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>

1 files changed, 11 insertions, 2 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 8b929e6a6eda..c8e00f8b4be1 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) {