From: Thomas Hellstrom <thellstrom@vmware.com>
Date: Mon, 12 Oct 2015 08:49:39 +0000 (-0700)
Subject: drm/vmwgfx: Fix kernel NULL pointer dereference on older hardware
X-Git-Tag: v3.16.35~1186
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fd3a964b3ccb088f6d3eacc9c261de8d5e8a206c;p=thirdparty%2Fkernel%2Fstable.git

drm/vmwgfx: Fix kernel NULL pointer dereference on older hardware

commit ed7d78b2da32198ca4c70172e3b63c6b3e2c570b upstream.

The commit "drm/vmwgfx: Fix up user_dmabuf refcounting", while fixing a
kernel crash introduced a NULL pointer dereference on older hardware.
Fix this.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 9e190db6cc370..17a4107639b2a 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -653,7 +653,8 @@ static void vmw_user_surface_base_release(struct ttm_base_object **p_base)
 	struct vmw_resource *res = &user_srf->srf.res;
 
 	*p_base = NULL;
-	ttm_base_object_unref(&user_srf->backup_base);
+	if (user_srf->backup_base)
+		ttm_base_object_unref(&user_srf->backup_base);
 	vmw_resource_unreference(&res);
 }