Commit 3bfdc639 authored by Keenan Dong's avatar Keenan Dong Committed by Thomas Gleixner
Browse files

rtmutex: Use waiter::task instead of current in remove_waiter() 



remove_waiter() is used by the slowlock paths, but it is also used for
proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from
futex_requeue().

In the latter case waiter::task is not current, but remove_waiter()
operates on current for the dequeue operation. That results in several
problems:

  1) the rbtree dequeue happens without waiter::task::pi_lock being held

  2) the waiter task's pi_blocked_on state is not cleared, which leaves a
     dangling pointer primed for UAF around.

  3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter
     task

Use waiter::task instead of current in all related operations in
remove_waiter() to cure those problems.

[ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the
  	changelog ]

Fixes: 8161239a ("rtmutex: Simplify PI algorithm and make highest prio task get lock")
Reported-by: default avatarYuan Tan <yuantan098@gmail.com>
Reported-by: default avatarYifan Wu <yifanwucs@gmail.com>
Reported-by: default avatarJuefei Pu <tomapufckgml@gmail.com>
Reported-by: default avatarXin Liu <bird@lzu.edu.cn>
Signed-off-by: default avatarKeenan Dong <keenanat2000@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
parent c1f49dea

kernel/locking/rtmutex.c

+8 −5
Original line number Diff line number Diff line
@@ -1544,6 +1544,8 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, 
 *

 * Must be called with lock->wait_lock held and interrupts disabled. It must

 * have just failed to try_to_take_rt_mutex().

 *

 * When invoked from rt_mutex_start_proxy_lock() waiter::task != current !

 */

static void __sched remove_waiter(struct rt_mutex_base *lock,

				  struct rt_mutex_waiter *waiter)
@@ -1551,14 +1553,15 @@ static void __sched remove_waiter(struct rt_mutex_base *lock, 
{

	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));

	struct task_struct *owner = rt_mutex_owner(lock);

	struct task_struct *waiter_task = waiter->task;

	struct rt_mutex_base *next_lock;



	lockdep_assert_held(&lock->wait_lock);



	raw_spin_lock(&current->pi_lock);

	scoped_guard(raw_spinlock, &waiter_task->pi_lock) {

		rt_mutex_dequeue(lock, waiter);

	current->pi_blocked_on = NULL;

	raw_spin_unlock(&current->pi_lock);

		waiter_task->pi_blocked_on = NULL;

	}



	/*

	 * Only update priority if the waiter was the highest priority
@@ -1594,7 +1597,7 @@ static void __sched remove_waiter(struct rt_mutex_base *lock, 
	raw_spin_unlock_irq(&lock->wait_lock);



	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,

				   next_lock, NULL, current);

				   next_lock, NULL, waiter_task);



	raw_spin_lock_irq(&lock->wait_lock);

}