view mercurial/hgweb/hgweb_mod.py @ 30766:d7bf7d2bd5ab

hgweb: support Content Security Policy

Content-Security-Policy (CSP) is a web security feature that allows
servers to declare what loaded content is allowed to do. For example,
a policy can prevent loading of images, JavaScript, CSS, etc unless
the source of that content is whitelisted (by hostname, URI scheme,
hashes of content, etc). It's a nifty security feature that provides
extra mitigation against some attacks, notably XSS.

Mitigation against these attacks is important for Mercurial because
hgweb renders repository data, which is commonly untrusted. While we
make attempts to escape things, etc, there's the possibility that
malicious data could be injected into the site content. If this happens
today, the full power of the web browser is available to that
malicious content. A restrictive CSP policy (defined by the server
operator and sent in an HTTP header which is outside the control of
malicious content), could restrict browser capabilities and mitigate
security problems posed by malicious data.

CSP works by emitting an HTTP header declaring the policy that browsers
should apply. Ideally, this header would be emitted by a layer above
Mercurial (likely the HTTP server doing the WSGI "proxying"). This
works for some CSP policies, but not all.

For example, policies to allow inline JavaScript may require setting
a "nonce" attribute on <script>. This attribute value must be unique
and non-guessable. And, the value must be present in the HTTP header
and the HTML body. This means that coordinating the value between
Mercurial and another HTTP server could be difficult: it is much
easier to generate and emit the nonce in a central location.

This commit introduces support for emitting a
Content-Security-Policy header from hgweb. A config option defines
the header value. If present, the header is emitted. A special
"%nonce%" syntax in the value triggers generation of a nonce and
inclusion in <script> elements in templates. The inclusion of a
nonce does not occur unless "%nonce%" is present. This makes this
commit completely backwards compatible and the feature opt-in.

The nonce is a type 4 UUID, which is the flavor that is randomly
generated. It has 122 random bits, which should be plenty to satisfy
the guarantees of a nonce.

# hgweb/hgweb_mod.py - Web interface for a repository.
#
# Copyright 21 May 2005 - (c) 2005 Jake Edge <[e-mail]>
# Copyright 2005-2007 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import contextlib
import os

from .common import (
    ErrorResponse,
    HTTP_BAD_REQUEST,
    HTTP_NOT_FOUND,
    HTTP_NOT_MODIFIED,
    HTTP_OK,
    HTTP_SERVER_ERROR,
    caching,
    cspvalues,
    permhooks,
)
from .request import wsgirequest

from .. import (
    encoding,
    error,
    hg,
    hook,
    profiling,
    repoview,
    templatefilters,
    templater,
    ui as uimod,
    util,
)

from . import (
    protocol,
    webcommands,
    webutil,
    wsgicgi,
)

perms = {
    'changegroup': 'pull',
    'changegroupsubset': 'pull',
    'getbundle': 'pull',
    'stream_out': 'pull',
    'listkeys': 'pull',
    'unbundle': 'push',
    'pushkey': 'push',
}

archivespecs = util.sortdict((
    ('zip', ('application/zip', 'zip', '.zip', None)),
    ('gz', ('application/x-gzip', 'tgz', '.tar.gz', None)),
    ('bz2', ('application/x-bzip2', 'tbz2', '.tar.bz2', None)),
))

def makebreadcrumb(url, prefix=''):
    '''Return a 'URL breadcrumb' list

    A 'URL breadcrumb' is a list of URL-name pairs,
    corresponding to each of the path items on a URL.
    This can be used to create path navigation entries.
    '''
    if url.endswith('/'):
        url = url[:-1]
    if prefix:
        url = '/' + prefix + url
    relpath = url
    if relpath.startswith('/'):
        relpath = relpath[1:]

    breadcrumb = []
    urlel = url
    pathitems = [''] + relpath.split('/')
    for pathel in reversed(pathitems):
        if not pathel or not urlel:
            break
        breadcrumb.append({'url': urlel, 'name': pathel})
        urlel = os.path.dirname(urlel)
    return reversed(breadcrumb)

class requestcontext(object):
    """Holds state/context for an individual request.

