From b8c899cf5e7be29840a172c183dedd8d3e7a0287 Mon Sep 17 00:00:00 2001 From: Nguyen Dinh Phi Date: Fri, 14 Aug 2026 01:30:18 +0800 Subject: [PATCH 1/3] vsock: don't check the listener's sk_err in vsock_accept() Syzbot reported 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}) -> -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. For a non-blocking connect(), vsock_connect() may return -EINPROGRESS immediately, and vsock_connect_timeout() can later set sk->sk_err asynchronously. Since no vsock transport ever sets sk_err on a socket while it is in TCP_LISTEN state, checking it in vsock_accept() serves no purpose and only carries forward errors left behind by earlier, unrelated connection attempts on the same socket. Remove the checks so accept() no longer rejects valid incoming connections because of a stale error, which also avoids the resource leak described above. Fixes: d021c344051a ("VSOCK: Introduce VM Sockets") Reported-by: syzbot+1b2c9c4a0f8708082678@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=1b2c9c4a0f8708082678 Suggested-by: Michal Luczaj Signed-off-by: Nguyen Dinh Phi Reviewed-by: Stefano Garzarella Link: https://patch.msgid.link/20260813173024.2362935-2-phind.uet@gmail.com Signed-off-by: Paolo Abeni --- net/vmw_vsock/af_vsock.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 622dbd046799..3cd5c3561be3 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -1893,7 +1893,7 @@ static int vsock_accept(struct socket *sock, struct socket *newsock, timeout = sock_rcvtimeo(listener, arg->flags & O_NONBLOCK); while ((connected = vsock_dequeue_accept(listener)) == NULL && - listener->sk_err == 0 && timeout != 0) { + timeout != 0) { prepare_to_wait(sk_sleep(listener), &wait, TASK_INTERRUPTIBLE); release_sock(listener); timeout = schedule_timeout(timeout); @@ -1906,13 +1906,9 @@ static int vsock_accept(struct socket *sock, struct socket *newsock, } } - if (listener->sk_err) { - err = -listener->sk_err; - } else if (!connected) { + if (!connected) { err = -EAGAIN; - } - - if (connected) { + } else { sk_acceptq_removed(listener); lock_sock_nested(connected, SINGLE_DEPTH_NESTING); From 81fc0f369637ed6ee615d089d3016ba88b2bab71 Mon Sep 17 00:00:00 2001 From: Nguyen Dinh Phi Date: Fri, 14 Aug 2026 01:30:19 +0800 Subject: [PATCH 2/3] vsock: remove the now-unused rejected flag After previous patch, the branch marking a socket rejected in vsock_accept() is unreachable, and nothing ever sets vsk->rejected elsewhere. In fact, since commit d021c344051a ("VSOCK: Introduce VM Sockets"), where `rejected` was introduced, there has never been a path that sets sk_err on a listening socket, so that branch has been dead code since the beginning. Therefore, we can remove the `rejected` field from vsock_sock structure. Suggested-by: Stefano Garzarella Signed-off-by: Nguyen Dinh Phi Reviewed-by: Stefano Garzarella Link: https://patch.msgid.link/20260813173024.2362935-3-phind.uet@gmail.com Signed-off-by: Paolo Abeni --- include/net/af_vsock.h | 5 +---- net/vmw_vsock/af_vsock.c | 46 +++++++++++++--------------------------- 2 files changed, 16 insertions(+), 35 deletions(-) diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index 30046a3c20f7..3357ee62d10b 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -52,13 +52,10 @@ struct vsock_sock { * The listening socket is the head for both lists. Sockets created * for connection requests are placed in the pending list until they * are connected, at which point they are put in the accept queue list - * so they can be accepted in accept(). If accept() cannot accept the - * connection, it is marked as rejected so the cleanup function knows - * to clean up the socket. + * so they can be accepted in accept(). */ struct list_head pending_links; struct list_head accept_queue; - bool rejected; struct delayed_work connect_work; struct delayed_work pending_work; struct delayed_work close_work; diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 3cd5c3561be3..62e22c4b13c0 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -38,10 +38,9 @@ * pending socket. When that socket reaches the connected state, it is removed * from the listener socket's pending list and