drm/vmwgfx: Fix up user_dmabuf refcounting
If user space calls unreference on a user_dmabuf it will typically
kill the struct ttm_base_object member which is responsible for the
user-space visibility. However the dmabuf part may still be alive and
refcounted. In some situations, like for shared guest-backed surface
referencing/opening, the driver may try to reference the
struct ttm_base_object member again, causing an immediate kernel warning
and a later kernel NULL pointer dereference.
Fix this by always maintaining a reference on the struct
ttm_base_object member, in situations where it might subsequently be
referenced.
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 3361769..64b5040 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -46,6 +46,7 @@
struct vmw_surface srf;
uint32_t size;
struct drm_master *master;
+ struct ttm_base_object *backup_base;
};
/**
@@ -656,6 +657,7 @@
struct vmw_resource *res = &user_srf->srf.res;
*p_base = NULL;
+ ttm_base_object_unref(&user_srf->backup_base);
vmw_resource_unreference(&res);
}
@@ -851,7 +853,8 @@
res->backup_size,
true,
&backup_handle,
- &res->backup);
+ &res->backup,
+ &user_srf->backup_base);
if (unlikely(ret != 0)) {
vmw_resource_unreference(&res);
goto out_unlock;
@@ -1321,7 +1324,8 @@
if (req->buffer_handle != SVGA3D_INVALID_ID) {
ret = vmw_user_dmabuf_lookup(tfile, req->buffer_handle,
- &res->backup);
+ &res->backup,
+ &user_srf->backup_base);
if (ret == 0 && res->backup->base.num_pages * PAGE_SIZE <
res->backup_size) {
DRM_ERROR("Surface backup buffer is too small.\n");
@@ -1335,7 +1339,8 @@
req->drm_surface_flags &
drm_vmw_surface_flag_shareable,
&backup_handle,
- &res->backup);
+ &res->backup,
+ &user_srf->backup_base);
if (unlikely(ret != 0)) {
vmw_resource_unreference(&res);