[PATCH net] l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

[Paul Hüber]

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 <phue...@kernsp.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