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

From: mark gross <markgross@thegnar.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: linux-pm@lists.linux-foundation.org,
	Dan Carpenter <error27@gmail.com>,
	markgross@thegnar.org
Subject: Re: [PATCH] PM QoS: Allow parsing of ASCII values
Date: Tue, 29 Mar 2011 20:59:11 -0700	[thread overview]
Message-ID: <20110330035910.GA7163@gvim.org> (raw)
In-Reply-To: <201103292201.24270.rjw@sisk.pl>

On Tue, Mar 29, 2011 at 10:01:24PM +0200, Rafael J. Wysocki wrote:
> 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
> 

Yes.  There is was some discussion on if we should relax the value
checking beyond this that died off.  But, at a minimum I think this
should be merged as it fixes the usability issue raised by Simon.

thanks,

--mark

> 
> > 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;
> >  
> > 
> 