    Servers can be multi-threaded. Holding state on the WSGI application
    is prone to race conditions. Instances of this class exist to hold
    mutable and race-free state for requests.
    """
    def __init__(self, app, repo):
        self.repo = repo
        self.reponame = app.reponame

        self.archivespecs = archivespecs

        self.maxchanges = self.configint('web', 'maxchanges', 10)
        self.stripecount = self.configint('web', 'stripes', 1)
        self.maxshortchanges = self.configint('web', 'maxshortchanges', 60)
        self.maxfiles = self.configint('web', 'maxfiles', 10)
        self.allowpull = self.configbool('web', 'allowpull', True)

        # we use untrusted=False to prevent a repo owner from using
        # web.templates in .hg/hgrc to get access to any file readable
        # by the user running the CGI script
        self.templatepath = self.config('web', 'templates', untrusted=False)

        # This object is more expensive to build than simple config values.
        # It is shared across requests. The app will replace the object
        # if it is updated. Since this is a reference and nothing should
        # modify the underlying object, it should be constant for the lifetime
        # of the request.
        self.websubtable = app.websubtable

        self.csp, self.nonce = cspvalues(self.repo.ui)

    # Trust the settings from the .hg/hgrc files by default.
    def config(self, section, name, default=None, untrusted=True):
        return self.repo.ui.config(section, name, default,
                                   untrusted=untrusted)

    def configbool(self, section, name, default=False, untrusted=True):
        return self.repo.ui.configbool(section, name, default,
                                       untrusted=untrusted)

    def configint(self, section, name, default=None, untrusted=True):
        return self.repo.ui.configint(section, name, default,
                                      untrusted=untrusted)

    def configlist(self, section, name, default=None, untrusted=True):
        return self.repo.ui.configlist(section, name, default,
                                       untrusted=untrusted)

    def archivelist(self, nodeid):
        allowed = self.configlist('web', 'allow_archive')
        for typ, spec in self.archivespecs.iteritems():
            if typ in allowed or self.configbool('web', 'allow%s' % typ):
                yield {'type': typ, 'extension': spec[2], 'node': nodeid}

    def templater(self, req):
        # determine scheme, port and server name
        # this is needed to create absolute urls

        proto = req.env.get('wsgi.url_scheme')
        if proto == 'https':
            proto = 'https'
            default_port = '443'
        else:
            proto = 'http'
            default_port = '80'

        port = req.env['SERVER_PORT']
        port = port != default_port and (':' + port) or ''
        urlbase = '%s://%s%s' % (proto, req.env['SERVER_NAME'], port)
        logourl = self.config('web', 'logourl', 'https://mercurial-scm.org/')
        logoimg = self.config('web', 'logoimg', 'hglogo.png')
        staticurl = self.config('web', 'staticurl') or req.url + 'static/'
        if not staticurl.endswith('/'):
            staticurl += '/'

        # some functions for the templater

        def motd(**map):
            yield self.config('web', 'motd', '')

        # figure out which style to use

        vars = {}
        styles = (
            req.form.get('style', [None])[0],
            self.config('web', 'style'),
            'paper',
        )
        style, mapfile = templater.stylemap(styles, self.templatepath)
        if style == styles[0]:
            vars['style'] = style

        start = req.url[-1] == '?' and '&' or '?'
        sessionvars = webutil.sessionvars(vars, start)

        if not self.reponame:
            self.reponame = (self.config('web', 'name')
                             or req.env.get('REPO_NAME')
                             or req.url.strip('/') or self.repo.root)

        def websubfilter(text):
            return templatefilters.websub(text, self.websubtable)

        # create the templater

        defaults = {
            'url': req.url,
            'logourl': logourl,
            'logoimg': logoimg,
            'staticurl': staticurl,
            'urlbase': urlbase,
            'repo': self.reponame,
            'encoding': encoding.encoding,
            'motd': motd,
            'sessionvars': sessionvars,
            'pathdef': makebreadcrumb(req.url),
            'style': style,
            'nonce': self.nonce,
        }
        tmpl = templater.templater.frommapfile(mapfile,
                                               filters={'websub': websubfilter},
                                               defaults=defaults)
        return tmpl


class hgweb(object):
    """HTTP server for individual repositories.

    Instances of this class serve HTTP responses for a particular
    repository.

    Instances are typically used as WSGI applications.

