linux-kernel - Re: KASAN: slab-out-of-bounds Read in bacpy

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Date:   Sun, 17 Mar 2019 18:11:49 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     syzbot <syzbot+660883c56e2fa65d4497@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Michal Marek <mmarek@...e.com>,
        Netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: slab-out-of-bounds Read in bacpy

On Sun, Mar 17, 2019 at 5:35 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Sun, Mar 17, 2019 at 3:43 AM syzbot
> <syzbot+660883c56e2fa65d4497@...kaller.appspotmail.com> wrote:
> >
> > syzbot has bisected this bug to:
> >
> > commit c470abd4fde40ea6a0846a2beab642a578c0b8cd
> > Author: Linus Torvalds <torvalds@...ux-foundation.org>
> > Date:   Sun Feb 19 22:34:00 2017 +0000
>
> Heh. Yeah, I doubt it.
>
> It would probably be good if syzbot did some confidence testing before
> bisecting.
>
> Don't get me wrong, "git bisect" is absolutely wonderful and has done
> a ton to help us fix bugs, but bisection has one major downside: if
> the bug you are bisecting isn't 100% repeatable, the bisection will go
> off into the random weeds and give completely nonsensical results.
> They won't even be *close*. What makes bisection so powerful is also
> what makes it then completely random if there's even *one* mistaken
> bisection point.
>
> So it would probably be good to test each bisection point at least
> twice, and if they don't agree, report it as being unbisectable rather
> than give a random "this is what introduced the problem".
>
> Hmm?


Hi Linus,

Please see https://github.com/google/syzkaller/blob/master/docs/syzbot.md#bisection
it should answer all of your questions. It does 2 and more.
And in this case it seems to be working as intended bisecting it to a
release tag.