Patch "openvswitch: Delete conntrack entry clashing with an expectation." has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

openvswitch: Delete conntrack entry clashing with an expectation.

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
openvswitch-delete-conntrack-entry-clashing-with-an-expectation.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jarno Rajahalme <[email protected]>
Date: Fri, 14 Apr 2017 14:26:38 -0700
Subject: openvswitch: Delete conntrack entry clashing with an expectation.

From: Jarno Rajahalme <[email protected]>

[ Upstream commit cf5d70918877c6a6655dc1e92e2ebb661ce904fd ]

Conntrack helpers do not check for a potentially clashing conntrack entry when creating a new expectation. Also, nf_conntrack_in() will check expectations (via init_conntrack()) only if a conntrack entry can not be found. The expectation for a packet which also matches an existing conntrack entry will not be removed by conntrack, and is currently handled inconsistently by OVS, as OVS expects the expectation to be removed when the connection tracking entry matching that expectation is confirmed.

It should be noted that normally an IP stack would not allow reuse of a 5-tuple of an old (possibly lingering) connection for a new data connection, so this is somewhat unlikely corner case. However, it is possible that a misbehaving source could cause conntrack entries be created that could then interfere with new related connections.

Fix this in the OVS module by deleting the clashing conntrack entry after an expectation has been matched. This causes the following nf_conntrack_in() call also find the expectation and remove it when creating the new conntrack entry, as well as the forthcoming reply direction packets to match the new related connection instead of the old clashing conntrack entry.

---
 net/openvswitch/conntrack.c |   30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

@@ -361,10 +361,38 @@ ovs_ct_expect_find(struct net *net, cons
 		   u16 proto, const struct sk_buff *skb)
 {
 	struct nf_conntrack_tuple tuple;
+	struct nf_conntrack_expect *exp;
 
 	if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb), proto, net, &tuple))
 		return NULL;
-	return __nf_ct_expect_find(net, zone, &tuple);
+
+	exp = __nf_ct_expect_find(net, zone, &tuple);
+	if (exp) {
+		struct nf_conntrack_tuple_hash *h;
+
+		/* Delete existing conntrack entry, if it clashes with the
+		 * expectation.  This can happen since conntrack ALGs do not
+		 * check for clashes between (new) expectations and existing
+		 * conntrack entries.  nf_conntrack_in() will check the
+		 * expectations only if a conntrack entry can not be found,
+		 * which can lead to OVS finding the expectation (here) in the
+		 * init direction, but which will not be removed by the
+		 * nf_conntrack_in() call, if a matching conntrack entry is
+		 * found instead.  In this case all init direction packets
+		 * would be reported as new related packets, while reply
+		 * direction packets would be reported as un-related
+		 * established packets.
+		 */
+		h = nf_conntrack_find_get(net, zone, &tuple);
+		if (h) {
+			struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
+
+			nf_ct_delete(ct, 0, 0);
+			nf_conntrack_put(&ct->ct_general);
+		}
+	}
+
+	return exp;
 }
 
 /* Determine whether skb->nfct is equal to the result of conntrack lookup. */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/openvswitch-delete-conntrack-entry-clashing-with-an-expectation.patch