
			skb1 = NULL;
			break;
		}
		skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
	}

	/* Do skb overlap to previous one? */
	if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
		if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
			/* All the bits are present. Drop. */
			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
			tcp_drop(sk, skb);
			skb = NULL;
			tcp_dsack_set(sk, seq, end_seq);
			goto add_sack;
		}
		if (after(seq, TCP_SKB_CB(skb1)->seq)) {
			/* Partial overlap. */
			tcp_dsack_set(sk, seq,
				      TCP_SKB_CB(skb1)->end_seq);
		} else {
			if (skb_queue_is_first(&tp->out_of_order_queue,
					       skb1))
				skb1 = NULL;
			else
				skb1 = skb_queue_prev(
					&tp->out_of_order_queue,
					skb1);
		}
	}
	if (!skb1)
		__skb_queue_head(&tp->out_of_order_queue, skb);
	else
		__skb_queue_after(&tp->out_of_order_queue, skb1, skb);

	/* And clean segments covered by new one as whole. */
	while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
		skb1 = skb_queue_next(&tp->out_of_order_queue, skb);

		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
			break;
		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
					 end_seq);
			break;
		}
		__skb_unlink(skb1, &tp->out_of_order_queue);
		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
				 TCP_SKB_CB(skb1)->end_seq);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
		tcp_drop(sk, skb1);
	}

add_sack:
	if (tcp_is_sack(tp))
		tcp_sack_new_ofo_skb(sk, seq, end_seq);
end:
	if (skb) {
		tcp_grow_window(sk, skb);
		skb_set_owner_r(skb, sk);
	}
}

Project: net
File: tcp_input.c

static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
					struct tcp_sack_block *next_dup,
					struct tcp_sacktag_state *state,
					u32 start_seq, u32 end_seq,
					bool dup_sack_in)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *tmp;

	tcp_for_write_queue_from(skb, sk) {
		int in_sack = 0;
		bool dup_sack = dup_sack_in;

		if (skb == tcp_send_head(sk))
			break;

		/* queue is in-order => we can short-circuit the walk early */
		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
			break;

		if (next_dup  &&
		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
			in_sack = tcp_match_skb_to_sack(sk, skb,
							next_dup->start_seq,
							next_dup->end_seq);
			if (in_sack > 0)
				dup_sack = true;
		}

		/* skb reference here is a bit tricky to get right, since
		 * shifting can eat and free both this skb and the next,
		 * so not even _safe variant of the loop is enough.
		 */
		if (in_sack <= 0) {
			tmp = tcp_shift_skb_data(sk, skb, state,
						 start_seq, end_seq, dup_sack);
			if (tmp) {
				if (tmp != skb) {
					skb = tmp;
					continue;
				}

				in_sack = 0;
			} else {
				in_sack = tcp_match_skb_to_sack(sk, skb,
								start_seq,
								end_seq);
			}
		}

		if (unlikely(in_sack < 0))
			break;

		if (in_sack) {
			TCP_SKB_CB(skb)->sacked =
				tcp_sacktag_one(sk,
						state,
						TCP_SKB_CB(skb)->sacked,
						TCP_SKB_CB(skb)->seq,
						TCP_SKB_CB(skb)->end_seq,
						dup_sack,
						tcp_skb_pcount(skb),
						&skb->skb_mstamp);

			if (!before(TCP_SKB_CB(skb)->seq,
				    tcp_highest_sack_seq(tp)))
				tcp_advance_highest_sack(sk, skb);
		}

		state->fack_count += tcp_skb_pcount(skb);
	}
	return skb;
}

Project: net
File: tcp_input.c

static inline int tcp_fackets_out(const struct tcp_sock *tp)
{
	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
}

Project: net
File: tcp_input.c

static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int chunk = skb->len - hlen;
	int err;

	if (skb_csum_unnecessary(skb))
		err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
	else
		err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);

	if (!err) {
		tp->ucopy.len -= chunk;
		tp->copied_seq += chunk;
		tcp_rcv_space_adjust(sk);
	}

	return err;
}

Project: net
File: tcp_input.c

void tcp_init_buffer_space(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int maxwin;

	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
		tcp_fixup_rcvbuf(sk);
	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
		tcp_sndbuf_expand(sk);

	tp->rcvq_space.space = tp->rcv_wnd;
	tp->rcvq_space.time = tcp_time_stamp;
	tp->rcvq_space.seq = tp->copied_seq;

	maxwin = tcp_full_space(sk);

	if (tp->window_clamp >= maxwin) {
		tp->window_clamp = maxwin;

		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
			tp->window_clamp = max(maxwin -
					       (maxwin >> sysctl_tcp_app_win),
					       4 * tp->advmss);
	}

	/* Force reservation of one segment. */
	if (sysctl_tcp_app_win &&
	    tp->window_clamp > 2 * tp->advmss &&
	    tp->window_clamp + tp->advmss > maxwin)
		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);

	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

Project: net
File: tcp_input.c

void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	tcp_set_state(sk, TCP_ESTABLISHED);

	if (skb) {
		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
		security_inet_conn_established(sk, skb);
	}

	/* Make sure socket is routed, for correct metrics.  */
	icsk->icsk_af_ops->rebuild_header(sk);

	tcp_init_metrics(sk);

	tcp_init_congestion_control(sk);

	/* Prevent spurious tcp_cwnd_restart() on first data
	 * packet.
	 */
	tp->lsndtime = tcp_time_stamp;

	tcp_init_buffer_space(sk);

	if (sock_flag(sk, SOCK_KEEPOPEN))
		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));

	if (!tp->rx_opt.snd_wscale)
		__tcp_fast_path_on(tp, tp->snd_wnd);
	else
		tp->pred_flags = 0;

	if (!sock_flag(sk, SOCK_DEAD)) {
		sk->sk_state_change(sk);
		sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
	}
}

Project: net
File: tcp_input.c

static bool tcp_fast_parse_options(const struct sk_buff *skb,
				   const struct tcphdr *th, struct tcp_sock *tp)
{
	/* In the spirit of fast parsing, compare doff directly to constant
	 * values.  Because equality is used, short doff can be ignored here.
	 */
	if (th->doff == (sizeof(*th) / 4)) {
		tp->rx_opt.saw_tstamp = 0;
		return false;
	} else if (tp->rx_opt.tstamp_ok &&
		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
		if (tcp_parse_aligned_timestamp(tp, th))
			return true;
	}

	tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
		tp->rx_opt.rcv_tsecr -= tp->tsoffset;

	return true;
}

Project: net
File: tcp_input.c

static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
			       u32 prior_snd_una, int *acked,
			       struct tcp_sacktag_state *sack)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct skb_mstamp first_ackt, last_ackt, now;
	struct tcp_sock *tp = tcp_sk(sk);
	u32 prior_sacked = tp->sacked_out;
	u32 reord = tp->packets_out;
	bool fully_acked = true;
	long sack_rtt_us = -1L;
	long seq_rtt_us = -1L;
	long ca_rtt_us = -1L;
	struct sk_buff *skb;
	u32 pkts_acked = 0;
	bool rtt_update;
	int flag = 0;

	first_ackt.v64 = 0;

	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
		u8 sacked = scb->sacked;
		u32 acked_pcount;

		tcp_ack_tstamp(sk, skb, prior_snd_una);

		/* Determine how many packets and what bytes were acked, tso and else */
		if (after(scb->end_seq, tp->snd_una)) {
			if (tcp_skb_pcount(skb) == 1 ||
			    !after(tp->snd_una, scb->seq))
				break;

			acked_pcount = tcp_tso_acked(sk, skb);
			if (!acked_pcount)
				break;

			fully_acked = false;
		} else {
			/* Speedup tcp_unlink_write_queue() and next loop */
			prefetchw(skb->next);
			acked_pcount = tcp_skb_pcount(skb);
		}

		if (unlikely(sacked & TCPCB_RETRANS)) {
			if (sacked & TCPCB_SACKED_RETRANS)
				tp->retrans_out -= acked_pcount;
			flag |= FLAG_RETRANS_DATA_ACKED;
		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
			last_ackt = skb->skb_mstamp;
			WARN_ON_ONCE(last_ackt.v64 == 0);
			if (!first_ackt.v64)
				first_ackt = last_ackt;

			reord = min(pkts_acked, reord);
			if (!after(scb->end_seq, tp->high_seq))
				flag |= FLAG_ORIG_SACK_ACKED;
		}

		if (sacked & TCPCB_SACKED_ACKED) {
			tp->sacked_out -= acked_pcount;
		} else if (tcp_is_sack(tp)) {
			tp->delivered += acked_pcount;
			if (!tcp_skb_spurious_retrans(tp, skb))
				tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
		}
		if (sacked & TCPCB_LOST)
			tp->lost_out -= acked_pcount;

		tp->packets_out -= acked_pcount;
		pkts_acked += acked_pcount;

		/* Initial outgoing SYN's get put onto the write_queue
		 * just like anything else we transmit.  It is not
		 * true data, and if we misinform our callers that
		 * this ACK acks real data, we will erroneously exit
		 * connection startup slow start one packet too
		 * quickly.  This is severely frowned upon behavior.
		 */
		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
			flag |= FLAG_DATA_ACKED;
		} else {
			flag |= FLAG_SYN_ACKED;
			tp->retrans_stamp = 0;
		}

		if (!fully_acked)
			break;

		tcp_unlink_write_queue(skb, sk);
		sk_wmem_free_skb(sk, skb);
		if (unlikely(skb == tp->retransmit_skb_hint))
			tp->retransmit_skb_hint = NULL;
		if (unlikely(skb == tp->lost_skb_hint))
			tp->lost_skb_hint = NULL;
	}

	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
		tp->snd_up = tp->snd_una;

	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
		flag |= FLAG_SACK_RENEGING;

	skb_mstamp_get(&now);
	if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
		seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
		ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
	}
	if (sack->first_sackt.v64) {
		sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
		ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
	}

	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
					ca_rtt_us);

	if (flag & FLAG_ACKED) {
		tcp_rearm_rto(sk);
		if (unlikely(icsk->icsk_mtup.probe_size &&
			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
			tcp_mtup_probe_success(sk);
		}

		if (tcp_is_reno(tp)) {
			tcp_remove_reno_sacks(sk, pkts_acked);
		} else {
			int delta;

			/* Non-retransmitted hole got filled? That's reordering */
			if (reord < prior_fackets)
				tcp_update_reordering(sk, tp->fackets_out - reord, 0);

			delta = tcp_is_fack(tp) ? pkts_acked :
						  prior_sacked - tp->sacked_out;
			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
		}

		tp->fackets_out -= min(pkts_acked, tp->fackets_out);

	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
		   sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
		/* Do not re-arm RTO if the sack RTT is measured from data sent
		 * after when the head was last (re)transmitted. Otherwise the
		 * timeout may continue to extend in loss recovery.
		 */
		tcp_rearm_rto(sk);
	}

	if (icsk->icsk_ca_ops->pkts_acked) {
		struct ack_sample sample = { .pkts_acked = pkts_acked,
					     .rtt_us = ca_rtt_us };

		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
	}

#if FASTRETRANS_DEBUG > 0
	WARN_ON((int)tp->sacked_out < 0);
	WARN_ON((int)tp->lost_out < 0);
	WARN_ON((int)tp->retrans_out < 0);
	if (!tp->packets_out && tcp_is_sack(tp)) {
		icsk = inet_csk(sk);
		if (tp->lost_out) {
			pr_debug("Leak l=%u %d\n",
				 tp->lost_out, icsk->icsk_ca_state);
			tp->lost_out = 0;
		}
		if (tp->sacked_out) {
			pr_debug("Leak s=%u %d\n",
				 tp->sacked_out, icsk->icsk_ca_state);
			tp->sacked_out = 0;
		}
		if (tp->retrans_out) {
			pr_debug("Leak r=%u %d\n",
				 tp->retrans_out, icsk->icsk_ca_state);
			tp->retrans_out = 0;
		}
	}
#endif
	*acked = pkts_acked;
	return flag;
}

Project: net
File: tcp_input.c

int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	const struct tcphdr *th = tcp_hdr(skb);
	struct request_sock *req;
	int queued = 0;
	bool acceptable;

	switch (sk->sk_state) {
	case TCP_CLOSE:
		goto discard;

	case TCP_LISTEN:
		if (th->ack)
			return 1;

		if (th->rst)
			goto discard;

		if (th->syn) {
			if (th->fin)
				goto discard;
			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
				return 1;

			consume_skb(skb);
			return 0;
		}
		goto discard;

	case TCP_SYN_SENT:
		tp->rx_opt.saw_tstamp = 0;
		queued = tcp_rcv_synsent_state_process(sk, skb, th);
		if (queued >= 0)
			return queued;

		/* Do step6 onward by hand. */
		tcp_urg(sk, skb, th);
		__kfree_skb(skb);
		tcp_data_snd_check(sk);
		return 0;
	}

	tp->rx_opt.saw_tstamp = 0;
	req = tp->fastopen_rsk;
	if (req) {
		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
		    sk->sk_state != TCP_FIN_WAIT1);

		if (!tcp_check_req(sk, skb, req, true))
			goto discard;
	}

	if (!th->ack && !th->rst && !th->syn)
		goto discard;

	if (!tcp_validate_incoming(sk, skb, th, 0))
		return 0;

	/* step 5: check the ACK field */
	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
				      FLAG_UPDATE_TS_RECENT) > 0;

	switch (sk->sk_state) {
	case TCP_SYN_RECV:
		if (!acceptable)
			return 1;

		if (!tp->srtt_us)
			tcp_synack_rtt_meas(sk, req);

		/* Once we leave TCP_SYN_RECV, we no longer need req
		 * so release it.
		 */
		if (req) {
			tp->total_retrans = req->num_retrans;
			reqsk_fastopen_remove(sk, req, false);
		} else {
			/* Make sure socket is routed, for correct metrics. */
			icsk->icsk_af_ops->rebuild_header(sk);
			tcp_init_congestion_control(sk);

			tcp_mtup_init(sk);
			tp->copied_seq = tp->rcv_nxt;
			tcp_init_buffer_space(sk);
		}
		smp_mb();
		tcp_set_state(sk, TCP_ESTABLISHED);
		sk->sk_state_change(sk);

		/* Note, that this wakeup is only for marginal crossed SYN case.
		 * Passively open sockets are not waked up, because
		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
		 */
		if (sk->sk_socket)
			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);

		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);

		if (tp->rx_opt.tstamp_ok)
			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;

		if (req) {
			/* Re-arm the timer because data may have been sent out.
			 * This is similar to the regular data transmission case
			 * when new data has just been ack'ed.
			 *
			 * (TFO) - we could try to be more aggressive and
			 * retransmitting any data sooner based on when they
			 * are sent out.
			 */
			tcp_rearm_rto(sk);
		} else
			tcp_init_metrics(sk);

		tcp_update_pacing_rate(sk);

		/* Prevent spurious tcp_cwnd_restart() on first data packet */
		tp->lsndtime = tcp_time_stamp;

		tcp_initialize_rcv_mss(sk);
		tcp_fast_path_on(tp);
		break;

	case TCP_FIN_WAIT1: {
		struct dst_entry *dst;
		int tmo;

