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

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Date:	Thu, 28 Jul 2011 16:44:09 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	manfred@...orfullife.com, eric.dumazet@...il.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com
Subject: [PATCH] [5/50] ipc/sem.c: fix race with concurrent semtimedop() timeouts

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Manfred Spraul <manfred@...orfullife.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@...z.com>
Reported-by: Harald Laabs <kernel@...r.de>
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Acked-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: <stable@...nel.org>		[2.6.35+]
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Andi Kleen <ak@...ux.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) {
--
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