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

[mark gross <markgross@thegnar.org>]

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>


>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;
 
-- 
1.7.1