Commit message: tcp: do not inherit fastopen_req from parent

Under fuzzer stress, it is possible that a child gets a non NULL
fastopen_req pointer from its parent at accept() time, when/if parent
morphs from listener to active session.

We need to make sure this can not happen, by clearing the field after
socket cloning.

BUG: Double free or freeing an invalid pointer
Unexpected shadow byte: 0xFB
CPU: 3 PID: 20933 Comm: syz-executor3 Not tainted 4.11.0+ #306
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x292/0x395 lib/dump_stack.c:52
 kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
 kasan_report_double_free+0x5c/0x70 mm/kasan/report.c:185
 kasan_slab_free+0x9d/0xc0 mm/kasan/kasan.c:580
 slab_free_hook mm/slub.c:1357 [inline]
 slab_free_freelist_hook mm/slub.c:1379 [inline]
 slab_free mm/slub.c:2961 [inline]
 kfree+0xe8/0x2b0 mm/slub.c:3882
 tcp_free_fastopen_req net/ipv4/tcp.c:1077 [inline]
 tcp_disconnect+0xc15/0x13e0 net/ipv4/tcp.c:2328
 inet_child_forget+0xb8/0x600 net/ipv4/inet_connection_sock.c:898
 inet_csk_reqsk_queue_add+0x1e7/0x250
net/ipv4/inet_connection_sock.c:928
 tcp_get_cookie_sock+0x21a/0x510 net/ipv4/syncookies.c:217
 cookie_v4_check+0x1a19/0x28b0 net/ipv4/syncookies.c:384
 tcp_v4_cookie_check net/ipv4/tcp_ipv4.c:1384 [inline]
 tcp_v4_do_rcv+0x731/0x940 net/ipv4/tcp_ipv4.c:1421
 tcp_v4_rcv+0x2dc0/0x31c0 net/ipv4/tcp_ipv4.c:1715
 ip_local_deliver_finish+0x4cc/0xc20 net/ipv4/ip_input.c:216
 NF_HOOK include/linux/netfilter.h:257 [inline]
 ip_local_deliver+0x1ce/0x700 net/ipv4/ip_input.c:257
 dst_input include/net/dst.h:492 [inline]
 ip_rcv_finish+0xb1d/0x20b0 net/ipv4/ip_input.c:396
 NF_HOOK include/linux/netfilter.h:257 [inline]
 ip_rcv+0xd8c/0x19c0 net/ipv4/ip_input.c:487
 __netif_receive_skb_core+0x1ad1/0x3400 net/core/dev.c:4210
 __netif_receive_skb+0x2a/0x1a0 net/core/dev.c:4248
 process_backlog+0xe5/0x6c0 net/core/dev.c:4868
 napi_poll net/core/dev.c:5270 [inline]
 net_rx_action+0xe70/0x18e0 net/core/dev.c:5335
 __do_softirq+0x2fb/0xb99 kernel/softirq.c:284
 do_softirq_own_stack+0x1c/0x30 arch/x86/entry/entry_64.S:899
 </IRQ>
 do_softirq.part.17+0x1e8/0x230 kernel/softirq.c:328
 do_softirq kernel/softirq.c:176 [inline]
 __local_bh_enable_ip+0x1cf/0x1e0 kernel/softirq.c:181
 local_bh_enable include/linux/bottom_half.h:31 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:931 [inline]
 ip_finish_output2+0x9ab/0x15e0 net/ipv4/ip_output.c:230
 ip_finish_output+0xa35/0xdf0 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:246 [inline]
 ip_output+0x1f6/0x7b0 net/ipv4/ip_output.c:404
 dst_output include/net/dst.h:486 [inline]
 ip_local_out+0x95/0x160 net/ipv4/ip_output.c:124
 ip_queue_xmit+0x9a8/0x1a10 net/ipv4/ip_output.c:503
 tcp_transmit_skb+0x1ade/0x3470 net/ipv4/tcp_output.c:1057
 tcp_write_xmit+0x79e/0x55b0 net/ipv4/tcp_output.c:2265
 __tcp_push_pending_frames+0xfa/0x3a0 net/ipv4/tcp_output.c:2450
 tcp_push+0x4ee/0x780 net/ipv4/tcp.c:683
 tcp_sendmsg+0x128d/0x39b0 net/ipv4/tcp.c:1342
 inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:762
 sock_sendmsg_nosec net/socket.c:633 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:643
 SYSC_sendto+0x660/0x810 net/socket.c:1696
 SyS_sendto+0x40/0x50 net/socket.c:1664
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x446059
RSP: 002b:00007faa6761fb58 EFLAGS: 00000282 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000017 RCX: 0000000000446059
RDX: 0000000000000001 RSI: 0000000020ba3fcd RDI: 0000000000000017
RBP: 00000000006e40a0 R08: 0000000020ba4ff0 R09: 0000000000000010
R10: 0000000020000000 R11: 0000000000000282 R12: 0000000000708150
R13: 0000000000000000 R14: 00007faa676209c0 R15: 00007faa67620700
Object at ffff88003b5bbcb8, in cache kmalloc-64 size: 64
Allocated:
PID = 20909
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745
 kmalloc include/linux/slab.h:490 [inline]
 kzalloc include/linux/slab.h:663 [inline]
 tcp_sendmsg_fastopen net/ipv4/tcp.c:1094 [inline]
 tcp_sendmsg+0x221a/0x39b0 net/ipv4/tcp.c:1139
 inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:762
 sock_sendmsg_nosec net/socket.c:633 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:643
 SYSC_sendto+0x660/0x810 net/socket.c:1696
 SyS_sendto+0x40/0x50 net/socket.c:1664
 entry_SYSCALL_64_fastpath+0x1f/0xbe
Freed:
PID = 20909
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589
 slab_free_hook mm/slub.c:1357 [inline]
 slab_free_freelist_hook mm/slub.c:1379 [inline]
 slab_free mm/slub.c:2961 [inline]
 kfree+0xe8/0x2b0 mm/slub.c:3882
 tcp_free_fastopen_req net/ipv4/tcp.c:1077 [inline]
 tcp_disconnect+0xc15/0x13e0 net/ipv4/tcp.c:2328
 __inet_stream_connect+0x20c/0xf90 net/ipv4/af_inet.c:593
 tcp_sendmsg_fastopen net/ipv4/tcp.c:1111 [inline]
 tcp_sendmsg+0x23a8/0x39b0 net/ipv4/tcp.c:1139
 inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:762
 sock_sendmsg_nosec net/socket.c:633 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:643
 SYSC_sendto+0x660/0x810 net/socket.c:1696
 SyS_sendto+0x40/0x50 net/socket.c:1664
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
Fixes: 7db92362d2fe ("tcp: fix potential double free issue for fastopen_req")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2017-8890
CWE: CWE-415
Vulnerability description: The inet_csk_clone_lock function in net/ipv4/inet_connection_sock.c in the Linux kernel through 4.10.15 allows attackers to cause a denial of service (double free) or possibly have unspecified other impact by leveraging use of the accept system call.

