openvswitch: Fix IPv6 exthdr handling with ct helpers.

Static code analysis reveals the following bug:

        net/openvswitch/conntrack.c:281 ovs_ct_helper()
        warn: unsigned 'protoff' is never less than zero.

This signedness bug breaks error handling for IPv6 extension headers when
using conntrack helpers. Fix the error by using a local signed variable.

Fixes:  cae3a2627520: "openvswitch: Allow attaching helpers to ct
action"
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index e8e524a..002a755 100644 (file)
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -275,13 +275,15 @@ static int ovs_ct_helper(struct sk_buff *skb, u16 proto)
        case NFPROTO_IPV6: {
                u8 nexthdr = ipv6_hdr(skb)->nexthdr;
                __be16 frag_off;
+               int ofs;
 
-               protoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr),
-                                          &nexthdr, &frag_off);
-               if (protoff < 0 || (frag_off & htons(~0x7)) != 0) {
+               ofs = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
+                                      &frag_off);
+               if (ofs < 0 || (frag_off & htons(~0x7)) != 0) {
                        pr_debug("proto header not found\n");
                        return NF_ACCEPT;
                }
+               protoff = ofs;
                break;
        }
        default: