@@ -834,7 +834,8 @@ static int choose_rate(struct snd_pcm_substream *substream,
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(struct snd_pcm_substream *substream)
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);
@@ -1092,7 +1096,7 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil
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;
}
@@ -1132,7 +1136,7 @@ static int snd_pcm_oss_make_ready(struct snd_pcm_substream *substream)
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;
}
@@ -2163,7 +2167,7 @@ static int snd_pcm_oss_get_space(struct snd_pcm_oss_file *pcm_oss_file, int stre
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;
@@ -2800,7 +2804,12 @@ static int snd_pcm_oss_mmap(struct file *file, struct vm_area_struct *area)
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
This is a note to let you know that I have just added a patch titled ALSA: pcm: Fix potential deadlock in OSS emulation to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue This patch is scheduled to be released in version 4.2.8-ckt5. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 4.2.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ---8<------------------------------------------------------------ From 2f5b533176d6141ec531e8a4acc7b9850e61d5f8 Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@suse.de> Date: Sun, 31 Jan 2016 10:32:37 +0100 Subject: ALSA: pcm: Fix potential deadlock in OSS emulation 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 <dvyukov@google.com> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- sound/core/oss/pcm_oss.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) -- 2.7.0