		/* If we enter the TCP_FIN_WAIT1 state and we are a
		 * Fast Open socket and this is the first acceptable
		 * ACK we have received, this would have acknowledged
		 * our SYNACK so stop the SYNACK timer.
		 */
		if (req) {
			/* Return RST if ack_seq is invalid.
			 * Note that RFC793 only says to generate a
			 * DUPACK for it but for TCP Fast Open it seems
			 * better to treat this case like TCP_SYN_RECV
			 * above.
			 */
			if (!acceptable)
				return 1;
			/* We no longer need the request sock. */
			reqsk_fastopen_remove(sk, req, false);
			tcp_rearm_rto(sk);
		}
		if (tp->snd_una != tp->write_seq)
			break;

		tcp_set_state(sk, TCP_FIN_WAIT2);
		sk->sk_shutdown |= SEND_SHUTDOWN;

		dst = __sk_dst_get(sk);
		if (dst)
			dst_confirm(dst);

		if (!sock_flag(sk, SOCK_DEAD)) {
			/* Wake up lingering close() */
			sk->sk_state_change(sk);
			break;
		}

		if (tp->linger2 < 0 ||
		    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
		     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
			tcp_done(sk);
			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
			return 1;
		}

		tmo = tcp_fin_time(sk);
		if (tmo > TCP_TIMEWAIT_LEN) {
			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
		} else if (th->fin || sock_owned_by_user(sk)) {
			/* Bad case. We could lose such FIN otherwise.
			 * It is not a big problem, but it looks confusing
			 * and not so rare event. We still can lose it now,
			 * if it spins in bh_lock_sock(), but it is really
			 * marginal case.
			 */
			inet_csk_reset_keepalive_timer(sk, tmo);
		} else {
			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
			goto discard;
		}
		break;
	}

	case TCP_CLOSING:
		if (tp->snd_una == tp->write_seq) {
			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
			goto discard;
		}
		break;

	case TCP_LAST_ACK:
		if (tp->snd_una == tp->write_seq) {
			tcp_update_metrics(sk);
			tcp_done(sk);
			goto discard;
		}
		break;
	}

	/* step 6: check the URG bit */
	tcp_urg(sk, skb, th);

	/* step 7: process the segment text */
	switch (sk->sk_state) {
	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
	case TCP_LAST_ACK:
		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
			break;
	case TCP_FIN_WAIT1:
	case TCP_FIN_WAIT2:
		/* RFC 793 says to queue data in these states,
		 * RFC 1122 says we MUST send a reset.
		 * BSD 4.4 also does reset.
		 */
		if (sk->sk_shutdown & RCV_SHUTDOWN) {
			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
				tcp_reset(sk);
				return 1;
			}
		}
		/* Fall through */
	case TCP_ESTABLISHED:
		tcp_data_queue(sk, skb);
		queued = 1;
		break;
	}

	/* tcp_data could move socket to TIME-WAIT */
	if (sk->sk_state != TCP_CLOSE) {
		tcp_data_snd_check(sk);
		tcp_ack_snd_check(sk);
	}

	if (!queued) {
discard:
		tcp_drop(sk, skb);
	}
	return 0;
}

Project: net
File: tcp_input.c

static void tcp_new_space(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tcp_should_expand_sndbuf(sk)) {
		tcp_sndbuf_expand(sk);
		tp->snd_cwnd_stamp = tcp_time_stamp;
	}

	sk->sk_write_space(sk);
}

Project: net
File: tcp_input.c

static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 ptr = ntohs(th->urg_ptr);

	if (ptr && !sysctl_tcp_stdurg)
		ptr--;
	ptr += ntohl(th->seq);

	/* Ignore urgent data that we've already seen and read. */
	if (after(tp->copied_seq, ptr))
		return;

	/* Do not replay urg ptr.
	 *
	 * NOTE: interesting situation not covered by specs.
	 * Misbehaving sender may send urg ptr, pointing to segment,
	 * which we already have in ofo queue. We are not able to fetch
	 * such data and will stay in TCP_URG_NOTYET until will be eaten
	 * by recvmsg(). Seems, we are not obliged to handle such wicked
	 * situations. But it is worth to think about possibility of some
	 * DoSes using some hypothetical application level deadlock.
	 */
	if (before(ptr, tp->rcv_nxt))
		return;

	/* Do we already have a newer (or duplicate) urgent pointer? */
	if (tp->urg_data && !after(ptr, tp->urg_seq))
		return;

	/* Tell the world about our new urgent pointer. */
	sk_send_sigurg(sk);

	/* We may be adding urgent data when the last byte read was
	 * urgent. To do this requires some care. We cannot just ignore
	 * tp->copied_seq since we would read the last urgent byte again
	 * as data, nor can we alter copied_seq until this data arrives
	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
	 *
	 * NOTE. Double Dutch. Rendering to plain English: author of comment
	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
	 * and expect that both A and B disappear from stream. This is _wrong_.
	 * Though this happens in BSD with high probability, this is occasional.
	 * Any application relying on this is buggy. Note also, that fix "works"
	 * only in this artificial test. Insert some normal data between A and B and we will
	 * decline of BSD again. Verdict: it is better to remove to trap
	 * buggy users.
	 */
	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
		tp->copied_seq++;
		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
			__skb_unlink(skb, &sk->sk_receive_queue);
			__kfree_skb(skb);
		}
	}

	tp->urg_data = TCP_URG_NOTYET;
	tp->urg_seq = ptr;

	/* Disable header prediction. */
	tp->pred_flags = 0;
}

Project: net
File: tcp_input.c

static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_sack_block *sp = &tp->selective_acks[0];
	int cur_sacks = tp->rx_opt.num_sacks;
	int this_sack;

	if (!cur_sacks)
		goto new_sack;

	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
		if (tcp_sack_extend(sp, seq, end_seq)) {
			/* Rotate this_sack to the first one. */
			for (; this_sack > 0; this_sack--, sp--)
				swap(*sp, *(sp - 1));
			if (cur_sacks > 1)
				tcp_sack_maybe_coalesce(tp);
			return;
		}
	}

	/* Could not find an adjacent existing SACK, build a new one,
	 * put it at the front, and shift everyone else down.  We
	 * always know there is at least one SACK present already here.
	 *
	 * If the sack array is full, forget about the last one.
	 */
	if (this_sack >= TCP_NUM_SACKS) {
		this_sack--;
		tp->rx_opt.num_sacks--;
		sp--;
	}
	for (; this_sack > 0; this_sack--, sp--)
		*sp = *(sp - 1);

new_sack:
	/* Build the new head SACK, and we're done. */
	sp->start_seq = seq;
	sp->end_seq = end_seq;
	tp->rx_opt.num_sacks++;
}

Project: net
File: tcp_input.c

static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
		tcp_verify_retransmit_hint(tp, skb);

		tp->lost_out += tcp_skb_pcount(skb);
		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
	}
}

Project: net
File: tcp_input.c

static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
{
	if (tp->rcv_rtt_est.time == 0)
		goto new_measure;
	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
		return;
	tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);

new_measure:
	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
	tp->rcv_rtt_est.time = tcp_time_stamp;
}

Project: net
File: tcp_input.c

static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int mib_idx;

	if (tcp_is_reno(tp))
		mib_idx = LINUX_MIB_TCPRENORECOVERY;
	else
		mib_idx = LINUX_MIB_TCPSACKRECOVERY;

	NET_INC_STATS(sock_net(sk), mib_idx);

	tp->prior_ssthresh = 0;
	tcp_init_undo(tp);

	if (!tcp_in_cwnd_reduction(sk)) {
		if (!ece_ack)
			tp->prior_ssthresh = tcp_current_ssthresh(sk);
		tcp_init_cwnd_reduction(sk);
	}
	tcp_set_ca_state(sk, TCP_CA_Recovery);
}

Project: net
File: tcp_input.c

void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
{
	long rtt_us = -1L;

	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack.v64) {
		struct skb_mstamp now;

		skb_mstamp_get(&now);
		rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack);
	}

	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us);
}

Project: net
File: tcp_input.c

static bool tcp_any_retrans_done(const struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	if (tp->retrans_out)
		return true;

	skb = tcp_write_queue_head(sk);
	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
		return true;

	return false;
}

Project: net
File: tcp_input.c

static void tcp_fixup_rcvbuf(struct sock *sk)
{
	u32 mss = tcp_sk(sk)->advmss;
	int rcvmem;

	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
		 tcp_default_init_rwnd(mss);

	/* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
	 * Allow enough cushion so that sender is not limited by our window
	 */
	if (sysctl_tcp_moderate_rcvbuf)
		rcvmem <<= 2;

	if (sk->sk_rcvbuf < rcvmem)
		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
}

Project: net
File: tcp_input.c

static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
{
	if (!tp->retransmit_skb_hint ||
	    before(TCP_SKB_CB(skb)->seq,
		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
		tp->retransmit_skb_hint = skb;

	if (!tp->lost_out ||
	    after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
		tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
}

Project: net
File: tcp_input.c

static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	bool fragstolen = false;
	int eaten = -1;

	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
		__kfree_skb(skb);
		return;
	}
	skb_dst_drop(skb);
	__skb_pull(skb, tcp_hdr(skb)->doff * 4);

	tcp_ecn_accept_cwr(tp, skb);

	tp->rx_opt.dsack = 0;

	/*  Queue data for delivery to the user.
	 *  Packets in sequence go to the receive queue.
	 *  Out of sequence packets to the out_of_order_queue.
	 */
	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
		if (tcp_receive_window(tp) == 0)
			goto out_of_window;

		/* Ok. In sequence. In window. */
		if (tp->ucopy.task == current &&
		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
		    sock_owned_by_user(sk) && !tp->urg_data) {
			int chunk = min_t(unsigned int, skb->len,
					  tp->ucopy.len);

			__set_current_state(TASK_RUNNING);

			if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
				tp->ucopy.len -= chunk;
				tp->copied_seq += chunk;
				eaten = (chunk == skb->len);
				tcp_rcv_space_adjust(sk);
			}
		}

		if (eaten <= 0) {
queue_and_out:
			if (eaten < 0) {
				if (skb_queue_len(&sk->sk_receive_queue) == 0)
					sk_forced_mem_schedule(sk, skb->truesize);
				else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
					goto drop;
			}
			eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
		}
		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
		if (skb->len)
			tcp_event_data_recv(sk, skb);
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
			tcp_fin(sk);

		if (!skb_queue_empty(&tp->out_of_order_queue)) {
			tcp_ofo_queue(sk);

			/* RFC2581. 4.2. SHOULD send immediate ACK, when
			 * gap in queue is filled.
			 */
			if (skb_queue_empty(&tp->out_of_order_queue))
				inet_csk(sk)->icsk_ack.pingpong = 0;
		}

		if (tp->rx_opt.num_sacks)
			tcp_sack_remove(tp);

		tcp_fast_path_check(sk);

		if (eaten > 0)
			kfree_skb_partial(skb, fragstolen);
		if (!sock_flag(sk, SOCK_DEAD))
			sk->sk_data_ready(sk);
		return;
	}

	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
		/* A retransmit, 2nd most common case.  Force an immediate ack. */
		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);

out_of_window:
		tcp_enter_quickack_mode(sk);
		inet_csk_schedule_ack(sk);
drop:
		tcp_drop(sk, skb);
		return;
	}

	/* Out of window. F.e. zero window probe. */
	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
		goto out_of_window;

	tcp_enter_quickack_mode(sk);

	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		/* Partial packet, seq < rcv_next < end_seq */
		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
			   TCP_SKB_CB(skb)->end_seq);

		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);

		/* If window is closed, drop tail of packet. But after
		 * remembering D-SACK for its head made in previous line.
		 */
		if (!tcp_receive_window(tp))
			goto out_of_window;
		goto queue_and_out;
	}

	tcp_data_queue_ofo(sk, skb);
}

Project: net
File: tcp_input.c

static bool tcp_prune_ofo_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	bool res = false;

	if (!skb_queue_empty(&tp->out_of_order_queue)) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
		__skb_queue_purge(&tp->out_of_order_queue);

		/* Reset SACK state.  A conforming SACK implementation will
		 * do the same at a timeout based retransmit.  When a connection
		 * is in a sad state like this, we care only about integrity
		 * of the connection not performance.
		 */
		if (tp->rx_opt.sack_ok)
			tcp_sack_reset(&tp->rx_opt);
		sk_mem_reclaim(sk);
		res = true;
	}
	return res;
}

Project: net
File: tcp_input.c

static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
				      long seq_rtt_us, long sack_rtt_us,
				      long ca_rtt_us)
{
	const struct tcp_sock *tp = tcp_sk(sk);

	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
	 * Karn's algorithm forbids taking RTT if some retransmitted data
	 * is acked (RFC6298).
	 */
	if (seq_rtt_us < 0)
		seq_rtt_us = sack_rtt_us;

	/* RTTM Rule: A TSecr value received in a segment is used to
	 * update the averaged RTT measurement only if the segment
	 * acknowledges some new data, i.e., only if it advances the
	 * left edge of the send window.
	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
	 */
	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
	    flag & FLAG_ACKED)
		seq_rtt_us = ca_rtt_us = jiffies_to_usecs(tcp_time_stamp -
							  tp->rx_opt.rcv_tsecr);
	if (seq_rtt_us < 0)
		return false;

	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
	 * always taken together with ACK, SACK, or TS-opts. Any negative
	 * values will be skipped with the seq_rtt_us < 0 check above.
	 */
	tcp_update_rtt_min(sk, ca_rtt_us);
	tcp_rtt_estimator(sk, seq_rtt_us);
	tcp_set_rto(sk);

	/* RFC6298: only reset backoff on valid RTT measurement. */
	inet_csk(sk)->icsk_backoff = 0;
	return true;
}

Project: net
File: tcp_input.c

static void tcp_incr_quickack(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);

	if (quickacks == 0)
		quickacks = 2;
	if (quickacks > icsk->icsk_ack.quick)
		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
}

Project: net
File: tcp_input.c

void tcp_reset(struct sock *sk)
{
	/* We want the right error as BSD sees it (and indeed as we do). */
	switch (sk->sk_state) {
	case TCP_SYN_SENT:
		sk->sk_err = ECONNREFUSED;
		break;
	case TCP_CLOSE_WAIT:
		sk->sk_err = EPIPE;
		break;
	case TCP_CLOSE:
		return;
	default:
		sk->sk_err = ECONNRESET;
	}
	/* This barrier is coupled with smp_rmb() in tcp_poll() */
	smp_wmb();

	if (!sock_flag(sk, SOCK_DEAD))
		sk->sk_error_report(sk);

	tcp_done(sk);
}

Project: net
File: tcp_input.c

tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
			u32 prior_snd_una, struct tcp_sacktag_state *state)
{
	struct tcp_sock *tp = tcp_sk(sk);
	const unsigned char *ptr = (skb_transport_header(ack_skb) +
				    TCP_SKB_CB(ack_skb)->sacked);
	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
	struct tcp_sack_block sp[TCP_NUM_SACKS];
	struct tcp_sack_block *cache;
	struct sk_buff *skb;
	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
	int used_sacks;
	bool found_dup_sack = false;
	int i, j;
	int first_sack_index;

	state->flag = 0;
	state->reord = tp->packets_out;

	if (!tp->sacked_out) {
		if (WARN_ON(tp->fackets_out))
			tp->fackets_out = 0;
		tcp_highest_sack_reset(sk);
	}

