view scripts/generate-ini.py @ 6532:33b71a130b16

templates: properly escape inline JavaScript values TLDR: Kallithea has issues with escaping values for use in inline JS. Despite judicious poking of the code, no actual security vulnerabilities have been found, just lots of corner-case bugs. This patch fixes those, and hardens the code against actual security issues. The long version: To embed a Python value (typically a 'unicode' plain-text value) in a larger file, it must be escaped in a context specific manner. Example: >>> s = u'<script>alert("It\'s a trap!");</script>' 1) Escaped for insertion into HTML element context >>> print cgi.escape(s) &lt;script&gt;alert("It's a trap!");&lt;/script&gt; 2) Escaped for insertion into HTML element or attribute context >>> print h.escape(s) &lt;script&gt;alert(&#34;It&#39;s a trap!&#34;);&lt;/script&gt; This is the default Mako escaping, as usually used by Kallithea. 3) Encoded as JSON >>> print json.dumps(s) "<script>alert(\"It's a trap!\");</script>" 4) Escaped for insertion into a JavaScript file >>> print '(' + json.dumps(s) + ')' ("<script>alert(\"It's a trap!\");</script>") The parentheses are not actually required for strings, but may be needed to avoid syntax errors if the value is a number or dict (object). 5) Escaped for insertion into a HTML inline <script> element >>> print h.js(s) ("\x3cscript\x3ealert(\"It's a trap!\");\x3c/script\x3e") Here, we need to combine JS and HTML escaping, further complicated by the fact that "<script>" tag contents can either be parsed in XHTML mode (in which case '<', '>' and '&' must additionally be XML escaped) or HTML mode (in which case '</script>' must be escaped, but not using HTML escaping, which is not available in HTML "<script>" tags). Therefore, the XML special characters (which can only occur in string literals) are escaped using JavaScript string literal escape sequences. (This, incidentally, is why modern web security best practices ban all use of inline JavaScript...) Unsurprisingly, Kallithea does not do (5) correctly. In most cases, Kallithea might slap a pair of single quotes around the HTML escaped Python value. A typical benign example: $('#child_link').html('${_('No revisions')}'); This works in English, but if a localized version of the string contains an apostrophe, the result will be broken JavaScript. In the more severe cases, where the text is user controllable, it leaves the door open to injections. In this example, the script inserts the string as HTML, so Mako's implicit HTML escaping makes sense; but in many other cases, HTML escaping is actually an error, because the value is not used by the script in an HTML context. The good news is that the HTML escaping thwarts attempts at XSS, since it's impossible to inject syntactically valid JavaScript of any useful complexity. It does allow JavaScript errors and gibberish to appear on the page, though. In these cases, the escaping has been fixed to use either the new 'h.js' helper, which does JavaScript escaping (but not HTML escaping), OR the new 'h.jshtml' helper (which does both), in those cases where it was unclear if the value might be used (by the script) in an HTML context. Some of these can probably be "relaxed" from h.jshtml to h.js later, but for now, using h.jshtml fixes escaping and doesn't introduce new errors. In a few places, Kallithea JSON encodes values in the controller, then inserts the JSON (without any further escaping) into <script> tags. This is also wrong, and carries actual risk of XSS vulnerabilities. However, in all cases, security vulnerabilities were narrowly avoided due to other filtering in Kallithea. (E.g. many special characters are banned from appearing in usernames.) In these cases, the escaping has been fixed and moved to the template, making it immediately visible that proper escaping has been performed. Mini-FAQ (frequently anticipated questions): Q: Why do everything in one big, hard to review patch? Q: Why add escaping in specific case FOO, it doesn't seem needed? Because the goal here is to have "escape everywhere" as the default policy, rather than identifying individual bugs and fixing them one by one by adding escaping where needed. As such, this patch surely introduces a lot of needless escaping. This is no different from how Mako/Pylons HTML escape everything by default, even when not needed: it's errs on the side of needless work, to prevent erring on the side of skipping required (and security critical) work. As for reviewability, the most important thing to notice is not where escaping has been introduced, but any places where it might have been missed (or where h.jshtml is needed, but h.js is used). Q: The added escaping is kinda verbose/ugly. That is not a question, but yes, I agree. Hopefully it'll encourage us to move away from inline JavaScript altogether. That's a significantly larger job, though; with luck this patch will keep us safe and secure until such a time as we can implement the real fix. Q: Why not use Mako filter syntax ("${val|h.js}")? Because of long-standing Mako bug #140, preventing use of 'h' in filters. Q: Why not work around bug #140, or even use straight "${val|js}"? Because Mako still applies the default h.escape filter before the explicitly specified filters. Q: Where do we go from here? Longer term, we should stop doing variable expansions in script blocks, and instead pass data to JS via e.g. data attributes, or asynchronously using AJAX calls. Once we've done that, we can remove inline JavaScript altogether in favor of separate script files, and set a strict Content Security Policy explicitly blocking inline scripting, and thus also the most common kind of cross-site scripting attack.
author Søren Løvborg <sorenl@unity3d.com>
date Tue, 28 Feb 2017 17:19:00 +0100
parents d89d586b26ae
children 213085032127
line wrap: on
line source

