On Mon, Mar 11, 2013 at 3:00 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Mar 11, 2013 at 02:23:29PM -0700, Kees Cook wrote:
>> It is possible to wrap the counter used to allocate the buffer for
>> relocation copies. This could lead to heap writing overflows.
>
> I'd keep the return value as EINVAL so that we can continue to
> distinguish between the user passing garbage and hitting an oom. And
> total_relocs is preferrable to total, which also leads us to think more
> carefully about the error condition. I think the check should be against
> INT_MAX / sizeof(struct reloc_entry) for consistency with our other
> guard against overflows whilst allocating.
I've ended up with this:
int max_alloc = INT_MAX / sizeof(struct drm_i915_gem_relocation_entry);
...
/* First check for malicious input causing overflow */
if (exec[i].relocation_count > max_alloc)
return -EINVAL;
if (exec[i].relocation_count > max_alloc - total_relocs)
return -EINVAL;
total_relocs += exec[i].relocation_count;
And looking at that, I wonder if we should just eliminate the first if entirely?
-Kees
--
Kees Cook
Chrome OS Security
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