Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752524AbdHKDI7 (ORCPT ); Thu, 10 Aug 2017 23:08:59 -0400 Received: from mail-pf0-f176.google.com ([209.85.192.176]:32955 "EHLO mail-pf0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752190AbdHKDI5 (ORCPT ); Thu, 10 Aug 2017 23:08:57 -0400 From: Daniel Mentz To: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, perex@perex.cz Cc: Daniel Mentz , stable@vger.kernel.org, Takashi Iwai Subject: [PATCH] ALSA: seq: 2nd attempt at fixing race creating a q Date: Thu, 10 Aug 2017 20:07:34 -0700 Message-Id: <20170811030734.37741-1-danielmentz@google.com> X-Mailer: git-send-email 2.14.0.434.g98096fd7a8-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4105 Lines: 115 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. " The last phrase in that commit message refers to calling queue_use(q, client, 1) which increments queue->clients, but that does not prevent the DELETE_QUEUE ioctl() and queue_delete() from kfree()ing the queue. Hence, the commit is not effective at preventing the race. This commit adds code to effectively prevent the removal of the queue by calling snd_use_lock_use(). Reported-by: Dmitry Vyukov Cc: Cc: Takashi Iwai Signed-off-by: Daniel Mentz --- 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(-) diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c index 272c55fe17c8..ea2d0ae85bd3 100644 --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -1502,16 +1502,11 @@ static int snd_seq_ioctl_unsubscribe_port(struct snd_seq_client *client, static int snd_seq_ioctl_create_queue(struct snd_seq_client *client, void *arg) { struct snd_seq_queue_info *info = arg; - int result; struct snd_seq_queue *q; - 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; @@ -1521,7 +1516,7 @@ static int snd_seq_ioctl_create_queue(struct snd_seq_client *client, void *arg) 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); return 0; } diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c index 450c5187eecb..79e0c5604ef8 100644 --- 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 */ diff --git a/sound/core/seq/seq_queue.h b/sound/core/seq/seq_queue.h index 30c8111477f6..719093489a2c 100644 --- 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); -- 2.14.0.434.g98096fd7a8-goog