Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753557AbdGPOQn (ORCPT ); Sun, 16 Jul 2017 10:16:43 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:44316 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753532AbdGPOQj (ORCPT ); Sun, 16 Jul 2017 10:16:39 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Takashi Iwai" , "Ben Hutchings" Date: Sun, 16 Jul 2017 14:56:46 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 149/178] ALSA: seq: Don't break snd_use_lock_sync() loop by timeout In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1934 Lines: 55 3.16.46-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit 4e7655fd4f47c23e5249ea260dc802f909a64611 upstream. The snd_use_lock_sync() (thus its implementation snd_use_lock_sync_helper()) has the 5 seconds timeout to break out of the sync loop. It was introduced from the beginning, just to be "safer", in terms of avoiding the stupid bugs. However, as Ben Hutchings suggested, this timeout rather introduces a potential leak or use-after-free that was apparently fixed by the commit 2d7d54002e39 ("ALSA: seq: Fix race during FIFO resize"): for example, snd_seq_fifo_event_in() -> snd_seq_event_dup() -> copy_from_user() could block for a long time, and snd_use_lock_sync() goes timeout and still leaves the cell at releasing the pool. For fixing such a problem, we remove the break by the timeout while still keeping the warning. Suggested-by: Ben Hutchings Signed-off-by: Takashi Iwai Signed-off-by: Ben Hutchings --- sound/core/seq/seq_lock.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) --- a/sound/core/seq/seq_lock.c +++ b/sound/core/seq/seq_lock.c @@ -28,19 +28,16 @@ /* wait until all locks are released */ void snd_use_lock_sync_helper(snd_use_lock_t *lockp, const char *file, int line) { - int max_count = 5 * HZ; + int warn_count = 5 * HZ; if (atomic_read(lockp) < 0) { pr_warn("ALSA: seq_lock: lock trouble [counter = %d] in %s:%d\n", atomic_read(lockp), file, line); return; } while (atomic_read(lockp) > 0) { - if (max_count == 0) { - pr_warn("ALSA: seq_lock: timeout [%d left] in %s:%d\n", atomic_read(lockp), file, line); - break; - } + if (warn_count-- == 0) + pr_warn("ALSA: seq_lock: waiting [%d left] in %s:%d\n", atomic_read(lockp), file, line); schedule_timeout_uninterruptible(1); - max_count--; } }