Re: [PATCH] PM QoS: Allow parsing of ASCII values

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Sunday, March 06, 2011, mark gross wrote:
> On Thu, Feb 24, 2011 at 12:00:35PM -0500, Alan Stern wrote:
> > On Thu, 24 Feb 2011, mark gross wrote:
> > 
> > > > How careful do you want to be here?  For example, which of the
> > > > following inputs do you want to accept?
> > > > 
> > > > 	0x1234
> > > > 	abcd1234
> > > > 	abcd123456
> > > > 	abcd123456\n
> > > > 	abcd1234567
> > > > 	1234567890
> > > > 	1234567890\n
> > > > 	12345678901
> > > 
> > > > 	0x12345678
> > > > 	0x12345678\n
> > > just these 2 are what I had planned to allow after this email thread.
> > > 
> > > > 	0x123456789
> > > > 
> > > > Maybe it's okay to be a little relaxed about this, and trust the caller 
> > > > to pass in data that makes sense.
> > > yeah but is it worth the effort?
> > 
> > Checking for exactly those two forms really is a lot of effort.  You
> > have to make sure the first two characters are "0x" or "0X", you have
> > to check that each of the next eight characters is a valid hex digit,
> > and you have to verify that the 11th character, if present, is a
> > newline.
> > 
> > If you can get results that are good enough just by calling
> > strict_strtoul() without all these checks, it's probably worthwhile.
> >
> I just don't want any buffer overrun bugs in code I'm writing.
> 
> I like the attached thank you for all the really useful input.
> 
> --mark
> Signed-off-by: mark gross <markgross@thegnar.org>

Mark, do you want the patch below to be merged?

Rafael


> From df199e491c750c529abcfb0e2256f508f1afd061 Mon Sep 17 00:00:00 2001
> From: mark gross <markgross@thegnar.org>
> Date: Sun, 6 Mar 2011 05:45:44 -0800
> Subject: [PATCH] correct PM QOS's user mode interface to work with ascii input per
>  what is in the kernel docs.  Writing a string to the ABI from user mode
>  comes in 2 flavors.  one with and one without a '\n' at the end.  this
>  change accepts both.
> 
>  echo 0x12345678 > /dev/cpu_dma_latency
> and
>  echo -n 0x12345678 > /dev/cpu_dma_latency
> now both work.
> ---
>  kernel/pm_qos_params.c |   15 ++++++++-------
>  1 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
> index aeaa7f8..b315446 100644
> --- a/kernel/pm_qos_params.c
> +++ b/kernel/pm_qos_params.c
> @@ -40,6 +40,7 @@
>  #include <linux/string.h>
>  #include <linux/platform_device.h>
>  #include <linux/init.h>
> +#include <linux/kernel.h>
>  
>  #include <linux/uaccess.h>
>  
> @@ -387,15 +388,15 @@ static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf,
>  	if (count == sizeof(s32)) {
>  		if (copy_from_user(&value, buf, sizeof(s32)))
>  			return -EFAULT;
> -	} else if (count == 11) { /* len('0x12345678/0') */
> -		if (copy_from_user(ascii_value, buf, 11))
> +	} else if (count == 10 || count == 11) { /* '0x12345678' or
> +						    '0x12345678/n'*/
> +		ascii_value[count] = 0;
> +		if (copy_from_user(ascii_value, buf, count))
>  			return -EFAULT;
> -		if (strlen(ascii_value) != 10)
> +		if ((x=strict_strtol(ascii_value, 16, &value)) != 0){
> +			pr_debug("%s, 0x%x, 0x%x\n",ascii_value, value, x);
>  			return -EINVAL;
> -		x = sscanf(ascii_value, "%x", &value);
> -		if (x != 1)
> -			return -EINVAL;
> -		pr_debug("%s, %d, 0x%x\n", ascii_value, x, value);
> +		}
>  	} else
>  		return -EINVAL;
>  
>