Project: linux
File: tcp_minisocks.c

tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
				  const struct sk_buff *skb, int mib_idx)
{
	struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);

	if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
				  &tcptw->tw_last_oow_ack_time)) {
		/* Send ACK. Note, we do not put the bucket,
		 * it will be released by caller.
		 */
		return TCP_TW_ACK;
	}

	/* We are rate-limiting, so just release the tw sock and drop skb. */
	inet_twsk_put(tw);
	return TCP_TW_SUCCESS;
}

Project: linux
File: tcp_minisocks.c

void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
	bool ca_got_dst = false;

	if (ca_key != TCP_CA_UNSPEC) {
		const struct tcp_congestion_ops *ca;

		rcu_read_lock();
		ca = tcp_ca_find_key(ca_key);
		if (likely(ca && try_module_get(ca->owner))) {
			icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
			icsk->icsk_ca_ops = ca;
			ca_got_dst = true;
		}
		rcu_read_unlock();
	}

	/* If no valid choice made yet, assign current system default ca. */
	if (!ca_got_dst &&
	    (!icsk->icsk_ca_setsockopt ||
	     !try_module_get(icsk->icsk_ca_ops->owner)))
		tcp_assign_congestion_control(sk);

	tcp_set_ca_state(sk, TCP_CA_Open);
}

Project: linux
File: tcp_minisocks.c

void tcp_openreq_init_rwin(struct request_sock *req,
			   const struct sock *sk_listener,
			   const struct dst_entry *dst)
{
	struct inet_request_sock *ireq = inet_rsk(req);
	const struct tcp_sock *tp = tcp_sk(sk_listener);
	int full_space = tcp_full_space(sk_listener);
	u32 window_clamp;
	__u8 rcv_wscale;
	int mss;

