[PATCH 3.16 139/192] l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

Ben Hutchings
2017-10-09T13:54:24Z

From: Paul Hüber <phueber@kernsp.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@kernsp.in>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/l2tp/l2tp_ip.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -390,7 +390,7 @@ static int l2tp_ip_backlog_recv(struct s
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