[bug report] drm/vmwgfx: Do not drop the reference to the handle too soon

[Dan Carpenter]

Hello Zack Rusin,

The patch 9ef8d83e8e25: "drm/vmwgfx: Do not drop the reference to the
handle too soon" from Feb 11, 2023, leads to the following Smatch
static checker warning:

	drivers/gpu/drm/vmwgfx/vmwgfx_bo.c:698 vmw_dumb_create()
	error: uninitialized symbol 'vbo'.

drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
    669 int vmw_dumb_create(struct drm_file *file_priv,
    670                     struct drm_device *dev,
    671                     struct drm_mode_create_dumb *args)
    672 {
    673         struct vmw_private *dev_priv = vmw_priv(dev);
    674         struct vmw_bo *vbo;
    675         int cpp = DIV_ROUND_UP(args->bpp, 8);
    676         int ret;
    677 
    678         switch (cpp) {
    679         case 1: /* DRM_FORMAT_C8 */
    680         case 2: /* DRM_FORMAT_RGB565 */
    681         case 4: /* DRM_FORMAT_XRGB8888 */
    682                 break;
    683         default:
    684                 /*
    685                  * Dumb buffers don't allow anything else.
    686                  * This is tested via IGT's dumb_buffers
    687                  */
    688                 return -EINVAL;
    689         }
    690 
    691         args->pitch = args->width * cpp;
    692         args->size = ALIGN(args->pitch * args->height, PAGE_SIZE);
    693 
    694         ret = vmw_gem_object_create_with_handle(dev_priv, file_priv,
    695                                                 args->size, &args->handle,
    696                                                 &vbo);
    697         /* drop reference from allocate - handle holds it now */
--> 698         drm_gem_object_put(&vbo->tbo.base);

This is a false positive, but the code is buggy.  The bug is that if
"ret" is failure then "vbo" is NULL leading to an Oops.

    699         return ret;
    700 }

regards,
dan carpenter