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
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
|
# Copyright 2009-2011 Canonical Ltd. This software is licensed under the
# GNU Affero General Public License version 3 (see the file LICENSE).
"""Safe branch opening."""
__metaclass__ = type
import threading
from bzrlib import (
errors,
trace,
urlutils,
)
from bzrlib.branch import Branch
from bzrlib.bzrdir import (
BzrProber,
RemoteBzrProber,
)
from bzrlib.transport import (
do_catching_redirections,
get_transport,
)
from lazr.uri import URI
__all__ = [
'AcceptAnythingPolicy',
'BadUrl',
'BlacklistPolicy',
'BranchLoopError',
'BranchOpenPolicy',
'BranchReferenceForbidden',
'SafeBranchOpener',
'WhitelistPolicy',
'safe_open',
]
# TODO JelmerVernooij 2011-08-06: This module is generic enough to be
# in bzrlib, and may be of use to others. bug=850843
# These are the default probers that SafeBranchOpener will try to use,
# unless a different set was specified.
DEFAULT_PROBERS = [BzrProber, RemoteBzrProber]
class BadUrl(Exception):
"""Tried to access a branch from a bad URL."""
class BranchReferenceForbidden(Exception):
"""Trying to mirror a branch reference and the branch type does not allow
references.
"""
class BranchLoopError(Exception):
"""Encountered a branch cycle.
A URL may point to a branch reference or it may point to a stacked branch.
In either case, it's possible for there to be a cycle in these references,
and this exception is raised when we detect such a cycle.
"""
class BranchOpenPolicy:
"""Policy on how to open branches.
In particular, a policy determines which branches are safe to open by
checking their URLs and deciding whether or not to follow branch
references.
"""
def shouldFollowReferences(self):
"""Whether we traverse references when mirroring.
Subclasses must override this method.
If we encounter a branch reference and this returns false, an error is
raised.
:returns: A boolean to indicate whether to follow a branch reference.
"""
raise NotImplementedError(self.shouldFollowReferences)
def transformFallbackLocation(self, branch, url):
"""Validate, maybe modify, 'url' to be used as a stacked-on location.
:param branch: The branch that is being opened.
:param url: The URL that the branch provides for its stacked-on
location.
:return: (new_url, check) where 'new_url' is the URL of the branch to
actually open and 'check' is true if 'new_url' needs to be
validated by checkAndFollowBranchReference.
"""
raise NotImplementedError(self.transformFallbackLocation)
def checkOneURL(self, url):
"""Check the safety of the source URL.
Subclasses must override this method.
:param url: The source URL to check.
:raise BadUrl: subclasses are expected to raise this or a subclass
when it finds a URL it deems to be unsafe.
"""
raise NotImplementedError(self.checkOneURL)
class BlacklistPolicy(BranchOpenPolicy):
"""Branch policy that forbids certain URLs."""
def __init__(self, should_follow_references, unsafe_urls=None):
if unsafe_urls is None:
unsafe_urls = set()
self._unsafe_urls = unsafe_urls
self._should_follow_references = should_follow_references
def shouldFollowReferences(self):
return self._should_follow_references
def checkOneURL(self, url):
if url in self._unsafe_urls:
raise BadUrl(url)
def transformFallbackLocation(self, branch, url):
"""See `BranchOpenPolicy.transformFallbackLocation`.
This class is not used for testing our smarter stacking features so we
just do the simplest thing: return the URL that would be used anyway
and don't check it.
"""
return urlutils.join(branch.base, url), False
class AcceptAnythingPolicy(BlacklistPolicy):
"""Accept anything, to make testing easier."""
def __init__(self):
super(AcceptAnythingPolicy, self).__init__(True, set())
class WhitelistPolicy(BranchOpenPolicy):
"""Branch policy that only allows certain URLs."""
def __init__(self, should_follow_references, allowed_urls=None,
check=False):
if allowed_urls is None:
allowed_urls = []
self.allowed_urls = set(url.rstrip('/') for url in allowed_urls)
self.check = check
def shouldFollowReferences(self):
return self._should_follow_references
def checkOneURL(self, url):
if url.rstrip('/') not in self.allowed_urls:
raise BadUrl(url)
def transformFallbackLocation(self, branch, url):
"""See `BranchOpenPolicy.transformFallbackLocation`.
Here we return the URL that would be used anyway and optionally check
it.
"""
return urlutils.join(branch.base, url), self.check
class SingleSchemePolicy(BranchOpenPolicy):
"""Branch open policy that rejects URLs not on the given scheme."""
def __init__(self, allowed_scheme):
self.allowed_scheme = allowed_scheme
def shouldFollowReferences(self):
return True
def transformFallbackLocation(self, branch, url):
return urlutils.join(branch.base, url), True
def checkOneURL(self, url):
"""Check that `url` is safe to open."""
if URI(url).scheme != self.allowed_scheme:
raise BadUrl(url)
class SafeBranchOpener(object):
"""Safe branch opener.