	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
					 num_sacks, prior_snd_una);
	if (found_dup_sack)
		state->flag |= FLAG_DSACKING_ACK;

	/* Eliminate too old ACKs, but take into
	 * account more or less fresh ones, they can
	 * contain valid SACK info.
	 */
	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
		return 0;

	if (!tp->packets_out)
		goto out;

	used_sacks = 0;
	first_sack_index = 0;
	for (i = 0; i < num_sacks; i++) {
		bool dup_sack = !i && found_dup_sack;

		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);

		if (!tcp_is_sackblock_valid(tp, dup_sack,
					    sp[used_sacks].start_seq,
					    sp[used_sacks].end_seq)) {
			int mib_idx;

			if (dup_sack) {
				if (!tp->undo_marker)
					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
				else
					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
			} else {
				/* Don't count olds caused by ACK reordering */
				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
				    !after(sp[used_sacks].end_seq, tp->snd_una))
					continue;
				mib_idx = LINUX_MIB_TCPSACKDISCARD;
			}

			NET_INC_STATS(sock_net(sk), mib_idx);
			if (i == 0)
				first_sack_index = -1;
			continue;
		}

		/* Ignore very old stuff early */
		if (!after(sp[used_sacks].end_seq, prior_snd_una))
			continue;

		used_sacks++;
	}

	/* order SACK blocks to allow in order walk of the retrans queue */
	for (i = used_sacks - 1; i > 0; i--) {
		for (j = 0; j < i; j++) {
			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
				swap(sp[j], sp[j + 1]);

				/* Track where the first SACK block goes to */
				if (j == first_sack_index)
					first_sack_index = j + 1;
			}
		}
	}

	skb = tcp_write_queue_head(sk);
	state->fack_count = 0;
	i = 0;

	if (!tp->sacked_out) {
		/* It's already past, so skip checking against it */
		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
	} else {
		cache = tp->recv_sack_cache;
		/* Skip empty blocks in at head of the cache */
		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
		       !cache->end_seq)
			cache++;
	}

	while (i < used_sacks) {
		u32 start_seq = sp[i].start_seq;
		u32 end_seq = sp[i].end_seq;
		bool dup_sack = (found_dup_sack && (i == first_sack_index));
		struct tcp_sack_block *next_dup = NULL;

		if (found_dup_sack && ((i + 1) == first_sack_index))
			next_dup = &sp[i + 1];

		/* Skip too early cached blocks */
		while (tcp_sack_cache_ok(tp, cache) &&
		       !before(start_seq, cache->end_seq))
			cache++;

		/* Can skip some work by looking recv_sack_cache? */
		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
		    after(end_seq, cache->start_seq)) {

			/* Head todo? */
			if (before(start_seq, cache->start_seq)) {
				skb = tcp_sacktag_skip(skb, sk, state,
						       start_seq);
				skb = tcp_sacktag_walk(skb, sk, next_dup,
						       state,
						       start_seq,
						       cache->start_seq,
						       dup_sack);
			}

			/* Rest of the block already fully processed? */
			if (!after(end_seq, cache->end_seq))
				goto advance_sp;

			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
						       state,
						       cache->end_seq);

			/* ...tail remains todo... */
			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
				/* ...but better entrypoint exists! */
				skb = tcp_highest_sack(sk);
				if (!skb)
					break;
				state->fack_count = tp->fackets_out;
				cache++;
				goto walk;
			}

			skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
			/* Check overlap against next cached too (past this one already) */
			cache++;
			continue;
		}

		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
			skb = tcp_highest_sack(sk);
			if (!skb)
				break;
			state->fack_count = tp->fackets_out;
		}
		skb = tcp_sacktag_skip(skb, sk, state, start_seq);

walk:
		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
				       start_seq, end_seq, dup_sack);

advance_sp:
		i++;
	}

	/* Clear the head of the cache sack blocks so we can skip it next time */
	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
		tp->recv_sack_cache[i].start_seq = 0;
		tp->recv_sack_cache[i].end_seq = 0;
	}
	for (j = 0; j < used_sacks; j++)
		tp->recv_sack_cache[i++] = sp[j];

	if ((state->reord < tp->fackets_out) &&
	    ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
		tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);

	tcp_verify_left_out(tp);
out:

#if FASTRETRANS_DEBUG > 0
	WARN_ON((int)tp->sacked_out < 0);
	WARN_ON((int)tp->lost_out < 0);
	WARN_ON((int)tp->retrans_out < 0);
	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
#endif
	return state->flag;
}

Project: net
File: tcp_input.c

static bool tcp_try_undo_partial(struct sock *sk, const int acked)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->undo_marker && tcp_packet_delayed(tp)) {
		/* Plain luck! Hole if filled with delayed
		 * packet, rather than with a retransmit.
		 */
		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);

		/* We are getting evidence that the reordering degree is higher
		 * than we realized. If there are no retransmits out then we
		 * can undo. Otherwise we clock out new packets but do not
		 * mark more packets lost or retransmit more.
		 */
		if (tp->retrans_out)
			return true;

		if (!tcp_any_retrans_done(sk))
			tp->retrans_stamp = 0;

		DBGUNDO(sk, "partial recovery");
		tcp_undo_cwnd_reduction(sk, true);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
		tcp_try_keep_open(sk);
		return true;
	}
	return false;
}

Project: net
File: tcp_input.c

static void DBGUNDO(struct sock *sk, const char *msg)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_sock *inet = inet_sk(sk);

	if (sk->sk_family == AF_INET) {
		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
			 msg,
			 &inet->inet_daddr, ntohs(inet->inet_dport),
			 tp->snd_cwnd, tcp_left_out(tp),
			 tp->snd_ssthresh, tp->prior_ssthresh,
			 tp->packets_out);
	}
#if IS_ENABLED(CONFIG_IPV6)
	else if (sk->sk_family == AF_INET6) {
		struct ipv6_pinfo *np = inet6_sk(sk);
		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
			 msg,
			 &np->daddr, ntohs(inet->inet_dport),
			 tp->snd_cwnd, tcp_left_out(tp),
			 tp->snd_ssthresh, tp->prior_ssthresh,
			 tp->packets_out);
	}
#endif
}

Project: net
File: tcp_input.c

static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
				 u32 ack_seq)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int flag = 0;
	u32 nwin = ntohs(tcp_hdr(skb)->window);

	if (likely(!tcp_hdr(skb)->syn))
		nwin <<= tp->rx_opt.snd_wscale;

	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
		flag |= FLAG_WIN_UPDATE;
		tcp_update_wl(tp, ack_seq);

		if (tp->snd_wnd != nwin) {
			tp->snd_wnd = nwin;

			/* Note, it is the only place, where
			 * fast path is recovered for sending TCP.
			 */
			tp->pred_flags = 0;
			tcp_fast_path_check(sk);

			if (tcp_send_head(sk))
				tcp_slow_start_after_idle_check(sk);

			if (nwin > tp->max_window) {
				tp->max_window = nwin;
				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
			}
		}
	}

	tcp_snd_una_update(tp, ack);

	return flag;
}

Project: net
File: tcp_input.c

static void tcp_update_pacing_rate(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	u64 rate;

	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);

	/* current rate is (cwnd * mss) / srtt
	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
	 * In Congestion Avoidance phase, set it to 120 % the current rate.
	 *
	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
	 *	 end of slow start and should slow down.
	 */
	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
		rate *= sysctl_tcp_pacing_ss_ratio;
	else
		rate *= sysctl_tcp_pacing_ca_ratio;

	rate *= max(tp->snd_cwnd, tp->packets_out);

	if (likely(tp->srtt_us))
		do_div(rate, tp->srtt_us);

	/* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
	 * without any lock. We want to make sure compiler wont store
	 * intermediate values in this location.
	 */
	ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
						sk->sk_max_pacing_rate);
}

Project: net
File: tcp_input.c

static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
{
	u32 new_sample = tp->rcv_rtt_est.rtt;
	long m = sample;

	if (m == 0)
		m = 1;

	if (new_sample != 0) {
		/* If we sample in larger samples in the non-timestamp
		 * case, we could grossly overestimate the RTT especially
		 * with chatty applications or bulk transfer apps which
		 * are stalled on filesystem I/O.
		 *
		 * Also, since we are only going for a minimum in the
		 * non-timestamp case, we do not smooth things out
		 * else with timestamps disabled convergence takes too
		 * long.
		 */
		if (!win_dep) {
			m -= (new_sample >> 3);
			new_sample += m;
		} else {
			m <<= 3;
			if (m < new_sample)
				new_sample = m;
		}
	} else {
		/* No previous measure. */
		new_sample = m << 3;
	}

	if (tp->rcv_rtt_est.rtt != new_sample)
		tp->rcv_rtt_est.rtt = new_sample;
}

Project: net
File: tcp_input.c

static bool tcp_try_coalesce(struct sock *sk,
			     struct sk_buff *to,
			     struct sk_buff *from,
			     bool *fragstolen)
{
	int delta;

	*fragstolen = false;

	/* Its possible this segment overlaps with prior segment in queue */
	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
		return false;

	if (!skb_try_coalesce(to, from, fragstolen, &delta))
		return false;

	atomic_add(delta, &sk->sk_rmem_alloc);
	sk_mem_charge(sk, delta);
	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
	return true;
}

Project: net
File: tcp_input.c

static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
				  const struct tcphdr *th, int syn_inerr)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* RFC1323: H1. Apply PAWS check first. */
	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
	    tcp_paws_discard(sk, skb)) {
		if (!th->rst) {
			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
			if (!tcp_oow_rate_limited(sock_net(sk), skb,
						  LINUX_MIB_TCPACKSKIPPEDPAWS,
						  &tp->last_oow_ack_time))
				tcp_send_dupack(sk, skb);
			goto discard;
		}
		/* Reset is accepted even if it did not pass PAWS. */
	}

	/* Step 1: check sequence number */
	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
		/* RFC793, page 37: "In all states except SYN-SENT, all reset
		 * (RST) segments are validated by checking their SEQ-fields."
		 * And page 69: "If an incoming segment is not acceptable,
		 * an acknowledgment should be sent in reply (unless the RST
		 * bit is set, if so drop the segment and return)".
		 */
		if (!th->rst) {
			if (th->syn)
				goto syn_challenge;
			if (!tcp_oow_rate_limited(sock_net(sk), skb,
						  LINUX_MIB_TCPACKSKIPPEDSEQ,
						  &tp->last_oow_ack_time))
				tcp_send_dupack(sk, skb);
		}
		goto discard;
	}

	/* Step 2: check RST bit */
	if (th->rst) {
		/* RFC 5961 3.2 :
		 * If sequence number exactly matches RCV.NXT, then
		 *     RESET the connection
		 * else
		 *     Send a challenge ACK
		 */
		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
			tcp_reset(sk);
		else
			tcp_send_challenge_ack(sk, skb);
		goto discard;
	}

	/* step 3: check security and precedence [ignored] */

	/* step 4: Check for a SYN
	 * RFC 5961 4.2 : Send a challenge ack
	 */
	if (th->syn) {
syn_challenge:
		if (syn_inerr)
			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
		tcp_send_challenge_ack(sk, skb);
		goto discard;
	}

	return true;

discard:
	tcp_drop(sk, skb);
	return false;
}

Project: net
File: tcp_input.c

static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
			     int flag)
{
	if (tcp_in_cwnd_reduction(sk)) {
		/* Reduce cwnd if state mandates */
		tcp_cwnd_reduction(sk, acked_sacked, flag);
	} else if (tcp_may_raise_cwnd(sk, flag)) {
		/* Advance cwnd if state allows */
		tcp_cong_avoid(sk, ack, acked_sacked);
	}
	tcp_update_pacing_rate(sk);
}

Project: net
File: tcp_input.c

static void tcp_store_ts_recent(struct tcp_sock *tp)
{
	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
	tp->rx_opt.ts_recent_stamp = get_seconds();
}

Project: net
File: tcp_input.c

static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
					 const struct tcphdr *th)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_fastopen_cookie foc = { .len = -1 };
	int saved_clamp = tp->rx_opt.mss_clamp;

	tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
		tp->rx_opt.rcv_tsecr -= tp->tsoffset;

	if (th->ack) {
		/* rfc793:
		 * "If the state is SYN-SENT then
		 *    first check the ACK bit
		 *      If the ACK bit is set
		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
		 *        a reset (unless the RST bit is set, if so drop
		 *        the segment and return)"
		 */
		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
			goto reset_and_undo;

		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
			     tcp_time_stamp)) {
			NET_INC_STATS(sock_net(sk),
					LINUX_MIB_PAWSACTIVEREJECTED);
			goto reset_and_undo;
		}

		/* Now ACK is acceptable.
		 *
		 * "If the RST bit is set
		 *    If the ACK was acceptable then signal the user "error:
		 *    connection reset", drop the segment, enter CLOSED state,
		 *    delete TCB, and return."
		 */

		if (th->rst) {
			tcp_reset(sk);
			goto discard;
		}

		/* rfc793:
		 *   "fifth, if neither of the SYN or RST bits is set then
		 *    drop the segment and return."
		 *
		 *    See note below!
		 *                                        --ANK(990513)
		 */
		if (!th->syn)
			goto discard_and_undo;

		/* rfc793:
		 *   "If the SYN bit is on ...
		 *    are acceptable then ...
		 *    (our SYN has been ACKed), change the connection
		 *    state to ESTABLISHED..."
		 */

		tcp_ecn_rcv_synack(tp, th);

		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
		tcp_ack(sk, skb, FLAG_SLOWPATH);

		/* Ok.. it's good. Set up sequence numbers and
		 * move to established.
		 */
		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;

		/* RFC1323: The window in SYN & SYN/ACK segments is
		 * never scaled.
		 */
		tp->snd_wnd = ntohs(th->window);

		if (!tp->rx_opt.wscale_ok) {
			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
			tp->window_clamp = min(tp->window_clamp, 65535U);
		}

		if (tp->rx_opt.saw_tstamp) {
			tp->rx_opt.tstamp_ok	   = 1;
			tp->tcp_header_len =
				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
			tcp_store_ts_recent(tp);
		} else {
			tp->tcp_header_len = sizeof(struct tcphdr);
		}

		if (tcp_is_sack(tp) && sysctl_tcp_fack)
			tcp_enable_fack(tp);

		tcp_mtup_init(sk);
		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
		tcp_initialize_rcv_mss(sk);

