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1 | ### -*-python-*- |
2 | ### | |
3 | ### Services | |
4 | ### | |
5 | ### (c) 2013 Mark Wooding | |
6 | ### | |
7 | ||
8 | ###----- Licensing notice --------------------------------------------------- | |
9 | ### | |
10 | ### This file is part of Chopwood: a password-changing service. | |
11 | ### | |
12 | ### Chopwood is free software; you can redistribute it and/or modify | |
13 | ### it under the terms of the GNU Affero General Public License as | |
14 | ### published by the Free Software Foundation; either version 3 of the | |
15 | ### License, or (at your option) any later version. | |
16 | ### | |
17 | ### Chopwood is distributed in the hope that it will be useful, | |
18 | ### but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | ### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | ### GNU Affero General Public License for more details. | |
21 | ### | |
22 | ### You should have received a copy of the GNU Affero General Public | |
23 | ### License along with Chopwood; if not, see | |
24 | ### <http://www.gnu.org/licenses/>. | |
25 | ||
26 | from __future__ import with_statement | |
27 | ||
28 | import os as OS | |
29 | import re as RX | |
30 | import subprocess as SUB | |
31 | ||
32 | from auto import HOME | |
33 | import backend as B | |
ac377b4f | 34 | import cgi as CGI |
a2916c06 MW |
35 | import config as CONF; CFG = CONF.CFG |
36 | import hash as H | |
37 | import util as U | |
38 | ||
39 | ###-------------------------------------------------------------------------- | |
40 | ### Protocol. | |
41 | ### | |
42 | ### A service is a thing for which a user might have an account, with a login | |
43 | ### name and password. The service protocol is fairly straightforward: a | |
44 | ### password can be set to a particular value using `setpasswd' (which | |
45 | ### handles details of hashing and so on), or cleared (i.e., preventing | |
46 | ### logins using a password) using `clearpasswd'. Services also present | |
47 | ### `friendly' names, used by the user interface. | |
48 | ### | |
49 | ### A service may be local or remote. Local services are implemented in | |
50 | ### terms of a backend and hashing scheme. Information about a particular | |
51 | ### user of a service is maintained in an `account' object which keeps track | |
52 | ### of the backend record and hashing scheme; the service protocol operations | |
53 | ### are handed off to the account. Accounts provide additional protocol for | |
54 | ### clients which are willing to restrict themselves to the use of local | |
55 | ### services. | |
56 | ### | |
57 | ### A remote service doesn't have local knowledge of the password database: | |
58 | ### instead, it simply sends commands corresponding to the service protocol | |
59 | ### operations to some external service which is expected to act on them. | |
60 | ### The implementation here uses SSH, and the remote end is expected to be | |
61 | ### provided by another instance of `chpwd', but that needn't be the case: | |
62 | ### the protocol is very simple. | |
63 | ||
64 | UnknownUser = B.UnknownUser | |
65 | ||
66 | class IncorrectPassword (Exception): | |
67 | """ | |
68 | A failed password check is reported via an exception. | |
69 | ||
70 | This is /not/ an `ExpectedError', since we anticipate that whoever called | |
71 | `check' will have made their own arrangements to deal with the failure in | |
72 | some more useful way. | |
73 | """ | |
74 | pass | |
75 | ||
76 | class BasicService (object): | |
77 | """ | |
78 | A simple base class for services. | |
79 | """ | |
80 | ||
81 | def __init__(me, friendly, *args, **kw): | |
82 | super(BasicService, me).__init__(*args) | |
83 | me.friendly = friendly | |
84 | me.meta = kw | |
85 | ||
86 | ###-------------------------------------------------------------------------- | |
87 | ### Local services. | |
88 | ||
89 | class Account (object): | |
90 | """ | |
91 | An account represents information about a user of a particular service. | |
92 | ||
