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

[Zack Rusin <zack@xxxxxxx>]

From: Zack Rusin <zackr@xxxxxxxxxx>

It is possible for userspace to predict the next buffer handle and
to destroy the buffer while it's still used by the kernel. Delay
dropping the internal reference on the buffers until kernel is done
with them.

Signed-off-by: Zack Rusin <zackr@xxxxxxxxxx>
Fixes: 8afa13a0583f ("drm/vmwgfx: Implement DRIVER_GEM")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.17+
---
 drivers/gpu/drm/vmwgfx/vmwgfx_bo.c      | 3 ++-
 drivers/gpu/drm/vmwgfx/vmwgfx_gem.c     | 4 ++--
 drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 1 -
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
index 43ffa5c7acbd..65bd88c8fef9 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
@@ -708,7 +708,8 @@ int vmw_dumb_create(struct drm_file *file_priv,
 	ret = vmw_gem_object_create_with_handle(dev_priv, file_priv,
 						args->size, &args->handle,
 						&vbo);
-
+	/* drop reference from allocate - handle holds it now */
+	drm_gem_object_put(&vbo->tbo.base);
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
index 51bd1f8c5cc4..d6baf73a6458 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
@@ -133,8 +133,6 @@ int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
 	(*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
 
 	ret = drm_gem_handle_create(filp, &(*p_vbo)->tbo.base, handle);
-	/* drop reference from allocate - handle holds it now */
-	drm_gem_object_put(&(*p_vbo)->tbo.base);
 out_no_bo:
 	return ret;
 }
@@ -161,6 +159,8 @@ int vmw_gem_object_create_ioctl(struct drm_device *dev, void *data,
 	rep->map_handle = drm_vma_node_offset_addr(&vbo->tbo.base.vma_node);
 	rep->cur_gmr_id = handle;
 	rep->cur_gmr_offset = 0;
+	/* drop reference from allocate - handle holds it now */
+	drm_gem_object_put(&vbo->tbo.base);
 out_no_bo:
 	return ret;
 }
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 9d4ae9623a00..d18fec953fa7 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -867,7 +867,6 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data,
 			goto out_unlock;
 		}
 		vmw_bo_reference(res->guest_memory_bo);
-		drm_gem_object_get(&res->guest_memory_bo->tbo.base);
 	}
 
 	tmp = vmw_resource_reference(&srf->res);
-- 
2.38.1