<?php
/**
* Validates a font family list according to CSS spec
*/
class HTMLPurifier_AttrDef_CSS_FontFamily extends HTMLPurifier_AttrDef
{
protected $mask = null;
public function __construct() {
$this->mask = '- ';
for ($c = 'a'; $c <= 'z'; $c++) $this->mask .= $c;
for ($c = 'A'; $c <= 'Z'; $c++) $this->mask .= $c;
for ($c = '0'; $c <= '9'; $c++) $this->mask .= $c; // cast-y, but should be fine
// special bytes used by UTF-8
for ($i = 0x80; $i <= 0xFF; $i++) {
// We don't bother excluding invalid bytes in this range,
// because the our restriction of well-formed UTF-8 will
// prevent these from ever occurring.
$this->mask .= chr($i);
}
/*
PHP's internal strcspn implementation is
O(length of string * length of mask), making it inefficient
for large masks. However, it's still faster than
preg_match 8)
for (p = s1;;) {
spanp = s2;
do {
if (*spanp == c || p == s1_end) {
return p - s1;
}
} while (spanp++ < (s2_end - 1));
c = *++p;
}
*/
// possible optimization: invert the mask.
}
public function validate($string, $config, $context) {
static $generic_names = array(
'serif' => true,
'sans-serif' => true,
'monospace' => true,
'fantasy' => true,
'cursive' => true
);
$allowed_fonts = $config->get('CSS.AllowedFonts');
// assume that no font names contain commas in them
$fonts = explode(',', $string);
$final = '';
foreach($fonts as $font) {
$font = trim($font);
if ($font === '') continue;
// match a generic name
if (isset($generic_names[$font])) {
if ($allowed_fonts === null || isset($allowed_fonts[$font])) {
$final .= $font . ', ';
}
continue;
}
// match a quoted name
if ($font[0] === '"' || $font[0] === "'") {
$length = strlen($font);
if ($length <= 2) continue;
$quote = $font[0];
if ($font[$length - 1] !== $quote) continue;
$font = substr($font, 1, $length - 2);
}
$font = $this->expandCSSEscape($font);
// $font is a pure representation of the font name
if ($allowed_fonts !== null && !isset($allowed_fonts[$font])) {
continue;
}
if (ctype_alnum($font) && $font !== '') {
// very simple font, allow it in unharmed
$final .= $font . ', ';
continue;
}
// bugger out on whitespace. form feed (0C) really
// shouldn't show up regardless
$font = str_replace(array("\n", "\t", "\r", "\x0C"), ' ', $font);
// Here, there are various classes of characters which need
// to be treated differently:
// - Alphanumeric characters are essentially safe. We
// handled these above.
// - Spaces require quoting, though most parsers will do
// the right thing if there aren't any characters that
// can be misinterpreted
// - Dashes rarely occur, but they fairly unproblematic
// for parsing/rendering purposes.
// The above characters cover the majority of Western font
// names.
// - Arbitrary Unicode characters not in ASCII. Because
// most parsers give little thought to Unicode, treatment
// of these codepoints is basically uniform, even for
// punctuation-like codepoints. These characters can
// show up in non-Western pages and are supported by most
// major browsers, for example: "ＭＳ 明朝" is a
// legitimate font-name
// <http://ja.wikipedia.org/wiki/MS_明朝>. See
// the CSS3 spec for more examples:
// <http://www.w3.org/TR/2011/WD-css3-fonts-20110324/localizedfamilynames.png>
// You can see live samples of these on the Internet:
// <http://www.google.co.jp/search?q=font-family+ＭＳ+明朝|ゴシック>
// However, most of these fonts have ASCII equivalents:
// for example, 'MS Mincho', and it's considered
// professional to use ASCII font names instead of
// Unicode font names. Thanks Takeshi Terada for
// providing this information.
// The following characters, to my knowledge, have not been
// used to name font names.
// - Single quote. While theoretically you might find a
// font name that has a single quote in its name (serving
// as an apostrophe, e.g. Dave's Scribble), I haven't
// been able to find any actual examples of this.
// Internet Explorer's cssText translation (which I
// believe is invoked by innerHTML) normalizes any
// quoting to single quotes, and fails to escape single
// quotes. (Note that this is not IE's behavior for all
// CSS properties, just some sort of special casing for
// font-family). So a single quote *cannot* be used
// safely in the font-family context if there will be an
// innerHTML/cssText translation. Note that Firefox 3.x
// does this too.
// - Double quote. In IE, these get normalized to
// single-quotes, no matter what the encoding. (Fun
// fact, in IE8, the 'content' CSS property gained
// support, where they special cased to preserve encoded
// double quotes, but still translate unadorned double
// quotes into single quotes.) So, because their
// fixpoint behavior is identical to single quotes, they
// cannot be allowed either. Firefox 3.x displays
// single-quote style behavior.
// - Backslashes are reduced by one (so \\ -> \) every
// iteration, so they cannot be used safely. This shows
// up in IE7, IE8 and FF3
// - Semicolons, commas and backticks are handled properly.
// - The rest of the ASCII punctuation is handled properly.
// We haven't checked what browsers do to unadorned
// versions, but this is not important as long as the
// browser doesn't /remove/ surrounding quotes (as IE does
// for HTML).
//
// With these results in hand, we conclude that there are
// various levels of safety:
// - Paranoid: alphanumeric, spaces and dashes(?)
// - International: Paranoid + non-ASCII Unicode
// - Edgy: Everything except quotes, backslashes
// - NoJS: Standards compliance, e.g. sod IE. Note that
// with some judicious character escaping (since certain
// types of escaping doesn't work) this is theoretically
// OK as long as innerHTML/cssText is not called.
// We believe that international is a reasonable default
// (that we will implement now), and once we do more
// extensive research, we may feel comfortable with dropping
// it down to edgy.
// Edgy: alphanumeric, spaces, dashes and Unicode. Use of
// str(c)spn assumes that the string was already well formed
// Unicode (which of course it is).
if (strspn($font, $this->mask) !== strlen($font)) {
continue;
}
// Historical:
// In the absence of innerHTML/cssText, these ugly
// transforms don't pose a security risk (as \\ and \"
// might--these escapes are not supported by most browsers).
// We could try to be clever and use single-quote wrapping
// when there is a double quote present, but I have choosen
// not to implement that. (NOTE: you can reduce the amount
// of escapes by one depending on what quoting style you use)
// $font = str_replace('\\', '\\5C ', $font);
// $font = str_replace('"', '\\22 ', $font);
// $font = str_replace("'", '\\27 ', $font);
// font possibly with spaces, requires quoting
$final .= "'$font', ";
}
$final = rtrim($final, ', ');
if ($final === '') return false;
return $final;
}
}
// vim: et sw=4 sts=4
