From: Paul Hüber <phueber@kernsp.in>
Date: Sun, 26 Feb 2017 16:58:19 +0000 (+0100)
Subject: l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv
X-Git-Tag: v4.10.5~50
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4c94beba3aee225c8ef57d9eb0730d868d02c9cc;p=thirdparty%2Fkernel%2Fstable.git

l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

[ Upstream commit 51fb60eb162ab84c5edf2ae9c63cf0b878e5547e ]

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@kernsp.in>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 28c21546d5b60..3ed30153a6f5c 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -381,7 +381,7 @@ static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
 drop:
 	IP_INC_STATS(sock_net(sk), IPSTATS_MIB_INDISCARDS);
 	kfree_skb(skb);
-	return -1;
+	return 0;
 }
 
 /* Userspace will call sendmsg() on the tunnel socket to send L2TP