From 9c0750ac5263da10e5668d92531812a31ed2295e Mon Sep 17 00:00:00 2001
From: Dion Hulse <dd32@git.wordpress.org>
Date: Fri, 19 Jun 2015 03:48:55 +0000
Subject: [PATCH] When updating plugins/themes verify that the files to be
 deleted can be modified before starting the deletion process. This will avoid
 partially deleting an item during update which has inconsistent permissions.
 This change only affects those using the direct & ssh transports as FTP's
 is_writable() currently always returns `true`. Fixes #30921

git-svn-id: https://develop.svn.wordpress.org/trunk@32854 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/includes/class-wp-upgrader.php | 73 ++++++++++++++++++---
 1 file changed, 64 insertions(+), 9 deletions(-)

diff --git a/src/wp-admin/includes/class-wp-upgrader.php b/src/wp-admin/includes/class-wp-upgrader.php
index 4f5151206b..0f00f7dbed 100644
--- a/src/wp-admin/includes/class-wp-upgrader.php
+++ b/src/wp-admin/includes/class-wp-upgrader.php
@@ -132,6 +132,7 @@ class WP_Upgrader {
 		$this->strings['folder_exists'] = __('Destination folder already exists.');
 		$this->strings['mkdir_failed'] = __('Could not create directory.');
 		$this->strings['incompatible_archive'] = __('The package could not be installed.');
+		$this->strings['files_not_writable'] = __( 'The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.' );
 
 		$this->strings['maintenance_start'] = __('Enabling Maintenance mode&#8230;');
 		$this->strings['maintenance_end'] = __('Disabling Maintenance mode&#8230;');
@@ -292,6 +293,64 @@ class WP_Upgrader {
 		return $working_dir;
 	}
 
+	/**
+	 * Clears the directory where this item is going to be installed into.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @global WP_Filesystem_Base $wp_filesystem Subclass
+	 *
+	 * @param string $remote_destination The location on the remote filesystem to be cleared
+	 *
+	 * @return bool|WP_Error true upon success, {@see WP_Error} on failure.
+	 */
+	function clear_destination( $remote_destination ) {
+		global $wp_filesystem;
+
+		if ( ! $wp_filesystem->exists( $remote_destination ) ) {
+			return true;
+		}
+
+		// Check all files are writable before attempting to clear the destination
+		$unwritable_files = array();
+
+		$_files = $wp_filesystem->dirlist( $remote_destination, true, true );
+		// Flatten the resulting array, iterate using each as we append to the array during iteration
+		while ( $f = each( $_files ) ) {
+			$file = $f['value'];
+			$name = $f['key'];
+
+			if ( ! isset( $file['files'] ) ) {
+				continue;
+			}
+
+			foreach ( $file['files'] as $filename => $details ) {
+				$_files[ $name . '/' . $filename ] = $details;
+			}
+		}
+
+		// Check writability
+		foreach ( $_files as $filename => $file_details ) {
+			if ( ! $wp_filesystem->is_writable( $remote_destination . $filename ) ) {
+				// Attempt to alter permissions to allow writes and try again
+				$wp_filesystem->chmod( $remote_destination . $filename, ( 'd' == $file_details['type'] ? FS_CHMOD_DIR : FS_CHMOD_FILE ) );
+				if ( ! $wp_filesystem->is_writable( $remote_destination . $filename ) ) {
+					$unwritable_files[] = $filename;
+				}
+			}
+		}
+
+		if ( ! empty( $unwritable_files ) ) {
+			return new WP_Error( 'files_not_writable', $this->strings['files_not_writable'], implode( ', ', $unwritable_files ) );
+		}
+
+		if ( ! $wp_filesystem->delete( $remote_destination, true ) ) {
+			return new WP_Error( 'remove_old_failed', $this->strings['remove_old_failed'] );
+		}
+
+		return true;
+	}
+
 	/**
 	 * Install a package.
 	 *
@@ -417,29 +476,25 @@ class WP_Upgrader {
 		}
 
 		if ( $clear_destination ) {
-			//We're going to clear the destination if there's something there
+			// We're going to clear the destination if there's something there
 			$this->skin->feedback('remove_old');
-			$removed = true;
-			if ( $wp_filesystem->exists( $remote_destination ) ) {
-				$removed = $wp_filesystem->delete( $remote_destination, true );
-			}
+
+			$removed = $this->clear_destination( $remote_destination );
 
 			/**
 			 * Filter whether the upgrader cleared the destination.
 			 *
 			 * @since 2.8.0
 			 *
-			 * @param bool   $removed            Whether the destination was cleared.
+			 * @param mixed  $removed            Whether the destination was cleared. true on success, WP_Error on failure
 			 * @param string $local_destination  The local package destination.
 			 * @param string $remote_destination The remote package destination.
 			 * @param array  $hook_extra         Extra arguments passed to hooked filters.
 			 */
 			$removed = apply_filters( 'upgrader_clear_destination', $removed, $local_destination, $remote_destination, $args['hook_extra'] );
 
-			if ( is_wp_error($removed) ) {
+			if ( is_wp_error( $removed ) ) {
 				return $removed;
-			} elseif ( ! $removed ) {
-				return new WP_Error('remove_old_failed', $this->strings['remove_old_failed']);
 			}
 		} elseif ( $args['abort_if_destination_exists'] && $wp_filesystem->exists($remote_destination) ) {
 			//If we're not clearing the destination folder and something exists there already, Bail.