linux-kernel - Re: [PATCH] umh: fix UAF when the process is being killed

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Message-ID: <Y9AXzi0khgjFnLpJ@bombadil.infradead.org>
Date:   Tue, 24 Jan 2023 09:39:26 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org,
        syzbot+10d19d528d9755d9af22@...kaller.appspotmail.com,
        syzbot+70d5d5d83d03db2c813d@...kaller.appspotmail.com,
        syzbot+83cb0411d0fcf0a30fc1@...kaller.appspotmail.com
Subject: Re: [PATCH] umh: fix UAF when the process is being killed

On Fri, Jan 13, 2023 at 01:42:05PM +0800, Schspa Shi wrote:
> 
> Luis Chamberlain <mcgrof@...nel.org> writes:
> 
> > On Thu, Dec 22, 2022 at 08:09:38PM +0800, Schspa Shi wrote:
> >> 
> >> Attaching the full test program in case anyone wants to add some
> >> comments.
> >
> > Good stuff.
> >
> > That looks like a kernel sefltest. So you can just add it as an
> > initial selftest for completion so lib/test_completion.c and extend
> > lib/Kconfig.debug for a new kconfig symbol for it, and then just add
> > a script on tools/testing/selftets/completion/ with a simple makefile
> > which references a script which just calls modprobe. You can look at
> > tools/testing/selftests/kmod/ for an example.
> 
> OK, but I want to know, is it enough to add only positive examples for
> the test items here? Do we need a reverse example to prove that the
> previous writing is wrong?

That would mean adding code which would cause a UAF, perhaps useful if
disabled by default.

> > But I still think you may want an SmPL Coccinelle grammer patch to hunt
> > down other users with this pattern. The beneefit is that then you can
> > use the same Coccinelle patch to also then *fix* the issue in other
> > places.
> >
> 
> Yes, I'm learning about SmPL, and I'll add this syntax patch later to
> find more problems.

Great thanks.

  Luis