linux-kernel - Re: [PATCH] RTC: Prevents a division by zero in kernel code.

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Date:	Wed, 02 Feb 2011 12:34:33 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Marcelo Roberto Jimenez <mroberto@...i.cetuc.puc-rio.br>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	a.zummo@...ertech.it, rtc-linux@...glegroups.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RTC: Prevents a division by zero in kernel code.

On Wed, 2011-02-02 at 16:04 -0200, Marcelo Roberto Jimenez wrote:
> This patch prevents a user space program from calling the RTC_IRQP_SET
> ioctl with a negative value of frequency. Also, if this call is make
> with a zero value of frequency, there would be a division by zero in the
> kernel code.
> 
> Signed-off-by: Marcelo Roberto Jimenez <mroberto@...i.cetuc.puc-rio.br>

Probably need to also initialize irq_freq to 1 on rtc_device_register so
we don't trip over the divbyzero on rtc devices that don't initialize
that value.

I'll add that and fwd on your patch!

Great catch!

thanks
-john

> ---
>  drivers/rtc/interface.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> index 925006d..a0c0196 100644
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -464,6 +464,9 @@ int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq)
>  	int err = 0;
>  	unsigned long flags;
> 
> +	if (freq <= 0)
> +		return -EINVAL;
> +
>  	spin_lock_irqsave(&rtc->irq_task_lock, flags);
>  	if (rtc->irq_task != NULL && task == NULL)
>  		err = -EBUSY;


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