posix-timers: fix deletion race
timer_delete does: lock_timer(); timer->it_process = NULL; unlock_timer(); release_posix_timer(); timer->it_process is checked in lock_timer() to prevent access to a timer, which is on the way to be deleted, but the check happens after idr_lock is dropped. This allows release_posix_timer() to delete the timer before the lock code can check the timer: CPU 0 CPU 1 lock_timer(); timer->it_process = NULL; unlock_timer(); lock_timer() spin_lock(idr_lock); timer = idr_find(); spin_lock(timer->lock); spin_unlock(idr_lock); release_posix_timer(); spin_lock(idr_lock); idr_remove(timer); spin_unlock(idr_lock); free_timer(timer); if (timer->......) Change the locking to prevent this. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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928923c76b
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179394af7a
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@ -605,13 +605,14 @@ static struct k_itimer * lock_timer(timer_t timer_id, unsigned long *flags)
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timr = (struct k_itimer *) idr_find(&posix_timers_id, (int) timer_id);
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if (timr) {
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spin_lock(&timr->it_lock);
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spin_unlock(&idr_lock);
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if ((timr->it_id != timer_id) || !(timr->it_process) ||
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timr->it_process->tgid != current->tgid) {
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unlock_timer(timr, *flags);
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spin_unlock(&timr->it_lock);
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spin_unlock_irqrestore(&idr_lock, *flags);
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timr = NULL;
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}
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} else
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spin_unlock(&idr_lock);
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} else
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spin_unlock_irqrestore(&idr_lock, *flags);
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