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>

diff --git a/ipc/sem.c b/ipc/sem.c
index 8b929e6a6eda22e96da29cb72423cdb06cef0685..c8e00f8b4be1b79bd49bf841924d8d8ea5945b8c 100644 (file)
--- 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) {