drm: fix use of freed memory in drm_mode_setcrtc

tomba · tomba · commit 064253c1c062 · 2018-10-05T15:55:17.000+03:00
drm_mode_setcrtc() retries modesetting in case one of the functions it calls returns -EDEADLK. connector_set, mode and fb are freed before retrying, but they are not set to NULL. This can cause drm_mode_setcrtc() to use those variables. For example: On the first try __drm_mode_set_config_internal() returns -EDEADLK. connector_set, mode and fb are freed. Next retry starts, and drm_modeset_lock_all_ctx() returns -EDEADLK, and we jump to 'out'. The code will happily try to release all three again. This leads to crashes of different kinds, depending on the sequence the EDEADLKs happen. Fix this by setting the three variables to NULL at the start of the retry loop. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20180917110054.4053-1-tomi.valkeinen@ti.com
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
@@ -567,9 +567,9 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	struct drm_mode_crtc *crtc_req = data;
 	struct drm_crtc *crtc;
 	struct drm_plane *plane;
-	struct drm_connector **connector_set = NULL, *connector;
-	struct drm_framebuffer *fb = NULL;
-	struct drm_display_mode *mode = NULL;
+	struct drm_connector **connector_set, *connector;
+	struct drm_framebuffer *fb;
+	struct drm_display_mode *mode;
 	struct drm_mode_set set;
 	uint32_t __user *set_connectors_ptr;
 	struct drm_modeset_acquire_ctx ctx;
@@ -598,6 +598,10 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	mutex_lock(&crtc->dev->mode_config.mutex);
 	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
+	connector_set = NULL;
+	fb = NULL;
+	mode = NULL;
+
 	ret = drm_modeset_lock_all_ctx(crtc->dev, &ctx);
 	if (ret)
 		goto out;
