Rewrite CSS url() and font-family output logic.

The new logic is as follows:

* Given a URL to insert into url(), check that it is properly URL
  encoded (in particular, a doublequote and backslash never occurs
  within it) and then place it as url("http://example.com").

* Given a font name, if it is strictly alphanumeric, it is safe to omit
  quotes. Otherwise, wrap in double quotes and replace '"' with '\22 '
  (note trailing space) and '\' with '\5C ' (ditto).

We introduce expandCSSEscape() which is a hack for common parsing
idioms in CSS; this means that CSS escapes are now recognized inside
URLs as well as unquoted font names.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

NEWS

@@ -10,6 +10,9 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
 ==========================
 
 4.1.1, unknown release date
+- Rewrite CSS output logic for font-family and url().  Thanks Mario
+  Heiderich <mario.heiderich@googlemail.com> for reporting and Takeshi
+  Terada <t-terada@violet.plala.or.jp> for suggesting the fix.
 - Emit an error for CollectErrors if a body is extracted
 - Fix bug where in background-position for center keyword handling.
 - Fix infinite loop when a wrapper element is inserted in a context

library/HTMLPurifier/AttrDef.php

@@ -82,6 +82,42 @@ abstract class HTMLPurifier_AttrDef
         return preg_replace('/rgb\((\d+)\s*,\s*(\d+)\s*,\s*(\d+)\)/', 'rgb(\1,\2,\3)', $string);
     }
 
+    /**
+     * Parses a possibly escaped CSS string and returns the "pure" 
+     * version of it.
+     */
+    protected function expandCSSEscape($string) {
+        // flexibly parse it
+        $ret = '';
+        for ($i = 0, $c = strlen($string); $i < $c; $i++) {
+            if ($string[$i] === '\\') {
+                $i++;
+                if ($i >= $c) {
+                    $ret .= '\\';
+                    break;
+                }
+                if (ctype_xdigit($string[$i])) {
+                    $code = $string[$i];
+                    for ($a = 1, $i++; $i < $c && $a < 6; $i++, $a++) {
+                        if (!ctype_xdigit($string[$i])) break;
+                        $code .= $string[$i];
+                    }
+                    // We have to be extremely careful when adding
+                    // new characters, to make sure we're not breaking
+                    // the encoding.
+                    $char = HTMLPurifier_Encoder::unichr(hexdec($code));
+                    if (HTMLPurifier_Encoder::cleanUTF8($char) === '') continue;
+                    $ret .= $char;
+                    if ($i < $c && trim($string[$i]) !== '') $i--;
+                    continue;
+                }
+                if ($string[$i] === "\n") continue;
+            }
+            $ret .= $string[$i];
+        }
+        return $ret;
+    }
+
 }
 
 // vim: et sw=4 sts=4

library/HTMLPurifier/AttrDef/CSS/FontFamily.php

@@ -34,37 +34,10 @@ class HTMLPurifier_AttrDef_CSS_FontFamily extends HTMLPurifier_AttrDef
                 $quote = $font[0];
                 if ($font[$length - 1] !== $quote) continue;
                 $font = substr($font, 1, $length - 2);
-
-                $new_font = '';
-                for ($i = 0, $c = strlen($font); $i < $c; $i++) {
-                    if ($font[$i] === '\\') {
-                        $i++;
-                        if ($i >= $c) {
-                            $new_font .= '\\';
-                            break;
-                        }
-                        if (ctype_xdigit($font[$i])) {
-                            $code = $font[$i];
-                            for ($a = 1, $i++; $i < $c && $a < 6; $i++, $a++) {
-                                if (!ctype_xdigit($font[$i])) break;
-                                $code .= $font[$i];
-                            }
-                            // We have to be extremely careful when adding
-                            // new characters, to make sure we're not breaking
-                            // the encoding.
-                            $char = HTMLPurifier_Encoder::unichr(hexdec($code));
-                            if (HTMLPurifier_Encoder::cleanUTF8($char) === '') continue;
-                            $new_font .= $char;
-                            if ($i < $c && trim($font[$i]) !== '') $i--;
-                            continue;
-                        }
-                        if ($font[$i] === "\n") continue;
-                    }
-                    $new_font .= $font[$i];
-                }
-
-                $font = $new_font;
             }
+
+            $font = $this->expandCSSEscape($font);
+
             // $font is a pure representation of the font name
 
             if (ctype_alnum($font) && $font !== '') {
@@ -73,12 +46,21 @@ class HTMLPurifier_AttrDef_CSS_FontFamily extends HTMLPurifier_AttrDef
                 continue;
             }
 
