linux-kernel - [PATCH 3.10 178/268] l2tp: avoid use-after-free caused by l2tp_ip_backlog

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Message-Id: <1497897167-14556-179-git-send-email-w@1wt.eu>
Date:   Mon, 19 Jun 2017 20:31:17 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Paul Hüber <phueber@...nsp.in>,
        "David S . Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 178/268] l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

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: Willy Tarreau <w@....eu>
---
 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 f4d30b5..1f65095 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -382,7 +382,7 @@ 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
-- 
2.8.0.rc2.1.gbe9624a