ipv6: fix possible use-after-free in ip6_xmit()

edumazet · davem330 · commit bbd6528d28c1 · 2018-09-17T07:56:02.000-07:00
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: 1da177e ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git 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);