-            // complicated font, requires quoting
+            // bugger out on whitespace.  form feed (0C) really
+            // shouldn't show up regardless
+            $font = str_replace(array("\n", "\t", "\r", "\x0C"), ' ', $font);
 
-            // armor single quotes and new lines
+            // These ugly transforms don't pose a security
-            $font = str_replace("\\", "\\\\", $font);
+            // risk (as \\ and \" might).  We could try to be clever and
-            $font = str_replace("'", "\\'", $font);
+            // use single-quote wrapping when there is a double quote
-            $final .= "'$font', ";
+            // present, but I have choosen not to implement that.
+            // (warning: this code relies on the selection of quotation
+            // mark below)
+            $font = str_replace('\\', '\\5C ', $font);
+            $font = str_replace('"',  '\\22 ', $font);
+
+            // complicated font, requires quoting
+            $final .= "\"$font\", "; // note that this will later get turned into &quot;
         }
         $final = rtrim($final, ', ');
         if ($final === '') return false;

library/HTMLPurifier/AttrDef/CSS/URI.php

@@ -34,20 +34,16 @@ class HTMLPurifier_AttrDef_CSS_URI extends HTMLPurifier_AttrDef_URI
             $uri = substr($uri, 1, $new_length - 1);
         }
 
-        $keys   = array(  '(',   ')',   ',',   ' ',   '"',   "'");
+        $uri = $this->expandCSSEscape($uri);
-        $values = array('\\(', '\\)', '\\,', '\\ ', '\\"', "\\'");
-        $uri = str_replace($values, $keys, $uri);
 
         $result = parent::validate($uri, $config, $context);
 
         if ($result === false) return false;
 
-        // escape necessary characters according to CSS spec
+        // extra sanity check; should have been done by URI
-        // except for the comma, none of these should appear in the
+        $result = str_replace(array('"', "\\", "\n", "\x0c", "\r"), "", $result);
-        // URI at all
-        $result = str_replace($keys, $values, $result);
 
-        return "url('$result')";
+        return "url(\"$result\")";
 
     }
 

tests/HTMLPurifier/AttrDef/CSS/BackgroundTest.php

@@ -8,12 +8,12 @@ class HTMLPurifier_AttrDef_CSS_BackgroundTest extends HTMLPurifier_AttrDefHarnes
         $config = HTMLPurifier_Config::createDefault();
         $this->def = new HTMLPurifier_AttrDef_CSS_Background($config);
 
-        $valid = '#333 url(\'chess.png\') repeat fixed 50% top';
+        $valid = '#333 url("chess.png") repeat fixed 50% top';
         $this->assertDef($valid);
-        $this->assertDef('url("chess.png") #333 50% top repeat fixed', $valid);
+        $this->assertDef('url(\'chess.png\') #333 50% top repeat fixed', $valid);
         $this->assertDef(
             'rgb(34, 56, 33) url(chess.png) repeat fixed top',
-            'rgb(34,56,33) url(\'chess.png\') repeat fixed top'
+            'rgb(34,56,33) url("chess.png") repeat fixed top'
         );
 
     }

tests/HTMLPurifier/AttrDef/CSS/FontFamilyTest.php

@@ -8,29 +8,29 @@ class HTMLPurifier_AttrDef_CSS_FontFamilyTest extends HTMLPurifier_AttrDefHarnes
         $this->def = new HTMLPurifier_AttrDef_CSS_FontFamily();
 
         $this->assertDef('Gill, Helvetica, sans-serif');
-        $this->assertDef('\'Times New Roman\', serif');
+        $this->assertDef('"Times New Roman", serif');
-        $this->assertDef('"Times New Roman"', "'Times New Roman'");
+        $this->assertDef('\'Times New Roman\'', '"Times New Roman"');
         $this->assertDef('01234');
         $this->assertDef(',', false);
-        $this->assertDef('Times New Roman, serif', '\'Times New Roman\', serif');
+        $this->assertDef('Times New Roman, serif', '"Times New Roman", serif');
-        $this->assertDef($d = "'John\\'s Font'");
+        $this->assertDef($d = '"John\'s Font"');
         $this->assertDef("John's Font", $d);
-        $this->assertDef($d = "'\xE5\xAE\x8B\xE4\xBD\x93'");
+        $this->assertDef($d = "\"\xE5\xAE\x8B\xE4\xBD\x93\"");
         $this->assertDef("\xE5\xAE\x8B\xE4\xBD\x93", $d);
-        $this->assertDef("'\\','f'", "'\\\\', f");
+        $this->assertDef("'\\','f'", "\"\\5C \", f");
-        $this->assertDef("'\\01'", "''");
+        $this->assertDef("'\\01'", "\"\"");
-        $this->assertDef("'\\20'", "' '");
+        $this->assertDef("'\\20'", "\" \"");
-        $this->assertDef("\\0020", "'\\\\0020'");
+        $this->assertDef("\\0020", "\" \"");
         $this->assertDef("'\\000045'", "E");
         $this->assertDef("','", false);
-        $this->assertDef("',' foobar','", "' foobar'");
+        $this->assertDef("',' foobar','", "\" foobar\"");
-        $this->assertDef("'\\27'", "'\''");
+        $this->assertDef("'\\27'", "\"'\"");
-        $this->assertDef('"\\22"', "'\"'");
+        $this->assertDef('"\\22"', "\"\\22 \"");
-        $this->assertDef('"\\""', "'\"'");
+        $this->assertDef('"\\""', "\"\\22 \"");
-        $this->assertDef('"\'"', "'\\''");
+        $this->assertDef('"\'"', "\"'\"");
         $this->assertDef("'\\000045a'", "Ea");
         $this->assertDef("'\\00045 a'", "Ea");
-        $this->assertDef("'\\00045  a'", "'E a'");
+        $this->assertDef("'\\00045  a'", "\"E a\"");
         $this->assertDef("'\\\nf'", "f");
     }
 

