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

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Date:   Thu, 13 Jun 2019 12:28:05 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+e4c8abb920efa77bace9@...kaller.appspotmail.com
Subject: Re: [PATCH 4.14 61/81] ALSA: seq: Protect in-kernel ioctl calls with
 mutex

On Thu, Jun 13, 2019 at 05:44:15PM +0200, Takashi Iwai wrote:
>On Thu, 13 Jun 2019 17:39:46 +0200,
>Sasha Levin wrote:
>>
>> 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@...kaller.appspotmail.com
>> >> > > Signed-off-by: Takashi Iwai <tiwai@...e.de>
>> >> > > Signed-off-by: Sasha Levin <sashal@...nel.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.
>
>OK, good to hear.  So this time must be some exceptional error.

I still run these manually (I guess it's time to automate that too), so
it happens sometimes that folks notice these faster :)

--
Thanks,
Sasha