In the Linux kernel, the following vulnerability has been resolved:
nfc: llcp: Fix race condition in accept_queue lifecycle
In nfc_llcp_socket_release(), sockets and listener accept queues are
walked under the local sockets rwlock and bh_lock_sock(). However,
bh_lock_sock() does not synchronise against process-context lock_sock()
held by nfc_llcp_accept_dequeue() during accept(). Because
socket_release() does not check sock_owned_by_user(), both paths can
concurrently unlink and release the same child socket, resulting in
use-after-free or a NULL pointer dereference of child->parent in
nfc_llcp_accept_unlink().
Fix this synchronisation race by having nfc_llcp_socket_release() use
process-context lock_sock() instead of bh_lock_sock():
1. Pop sockets from the local sockets list under the write lock using
nfc_llcp_sock_list_pop() so lock_sock() can be acquired without
holding the rwlock.
2. Because lock_sock() can sleep, defer the final release of the
nfc_llcp_local structure to a workqueue (release_work). This avoids
a sleeping-in-atomic bug when the last local reference is dropped
from softirq context. Additionally, hold a single device reference
on local from registration until final destruction.
3. In nfc_llcp_local_get(), use kref_get_unless_zero() to prevent
resurrecting a local object whose teardown has been scheduled.
4. In llcp_sock_accept(), verify that the listener socket state is still
LLCP_LISTEN after waking from schedule_timeout() to prevent hangs if
the listener is closed concurrently.
5. When unlinking unaccepted child sockets during listener release,
unlink them from local->sockets, call sock_orphan(), and drop their
initial sk_alloc creation reference via sock_put().
6. Make nfc_llcp_accept_unlink() idempotent by guarding parent access with
a NULL check.
