[PATCH 3.18 010/120] ipv6: fix possible use-after-free in ip6_xmit()

Greg Kroah-Hartman
2018-10-11T15:36:01Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit bbd6528d28c1b8e80832b3b018ec402b6f5c3215 ]

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 <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/ip6_output.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- 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);