linux-kernel - Re: KASAN: use-after-free Read in userfaultfd

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Date:   Tue, 21 Jul 2020 14:32:33 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Qian Cai <cai@....pw>
Cc:     syzbot <syzbot+75867c44841cb6373570@...kaller.appspotmail.com>,
        Markus.Elfring@....de, casey@...aufler-ca.com, dancol@...gle.com,
        hdanton@...a.com, jmorris@...ei.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, stephen.smalley.work@...il.com,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk,
        yanfei.xu@...driver.com, linux-next@...r.kernel.org
Subject: Re: KASAN: use-after-free Read in userfaultfd_release (2)

Hi all,

On Mon, 20 Jul 2020 11:50:25 -0400 Qian Cai <cai@....pw> wrote:
>
> On Fri, Jul 17, 2020 at 11:05:41AM -0400, Qian Cai wrote:
> > On Mon, Jul 13, 2020 at 08:34:06AM -0700, syzbot wrote:  
> > > syzbot has bisected this bug to:
> > > 
> > > commit d08ac70b1e0dc71ac2315007bcc3efb283b2eae4
> > > Author: Daniel Colascione <dancol@...gle.com>
> > > Date:   Wed Apr 1 21:39:03 2020 +0000
> > > 
> > >     Wire UFFD up to SELinux
> > > 
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14a79d13100000
> > > start commit:   89032636 Add linux-next specific files for 20200708
> > > git tree:       linux-next
> > > final crash:    https://syzkaller.appspot.com/x/report.txt?x=16a79d13100000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=12a79d13100000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=64a250ebabc6c320
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=75867c44841cb6373570
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13c4c8db100000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12cbb68f100000
> > > 
> > > Reported-by: syzbot+75867c44841cb6373570@...kaller.appspotmail.com
> > > Fixes: d08ac70b1e0d ("Wire UFFD up to SELinux")
> > > 
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection  
> > 
> > This is rather easy to reproduce here,  
> 
> James, Stephen, can you drop this patch? Daniel's email was bounced, and Viro
> mentioned the patch could be quite bad,
> 
> https://lore.kernel.org/lkml/20200719165746.GJ2786714@ZenIV.linux.org.uk/

I have reverted that commit in linux-next today.

-- 
Cheers,
Stephen Rothwell

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