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 <[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.
I think we might schedule the cleanup worker to run in the rejection
path for these transports as well.
Thanks,
Phi
