Commit d694ad62 authored Jul 25, 2011 by Manfred Spraul Committed by Linus Torvalds Jul 25, 2011

ipc/sem.c: fix race with concurrent semtimedop() timeouts and IPC_RMID

If a semaphore array is removed and in parallel a sleeping task is woken
up (signal or timeout, does not matter), then the woken up task does not
wait until wake_up_sem_queue_do() is completed.  This will cause crashes,
because wake_up_sem_queue_do() will read from a stale pointer.

The fix is simple: Regardless of anything, always call get_queue_result().
This function waits until wake_up_sem_queue_do() has finished it's task.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=27142



Reported-by: Yuriy Yevtukhov <yuriy@ucoz.com>
Reported-by: Harald Laabs <kernel@dasr.de>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: <stable@kernel.org>		[2.6.35+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 8405b044

ipc/sem.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -1450,15 +1450,24 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
		}

		sma = sem_lock(ns, semid);

		/*
		* Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
		*/
		error = get_queue_result(&queue);

		/*
		* Array removed? If yes, leave without sem_unlock().
		*/
		if (IS_ERR(sma)) {
		error = -EIDRM;
		goto out_free;
		}

		error = get_queue_result(&queue);

		/*
		* If queue.status != -EINTR we are woken up by another process
		* If queue.status != -EINTR we are woken up by another process.
		* Leave without unlink_queue(), but with sem_unlock().
		*/

		if (error != -EINTR) {