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| author | Takashi Iwai <tiwai@suse.de> | 2018-04-02 22:41:43 +0200 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2018-04-03 08:36:40 +0200 |
| commit | a820ccbe21e8ce8e86c39cd1d3bc8c7d1cbb949b (patch) | |
| tree | e5b3fd50df32c9c9fa8b18f96079f5eb0a476888 | |
| parent | 903d271a3f83826ef810a4b5dbbd9842cf0465d6 (diff) | |
| download | linux-a820ccbe21e8ce8e86c39cd1d3bc8c7d1cbb949b.tar.bz2 | |
ALSA: pcm: Fix UAF at PCM release via PCM timer access
The PCM runtime object is created and freed dynamically at PCM stream
open / close time. This is tracked via substream->runtime, and it's
cleared at snd_pcm_detach_substream().
The runtime object assignment is protected by PCM open_mutex, so for
all PCM operations, it's safely handled. However, each PCM substream
provides also an ALSA timer interface, and user-space can access to
this while closing a PCM substream. This may eventually lead to a
UAF, as snd_pcm_timer_resolution() tries to access the runtime while
clearing it in other side.
Fortunately, it's the only concurrent access from the PCM timer, and
it merely reads runtime->timer_resolution field. So, we can avoid the
race by reordering kfree() and wrapping the substream->runtime
clearance with the corresponding timer lock.
Reported-by: syzbot+8e62ff4e07aa2ce87826@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
| -rw-r--r-- | sound/core/pcm.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/sound/core/pcm.c b/sound/core/pcm.c index 09ee8c6b9f75..66ac89aad681 100644 --- a/sound/core/pcm.c +++ b/sound/core/pcm.c @@ -28,6 +28,7 @@ #include <sound/core.h> #include <sound/minors.h> #include <sound/pcm.h> +#include <sound/timer.h> #include <sound/control.h> #include <sound/info.h> @@ -1054,8 +1055,13 @@ void snd_pcm_detach_substream(struct snd_pcm_substream *substream) snd_free_pages((void*)runtime->control, PAGE_ALIGN(sizeof(struct snd_pcm_mmap_control))); kfree(runtime->hw_constraints.rules); - kfree(runtime); + /* Avoid concurrent access to runtime via PCM timer interface */ + if (substream->timer) + spin_lock_irq(&substream->timer->lock); substream->runtime = NULL; + if (substream->timer) + spin_unlock_irq(&substream->timer->lock); + kfree(runtime); put_pid(substream->pid); substream->pid = NULL; substream->pstr->substream_opened--; |