linux-kernel - Re: dangers of bots on the mailing lists was Re: divide error in ___bpf_prog

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Message-ID: <20180118002111.b7ejjd2adunmkooj@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 17 Jan 2018 16:21:13 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Theodore Ts'o <tytso@....edu>, Dmitry Vyukov <dvyukov@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: dangers of bots on the mailing lists was Re: divide error in
 ___bpf_prog_run

On Wed, Jan 17, 2018 at 03:47:35PM -0500, Theodore Ts'o wrote:
> On Wed, Jan 17, 2018 at 12:09:18PM +0100, Dmitry Vyukov wrote:
> > On Wed, Jan 17, 2018 at 10:49 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
> > > Don't know if there's such a possibility, but it would be nice if we could
> > > target fuzzing for specific subsystems in related subtrees directly (e.g.
> > > for bpf in bpf and bpf-next trees as one example). Dmitry?
> > 
> > Hi Daniel,
> > 
> > It's doable.
> > Let's start with one bpf tree. Will it be bpf or bpf-next? Which one
> > contains more ongoing work? What's the exact git repo address/branch,
> > so that I don't second guess?
> 
> As a suggestion, until the bpf subsystem is free from problems that
> can be found by Syzkaller in Linus's upstream tree, maybe it's not
> worth trying to test individual subsystem trees such as the bpf tree?
> After all, there's no point trying to bisect our way checking to see
> if the problem is with a newly added commit in a development tree, if
> it turns out the problem was first introduced years ago in the 4.1 or
> 3.19 timeframe.
> 
> After all, finding these older problems is going to have much higher
> value, since these are the sorts of potential security problems that
> are worth backporting to real device kernels for Android/ChromeOS, and
> for enterprise distro kernels.  So from an "impact to the industry"
> perspective, focusing on Linus's tree is going to be far more
> productive.  That's a win for the community, and it's a win for those
> people on the Syzkaller team who might be going up for promo or
> listing their achievements at performance review time.  :-)

all correct, but if there is capacity in syzkaller server farm
to test bpf and bpf-next trees it will be huge win for everyone as well.
For example in the recent speculation fix we missed integer overflow case
and it was found by syzkaller only when the patches landed in net tree.
We did quick follow up patch, but it caused double work for
us and all stable maintainers.
I think finding bugs in the development trees is just as important
as bugs in Linus's tree, since it improves quality of
patches before they reach mainline.

If syzkaller can only test one tree than linux-next should be the one.

There is some value of testing stable trees, but any developer
will first ask for a reproducer in the latest, so usefulness of
reporting such bugs will be limited.