The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x f7c877e7535260cc7a21484c994e8ce7e8cb6780 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025102616-navy-creatable-7fad@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f7c877e7535260cc7a21484c994e8ce7e8cb6780 Mon Sep 17 00:00:00 2001 From: Stefano Garzarella sgarzare@redhat.com Date: Tue, 21 Oct 2025 14:17:18 +0200 Subject: [PATCH] vsock: fix lock inversion in vsock_assign_transport()

Syzbot reported a potential lock inversion deadlock between vsock_register_mutex and sk_lock-AF_VSOCK when vsock_linger() is called.

The issue was introduced by commit 687aa0c5581b ("vsock: Fix transport_* TOCTOU") which added vsock_register_mutex locking in vsock_assign_transport() around the transport->release() call, that can call vsock_linger(). vsock_assign_transport() can be called with sk_lock held. vsock_linger() calls sk_wait_event() that temporarily releases and re-acquires sk_lock. During this window, if another thread hold vsock_register_mutex while trying to acquire sk_lock, a circular dependency is created.

Fix this by releasing vsock_register_mutex before calling transport->release() and vsock_deassign_transport(). This is safe because we don't need to hold vsock_register_mutex while releasing the old transport, and we ensure the new transport won't disappear by obtaining a module reference first via try_module_get().

Reported-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com Tested-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com Fixes: 687aa0c5581b ("vsock: Fix transport_* TOCTOU") Cc: mhal@rbox.co Cc: stable@vger.kernel.org Signed-off-by: Stefano Garzarella sgarzare@redhat.com Link: https://patch.msgid.link/20251021121718.137668-1-sgarzare@redhat.com Signed-off-by: Paolo Abeni pabeni@redhat.com

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 4c2db6cca557..76763247a377 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -487,12 +487,26 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) goto err; }

- if (vsk->transport) { - if (vsk->transport == new_transport) { - ret = 0; - goto err; - } + if (vsk->transport && vsk->transport == new_transport) { + ret = 0; + goto err; + }

+ /* We increase the module refcnt to prevent the transport unloading + * while there are open sockets assigned to it. + */ + if (!new_transport || !try_module_get(new_transport->module)) { + ret = -ENODEV; + goto err; + } + + /* It's safe to release the mutex after a successful try_module_get(). + * Whichever transport `new_transport` points at, it won't go away until + * the last module_put() below or in vsock_deassign_transport(). + */ + mutex_unlock(&vsock_register_mutex); + + if (vsk->transport) { /* transport->release() must be called with sock lock acquired. * This path can only be taken during vsock_connect(), where we * have already held the sock lock. In the other cases, this @@ -512,20 +526,6 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk) vsk->peer_shutdown = 0; }

- /* We increase the module refcnt to prevent the transport unloading - * while there are open sockets assigned to it. - */ - if (!new_transport || !try_module_get(new_transport->module)) { - ret = -ENODEV; - goto err; - } - - /* It's safe to release the mutex after a successful try_module_get(). - * Whichever transport `new_transport` points at, it won't go away until - * the last module_put() below or in vsock_deassign_transport(). - */ - mutex_unlock(&vsock_register_mutex); - if (sk->sk_type == SOCK_SEQPACKET) { if (!new_transport->seqpacket_allow || !new_transport->seqpacket_allow(remote_cid)) {