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authorTakashi Iwai <tiwai@suse.de>2016-01-31 10:32:37 +0100
committerTakashi Iwai <tiwai@suse.de>2016-02-01 12:23:29 +0100
commitb248371628aad599a48540962f6b85a21a8a0c3f (patch)
treeb53a2028b511afaa11cacf8eecbb09cd43aaa190 /sound/core
parentcc85f7a634cfaf9f0713c6aa06d08817424db37a (diff)
ALSA: pcm: Fix potential deadlock in OSS emulation
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> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/oss/pcm_oss.c21
1 files changed, 15 insertions, 6 deletions
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 0e73d03b30e3..ebc9fdfe64df 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -835,7 +835,8 @@ 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;
@@ -849,7 +850,10 @@ 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 = kzalloc(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;
@@ -2804,7 +2808,12 @@ 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