Re: [PATCH] net/vmw_vsock: fix NULL pointer deref and improve locking

[Eric Dumazet <eric.dumazet@gmail.com>]

On 2/4/21 10:28 PM, Norbert Slusarek wrote:
> From: Norbert Slusarek <nslusarek@gmx.net>
> Date: Thu, 4 Feb 2021 18:49:24 +0100
> Subject: [PATCH] net/vmw_vsock: fix NULL pointer deref and improve locking
> 
> In vsock_stream_connect(), a thread will enter schedule_timeout().
> While being scheduled out, another thread can enter vsock_stream_connect() as
> well and set vsk->transport to NULL. In case a signal was sent, the first
> thread can leave schedule_timeout() and vsock_transport_cancel_pkt() will be
> called right after. Inside vsock_transport_cancel_pkt(), a null dereference
> will happen on transport->cancel_pkt.
> 
> The patch also features improved locking inside vsock_connect_timeout().


We request Fixes: tag for patches targeting net tree.

You could also mention the vsock_connect_timeout()
issue was found by a reviewer and give some credits ;)

> 
> Signed-off-by: Norbert Slusarek <nslusarek@gmx.net>
> ---
>  net/vmw_vsock/af_vsock.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 3b480ed0953a..ea7b9d208724 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1233,7 +1233,7 @@ static int vsock_transport_cancel_pkt(struct vsock_sock *vsk)
>  {
>  	const struct vsock_transport *transport = vsk->transport;
> 
> -	if (!transport->cancel_pkt)
> +	if (!transport || !transport->cancel_pkt)
>  		return -EOPNOTSUPP;
> 
>  	return transport->cancel_pkt(vsk);
> @@ -1243,7 +1243,6 @@ static void vsock_connect_timeout(struct work_struct *work)
>  {
>  	struct sock *sk;
>  	struct vsock_sock *vsk;
> -	int cancel = 0;
> 
>  	vsk = container_of(work, struct vsock_sock, connect_work.work);
>  	sk = sk_vsock(vsk);
> @@ -1254,11 +1253,9 @@ static void vsock_connect_timeout(struct work_struct *work)
>  		sk->sk_state = TCP_CLOSE;
>  		sk->sk_err = ETIMEDOUT;
>  		sk->sk_error_report(sk);
> -		cancel = 1;
> +		vsock_transport_cancel_pkt(vsk);
>  	}
>  	release_sock(sk);
> -	if (cancel)
> -		vsock_transport_cancel_pkt(vsk);
> 
>  	sock_put(sk);
>  }
> --
> 2.30.0
>