    Some servers are multi-threaded. On these servers, there may
    be multiple active threads inside __call__.
    """
    def __init__(self, repo, name=None, baseui=None):
        if isinstance(repo, str):
            if baseui:
                u = baseui.copy()
            else:
                u = uimod.ui.load()
            r = hg.repository(u, repo)
        else:
            # we trust caller to give us a private copy
            r = repo

        r.ui.setconfig('ui', 'report_untrusted', 'off', 'hgweb')
        r.baseui.setconfig('ui', 'report_untrusted', 'off', 'hgweb')
        r.ui.setconfig('ui', 'nontty', 'true', 'hgweb')
        r.baseui.setconfig('ui', 'nontty', 'true', 'hgweb')
        # resolve file patterns relative to repo root
        r.ui.setconfig('ui', 'forcecwd', r.root, 'hgweb')
        r.baseui.setconfig('ui', 'forcecwd', r.root, 'hgweb')
        # displaying bundling progress bar while serving feel wrong and may
        # break some wsgi implementation.
        r.ui.setconfig('progress', 'disable', 'true', 'hgweb')
        r.baseui.setconfig('progress', 'disable', 'true', 'hgweb')
        self._repos = [hg.cachedlocalrepo(self._webifyrepo(r))]
        self._lastrepo = self._repos[0]
        hook.redirect(True)
        self.reponame = name

    def _webifyrepo(self, repo):
        repo = getwebview(repo)
        self.websubtable = webutil.getwebsubs(repo)
        return repo

    @contextlib.contextmanager
    def _obtainrepo(self):
        """Obtain a repo unique to the caller.

        Internally we maintain a stack of cachedlocalrepo instances
        to be handed out. If one is available, we pop it and return it,
        ensuring it is up to date in the process. If one is not available,
        we clone the most recently used repo instance and return it.

        It is currently possible for the stack to grow without bounds
        if the server allows infinite threads. However, servers should
        have a thread limit, thus establishing our limit.
        """
        if self._repos:
            cached = self._repos.pop()
            r, created = cached.fetch()
        else:
            cached = self._lastrepo.copy()
            r, created = cached.fetch()
        if created:
            r = self._webifyrepo(r)

        self._lastrepo = cached
        self.mtime = cached.mtime
        try:
            yield r
        finally:
            self._repos.append(cached)

    def run(self):
        """Start a server from CGI environment.

        Modern servers should be using WSGI and should avoid this
        method, if possible.
        """
        if not encoding.environ.get('GATEWAY_INTERFACE',
                                    '').startswith("CGI/1."):
            raise RuntimeError("This function is only intended to be "
                               "called while running as a CGI script.")
        wsgicgi.launch(self)

    def __call__(self, env, respond):
        """Run the WSGI application.

        This may be called by multiple threads.
        """
        req = wsgirequest(env, respond)
        return self.run_wsgi(req)

    def run_wsgi(self, req):
        """Internal method to run the WSGI application.

        This is typically only called by Mercurial. External consumers
        should be using instances of this class as the WSGI application.
        """
        with self._obtainrepo() as repo:
            with profiling.maybeprofile(repo.ui):
                for r in self._runwsgi(req, repo):
                    yield r

    def _runwsgi(self, req, repo):
        rctx = requestcontext(self, repo)

        # This state is global across all threads.
        encoding.encoding = rctx.config('web', 'encoding', encoding.encoding)
        rctx.repo.ui.environ = req.env

        if rctx.csp:
            # hgwebdir may have added CSP header. Since we generate our own,
            # replace it.
            req.headers = [h for h in req.headers
                           if h[0] != 'Content-Security-Policy']
            req.headers.append(('Content-Security-Policy', rctx.csp))

        # work with CGI variables to create coherent structure
        # use SCRIPT_NAME, PATH_INFO and QUERY_STRING as well as our REPO_NAME

        req.url = req.env['SCRIPT_NAME']
        if not req.url.endswith('/'):
            req.url += '/'
        if 'REPO_NAME' in req.env:
            req.url += req.env['REPO_NAME'] + '/'

        if 'PATH_INFO' in req.env:
            parts = req.env['PATH_INFO'].strip('/').split('/')
            repo_parts = req.env.get('REPO_NAME', '').split('/')
            if parts[:len(repo_parts)] == repo_parts:
                parts = parts[len(repo_parts):]
            query = '/'.join(parts)
        else:
            query = req.env['QUERY_STRING'].partition('&')[0]
            query = query.partition(';')[0]

