[PATCH 3.16 243/328] ipv6: fix possible use-after-free in ip6_xmit()

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <eduma...@google.com>

commit bbd6528d28c1b8e80832b3b018ec402b6f5c3215 upstream.

In the unlikely case ip6_xmit() has to call skb_realloc_headroom(),
we need to call skb_set_owner_w() before consuming original skb,
otherwise we risk a use-after-free.

Bring IPv6 in line with what we do in IPv4 to fix this.

Fixes: 1da177e4c3f41 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: syzbot <syzkal...@googlegroups.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -183,9 +183,10 @@ int ip6_xmit(struct sock *sk, struct sk_
                                kfree_skb(skb);
                                return -ENOBUFS;
                        }
+                       if (skb->sk)
+                               skb_set_owner_w(skb2, skb->sk);
                        consume_skb(skb);
                        skb = skb2;
-                       skb_set_owner_w(skb, sk);
                }
                if (opt->opt_flen)
                        ipv6_push_frag_opts(skb, opt, &proto);