linux-kernel - Re: BUG: unable to handle kernel paging request in dqput

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Message-ID: <20200929143031.GP10896@quack2.suse.cz>
Date:   Tue, 29 Sep 2020 16:30:31 +0200
From:   Jan Kara <jack@...e.cz>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     syzbot <syzbot+f816042a7ae2225f25ba@...kaller.appspotmail.com>,
        adi@...rat.com, alsa-devel@...a-project.org,
        coreteam@...filter.org, davem@...emloft.net, jack@...e.com,
        kaber@...sh.net, kadlec@...ckhole.kfki.hu,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, pablo@...filter.org,
        perex@...ex.cz, syzkaller-bugs@...glegroups.com, tiwai@...e.com
Subject: Re: BUG: unable to handle kernel paging request in dqput

On Sun 27-09-20 09:07:02, Takashi Iwai wrote:
> On Sat, 26 Sep 2020 22:48:15 +0200,
> syzbot wrote:
> > 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    98477740 Merge branch 'rcu/urgent' of git://git.kernel.org..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=17930875900000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=af502ec9a451c9fc
> > dashboard link: https://syzkaller.appspot.com/bug?extid=f816042a7ae2225f25ba
> > compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133783ab900000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13bb5973900000
> > 
> > The issue was bisected to:
> > 
> > commit 1d0f953086f090a022f2c0e1448300c15372db46
> > Author: Ioan-Adrian Ratiu <adi@...rat.com>
> > Date:   Wed Jan 4 22:37:46 2017 +0000
> > 
> >     ALSA: usb-audio: Fix irq/process data synchronization
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=133362c3900000
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=10b362c3900000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=173362c3900000
> 
> This commit looks really irrelevant from the Oops code path.
> It must be a different reason.

Yeah, it seems the bisection got confused because it hit a different error
during the bisection. Looking at the original oops, I think the actual
reason of a crash is that quota file got corrupted in a particular way.
Quota code is not very paranoid when checking on disk contents. I'll work
on adding more sanity checks to quota code...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR