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

v3: Fix vmw_user_bo_lookup which was also dropping the gem reference
before the kernel was done with buffer depending on userspace doing
the right thing. Same bug, different spot.

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.

Instead of immediately dropping the gem reference in vmw_user_bo_lookup
and vmw_gem_object_create_with_handle let the callers decide when they're
ready give the control back to userspace.

Also fixes the second usage of vmw_gem_object_create_with_handle in
vmwgfx_surface.c which wasn't grabbing an explicit reference
to the gem object which could have been destroyed by the userspace
on the owning surface at any point.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Fixes: 8afa13a0583f ("drm/vmwgfx: Implement DRIVER_GEM")
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Maaz Mombasawala <mombasawalam@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230211050514.2431155-1-zack@kde.org
(cherry picked from commit 9ef8d83e8e25d5f1811b3a38eb1484f85f64296c)
Cc: <stable@vger.kernel.org> # v5.17+

7 files changed, 20 insertions, 10 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
index 53da183e2bfe..4dcf2eb7aa80 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
@@ -598,6 +598,7 @@ static int vmw_user_bo_synccpu_release(struct drm_file *filp,
 		ttm_bo_put(&vmw_bo->base);
 	}
 
+	drm_gem_object_put(&vmw_bo->base.base);
 	return ret;
 }
 
@@ -638,6 +639,7 @@ int vmw_user_bo_synccpu_ioctl(struct drm_device *dev, void *data,
 
 		ret = vmw_user_bo_synccpu_grab(vbo, arg->flags);
 		vmw_bo_unreference(&vbo);
+		drm_gem_object_put(&vbo->base.base);
 		if (unlikely(ret != 0)) {
 			if (ret == -ERESTARTSYS || ret == -EBUSY)
 				return -EBUSY;
@@ -695,7 +697,7 @@ int vmw_bo_unref_ioctl(struct drm_device *dev, void *data,
  * struct vmw_buffer_object should be placed.
  * Return: Zero on success, Negative error code on error.
  *
- * The vmw buffer object pointer will be refcounted.
+ * The vmw buffer object pointer will be refcounted (both ttm and gem)
  */
 int vmw_user_bo_lookup(struct drm_file *filp,
 		       uint32_t handle,
@@ -712,7 +714,6 @@ int vmw_user_bo_lookup(struct drm_file *filp,
 
 	*out = gem_to_vmw_bo(gobj);
 	ttm_bo_get(&(*out)->base);
-	drm_gem_object_put(gobj);
 
 	return 0;
 }
@@ -793,7 +794,8 @@ 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->base.base);
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index a44d53e33cdb..c0686283ffd1 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -1160,6 +1160,7 @@ static int vmw_translate_mob_ptr(struct vmw_private *dev_priv,
 	}
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo, true, false);
 	ttm_bo_put(&vmw_bo->base);
+	drm_gem_object_put(&vmw_bo->base.base);
 	if (unlikely(ret != 0))
 		return ret;
 
@@ -1214,6 +1215,7 @@ static int vmw_translate_guest_ptr(struct vmw_private *dev_priv,
 	}
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo, false, false);
 	ttm_bo_put(&vmw_bo->base);
+	drm_gem_object_put(&vmw_bo->base.base);
 	if (unlikely(ret != 0))
 		return ret;
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
index 83d8f18cc16f..4d2c28e39f4e 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
@@ -152,8 +152,6 @@ int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
 	(*p_vbo)->base.base.funcs = &vmw_gem_object_funcs;
 
 	ret = drm_gem_handle_create(filp, &(*p_vbo)->base.base, handle);
-	/* drop reference from allocate - handle holds it now */
-	drm_gem_object_put(&(*p_vbo)->base.base);
 out_no_bo:
 	return ret;
 }
@@ -180,6 +178,8 @@ int vmw_gem_object_create_ioctl(struct drm_device *dev, void *data,
 	rep->map_handle = drm_vma_node_offset_addr(&vbo->base.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->base.base);
 out_no_bo:
 	return ret;
 }
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index 257f090071f1..445d619e1fdc 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -1815,8 +1815,10 @@ static struct drm_framebuffer *vmw_kms_fb_create(struct drm_device *dev,
 
 err_out:
 	/* vmw_user_lookup_handle takes one ref so does new_fb */
-	if (bo)
+	if (bo) {
 		vmw_bo_unreference(&bo);
+		drm_gem_object_put(&bo->base.base);
+	}
 	if (surface)
 		vmw_surface_unreference(&surface);
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c b/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
index e9f5c89b4ca6..b5b311f2a91a 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c
@@ -458,6 +458,7 @@ int vmw_overlay_ioctl(struct drm_device *dev, void *data,
 	ret = vmw_overlay_update_stream(dev_priv, buf, arg, true);
 
 	vmw_bo_unreference(&buf);
+	drm_gem_object_put(&buf->base.base);
 
 out_unlock:
 	mutex_unlock(&overlay->mutex);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
index 108a496b5d18..51e83dfa1cac 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_shader.c
@@ -807,6 +807,7 @@ static int vmw_shader_define(struct drm_device *dev, struct drm_file *file_priv,
 				    num_output_sig, tfile, shader_handle);
 out_bad_arg:
 	vmw_bo_unreference(&buffer);
+	drm_gem_object_put(&buffer->base.base);
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 3bc63ae768f3..dcfb003841b3 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -683,7 +683,7 @@ static void vmw_user_surface_base_release(struct ttm_base_object **p_base)
 	    container_of(base, struct vmw_user_surface, prime.base);
 	struct vmw_resource *res = &user_srf->srf.res;
 
-	if (base->shareable && res && res->backup)
+	if (res && res->backup)
 		drm_gem_object_put(&res->backup->base.base);
 
 	*p_base = NULL;
@@ -864,7 +864,11 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data,
 			goto out_unlock;
 		}
 		vmw_bo_reference(res->backup);
-		drm_gem_object_get(&res->backup->base.base);
+		/*
+		 * We don't expose the handle to the userspace and surface
+		 * already holds a gem reference
+		 */
+		drm_gem_handle_delete(file_priv, backup_handle);
 	}
 
 	tmp = vmw_resource_reference(&srf->res);
@@ -1568,8 +1572,6 @@ vmw_gb_surface_define_internal(struct drm_device *dev,
 			drm_vma_node_offset_addr(&res->backup->base.base.vma_node);
 		rep->buffer_size = res->backup->base.base.size;
 		rep->buffer_handle = backup_handle;
-		if (user_srf->prime.base.shareable)
-			drm_gem_object_get(&res->backup->base.base);
 	} else {
 		rep->buffer_map_handle = 0;
 		rep->buffer_size = 0;