netdev - Re: [PATCH net 1/2] vsock/virtio: discard packets if the transport changes

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Message-ID: <2b3062e3-bdaa-4c94-a3c0-2930595b9670@rbox.co>
Date: Thu, 9 Jan 2025 14:34:28 +0100
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>, netdev@...r.kernel.org
Cc: Simon Horman <horms@...nel.org>, Stefan Hajnoczi <stefanha@...hat.com>,
 linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Wongi Lee <qwerty@...ori.io>,
 "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>,
 Jason Wang <jasowang@...hat.com>,
 Bobby Eshleman <bobby.eshleman@...edance.com>,
 virtualization@...ts.linux.dev, Eugenio Pérez
 <eperezma@...hat.com>, Luigi Leonardi <leonardi@...hat.com>,
 bpf@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
 "Michael S. Tsirkin" <mst@...hat.com>, Hyunwoo Kim <v4bel@...ori.io>,
 kvm@...r.kernel.org
Subject: Re: [PATCH net 1/2] vsock/virtio: discard packets if the transport
 changes

On 1/8/25 19:06, Stefano Garzarella wrote:
> If the socket has been de-assigned or assigned to another transport,
> we must discard any packets received because they are not expected
> and would cause issues when we access vsk->transport.
> 
> A possible scenario is described by Hyunwoo Kim in the attached link,
> where after a first connect() interrupted by a signal, and a second
> connect() failed, we can find `vsk->transport` at NULL, leading to a
> NULL pointer dereference.
> 
> Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
> Reported-by: Hyunwoo Kim <v4bel@...ori.io>
> Reported-by: Wongi Lee <qwerty@...ori.io>
> Closes: https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>  net/vmw_vsock/virtio_transport_common.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 9acc13ab3f82..51a494b69be8 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -1628,8 +1628,11 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
>  
>  	lock_sock(sk);
>  
> -	/* Check if sk has been closed before lock_sock */
> -	if (sock_flag(sk, SOCK_DONE)) {
> +	/* Check if sk has been closed or assigned to another transport before
> +	 * lock_sock (note: listener sockets are not assigned to any transport)
> +	 */
> +	if (sock_flag(sk, SOCK_DONE) ||
> +	    (sk->sk_state != TCP_LISTEN && vsk->transport != &t->transport)) {
>  		(void)virtio_transport_reset_no_sock(t, skb);
>  		release_sock(sk);
>  		sock_put(sk);

FWIW, I've tried simplifying Hyunwoo's repro to toy with some tests. Ended
up with

```
from threading import *
from socket import *
from signal import *

def listener(tid):
	while True:
		s = socket(AF_VSOCK, SOCK_SEQPACKET)
		s.bind((1, 1234))
		s.listen()
		pthread_kill(tid, SIGUSR1)

signal(SIGUSR1, lambda *args: None)
Thread(target=listener, args=[get_ident()]).start()

while True:
	c = socket(AF_VSOCK, SOCK_SEQPACKET)
	c.connect_ex((1, 1234))
	c.connect_ex((42, 1234))
```

which gives me splats with or without this patch.

That said, when I apply this patch, but drop the `sk->sk_state !=
TCP_LISTEN &&`: no more splats.