#!/usr/bin/env python2
"""
Based on kallithea/bin/template.ini.mako, generate
  kallithea/config/deployment.ini_tmpl
  development.ini
  kallithea/tests/test.ini
"""

import re

makofile = 'kallithea/bin/template.ini.mako'

# the mako conditionals used in all other ini files and templates
selected_mako_conditionals = set([
    "database_engine == 'sqlite'",
    "http_server == 'waitress'",
    "error_aggregation_service == 'appenlight'",
    "error_aggregation_service == 'sentry'",
])

# the mako variables used in all other ini files and templates
mako_variable_values = {
    'host': '127.0.0.1',
    'port': '5000',
    'here': '%(here)s',
    'uuid()': '${app_instance_uuid}',
}

# files to be generated from the mako template
ini_files = [
    ('kallithea/config/deployment.ini_tmpl',
        '''
        Kallithea - Example config

        The %(here)s variable will be replaced with the parent directory of this file
        ''',
        {}, # exactly the same settings as template.ini.mako
    ),
    ('kallithea/tests/test.ini',
        '''
        Kallithea - config for tests:
        initial_repo_scan = true
        sqlalchemy and kallithea_test.sqlite
        custom logging

        The %(here)s variable will be replaced with the parent directory of this file
        ''',
        {
            '[server:main]': {
                'port': '4999',
            },
            '[app:main]': {
                'initial_repo_scan': 'true',
                'app_instance_uuid': 'test',
                'show_revision_number': 'true',
                'beaker.cache.sql_cache_short.expire': '1',
                'beaker.session.secret': '{74e0cd75-b339-478b-b129-07dd221def1f}',
                'cache_dir': '%(here)s/../../data/test/cache',
                'index_dir': '%(here)s/../../data/test/index',
                'archive_cache_dir': '%(here)s/../../data/test/tarballcache',
                'beaker.cache.data_dir': '%(here)s/../../data/test/cache/data',
                'beaker.cache.lock_dir': '%(here)s/../../data/test/cache/lock',
                'sqlalchemy.url': 'sqlite:///%(here)s/kallithea_test.sqlite',
            },
            '[handler_console]': {
                'level': 'DEBUG',
                'formatter': 'color_formatter',
            },
            # The 'handler_console_sql' block is very similar to the one in
            # development.ini, but without the explicit 'level=DEBUG' setting:
            # it causes duplicate sqlalchemy debug logs, one through
            # handler_console_sql and another through another path.
            '[handler_console_sql]': {
                'formatter': 'color_formatter_sql',
            },
        },
    ),
    ('development.ini',
        '''
        Kallithea - Development config:
        listening on *:5000
        sqlite and kallithea.db
        initial_repo_scan = true
        set debug = true
        verbose and colorful logging

