On Mon, Mar 11, 2013 at 03:25:59PM -0700, Kees Cook wrote: > On Mon, Mar 11, 2013 at 3:00 PM, Chris Wilson <chris at chris-wilson.co.uk> > 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?
Aye, seems reasonable. So perhaps, /* First check for malicious input causing overflow in the worst case * where we need to allocate the entire relocation tree as a single * array. */ -Chris -- Chris Wilson, Intel Open Source Technology Centre
