Re: [PATCH 4.14 61/81] ALSA: seq: Protect in-kernel ioctl calls with mutex

Sasha Levin
2019-06-13T15:39:54Z

On Thu, Jun 13, 2019 at 11:13:55AM +0200, Takashi Iwai wrote:
>On Thu, 13 Jun 2019 11:11:22 +0200,
>Greg Kroah-Hartman wrote:
>>
>> On Thu, Jun 13, 2019 at 11:02:54AM +0200, Takashi Iwai wrote:
>> > On Thu, 13 Jun 2019 10:33:44 +0200,
>> > Greg Kroah-Hartman wrote:
>> > >
>> > > [ Upstream commit feb689025fbb6f0aa6297d3ddf97de945ea4ad32 ]
>> > >
>> > > ALSA OSS sequencer calls the ioctl function indirectly via
>> > > snd_seq_kernel_client_ctl(). While we already applied the protection
>> > > against races between the normal ioctls and writes via the client's
>> > > ioctl_mutex, this code path was left untouched. And this seems to be
>> > > the cause of still remaining some rare UAF as spontaneously triggered
>> > > by syzkaller.
>> > >
>> > > For the sake of robustness, wrap the ioctl_mutex also for the call via
>> > > snd_seq_kernel_client_ctl(), too.
>> > >
>> > > Reported-by: syzbot+e4c8abb920efa77bace9@syzkaller.appspotmail.com
>> > > Signed-off-by: Takashi Iwai <tiwai@suse.de>
>> > > Signed-off-by: Sasha Levin <sashal@kernel.org>
>> >
>> > This commit is reverted later by commit f0654ba94e33.
>> > So please drop this. The proper fix is done later by commit
>> > 7c32ae35fbf9 ("ALSA: seq: Cover unsubscribe_port() in list_mutex")
>> >
>> > Ditto for 4.19.y and 5.1.y.
>>
>> Now dropped everywhere, and I added 7c32ae35fbf9 ("ALSA: seq: Cover
>> unsubscribe_port() in list_mutex") everywhere instead.
>
>Thanks!
>
>BTW, do we have a systematic check whether the selected stable commit
>is reverted in a later commit? At least, you can track it as long as
>Fixes tag is properly set.

I have that scripting in place, and I usually check it once before I
send the initial reviews and then once Greg does the -rc release.

--
Thanks,
Sasha