	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
	window_clamp = READ_ONCE(tp->window_clamp);
	/* Set this up on the first call only */
	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);

	/* limit the window selection if the user enforce a smaller rx buffer */
	if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
	    (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
		req->rsk_window_clamp = full_space;

	/* tcp_full_space because it is guaranteed to be the first packet */
	tcp_select_initial_window(full_space,
		mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
		&req->rsk_rcv_wnd,
		&req->rsk_window_clamp,
		ireq->wscale_ok,
		&rcv_wscale,
		dst_metric(dst, RTAX_INITRWND));
	ireq->rcv_wscale = rcv_wscale;
}

Project: linux
File: tcp_minisocks.c

struct sock *tcp_create_openreq_child(const struct sock *sk,
				      struct request_sock *req,
				      struct sk_buff *skb)
{
	struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);

	if (newsk) {
		const struct inet_request_sock *ireq = inet_rsk(req);
		struct tcp_request_sock *treq = tcp_rsk(req);
		struct inet_connection_sock *newicsk = inet_csk(newsk);
		struct tcp_sock *newtp = tcp_sk(newsk);

		/* Now setup tcp_sock */
		newtp->pred_flags = 0;

		newtp->rcv_wup = newtp->copied_seq =
		newtp->rcv_nxt = treq->rcv_isn + 1;
		newtp->segs_in = 1;

		newtp->snd_sml = newtp->snd_una =
		newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;

		tcp_prequeue_init(newtp);
		INIT_LIST_HEAD(&newtp->tsq_node);

		tcp_init_wl(newtp, treq->rcv_isn);

		newtp->srtt_us = 0;
		newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
		minmax_reset(&newtp->rtt_min, tcp_time_stamp, ~0U);
		newicsk->icsk_rto = TCP_TIMEOUT_INIT;
		newicsk->icsk_ack.lrcvtime = tcp_time_stamp;

		newtp->packets_out = 0;
		newtp->retrans_out = 0;
		newtp->sacked_out = 0;
		newtp->fackets_out = 0;
		newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
		newtp->tlp_high_seq = 0;
		newtp->lsndtime = treq->snt_synack.stamp_jiffies;
		newsk->sk_txhash = treq->txhash;
		newtp->last_oow_ack_time = 0;
		newtp->total_retrans = req->num_retrans;

		/* So many TCP implementations out there (incorrectly) count the
		 * initial SYN frame in their delayed-ACK and congestion control
		 * algorithms that we must have the following bandaid to talk
		 * efficiently to them.  -DaveM
		 */
		newtp->snd_cwnd = TCP_INIT_CWND;
		newtp->snd_cwnd_cnt = 0;

		/* There's a bubble in the pipe until at least the first ACK. */
		newtp->app_limited = ~0U;

		tcp_init_xmit_timers(newsk);
		newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;

		newtp->rx_opt.saw_tstamp = 0;

		newtp->rx_opt.dsack = 0;
		newtp->rx_opt.num_sacks = 0;

		newtp->urg_data = 0;

		if (sock_flag(newsk, SOCK_KEEPOPEN))
			inet_csk_reset_keepalive_timer(newsk,
						       keepalive_time_when(newtp));

		newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
		if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
			if (sysctl_tcp_fack)
				tcp_enable_fack(newtp);
		}
		newtp->window_clamp = req->rsk_window_clamp;
		newtp->rcv_ssthresh = req->rsk_rcv_wnd;
		newtp->rcv_wnd = req->rsk_rcv_wnd;
		newtp->rx_opt.wscale_ok = ireq->wscale_ok;
		if (newtp->rx_opt.wscale_ok) {
			newtp->rx_opt.snd_wscale = ireq->snd_wscale;
			newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
		} else {
			newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
			newtp->window_clamp = min(newtp->window_clamp, 65535U);
		}
		newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
				  newtp->rx_opt.snd_wscale);
		newtp->max_window = newtp->snd_wnd;

