Re: [PATCH v2] vsock: use sock_error() to consume sk_err after a

[mawupeng]

On 周一 2026-7-27 15:13, phind.uet@xxxxxxxxx wrote:
> From: Nguyen Dinh Phi <phind.uet@xxxxxxxxx>
> 
> Syzbot report an issue which can be reproduced with these steps:
>    r0 = socket(AF_VSOCK, SOCK_STREAM, 0)
>    bind(r0, {VMADDR_CID_ANY, PORT})
>    connect(r0, {VMADDR_CID_LOCAL, PORT})
>    listen(r0, backlog)
> 
>    r1 = socket(AF_VSOCK, SOCK_STREAM, 0)
>    connect(r1, {VMADDR_CID_LOCAL, PORT})
>    connect(r0 -> self) -> -1, EPROTO
>   
>    listen(r0)          -> 0
>    connect(r1 -> r0)   -> 0
>    accept(r0)          -> -1, EPROTO
> 
> Basically, it creates a socket (r0) and triggers a self-connect after
> binding it. This self-connect fails with EPROTO because it loops back to
> r0 while the socket is still in the TCP_SYN_SENT state, causing it to be
> incorrectly dispatched to the connecting-client path. The unexpected
> packet type encountered there sets sk_err to EPROTO.
> 
> After that, it invokes a listen() call on the same socket. This listen()
> call succeeds because the kernel's listening path never inspects or
> clears sk_err. Then, a new socket (r1) is created as a normal client and
> connects to r0. However, vsock_accept() rejects this incoming connection
> because the listener's sk_err still holds the EPROTO error from the
> earlier failed self-connect.
> 
> This rejection causes the child socket created for r1's connection to
> never be freed on virtio or hyperv transports; only the VMCI transport
> implements pending_work to revisit and clean up a rejected socket
> 
> Fix the issue by using sock_error() to read the sk_err to prevent the
> rejection branch from occurring  in this scenario.
> 
> sock_error() atomically reads and clears sk_err, ensuring the error is
> consumed when vsock_connect() returns and cannot affect subsequent
> operations on the same socket. This matches the established pattern
> used by other protocol connect() implementations in the network
> stack like __inet_stream_connect(), tipc_wait_for_connect()...
> 
> Reported-by: syzbot+1b2c9c4a0f8708082678@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=1b2c9c4a0f8708082678
> Fixes: d021c344051af ("VSOCK: Introduce VM Sockets")
> Signed-off-by: Nguyen Dinh Phi <phind.uet@xxxxxxxxx>

Thanks for your patch.

Test-by: Wupeng Ma <mawupeng1@xxxxxxxxxx>

> ---
> V2: Add reproducer steps to commit message.
> 
>  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 622dbd046799..43eddc33ed12 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1847,14 +1847,11 @@ static int vsock_connect(struct socket *sock, struct sockaddr_unsized *addr,
>  		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
>  	}
>  
> -	if (sk->sk_err) {
> -		err = -sk->sk_err;
> +	err = sock_error(sk);
> +	if (err) {
>  		sk->sk_state = TCP_CLOSE;
>  		sock->state = SS_UNCONNECTED;
> -	} else {
> -		err = 0;
>  	}
> -
>  out_wait:
>  	finish_wait(sk_sleep(sk), &wait);
>  out: