l2tp: avoid use-after-free caused by l2tp_ip_backlog_recv

p-hueber · gregkh · commit 2cd0afc64e33 · 2017-03-22T12:04:14.000+01:00
[ Upstream commit 51fb60eb162ab84c5edf2ae9c63cf0b878e5547e ]

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 &lt;phueber@kernsp.in&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
@@ -383,7 +383,7 @@ 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

Original file line number	Diff line number	Diff line change
`@@ -383,7 +383,7 @@ static int l2tp_ip_backlog_recv(struct sock sk, struct sk_buff skb)`
`383`	`383`	`drop:`
`384`	`384`	`IP_INC_STATS(sock_net(sk), IPSTATS_MIB_INDISCARDS);`
`385`	`385`	`kfree_skb(skb);`
`386`		`- return -1;`
	`386`	`+ return 0;`
`387`	`387`	`}`
`388`	`388`
`389`	`389`	`/* Userspace will call sendmsg() on the tunnel socket to send L2TP`