Commit 3c24783b authored by Manfred Spraul's avatar Manfred Spraul Committed by Linus Torvalds

ipc/sem.c: fix return code race with semop vs. semop +semctl(IPC_RMID)

sys_semtimedop() may return -EIDRM although the semaphore operation
completed successfully:

thread 1:	thread 2:
		semtimedop(), sleeps
semop():
* acquires sem_lock()
		semtimedop() woken up due to timeout
		sem_lock() loops
* notices that thread 2 could be completed.
* performs the operations that thread 2 is sleeping on.
* marks the semaphore operation as IN_WAKEUP
* drops sem_lock(), does wakeup, sets return code to 0
		* thread delayed due to interrupt, whatever
* returns to user space
		* thread still delayed
semctl(IPC_RMID)
* acquires sem_lock()
* ipc_rmid(), ipcp->deleted=1
* drops sem_lock()
		* thread finally continues - but seem_lock()
		  now fails due to ipcp->deleted == 1
		* returns -EIDRM instead of 0

The fix is trivial: Always use the return code in queue.status.

In real world, the race probably doesn't matter:
If the semaphore array is destroyed, the app is probably not interested
if the last operation succeeded or was already cancelled.
Signed-off-by: default avatarManfred Spraul <manfred@colorfullife.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Galbraith <efault@gmx.de>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 46cbc1d3
...@@ -1460,7 +1460,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, ...@@ -1460,7 +1460,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* Array removed? If yes, leave without sem_unlock(). * Array removed? If yes, leave without sem_unlock().
*/ */
if (IS_ERR(sma)) { if (IS_ERR(sma)) {
error = -EIDRM;
goto out_free; goto out_free;
} }
......
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