        The %(here)s variable will be replaced with the parent directory of this file
        ''',
        {
            '[server:main]': {
                'host': '0.0.0.0',
            },
            '[app:main]': {
                'initial_repo_scan': 'true',
                'set debug': 'true',
                'app_instance_uuid': 'development-not-secret',
                'beaker.session.secret': 'development-not-secret',
            },
            '[handler_console]': {
                'level': 'DEBUG',
                'formatter': 'color_formatter',
            },
            '[handler_console_sql]': {
                'level': 'DEBUG',
                'formatter': 'color_formatter_sql',
            },
        },
    ),
]


def main():
    # make sure all mako lines starting with '#' (the '##' comments) are marked up as <text>
    print 'reading:', makofile
    mako_org = file(makofile).read()
    mako_no_text_markup = re.sub(r'</?%text>', '', mako_org)
    mako_marked_up = re.sub(r'\n(##.*)', r'\n<%text>\1</%text>', mako_no_text_markup, flags=re.MULTILINE)
    if mako_marked_up != mako_org:
        print 'writing:', makofile
        file(makofile, 'w').write(mako_marked_up)

    # select the right mako conditionals for the other less sophisticated formats
    def sub_conditionals(m):
        """given a %if...%endif match, replace with just the selected
        conditional sections enabled and the rest as comments
        """
        conditional_lines = m.group(1)
        def sub_conditional(m):
            """given a conditional and the corresponding lines, return them raw
            or commented out, based on whether conditional is selected
            """
            criteria, lines = m.groups()
            if criteria not in selected_mako_conditionals:
                lines = '\n'.join((l if not l or l.startswith('#') else '#' + l) for l in lines.split('\n'))
            return lines
        conditional_lines = re.sub(r'^%(?:el)?if (.*):\n((?:^[^%\n].*\n|\n)*)',
            sub_conditional, conditional_lines, flags=re.MULTILINE)
        return conditional_lines
    mako_no_conditionals = re.sub(r'^(%if .*\n(?:[^%\n].*\n|%elif .*\n|\n)*)%endif\n',
        sub_conditionals, mako_no_text_markup, flags=re.MULTILINE)

    # expand mako variables
    def pyrepl(m):
        return mako_variable_values.get(m.group(1), m.group(0))
    mako_no_variables = re.sub(r'\${([^}]*)}', pyrepl, mako_no_conditionals)

    # remove utf-8 coding header
    base_ini = re.sub(r'^## -\*- coding: utf-8 -\*-\n', '', mako_no_variables)

    # create ini files
    for fn, desc, settings in ini_files:
        print 'updating:', fn
        ini_lines = re.sub(
            '# Kallithea - config file generated with kallithea-config *#\n',
            ''.join('# %-77s#\n' % l.strip() for l in desc.strip().split('\n')),
            base_ini)
        def process_section(m):
            """process a ini section, replacing values as necessary"""
            sectionname, lines = m.groups()
            if sectionname in settings:
                section_settings = settings[sectionname]
                def process_line(m):
                    """process a section line and update value if necessary"""
                    setting, value = m.groups()
                    line = m.group(0)
                    if setting in section_settings:
                        line = '%s = %s' % (setting, section_settings[setting])
                        if '$' not in value:
                            line = '#%s = %s\n%s' % (setting, value, line)
                    return line.rstrip()
                lines = re.sub(r'^([^#\n].*) = ?(.*)', process_line, lines, flags=re.MULTILINE)
            return sectionname + '\n' + lines
        ini_lines = re.sub(r'^(\[.*\])\n((?:(?:[^[\n].*)?\n)*)', process_section, ini_lines, flags=re.MULTILINE)
        file(fn, 'w').write(ini_lines)

if __name__ == '__main__':
    main()