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

[Stefano Garzarella <sgarzare@redhat.com>]

commit title seems truncated, can you check?

On Mon, Jul 27, 2026 at 03:13:02PM +0800, phind.uet@gmail.com wrote:
>From: Nguyen Dinh Phi <phind.uet@gmail.com>
>
>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

I spent some time to understand this, what about changing in this way
(or something similar):

     r0 = socket(AF_VSOCK, SOCK_STREAM, 0)
     bind(r0, {VMADDR_CID_ANY, PORT})
     connect(r0, {VMADDR_CID_LOCAL, PORT})   -> -1, EPROTO  (self-connect)
     listen(r0, backlog)                     -> 0
     r1 = socket(AF_VSOCK, SOCK_STREAM, 0)
     connect(r1, {VMADDR_CID_LOCAL, PORT})   -> 0
     accept(r0)                              -> -1, EPROTO  (stale sk_err)

>
>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@syzkaller.appspotmail.com
>Closes: https://syzkaller.appspot.com/bug?extid=1b2c9c4a0f8708082678
>Fixes: d021c344051af ("VSOCK: Introduce VM Sockets")
>Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>---
>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);

Should we do the same in other paths (e.g. send/recv) as well in a 
follwup patch or in a series?

The patch itself LGTM.

Thanks,
Stefano

>+	if (err) {
> 		sk->sk_state = TCP_CLOSE;
> 		sock->state = SS_UNCONNECTED;
>-	} else {
>-		err = 0;
> 	}
>-
> out_wait:
> 	finish_wait(sk_sleep(sk), &wait);
> out:
>-- 
>2.53.0
>