		/* Remember, tcp_poll() does not lock socket!
		 * Change state from SYN-SENT only after copied_seq
		 * is initialized. */
		tp->copied_seq = tp->rcv_nxt;

		smp_mb();

		tcp_finish_connect(sk, skb);

		if ((tp->syn_fastopen || tp->syn_data) &&
		    tcp_rcv_fastopen_synack(sk, skb, &foc))
			return -1;

		if (sk->sk_write_pending ||
		    icsk->icsk_accept_queue.rskq_defer_accept ||
		    icsk->icsk_ack.pingpong) {
			/* Save one ACK. Data will be ready after
			 * several ticks, if write_pending is set.
			 *
			 * It may be deleted, but with this feature tcpdumps
			 * look so _wonderfully_ clever, that I was not able
			 * to stand against the temptation 8)     --ANK
			 */
			inet_csk_schedule_ack(sk);
			icsk->icsk_ack.lrcvtime = tcp_time_stamp;
			tcp_enter_quickack_mode(sk);
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
						  TCP_DELACK_MAX, TCP_RTO_MAX);

discard:
			tcp_drop(sk, skb);
			return 0;
		} else {
			tcp_send_ack(sk);
		}
		return -1;
	}

	/* No ACK in the segment */

	if (th->rst) {
		/* rfc793:
		 * "If the RST bit is set
		 *
		 *      Otherwise (no ACK) drop the segment and return."
		 */

		goto discard_and_undo;
	}

	/* PAWS check. */
	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
	    tcp_paws_reject(&tp->rx_opt, 0))
		goto discard_and_undo;

	if (th->syn) {
		/* We see SYN without ACK. It is attempt of
		 * simultaneous connect with crossed SYNs.
		 * Particularly, it can be connect to self.
		 */
		tcp_set_state(sk, TCP_SYN_RECV);

		if (tp->rx_opt.saw_tstamp) {
			tp->rx_opt.tstamp_ok = 1;
			tcp_store_ts_recent(tp);
			tp->tcp_header_len =
				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
		} else {
			tp->tcp_header_len = sizeof(struct tcphdr);
		}

		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
		tp->copied_seq = tp->rcv_nxt;
		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;

		/* RFC1323: The window in SYN & SYN/ACK segments is
		 * never scaled.
		 */
		tp->snd_wnd    = ntohs(th->window);
		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
		tp->max_window = tp->snd_wnd;

		tcp_ecn_rcv_syn(tp, th);

		tcp_mtup_init(sk);
		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
		tcp_initialize_rcv_mss(sk);

		tcp_send_synack(sk);
#if 0
		/* Note, we could accept data and URG from this segment.
		 * There are no obstacles to make this (except that we must
		 * either change tcp_recvmsg() to prevent it from returning data
		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
		 *
		 * However, if we ignore data in ACKless segments sometimes,
		 * we have no reasons to accept it sometimes.
		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
		 * is not flawless. So, discard packet for sanity.
		 * Uncomment this return to process the data.
		 */
		return -1;
#else
		goto discard;
#endif
	}
	/* "fifth, if neither of the SYN or RST bits is set then
	 * drop the segment and return."
	 */

discard_and_undo:
	tcp_clear_options(&tp->rx_opt);
	tp->rx_opt.mss_clamp = saved_clamp;
	goto discard;

reset_and_undo:
	tcp_clear_options(&tp->rx_opt);
	tp->rx_opt.mss_clamp = saved_clamp;
	return 1;
}

Project: net
File: tcp_input.c

static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	int cnt, oldcnt, lost;
	unsigned int mss;
	/* Use SACK to deduce losses of new sequences sent during recovery */
	const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;

	WARN_ON(packets > tp->packets_out);
	if (tp->lost_skb_hint) {
		skb = tp->lost_skb_hint;
		cnt = tp->lost_cnt_hint;
		/* Head already handled? */
		if (mark_head && skb != tcp_write_queue_head(sk))
			return;
	} else {
		skb = tcp_write_queue_head(sk);
		cnt = 0;
	}

	tcp_for_write_queue_from(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;
		/* TODO: do this better */
		/* this is not the most efficient way to do this... */
		tp->lost_skb_hint = skb;
		tp->lost_cnt_hint = cnt;

		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
			break;

		oldcnt = cnt;
		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
			cnt += tcp_skb_pcount(skb);

		if (cnt > packets) {
			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
			    (oldcnt >= packets))
				break;

			mss = tcp_skb_mss(skb);
			/* If needed, chop off the prefix to mark as lost. */
			lost = (packets - oldcnt) * mss;
			if (lost < skb->len &&
			    tcp_fragment(sk, skb, lost, mss, GFP_ATOMIC) < 0)
				break;
			cnt = packets;
		}

		tcp_skb_mark_lost(tp, skb);

		if (mark_head)
			break;
	}
	tcp_verify_left_out(tp);
}

Project: net
File: tcp_input.c

static bool tcp_try_undo_dsack(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->undo_marker && !tp->undo_retrans) {
		DBGUNDO(sk, "D-SACK");
		tcp_undo_cwnd_reduction(sk, false);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
		return true;
	}
	return false;
}

Project: net
File: tcp_input.c

static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
{
	if (tcp_hdr(skb)->cwr)
		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
}

Project: net
File: tcp_input.c

int tcp_conn_request(struct request_sock_ops *rsk_ops,
		     const struct tcp_request_sock_ops *af_ops,
		     struct sock *sk, struct sk_buff *skb)
{
	struct tcp_fastopen_cookie foc = { .len = -1 };
	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
	struct tcp_options_received tmp_opt;
	struct tcp_sock *tp = tcp_sk(sk);
	struct net *net = sock_net(sk);
	struct sock *fastopen_sk = NULL;
	struct dst_entry *dst = NULL;
	struct request_sock *req;
	bool want_cookie = false;
	struct flowi fl;

	/* TW buckets are converted to open requests without
	 * limitations, they conserve resources and peer is
	 * evidently real one.
	 */
	if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
	     inet_csk_reqsk_queue_is_full(sk)) && !isn) {
		want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
		if (!want_cookie)
			goto drop;
	}


	/* Accept backlog is full. If we have already queued enough
	 * of warm entries in syn queue, drop request. It is better than
	 * clogging syn queue with openreqs with exponentially increasing
	 * timeout.
	 */
	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
		goto drop;
	}

	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
	if (!req)
		goto drop;

	tcp_rsk(req)->af_specific = af_ops;

	tcp_clear_options(&tmp_opt);
	tmp_opt.mss_clamp = af_ops->mss_clamp;
	tmp_opt.user_mss  = tp->rx_opt.user_mss;
	tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);

	if (want_cookie && !tmp_opt.saw_tstamp)
		tcp_clear_options(&tmp_opt);

	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
	tcp_openreq_init(req, &tmp_opt, skb, sk);

	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);

	af_ops->init_req(req, sk, skb);

	if (security_inet_conn_request(sk, skb, req))
		goto drop_and_free;

	if (!want_cookie && !isn) {
		/* VJ's idea. We save last timestamp seen
		 * from the destination in peer table, when entering
		 * state TIME-WAIT, and check against it before
		 * accepting new connection request.
		 *
		 * If "isn" is not zero, this request hit alive
		 * timewait bucket, so that all the necessary checks
		 * are made in the function processing timewait state.
		 */
		if (tcp_death_row.sysctl_tw_recycle) {
			bool strict;

			dst = af_ops->route_req(sk, &fl, req, &strict);

			if (dst && strict &&
			    !tcp_peer_is_proven(req, dst, true,
						tmp_opt.saw_tstamp)) {
				NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
				goto drop_and_release;
			}
		}
		/* Kill the following clause, if you dislike this way. */
		else if (!net->ipv4.sysctl_tcp_syncookies &&
			 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
			  (sysctl_max_syn_backlog >> 2)) &&
			 !tcp_peer_is_proven(req, dst, false,
					     tmp_opt.saw_tstamp)) {
			/* Without syncookies last quarter of
			 * backlog is filled with destinations,
			 * proven to be alive.
			 * It means that we continue to communicate
			 * to destinations, already remembered
			 * to the moment of synflood.
			 */
			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
				    rsk_ops->family);
			goto drop_and_release;
		}

		isn = af_ops->init_seq(skb);
	}
	if (!dst) {
		dst = af_ops->route_req(sk, &fl, req, NULL);
		if (!dst)
			goto drop_and_free;
	}

	tcp_ecn_create_request(req, skb, sk, dst);

	if (want_cookie) {
		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
		req->cookie_ts = tmp_opt.tstamp_ok;
		if (!tmp_opt.tstamp_ok)
			inet_rsk(req)->ecn_ok = 0;
	}

	tcp_rsk(req)->snt_isn = isn;
	tcp_rsk(req)->txhash = net_tx_rndhash();
	tcp_openreq_init_rwin(req, sk, dst);
	if (!want_cookie) {
		tcp_reqsk_record_syn(sk, req, skb);
		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
	}
	if (fastopen_sk) {
		af_ops->send_synack(fastopen_sk, dst, &fl, req,
				    &foc, TCP_SYNACK_FASTOPEN);
		/* Add the child socket directly into the accept queue */
		inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
		sk->sk_data_ready(sk);
		bh_unlock_sock(fastopen_sk);
		sock_put(fastopen_sk);
	} else {
		tcp_rsk(req)->tfo_listener = false;
		if (!want_cookie)
			inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
		af_ops->send_synack(sk, dst, &fl, req, &foc,
				    !want_cookie ? TCP_SYNACK_NORMAL :
						   TCP_SYNACK_COOKIE);
		if (want_cookie) {
			reqsk_free(req);
			return 0;
		}
	}
	reqsk_put(req);
	return 0;

drop_and_release:
	dst_release(dst);
drop_and_free:
	reqsk_free(req);
drop:
	tcp_listendrop(sk);
	return 0;
}

Project: net
File: tcp_input.c

static void tcp_check_space(struct sock *sk)
{
	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
		/* pairs with tcp_poll() */
		smp_mb__after_atomic();
		if (sk->sk_socket &&
		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
			tcp_new_space(sk);
	}
}

Project: net
File: tcp_input.c

static void tcp_enter_quickack_mode(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	tcp_incr_quickack(sk);
	icsk->icsk_ack.pingpong = 0;
	icsk->icsk_ack.ato = TCP_ATO_MIN;
}

Project: net
File: tcp_input.c

void tcp_disable_fack(struct tcp_sock *tp)
{
	/* RFC3517 uses different metric in lost marker => reset on change */
	if (tcp_is_fack(tp))
		tp->lost_skb_hint = NULL;
	tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
}

Project: net
File: tcp_input.c

static void tcp_collapse_ofo_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
	struct sk_buff *head;
	u32 start, end;

	if (!skb)
		return;

	start = TCP_SKB_CB(skb)->seq;
	end = TCP_SKB_CB(skb)->end_seq;
	head = skb;

	for (;;) {
		struct sk_buff *next = NULL;

		if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
			next = skb_queue_next(&tp->out_of_order_queue, skb);
		skb = next;

		/* Segment is terminated when we see gap or when
		 * we are at the end of all the queue. */
		if (!skb ||
		    after(TCP_SKB_CB(skb)->seq, end) ||
		    before(TCP_SKB_CB(skb)->end_seq, start)) {
			tcp_collapse(sk, &tp->out_of_order_queue,
				     head, skb, start, end);
			head = skb;
			if (!skb)
				break;
			/* Start new segment */
			start = TCP_SKB_CB(skb)->seq;
			end = TCP_SKB_CB(skb)->end_seq;
		} else {
			if (before(TCP_SKB_CB(skb)->seq, start))
				start = TCP_SKB_CB(skb)->seq;
			if (after(TCP_SKB_CB(skb)->end_seq, end))
				end = TCP_SKB_CB(skb)->end_seq;
		}
	}
}

Project: net
File: tcp_input.c

static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
{
	u32 delta = seq - tp->rcv_nxt;

	sock_owned_by_me((struct sock *)tp);
	u64_stats_update_begin_raw(&tp->syncp);
	tp->bytes_received += delta;
	u64_stats_update_end_raw(&tp->syncp);
	tp->rcv_nxt = seq;
}

Project: net
File: tcp_input.c

static void tcp_fastretrans_alert(struct sock *sk, const int acked,
				  bool is_dupack, int *ack_flag, int *rexmit)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	int fast_rexmit = 0, flag = *ack_flag;
	bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
				    (tcp_fackets_out(tp) > tp->reordering));

	if (WARN_ON(!tp->packets_out && tp->sacked_out))
		tp->sacked_out = 0;
	if (WARN_ON(!tp->sacked_out && tp->fackets_out))
		tp->fackets_out = 0;

	/* Now state machine starts.
	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
	if (flag & FLAG_ECE)
		tp->prior_ssthresh = 0;

	/* B. In all the states check for reneging SACKs. */
	if (tcp_check_sack_reneging(sk, flag))
		return;

	/* C. Check consistency of the current state. */
	tcp_verify_left_out(tp);

	/* D. Check state exit conditions. State can be terminated
	 *    when high_seq is ACKed. */
	if (icsk->icsk_ca_state == TCP_CA_Open) {
		WARN_ON(tp->retrans_out != 0);
		tp->retrans_stamp = 0;
	} else if (!before(tp->snd_una, tp->high_seq)) {
		switch (icsk->icsk_ca_state) {
		case TCP_CA_CWR:
			/* CWR is to be held something *above* high_seq
			 * is ACKed for CWR bit to reach receiver. */
			if (tp->snd_una != tp->high_seq) {
				tcp_end_cwnd_reduction(sk);
				tcp_set_ca_state(sk, TCP_CA_Open);
			}
			break;

		case TCP_CA_Recovery:
			if (tcp_is_reno(tp))
				tcp_reset_reno_sack(tp);
			if (tcp_try_undo_recovery(sk))
				return;
			tcp_end_cwnd_reduction(sk);
			break;
		}
	}

	/* Use RACK to detect loss */
	if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
	    tcp_rack_mark_lost(sk)) {
		flag |= FLAG_LOST_RETRANS;
		*ack_flag |= FLAG_LOST_RETRANS;
	}

	/* E. Process state. */
	switch (icsk->icsk_ca_state) {
	case TCP_CA_Recovery:
		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
			if (tcp_is_reno(tp) && is_dupack)
				tcp_add_reno_sack(sk);
		} else {
			if (tcp_try_undo_partial(sk, acked))
				return;
			/* Partial ACK arrived. Force fast retransmit. */
			do_lost = tcp_is_reno(tp) ||
				  tcp_fackets_out(tp) > tp->reordering;
		}
		if (tcp_try_undo_dsack(sk)) {
			tcp_try_keep_open(sk);
			return;
		}
		break;
	case TCP_CA_Loss:
		tcp_process_loss(sk, flag, is_dupack, rexmit);
		if (icsk->icsk_ca_state != TCP_CA_Open &&
		    !(flag & FLAG_LOST_RETRANS))
			return;
		/* Change state if cwnd is undone or retransmits are lost */
	default:
		if (tcp_is_reno(tp)) {
			if (flag & FLAG_SND_UNA_ADVANCED)
				tcp_reset_reno_sack(tp);
			if (is_dupack)
				tcp_add_reno_sack(sk);
		}

		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
			tcp_try_undo_dsack(sk);

		if (!tcp_time_to_recover(sk, flag)) {
			tcp_try_to_open(sk, flag);
			return;
		}

