l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

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>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index c59712057dc8..d25038cfd64e 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -388,7 +388,7 @@ 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