REST API: Prevent deletion of post revisions.

Allowing the client to delete revisions breaks the "audit trail" functionality. This is not allowed in WordPress and shouldn't be allowed through the API.
While not recommended, a plugin may opt-in to the previous behavior by setting a custom 'delete_post' capability for the revisions post type.

Props dlh, danielbachhuber, TimothyBlynJacobs, azaozz, kadamwhite.
Fixes #43709.



git-svn-id: https://develop.svn.wordpress.org/trunk@45812 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/capabilities.php

@@ -72,11 +72,8 @@ function map_meta_cap( $cap, $user_id, ...$args ) {
 			}
 
 			if ( 'revision' == $post->post_type ) {
-				$post = get_post( $post->post_parent );
-				if ( ! $post ) {
-					$caps[] = 'do_not_allow';
-					break;
-				}
+				$caps[] = 'do_not_allow';
+				break;
 			}
 
 			if ( ( get_option( 'page_for_posts' ) == $post->ID ) || ( get_option( 'page_on_front' ) == $post->ID ) ) {

src/wp-includes/rest-api/endpoints/class-wp-rest-revisions-controller.php

@@ -349,6 +349,11 @@ public function get_item( $request ) {
 			return $parent;
 		}
 
+		$parent_post_type = get_post_type_object( $parent->post_type );
+		if ( ! current_user_can( $parent_post_type->cap->delete_post, $parent->ID ) ) {
+			return new WP_Error( 'rest_cannot_delete', __( 'Sorry, you are not allowed to delete revisions of this post.' ), array( 'status' => rest_authorization_required_code() ) );
+		}
+
 		$revision = $this->get_revision( $request['id'] );
 		if ( is_wp_error( $revision ) ) {
 			return $revision;
@@ -383,7 +388,12 @@ public function delete_item_permissions_check( $request ) {
 		}
 
 		$post_type = get_post_type_object( 'revision' );
-		return current_user_can( $post_type->cap->delete_post, $revision->ID );
+
+		if ( ! current_user_can( $post_type->cap->delete_post, $revision->ID ) ) {
+			return new WP_Error( 'rest_cannot_delete', __( 'Sorry, you are not allowed to delete this revision.' ), array( 'status' => rest_authorization_required_code() ) );
+		}
+
+		return true;
 	}
 
 	/**

tests/phpunit/tests/rest-api/rest-revisions-controller.php

@@ -76,6 +76,27 @@ public function setUp() {
 		$this->revision_id3    = $this->revision_3->ID;
 	}
 
+	public function tearDown() {
+		parent::tearDown();
+
+		remove_filter( 'map_meta_cap', array( $this, '_filter_map_meta_cap_remove_no_allow_revisions' ) );
+	}
+
+	public function _filter_map_meta_cap_remove_no_allow_revisions( $caps, $cap, $user_id, $args ) {
+		if ( 'delete_post' !== $cap || empty( $args ) ) {
+			return $caps;
+		}
+		$post = get_post( $args[0] );
+		if ( ! $post || 'revision' !== $post->post_type ) {
+			return $caps;
+		}
+		$key = array_search( 'do_not_allow', $caps, true );
+		if ( false !== $key ) {
+			unset( $caps[ $key ] );
+		}
+		return $caps;
+	}
+
 	public function test_register_routes() {
 		$routes = rest_get_server()->get_routes();
 		$this->assertArrayHasKey( '/wp/v2/posts/(?P<parent>[\d]+)/revisions', $routes );
@@ -216,13 +237,32 @@ public function test_delete_item() {
 		$request = new WP_REST_Request( 'DELETE', '/wp/v2/posts/' . self::$post_id . '/revisions/' . $this->revision_id1 );
 		$request->set_param( 'force', true );
 		$response = rest_get_server()->dispatch( $request );
+		$this->assertErrorResponse( 'rest_cannot_delete', $response, 403 );
+		$this->assertNotNull( get_post( $this->revision_id1 ) );
+	}
+
+	public function test_delete_item_remove_do_not_allow() {
+		wp_set_current_user( self::$editor_id );
+		add_filter( 'map_meta_cap', array( $this, '_filter_map_meta_cap_remove_no_allow_revisions' ), 10, 4 );
+		$request = new WP_REST_Request( 'DELETE', '/wp/v2/posts/' . self::$post_id . '/revisions/' . $this->revision_id1 );
+		$request->set_param( 'force', true );
+		$response = rest_get_server()->dispatch( $request );
 		$this->assertEquals( 200, $response->get_status() );
 		$this->assertNull( get_post( $this->revision_id1 ) );
 	}
 
-	public function test_delete_item_no_trash() {
+	public function test_delete_item_cannot_delete_parent() {
 		wp_set_current_user( self::$editor_id );
+		$request = new WP_REST_Request( 'DELETE', '/wp/v2/posts/' . self::$post_id . '/revisions/' . $this->revision_id1 );
+		$request->set_param( 'force', true );
+		$response = rest_get_server()->dispatch( $request );
+		$this->assertErrorResponse( 'rest_cannot_delete', $response, 403 );
+		$this->assertNotNull( get_post( $this->revision_id1 ) );
+	}
 
+	public function test_delete_item_no_trash() {
+		wp_set_current_user( self::$editor_id );
+		add_filter( 'map_meta_cap', array( $this, '_filter_map_meta_cap_remove_no_allow_revisions' ), 10, 4 );
 		$request  = new WP_REST_Request( 'DELETE', '/wp/v2/posts/' . self::$post_id . '/revisions/' . $this->revision_id1 );
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertErrorResponse( 'rest_trash_not_supported', $response, 501 );