linux-kernel - Re: [patch 2/2] posix-timers: Sanitize overrun handling

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Date:   Thu, 28 Jun 2018 21:24:42 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        air icy <icytxw@...il.com>
Subject: Re: [patch 2/2] posix-timers: Sanitize overrun handling

On Tue, Jun 26, 2018 at 6:21 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> The posix timer overrun handling is broken because the forwarding functions
> can return a huge number of overruns which does not fit in an int. As a
> consequence timer_getoverrun(2) and siginfo::si_overrun can turn into
> random number generators.
>
> The k_clock::timer_forward() callbacks return a 64 bit value now. Make
> k_itimer::ti_overrun[_last] 64bit as well, so the kernel internal
> accounting is correct. 3Remove the temporary (int) casts.
>
> Add a helper function which clamps the overrun value returned to user space
> via timer_getoverrun(2) or siginfo::si_overrun limited to a positive value
> between 0 and INT_MAX. INT_MAX is an indicator for user space that the
> overrun value has been clamped.
>
> Reported-by: air icy <icytxw@...il.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Looks ok, and doesn't trip any regressions in testing so far.

Acked-by: John Stultz <john.stultz@...aro.org>

thanks
-john