		/* MTU probe failure: don't reduce cwnd */
		if (icsk->icsk_ca_state < TCP_CA_CWR &&
		    icsk->icsk_mtup.probe_size &&
		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
			tcp_mtup_probe_failed(sk);
			/* Restores the reduction we did in tcp_mtup_probe() */
			tp->snd_cwnd++;
			tcp_simple_retransmit(sk);
			return;
		}

		/* Otherwise enter Recovery state */
		tcp_enter_recovery(sk, (flag & FLAG_ECE));
		fast_rexmit = 1;
	}

	if (do_lost)
		tcp_update_scoreboard(sk, fast_rexmit);
	*rexmit = REXMIT_LOST;
}

Project: net
File: tcp_input.c

static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
{
	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
}

Project: net
File: tcp_input.c

static bool tcp_in_quickack_mode(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);

	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
		(icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
}

Project: net
File: tcp_input.c

static void tcp_ecn_create_request(struct request_sock *req,
				   const struct sk_buff *skb,
				   const struct sock *listen_sk,
				   const struct dst_entry *dst)
{
	const struct tcphdr *th = tcp_hdr(skb);
	const struct net *net = sock_net(listen_sk);
	bool th_ecn = th->ece && th->cwr;
	bool ect, ecn_ok;
	u32 ecn_ok_dst;

	if (!th_ecn)
		return;

	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
	ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;

	if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
	    (ecn_ok_dst & DST_FEATURE_ECN_CA))
		inet_rsk(req)->ecn_ok = 1;
}

Project: net
File: tcp_input.c

static void tcp_xmit_recovery(struct sock *sk, int rexmit)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (rexmit == REXMIT_NONE)
		return;

	if (unlikely(rexmit == 2)) {
		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
					  TCP_NAGLE_OFF);
		if (after(tp->snd_nxt, tp->high_seq))
			return;
		tp->frto = 0;
	}
	tcp_xmit_retransmit_queue(sk);
}

Project: net
File: tcp_input.c

tcp_collapse(struct sock *sk, struct sk_buff_head *list,
	     struct sk_buff *head, struct sk_buff *tail,
	     u32 start, u32 end)
{
	struct sk_buff *skb, *n;
	bool end_of_skbs;

	/* First, check that queue is collapsible and find
	 * the point where collapsing can be useful. */
	skb = head;
restart:
	end_of_skbs = true;
	skb_queue_walk_from_safe(list, skb, n) {
		if (skb == tail)
			break;
		/* No new bits? It is possible on ofo queue. */
		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
			skb = tcp_collapse_one(sk, skb, list);
			if (!skb)
				break;
			goto restart;
		}

		/* The first skb to collapse is:
		 * - not SYN/FIN and
		 * - bloated or contains data before "start" or
		 *   overlaps to the next one.
		 */
		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
		    (tcp_win_from_space(skb->truesize) > skb->len ||
		     before(TCP_SKB_CB(skb)->seq, start))) {
			end_of_skbs = false;
			break;
		}

		if (!skb_queue_is_last(list, skb)) {
			struct sk_buff *next = skb_queue_next(list, skb);
			if (next != tail &&
			    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
				end_of_skbs = false;
				break;
			}
		}

		/* Decided to skip this, advance start seq. */
		start = TCP_SKB_CB(skb)->end_seq;
	}
	if (end_of_skbs ||
	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
		return;

	while (before(start, end)) {
		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
		struct sk_buff *nskb;

		nskb = alloc_skb(copy, GFP_ATOMIC);
		if (!nskb)
			return;

		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
		__skb_queue_before(list, skb, nskb);
		skb_set_owner_r(nskb, sk);

		/* Copy data, releasing collapsed skbs. */
		while (copy > 0) {
			int offset = start - TCP_SKB_CB(skb)->seq;
			int size = TCP_SKB_CB(skb)->end_seq - start;

			BUG_ON(offset < 0);
			if (size > 0) {
				size = min(copy, size);
				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
					BUG();
				TCP_SKB_CB(nskb)->end_seq += size;
				copy -= size;
				start += size;
			}
			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
				skb = tcp_collapse_one(sk, skb, list);
				if (!skb ||
				    skb == tail ||
				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
					return;
			}
		}
	}
}

Project: net
File: tcp_input.c

static bool tcp_syn_flood_action(const struct sock *sk,
				 const struct sk_buff *skb,
				 const char *proto)
{
	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
	const char *msg = "Dropping request";
	bool want_cookie = false;
	struct net *net = sock_net(sk);

#ifdef CONFIG_SYN_COOKIES
	if (net->ipv4.sysctl_tcp_syncookies) {
		msg = "Sending cookies";
		want_cookie = true;
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
	} else
#endif
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);

	if (!queue->synflood_warned &&
	    net->ipv4.sysctl_tcp_syncookies != 2 &&
	    xchg(&queue->synflood_warned, 1) == 0)
		pr_info("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
			proto, ntohs(tcp_hdr(skb)->dest), msg);

	return want_cookie;
}

Project: net
File: tcp_input.c

static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tcp_is_reno(tp)) {
		tcp_mark_head_lost(sk, 1, 1);
	} else if (tcp_is_fack(tp)) {
		int lost = tp->fackets_out - tp->reordering;
		if (lost <= 0)
			lost = 1;
		tcp_mark_head_lost(sk, lost, 0);
	} else {
		int sacked_upto = tp->sacked_out - tp->reordering;
		if (sacked_upto >= 0)
			tcp_mark_head_lost(sk, sacked_upto, 0);
		else if (fast_rexmit)
			tcp_mark_head_lost(sk, 1, 1);
	}
}

Project: net
File: tcp_input.c

static void tcp_dsack_seen(struct tcp_sock *tp)
{
	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
}

Project: net
File: tcp_input.c

void tcp_resume_early_retransmit(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	tcp_rearm_rto(sk);

	/* Stop if ER is disabled after the delayed ER timer is scheduled */
	if (!tp->do_early_retrans)
		return;

	tcp_enter_recovery(sk, false);
	tcp_update_scoreboard(sk, 1);
	tcp_xmit_retransmit_queue(sk);
}

Project: net
File: tcp_input.c

bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
			  int mib_idx, u32 *last_oow_ack_time)
{
	/* Data packets without SYNs are not likely part of an ACK loop. */
	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
	    !tcp_hdr(skb)->syn)
		goto not_rate_limited;

	if (*last_oow_ack_time) {
		s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);

		if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
			NET_INC_STATS(net, mib_idx);
			return true;	/* rate-limited: don't send yet! */
		}
	}

	*last_oow_ack_time = tcp_time_stamp;

not_rate_limited:
	return false;	/* not rate-limited: go ahead, send dupack now! */
}

Project: net
File: tcp_input.c

static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
			     int *rexmit)
{
	struct tcp_sock *tp = tcp_sk(sk);
	bool recovered = !before(tp->snd_una, tp->high_seq);

	if ((flag & FLAG_SND_UNA_ADVANCED) &&
	    tcp_try_undo_loss(sk, false))
		return;

	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
		/* Step 3.b. A timeout is spurious if not all data are
		 * lost, i.e., never-retransmitted data are (s)acked.
		 */
		if ((flag & FLAG_ORIG_SACK_ACKED) &&
		    tcp_try_undo_loss(sk, true))
			return;

		if (after(tp->snd_nxt, tp->high_seq)) {
			if (flag & FLAG_DATA_SACKED || is_dupack)
				tp->frto = 0; /* Step 3.a. loss was real */
		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
			tp->high_seq = tp->snd_nxt;
			/* Step 2.b. Try send new data (but deferred until cwnd
			 * is updated in tcp_ack()). Otherwise fall back to
			 * the conventional recovery.
			 */
			if (tcp_send_head(sk) &&
			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
				*rexmit = REXMIT_NEW;
				return;
			}
			tp->frto = 0;
		}
	}

	if (recovered) {
		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
		tcp_try_undo_recovery(sk);
		return;
	}
	if (tcp_is_reno(tp)) {
		/* A Reno DUPACK means new data in F-RTO step 2.b above are
		 * delivered. Lower inflight to clock out (re)tranmissions.
		 */
		if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
			tcp_add_reno_sack(sk);
		else if (flag & FLAG_SND_UNA_ADVANCED)
			tcp_reset_reno_sack(tp);
	}
	*rexmit = REXMIT_LOST;
}

Project: net
File: tcp_input.c

static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	const unsigned int lss = icsk->icsk_ack.last_seg_size;
	unsigned int len;

	icsk->icsk_ack.last_seg_size = 0;

	/* skb->len may jitter because of SACKs, even if peer
	 * sends good full-sized frames.
	 */
	len = skb_shinfo(skb)->gso_size ? : skb->len;
	if (len >= icsk->icsk_ack.rcv_mss) {
		icsk->icsk_ack.rcv_mss = len;
	} else {
		/* Otherwise, we make more careful check taking into account,
		 * that SACKs block is variable.
		 *
		 * "len" is invariant segment length, including TCP header.
		 */
		len += skb->data - skb_transport_header(skb);
		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
		    /* If PSH is not set, packet should be
		     * full sized, provided peer TCP is not badly broken.
		     * This observation (if it is correct 8)) allows
		     * to handle super-low mtu links fairly.
		     */
		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
			/* Subtract also invariant (if peer is RFC compliant),
			 * tcp header plus fixed timestamp option length.
			 * Resulting "len" is MSS free of SACK jitter.
			 */
			len -= tcp_sk(sk)->tcp_header_len;
			icsk->icsk_ack.last_seg_size = len;
			if (len == lss) {
				icsk->icsk_ack.rcv_mss = len;
				return;
			}
		}
		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
	}
}

Project: net
File: tcp_input.c

void tcp_rearm_rto(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);

	/* If the retrans timer is currently being used by Fast Open
	 * for SYN-ACK retrans purpose, stay put.
	 */
	if (tp->fastopen_rsk)
		return;

	if (!tp->packets_out) {
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
	} else {
		u32 rto = inet_csk(sk)->icsk_rto;
		/* Offset the time elapsed after installing regular RTO */
		if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
			struct sk_buff *skb = tcp_write_queue_head(sk);
			const u32 rto_time_stamp =
				tcp_skb_timestamp(skb) + rto;
			s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
			/* delta may not be positive if the socket is locked
			 * when the retrans timer fires and is rescheduled.
			 */
			if (delta > 0)
				rto = delta;
		}
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
					  TCP_RTO_MAX);
	}
}

Project: net
File: tcp_input.c

static int tcp_prune_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);

	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);

	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
		tcp_clamp_window(sk);
	else if (tcp_under_memory_pressure(sk))
		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);

	tcp_collapse_ofo_queue(sk);
	if (!skb_queue_empty(&sk->sk_receive_queue))
		tcp_collapse(sk, &sk->sk_receive_queue,
			     skb_peek(&sk->sk_receive_queue),
			     NULL,
			     tp->copied_seq, tp->rcv_nxt);
	sk_mem_reclaim(sk);

	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
		return 0;

	/* Collapsing did not help, destructive actions follow.
	 * This must not ever occur. */

	tcp_prune_ofo_queue(sk);

	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
		return 0;

	/* If we are really being abused, tell the caller to silently
	 * drop receive data on the floor.  It will get retransmitted
	 * and hopefully then we'll have sufficient space.
	 */
	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);

	/* Massive buffer overcommit. */
	tp->pred_flags = 0;
	return -1;
}

Project: net
File: tcp_input.c

static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
		tcp_enter_quickack_mode(sk);

		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
			u32 end_seq = TCP_SKB_CB(skb)->end_seq;

			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
				end_seq = tp->rcv_nxt;
			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
		}
	}

	tcp_send_ack(sk);
}

Project: net
File: tcp_input.c

static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (frto_undo || tcp_may_undo(tp)) {
		tcp_undo_cwnd_reduction(sk, true);

		DBGUNDO(sk, "partial loss");
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
		if (frto_undo)
			NET_INC_STATS(sock_net(sk),
					LINUX_MIB_TCPSPURIOUSRTOS);
		inet_csk(sk)->icsk_retransmits = 0;
		if (frto_undo || tcp_is_sack(tp))
			tcp_set_ca_state(sk, TCP_CA_Open);
		return true;
	}
	return false;
}

Project: net
File: tcp_input.c

static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
{
	u32 delta = ack - tp->snd_una;

	sock_owned_by_me((struct sock *)tp);
	u64_stats_update_begin_raw(&tp->syncp);
	tp->bytes_acked += delta;
	u64_stats_update_end_raw(&tp->syncp);
	tp->snd_una = ack;
}

Project: net
File: tcp_input.c

static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned long delay;

	/* Delay early retransmit and entering fast recovery for
	 * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
	 * available, or RTO is scheduled to fire first.
	 */
	if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
	    (flag & FLAG_ECE) || !tp->srtt_us)
		return false;

	delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
		    msecs_to_jiffies(2));

	if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
		return false;

	inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
				  TCP_RTO_MAX);
	return true;
}

Project: net
File: tcp_input.c

void tcp_enter_loss(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct net *net = sock_net(sk);
	struct sk_buff *skb;
	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
	bool is_reneg;			/* is receiver reneging on SACKs? */

	/* Reduce ssthresh if it has not yet been made inside this window. */
	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
	    !after(tp->high_seq, tp->snd_una) ||
	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
		tp->prior_ssthresh = tcp_current_ssthresh(sk);
		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
		tcp_ca_event(sk, CA_EVENT_LOSS);
		tcp_init_undo(tp);
	}
	tp->snd_cwnd	   = 1;
	tp->snd_cwnd_cnt   = 0;
	tp->snd_cwnd_stamp = tcp_time_stamp;

	tp->retrans_out = 0;
	tp->lost_out = 0;

	if (tcp_is_reno(tp))
		tcp_reset_reno_sack(tp);

	skb = tcp_write_queue_head(sk);
	is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
	if (is_reneg) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
		tp->sacked_out = 0;
		tp->fackets_out = 0;
	}
	tcp_clear_all_retrans_hints(tp);

	tcp_for_write_queue(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;

		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
			tp->lost_out += tcp_skb_pcount(skb);
			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
		}
	}
	tcp_verify_left_out(tp);

	/* Timeout in disordered state after receiving substantial DUPACKs
	 * suggests that the degree of reordering is over-estimated.
	 */
	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
	    tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
		tp->reordering = min_t(unsigned int, tp->reordering,
				       net->ipv4.sysctl_tcp_reordering);
	tcp_set_ca_state(sk, TCP_CA_Loss);
	tp->high_seq = tp->snd_nxt;
	tcp_ecn_queue_cwr(tp);

	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
	 * loss recovery is underway except recurring timeout(s) on
	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
	 */
	tp->frto = sysctl_tcp_frto &&
		   (new_recovery || icsk->icsk_retransmits) &&
		   !inet_csk(sk)->icsk_mtup.probe_size;
}

Project: net
File: tcp_input.c

static void tcp_ofo_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	__u32 dsack_high = tp->rcv_nxt;
	struct sk_buff *skb, *tail;
	bool fragstolen, eaten;

	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
			break;

		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
			__u32 dsack = dsack_high;
			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
				dsack_high = TCP_SKB_CB(skb)->end_seq;
			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
		}

