[PATCH] [5/50] ipc/sem.c: fix race with concurrent semtimedop() timeouts

Andi Kleen
2011-07-28T23:44:31Z

From: Manfred Spraul <manfred@colorfullife.com>

[ upstream commit d694ad62bf539dbb20a0899ac2a954555f9e4a83 ]
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>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/ipc/sem.c
===================================================================
--- linux-2.6.35.y.orig/ipc/sem.c
+++ linux-2.6.35.y/ipc/sem.c
@@ -1452,15 +1452,24 @@ SYSCALL_DEFINE4(semtimedop, int, semid,
}

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) {