drm/fb-helper: Fix potential NULL pointer dereference

fb_helper is being dereferenced before it is null checked,
hence there is a potential null pointer dereference.

Fix this by moving the pointer dereference after fb_helper
has been null checked.

This issue was detected with the help of Coccinelle.

Fixes: c777990fb45b ("drm/fb-helper: Handle function NULL argument")
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171205174628.GA31189@embeddedor.com

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 6654f2f..04a3a5c 100644 (file)
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -178,7 +178,7 @@ EXPORT_SYMBOL(drm_fb_helper_add_one_connector);
  */
 int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
 {
-       struct drm_device *dev = fb_helper->dev;
+       struct drm_device *dev;
        struct drm_connector *connector;
        struct drm_connector_list_iter conn_iter;
        int i, ret = 0;
@@ -186,6 +186,8 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
        if (!drm_fbdev_emulation || !fb_helper)
                return 0;
 
+       dev = fb_helper->dev;
+
        mutex_lock(&fb_helper->lock);
        drm_connector_list_iter_begin(dev, &conn_iter);
        drm_for_each_connector_iter(connector, &conn_iter) {