[PATCH] openvswitch: Ensure nf_ct_put is not called with null pointer

[Mark Mielke <mark.mielke@gmail.com>]

A recent commit replaced calls to nf_conntrack_put() with calls
to nf_ct_put(). nf_conntrack_put() permitted the caller to pass
null without side effects, while nf_ct_put() performs WARN_ON()
and proceeds to try and de-reference the pointer. ovs-vswitchd
triggers the warning on startup:

[   22.178881] WARNING: CPU: 69 PID: 2157 at include/net/netfilter/nf_conntrack.h:176 __ovs_ct_lookup+0x4e2/0x6a0 [openvswitch]
...
[   22.213573] Call Trace:
[   22.214318]  <TASK>
[   22.215064]  ovs_ct_execute+0x49c/0x7f0 [openvswitch]
...

Cc: stable@vger.kernel.org
Fixes: 408bdcfce8df ("net: prefer nf_ct_put instead of nf_conntrack_put")
Signed-off-by: Mark Mielke <mark.mielke@gmail.com>
---
 net/openvswitch/conntrack.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index 4a947c13c813..69972f037d21 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -970,7 +970,8 @@ static int __ovs_ct_lookup(struct net *net, struct sw_flow_key *key,
 		/* Associate skb with specified zone. */
 		if (tmpl) {
 			ct = nf_ct_get(skb, &ctinfo);
-			nf_ct_put(ct);
+			if (ct)
+				nf_ct_put(ct);
 			nf_conntrack_get(&tmpl->ct_general);
 			nf_ct_set(skb, tmpl, IP_CT_NEW);
 		}
@@ -1339,8 +1340,8 @@ int ovs_ct_clear(struct sk_buff *skb, struct sw_flow_key *key)
 	struct nf_conn *ct;
 
 	ct = nf_ct_get(skb, &ctinfo);
-
-	nf_ct_put(ct);
+	if (ct)
+		nf_ct_put(ct);
 	nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
 	ovs_ct_fill_key(skb, key, false);
 
-- 
2.35.1