tests/HTMLPurifier/AttrDef/CSS/FontTest.php

@@ -11,10 +11,10 @@ class HTMLPurifier_AttrDef_CSS_FontTest extends HTMLPurifier_AttrDefHarness
         // hodgepodge of usage cases from W3C spec, but " -> '
         $this->assertDef('12px/14px sans-serif');
         $this->assertDef('80% sans-serif');
-        $this->assertDef('x-large/110% \'New Century Schoolbook\', serif');
+        $this->assertDef('x-large/110% "New Century Schoolbook", serif');
         $this->assertDef('bold italic large Palatino, serif');
         $this->assertDef('normal small-caps 120%/120% fantasy');
-        $this->assertDef('300 italic 1.3em/1.7em \'FB Armada\', sans-serif');
+        $this->assertDef('300 italic 1.3em/1.7em "FB Armada", sans-serif');
         $this->assertDef('600 9px Charcoal');
         $this->assertDef('600 9px/ 12px Charcoal', '600 9px/12px Charcoal');
 

tests/HTMLPurifier/AttrDef/CSS/ListStyleTest.php

@@ -13,14 +13,14 @@ class HTMLPurifier_AttrDef_CSS_ListStyleTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('circle outside');
         $this->assertDef('inside');
         $this->assertDef('none');
-        $this->assertDef('url(\'foo.gif\')');
+        $this->assertDef('url("foo.gif")');
-        $this->assertDef('circle url(\'foo.gif\') inside');
+        $this->assertDef('circle url("foo.gif") inside');
 
         // invalid values
         $this->assertDef('outside inside', 'outside');
 
         // ordering
-        $this->assertDef('url(foo.gif) none', 'none url(\'foo.gif\')');
+        $this->assertDef('url(foo.gif) none', 'none url("foo.gif")');
         $this->assertDef('circle lower-alpha', 'circle');
         // the spec is ambiguous about what happens in these
         // cases, so we're going off the W3C CSS validator

tests/HTMLPurifier/AttrDef/CSS/URITest.php

@@ -12,20 +12,16 @@ class HTMLPurifier_AttrDef_CSS_URITest extends HTMLPurifier_AttrDefHarness
         // we could be nice but we won't be
         $this->assertDef('http://www.example.com/', false);
 
-        // no quotes are used, since that's the most widely supported
-        // syntax
         $this->assertDef('url(', false);
-        $this->assertDef('url(\'\')', true);
+        $this->assertDef('url("")', true);
-        $result = "url('http://www.example.com/')";
+        $result = 'url("http://www.example.com/")';
         $this->assertDef('url(http://www.example.com/)', $result);
         $this->assertDef('url("http://www.example.com/")', $result);
         $this->assertDef("url('http://www.example.com/')", $result);
         $this->assertDef(
             '  url(  "http://www.example.com/" )   ', $result);
-
-        // escaping
         $this->assertDef("url(http://www.example.com/foo,bar\))",
-            "url('http://www.example.com/foo\,bar\)')");
+            'url("http://www.example.com/foo,bar)")');
     }
 
