From: Keenan Dong Date: Wed, 8 Apr 2026 08:46:00 +0000 (+0800) Subject: rtmutex: Use waiter::task instead of current in remove_waiter() X-Git-Tag: v7.1-rc1~25^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3bfdc63936dd4773109b7b8c280c0f3b5ae7d349;p=thirdparty%2Fkernel%2Flinux.git 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") 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 --- diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index ccaba6148b61..4f386ea6c792 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -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(¤t->pi_lock); - rt_mutex_dequeue(lock, waiter); - current->pi_blocked_on = NULL; - raw_spin_unlock(¤t->pi_lock); + scoped_guard(raw_spinlock, &waiter_task->pi_lock) { + rt_mutex_dequeue(lock, waiter); + 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); }