Re: [PATCH v4 1/6] timer: kasan: record timer stack

[Thomas Gleixner]

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?

> 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.

> 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.

Try again please.

Thanks,

        tglx