Re: [PATCH] Fix argument checking in sched_setaffinity

[Andi Kleen]

On Sat, Sep 04, 2004 at 09:52:05PM -0700, Paul Jackson wrote:
> > starting with backing out the changes made to it this week.
> 
> Andi,
> 
> Given that Linus has gutted most of your patch to sched_setaffinity,
> do you have a preference between where the code started the week,
> and where it ended?
> 
> If I'm reading Linus' mind right (well ... there's a first time
> for everything) then your preference, either way, would likely
> carry the day.

The only change I would like to have is to check the excess bytes
to make sure they don't contain some random value. They should
be either all 0 or all 0xff. 

-Andi

Here's a patch for bk12: 

Linus, does this look better?

--------------------------------------------------------

For excess cpumask bits passed from user space ensure
they are all zero or all one.  This minimizes binary incompatibilities
when the kernel is recompiled with a bigger cpumask_t type.

diff -u linux-2.6.8/kernel/sched.c-o linux-2.6.8/kernel/sched.c
--- linux-2.6.8/kernel/sched.c-o	2004-09-06 20:06:58.000000000 +0200
+++ linux-2.6.8/kernel/sched.c	2004-09-06 20:16:33.940579241 +0200
@@ -3368,6 +3368,19 @@
 	if (len < sizeof(cpumask_t)) {
 		memset(new_mask, 0, sizeof(cpumask_t));
 	} else if (len > sizeof(cpumask_t)) {
+		unsigned i;
+		unsigned char val, initval;
+		if (len > PAGE_SIZE)
+			return -EINVAL;
+		/* excess bytes must be all 0 or all 0xff */
+		for (i = sizeof(cpumask_t); i < len; i++) { 
+			if (get_user(val, (char *)new_mask + i))
+				return -EFAULT; 
+			if (i == sizeof(cpumask_t))
+				initval = val;
+			if (!(val == 0 || val == 0xff) || val != initval)
+				return -EINVAL; 
+		} 
 		len = sizeof(cpumask_t);
 	}
 	return copy_from_user(new_mask, user_mask_ptr, len) ? -EFAULT : 0;
-
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