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| author | Takashi Iwai <tiwai@suse.de> | 2016-01-31 10:32:37 +0100 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2016-03-12 14:25:45 +0100 |
| commit | 937524d03c6eaf3a5d00b714eaaf15a1a9c8478a (patch) | |
| tree | 3ff32e4f16e9512e683dccbc29dc508a540ea1c2 | |
| parent | 51a155faf4bbaa05cf279192f8ff47733933d85f (diff) | |
| download | lwn-937524d03c6eaf3a5d00b714eaaf15a1a9c8478a.tar.gz lwn-937524d03c6eaf3a5d00b714eaaf15a1a9c8478a.zip | |
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: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Willy Tarreau <w@1wt.eu>
| -rw-r--r-- | sound/core/oss/pcm_oss.c | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c index d9c96353121a..07a249e58cf7 100644 --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -826,7 +826,8 @@ 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; @@ -839,7 +840,10 @@ 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); @@ -1079,7 +1083,7 @@ 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; } @@ -1118,7 +1122,7 @@ 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; } @@ -2149,7 +2153,7 @@ 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; @@ -2770,7 +2774,12 @@ 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 |