		if (newtp->rx_opt.tstamp_ok) {
			newtp->rx_opt.ts_recent = req->ts_recent;
			newtp->rx_opt.ts_recent_stamp = get_seconds();
			newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
		} else {
			newtp->rx_opt.ts_recent_stamp = 0;
			newtp->tcp_header_len = sizeof(struct tcphdr);
		}
		newtp->tsoffset = treq->ts_off;
#ifdef CONFIG_TCP_MD5SIG
		newtp->md5sig_info = NULL;	/*XXX*/
		if (newtp->af_specific->md5_lookup(sk, newsk))
			newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif
		if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
			newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
		newtp->rx_opt.mss_clamp = req->mss;
		tcp_ecn_openreq_child(newtp, req);
		newtp->fastopen_req = NULL;
		newtp->fastopen_rsk = NULL;
		newtp->syn_data_acked = 0;
		newtp->rack.mstamp.v64 = 0;
		newtp->rack.advanced = 0;

		__TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
	}
	return newsk;
}

Project: linux
File: tcp_minisocks.c

static void tcp_ecn_openreq_child(struct tcp_sock *tp,
				  const struct request_sock *req)
{
	tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
}

Project: linux
File: tcp_minisocks.c

tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
			   const struct tcphdr *th)
{
	struct tcp_options_received tmp_opt;
	struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
	bool paws_reject = false;

	tmp_opt.saw_tstamp = 0;
	if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
		tcp_parse_options(skb, &tmp_opt, 0, NULL);

		if (tmp_opt.saw_tstamp) {
			if (tmp_opt.rcv_tsecr)
				tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
			tmp_opt.ts_recent	= tcptw->tw_ts_recent;
			tmp_opt.ts_recent_stamp	= tcptw->tw_ts_recent_stamp;
			paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
		}
	}

	if (tw->tw_substate == TCP_FIN_WAIT2) {
		/* Just repeat all the checks of tcp_rcv_state_process() */

		/* Out of window, send ACK */
		if (paws_reject ||
		    !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
				   tcptw->tw_rcv_nxt,
				   tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
			return tcp_timewait_check_oow_rate_limit(
				tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);

		if (th->rst)
			goto kill;

		if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
			return TCP_TW_RST;

		/* Dup ACK? */
		if (!th->ack ||
		    !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
			inet_twsk_put(tw);
			return TCP_TW_SUCCESS;
		}

		/* New data or FIN. If new data arrive after half-duplex close,
		 * reset.
		 */
		if (!th->fin ||
		    TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
			return TCP_TW_RST;

		/* FIN arrived, enter true time-wait state. */
		tw->tw_substate	  = TCP_TIME_WAIT;
		tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
		if (tmp_opt.saw_tstamp) {
			tcptw->tw_ts_recent_stamp = get_seconds();
			tcptw->tw_ts_recent	  = tmp_opt.rcv_tsval;
		}

		inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
		return TCP_TW_ACK;
	}

	/*
	 *	Now real TIME-WAIT state.
	 *
	 *	RFC 1122:
	 *	"When a connection is [...] on TIME-WAIT state [...]
	 *	[a TCP] MAY accept a new SYN from the remote TCP to
	 *	reopen the connection directly, if it:
	 *
	 *	(1)  assigns its initial sequence number for the new
	 *	connection to be larger than the largest sequence
	 *	number it used on the previous connection incarnation,
	 *	and
	 *
	 *	(2)  returns to TIME-WAIT state if the SYN turns out
	 *	to be an old duplicate".
	 */

	if (!paws_reject &&
	    (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
	     (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
		/* In window segment, it may be only reset or bare ack. */

		if (th->rst) {
			/* This is TIME_WAIT assassination, in two flavors.
			 * Oh well... nobody has a sufficient solution to this
			 * protocol bug yet.
			 */
			if (sysctl_tcp_rfc1337 == 0) {
kill:
				inet_twsk_deschedule_put(tw);
				return TCP_TW_SUCCESS;
			}
		}
		inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);

		if (tmp_opt.saw_tstamp) {
			tcptw->tw_ts_recent	  = tmp_opt.rcv_tsval;
			tcptw->tw_ts_recent_stamp = get_seconds();
		}

		inet_twsk_put(tw);
		return TCP_TW_SUCCESS;
	}

	/* Out of window segment.

	   All the segments are ACKed immediately.

