Commit message: netfilter: nf_conntrack_dccp: fix skb_header_pointer API usages

Some occurences in the netfilter tree use skb_header_pointer() in
the following way ...

  struct dccp_hdr _dh, *dh;
  ...
  skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);

... where dh itself is a pointer that is being passed as the copy
buffer. Instead, we need to use &_dh as the forth argument so that
we're copying the data into an actual buffer that sits on the stack.

Currently, we probably could overwrite memory on the stack (e.g.
with a possibly mal-formed DCCP packet), but unintentionally, as
we only want the buffer to be placed into _dh variable.

Fixes: 2bc780499aa3 ("[NETFILTER]: nf_conntrack: add DCCP protocol support")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
CVE: CVE-2014-2523
CWE: CWE-20
Vulnerability description: net/netfilter/nf_conntrack_proto_dccp.c in the Linux kernel through 3.13.6 uses a DCCP header pointer incorrectly, which allows remote attackers to cause a denial of service (system crash) or possibly execute arbitrary code via a DCCP packet that triggers a call to the (1) dccp_new, (2) dccp_packet, or (3) dccp_error function.

Project: linux
File: nf_conntrack_proto_dccp.c

static int dccp_error(struct net *net, struct nf_conn *tmpl,
		      struct sk_buff *skb, unsigned int dataoff,
		      enum ip_conntrack_info *ctinfo,
		      u_int8_t pf, unsigned int hooknum)
{
	struct dccp_hdr _dh, *dh;
	unsigned int dccp_len = skb->len - dataoff;
 	unsigned int cscov;
 	const char *msg;
 
	dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
 	if (dh == NULL) {
 		msg = "nf_ct_dccp: short packet ";
 		goto out_invalid;
	}

	if (dh->dccph_doff * 4 < sizeof(struct dccp_hdr) ||
	    dh->dccph_doff * 4 > dccp_len) {
		msg = "nf_ct_dccp: truncated/malformed packet ";
		goto out_invalid;
	}

	cscov = dccp_len;
	if (dh->dccph_cscov) {
		cscov = (dh->dccph_cscov - 1) * 4;
		if (cscov > dccp_len) {
			msg = "nf_ct_dccp: bad checksum coverage ";
			goto out_invalid;
		}
	}

	if (net->ct.sysctl_checksum && hooknum == NF_INET_PRE_ROUTING &&
	    nf_checksum_partial(skb, hooknum, dataoff, cscov, IPPROTO_DCCP,
				pf)) {
		msg = "nf_ct_dccp: bad checksum ";
		goto out_invalid;
	}

	if (dh->dccph_type >= DCCP_PKT_INVALID) {
		msg = "nf_ct_dccp: reserved packet type ";
		goto out_invalid;
	}

	return NF_ACCEPT;

out_invalid:
	if (LOG_INVALID(net, IPPROTO_DCCP))
		nf_log_packet(net, pf, 0, skb, NULL, NULL, NULL, "%s", msg);
	return -NF_ACCEPT;
}

Project: linux
File: nf_conntrack_proto_dccp.c

static bool dccp_new(struct nf_conn *ct, const struct sk_buff *skb,
		     unsigned int dataoff, unsigned int *timeouts)
{
	struct net *net = nf_ct_net(ct);
	struct dccp_net *dn;
	struct dccp_hdr _dh, *dh;
 	const char *msg;
 	u_int8_t state;
 
	dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
 	BUG_ON(dh == NULL);
 
 	state = dccp_state_table[CT_DCCP_ROLE_CLIENT][dh->dccph_type][CT_DCCP_NONE];
	switch (state) {
	default:
		dn = dccp_pernet(net);
		if (dn->dccp_loose == 0) {
			msg = "nf_ct_dccp: not picking up existing connection ";
			goto out_invalid;
		}
	case CT_DCCP_REQUEST:
		break;
	case CT_DCCP_INVALID:
		msg = "nf_ct_dccp: invalid state transition ";
		goto out_invalid;
	}

	ct->proto.dccp.role[IP_CT_DIR_ORIGINAL] = CT_DCCP_ROLE_CLIENT;
	ct->proto.dccp.role[IP_CT_DIR_REPLY] = CT_DCCP_ROLE_SERVER;
	ct->proto.dccp.state = CT_DCCP_NONE;
	ct->proto.dccp.last_pkt = DCCP_PKT_REQUEST;
	ct->proto.dccp.last_dir = IP_CT_DIR_ORIGINAL;
	ct->proto.dccp.handshake_seq = 0;
	return true;

out_invalid:
	if (LOG_INVALID(net, IPPROTO_DCCP))
		nf_log_packet(net, nf_ct_l3num(ct), 0, skb, NULL, NULL,
			      NULL, "%s", msg);
	return false;
}

