On Tue, Jul 28, 2026 at 11:14:31AM +0800, mawupeng wrote:
On 周一 2026-7-27 15:13, [email protected] wrote:
From: Nguyen Dinh Phi <[email protected]>
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: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=1b2c9c4a0f8708082678
Fixes: d021c344051af ("VSOCK: Introduce VM Sockets")
Signed-off-by: Nguyen Dinh Phi <[email protected]>
Thanks for your patch.
Test-by: Wupeng Ma <[email protected]>
Thanks for testing, just a note, the right tag should be Tested-by:
Anyway, @Phi can you bring this with the right tag to the v3 if the code
will not change?
Thanks,
Stefano
