[PATCH 4.19 12/52] pptp: dst_release sk_dst_cache in pptp_sock_destruct

From: Greg Kroah-Hartman
Date: Mon Mar 18 2019 - 05:43:43 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Xin Long <lucien.xin@xxxxxxxxx>

[ Upstream commit 9417d81f4f8adfe20a12dd1fadf73a618cbd945d ]

sk_setup_caps() is called to set sk->sk_dst_cache in pptp_connect,
so we have to dst_release(sk->sk_dst_cache) in pptp_sock_destruct,
otherwise, the dst refcnt will leak.

It can be reproduced by this syz log:

r1 = socket$pptp(0x18, 0x1, 0x2)
bind$pptp(r1, &(0x7f0000000100)={0x18, 0x2, {0x0, @local}}, 0x1e)
connect$pptp(r1, &(0x7f0000000000)={0x18, 0x2, {0x3, @remote}}, 0x1e)

Consecutive dmesg warnings will occur:

unregister_netdevice: waiting for lo to become free. Usage count = 1

- use rcu_dereference_protected() instead of rcu_dereference_check(),
as suggested by Eric.

Fixes: 00959ade36ac ("PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)")
Reported-by: Xiumei Mu <xmu@xxxxxxxxxx>
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/net/ppp/pptp.c | 1 +
1 file changed, 1 insertion(+)

--- a/drivers/net/ppp/pptp.c
+++ b/drivers/net/ppp/pptp.c
@@ -537,6 +537,7 @@ static void pptp_sock_destruct(struct so
+ dst_release(rcu_dereference_protected(sk->sk_dst_cache, 1));

static int pptp_create(struct net *net, struct socket *sock, int kern)