	   The only exception is new SYN. We accept it, if it is
	   not old duplicate and we are not in danger to be killed
	   by delayed old duplicates. RFC check is that it has
	   newer sequence number works at rates <40Mbit/sec.
	   However, if paws works, it is reliable AND even more,
	   we even may relax silly seq space cutoff.

	   RED-PEN: we violate main RFC requirement, if this SYN will appear
	   old duplicate (i.e. we receive RST in reply to SYN-ACK),
	   we must return socket to time-wait state. It is not good,
	   but not fatal yet.
	 */

	if (th->syn && !th->rst && !th->ack && !paws_reject &&
	    (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
	     (tmp_opt.saw_tstamp &&
	      (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
		u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
		if (isn == 0)
			isn++;
		TCP_SKB_CB(skb)->tcp_tw_isn = isn;
		return TCP_TW_SYN;
	}

	if (paws_reject)
		__NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);

	if (!th->rst) {
		/* In this case we must reset the TIMEWAIT timer.
		 *
		 * If it is ACKless SYN it may be both old duplicate
		 * and new good SYN with random sequence number <rcv_nxt.
		 * Do not reschedule in the last case.
		 */
		if (paws_reject || th->ack)
			inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);

		return tcp_timewait_check_oow_rate_limit(
			tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
	}
	inet_twsk_put(tw);
	return TCP_TW_SUCCESS;
}

Project: linux
File: tcp_minisocks.c

int tcp_child_process(struct sock *parent, struct sock *child,
		      struct sk_buff *skb)
{
	int ret = 0;
	int state = child->sk_state;

	/* record NAPI ID of child */
	sk_mark_napi_id(child, skb);

	tcp_segs_in(tcp_sk(child), skb);
	if (!sock_owned_by_user(child)) {
		ret = tcp_rcv_state_process(child, skb);
		/* Wakeup parent, send SIGIO */
		if (state == TCP_SYN_RECV && child->sk_state != state)
			parent->sk_data_ready(parent);
	} else {
		/* Alas, it is possible again, because we do lookup
		 * in main socket hash table and lock on listening
		 * socket does not protect us more.
		 */
		__sk_add_backlog(child, skb);
	}

	bh_unlock_sock(child);
	sock_put(child);
	return ret;
}

Project: linux
File: tcp_minisocks.c

struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
			   struct request_sock *req,
			   bool fastopen)
{
	struct tcp_options_received tmp_opt;
	struct sock *child;
	const struct tcphdr *th = tcp_hdr(skb);
	__be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
	bool paws_reject = false;
	bool own_req;

	tmp_opt.saw_tstamp = 0;
	if (th->doff > (sizeof(struct tcphdr)>>2)) {
		tcp_parse_options(skb, &tmp_opt, 0, NULL);

		if (tmp_opt.saw_tstamp) {
			tmp_opt.ts_recent = req->ts_recent;
			if (tmp_opt.rcv_tsecr)
				tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
			/* We do not store true stamp, but it is not required,
			 * it can be estimated (approximately)
			 * from another data.
			 */
			tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
			paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
		}
	}

	/* Check for pure retransmitted SYN. */
	if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
	    flg == TCP_FLAG_SYN &&
	    !paws_reject) {
		/*
		 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
		 * this case on figure 6 and figure 8, but formal
		 * protocol description says NOTHING.
		 * To be more exact, it says that we should send ACK,
		 * because this segment (at least, if it has no data)
		 * is out of window.
		 *
		 *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
		 *  describe SYN-RECV state. All the description
		 *  is wrong, we cannot believe to it and should
		 *  rely only on common sense and implementation
		 *  experience.
		 *
		 * Enforce "SYN-ACK" according to figure 8, figure 6
		 * of RFC793, fixed by RFC1122.
		 *
		 * Note that even if there is new data in the SYN packet
		 * they will be thrown away too.
		 *
		 * Reset timer after retransmitting SYNACK, similar to
		 * the idea of fast retransmit in recovery.
		 */
		if (!tcp_oow_rate_limited(sock_net(sk), skb,
					  LINUX_MIB_TCPACKSKIPPEDSYNRECV,
					  &tcp_rsk(req)->last_oow_ack_time) &&

		    !inet_rtx_syn_ack(sk, req)) {
			unsigned long expires = jiffies;

			expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
				       TCP_RTO_MAX);
			if (!fastopen)
				mod_timer_pending(&req->rsk_timer, expires);
			else
				req->rsk_timer.expires = expires;
		}
		return NULL;
	}

	/* Further reproduces section "SEGMENT ARRIVES"
	   for state SYN-RECEIVED of RFC793.
	   It is broken, however, it does not work only
	   when SYNs are crossed.

