drm/i915/gem: Detect overflow in calculating dumb buffer size

To multiply 2 u32 numbers to generate a u64 in C requires a bit of
forewarning for the compiler.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200123125934.1401755-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -265,7 +265,10 @@ i915_gem_dumb_create(struct drm_file *file,
 						    DRM_FORMAT_MOD_LINEAR))
 		args->pitch = ALIGN(args->pitch, 4096);
 
-	args->size = args->pitch * args->height;
+	if (args->pitch < args->width)
+		return -EINVAL;
+
+	args->size = mul_u32_u32(args->pitch, args->height);
 
 	mem_type = INTEL_MEMORY_SYSTEM;
 	if (HAS_LMEM(to_i915(dev)))