linux-kernel - [PATCH 3.2 66/74] l2tp: avoid use-after-free caused by l2tp_ip_backlog

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Date:   Mon, 09 Oct 2017 13:30:34 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
        "Paul Hüber" <phueber@...nsp.in>
Subject: [PATCH 3.2 66/74] l2tp: avoid use-after-free caused by
 l2tp_ip_backlog_recv

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

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

From: Paul Hüber <phueber@...nsp.in>

commit 51fb60eb162ab84c5edf2ae9c63cf0b878e5547e upstream.

l2tp_ip_backlog_recv may not return -1 if the packet gets dropped.
The return value is passed up to ip_local_deliver_finish, which treats
negative values as an IP protocol number for resubmission.

Signed-off-by: Paul Hüber <phueber@...nsp.in>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/l2tp/l2tp_ip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -432,7 +432,7 @@ static int l2tp_ip_backlog_recv(struct s
 drop:
 	IP_INC_STATS(&init_net, IPSTATS_MIB_INDISCARDS);
 	kfree_skb(skb);
-	return -1;
+	return 0;
 }
 
 /* Userspace will call sendmsg() on the tunnel socket to send L2TP