From 6efbfed6418ef34334185c3ec45c7a8a838b8849 Mon Sep 17 00:00:00 2001 From: Keenan Dong Date: Wed, 8 Apr 2026 16:46:00 +0800 Subject: [PATCH] BACKPORT: 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: 8161239a8bcc ("rtmutex: Simplify PI algorithm and make highest prio task get lock") Change-Id: I3ff8da2830773e04f55828b11c9d461ab6ee57c5 Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Xin Liu Signed-off-by: Keenan Dong Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org [Tashar02: Open-code scoped_guard() on msm-5.4] Signed-off-by: Tashfin Shakeer Rhythm --- kernel/locking/rtmutex.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 7c727c4944e6..96c67ba69130 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1063,20 +1063,23 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, * * Must be called with lock->wait_lock held and interrupts disabled. I must * have just failed to try_to_take_rt_mutex(). + * + * When invoked from rt_mutex_start_proxy_lock() waiter::task != current ! */ static void remove_waiter(struct rt_mutex *lock, struct rt_mutex_waiter *waiter) { 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 *next_lock; lockdep_assert_held(&lock->wait_lock); - raw_spin_lock(¤t->pi_lock); + raw_spin_lock(&waiter_task->pi_lock); rt_mutex_dequeue(lock, waiter); - current->pi_blocked_on = NULL; - raw_spin_unlock(¤t->pi_lock); + waiter_task->pi_blocked_on = NULL; + raw_spin_unlock(&waiter_task->pi_lock); /* * Only update priority if the waiter was the highest priority @@ -1112,7 +1115,7 @@ static void remove_waiter(struct rt_mutex *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); }