drm/i915: Check that the relocation points to within the target

commit cd0b9fb4 upstream.

Eric noted a potential concern with the low bits not being strictly used
as part of the absolute offset (instead part of the command stream to the
GPU), but in practice that should not be an issue.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Andy Whitcroft <apw@canonical.com>
Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/gpu/drm/i915/i915_gem.c

@@ -3006,6 +3006,16 @@ i915_gem_object_pin_and_relocate(struct drm_gem_object *obj,
 			return -EINVAL;
 		}
 
+		if (reloc->delta >= target_obj->size) {
+			DRM_ERROR("Relocation beyond target object bounds: "
+				  "obj %p target %d delta %d size %d.\n",
+				  obj, reloc->target_handle,
+				  (int) reloc->delta, (int) target_obj->size);
+			drm_gem_object_unreference(target_obj);
+			i915_gem_object_unpin(obj);
+			return -EINVAL;
+		}
+
 		if (reloc->write_domain & I915_GEM_DOMAIN_CPU ||
 		    reloc->read_domains & I915_GEM_DOMAIN_CPU) {
 			DRM_ERROR("reloc with read/write CPU domains: "