linux-kernel - Re: [syzbot] kernel BUG in assertfail

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Message-ID: <CACT4Y+bqevMT3cD5sXjSv9QYM_7CwjYmN_Ne5LSj=3-REZ+oTw@mail.gmail.com>
Date:   Mon, 31 May 2021 10:55:34 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     syzbot <syzbot+a6bf271c02e4fe66b4e4@...kaller.appspotmail.com>,
        Chris Mason <clm@...com>, dsterba@...e.com,
        Josef Bacik <josef@...icpanda.com>,
        linux-btrfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] kernel BUG in assertfail

On Mon, May 31, 2021 at 10:44 AM 'Nikolay Borisov' via syzkaller-bugs
<syzkaller-bugs@...glegroups.com> wrote:
> On 31.05.21 г. 10:53, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    1434a312 Merge branch 'for-5.13-fixes' of git://git.kernel..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=162843f3d00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=9f3da44a01882e99
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a6bf271c02e4fe66b4e4
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+a6bf271c02e4fe66b4e4@...kaller.appspotmail.com
> >
> > assertion failed: !memcmp(fs_info->fs_devices->fsid, fs_info->super_copy->fsid, BTRFS_FSID_SIZE), in fs/btrfs/disk-io.c:3282
>
> This means a device contains a btrfs filesystem which has a different
> FSID in its superblock than the fsid which all devices part of the same
> fs_devices should have. This can happen in 2 ways - memory corruption
> where either of the ->fsid member are corrupted or if there was a crash
> while a filesystem's fsid was being changed. We need more context about
> what the test did?

Hi Nikolay,

>From a semantic point of view we can consider that it just mounts /dev/random.
If syzbot comes up with a reproducer it will post it, but you seem to
already figure out what happened, so I assume you can write a unit
test for this.