On 22/7/26 15:55, Stefano Garzarella wrote:
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?
I prefer to keep it here 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 <[email protected]>
Reported-by: [email protected]
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.
I'll send a v2 with an expanded commit description and the Fixes tag.
Regarding the rejected socket cleanup, I agree it would be cleaner to
handle it entirely in af_vsock.c. I'll look at that as a follow-up.
Thanks,
Phi