	   You would think that SYN crossing is impossible here, since
	   we should have a SYN_SENT socket (from connect()) on our end,
	   but this is not true if the crossed SYNs were sent to both
	   ends by a malicious third party.  We must defend against this,
	   and to do that we first verify the ACK (as per RFC793, page
	   36) and reset if it is invalid.  Is this a true full defense?
	   To convince ourselves, let us consider a way in which the ACK
	   test can still pass in this 'malicious crossed SYNs' case.
	   Malicious sender sends identical SYNs (and thus identical sequence
	   numbers) to both A and B:

		A: gets SYN, seq=7
		B: gets SYN, seq=7

	   By our good fortune, both A and B select the same initial
	   send sequence number of seven :-)

		A: sends SYN|ACK, seq=7, ack_seq=8
		B: sends SYN|ACK, seq=7, ack_seq=8

	   So we are now A eating this SYN|ACK, ACK test passes.  So
	   does sequence test, SYN is truncated, and thus we consider
	   it a bare ACK.

	   If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
	   bare ACK.  Otherwise, we create an established connection.  Both
	   ends (listening sockets) accept the new incoming connection and try
	   to talk to each other. 8-)

	   Note: This case is both harmless, and rare.  Possibility is about the
	   same as us discovering intelligent life on another plant tomorrow.

	   But generally, we should (RFC lies!) to accept ACK
	   from SYNACK both here and in tcp_rcv_state_process().
	   tcp_rcv_state_process() does not, hence, we do not too.

	   Note that the case is absolutely generic:
	   we cannot optimize anything here without
	   violating protocol. All the checks must be made
	   before attempt to create socket.
	 */

	/* RFC793 page 36: "If the connection is in any non-synchronized state ...
	 *                  and the incoming segment acknowledges something not yet
	 *                  sent (the segment carries an unacceptable ACK) ...
	 *                  a reset is sent."
	 *
	 * Invalid ACK: reset will be sent by listening socket.
	 * Note that the ACK validity check for a Fast Open socket is done
	 * elsewhere and is checked directly against the child socket rather
	 * than req because user data may have been sent out.
	 */
	if ((flg & TCP_FLAG_ACK) && !fastopen &&
	    (TCP_SKB_CB(skb)->ack_seq !=
	     tcp_rsk(req)->snt_isn + 1))
		return sk;

	/* Also, it would be not so bad idea to check rcv_tsecr, which
	 * is essentially ACK extension and too early or too late values
	 * should cause reset in unsynchronized states.
	 */

	/* RFC793: "first check sequence number". */

	if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
					  tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
		/* Out of window: send ACK and drop. */
		if (!(flg & TCP_FLAG_RST) &&
		    !tcp_oow_rate_limited(sock_net(sk), skb,
					  LINUX_MIB_TCPACKSKIPPEDSYNRECV,
					  &tcp_rsk(req)->last_oow_ack_time))
			req->rsk_ops->send_ack(sk, skb, req);
		if (paws_reject)
			__NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
		return NULL;
	}

	/* In sequence, PAWS is OK. */

	if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
		req->ts_recent = tmp_opt.rcv_tsval;

	if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
		/* Truncate SYN, it is out of window starting
		   at tcp_rsk(req)->rcv_isn + 1. */
		flg &= ~TCP_FLAG_SYN;
	}

	/* RFC793: "second check the RST bit" and
	 *	   "fourth, check the SYN bit"
	 */
	if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
		__TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
		goto embryonic_reset;
	}

	/* ACK sequence verified above, just make sure ACK is
	 * set.  If ACK not set, just silently drop the packet.
	 *
	 * XXX (TFO) - if we ever allow "data after SYN", the
	 * following check needs to be removed.
	 */
	if (!(flg & TCP_FLAG_ACK))
		return NULL;

	/* For Fast Open no more processing is needed (sk is the
	 * child socket).
	 */
	if (fastopen)
		return sk;

	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
	if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
	    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
		inet_rsk(req)->acked = 1;
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
		return NULL;
	}