		__skb_unlink(skb, &tp->out_of_order_queue);
		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
			SOCK_DEBUG(sk, "ofo packet was already received\n");
			tcp_drop(sk, skb);
			continue;
		}
		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
			   TCP_SKB_CB(skb)->end_seq);

		tail = skb_peek_tail(&sk->sk_receive_queue);
		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
		if (!eaten)
			__skb_queue_tail(&sk->sk_receive_queue, skb);
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
			tcp_fin(sk);
		if (eaten)
			kfree_skb_partial(skb, fragstolen);
	}
}

Project: net
File: tcp_input.c

static u8 tcp_sacktag_one(struct sock *sk,
			  struct tcp_sacktag_state *state, u8 sacked,
			  u32 start_seq, u32 end_seq,
			  int dup_sack, int pcount,
			  const struct skb_mstamp *xmit_time)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int fack_count = state->fack_count;

	/* Account D-SACK for retransmitted packet. */
	if (dup_sack && (sacked & TCPCB_RETRANS)) {
		if (tp->undo_marker && tp->undo_retrans > 0 &&
		    after(end_seq, tp->undo_marker))
			tp->undo_retrans--;
		if (sacked & TCPCB_SACKED_ACKED)
			state->reord = min(fack_count, state->reord);
	}

	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
	if (!after(end_seq, tp->snd_una))
		return sacked;

	if (!(sacked & TCPCB_SACKED_ACKED)) {
		tcp_rack_advance(tp, xmit_time, sacked);

		if (sacked & TCPCB_SACKED_RETRANS) {
			/* If the segment is not tagged as lost,
			 * we do not clear RETRANS, believing
			 * that retransmission is still in flight.
			 */
			if (sacked & TCPCB_LOST) {
				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
				tp->lost_out -= pcount;
				tp->retrans_out -= pcount;
			}
		} else {
			if (!(sacked & TCPCB_RETRANS)) {
				/* New sack for not retransmitted frame,
				 * which was in hole. It is reordering.
				 */
				if (before(start_seq,
					   tcp_highest_sack_seq(tp)))
					state->reord = min(fack_count,
							   state->reord);
				if (!after(end_seq, tp->high_seq))
					state->flag |= FLAG_ORIG_SACK_ACKED;
				if (state->first_sackt.v64 == 0)
					state->first_sackt = *xmit_time;
				state->last_sackt = *xmit_time;
			}

			if (sacked & TCPCB_LOST) {
				sacked &= ~TCPCB_LOST;
				tp->lost_out -= pcount;
			}
		}

		sacked |= TCPCB_SACKED_ACKED;
		state->flag |= FLAG_DATA_SACKED;
		tp->sacked_out += pcount;
		tp->delivered += pcount;  /* Out-of-order packets delivered */

		fack_count += pcount;

		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
		if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
			tp->lost_cnt_hint += pcount;

		if (fack_count > tp->fackets_out)
			tp->fackets_out = fack_count;
	}

	/* D-SACK. We can detect redundant retransmission in S|R and plain R
	 * frames and clear it. undo_retrans is decreased above, L|R frames
	 * are accounted above as well.
	 */
	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
		sacked &= ~TCPCB_SACKED_RETRANS;
		tp->retrans_out -= pcount;
	}

	return sacked;
}

Project: net
File: tcp_input.c

const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
{
	int length = (th->doff << 2) - sizeof(*th);
	const u8 *ptr = (const u8 *)(th + 1);

	/* If the TCP option is too short, we can short cut */
	if (length < TCPOLEN_MD5SIG)
		return NULL;

	while (length > 0) {
		int opcode = *ptr++;
		int opsize;

		switch (opcode) {
		case TCPOPT_EOL:
			return NULL;
		case TCPOPT_NOP:
			length--;
			continue;
		default:
			opsize = *ptr++;
			if (opsize < 2 || opsize > length)
				return NULL;
			if (opcode == TCPOPT_MD5SIG)
				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
		}
		ptr += opsize - 2;
		length -= opsize;
	}
	return NULL;
}

Project: net
File: tcp_input.c

void tcp_fin(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	inet_csk_schedule_ack(sk);

	sk->sk_shutdown |= RCV_SHUTDOWN;
	sock_set_flag(sk, SOCK_DONE);

	switch (sk->sk_state) {
	case TCP_SYN_RECV:
	case TCP_ESTABLISHED:
		/* Move to CLOSE_WAIT */
		tcp_set_state(sk, TCP_CLOSE_WAIT);
		inet_csk(sk)->icsk_ack.pingpong = 1;
		break;

	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
		/* Received a retransmission of the FIN, do
		 * nothing.
		 */
		break;
	case TCP_LAST_ACK:
		/* RFC793: Remain in the LAST-ACK state. */
		break;

	case TCP_FIN_WAIT1:
		/* This case occurs when a simultaneous close
		 * happens, we must ack the received FIN and
		 * enter the CLOSING state.
		 */
		tcp_send_ack(sk);
		tcp_set_state(sk, TCP_CLOSING);
		break;
	case TCP_FIN_WAIT2:
		/* Received a FIN -- send ACK and enter TIME_WAIT. */
		tcp_send_ack(sk);
		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
		break;
	default:
		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
		 * cases we should never reach this piece of code.
		 */
		pr_err("%s: Impossible, sk->sk_state=%d\n",
		       __func__, sk->sk_state);
		break;
	}

	/* It _is_ possible, that we have something out-of-order _after_ FIN.
	 * Probably, we should reset in this case. For now drop them.
	 */
	__skb_queue_purge(&tp->out_of_order_queue);
	if (tcp_is_sack(tp))
		tcp_sack_reset(&tp->rx_opt);
	sk_mem_reclaim(sk);

	if (!sock_flag(sk, SOCK_DEAD)) {
		sk->sk_state_change(sk);

		/* Do not send POLL_HUP for half duplex close. */
		if (sk->sk_shutdown == SHUTDOWN_MASK ||
		    sk->sk_state == TCP_CLOSE)
			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
		else
			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
	}
}

Project: net
File: tcp_input.c

static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
					struct sk_buff_head *list)
{
	struct sk_buff *next = NULL;

	if (!skb_queue_is_last(list, skb))
		next = skb_queue_next(list, skb);

	__skb_unlink(skb, list);
	__kfree_skb(skb);
	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);

	return next;
}

Project: net
File: tcp_input.c

static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	u32 now;

	inet_csk_schedule_ack(sk);

	tcp_measure_rcv_mss(sk, skb);

	tcp_rcv_rtt_measure(tp);

	now = tcp_time_stamp;

	if (!icsk->icsk_ack.ato) {
		/* The _first_ data packet received, initialize
		 * delayed ACK engine.
		 */
		tcp_incr_quickack(sk);
		icsk->icsk_ack.ato = TCP_ATO_MIN;
	} else {
		int m = now - icsk->icsk_ack.lrcvtime;

		if (m <= TCP_ATO_MIN / 2) {
			/* The fastest case is the first. */
			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
		} else if (m < icsk->icsk_ack.ato) {
			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
			if (icsk->icsk_ack.ato > icsk->icsk_rto)
				icsk->icsk_ack.ato = icsk->icsk_rto;
		} else if (m > icsk->icsk_rto) {
			/* Too long gap. Apparently sender failed to
			 * restart window, so that we send ACKs quickly.
			 */
			tcp_incr_quickack(sk);
			sk_mem_reclaim(sk);
		}
	}
	icsk->icsk_ack.lrcvtime = now;

	tcp_ecn_check_ce(tp, skb);

	if (skb->len >= 128)
		tcp_grow_window(sk, skb);
}

Project: net
File: tcp_input.c

static void tcp_update_reordering(struct sock *sk, const int metric,
				  const int ts)
{
	struct tcp_sock *tp = tcp_sk(sk);
	if (metric > tp->reordering) {
		int mib_idx;

		tp->reordering = min(sysctl_tcp_max_reordering, metric);

		/* This exciting event is worth to be remembered. 8) */
		if (ts)
			mib_idx = LINUX_MIB_TCPTSREORDER;
		else if (tcp_is_reno(tp))
			mib_idx = LINUX_MIB_TCPRENOREORDER;
		else if (tcp_is_fack(tp))
			mib_idx = LINUX_MIB_TCPFACKREORDER;
		else
			mib_idx = LINUX_MIB_TCPSACKREORDER;

		NET_INC_STATS(sock_net(sk), mib_idx);
#if FASTRETRANS_DEBUG > 1
		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
			 tp->reordering,
			 tp->fackets_out,
			 tp->sacked_out,
			 tp->undo_marker ? tp->undo_retrans : 0);
#endif
		tcp_disable_fack(tp);
	}

	if (metric > 0)
		tcp_disable_early_retrans(tp);
	tp->rack.reord = 1;
}

Project: net
File: tcp_input.c

static void tcp_openreq_init(struct request_sock *req,
			     const struct tcp_options_received *rx_opt,
			     struct sk_buff *skb, const struct sock *sk)
{
	struct inet_request_sock *ireq = inet_rsk(req);

	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
	req->cookie_ts = 0;
	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
	skb_mstamp_get(&tcp_rsk(req)->snt_synack);
	tcp_rsk(req)->last_oow_ack_time = 0;
	req->mss = rx_opt->mss_clamp;
	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
	ireq->tstamp_ok = rx_opt->tstamp_ok;
	ireq->sack_ok = rx_opt->sack_ok;
	ireq->snd_wscale = rx_opt->snd_wscale;
	ireq->wscale_ok = rx_opt->wscale_ok;
	ireq->acked = 0;
	ireq->ecn_ok = 0;
	ireq->ir_rmt_port = tcp_hdr(skb)->source;
	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
	ireq->ir_mark = inet_request_mark(sk, skb);
}

Project: net
File: tcp_input.c

static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
{
	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
	case INET_ECN_NOT_ECT:
		/* Funny extension: if ECT is not set on a segment,
		 * and we already seen ECT on a previous segment,
		 * it is probably a retransmit.
		 */
		if (tp->ecn_flags & TCP_ECN_SEEN)
			tcp_enter_quickack_mode((struct sock *)tp);
		break;
	case INET_ECN_CE:
		if (tcp_ca_needs_ecn((struct sock *)tp))
			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);

		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
			/* Better not delay acks, sender can have a very low cwnd */
			tcp_enter_quickack_mode((struct sock *)tp);
			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
		}
		tp->ecn_flags |= TCP_ECN_SEEN;
		break;
	default:
		if (tcp_ca_needs_ecn((struct sock *)tp))
			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
		tp->ecn_flags |= TCP_ECN_SEEN;
		break;
	}
}

Project: net
File: tcp_input.c

static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
{
	if (tp->ecn_flags & TCP_ECN_OK)
		__tcp_ecn_check_ce(tp, skb);
}

Project: net
File: tcp_input.c

static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (unmark_loss) {
		struct sk_buff *skb;

		tcp_for_write_queue(skb, sk) {
			if (skb == tcp_send_head(sk))
				break;
			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
		}
		tp->lost_out = 0;
		tcp_clear_all_retrans_hints(tp);
	}

	if (tp->prior_ssthresh) {
		const struct inet_connection_sock *icsk = inet_csk(sk);

		if (icsk->icsk_ca_ops->undo_cwnd)
			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
		else
			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);

		if (tp->prior_ssthresh > tp->snd_ssthresh) {
			tp->snd_ssthresh = tp->prior_ssthresh;
			tcp_ecn_withdraw_cwr(tp);
		}
	}
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->undo_marker = 0;
}

Project: net
File: tcp_input.c

static void tcp_ack_probe(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	/* Was it a usable window open? */

	if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
		icsk->icsk_backoff = 0;
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
		/* Socket must be waked up by subsequent tcp_data_snd_check().
		 * This function is not for random using!
		 */
	} else {
		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);

		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
					  when, TCP_RTO_MAX);
	}
}

Project: net
File: tcp_input.c

static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_sacktag_state sack_state;
	u32 prior_snd_una = tp->snd_una;
	u32 ack_seq = TCP_SKB_CB(skb)->seq;
	u32 ack = TCP_SKB_CB(skb)->ack_seq;
	bool is_dupack = false;
	u32 prior_fackets;
	int prior_packets = tp->packets_out;
	u32 prior_delivered = tp->delivered;
	int acked = 0; /* Number of packets newly acked */
	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */

	sack_state.first_sackt.v64 = 0;

	/* We very likely will need to access write queue head. */
	prefetchw(sk->sk_write_queue.next);

	/* If the ack is older than previous acks
	 * then we can probably ignore it.
	 */
	if (before(ack, prior_snd_una)) {
		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
		if (before(ack, prior_snd_una - tp->max_window)) {
			tcp_send_challenge_ack(sk, skb);
			return -1;
		}
		goto old_ack;
	}

	/* If the ack includes data we haven't sent yet, discard
	 * this segment (RFC793 Section 3.9).
	 */
	if (after(ack, tp->snd_nxt))
		goto invalid_ack;

	if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
		tcp_rearm_rto(sk);

	if (after(ack, prior_snd_una)) {
		flag |= FLAG_SND_UNA_ADVANCED;
		icsk->icsk_retransmits = 0;
	}

	prior_fackets = tp->fackets_out;

	/* ts_recent update must be made after we are sure that the packet
	 * is in window.
	 */
	if (flag & FLAG_UPDATE_TS_RECENT)
		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);

	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
		/* Window is constant, pure forward advance.
		 * No more checks are required.
		 * Note, we use the fact that SND.UNA>=SND.WL2.
		 */
		tcp_update_wl(tp, ack_seq);
		tcp_snd_una_update(tp, ack);
		flag |= FLAG_WIN_UPDATE;

		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);

		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
	} else {
		u32 ack_ev_flags = CA_ACK_SLOWPATH;

		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
			flag |= FLAG_DATA;
		else
			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);

		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);

		if (TCP_SKB_CB(skb)->sacked)
			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
							&sack_state);

		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
			flag |= FLAG_ECE;
			ack_ev_flags |= CA_ACK_ECE;
		}

		if (flag & FLAG_WIN_UPDATE)
			ack_ev_flags |= CA_ACK_WIN_UPDATE;

		tcp_in_ack_event(sk, ack_ev_flags);
	}

	/* We passed data and got it acked, remove any soft error
	 * log. Something worked...
	 */
	sk->sk_err_soft = 0;
	icsk->icsk_probes_out = 0;
	tp->rcv_tstamp = tcp_time_stamp;
	if (!prior_packets)
		goto no_queue;

	/* See if we can take anything off of the retransmit queue. */
	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
				    &sack_state);

	if (tcp_ack_is_dubious(sk, flag)) {
		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
	}
	if (tp->tlp_high_seq)
		tcp_process_tlp_ack(sk, ack, flag);

