From fa96d5931826b936095022013e30ee5934018779 Mon Sep 17 00:00:00 2001
From: Adam Silverstein <adamsilverstein@git.wordpress.org>
Date: Tue, 2 Jun 2020 23:44:40 +0000
Subject: [PATCH] Formatting: add a new 'safe_style_disallowed_chars' filter.

Enable developers to change the regex used in `safecss_filter_attr` to limit characters in the parsed CSS.

Props paulschreiber, swissspidy, rmccue, bartekcholewa, miinasikk.
Fixes #37134.



git-svn-id: https://develop.svn.wordpress.org/trunk@47891 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/kses.php     | 23 ++++++---
 tests/phpunit/tests/kses.php | 95 +++++++++++++++++++++++++++++++++++-
 2 files changed, 111 insertions(+), 7 deletions(-)

diff --git a/src/wp-includes/kses.php b/src/wp-includes/kses.php
index 1aace6c4fa..f1372fbd52 100644
--- a/src/wp-includes/kses.php
+++ b/src/wp-includes/kses.php
@@ -2301,13 +2301,24 @@ function safecss_filter_attr( $css, $deprecated = '' ) {
 			}
 		}
 
-		// Remove any CSS containing containing \ ( & } = or comments, except for url() useage checked above.
-		if ( $found && ! preg_match( '%[\\\(&=}]|/\*%', $css_test_string ) ) {
-			if ( '' !== $css ) {
-				$css .= ';';
+		if ( $found ) {
+			/**
+			 * Filters the regex limiting the list of characters not allowed in CSS rules.
+			 *
+			 * Default behaviour is to remove any css containing \ ( & } = or comments, except for url() usage.
+			 *
+			 * @since 5.5.0
+			 *
+			 * @param string $regex           Regex pattern of disallowed characters in CSS rules. Default is '%[\\\(&=}]|/\*%'.
+			 * @param string $css_test_string CSS value to test.
+			 */
+			$disallowed_chars = apply_filters( 'safe_style_disallowed_chars', '%[\\\(&=}]|/\*%', $css_test_string );
+			if ( ! preg_match( $disallowed_chars, $css_test_string ) ) {
+				if ( '' !== $css ) {
+					$css .= ';';
+				}
+				$css .= $css_item;
 			}
-
-			$css .= $css_item;
 		}
 	}
 
diff --git a/tests/phpunit/tests/kses.php b/tests/phpunit/tests/kses.php
index ab675abbc3..7a846d5292 100644
--- a/tests/phpunit/tests/kses.php
+++ b/tests/phpunit/tests/kses.php
@@ -1002,7 +1002,21 @@ EOF;
 				'css'      => 'background: conic-gradient(at 0% 30%, red 10%, yellow 30%, #1e90ff 50%)',
 				'expected' => 'background: conic-gradient(at 0% 30%, red 10%, yellow 30%, #1e90ff 50%)',
 			),
-
+			// Expressions are not allowed.
+			array(
+				'css'      => 'height: expression( body.scrollTop + 50 + "px" )',
+				'expected' => '',
+			),
+			// RGB color values are not allowed.
+			array(
+				'css'      => 'color: rgb( 100, 100, 100 )',
+				'expected' => '',
+			),
+			// RGBA color values are not allowed.
+			array(
+				'css'      => 'color: rgb( 100, 100, 100, .4 )',
+				'expected' => '',
+			),
 		);
 	}
 
@@ -1247,4 +1261,83 @@ EOF;
 			),
 		);
 	}
+
+	/**
+	 * Filter for disallowed characters never matches thus allowing all characters.
+	 */
+	function _safe_style_disallowed_chars_filter( $regex ) {
+		return '%a^%'; // Regex with no matches.
+
+	}
+	/**
+	 * Testing the safecss_filter_attr() function with the safe_style_disallowed_chars filter.
+	 *
+	 * @ticket 37134
+	 *
+	 * @dataProvider data_test_safecss_filter_attr_filtered
+	 *
+	 * @param string $css      A string of CSS rules.
+	 * @param string $expected Expected string of CSS rules.
+	 */
+	public function test_safecss_filter_attr_filtered( $css, $expected ) {
+		add_filter( 'safe_style_disallowed_chars', array( $this, '_safe_style_disallowed_chars_filter' ) );
+		$this->assertSame( $expected, safecss_filter_attr( $css ) );
+		remove_filter( 'safe_style_disallowed_chars', array( $this, '_safe_style_disallowed_chars_filter' ) );
+	}
+
+	/**
+	 * Data Provider for test_safecss_filter_attr_filtered().
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @string string $css      A string of CSS rules.
+	 *         @string string $expected Expected string of CSS rules.
+	 *     }
+	 * }
+	 */
+	public function data_test_safecss_filter_attr_filtered() {
+		return array(
+
+			// A single attribute name, with a single value.
+			array(
+				'css'      => 'margin-top: 2px',
+				'expected' => 'margin-top: 2px',
+			),
+			// Backslash \ can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'margin-top: \2px',
+				'expected' => 'margin-top: \2px',
+			),
+			// Curly bracket } can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'margin-bottom: 2px}',
+				'expected' => 'margin-bottom: 2px}',
+			),
+			// Parenthesis ) can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'margin-bottom: 2px)',
+				'expected' => 'margin-bottom: 2px)',
+			),
+			// Ampersand & can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'margin-bottom: 2px&',
+				'expected' => 'margin-bottom: 2px&',
+			),
+			// Expressions can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'height: expression( body.scrollTop + 50 + "px" )',
+				'expected' => 'height: expression( body.scrollTop + 50 + "px" )',
+			),
+			// RGB color values can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'color: rgb( 100, 100, 100 )',
+				'expected' => 'color: rgb( 100, 100, 100 )',
+			),
+			// RGBA color values can be allowed with the 'safe_style_disallowed_chars' filter.
+			array(
+				'css'      => 'color: rgb( 100, 100, 100, .4 )',
+				'expected' => 'color: rgb( 100, 100, 100, .4 )',
+			),
+		);
+	}
 }