In the Linux kernel, the following vulnerability has been resolved: futex/requeue: Prevent NULL...

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

futex/requeue: Prevent NULL pointer dereference in remove_waiter() on self-deadlock

When FUTEX_CMP_REQUEUE_PI requeues a non-top waiter that already owns the target PI futex, task_blocks_on_rt_mutex() returns -EDEADLK before setting waiter->task.

The subsequent remove_waiter() in rt_mutex_start_proxy_lock() dereferences the NULL waiter->task, causing a kernel crash.

Add a self-deadlock check for non-top waiters before calling rt_mutex_start_proxy_lock(), analogous to the top-waiter check in futex_lock_pi_atomic().