        # process this if it's a protocol request
        # protocol bits don't need to create any URLs
        # and the clients always use the old URL structure

        cmd = req.form.get('cmd', [''])[0]
        if protocol.iscmd(cmd):
            try:
                if query:
                    raise ErrorResponse(HTTP_NOT_FOUND)
                if cmd in perms:
                    self.check_perm(rctx, req, perms[cmd])
                return protocol.call(rctx.repo, req, cmd)
            except ErrorResponse as inst:
                # A client that sends unbundle without 100-continue will
                # break if we respond early.
                if (cmd == 'unbundle' and
                    (req.env.get('HTTP_EXPECT',
                                 '').lower() != '100-continue') or
                    req.env.get('X-HgHttp2', '')):
                    req.drain()
                else:
                    req.headers.append(('Connection', 'Close'))
                req.respond(inst, protocol.HGTYPE,
                            body='0\n%s\n' % inst)
                return ''

        # translate user-visible url structure to internal structure

        args = query.split('/', 2)
        if 'cmd' not in req.form and args and args[0]:

            cmd = args.pop(0)
            style = cmd.rfind('-')
            if style != -1:
                req.form['style'] = [cmd[:style]]
                cmd = cmd[style + 1:]

            # avoid accepting e.g. style parameter as command
            if util.safehasattr(webcommands, cmd):
                req.form['cmd'] = [cmd]

            if cmd == 'static':
                req.form['file'] = ['/'.join(args)]
            else:
                if args and args[0]:
                    node = args.pop(0).replace('%2F', '/')
                    req.form['node'] = [node]
                if args:
                    req.form['file'] = args

            ua = req.env.get('HTTP_USER_AGENT', '')
            if cmd == 'rev' and 'mercurial' in ua:
                req.form['style'] = ['raw']

            if cmd == 'archive':
                fn = req.form['node'][0]
                for type_, spec in rctx.archivespecs.iteritems():
                    ext = spec[2]
                    if fn.endswith(ext):
                        req.form['node'] = [fn[:-len(ext)]]
                        req.form['type'] = [type_]

        # process the web interface request

        try:
            tmpl = rctx.templater(req)
            ctype = tmpl('mimetype', encoding=encoding.encoding)
            ctype = templater.stringify(ctype)

            # check read permissions non-static content
            if cmd != 'static':
                self.check_perm(rctx, req, None)

            if cmd == '':
                req.form['cmd'] = [tmpl.cache['default']]
                cmd = req.form['cmd'][0]

            # Don't enable caching if using a CSP nonce because then it wouldn't
            # be a nonce.
            if rctx.configbool('web', 'cache', True) and not rctx.nonce:
                caching(self, req) # sets ETag header or raises NOT_MODIFIED
            if cmd not in webcommands.__all__:
                msg = 'no such method: %s' % cmd
                raise ErrorResponse(HTTP_BAD_REQUEST, msg)
            elif cmd == 'file' and 'raw' in req.form.get('style', []):
                rctx.ctype = ctype
                content = webcommands.rawfile(rctx, req, tmpl)
            else:
                content = getattr(webcommands, cmd)(rctx, req, tmpl)
                req.respond(HTTP_OK, ctype)

            return content

        except (error.LookupError, error.RepoLookupError) as err:
            req.respond(HTTP_NOT_FOUND, ctype)
            msg = str(err)
            if (util.safehasattr(err, 'name') and
                not isinstance(err,  error.ManifestLookupError)):
                msg = 'revision not found: %s' % err.name
            return tmpl('error', error=msg)
        except (error.RepoError, error.RevlogError) as inst:
            req.respond(HTTP_SERVER_ERROR, ctype)
            return tmpl('error', error=str(inst))
        except ErrorResponse as inst:
            req.respond(inst, ctype)
            if inst.code == HTTP_NOT_MODIFIED:
                # Not allowed to return a body on a 304
                return ['']
            return tmpl('error', error=str(inst))

    def check_perm(self, rctx, req, op):
        for permhook in permhooks:
            permhook(rctx, req, op)

def getwebview(repo):
    """The 'web.view' config controls changeset filter to hgweb. Possible
    values are ``served``, ``visible`` and ``all``. Default is ``served``.
    The ``served`` filter only shows changesets that can be pulled from the
    hgweb instance.  The``visible`` filter includes secret changesets but
    still excludes "hidden" one.

    See the repoview module for details.

    The option has been around undocumented since Mercurial 2.5, but no
    user ever asked about it. So we better keep it undocumented for now."""
    viewconfig = repo.ui.config('web', 'view', 'served',
                                untrusted=True)
    if viewconfig == 'all':
        return repo.unfiltered()
    elif viewconfig in repoview.filtertable:
        return repo.filtered(viewconfig)
    else:
        return repo.filtered('served')