	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
		struct dst_entry *dst = __sk_dst_get(sk);
		if (dst)
			dst_confirm(dst);
	}

	if (icsk->icsk_pending == ICSK_TIME_RETRANS)
		tcp_schedule_loss_probe(sk);
	tcp_cong_control(sk, ack, tp->delivered - prior_delivered, flag);
	tcp_xmit_recovery(sk, rexmit);
	return 1;

no_queue:
	/* If data was DSACKed, see if we can undo a cwnd reduction. */
	if (flag & FLAG_DSACKING_ACK)
		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
	/* If this ack opens up a zero window, clear backoff.  It was
	 * being used to time the probes, and is probably far higher than
	 * it needs to be for normal retransmission.
	 */
	if (tcp_send_head(sk))
		tcp_ack_probe(sk);

	if (tp->tlp_high_seq)
		tcp_process_tlp_ack(sk, ack, flag);
	return 1;

invalid_ack:
	SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
	return -1;

old_ack:
	/* If data was SACKed, tag it and see if we should send more data.
	 * If data was DSACKed, see if we can undo a cwnd reduction.
	 */
	if (TCP_SKB_CB(skb)->sacked) {
		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
						&sack_state);
		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
		tcp_xmit_recovery(sk, rexmit);
	}

	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
	return 0;
}

Project: net
File: tcp_input.c

static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
{
	const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ;
	struct rtt_meas *m = tcp_sk(sk)->rtt_min;
	struct rtt_meas rttm = {
		.rtt = likely(rtt_us) ? rtt_us : jiffies_to_usecs(1),
		.ts = now,
	};
	u32 elapsed;

	/* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
	if (unlikely(rttm.rtt <= m[0].rtt))
		m[0] = m[1] = m[2] = rttm;
	else if (rttm.rtt <= m[1].rtt)
		m[1] = m[2] = rttm;
	else if (rttm.rtt <= m[2].rtt)
		m[2] = rttm;

	elapsed = now - m[0].ts;
	if (unlikely(elapsed > wlen)) {
		/* Passed entire window without a new min so make 2nd choice
		 * the new min & 3rd choice the new 2nd. So forth and so on.
		 */
		m[0] = m[1];
		m[1] = m[2];
		m[2] = rttm;
		if (now - m[0].ts > wlen) {
			m[0] = m[1];
			m[1] = rttm;
			if (now - m[0].ts > wlen)
				m[0] = rttm;
		}
	} else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
		/* Passed a quarter of the window without a new min so
		 * take 2nd choice from the 2nd quarter of the window.
		 */
		m[2] = m[1] = rttm;
	} else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
		/* Passed half the window without a new min so take the 3rd
		 * choice from the last half of the window.
		 */
		m[2] = rttm;
	}
}

Project: net
File: tcp_input.c

static void tcp_clamp_window(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	icsk->icsk_ack.quick = 0;

	if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
	    !tcp_under_memory_pressure(sk) &&
	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
		sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
				    sysctl_tcp_rmem[2]);
	}
	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
}

Project: net
File: tcp_input.c

static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
					  const struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	if (tp->rx_opt.rcv_tsecr &&
	    (TCP_SKB_CB(skb)->end_seq -
	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
}

Project: net
File: tcp_input.c

void tcp_parse_options(const struct sk_buff *skb,
		       struct tcp_options_received *opt_rx, int estab,
		       struct tcp_fastopen_cookie *foc)
{
	const unsigned char *ptr;
	const struct tcphdr *th = tcp_hdr(skb);
	int length = (th->doff * 4) - sizeof(struct tcphdr);

	ptr = (const unsigned char *)(th + 1);
	opt_rx->saw_tstamp = 0;

	while (length > 0) {
		int opcode = *ptr++;
		int opsize;

		switch (opcode) {
		case TCPOPT_EOL:
			return;
		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
			length--;
			continue;
		default:
			opsize = *ptr++;
			if (opsize < 2) /* "silly options" */
				return;
			if (opsize > length)
				return;	/* don't parse partial options */
			switch (opcode) {
			case TCPOPT_MSS:
				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
					u16 in_mss = get_unaligned_be16(ptr);
					if (in_mss) {
						if (opt_rx->user_mss &&
						    opt_rx->user_mss < in_mss)
							in_mss = opt_rx->user_mss;
						opt_rx->mss_clamp = in_mss;
					}
				}
				break;
			case TCPOPT_WINDOW:
				if (opsize == TCPOLEN_WINDOW && th->syn &&
				    !estab && sysctl_tcp_window_scaling) {
					__u8 snd_wscale = *(__u8 *)ptr;
					opt_rx->wscale_ok = 1;
					if (snd_wscale > 14) {
						net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
								     __func__,
								     snd_wscale);
						snd_wscale = 14;
					}
					opt_rx->snd_wscale = snd_wscale;
				}
				break;
			case TCPOPT_TIMESTAMP:
				if ((opsize == TCPOLEN_TIMESTAMP) &&
				    ((estab && opt_rx->tstamp_ok) ||
				     (!estab && sysctl_tcp_timestamps))) {
					opt_rx->saw_tstamp = 1;
					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
				}
				break;
			case TCPOPT_SACK_PERM:
				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
				    !estab && sysctl_tcp_sack) {
					opt_rx->sack_ok = TCP_SACK_SEEN;
					tcp_sack_reset(opt_rx);
				}
				break;

			case TCPOPT_SACK:
				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
				   opt_rx->sack_ok) {
					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
				}
				break;
#ifdef CONFIG_TCP_MD5SIG
			case TCPOPT_MD5SIG:
				/*
				 * The MD5 Hash has already been
				 * checked (see tcp_v{4,6}_do_rcv()).
				 */
				break;
#endif
			case TCPOPT_FASTOPEN:
				tcp_parse_fastopen_option(
					opsize - TCPOLEN_FASTOPEN_BASE,
					ptr, th->syn, foc, false);
				break;

			case TCPOPT_EXP:
				/* Fast Open option shares code 254 using a
				 * 16 bits magic number.
				 */
				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
				    get_unaligned_be16(ptr) ==
				    TCPOPT_FASTOPEN_MAGIC)
					tcp_parse_fastopen_option(opsize -
						TCPOLEN_EXP_FASTOPEN_BASE,
						ptr + 2, th->syn, foc, true);
				break;

			}
			ptr += opsize-2;
			length -= opsize;
		}
	}
}

Project: net
File: tcp_input.c

static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
{
	struct tcp_sock *tp = tcp_sk(sk);

	    /* More than one full frame received... */
	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
	     /* ... and right edge of window advances far enough.
	      * (tcp_recvmsg() will send ACK otherwise). Or...
	      */
	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
	    /* We ACK each frame or... */
	    tcp_in_quickack_mode(sk) ||
	    /* We have out of order data. */
	    (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
		/* Then ack it now */
		tcp_send_ack(sk);
	} else {
		/* Else, send delayed ack. */
		tcp_send_delayed_ack(sk);
	}
}

Project: net
File: tcp_input.c

static void tcp_sndbuf_expand(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	int sndmem, per_mss;
	u32 nr_segs;

	/* Worst case is non GSO/TSO : each frame consumes one skb
	 * and skb->head is kmalloced using power of two area of memory
	 */
	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
		  MAX_TCP_HEADER +
		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

	per_mss = roundup_pow_of_two(per_mss) +
		  SKB_DATA_ALIGN(sizeof(struct sk_buff));

	nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);

	/* Fast Recovery (RFC 5681 3.2) :
	 * Cubic needs 1.7 factor, rounded to 2 to include
	 * extra cushion (application might react slowly to POLLOUT)
	 */
	sndmem = 2 * nr_segs * per_mss;

	if (sk->sk_sndbuf < sndmem)
		sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
}

Project: net
File: tcp_input.c

static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);

	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
}

Project: net
File: tcp_input.c

static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
						struct sock *sk,
						struct tcp_sack_block *next_dup,
						struct tcp_sacktag_state *state,
						u32 skip_to_seq)
{
	if (!next_dup)
		return skb;

	if (before(next_dup->start_seq, skip_to_seq)) {
		skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
		skb = tcp_sacktag_walk(skb, sk, NULL, state,
				       next_dup->start_seq, next_dup->end_seq,
				       1);
	}

	return skb;
}

Project: net
File: tcp_input.c

static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
			   u32 prior_snd_una)
{
	const struct skb_shared_info *shinfo;

	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
		return;

	shinfo = skb_shinfo(skb);
	if (!before(shinfo->tskey, prior_snd_una) &&
	    before(shinfo->tskey, tcp_sk(sk)->snd_una))
		__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
}

Project: net
File: tcp_input.c

static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
				    struct tcp_fastopen_cookie *cookie)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
	bool syn_drop = false;

	if (mss == tp->rx_opt.user_mss) {
		struct tcp_options_received opt;

		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
		tcp_clear_options(&opt);
		opt.user_mss = opt.mss_clamp = 0;
		tcp_parse_options(synack, &opt, 0, NULL);
		mss = opt.mss_clamp;
	}

	if (!tp->syn_fastopen) {
		/* Ignore an unsolicited cookie */
		cookie->len = -1;
	} else if (tp->total_retrans) {
		/* SYN timed out and the SYN-ACK neither has a cookie nor
		 * acknowledges data. Presumably the remote received only
		 * the retransmitted (regular) SYNs: either the original
		 * SYN-data or the corresponding SYN-ACK was dropped.
		 */
		syn_drop = (cookie->len < 0 && data);
	} else if (cookie->len < 0 && !tp->syn_data) {
		/* We requested a cookie but didn't get it. If we did not use
		 * the (old) exp opt format then try so next time (try_exp=1).
		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
		 */
		try_exp = tp->syn_fastopen_exp ? 2 : 1;
	}

	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);

	if (data) { /* Retransmit unacked data in SYN */
		tcp_for_write_queue_from(data, sk) {
			if (data == tcp_send_head(sk) ||
			    __tcp_retransmit_skb(sk, data, 1))
				break;
		}
		tcp_rearm_rto(sk);
		NET_INC_STATS(sock_net(sk),
				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
		return true;
	}
	tp->syn_data_acked = tp->syn_data;
	if (tp->syn_data_acked)
		NET_INC_STATS(sock_net(sk),
				LINUX_MIB_TCPFASTOPENACTIVE);

	tcp_fastopen_add_skb(sk, synack);

	return false;
}

Project: net
File: tcp_input.c

static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
				  u32 start_seq, u32 end_seq)
{
	int err;
	bool in_sack;
	unsigned int pkt_len;
	unsigned int mss;

	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);

	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
		mss = tcp_skb_mss(skb);
		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);

		if (!in_sack) {
			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
			if (pkt_len < mss)
				pkt_len = mss;
		} else {
			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
			if (pkt_len < mss)
				return -EINVAL;
		}

		/* Round if necessary so that SACKs cover only full MSSes
		 * and/or the remaining small portion (if present)
		 */
		if (pkt_len > mss) {
			unsigned int new_len = (pkt_len / mss) * mss;
			if (!in_sack && new_len < pkt_len) {
				new_len += mss;
				if (new_len >= skb->len)
					return 0;
			}
			pkt_len = new_len;
		}
		err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
		if (err < 0)
			return err;
	}

	return in_sack;
}

Project: net
File: tcp_input.c

static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
				 unsigned int size)
{
	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
	    !sk_rmem_schedule(sk, skb, size)) {

		if (tcp_prune_queue(sk) < 0)
			return -1;

		if (!sk_rmem_schedule(sk, skb, size)) {
			if (!tcp_prune_ofo_queue(sk))
				return -1;

			if (!sk_rmem_schedule(sk, skb, size))
				return -1;
		}
	}
	return 0;
}

Project: net
File: tcp_input.c

static void tcp_check_reno_reordering(struct sock *sk, const int addend)
{
	struct tcp_sock *tp = tcp_sk(sk);
	if (tcp_limit_reno_sacked(tp))
		tcp_update_reordering(sk, tp->packets_out + addend, 0);
}

Project: net
File: tcp_input.c

static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
		int mib_idx;

		if (before(seq, tp->rcv_nxt))
			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
		else
			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;

		NET_INC_STATS(sock_net(sk), mib_idx);

		tp->rx_opt.dsack = 1;
		tp->duplicate_sack[0].start_seq = seq;
		tp->duplicate_sack[0].end_seq = end_seq;
	}
}

Project: net
File: tcp_input.c

static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	/* Optimize this! */
	int truesize = tcp_win_from_space(skb->truesize) >> 1;
	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;

	while (tp->rcv_ssthresh <= window) {
		if (truesize <= skb->len)
			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;

		truesize >>= 1;
		window >>= 1;
	}
	return 0;
}

Project: net
File: tcp_input.c

static bool tcp_time_to_recover(struct sock *sk, int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	__u32 packets_out;
	int tcp_reordering = sock_net(sk)->ipv4.sysctl_tcp_reordering;

	/* Trick#1: The loss is proven. */
	if (tp->lost_out)
		return true;

	/* Not-A-Trick#2 : Classic rule... */
	if (tcp_dupack_heuristics(tp) > tp->reordering)
		return true;

	/* Trick#4: It is still not OK... But will it be useful to delay
	 * recovery more?
	 */
	packets_out = tp->packets_out;
	if (packets_out <= tp->reordering &&
	    tp->sacked_out >= max_t(__u32, packets_out/2, tcp_reordering) &&
	    !tcp_may_send_now(sk)) {
		/* We have nothing to send. This connection is limited
		 * either by receiver window or by application.
		 */
		return true;
	}

	/* If a thin stream is detected, retransmit after first
	 * received dupack. Employ only if SACK is supported in order
	 * to avoid possible corner-case series of spurious retransmissions
	 * Use only if there are no unsent data.
	 */
	if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
	    tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
	    tcp_is_sack(tp) && !tcp_send_head(sk))
		return true;

	/* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
	 * retransmissions due to small network reorderings, we implement
	 * Mitigation A.3 in the RFC and delay the retransmission for a short
	 * interval if appropriate.
	 */
	if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
	    (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
	    !tcp_may_send_now(sk))
		return !tcp_pause_early_retransmit(sk, flag);

	return false;
}

Project: net
File: tcp_input.c

static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
					struct tcp_sacktag_state *state,
					u32 skip_to_seq)
{
	tcp_for_write_queue_from(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;

		if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
			break;

		state->fack_count += tcp_skb_pcount(skb);
	}
	return skb;
}

Project: net
File: tcp_input.c

static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
					  struct tcp_sacktag_state *state,
					  u32 start_seq, u32 end_seq,
					  bool dup_sack)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *prev;
	int mss;
	int pcount = 0;
	int len;
	int in_sack;

	if (!sk_can_gso(sk))
		goto fallback;

	/* Normally R but no L won't result in plain S */
	if (!dup_sack &&
	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
		goto fallback;
	if (!skb_can_shift(skb))
		goto fallback;
	/* This frame is about to be dropped (was ACKed). */
	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
		goto fallback;

	/* Can only happen with delayed DSACK + discard craziness */
	if (unlikely(skb == tcp_write_queue_head(sk)))
		goto fallback;
	prev = tcp_write_queue_prev(sk, skb);

	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
		goto fallback;

	if (!tcp_skb_can_collapse_to(prev))
		goto fallback;

	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);

	if (in_sack) {
		len = skb->len;
		pcount = tcp_skb_pcount(skb);
		mss = tcp_skb_seglen(skb);

		/* TODO: Fix DSACKs to not fragment already SACKed and we can
		 * drop this restriction as unnecessary
		 */
		if (mss != tcp_skb_seglen(prev))
			goto fallback;
	} else {
		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
			goto noop;
		/* CHECKME: This is non-MSS split case only?, this will
		 * cause skipped skbs due to advancing loop btw, original
		 * has that feature too
		 */
		if (tcp_skb_pcount(skb) <= 1)
			goto noop;

