1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
<?php
/**
* Validates a font family list according to CSS spec
*/
class HTMLPurifier_AttrDef_CSS_FontFamily extends HTMLPurifier_AttrDef
{
protected $mask = null;
public function __construct()
{
// Lowercase letters
$l = range('a', 'z');
// Uppercase letters
$u = range('A', 'Z');
// Digits
$d = range('0', '9');
// Special bytes used by UTF-8
$b = array_map('chr', range(0x80, 0xFF));
// All valid characters for the mask
$c = array_merge($l, $u, $d, $b);
// Concatenate all valid characters into a string
// Use '_- ' as an initial value
$this->mask = array_reduce($c, function ($carry, $value) {
return $carry . $value;
}, '_- ');
/*
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.
}
/**
* @param string $string
* @param HTMLPurifier_Config $config
* @param HTMLPurifier_Context $context
* @return bool|string
*/
public function validate($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, underscores 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
|