Project: linux
File: nf_conntrack_proto_dccp.c

static int dccp_packet(struct nf_conn *ct, const struct sk_buff *skb,
		       unsigned int dataoff, enum ip_conntrack_info ctinfo,
		       u_int8_t pf, unsigned int hooknum,
		       unsigned int *timeouts)
{
	struct net *net = nf_ct_net(ct);
	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
	struct dccp_hdr _dh, *dh;
 	u_int8_t type, old_state, new_state;
 	enum ct_dccp_roles role;
 
	dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
 	BUG_ON(dh == NULL);
 	type = dh->dccph_type;
 
	if (type == DCCP_PKT_RESET &&
	    !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
		/* Tear down connection immediately if only reply is a RESET */
		nf_ct_kill_acct(ct, ctinfo, skb);
		return NF_ACCEPT;
	}

	spin_lock_bh(&ct->lock);

	role = ct->proto.dccp.role[dir];
	old_state = ct->proto.dccp.state;
	new_state = dccp_state_table[role][type][old_state];

	switch (new_state) {
	case CT_DCCP_REQUEST:
		if (old_state == CT_DCCP_TIMEWAIT &&
		    role == CT_DCCP_ROLE_SERVER) {
			/* Reincarnation in the reverse direction: reopen and
			 * reverse client/server roles. */
			ct->proto.dccp.role[dir] = CT_DCCP_ROLE_CLIENT;
			ct->proto.dccp.role[!dir] = CT_DCCP_ROLE_SERVER;
		}
		break;
	case CT_DCCP_RESPOND:
		if (old_state == CT_DCCP_REQUEST)
			ct->proto.dccp.handshake_seq = dccp_hdr_seq(dh);
		break;
	case CT_DCCP_PARTOPEN:
		if (old_state == CT_DCCP_RESPOND &&
		    type == DCCP_PKT_ACK &&
		    dccp_ack_seq(dh) == ct->proto.dccp.handshake_seq)
			set_bit(IPS_ASSURED_BIT, &ct->status);
		break;
	case CT_DCCP_IGNORE:
		/*
		 * Connection tracking might be out of sync, so we ignore
		 * packets that might establish a new connection and resync
		 * if the server responds with a valid Response.
		 */
		if (ct->proto.dccp.last_dir == !dir &&
		    ct->proto.dccp.last_pkt == DCCP_PKT_REQUEST &&
		    type == DCCP_PKT_RESPONSE) {
			ct->proto.dccp.role[!dir] = CT_DCCP_ROLE_CLIENT;
			ct->proto.dccp.role[dir] = CT_DCCP_ROLE_SERVER;
			ct->proto.dccp.handshake_seq = dccp_hdr_seq(dh);
			new_state = CT_DCCP_RESPOND;
			break;
		}
		ct->proto.dccp.last_dir = dir;
		ct->proto.dccp.last_pkt = type;

		spin_unlock_bh(&ct->lock);
		if (LOG_INVALID(net, IPPROTO_DCCP))
			nf_log_packet(net, pf, 0, skb, NULL, NULL, NULL,
				      "nf_ct_dccp: invalid packet ignored ");
		return NF_ACCEPT;
	case CT_DCCP_INVALID:
		spin_unlock_bh(&ct->lock);
		if (LOG_INVALID(net, IPPROTO_DCCP))
			nf_log_packet(net, pf, 0, skb, NULL, NULL, NULL,
				      "nf_ct_dccp: invalid state transition ");
		return -NF_ACCEPT;
	}

	ct->proto.dccp.last_dir = dir;
	ct->proto.dccp.last_pkt = type;
	ct->proto.dccp.state = new_state;
	spin_unlock_bh(&ct->lock);

	if (new_state != old_state)
		nf_conntrack_event_cache(IPCT_PROTOINFO, ct);

	nf_ct_refresh_acct(ct, ctinfo, skb, timeouts[new_state]);

	return NF_ACCEPT;
}