ALSA: pcm: Fix endless loop for XRUN recovery in OSS emulation
authorTakashi Iwai <tiwai@suse.de>
Sat, 7 Apr 2018 09:48:58 +0000 (11:48 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 24 Apr 2018 07:36:35 +0000 (09:36 +0200)
commit312d02879f9f0ae9c6b011d0ead6a143115e9f93
treed34524319aa2f3521c17f881f224b0eb25ed06f2
parent157113cb7c89829b1cd2e2792a1f38932f31c965
ALSA: pcm: Fix endless loop for XRUN recovery in OSS emulation

commit e15dc99dbb9cf99f6432e8e3c0b3a8f7a3403a86 upstream.

The commit 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS
ioctls and read/write") split the PCM preparation code to a locked
version, and it added a sanity check of runtime->oss.prepare flag
along with the change.  This leaded to an endless loop when the stream
gets XRUN: namely, snd_pcm_oss_write3() and co call
snd_pcm_oss_prepare() without setting runtime->oss.prepare flag and
the loop continues until the PCM state reaches to another one.

As the function is supposed to execute the preparation
unconditionally, drop the invalid state check there.

The bug was triggered by syzkaller.

Fixes: 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS ioctls and read/write")
Reported-by: syzbot+150189c103427d31a053@syzkaller.appspotmail.com
Reported-by: syzbot+7e3f31a52646f939c052@syzkaller.appspotmail.com
Reported-by: syzbot+4f2016cf5185da7759dc@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>
sound/core/oss/pcm_oss.c