[PATCH nf] netfilter: conntrack: allow sctp hearbeat after connection re-use

[PATCH nf] netfilter: conntrack: allow sctp hearbeat after connection re-use

[Florian Westphal]

If an sctp connection gets re-used, heartbeats are flagged as invalid
because their vtag doesn't match.

Handle this in a similar way as TCP conntrack when it suspects that the
endpoints and conntrack are out-of-sync.

When a HEARTBEAT request fails its vtag validation, flag this in the
conntrack state and accept the packet.

When a HEARTBEAT_ACK is received with an invalid vtag in the reverse
direction after we allowed such a HEARTBEAT through, assume we are
out-of-sync and re-set the vtag info.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/linux/netfilter/nf_conntrack_sctp.h |  2 +
 net/netfilter/nf_conntrack_proto_sctp.c     | 43 ++++++++++++++++++---
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/include/linux/netfilter/nf_conntrack_sctp.h b/include/linux/netfilter/nf_conntrack_sctp.h
index 9a33f171aa82..625f491b95de 100644
--- a/include/linux/netfilter/nf_conntrack_sctp.h
+++ b/include/linux/netfilter/nf_conntrack_sctp.h
@@ -9,6 +9,8 @@ struct ip_ct_sctp {
 	enum sctp_conntrack state;
 
 	__be32 vtag[IP_CT_DIR_MAX];
+	u8 last_dir;
+	u8 flags;
 };
 
 #endif /* _NF_CONNTRACK_SCTP_H */
diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c
index 4f897b14b606..8b8b9ca61eef 100644
--- a/net/netfilter/nf_conntrack_proto_sctp.c
+++ b/net/netfilter/nf_conntrack_proto_sctp.c
@@ -62,6 +62,8 @@ static const unsigned int sctp_timeouts[SCTP_CONNTRACK_MAX] = {
 	[SCTP_CONNTRACK_HEARTBEAT_ACKED]	= 210 SECS,
 };
 
+#define	SCTP_FLAG_HEARTBEAT_VTAG_FAILED	1
+
 #define sNO SCTP_CONNTRACK_NONE
 #define	sCL SCTP_CONNTRACK_CLOSED
 #define	sCW SCTP_CONNTRACK_COOKIE_WAIT
@@ -369,6 +371,7 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
 	u_int32_t offset, count;
 	unsigned int *timeouts;
 	unsigned long map[256 / sizeof(unsigned long)] = { 0 };
+	bool ignore = false;
 
 	if (sctp_error(skb, dataoff, state))
 		return -NF_ACCEPT;
@@ -404,8 +407,9 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
 		goto out;
 	}
 
-	old_state = new_state = SCTP_CONNTRACK_NONE;
 	spin_lock_bh(&ct->lock);
+
+	old_state = ct->proto.sctp.state;
 	for_each_sctp_chunk (skb, sch, _sch, offset, dataoff, count) {
 		/* Special cases of Verification tag check (Sec 8.5.1) */
 		if (sch->type == SCTP_CID_INIT) {
@@ -427,19 +431,42 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
 			/* Sec 8.5.1 (D) */
 			if (sh->vtag != ct->proto.sctp.vtag[dir])
 				goto out_unlock;
-		} else if (sch->type == SCTP_CID_HEARTBEAT ||
-			   sch->type == SCTP_CID_HEARTBEAT_ACK) {
+		} else if (sch->type == SCTP_CID_HEARTBEAT) {
+			if (ct->proto.sctp.vtag[dir] == 0) {
+				pr_debug("Setting %d vtag %x for dir %d\n", sch->type, sh->vtag, dir);
+				ct->proto.sctp.vtag[dir] = sh->vtag;
+			} else if (sh->vtag != ct->proto.sctp.vtag[dir]) {
+				if (test_bit(SCTP_CID_DATA, map) || ignore)
+					goto out_unlock;
+
+				ct->proto.sctp.flags |= SCTP_FLAG_HEARTBEAT_VTAG_FAILED;
+				ct->proto.sctp.last_dir = dir;
+				ignore = true;
+				continue;
+			} else if (ct->proto.sctp.flags & SCTP_FLAG_HEARTBEAT_VTAG_FAILED) {
+				ct->proto.sctp.flags &= ~SCTP_FLAG_HEARTBEAT_VTAG_FAILED;
+			}
+		} else if (sch->type == SCTP_CID_HEARTBEAT_ACK) {
 			if (ct->proto.sctp.vtag[dir] == 0) {
 				pr_debug("Setting vtag %x for dir %d\n",
 					 sh->vtag, dir);
 				ct->proto.sctp.vtag[dir] = sh->vtag;
 			} else if (sh->vtag != ct->proto.sctp.vtag[dir]) {
-				pr_debug("Verification tag check failed\n");
-				goto out_unlock;
+				if (test_bit(SCTP_CID_DATA, map) || ignore)
+					goto out_unlock;
+
+				if ((ct->proto.sctp.flags & SCTP_FLAG_HEARTBEAT_VTAG_FAILED) == 0 ||
+				    ct->proto.sctp.last_dir == dir)
+					goto out_unlock;
+
+				ct->proto.sctp.flags &= ~SCTP_FLAG_HEARTBEAT_VTAG_FAILED;
+				ct->proto.sctp.vtag[dir] = sh->vtag;
+				ct->proto.sctp.vtag[!dir] = 0;
+			} else if (ct->proto.sctp.flags & SCTP_FLAG_HEARTBEAT_VTAG_FAILED) {
+				ct->proto.sctp.flags &= ~SCTP_FLAG_HEARTBEAT_VTAG_FAILED;
 			}
 		}
 
-		old_state = ct->proto.sctp.state;
 		new_state = sctp_new_state(dir, old_state, sch->type);
 
 		/* Invalid */
@@ -470,6 +497,10 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
 	}
 	spin_unlock_bh(&ct->lock);
 
+	/* allow but do not refresh timeout */
+	if (ignore)
+		return NF_ACCEPT;
+
 	timeouts = nf_ct_timeout_lookup(ct);
 	if (!timeouts)
 		timeouts = nf_sctp_pernet(nf_ct_net(ct))->timeouts;
-- 
2.26.2