linux-ext4 - Re: kernel BUG in ext4_free

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Date:   Fri, 16 Dec 2022 15:09:04 +0100
From:   Aleksandr Nogikh <nogikh@...gle.com>
To:     Lee Jones <lee@...nel.org>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        syzbot <syzbot+15cd994e273307bf5cfa@...kaller.appspotmail.com>,
        adilger.kernel@...ger.ca, gregkh@...uxfoundation.org,
        lczerner@...hat.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, sashal@...nel.org,
        stable@...r.kernel.org, syzkaller-android-bugs@...glegroups.com,
        tadeusz.struk@...aro.org
Subject: Re: kernel BUG in ext4_free_blocks (2)

On Fri, Dec 16, 2022 at 2:01 PM Lee Jones <lee@...nel.org> wrote:
>
> On Thu, 15 Dec 2022, Theodore Ts'o wrote:
>
> > On Thu, Dec 15, 2022 at 08:34:35AM -0800, syzbot wrote:
> > > This bug is marked as fixed by commit:
> > > ext4: block range must be validated before use in ext4_mb_clear_bb()
> > > But I can't find it in any tested tree for more than 90 days.
> > > Is it a correct commit? Please update it by replying:
> > > #syz fix: exact-commit-title
> > > Until then the bug is still considered open and
> > > new crashes with the same signature are ignored.
> >
> > I don't know what is going on with syzkaller's commit detection, but
> > commit 1e1c2b86ef86 ("ext4: block range must be validated before use
> > in ext4_mb_clear_bb()") is an exact match for the commit title, and
> > it's been in the upstream kernel since v6.0.
> >
> > How do we make syzkaller accept this?  I'll try this again, but I
> > don't hold out much hope.
>
> I don't see the original bug report (was it posted to a lore
> associated list?), so there is no way to tell what branch syzbot was
> fuzzing at the time.  My assumption is that it was !Mainline.

Syzbot is actually reacting here to this bug from the Android namespace:

https://syzkaller.appspot.com/bug?id=5266d464285a03cee9dbfda7d2452a72c3c2ae7c

>
> Although this does appear to be a Stable candidate, I do not see it
> in any of the Stable branches yet.  So I suspect the answer here is to
> wait for the fix to filter down.
>
> In the mean time, I guess we should discuss whether syzbot should
> really be posting scans of downstream trees to upstream lists.

In this particular case, syzbot has captured all the recipients from
the patch email [1], because that email Cc'd
syzbot+15cd994e273307bf5cfa@...kaller.appspotmail.com. To syzbot, all
these people were involved in the original bug discussion, and so it
notified them about the problem.

FWIW I've sent a PR[2] to make the "I can't find it in any tested
tree" message include the link to the syzkaller dashboard. Hopefully
it will help resolve such confusions faster.

[1] https://lore.kernel.org/all/20220713185904.64138-1-tadeusz.struk@linaro.org/
[2] https://github.com/google/syzkaller/pull/3591

--
Aleksandr


>
> > #syz fix: ext4: block range must be validated before use in ext4_mb_clear_bb()
> >
> > Syzkaller, go home, you're drunk.
>
> =:-)
>
> --
> Lee Jones [李琼斯]
>
> --
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