ipv6: Fix leak in ipv6_gso_segment().

commit e3e86b51 upstream.

If ip6_find_1stfragopt() fails and we return an error we have to free
up 'segs' because nobody else is going to.

Fixes: 2423496a ("ipv6: Prevent overrun when parsing v6 header options")
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/ipv6/af_inet6.c

@@ -824,8 +824,10 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb, u32 features)
 					   sizeof(*ipv6h));
 		if (proto == IPPROTO_UDP) {
 			int err = ip6_find_1stfragopt(skb, &prevhdr);
-			if (err < 0)
+			if (err < 0) {
+				kfree_skb_list(segs);
 				return ERR_PTR(err);
+			}
 			fptr = (struct frag_hdr *)(skb_network_header(skb) +
 				err);
 			fptr->frag_off = htons(offset);