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authorTakashi Iwai <tiwai@suse.de>2018-04-02 22:41:43 +0200
committerTakashi Iwai <tiwai@suse.de>2018-04-03 08:36:40 +0200
commita820ccbe21e8ce8e86c39cd1d3bc8c7d1cbb949b (patch)
treee5b3fd50df32c9c9fa8b18f96079f5eb0a476888 /sound/usb
parent903d271a3f83826ef810a4b5dbbd9842cf0465d6 (diff)
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>
Diffstat (limited to 'sound/usb')
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