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.
# unionrepo.py - repository class for viewing union of repository changesets
#
# Derived from bundlerepo.py
# Copyright 2006, 2007 Benoit Boissinot <bboissin@gmail.com>
# Copyright 2013 Unity Technologies, Mads Kiilerich <madski@unity3d.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""Repository class for "in-memory pull" of one local repository to another,
allowing operations like diff and log with revsets.
"""
from __future__ import absolute_import
from .i18n import _
from .node import nullid
from . import (
changelog,
cmdutil,
error,
filelog,
localrepo,
manifest,
mdiff,
pathutil,
pycompat,
revlog,
scmutil,
util,
)
class unionrevlog(revlog.revlog):
def __init__(self, opener, indexfile, revlog2, linkmapper):
# How it works:
# To retrieve a revision, we just need to know the node id so we can
# look it up in revlog2.
#
# To differentiate a rev in the second revlog from a rev in the revlog,
# we check revision against repotiprev.
opener = scmutil.readonlyvfs(opener)
revlog.revlog.__init__(self, opener, indexfile)
self.revlog2 = revlog2
n = len(self)
self.repotiprev = n - 1
self.bundlerevs = set() # used by 'bundle()' revset expression
for rev2 in self.revlog2:
rev = self.revlog2.index[rev2]
# rev numbers - in revlog2, very different from self.rev
_start, _csize, _rsize, base, linkrev, p1rev, p2rev, node = rev
flags = _start & 0xFFFF
if linkmapper is None: # link is to same revlog
assert linkrev == rev2 # we never link back
link = n
else: # rev must be mapped from repo2 cl to unified cl by linkmapper
link = linkmapper(linkrev)
if linkmapper is not None: # link is to same revlog
base = linkmapper(base)
if node in self.nodemap:
# this happens for the common revlog revisions
self.bundlerevs.add(self.nodemap[node])
continue
p1node = self.revlog2.node(p1rev)
p2node = self.revlog2.node(p2rev)
e = (flags, None, None, base,
link, self.rev(p1node), self.rev(p2node), node)
self.index.insert(-1, e)
self.nodemap[node] = n
self.bundlerevs.add(n)
n += 1
def _chunk(self, rev):
if rev <= self.repotiprev:
return revlog.revlog._chunk(self, rev)
return self.revlog2._chunk(self.node(rev))
def revdiff(self, rev1, rev2):
"""return or calculate a delta between two revisions"""
if rev1 > self.repotiprev and rev2 > self.repotiprev:
return self.revlog2.revdiff(
self.revlog2.rev(self.node(rev1)),
self.revlog2.rev(self.node(rev2)))
elif rev1 <= self.repotiprev and rev2 <= self.repotiprev:
return self.baserevdiff(rev1, rev2)
return mdiff.textdiff(self.revision(self.node(rev1)),
self.revision(self.node(rev2)))
def revision(self, nodeorrev, raw=False):
"""return an uncompressed revision of a given node or revision
number.
"""
if isinstance(nodeorrev, int):
rev = nodeorrev
node = self.node(rev)
else:
node = nodeorrev
rev = self.rev(node)
if node == nullid:
return ""
if rev > self.repotiprev:
text = self.revlog2.revision(node)
self._cache = (node, rev, text)
else:
text = self.baserevision(rev)
# already cached
return text
def baserevision(self, nodeorrev):
# Revlog subclasses may override 'revision' method to modify format of
# content retrieved from revlog. To use unionrevlog with such class one
# needs to override 'baserevision' and make more specific call here.
return revlog.revlog.revision(self, nodeorrev)
def baserevdiff(self, rev1, rev2):
# Exists for the same purpose as baserevision.
return revlog.revlog.revdiff(self, rev1, rev2)
def addrevision(self, text, transaction, link, p1=None, p2=None, d=None):
raise NotImplementedError
def addgroup(self, revs, linkmapper, transaction):
raise NotImplementedError
def strip(self, rev, minlink):
raise NotImplementedError
def checksize(self):
raise NotImplementedError
class unionchangelog(unionrevlog, changelog.changelog):
def __init__(self, opener, opener2):
changelog.changelog.__init__(self, opener)
linkmapper = None
changelog2 = changelog.changelog(opener2)
unionrevlog.__init__(self, opener, self.indexfile, changelog2,
linkmapper)
def baserevision(self, nodeorrev):
