From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756027AbcBWVsQ (ORCPT ); Tue, 23 Feb 2016 16:48:16 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41691 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755639AbcBWVpA (ORCPT ); Tue, 23 Feb 2016 16:45:00 -0500 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" , "Dmitry Vyukov" Date: Tue, 23 Feb 2016 21:42:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 33/67] ALSA: pcm: Fix potential deadlock in OSS emulation In-Reply-To: X-SA-Exim-Connect-IP: 92.40.248.141 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 3.2.78-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit b248371628aad599a48540962f6b85a21a8a0c3f upstream. There are potential deadlocks in PCM OSS emulation code while accessing read/write and mmap concurrently. This comes from the infamous mmap_sem usage in copy_from/to_user(). Namely, snd_pcm_oss_write() -> &runtime->oss.params_lock -> copy_to_user() -> &mm->mmap_sem mmap() -> &mm->mmap_sem -> snd_pcm_oss_mmap() -> &runtime->oss.params_lock Since we can't avoid taking params_lock from mmap code path, use trylock variant and aborts with -EAGAIN as a workaround of this AB/BA deadlock. BugLink: http://lkml.kernel.org/r/CACT4Y+bVrBKDG0G2_AcUgUQa+X91VKTeS4v+wN7BSHwHtqn3kQ@mail.gmail.com Reported-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Ben Hutchings --- sound/core/oss/pcm_oss.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -834,7 +834,8 @@ static int choose_rate(struct snd_pcm_su return snd_pcm_hw_param_near(substream, params, SNDRV_PCM_HW_PARAM_RATE, best_rate, NULL); } -static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream) +static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream, + bool trylock) { struct snd_pcm_runtime *runtime = substream->runtime; struct snd_pcm_hw_params *params, *sparams; @@ -848,7 +849,10 @@ static int snd_pcm_oss_change_params(str struct snd_mask sformat_mask; struct snd_mask mask; - if (mutex_lock_interruptible(&runtime->oss.params_lock)) + if (trylock) { + if (!(mutex_trylock(&runtime->oss.params_lock))) + return -EAGAIN; + } else if (mutex_lock_interruptible(&runtime->oss.params_lock)) return -EINTR; sw_params = kmalloc(sizeof(*sw_params), GFP_KERNEL); params = kmalloc(sizeof(*params), GFP_KERNEL); @@ -1091,7 +1095,7 @@ static int snd_pcm_oss_get_active_substr if (asubstream == NULL) asubstream = substream; if (substream->runtime->oss.params) { - err = snd_pcm_oss_change_params(substream); + err = snd_pcm_oss_change_params(substream, false); if (err < 0) return err; } @@ -1130,7 +1134,7 @@ static int snd_pcm_oss_make_ready(struct return 0; runtime = substream->runtime; if (runtime->oss.params) { - err = snd_pcm_oss_change_params(substream); + err = snd_pcm_oss_change_params(substream, false); if (err < 0) return err; } @@ -2168,7 +2172,7 @@ static int snd_pcm_oss_get_space(struct runtime = substream->runtime; if (runtime->oss.params && - (err = snd_pcm_oss_change_params(substream)) < 0) + (err = snd_pcm_oss_change_params(substream, false)) < 0) return err; info.fragsize = runtime->oss.period_bytes; @@ -2804,7 +2808,12 @@ static int snd_pcm_oss_mmap(struct file return -EIO; if (runtime->oss.params) { - if ((err = snd_pcm_oss_change_params(substream)) < 0) + /* use mutex_trylock() for params_lock for avoiding a deadlock + * between mmap_sem and params_lock taken by + * copy_from/to_user() in snd_pcm_oss_write/read() + */ + err = snd_pcm_oss_change_params(substream, true); + if (err < 0) return err; } #ifdef CONFIG_SND_PCM_OSS_PLUGINS