Patch "ALSA: seq: Fix leak of pool buffer at concurrent writes" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ALSA: seq: Fix leak of pool buffer at concurrent writes

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     alsa-seq-fix-leak-of-pool-buffer-at-concurrent-writes.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d99a36f4728fcbcc501b78447f625bdcce15b842 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Mon, 15 Feb 2016 16:20:24 +0100
Subject: ALSA: seq: Fix leak of pool buffer at concurrent writes

From: Takashi Iwai <tiwai@suse.de>

commit d99a36f4728fcbcc501b78447f625bdcce15b842 upstream.

When multiple concurrent writes happen on the ALSA sequencer device
right after the open, it may try to allocate vmalloc buffer for each
write and leak some of them.  It's because the presence check and the
assignment of the buffer is done outside the spinlock for the pool.

The fix is to move the check and the assignment into the spinlock.

(The current implementation is suboptimal, as there can be multiple
 unnecessary vmallocs because the allocation is done before the check
 in the spinlock.  But the pool size is already checked beforehand, so
 this isn't a big problem; that is, the only possible path is the
 multiple writes before any pool assignment, and practically seen, the
 current coverage should be "good enough".)

The issue was triggered by syzkaller fuzzer.

BugLink: http://lkml.kernel.org/r/CACT4Y+bSzazpXNvtAr=WXaL8hptqjHwqEyFA+VN2AWEx=aurkg@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 sound/core/seq/seq_memory.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -383,15 +383,20 @@ int snd_seq_pool_init(struct snd_seq_poo
 
 	if (snd_BUG_ON(!pool))
 		return -EINVAL;
-	if (pool->ptr)			/* should be atomic? */
-		return 0;
 
-	pool->ptr = vmalloc(sizeof(struct snd_seq_event_cell) * pool->size);
-	if (!pool->ptr)
+	cellptr = vmalloc(sizeof(struct snd_seq_event_cell) * pool->size);
+	if (!cellptr)
 		return -ENOMEM;
 
 	/* add new cells to the free cell list */
 	spin_lock_irqsave(&pool->lock, flags);
+	if (pool->ptr) {
+		spin_unlock_irqrestore(&pool->lock, flags);
+		vfree(cellptr);
+		return 0;
+	}
+
+	pool->ptr = cellptr;
 	pool->free = NULL;
 
 	for (cell = 0; cell < pool->size; cell++) {


Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.4/alsa-seq-fix-leak-of-pool-buffer-at-concurrent-writes.patch
queue-4.4/alsa-pcm-fix-rwsem-deadlock-for-non-atomic-pcm-stream.patch
queue-4.4/alsa-hda-cancel-probe-work-instead-of-flush-at-remove.patch
queue-4.4/alsa-seq-fix-double-port-list-deletion.patch