linux-kernel - Re: [PATCH] hrtimer: prevent overrun DoS in hrtimer

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Date:	Wed, 4 Apr 2007 23:11:59 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Chuck Ebbert <cebbert@...hat.com>,
	Johannes Bauer <JohannesBauer@....de>,
	linux-kernel@...r.kernel.org, schwab@...e.de,
	Stable Kernel Team <stable@...nel.org>,
	Greg KH <greg@...ah.com>, Andrew Morton <akpm@...l.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] hrtimer: prevent overrun DoS in hrtimer_forward()

On Wed, Mar 14, 2007 at 11:00:12AM +0100, Thomas Gleixner wrote:
> hrtimer_forward() does not check for the possible overflow of
> timer->expires. This can happen on 64 bit machines with large interval
> values and results currently in an endless loop in the softirq because
> the expiry value becomes negative and therefor the timer is expired all
> the time.
> 
> Check for this condition and set the expiry value to the max. expiry
> time in the future.
> 
> The fix should be applied to stable kernel series as well.


Is this relevant for 2.6.16?

I'm asking since KTIME_SEC_MAX is not used in 2.6.16, and therefore the 
check in ktime_set() is also missing.


> Signed-off-by: Thomas Gleixner <tglx@...utronix,de>
> 
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index ec4cb9f..5e7122d 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -644,6 +644,12 @@ hrtimer_forward(struct hrtimer *timer, k
>  		orun++;
>  	}
>  	timer->expires = ktime_add(timer->expires, interval);
> +	/*
> +	 * Make sure, that the result did not wrap with a very large
> +	 * interval.
> +	 */
> +	if (timer->expires.tv64 < 0)
> +		timer->expires = ktime_set(KTIME_SEC_MAX, 0);
>  
>  	return orun;
>  }
> 

cu
Adrian

-- 

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        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
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