[PATCH] vsock: use sock_error() to consume sk_err after connect timeout

[PATCH] vsock: use sock_error() to consume sk_err after connect timeout

[Nguyen Dinh Phi]

After vsock_connect() exits the wait loop due to sk->sk_err being
set, the error was read but not cleared. This left sk->sk_err set
for subsequent operations.
Switch to sock_error() which atomically reads and clears sk->sk_err,
so the error is consumed when returned.

Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com
---
 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:
-- 
2.53.0

Re: [PATCH] vsock: use sock_error() to consume sk_err after connect timeout

[Stefano Garzarella]

On Mon, Jul 20, 2026 at 05:57:47AM +0800, Nguyen Dinh Phi wrote:
>After vsock_connect() exits the wait loop due to sk->sk_err being
>set, the error was read but not cleared. This left sk->sk_err set
>for subsequent operations.

So, is this a fix? If yes, we should put a Fixes tag.

Also, can you describe how to trigger the issue?

Because I see this in vsock_connect(), so I thought it was in some way 
already handled:

		/* sk_err might have been set as a result of an earlier
		 * (failed) connect attempt.
		 */
		sk->sk_err = 0;

>Switch to sock_error() which atomically reads and clears sk->sk_err,
>so the error is consumed when returned.
>
>Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com

Can you explain how this patch fixes that issue?
(this should be the first information to be put in the commit message 
IMHO)

I'd like to understand better if this is a fix of real bug or just an 
improvement to the code (which is fine by me).

Thanks,
Stefano

>---
> 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:
>-- 
>2.53.0
>

Re: [PATCH] vsock: use sock_error() to consume sk_err after connect timeout

[Phi Nguyen]

On 7/20/2026 4:17 PM, Stefano Garzarella wrote:
> On Mon, Jul 20, 2026 at 05:57:47AM +0800, Nguyen Dinh Phi wrote:
>> After vsock_connect() exits the wait loop due to sk->sk_err being
>> set, the error was read but not cleared. This left sk->sk_err set
>> for subsequent operations.
> 
> So, is this a fix? If yes, we should put a Fixes tag.
> 
> Also, can you describe how to trigger the issue?
> 
> Because I see this in vsock_connect(), so I thought it was in some way 
> already handled:
> 
>          /* sk_err might have been set as a result of an earlier
>           * (failed) connect attempt.
>           */
>          sk->sk_err = 0;
> 
This only handles the case where the function following the failed 
connect is another connect() call.

>> Switch to sock_error() which atomically reads and clears sk->sk_err,
>> so the error is consumed when returned.
>>
>> Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>> Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com
> 
> Can you explain how this patch fixes that issue?
> (this should be the first information to be put in the commit message IMHO)
> 
> I'd like to understand better if this is a fix of real bug or just an 
> improvement to the code (which is fine by me).
> 
> Thanks,
> Stefano
> 
Here are the steps of the syzkaller reproducer:

   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
This patch will prevent the rejection branch to occur in this scenario.

I think we might schedule the cleanup worker to run in the rejection 
path for these transports as well.

Thanks,
Phi

Re: [PATCH] vsock: use sock_error() to consume sk_err after connect timeout

[Stefano Garzarella]

On Tue, Jul 21, 2026 at 01:34:03AM +0800, Phi Nguyen wrote:
>On 7/20/2026 4:17 PM, Stefano Garzarella wrote:
>>On Mon, Jul 20, 2026 at 05:57:47AM +0800, Nguyen Dinh Phi wrote:
>>>After vsock_connect() exits the wait loop due to sk->sk_err being
>>>set, the error was read but not cleared. This left sk->sk_err set
>>>for subsequent operations.
>>
>>So, is this a fix? If yes, we should put a Fixes tag.
>>
>>Also, can you describe how to trigger the issue?
>>
>>Because I see this in vsock_connect(), so I thought it was in some 
>>way already handled:
>>
>>         /* sk_err might have been set as a result of an earlier
>>          * (failed) connect attempt.
>>          */
>>         sk->sk_err = 0;
>>
>This only handles the case where the function following the failed 
>connect is another connect() call.

So, can we remove that with this patch, or better to leave as defensive
action?

>
>>>Switch to sock_error() which atomically reads and clears sk->sk_err,
>>>so the error is consumed when returned.
>>>
>>>Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>>>Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com
>>
>>Can you explain how this patch fixes that issue?
>>(this should be the first information to be put in the commit message IMHO)
>>
>>I'd like to understand better if this is a fix of real bug or just 
>>an improvement to the code (which is fine by me).
>>
>>Thanks,
>>Stefano
>>
>Here are the steps of the syzkaller reproducer:
>
>  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
>This patch will prevent the rejection branch to occur in this scenario.

Okay, get it now, thanks! Please include a summary of this in the commit 
description.

I understand that this resolves syzbot's specific test case, but it 
would be best to handle rejected sockets more effectively in af_vsock.c 
rather than in the transport layers (if possible). In any case, this can 
be done in another patch.

>
>I think we might schedule the cleanup worker to run in the rejection 
>path for these transports as well.

Yeah, we need to handle that part better, I think it's a leftover when 
we generalized AF_VSOCK to support more transport than vmci.

Indeed this part is a bit confusing:

		/* If the listener socket has received an error, then we should
		 * reject this socket and return.  Note that we simply mark the
		 * socket rejected, drop our reference, and let the cleanup
		 * function handle the cleanup; the fact that we found it in
		 * the listener's accept queue guarantees that the cleanup
		 * function hasn't run yet.
		 */
		if (err) {
			vconnected->rejected = true;
		} else {


Would be nice to handle everything in af_vsock.c in some way.

In conclusion, the patch LGTM, but please expand the commit description, 
add the Fixes tag, and target the net tree in the v2.

Thanks,
Stefano