ALSA: pcm: Fix tight loop of OSS capture stream

Browse source

commit e190161f96 upstream.

When the trigger=off is passed for a PCM OSS stream, it sets the
start_threshold of the given substream to the boundary size, so that
it won't be automatically started.  This can be problematic for a
capture stream, unfortunately, as detected by syzkaller.  The scenario
is like the following:

- In __snd_pcm_lib_xfer() that is invoked from snd_pcm_oss_read()
  loop, we have a check whether the stream was already started or the
  stream can be auto-started.
- The function at this check returns 0 with trigger=off since we
  explicitly disable the auto-start.
- The loop continues and repeats calling __snd_pcm_lib_xfer() tightly,
  which may lead to an RCU stall.

This patch fixes the bug by simply allowing the wait for non-started
stream in the case of OSS capture.  For native usages, it's supposed
to be done by the caller side (which is user-space), hence it returns
zero like before.

(In theory, __snd_pcm_lib_xfer() could wait even for the native API
 usage cases, too; but I'd like to stay in a safer side for not
 breaking the existing stuff for now.)

Reported-by: syzbot+fbe0496f92a0ce7b786c@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Takashi Iwai 2019-01-25 17:11:32 +01:00 • committed by Greg Kroah-Hartman

parent c697687f89

commit 3c66684e35

1 changed files with 8 additions and 1 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

9

sound/core/pcm_lib.c

View file