93 | From here, we can implement the service protocol operations, and also check | |
94 | passwords. | |
95 | ||
96 | Users are expected to acquire account objects via the `lookup' method of a | |
97 | `LocalService' or similar. | |
98 | """ | |
99 | ||
100 | def __init__(me, svc, rec): | |
101 | """ | |
102 | Create a new account, for the service SVC, holding the user record REC. | |
103 | """ | |
104 | me._svc = svc | |
105 | me._rec = rec | |
106 | me._hash = svc.hash | |
107 | ||
108 | def check(me, passwd): | |
109 | """ | |
110 | Check the password PASSWD against the information we have. If the | |
111 | password is correct, return normally; otherwise, raise | |
112 | `IncorrectPassword'. | |
113 | """ | |
114 | if not me._hash.check(me._rec, me._rec.passwd, passwd): | |
115 | raise IncorrectPassword | |
116 | ||
117 | def clearpasswd(me): | |
118 | """Service protocol: clear the user's password.""" | |
119 | if me._hash.NULL is None: | |
120 | raise U.ExpectedError, (400, "Can't clear this password") | |
121 | me._rec.passwd = me._hash.NULL | |
122 | me._rec.write() | |
123 | ||
124 | def setpasswd(me, passwd): | |
125 | """Service protocol: set the user's password to PASSWD.""" | |
126 | passwd = me._hash.hash(me._rec, passwd) | |
127 | me._rec.passwd = passwd | |
128 | me._rec.write() | |
129 | ||
130 | class LocalService (BasicService): | |
131 | """ | |
132 | A local service has immediate knowledge of a hashing scheme and a password | |
133 | storage backend. (Knowing connection details for a remote database server | |
134 | is enough to qualify for being a `local' service. The important bit is | |
135 | that the hashed passwords are exposed to us.) | |
136 | ||
137 | The service protocol is implemented via an `Account', acquired through the | |
138 | `find' method. Mainly for the benefit of the `Account' class, the | |
139 | service's hashing scheme is exposed in the `hash' attribute. | |
140 | """ | |
141 | ||
142 | def __init__(me, backend, hash, *args, **kw): | |
143 | """ | |
144 | Create a new local service with a FRIENDLY name, using the given BACKEND | |
145 | and HASH scheme. | |
146 | """ | |
147 | super(LocalService, me).__init__(*args, **kw) | |
148 | me._be = backend | |
149 | me.hash = hash | |
150 | ||
151 | def find(me, user): | |
152 | """Find the named USER, returning an `Account' object.""" | |
153 | rec = me._be.lookup(user) | |
154 | return Account(me, rec) | |
155 | ||
156 | def setpasswd(me, user, passwd): | |
157 | """Service protcol: set USER's password to PASSWD.""" | |
158 | me.find(user).setpasswd(passwd) | |
159 | ||
160 | def clearpasswd(me, user): | |
161 | """Service protocol: clear USER's password, preventing logins.""" | |
162 | me.find(user).clearpasswd() | |
163 | ||
164 | CONF.export('LocalService') | |
165 | ||
166 | ###-------------------------------------------------------------------------- | |
167 | ### Remote services. | |
168 | ||
169 | class BasicRemoteService (BasicService): | |
170 | """ | |
171 | A remote service transmits the simple service protocol operations to some | |
172 | remote system, which presumably is better able to implement them than we | |
173 | are. This is useful if, for example, the password file isn't available to | |
174 | us, or we don't have (or can't be allowed to have) access to the database | |
175 | tables containing password hashes, or must synchronize updates with some | |
176 | remote process. It can also be useful to integrate with services which | |
177 | don't present a conventional password file. | |
178 | ||
179 | This class provides common machinery for communicating with various kinds | |
180 | of remote service. Specific subclasses are provided for transporting | |
181 | requests through SSH and GNU Userv; others can be added easily in local | |
182 | configuration. | |
183 | """ | |
184 | ||
185 | def _run(me, cmd, input = None): | |
186 | """ | |
187 | This is the core of the remote service machinery. It issues a command | |
188 | and parses the response. It will generate strings of informational | |
