Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753266AbdHVTbp (ORCPT ); Tue, 22 Aug 2017 15:31:45 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:43534 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752768AbdHVTKL (ORCPT ); Tue, 22 Aug 2017 15:10:11 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dmitry Vyukov , Daniel Mentz , Takashi Iwai Subject: [PATCH 4.4 07/20] ALSA: seq: 2nd attempt at fixing race creating a queue Date: Tue, 22 Aug 2017 12:09:50 -0700 Message-Id: <20170822190915.657145449@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170822190915.345029476@linuxfoundation.org> References: <20170822190915.345029476@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4487 Lines: 130 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Mentz commit 7e1d90f60a0d501c8503e636942ca704a454d910 upstream. commit 4842e98f26dd80be3623c4714a244ba52ea096a8 ("ALSA: seq: Fix race at creating a queue") attempted to fix a race reported by syzkaller. That fix has been described as follows: " When a sequencer queue is created in snd_seq_queue_alloc(),it adds the new queue element to the public list before referencing it. Thus the queue might be deleted before the call of snd_seq_queue_use(), and it results in the use-after-free error, as spotted by syzkaller. The fix is to reference the queue object at the right time. " Even with that fix in place, syzkaller reported a use-after-free error. It specifically pointed to the last instruction "return q->queue" in snd_seq_queue_alloc(). The pointer q is being used after kfree() has been called on it. It turned out that there is still a small window where a race can happen. The window opens at snd_seq_ioctl_create_queue()->snd_seq_queue_alloc()->queue_list_add() and closes at snd_seq_ioctl_create_queue()->queueptr()->snd_use_lock_use(). Between these two calls, a different thread could delete the queue and possibly re-create a different queue in the same location in queue_list. This change prevents this situation by calling snd_use_lock_use() from snd_seq_queue_alloc() prior to calling queue_list_add(). It is then the caller's responsibility to call snd_use_lock_free(&q->use_lock). Fixes: 4842e98f26dd ("ALSA: seq: Fix race at creating a queue") Reported-by: Dmitry Vyukov Signed-off-by: Daniel Mentz Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/seq/seq_clientmgr.c | 13 ++++--------- sound/core/seq/seq_queue.c | 14 +++++++++----- sound/core/seq/seq_queue.h | 2 +- 3 files changed, 14 insertions(+), 15 deletions(-) --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -1530,19 +1530,14 @@ static int snd_seq_ioctl_create_queue(st void __user *arg) { struct snd_seq_queue_info info; - int result; struct snd_seq_queue *q; if (copy_from_user(&info, arg, sizeof(info))) return -EFAULT; - result = snd_seq_queue_alloc(client->number, info.locked, info.flags); - if (result < 0) - return result; - - q = queueptr(result); - if (q == NULL) - return -EINVAL; + q = snd_seq_queue_alloc(client->number, info.locked, info.flags); + if (IS_ERR(q)) + return PTR_ERR(q); info.queue = q->queue; info.locked = q->locked; @@ -1552,7 +1547,7 @@ static int snd_seq_ioctl_create_queue(st if (! info.name[0]) snprintf(info.name, sizeof(info.name), "Queue-%d", q->queue); strlcpy(q->name, info.name, sizeof(q->name)); - queuefree(q); + snd_use_lock_free(&q->use_lock); if (copy_to_user(arg, &info, sizeof(info))) return -EFAULT; --- a/sound/core/seq/seq_queue.c +++ b/sound/core/seq/seq_queue.c @@ -184,22 +184,26 @@ void __exit snd_seq_queues_delete(void) static void queue_use(struct snd_seq_queue *queue, int client, int use); /* allocate a new queue - - * return queue index value or negative value for error + * return pointer to new queue or ERR_PTR(-errno) for error + * The new queue's use_lock is set to 1. It is the caller's responsibility to + * call snd_use_lock_free(&q->use_lock). */ -int snd_seq_queue_alloc(int client, int locked, unsigned int info_flags) +struct snd_seq_queue *snd_seq_queue_alloc(int client, int locked, unsigned int info_flags) { struct snd_seq_queue *q; q = queue_new(client, locked); if (q == NULL) - return -ENOMEM; + return ERR_PTR(-ENOMEM); q->info_flags = info_flags; queue_use(q, client, 1); + snd_use_lock_use(&q->use_lock); if (queue_list_add(q) < 0) { + snd_use_lock_free(&q->use_lock); queue_delete(q); - return -ENOMEM; + return ERR_PTR(-ENOMEM); } - return q->queue; + return q; } /* delete a queue - queue must be owned by the client */ --- a/sound/core/seq/seq_queue.h +++ b/sound/core/seq/seq_queue.h @@ -71,7 +71,7 @@ void snd_seq_queues_delete(void); /* create new queue (constructor) */ -int snd_seq_queue_alloc(int client, int locked, unsigned int flags); +struct snd_seq_queue *snd_seq_queue_alloc(int client, int locked, unsigned int flags); /* delete queue (destructor) */ int snd_seq_queue_delete(int client, int queueid);