linux-kernel - Re: WARNING: filesystem loop5 was created with 512 inodes, the real maximum is 511, mounting anyway

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Message-ID: <CACT4Y+bQWBZa0b=sh84rM5TLPTrY-aBLge=eKXEOT=TDZEZxbg@mail.gmail.com>
Date:   Thu, 3 Dec 2020 13:55:19 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        syzbot <syzbot+3fd34060f26e766536ff@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: WARNING: filesystem loop5 was created with 512 inodes, the real
 maximum is 511, mounting anyway

On Thu, Dec 3, 2020 at 5:15 AM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> On 12/1/20 1:17 PM, Randy Dunlap wrote:
> > On 11/30/20 11:47 PM, Dmitry Vyukov wrote:
> >> On Tue, Dec 1, 2020 at 2:03 AM Randy Dunlap <rdunlap@...radead.org> wrote:
> >>>
> >>> On 11/30/20 12:43 AM, Dmitry Vyukov wrote:
> >>>> On Mon, Nov 30, 2020 at 5:29 AM Randy Dunlap <rdunlap@...radead.org> wrote:
> >>>>>
> >>>>> On 11/27/20 4:32 AM, syzbot wrote:
> >>>>>> Hello,
> >>>>>>
> >>>>>> syzbot found the following issue on:
> >>>>>>
> >>>>>> HEAD commit:    418baf2c Linux 5.10-rc5
> >>>>>> git tree:       upstream
> >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=171555b9500000
> >>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=b81aff78c272da44
> >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=3fd34060f26e766536ff
> >>>>>> compiler:       gcc (GCC) 10.1.0-syz 20200507
> >>>>>>
> >>>>>> 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+3fd34060f26e766536ff@...kaller.appspotmail.com
> >>>>>>
> >>>>>> BFS-fs: bfs_fill_super(): loop5 is unclean, continuing
> >>>>>> BFS-fs: bfs_fill_super(): WARNING: filesystem loop5 was created with 512 inodes, the real maximum is 511, mounting anyway
> >>>>>> BFS-fs: bfs_fill_super(): Last block not available on loop5: 120
> >>>>>> BFS-fs: bfs_fill_super(): loop5 is unclean, continuing
> >>>>>> BFS-fs: bfs_fill_super(): WARNING: filesystem loop5 was created with 512 inodes, the real maximum is 511, mounting anyway
> >>>>>> BFS-fs: bfs_fill_super(): Last block not available on loop5: 120
> >>>>>>
> >>>>>>
> >>>>>> ---
> >>>>>> This report is generated by a bot. It may contain errors.
> >>>>>> See https://goo.gl/tpsmEJ for more information about syzbot.
> >>>>>> syzbot engineers can be reached at syzkaller@...glegroups.com.
> >>>>>>
> >>>>>> syzbot will keep track of this issue. See:
> >>>>>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> ...
>
> >>>> Hi Randy,
> >>>>
> >>>> I see this bug was reported with a reproducer:
> >>>> https://syzkaller.appspot.com/bug?id=a32ebd5db2f7c957b82cf54b97bdecf367bf0421
> >>>> I assume it's a dup of this one.
> >>>
> >>> Sure, looks the same.
> >>>
> >>>> If you need the image itself, you can dump it to a file in the C
> >>>> reproducer inside of syz_mount_image before mount call.
> >>>
> >>> Yes, got that.
> >>>
> >>> What outcome or result are you looking for here?
> >>> Or what do you see as the problem?
> >>
> >> Hi Randy,
> >>
> >> "WARNING:" in kernel output is supposed to mean a kernel source bug.
> >> Presence of that kernel bug is what syzbot has reported.
> >>
> >> Note: the bug may be a misuse of the "WARNING:" for invalid user
> >> inputs in output as well :)
> >
> >
> > [adding Al Viro]
> >
> > Hi Dmitry,
> >
> > I expect that the "WARNING:" message is being interpreted incorrectly here,
> > but that's a minor issue IMO.
> >
> >       if (info->si_lasti == BFS_MAX_LASTI)
> >               printf("WARNING: filesystem %s was created with 512 inodes, the real maximum is 511, mounting anyway\n", s->s_id);
> >
>
> ...
>
> >
> >
> > However, in testing this, I see that the BFS image is not mounted
> > on /dev/loop# at all.
> >
> > 'mount' says:
> >
> > # mount -t bfs -o loop bfsfilesyz000.img  /mnt/stand
> > mount: /mnt/stand: mount(2) system call failed: Not a directory.
> >
> > (but it is a directory)
> >
> > and I have tracked that down to fs/namespace.c::graft_tree()
> > returning -ENOTDIR, but I don't know why that is happening.
> >
> >
> > Al, can you provide any insights on this?
>
> OK, with Al's help, here is the situation.
>
> If I use a regular file instead of a directory, the mount
> command succeeds.
>
> The printk() from fs/bfs/inode.c that uses the WARNING: string
> is not a WARN() or WARN_ON(). It's just a printk().
>
> <linux/asm-generic/bug.h> says:
>
>  * Do not include "BUG"/"WARNING" in format strings manually to make these
>  * conditions distinguishable from kernel issues.
>
> so if I change fs/bfs/inode.c to use "warning:" or "Warning," or "Note:",
> this little problem should go away.  Is that correct?

Hi,

Yes, any of these prefixes will work (not be considered as a kernel
issue). syzkaller only matches "WARNING:" verbatim. I don't know about
all other kernel testing systems, but at least it's distinguishable.

Maybe also worth adding "bfs:" prefix for cases when people stare at
dmesg afterwards.