189 | output from the command; error responses cause appropriate exceptions to | |
190 | be raised. | |
191 | ||
192 | The command is determined by passing the CMD argument to the `_mkcmd' | |
193 | method, which a subclass must implement; it should return a list of | |
194 | command-line arguments suitable for `subprocess.Popen'. The INPUT is a | |
195 | string to make available on the command's stdin; if None, then no input | |
196 | is provided to the command. The `_describe' method must provide a | |
197 | description of the remote service for use in timeout messages. | |
198 | ||
199 | We expect output on stdout in a simple line-based format. The first | |
200 | whitespace-separated token on each line is a type code: `OK' means the | |
201 | command completed successfully; `INFO' means the rest of the line is some | |
202 | useful (and expected) information; and `ERR' means an error occurred: the | |
203 | next token is an HTTP integer status code, and the remainder is a | |
204 | human-readable message. | |
205 | """ | |
206 | ||
207 | ## Run the command and collect its output and status. | |
ac377b4f | 208 | with U.timeout(30, "waiting for remote service %s" % me._describe()): |
a2916c06 MW |
209 | proc = SUB.Popen(me._mkcmd(cmd), |
210 | stdin = input is not None and SUB.PIPE or None, | |
211 | stdout = SUB.PIPE, stderr = SUB.PIPE) | |
212 | out, err = proc.communicate(input) | |
213 | st = proc.wait() | |
214 | ||
215 | ## If the program failed then report this: it obviously didn't work | |
216 | ## properly. | |
217 | if st or err: | |
218 | raise U.ExpectedError, ( | |
219 | 500, 'Remote service error: %r (rc = %d)' % (err, st)) | |
220 | ||
221 | ## Split a word off the front of a string; return the word and the | |
222 | ## remaining string. | |
223 | def nextword(line): | |
224 | ww = line.split(None, 1) | |
225 | n = len(ww) | |
226 | if not n: return None | |
227 | elif n == 1: return ww[0], '' | |
228 | else: return ww | |
229 | ||
230 | ## Work through the lines, parsing them. | |
231 | win = False | |
232 | for line in out.splitlines(): | |
233 | type, rest = nextword(line) | |
234 | if type == 'ERR': | |
235 | code, msg = nextword(rest) | |
236 | raise U.ExpectedError, (int(code), msg) | |
237 | elif type == 'INFO': | |
238 | yield rest | |
239 | elif type == 'OK': | |
240 | win = True | |
241 | else: | |
242 | raise U.ExpectedError, \ | |
243 | (500, 'Incomprehensible reply from remote service: %r' % line) | |
244 | ||
245 | ## If we didn't get any kind of verdict then something weird has | |
246 | ## happened. | |
247 | if not win: | |
248 | raise U.ExpectedError, (500, 'No reply from remote service') | |
249 | ||
250 | def _run_noout(me, cmd, input = None): | |
251 | """Like `_run', but expect no output.""" | |
252 | for _ in me._run(cmd, input): | |
253 | raise U.ExpectedError, (500, 'Unexpected output from remote service') | |
254 | ||
255 | class SSHRemoteService (BasicRemoteService): | |
256 | """ | |
257 | A remote service transported over SSH. | |
258 | ||
259 | The remote service is given commands of the form | |
260 | ||
261 | `set SERVICE USER' | |
262 | Set USER's password for SERVICE to the password provided on the next | |
263 | line of standard input. | |
264 | ||
265 | `clear SERVICE USER' | |
266 | Clear the USER's password for SERVICE. | |
267 | ||
268 | Arguments are form-url-encoded, since SSH doesn't preserve token boundaries | |
269 | in its argument list. | |
270 | ||
271 | It is expected that the remote user has an `.ssh/authorized_keys' file | |
272 | entry for us specifying a program to be run; the above commands will be | |
273 | left available to this program in the environment variable | |
274 | `SSH_ORIGINAL_COMMAND'. | |
275 | """ | |
276 | ||
277 | def __init__(me, remote, name, *args, **kw): | |
278 | """ | |
279 | Initialize an SSH remote service, contacting the SSH user REMOTE | |
280 | (probably of the form `LOGIN@HOSTNAME') and referring to the service | |
281 | NAME. | |
282 | """ | |
283 | super(SSHRemoteService, me).__init__(*args, **kw) | |
