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Subject[PATCH 1/3] ipc/sem.c: Fix return code race with semop vs. semop +semctl(IPC_RMID)
Date
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: Manfred Spraul <manfred@colorfullife.com>
---
ipc/sem.c | 1 -
1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index c8e00f8..fb13be1 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1460,7 +1460,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* Array removed? If yes, leave without sem_unlock().
*/
if (IS_ERR(sma)) {
- error = -EIDRM;
goto out_free;
}

--
1.7.6


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