		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
		if (!in_sack) {
			/* TODO: head merge to next could be attempted here
			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
			 * though it might not be worth of the additional hassle
			 *
			 * ...we can probably just fallback to what was done
			 * previously. We could try merging non-SACKed ones
			 * as well but it probably isn't going to buy off
			 * because later SACKs might again split them, and
			 * it would make skb timestamp tracking considerably
			 * harder problem.
			 */
			goto fallback;
		}

		len = end_seq - TCP_SKB_CB(skb)->seq;
		BUG_ON(len < 0);
		BUG_ON(len > skb->len);

		/* MSS boundaries should be honoured or else pcount will
		 * severely break even though it makes things bit trickier.
		 * Optimize common case to avoid most of the divides
		 */
		mss = tcp_skb_mss(skb);

		/* TODO: Fix DSACKs to not fragment already SACKed and we can
		 * drop this restriction as unnecessary
		 */
		if (mss != tcp_skb_seglen(prev))
			goto fallback;

		if (len == mss) {
			pcount = 1;
		} else if (len < mss) {
			goto noop;
		} else {
			pcount = len / mss;
			len = pcount * mss;
		}
	}

	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
		goto fallback;

	if (!skb_shift(prev, skb, len))
		goto fallback;
	if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
		goto out;

	/* Hole filled allows collapsing with the next as well, this is very
	 * useful when hole on every nth skb pattern happens
	 */
	if (prev == tcp_write_queue_tail(sk))
		goto out;
	skb = tcp_write_queue_next(sk, prev);

	if (!skb_can_shift(skb) ||
	    (skb == tcp_send_head(sk)) ||
	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
	    (mss != tcp_skb_seglen(skb)))
		goto out;

	len = skb->len;
	if (skb_shift(prev, skb, len)) {
		pcount += tcp_skb_pcount(skb);
		tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
	}

out:
	state->fack_count += pcount;
	return prev;

noop:
	return skb;

fallback:
	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
	return NULL;
}

Project: net
File: tcp_input.c

int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
{
	struct sk_buff *skb;
	int err = -ENOMEM;
	int data_len = 0;
	bool fragstolen;

	if (size == 0)
		return 0;

	if (size > PAGE_SIZE) {
		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);

		data_len = npages << PAGE_SHIFT;
		size = data_len + (size & ~PAGE_MASK);
	}
	skb = alloc_skb_with_frags(size - data_len, data_len,
				   PAGE_ALLOC_COSTLY_ORDER,
				   &err, sk->sk_allocation);
	if (!skb)
		goto err;

	skb_put(skb, size - data_len);
	skb->data_len = data_len;
	skb->len = size;

	if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
		goto err_free;

	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
	if (err)
		goto err_free;

	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;

	if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
		WARN_ON_ONCE(fragstolen); /* should not happen */
		__kfree_skb(skb);
	}
	return size;

err_free:
	kfree_skb(skb);
err:
	return err;

}

Project: net
File: tcp_input.c

static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
{
	return !tp->retrans_stamp ||
	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
}

Project: net
File: tcp_input.c

void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
			 const struct tcphdr *th, unsigned int len)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (unlikely(!sk->sk_rx_dst))
		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
	/*
	 *	Header prediction.
	 *	The code loosely follows the one in the famous
	 *	"30 instruction TCP receive" Van Jacobson mail.
	 *
	 *	Van's trick is to deposit buffers into socket queue
	 *	on a device interrupt, to call tcp_recv function
	 *	on the receive process context and checksum and copy
	 *	the buffer to user space. smart...
	 *
	 *	Our current scheme is not silly either but we take the
	 *	extra cost of the net_bh soft interrupt processing...
	 *	We do checksum and copy also but from device to kernel.
	 */

	tp->rx_opt.saw_tstamp = 0;

	/*	pred_flags is 0xS?10 << 16 + snd_wnd
	 *	if header_prediction is to be made
	 *	'S' will always be tp->tcp_header_len >> 2
	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
	 *  turn it off	(when there are holes in the receive
	 *	 space for instance)
	 *	PSH flag is ignored.
	 */

	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
		int tcp_header_len = tp->tcp_header_len;

		/* Timestamp header prediction: tcp_header_len
		 * is automatically equal to th->doff*4 due to pred_flags
		 * match.
		 */

		/* Check timestamp */
		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
			/* No? Slow path! */
			if (!tcp_parse_aligned_timestamp(tp, th))
				goto slow_path;

			/* If PAWS failed, check it more carefully in slow path */
			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
				goto slow_path;

			/* DO NOT update ts_recent here, if checksum fails
			 * and timestamp was corrupted part, it will result
			 * in a hung connection since we will drop all
			 * future packets due to the PAWS test.
			 */
		}

		if (len <= tcp_header_len) {
			/* Bulk data transfer: sender */
			if (len == tcp_header_len) {
				/* Predicted packet is in window by definition.
				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
				 * Hence, check seq<=rcv_wup reduces to:
				 */
				if (tcp_header_len ==
				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
				    tp->rcv_nxt == tp->rcv_wup)
					tcp_store_ts_recent(tp);

				/* We know that such packets are checksummed
				 * on entry.
				 */
				tcp_ack(sk, skb, 0);
				__kfree_skb(skb);
				tcp_data_snd_check(sk);
				return;
			} else { /* Header too small */
				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
				goto discard;
			}
		} else {
			int eaten = 0;
			bool fragstolen = false;

			if (tp->ucopy.task == current &&
			    tp->copied_seq == tp->rcv_nxt &&
			    len - tcp_header_len <= tp->ucopy.len &&
			    sock_owned_by_user(sk)) {
				__set_current_state(TASK_RUNNING);

				if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
					/* Predicted packet is in window by definition.
					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
					 * Hence, check seq<=rcv_wup reduces to:
					 */
					if (tcp_header_len ==
					    (sizeof(struct tcphdr) +
					     TCPOLEN_TSTAMP_ALIGNED) &&
					    tp->rcv_nxt == tp->rcv_wup)
						tcp_store_ts_recent(tp);

					tcp_rcv_rtt_measure_ts(sk, skb);

					__skb_pull(skb, tcp_header_len);
					tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
					NET_INC_STATS(sock_net(sk),
							LINUX_MIB_TCPHPHITSTOUSER);
					eaten = 1;
				}
			}
			if (!eaten) {
				if (tcp_checksum_complete(skb))
					goto csum_error;

				if ((int)skb->truesize > sk->sk_forward_alloc)
					goto step5;

				/* Predicted packet is in window by definition.
				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
				 * Hence, check seq<=rcv_wup reduces to:
				 */
				if (tcp_header_len ==
				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
				    tp->rcv_nxt == tp->rcv_wup)
					tcp_store_ts_recent(tp);

				tcp_rcv_rtt_measure_ts(sk, skb);

				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);

				/* Bulk data transfer: receiver */
				eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
						      &fragstolen);
			}

			tcp_event_data_recv(sk, skb);

			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
				/* Well, only one small jumplet in fast path... */
				tcp_ack(sk, skb, FLAG_DATA);
				tcp_data_snd_check(sk);
				if (!inet_csk_ack_scheduled(sk))
					goto no_ack;
			}

			__tcp_ack_snd_check(sk, 0);
no_ack:
			if (eaten)
				kfree_skb_partial(skb, fragstolen);
			sk->sk_data_ready(sk);
			return;
		}
	}

slow_path:
	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
		goto csum_error;

	if (!th->ack && !th->rst && !th->syn)
		goto discard;

	/*
	 *	Standard slow path.
	 */

	if (!tcp_validate_incoming(sk, skb, th, 1))
		return;

step5:
	if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
		goto discard;

	tcp_rcv_rtt_measure_ts(sk, skb);

	/* Process urgent data. */
	tcp_urg(sk, skb, th);

	/* step 7: process the segment text */
	tcp_data_queue(sk, skb);

	tcp_data_snd_check(sk);
	tcp_ack_snd_check(sk);
	return;

csum_error:
	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);

discard:
	tcp_drop(sk, skb);
}

Project: net
File: tcp_input.c

struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
				      struct sock *sk_listener,
				      bool attach_listener)
{
	struct request_sock *req = reqsk_alloc(ops, sk_listener,
					       attach_listener);

	if (req) {
		struct inet_request_sock *ireq = inet_rsk(req);

		kmemcheck_annotate_bitfield(ireq, flags);
		ireq->opt = NULL;
		atomic64_set(&ireq->ir_cookie, 0);
		ireq->ireq_state = TCP_NEW_SYN_RECV;
		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
		ireq->ireq_family = sk_listener->sk_family;
	}

	return req;
}

Project: net
File: tcp_input.c

static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
			    struct tcp_sacktag_state *state,
			    unsigned int pcount, int shifted, int mss,
			    bool dup_sack)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */

	BUG_ON(!pcount);

	/* Adjust counters and hints for the newly sacked sequence
	 * range but discard the return value since prev is already
	 * marked. We must tag the range first because the seq
	 * advancement below implicitly advances
	 * tcp_highest_sack_seq() when skb is highest_sack.
	 */
	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
			start_seq, end_seq, dup_sack, pcount,
			&skb->skb_mstamp);

	if (skb == tp->lost_skb_hint)
		tp->lost_cnt_hint += pcount;

	TCP_SKB_CB(prev)->end_seq += shifted;
	TCP_SKB_CB(skb)->seq += shifted;

	tcp_skb_pcount_add(prev, pcount);
	BUG_ON(tcp_skb_pcount(skb) < pcount);
	tcp_skb_pcount_add(skb, -pcount);

	/* When we're adding to gso_segs == 1, gso_size will be zero,
	 * in theory this shouldn't be necessary but as long as DSACK
	 * code can come after this skb later on it's better to keep
	 * setting gso_size to something.
	 */
	if (!TCP_SKB_CB(prev)->tcp_gso_size)
		TCP_SKB_CB(prev)->tcp_gso_size = mss;

	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
	if (tcp_skb_pcount(skb) <= 1)
		TCP_SKB_CB(skb)->tcp_gso_size = 0;

	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);

	if (skb->len > 0) {
		BUG_ON(!tcp_skb_pcount(skb));
		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
		return false;
	}

	/* Whole SKB was eaten :-) */

	if (skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = prev;
	if (skb == tp->lost_skb_hint) {
		tp->lost_skb_hint = prev;
		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
	}

	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
		TCP_SKB_CB(prev)->end_seq++;

	if (skb == tcp_highest_sack(sk))
		tcp_advance_highest_sack(sk, skb);

	tcp_skb_collapse_tstamp(prev, skb);
	tcp_unlink_write_queue(skb, sk);
	sk_wmem_free_skb(sk, skb);

	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);

	return true;
}

Project: net
File: tcp_input.c

static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
		  bool *fragstolen)
{
	int eaten;
	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);

	__skb_pull(skb, hdrlen);
	eaten = (tail &&
		 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
	if (!eaten) {
		__skb_queue_tail(&sk->sk_receive_queue, skb);
		skb_set_owner_r(skb, sk);
	}
	return eaten;
}

Project: net
File: tcp_input.c

void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
{
	tcp_verify_retransmit_hint(tp, skb);

	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
		tp->lost_out += tcp_skb_pcount(skb);
		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
	}
}

Project: net
File: tcp_input.c

static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
			       int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int sndcnt = 0;
	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);

	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
		return;

	tp->prr_delivered += newly_acked_sacked;
	if (delta < 0) {
		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
			       tp->prior_cwnd - 1;
		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
	} else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
		   !(flag & FLAG_LOST_RETRANS)) {
		sndcnt = min_t(int, delta,
			       max_t(int, tp->prr_delivered - tp->prr_out,
				     newly_acked_sacked) + 1);
	} else {
		sndcnt = min(delta, newly_acked_sacked);
	}
	/* Force a fast retransmit upon entering fast recovery */
	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
}

Project: net
File: tcp_input.c

static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
{
	/* unprotected vars, we dont care of overwrites */
	static u32 challenge_timestamp;
	static unsigned int challenge_count;
	struct tcp_sock *tp = tcp_sk(sk);
	u32 count, now;

	/* First check our per-socket dupack rate limit. */
	if (tcp_oow_rate_limited(sock_net(sk), skb,
				 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
				 &tp->last_oow_ack_time))
		return;

	/* Then check host-wide RFC 5961 rate limit. */
	now = jiffies / HZ;
	if (now != challenge_timestamp) {
		u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;

		challenge_timestamp = now;
		WRITE_ONCE(challenge_count, half +
			   prandom_u32_max(sysctl_tcp_challenge_ack_limit));
	}
	count = READ_ONCE(challenge_count);
	if (count > 0) {
		WRITE_ONCE(challenge_count, count - 1);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
		tcp_send_ack(sk);
	}
}

Project: net
File: tcp_input.c

void tcp_clear_retrans(struct tcp_sock *tp)
{
	tp->retrans_out = 0;
	tp->lost_out = 0;
	tp->undo_marker = 0;
	tp->undo_retrans = -1;
	tp->fackets_out = 0;
	tp->sacked_out = 0;
}

Project: net
File: tcp_input.c

static bool tcp_try_undo_recovery(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tcp_may_undo(tp)) {
		int mib_idx;

		/* Happy end! We did not retransmit anything
		 * or our original transmission succeeded.
		 */
		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
		tcp_undo_cwnd_reduction(sk, false);
		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
			mib_idx = LINUX_MIB_TCPLOSSUNDO;
		else
			mib_idx = LINUX_MIB_TCPFULLUNDO;

		NET_INC_STATS(sock_net(sk), mib_idx);
	}
	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
		/* Hold old state until something *above* high_seq
		 * is ACKed. For Reno it is MUST to prevent false
		 * fast retransmits (RFC2582). SACK TCP is safe. */
		if (!tcp_any_retrans_done(sk))
			tp->retrans_stamp = 0;
		return true;
	}
	tcp_set_ca_state(sk, TCP_CA_Open);
	return false;
}

Project: net
File: tcp_input.c

static void tcp_sack_remove(struct tcp_sock *tp)
{
	struct tcp_sack_block *sp = &tp->selective_acks[0];
	int num_sacks = tp->rx_opt.num_sacks;
	int this_sack;

	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
	if (skb_queue_empty(&tp->out_of_order_queue)) {
		tp->rx_opt.num_sacks = 0;
		return;
	}

	for (this_sack = 0; this_sack < num_sacks;) {
		/* Check if the start of the sack is covered by RCV.NXT. */
		if (!before(tp->rcv_nxt, sp->start_seq)) {
			int i;

			/* RCV.NXT must cover all the block! */
			WARN_ON(before(tp->rcv_nxt, sp->end_seq));

			/* Zap this SACK, by moving forward any other SACKS. */
			for (i = this_sack+1; i < num_sacks; i++)
				tp->selective_acks[i-1] = tp->selective_acks[i];
			num_sacks--;
			continue;
		}
		this_sack++;
		sp++;
	}
	tp->rx_opt.num_sacks = num_sacks;
}