 }

tests/HTMLPurifier/AttrDef/CSSTest.php

@@ -25,7 +25,7 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('text-transform:capitalize;');
         $this->assertDef('background-color:rgb(0,0,255);');
         $this->assertDef('background-color:transparent;');
-        $this->assertDef('background:#333 url(\'chess.png\') repeat fixed 50% top;');
+        $this->assertDef('background:#333 url("chess.png") repeat fixed 50% top;');
         $this->assertDef('color:#F00;');
         $this->assertDef('border-top-color:#F00;');
         $this->assertDef('border-color:#F00 #FF0;');
@@ -62,7 +62,7 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('width:-50px;', false);
         $this->assertDef('text-decoration:underline;');
         $this->assertDef('font-family:sans-serif;');
-        $this->assertDef('font-family:Gill, \'Times New Roman\', sans-serif;');
+        $this->assertDef('font-family:Gill, "Times New Roman", sans-serif;');
         $this->assertDef('font:12px serif;');
         $this->assertDef('border:1px solid #000;');
         $this->assertDef('border-bottom:2em double #FF00FA;');
@@ -73,9 +73,9 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('vertical-align:12px;');
         $this->assertDef('vertical-align:50%;');
         $this->assertDef('table-layout:fixed;');
-        $this->assertDef('list-style-image:url(\'nice.jpg\');');
+        $this->assertDef('list-style-image:url("nice.jpg");');
-        $this->assertDef('list-style:disc url(\'nice.jpg\') inside;');
+        $this->assertDef('list-style:disc url("nice.jpg") inside;');
-        $this->assertDef('background-image:url(\'foo.jpg\');');
+        $this->assertDef('background-image:url("foo.jpg");');
         $this->assertDef('background-image:none;');
         $this->assertDef('background-repeat:repeat-y;');
         $this->assertDef('background-attachment:fixed;');

tests/HTMLPurifier/Filter/ExtractStyleBlocksTest.php

@@ -81,7 +81,7 @@ class HTMLPurifier_Filter_ExtractStyleBlocksTest extends HTMLPurifier_Harness
     function test_cleanCSS_angledBrackets() {
         $this->assertCleanCSS(
             ".class {\nfont-family:'</style>';\n}",
-            ".class {\nfont-family:'\\3C /style\\3E ';\n}"
+            ".class {\nfont-family:\"\\3C /style\\3E \";\n}"
         );
     }
 
@@ -99,14 +99,14 @@ class HTMLPurifier_Filter_ExtractStyleBlocksTest extends HTMLPurifier_Harness
 
     function test_cleanCSS_escapeCodes() {
         $this->assertCleanCSS(
-            ".class {\nfont-family:'\\3C /style\\3E ';\n}"
+            ".class {\nfont-family:\"\\3C /style\\3E \";\n}"
         );
     }
 
     function test_cleanCSS_noEscapeCodes() {
         $this->config->set('Filter.ExtractStyleBlocks.Escaping', false);
         $this->assertCleanCSS(
-            ".class {\nfont-family:'</style>';\n}"
+            ".class {\nfont-family:\"</style>\";\n}"
         );
     }
 

tests/HTMLPurifier/HTMLT/munge-extra.htmlt

@@ -7,5 +7,5 @@ URI.MungeResources = true
 <img src="http://example.com" style="background-image:url(http://example.com);" alt="example.com" />
 --EXPECT--
 <a href="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=&amp;n=a&amp;m=href&amp;p=">Link</a>
-<img src="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=src&amp;p=" style="background-image:url('/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=style&amp;p=background-image');" alt="example.com" />
+<img src="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=src&amp;p=" style="background-image:url(&quot;/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=style&amp;p=background-image&quot;);" alt="example.com" />
 --# vim: et sw=4 sts=4

tests/HTMLPurifier/HTMLT/shift-jis-preserve-yen.htmlt

@@ -4,5 +4,5 @@ if (!function_exists('iconv')) return true;
 Core.Encoding = "Shift_JIS"
 Core.EscapeNonASCIICharacters = true
 --HTML--
-<b style="font-family:'&#165;';">111</b>
+<b style="font-family:&quot;&#165;&quot;;">111</b>
 --# vim: et sw=4 sts=4

tests/HTMLPurifier/HTMLT/shift-jis-remove-yen.htmlt

@@ -3,7 +3,7 @@ if (!function_exists('iconv')) return true;
 --INI--
 Core.Encoding = Shift_JIS
 --HTML--
-<b style="font-family:'&#165;';">111</b>
+<b style="font-family:&quot;&#165;&quot;;">111</b>
 --EXPECT--
-<b style="font-family:'';">111</b>
+<b style="font-family:&quot;&quot;;">111</b>
 --# vim: et sw=4 sts=4

tests/HTMLPurifier/HTMLT/tidy-background.htmlt

@@ -1,5 +1,5 @@
 --HTML--
 <table background="logo.png"><tr><td>asdf</td></tr></table>
 --EXPECT--
-<table style="background-image:url('logo.png');"><tr><td>asdf</td></tr></table>
+<table style="background-image:url(&quot;logo.png&quot;);"><tr><td>asdf</td></tr></table>
 --# vim: et sw=4 sts=4