All locations that are opened (stacked-on branches, references) are
checked against a policy object.
The policy object is expected to have the following methods:
* checkOneURL
* shouldFollowReferences
* transformFallbackLocation
"""
_threading_data = threading.local()
def __init__(self, policy, probers=None):
"""Create a new SafeBranchOpener.
:param policy: The opener policy to use.
:param probers: Optional list of probers to allow.
Defaults to local and remote bzr probers.
"""
self.policy = policy
self._seen_urls = set()
if probers is None:
self.probers = list(DEFAULT_PROBERS)
else:
self.probers = probers
@classmethod
def install_hook(cls):
"""Install the ``transformFallbackLocation`` hook.
This is done at module import time, but transformFallbackLocationHook
doesn't do anything unless the `_active_openers` threading.Local
object has a 'opener' attribute in this thread.
This is in a module-level function rather than performed at module
level so that it can be called in setUp for testing `SafeBranchOpener`
as bzrlib.tests.TestCase.setUp clears hooks.
"""
Branch.hooks.install_named_hook(
'transform_fallback_location',
cls.transformFallbackLocationHook,
'SafeBranchOpener.transformFallbackLocationHook')
def checkAndFollowBranchReference(self, url):
"""Check URL (and possibly the referenced URL) for safety.
This method checks that `url` passes the policy's `checkOneURL`
method, and if `url` refers to a branch reference, it checks whether
references are allowed and whether the reference's URL passes muster
also -- recursively, until a real branch is found.
:param url: URL to check
:raise BranchLoopError: If the branch references form a loop.
:raise BranchReferenceForbidden: If this opener forbids branch
references.
"""
while True:
if url in self._seen_urls:
raise BranchLoopError()
self._seen_urls.add(url)
self.policy.checkOneURL(url)
next_url = self.followReference(url)
if next_url is None:
return url
url = next_url
if not self.policy.shouldFollowReferences():
raise BranchReferenceForbidden(url)
@classmethod
def transformFallbackLocationHook(cls, branch, url):
"""Installed as the 'transform_fallback_location' Branch hook.
This method calls `transformFallbackLocation` on the policy object and
either returns the url it provides or passes it back to
checkAndFollowBranchReference.
"""
try:
opener = getattr(cls._threading_data, "opener")
except AttributeError:
return url
new_url, check = opener.policy.transformFallbackLocation(branch, url)
if check:
return opener.checkAndFollowBranchReference(new_url)
else:
return new_url
def runWithTransformFallbackLocationHookInstalled(
self, callable, *args, **kw):
assert (self.transformFallbackLocationHook in
Branch.hooks['transform_fallback_location'])
self._threading_data.opener = self
try:
return callable(*args, **kw)
finally:
del self._threading_data.opener
# We reset _seen_urls here to avoid multiple calls to open giving
# spurious loop exceptions.
self._seen_urls = set()
def followReference(self, url):
"""Get the branch-reference value at the specified url.
This exists as a separate method only to be overriden in unit tests.
"""
bzrdir = self._open_dir(url)
return bzrdir.get_branch_reference()
def _open_dir(self, url):
"""Simple BzrDir.open clone that only uses specific probers.
:param url: URL to open
:return: ControlDir instance
"""
def redirected(transport, e, redirection_notice):
self.policy.checkOneURL(e.target)
redirected_transport = transport._redirected_to(
e.source, e.target)
if redirected_transport is None:
raise errors.NotBranchError(e.source)
trace.note('%s is%s redirected to %s',
transport.base, e.permanently, redirected_transport.base)
return redirected_transport
def find_format(transport):
last_error = errors.NotBranchError(transport.base)
for prober_kls in self.probers:
prober = prober_kls()
try:
return transport, prober.probe_transport(transport)
except errors.NotBranchError, e:
last_error = e
else:
raise last_error
transport = get_transport(url)
transport, format = do_catching_redirections(find_format, transport,
redirected)
return format.open(transport)
def open(self, url):
"""Open the Bazaar branch at url, first checking for safety.
What safety means is defined by a subclasses `followReference` and
`checkOneURL` methods.
"""
url = self.checkAndFollowBranchReference(url)
def open_branch(url):
dir = self._open_dir(url)
return dir.open_branch()
return self.runWithTransformFallbackLocationHookInstalled(
open_branch, url)
def safe_open(allowed_scheme, url):
"""Open the branch at `url`, only accessing URLs on `allowed_scheme`.
:raises BadUrl: An attempt was made to open a URL that was not on
`allowed_scheme`.
"""
return SafeBranchOpener(SingleSchemePolicy(allowed_scheme)).open(url)
SafeBranchOpener.install_hook()
|