linux-kernel - Re: [PATCH v4 0/6] kasan: add workqueue and timer stack for generic KASAN

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Message-ID: <CACT4Y+Yy8S0L18u3q1Y1K1r-qqXRWzrVVLPNR_En0hJ9nX7Tbw@mail.gmail.com>
Date:   Tue, 1 Dec 2020 15:02:38 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Walter Wu <walter-zh.wu@...iatek.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v4 0/6] kasan: add workqueue and timer stack for generic KASAN

On Tue, Dec 1, 2020 at 12:17 PM Walter Wu <walter-zh.wu@...iatek.com> wrote:
>
> Hi Dmitry,
>
> On Tue, 2020-12-01 at 08:59 +0100, 'Dmitry Vyukov' via kasan-dev wrote:
> > On Wed, Sep 30, 2020 at 5:29 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > >
> > > On Thu, Sep 24 2020 at 12:01, Walter Wu wrote:
> > > > Syzbot reports many UAF issues for workqueue or timer, see [1] and [2].
> > > > In some of these access/allocation happened in process_one_work(),
> > > > we see the free stack is useless in KASAN report, it doesn't help
> > > > programmers to solve UAF on workqueue. The same may stand for times.
> > > >
> > > > This patchset improves KASAN reports by making them to have workqueue
> > > > queueing stack and timer stack information. It is useful for programmers
> > > > to solve use-after-free or double-free memory issue.
> > > >
> > > > Generic KASAN also records the last two workqueue and timer stacks and
> > > > prints them in KASAN report. It is only suitable for generic KASAN.
> >
> > Walter, did you mail v5?
> > Checking statuses of KASAN issues and this seems to be not in linux-next.
> >
>
> Sorry for the delay in responding to this patch. I'm busy these few
> months, so that suspend processing it.
> Yes, I will send it next week. But v4 need to confirm the timer stack is
> useful. I haven't found an example. Do you have some suggestion about
> timer?

Good question.

We had some use-after-free's what mention call_timer_fn:
https://groups.google.com/g/syzkaller-bugs/search?q=%22kasan%22%20%22use-after-free%22%20%22expire_timers%22%20%22call_timer_fn%22%20
In the reports I checked call_timer_fn appears in the "access" stack
rather in the "free" stack.

Looking at these reports I cannot conclude that do_init_timer stack
would be useful.
I am mildly leaning towards not memorizing do_init_timer stack for now
(until we have clear use cases) as the number of aux stacks is very
limited (2).