linux-kernel - Re: general protection fault in percpu_ref

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Message-ID: <20201009040525.GB27356@T590>
Date:   Fri, 9 Oct 2020 12:05:25 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     syzbot <syzbot+fd15ff734dace9e16437@...kaller.appspotmail.com>,
        bcrl@...ck.org, hch@....de, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, tj@...nel.org,
        viro@...iv.linux.org.uk, vkabatov@...hat.com
Subject: Re: general protection fault in percpu_ref_exit

On Thu, Oct 08, 2020 at 07:23:02PM -0600, Jens Axboe wrote:
> On 10/8/20 2:28 PM, syzbot wrote:
> > syzbot has bisected this issue to:
> > 
> > commit 2b0d3d3e4fcfb19d10f9a82910b8f0f05c56ee3e
> > Author: Ming Lei <ming.lei@...hat.com>
> > Date:   Thu Oct 1 15:48:41 2020 +0000
> > 
> >     percpu_ref: reduce memory footprint of percpu_ref in fast path
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=126930d0500000
> > start commit:   8b787da7 Add linux-next specific files for 20201007
> > git tree:       linux-next
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=116930d0500000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=166930d0500000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=aac055e9c8fbd2b8
> > dashboard link: https://syzkaller.appspot.com/bug?extid=fd15ff734dace9e16437
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=119a0568500000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=106c0a8b900000
> > 
> > Reported-by: syzbot+fd15ff734dace9e16437@...kaller.appspotmail.com
> > Fixes: 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of percpu_ref in fast path")
> > 
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> Ming, this looks like a call of percpu_ref_exit() on a zeroed refs (that
> hasn't been initialized). Really a caller error imho, but might make sense
> to be a bit safer there.

Hello Jens,

The fix is sent out as:

https://lore.kernel.org/linux-block/20201009040356.43802-1-ming.lei@redhat.com/T/#u

Sorry for making the trouble.

Thanks,
Ming