CVE-2025-40231

In the Linux kernel, the following vulnerability has been resolved:

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().