	/* OK, ACK is valid, create big socket and
	 * feed this segment to it. It will repeat all
	 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
	 * ESTABLISHED STATE. If it will be dropped after
	 * socket is created, wait for troubles.
	 */
	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
							 req, &own_req);
	if (!child)
		goto listen_overflow;

	sock_rps_save_rxhash(child, skb);
	tcp_synack_rtt_meas(child, req);
	return inet_csk_complete_hashdance(sk, child, req, own_req);

listen_overflow:
	if (!sysctl_tcp_abort_on_overflow) {
		inet_rsk(req)->acked = 1;
		return NULL;
	}

embryonic_reset:
	if (!(flg & TCP_FLAG_RST)) {
		/* Received a bad SYN pkt - for TFO We try not to reset
		 * the local connection unless it's really necessary to
		 * avoid becoming vulnerable to outside attack aiming at
		 * resetting legit local connections.
		 */
		req->rsk_ops->send_reset(sk, skb);
	} else if (fastopen) { /* received a valid RST pkt */
		reqsk_fastopen_remove(sk, req, true);
		tcp_reset(sk);
	}
	if (!fastopen) {
		inet_csk_reqsk_queue_drop(sk, req);
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
	}
	return NULL;
}

Project: linux
File: tcp_minisocks.c

static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
{
	if (seq == s_win)
		return true;
	if (after(end_seq, s_win) && before(seq, e_win))
		return true;
	return seq == e_win && seq == end_seq;
}

Project: linux
File: tcp_minisocks.c

void tcp_twsk_destructor(struct sock *sk)
{
#ifdef CONFIG_TCP_MD5SIG
	struct tcp_timewait_sock *twsk = tcp_twsk(sk);

	if (twsk->tw_md5_key)
		kfree_rcu(twsk->tw_md5_key, rcu);
#endif
}

Project: linux
File: tcp_minisocks.c

void tcp_time_wait(struct sock *sk, int state, int timeo)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	const struct tcp_sock *tp = tcp_sk(sk);
	struct inet_timewait_sock *tw;
	struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;

	tw = inet_twsk_alloc(sk, tcp_death_row, state);

	if (tw) {
		struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
		const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
		struct inet_sock *inet = inet_sk(sk);

		tw->tw_transparent	= inet->transparent;
		tw->tw_rcv_wscale	= tp->rx_opt.rcv_wscale;
		tcptw->tw_rcv_nxt	= tp->rcv_nxt;
		tcptw->tw_snd_nxt	= tp->snd_nxt;
		tcptw->tw_rcv_wnd	= tcp_receive_window(tp);
		tcptw->tw_ts_recent	= tp->rx_opt.ts_recent;
		tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
		tcptw->tw_ts_offset	= tp->tsoffset;
		tcptw->tw_last_oow_ack_time = 0;

#if IS_ENABLED(CONFIG_IPV6)
		if (tw->tw_family == PF_INET6) {
			struct ipv6_pinfo *np = inet6_sk(sk);

			tw->tw_v6_daddr = sk->sk_v6_daddr;
			tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
			tw->tw_tclass = np->tclass;
			tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
			tw->tw_ipv6only = sk->sk_ipv6only;
		}
#endif

#ifdef CONFIG_TCP_MD5SIG
		/*
		 * The timewait bucket does not have the key DB from the
		 * sock structure. We just make a quick copy of the
		 * md5 key being used (if indeed we are using one)
		 * so the timewait ack generating code has the key.
		 */
		do {
			struct tcp_md5sig_key *key;
			tcptw->tw_md5_key = NULL;
			key = tp->af_specific->md5_lookup(sk, sk);
			if (key) {
				tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
				if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
					BUG();
			}
		} while (0);
#endif

		/* Get the TIME_WAIT timeout firing. */
		if (timeo < rto)
			timeo = rto;

		tw->tw_timeout = TCP_TIMEWAIT_LEN;
		if (state == TCP_TIME_WAIT)
			timeo = TCP_TIMEWAIT_LEN;

		inet_twsk_schedule(tw, timeo);
		/* Linkage updates. */
		__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
		inet_twsk_put(tw);
	} else {
		/* Sorry, if we're out of memory, just CLOSE this
		 * socket up.  We've got bigger problems than
		 * non-graceful socket closings.
		 */
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
	}

	tcp_update_metrics(sk);
	tcp_done(sk);
}