From: Takashi Iwai <tiwai@xxxxxxx>
This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
===============
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@xxxxxxxxxxxxxx
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
sound/core/oss/pcm_oss.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 4c1cc51772e6..7417f96cea6e 100644
--- 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_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);
@@ -1091,7 +1095,7 @@ 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;
}
@@ -1130,7 +1134,7 @@ 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;
}
@@ -2168,7 +2172,7 @@ 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
--
2.7.1
--
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