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 11:13:55 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+e4c8abb920efa77bace9@...kaller.appspotmail.com,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.14 61/81] ALSA: seq: Protect in-kernel ioctl calls with mutex

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.


Takashi