From: Walter Wu <walter-zh.wu@mediatek.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
John Stultz <john.stultz@linaro.org>,
Stephen Boyd <sboyd@kernel.org>, Marco Elver <elver@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
"Alexander Potapenko" <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
"Andrey Konovalov" <andreyknvl@google.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
<kasan-dev@googlegroups.com>, <linux-mm@kvack.org>,
<linux-kernel@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
wsd_upstream <wsd_upstream@mediatek.com>,
<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v4 1/6] timer: kasan: record timer stack
Date: Fri, 25 Sep 2020 15:18:43 +0800 [thread overview]
Message-ID: <1601018323.28162.4.camel@mtksdccf07> (raw)
In-Reply-To: <87h7rm97js.fsf@nanos.tec.linutronix.de>
On Thu, 2020-09-24 at 23:41 +0200, Thomas Gleixner wrote:
> On Thu, Sep 24 2020 at 12:03, Walter Wu wrote:
> > When analyze use-after-free or double-free issue, recording the timer
> > stacks is helpful to preserve usage history which potentially gives
> > a hint about the affected code.
> >
> > Record the most recent two timer init calls in KASAN which are printed
> > on failure in the KASAN report.
> >
> > For timers it has turned out to be useful to record the stack trace
> > of the timer init call.
>
> In which way? And what kind of bug does it catch which cannot be catched
> by existing debug mechanisms already?
>
We only provide another debug mechanisms to debug use-after-free or
double-free, it can be displayed together in KASAN report and have a
chance to debug, and it doesn't need to enable existing debug mechanisms
at the same time. then it has a chance to resolve issue.
> > Because if the UAF root cause is in timer init, then user can see
> > KASAN report to get where it is registered and find out the root
> > cause.
>
> What? If the UAF root cause is in timer init, then registering it after
> using it in that very same function is pretty pointless.
>
See [1], the call stack shows UAF happen at dummy_timer(), it is the
callback function and set by timer_setup(), if KASAN report shows the
timer call stack, it should be useful for programmer.
[1]
https://syzkaller.appspot.com/bug?id=34e69b7c8c0165658cbc987da0b61dadec644b6b
> > It don't need to enable DEBUG_OBJECTS_TIMERS, but they have a chance
> > to find out the root cause.
>
> There is a lot of handwaving how useful this is, but TBH I don't see the
> value at all.
>
> DEBUG_OBJECTS_TIMERS does a lot more than crashing on UAF. If KASAN
> provides additional value over DEBUG_OBJECTS_TIMERS then spell it out,
> but just saying that you don't need to enable DEBUG_OBJECTS_TIMERS is
> not making an argument for that change.
>
We don't want to replace DEBUG_OBJECTS_TIMERS with this patches, only
hope to use low overhead(compare with DEBUG_OBJECTS_TIMERS) to debug
use-after-free/double-free issue. If you have some concerns, we can add
those message into commit log.
Thanks.
Walter
next prev parent reply other threads:[~2020-09-25 7:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 4:03 [PATCH v4 1/6] timer: kasan: record timer stack Walter Wu
2020-09-24 21:41 ` Thomas Gleixner
2020-09-25 7:18 ` Walter Wu [this message]
2020-09-25 8:55 ` Thomas Gleixner
2020-09-25 9:15 ` Walter Wu
2020-09-25 22:59 ` Thomas Gleixner
2020-09-26 17:11 ` Walter Wu
2020-09-30 7:18 ` Thomas Gleixner
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