drm/i915: Reject invalid-pad for context-destroy and -create ioctls

Unknown parameters, especially structure padding, are expected to invoke
rejection with -EINVAL.

v2: similar issue exists for context-create

Testcase: igt/gem_ctx_create/invalid-pad
Testcase: igt/gem_ctx_bad_destroy/invalid-pad
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89602
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93999
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1454690759-31201-1-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -855,6 +855,9 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
 	if (!contexts_enabled(dev))
 		return -ENODEV;
 
+	if (args->pad != 0)
+		return -EINVAL;
+
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
 		return ret;
@@ -878,6 +881,9 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 	struct intel_context *ctx;
 	int ret;
 
+	if (args->pad != 0)
+		return -EINVAL;
+
 	if (args->ctx_id == DEFAULT_CONTEXT_HANDLE)
 		return -ENOENT;