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-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3a45ed9afc5d3f009e8358ae01a8360c70ae6e32;p=pandora-kernel.git

l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

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@kernsp.in>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index a753c9b2336f..6f12fd694d29 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -432,7 +432,7 @@ static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
 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