linux-kernel - [PATCH 3.16 243/328] ipv6: fix possible use-after-free in ip6

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Message-ID: <lsq.1544392233.534264894@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        "syzbot" <syzkaller@...glegroups.com>
Subject: [PATCH 3.16 243/328] ipv6: fix possible use-after-free in ip6_xmit()

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

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

From: Eric Dumazet <edumazet@...gle.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 <edumazet@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.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);