284 | me._remote = remote | |
285 | me._name = name | |
286 | ||
287 | def _describe(me): | |
288 | """Description of the remote service.""" | |
289 | return "`%s' via SSH to `%s'" % (me._name, me._remote), | |
290 | ||
291 | def _mkcmd(me, cmd): | |
292 | """Format a command for SSH. Mainly escaping arguments.""" | |
ac377b4f | 293 | return ['ssh', me._remote, ' '.join(map(CGI.urlencode, cmd))] |
a2916c06 MW |
294 | |
295 | def setpasswd(me, user, passwd): | |
296 | """Service protocol: set the USER's password to PASSWD.""" | |
297 | me._run_noout(['set', me._name, user], passwd + '\n') | |
298 | ||
299 | def clearpasswd(me, user): | |
300 | """Service protocol: clear the USER's password.""" | |
301 | me._run_noout(['clear', me._name, user]) | |
302 | ||
303 | CONF.export('SSHRemoteService') | |
304 | ||
305 | class CommandRemoteService (BasicRemoteService): | |
306 | """ | |
307 | A remote service transported over a standard Unix command. | |
308 | ||
309 | This is left rather generic. We need to know some command lists SET and | |
310 | CLEAR containing the relevant service names and arguments. These are | |
311 | simply executed, after simple placeholder substitution. | |
312 | ||
313 | The SET command should read a password as its first line on stdin, and set | |
314 | that as the user's new password. The CLEAR command should simply prevent | |
315 | the user from logging in with a password. On success, the commands should | |
316 | print a line `OK' to standard output, and on any kind of anticipated | |
317 | failure, they should print `ERR' followed by an HTTP status code and a | |
318 | message; in either case, the program should exit with status zero. In | |
319 | disastrous cases, it's acceptable to print an error message to stderr | |
320 | and/or exit with a nonzero status. | |
321 | ||
322 | The placeholders are as follows. | |
323 | ||
324 | `%u' the user's name | |
325 | `%%' a single `%' character | |
326 | """ | |
327 | ||
328 | R_PAT = RX.compile('%(.)') | |
329 | ||
330 | def __init__(me, set, clear, *args, **kw): | |
331 | """ | |
332 | Initialize the command remote service. | |
333 | """ | |
334 | super(CommandRemoteService, me).__init__(*args, **kw) | |
335 | me._set = set | |
336 | me._clear = clear | |
337 | me._map = dict(u = user) | |
338 | ||
339 | def _subst(me, c): | |
340 | """Return the substitution for the placeholder `%C'.""" | |
341 | return me._map.get(c, c) | |
342 | ||
343 | def _mkcmd(me, cmd): | |
344 | """Construct the command to be executed, by substituting placeholders.""" | |
345 | return [me.R_PAT.sub(lambda m: me._subst(m.group(1))) for arg in cmd] | |
346 | ||
347 | def setpasswd(me, user, passwd): | |
348 | """Service protocol: set the USER's password to PASSWD.""" | |
349 | me._run_noout(me._set, passwd + '\n') | |
350 | ||
351 | def clearpasswd(me, user): | |
352 | """Service protocol: clear the USER's password.""" | |
353 | me._run_noout(me._clear) | |
354 | ||
355 | CONF.export('CommandRemoteService') | |
356 | ||
357 | ###-------------------------------------------------------------------------- | |
358 | ### Services registry. | |
359 | ||
360 | ## The registry of services. | |
361 | SERVICES = {} | |
362 | CONF.export('SERVICES') | |
363 | ||
364 | ## Set some default configuration. | |
365 | CONF.DEFAULTS.update( | |
366 | ||
367 | ## The master database, as a pair (MODNAME, MODARGS). | |
368 | DB = ('sqlite3', [OS.path.join(HOME, 'chpwd.db')]), | |
369 | ||
370 | ## The hash to use for our master password database. | |
371 | HASH = H.CryptHash('md5')) | |
372 | ||
373 | ## Post-configuration hook: add the master service. | |
374 | @CONF.hook | |
375 | def add_master_service(): | |
376 | dbmod, dbargs = CFG.DB | |
377 | SERVICES['master'] = \ | |
378 | LocalService(B.DatabaseBackend(dbmod, dbargs, | |
379 | 'users', 'user', 'passwd'), | |
380 | CFG.HASH, | |
381 | friendly = 'Password changing service') | |
382 | ||
383 | ###----- That's all, folks -------------------------------------------------- |