On 03/07/2019 11:25 PM, Xin Long wrote:
> 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
>
> Fixes: 00959ade36ac ("PPTP: PPP over IPv4 (Point-to-Point Tunneling
> Protocol)")
> Reported-by: Xiumei Mu <x...@redhat.com>
> Signed-off-by: Xin Long <lucien....@gmail.com>
> ---
> drivers/net/ppp/pptp.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c
> index 8f09edd..76172c2 100644
> --- a/drivers/net/ppp/pptp.c
> +++ b/drivers/net/ppp/pptp.c
> @@ -532,6 +532,7 @@ static void pptp_sock_destruct(struct sock *sk)
> pppox_unbind_sock(sk);
> }
> skb_queue_purge(&sk->sk_receive_queue);
> + dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
rcu_dereference_protected() is probably more appropriate. (No barrier is needed)
> }
>
> static int pptp_create(struct net *net, struct socket *sock, int kern)
>