# Although changelog doesn't override 'revision' method, some extensions
# may replace this class with another that does. Same story with
# manifest and filelog classes.
return changelog.changelog.revision(self, nodeorrev)
def baserevdiff(self, rev1, rev2):
return changelog.changelog.revdiff(self, rev1, rev2)
class unionmanifest(unionrevlog, manifest.manifestrevlog):
def __init__(self, opener, opener2, linkmapper):
manifest.manifestrevlog.__init__(self, opener)
manifest2 = manifest.manifestrevlog(opener2)
unionrevlog.__init__(self, opener, self.indexfile, manifest2,
linkmapper)
def baserevision(self, nodeorrev):
return manifest.manifestrevlog.revision(self, nodeorrev)
def baserevdiff(self, rev1, rev2):
return manifest.manifestrevlog.revdiff(self, rev1, rev2)
class unionfilelog(unionrevlog, filelog.filelog):
def __init__(self, opener, path, opener2, linkmapper, repo):
filelog.filelog.__init__(self, opener, path)
filelog2 = filelog.filelog(opener2, path)
unionrevlog.__init__(self, opener, self.indexfile, filelog2,
linkmapper)
self._repo = repo
def baserevision(self, nodeorrev):
return filelog.filelog.revision(self, nodeorrev)
def baserevdiff(self, rev1, rev2):
return filelog.filelog.revdiff(self, rev1, rev2)
def iscensored(self, rev):
"""Check if a revision is censored."""
if rev <= self.repotiprev:
return filelog.filelog.iscensored(self, rev)
node = self.node(rev)
return self.revlog2.iscensored(self.revlog2.rev(node))
class unionpeer(localrepo.localpeer):
def canpush(self):
return False
class unionrepository(localrepo.localrepository):
def __init__(self, ui, path, path2):
localrepo.localrepository.__init__(self, ui, path)
self.ui.setconfig('phases', 'publish', False, 'unionrepo')
self._url = 'union:%s+%s' % (util.expandpath(path),
util.expandpath(path2))
self.repo2 = localrepo.localrepository(ui, path2)
@localrepo.unfilteredpropertycache
def changelog(self):
return unionchangelog(self.svfs, self.repo2.svfs)
def _clrev(self, rev2):
"""map from repo2 changelog rev to temporary rev in self.changelog"""
node = self.repo2.changelog.node(rev2)
return self.changelog.rev(node)
def _constructmanifest(self):
return unionmanifest(self.svfs, self.repo2.svfs,
self.unfiltered()._clrev)
def url(self):
return self._url
def file(self, f):
return unionfilelog(self.svfs, f, self.repo2.svfs,
self.unfiltered()._clrev, self)
def close(self):
self.repo2.close()
def cancopy(self):
return False
def peer(self):
return unionpeer(self)
def getcwd(self):
return pycompat.getcwd() # always outside the repo
def instance(ui, path, create):
if create:
raise error.Abort(_('cannot create new union repository'))
parentpath = ui.config("bundle", "mainreporoot", "")
if not parentpath:
# try to find the correct path to the working directory repo
parentpath = cmdutil.findrepo(pycompat.getcwd())
if parentpath is None:
parentpath = ''
if parentpath:
# Try to make the full path relative so we get a nice, short URL.
# In particular, we don't want temp dir names in test outputs.
cwd = pycompat.getcwd()
if parentpath == cwd:
parentpath = ''
else:
cwd = pathutil.normasprefix(cwd)
if parentpath.startswith(cwd):
parentpath = parentpath[len(cwd):]
if path.startswith('union:'):
s = path.split(":", 1)[1].split("+", 1)
if len(s) == 1:
repopath, repopath2 = parentpath, s[0]
else:
repopath, repopath2 = s
else:
repopath, repopath2 = parentpath, path
return unionrepository(ui, repopath, repopath2)