From d694ad62bf539dbb20a0899ac2a954555f9e4a83 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Mon, 25 Jul 2011 17:11:47 -0700 Subject: [PATCH] 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 Reported-by: Harald Laabs Signed-off-by: Manfred Spraul Acked-by: Eric Dumazet Cc: [2.6.35+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/ipc/sem.c b/ipc/sem.c index 8b929e6..c8e00f8 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -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) { -- 2.7.4