[PATCH net] ipv6: fix possible use-after-free in ip6_xmit()

[Eric Dumazet]

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>
---
 net/ipv6/ip6_output.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 
16f200f06500758c4cae84ea16229d5dbce912cb..f9f8f554d141676a7d342f85088d12d9a6815e9d
 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -219,12 +219,10 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, 
struct flowi6 *fl6,
                                kfree_skb(skb);
                                return -ENOBUFS;
                        }
+                       if (skb->sk)
+                               skb_set_owner_w(skb2, skb->sk);
                        consume_skb(skb);
                        skb = skb2;
-                       /* skb_set_owner_w() changes sk->sk_wmem_alloc 
atomically,
-                        * it is safe to call in our context (socket lock not 
held)
-                        */
-                       skb_set_owner_w(skb, (struct sock *)sk);
                }
                if (opt->opt_flen)
                        ipv6_push_frag_opts(skb, opt, &proto);
-- 
2.19.0.397.gdd90340f6a-goog