enqueued in the listener * socket's accept queue. Callers of accept(2) will accept connected sockets - * from the listener socket's accept queue. If the socket cannot be accepted - * for some reason then it is marked rejected. Once the connection is - * accepted, it is owned by the user process and the responsibility for cleanup - * falls with that user process. + * from the listener socket's accept queue. Once the connection is accepted, + * it is owned by the user process and the responsibility for cleanup falls + * with that user process. * * - It is possible that these pending sockets will never reach the connected * state; in fact, we may never receive another packet after the connection @@ -49,9 +48,7 @@ * future, after some amount of time passes where a connection should have been * established. This function ensures that the socket is off all lists so it * cannot be retrieved, then drops all references to the socket so it is cleaned - * up (sock_put() -> sk_free() -> our sk_destruct implementation). Note this - * function will also cleanup rejected sockets, those that reach the connected - * state but leave it before they have been accepted. + * up (sock_put() -> sk_free() -> our sk_destruct implementation). * * - Lock ordering for pending or accept queue sockets is: * @@ -774,11 +771,10 @@ static void vsock_pending_work(struct work_struct *work) if (vsock_is_pending(sk)) { vsock_remove_pending(listener, sk); - } else if (!vsk->rejected) { - /* We are not on the pending list and accept() did not reject - * us, so we must have been accepted by our user process. We - * just need to drop our references to the sockets and be on - * our way. + } else { + /* We are not on the pending list so we must have been accepted + * by our user process. We just need to drop our references to + * the sockets and be on our way. */ cleanup = false; goto out; @@ -942,7 +938,6 @@ static struct sock *__vsock_create(struct net *net, vsk->listener = NULL; INIT_LIST_HEAD(&vsk->pending_links); INIT_LIST_HEAD(&vsk->accept_queue); - vsk->rejected = false; vsk->sent_request = false; vsk->ignore_connecting_rst = false; WRITE_ONCE(vsk->peer_shutdown, 0); @@ -1914,27 +1909,16 @@ static int vsock_accept(struct socket *sock, struct socket *newsock, lock_sock_nested(connected, SINGLE_DEPTH_NESTING); vconnected = vsock_sk(connected); - /* 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 { - newsock->state = SS_CONNECTED; - sock_graft(connected, newsock); + newsock->state = SS_CONNECTED; + sock_graft(connected, newsock); - set_bit(SOCK_CUSTOM_SOCKOPT, + set_bit(SOCK_CUSTOM_SOCKOPT, + &connected->sk_socket->flags); + + if (vsock_msgzerocopy_allow(vconnected->transport)) + set_bit(SOCK_SUPPORT_ZC, &connected->sk_socket->flags); - if (vsock_msgzerocopy_allow(vconnected->transport)) - set_bit(SOCK_SUPPORT_ZC, - &connected->sk_socket->flags); - } - release_sock(connected); sock_put(connected); } From 96cbf89993091a163bfedec52a3bd683dc94b3b4 Mon Sep 17 00:00:00 2001 From: Nguyen Dinh Phi Date: Fri, 14 Aug 2026 01:30:20 +0800 Subject: [PATCH 3/3] vsock: use sock_error() to consume sk_err after a failed connect vsock_connect() returns sk_err to userspace but does not clear it: if (sk->sk_err) { err = -sk->sk_err; For a blocking connect() the error has already been delivered as connect()'s return value, so leaving it set causes subsequent operations like poll()/epoll() to keep reporting POLLERR even though the connect failure was already delivered. The error should be consumed once it has been returned to userspace. Switch to sock_error(), which reads and clears sk_err atomically, matching the behavior of other protocol implementations such as __inet_stream_connect(). Fixes: d021c344051a ("VSOCK: Introduce VM Sockets") Tested-by: Wupeng Ma Reviewed-by: Stefano Garzarella Signed-off-by: Nguyen Dinh Phi Link: https://patch.msgid.link/20260813173024.2362935-4-phind.uet@gmail.com Signed-off-by: Paolo Abeni --- net/vmw_vsock/af_vsock.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 62e22c4b13c0..e89cb84b8d73 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -1842,12 +1842,10 @@ 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: