linux-kernel - [PATCH] l2tp: avoid use-after-free caused by l2tp_ip_backlog

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Message-Id: <20170215232849.12991-1-phueber@kernsp.in>
Date:   Thu, 16 Feb 2017 00:28:49 +0100
From:   Paul Hüber <phueber@...nsp.in>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

l2tp_ip_backlog_recv may not return -1 if the packet gets dropped, as
the 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>
---
 net/l2tp/l2tp_ip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 28c21546d5b6..3ed30153a6f5 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
-- 
2.11.1