Annotation of wikisrc/tutorials/openldap_authentication_on_netbsd.mdwn, revision 1.5
1.2 schmonz 1: **Contents**
2:
3: [[!toc levels=3]]
4:
5: # Author's note
6:
7: This document really describes (what I remember of installing) my system, with tidbits I've forgotten from various sources on the net. I can't guarantee that following this document you'll get a working system, but I hope it will provide some insights into how the thing is supposed to work.
8:
9: Staffan Thom´en <duck@shangtai.net>
10:
11: # Server setup
12:
13: First things first, you'll need to set up an openldap server somewhere, this is fairly straightforward, as it's available in pkgsrc. The tricky bit is really configuring the ACL:s, since the openldap logs are incredibly hard to read. Generally it's probably a good idea to firewall it from outside and worry about the ACL setup later if you want to do things like let other departments to see your users or let the public see contact information for example.
14:
15: An example config file is included in the package (${LOCALBASE}/etc/opeldap/slapd.conf), and the only thing that really has to be added is to include some schemas for user authentication:
16:
17: cosine.schema
18: inetorgperson.schema
19: nis.schema
20:
21:
1.3 tron 22: These are (in pkgsrc-2014Q1) installed in ${LOCALBASE}/share/examples/openldap/schema, and can just be included from there, and tells the server which record keys (as in key-value pairs) it shall accept.
1.2 schmonz 23:
24: And that really is it for the server bit. Next comes testing it out with a few ldap commands.
25:
26: The basic commands of talking directly with the ldap database are ldapadd, ldapmodify and ldapsearch. These are in the openldap-client package, so you won't have to install the entire server on a client machine.
27:
1.3 tron 28: Options you'll be using alot like -b (base) and -H (host URI) can conveninently be stuck in a client configuration file, ${PKG_SYSCONFBASE}/openldap/ldap.conf, which will save you time and aggravation from having to type them all the time.
1.2 schmonz 29:
30: To talk to your ldap server, try running ldapsearch;
31:
32: % ldapsearch -H ldap://my.server/
33:
34:
35: This really means dump everything, but since we've nothing in the database it will respond with an error.
36:
37: To set this database up for user authentication, we'll need to lay down some structure. LDAP is generally a hierachial database of records with key-value pairs. We'll first need to tell it about our organisation and then add a user.
38:
39: Here we'll be using ldapadd, which reads a format called ldif. It is a flat text format that looks something like this:
40:
41: dn: cn=example,dc=org
42: objectClass: dcObject
43: objectClass: organization
44: objectClass: top
45: o: Example Organisation
46: dc: example
47:
48:
49: dn: ou=groups,dc=example,dc=org
50: objectClass: top
51: objectClass: organizationalUnit
52: ou: groups
53:
54:
55: dn: ou=people,dc=example,dc=org
56: objectClass: top
57: objectClass: organizationalUnit
58: ou: people
59:
60:
61: The text above define three records, they start with a distinguished name of the record (dn:), which is a unique identifier for the record.
62:
63: "cn=example,dc=org" is the root of this organisation, with a common name (cn) example and a domain component (dc) of org. Next come the objectClass lines which tells us that this is domain component object, an organisation object and a top-level object. We then have an organisation (o:) line which is a descriptive text and finally a domain component line (dc:) which is the stored value for the dc (same as in the distinguished name).
64:
65: Following this are two records which define something called in ldap terms organisational units, and as you see from the dn:, essentially two branches of the main tree. They are here to be used for the user groups (yes, like /etc/groups) and the actual users.
66:
67: If you want you can just stick all of this in one file (even the user below) and add it with ldapadd -f file.ldif, this will create the initial structure of your database.
68:
69: Adding a group and then a user user is no more difficult, you just have to fill out the right fields.
70:
71: dn: cn=ldapusers,ou=groups,dc=example,dc=org
72: objectClass: top
73: objectClass: posixGroup
74: cn: ldapusers
75: gidNumber: 101
76: memberUid: bill
77: memberUid: george
78:
79:
80: A group named ldapusers with the number 101, and the secondary users bill and george (these are of course not required).
81:
82: dn: uid=test,ou=people,dc=example,dc=org
83: objectClass: top
84: objectClass: posixAccount
85: objectClass: inetOrgPerson
86: uid: test
87: uidNumber: 2000
88: gidNumber: 101
89: o: Example Organisation
90: cn: Test User
91: givenName: Test
92: sn: User
93: gecos: Test User,3b,+358800128128,+35801234567
94: loginShell: /bin/ksh
95: homeDirectory: /home/test
96: mail: test@example.org
97: displayName: El Magnifico Test User
98:
99:
100: A user with the uid test, belonging to group ldapusers (101); o: is the same as the root record above and the others apart from sn (surname) is fairly obvious. The GECOS field contains comma separated values, apparently it's pulled straight into the client system.
101:
102: The fields actually required by the schemes are:
103:
104: uid
105: uidNumber
106: gidNumber
107: cn
108: sn
109: homeDirectory
110:
111:
112: LDAP can store multiple roots and each user entry for example can be more than just the login information, as above it also mentions email, phone numbers and so on for our test user, and it can also include binary data like a mugshot and them playing the corporate theme on banjo. As far as authentication is concerned, we've got what we want though.
113:
114: So far so good, this should not cause much trouble to set up, I believe I've covered everything required; the thing I had most problem with in relation to the database itself was that it was so unstructured, you have to provide all the structure yourself.
115:
116: # Client Setup
117:
118: In order to log in on a NetBSD system we need to provide two things, a way for the system to authenticate you and a way for it to find out what your group, user id, etc. is.
119:
120: The first part of this, authentication is taken care of by PAM (or possibly by some BSD auth scheme, but this is not yet implemented as far as I know.)
121:
122: The second part is done via libc and the NSS subsystem.
123:
124: In order to do this, we need to provide some plugins for either system that enables LDAP support in them. The plugins are in pkgsrc and are called
125:
126: security/pam-ldap
127:
128:
129: and
130:
131: databases/nss_ldap
132:
133:
1.3 tron 134: The latest version of these packages (pkgrsc-2014Q2 and newer) will automatically created the necessary symbolic links in /usr/lib and /usr/lib/security to be able to use these modules. For older version you will have create a symbolic link from /usr/lib/nss_ldap.so.0 to ${LOCALBASE}/lib/nss_ldap.so.1 and from /usr/lib/security/pam_ldap.so to ${LOCALBASE}/lib/security/pam_ldap.so
1.2 schmonz 135:
136: Before we go any further, I'd like to introduce some security into the mix; up til now we've talked to the ldap server without any limitations and what's called anonymous binds, i.e. not logged in.
137:
138: XXX can anonymous binds actually write to a db without ACLs?
139:
140: This is an ldap user, just like the test user outlined above, since the ldap database can authenticate against itself. (You don't have to, but I haven't explored the other possibilities such as SASL)
141:
142: So we'll create a user called nss
143:
144: dn: cn=nss,dc=example,dc=org
145: objectClass: top
146: objectClass: inetOrgPerson
147: o: Example Organisation
148: cn: nss
149: sn: manager
150:
151:
152: We'll attach a password so that not just anyone can connect, and also change our LDAP configuration slightly so that we use encrypted passwords.
153:
154: userPassword: {SSHA}w5aocfmGgZqq3h8AjvaZiw8WKdrRTjTi
155:
156:
157: To generate this password I use (bundled with openldap-server) slapdpasswd
158:
159: % slappasswd -h "{SSHA}"
160:
161:
162:
163: And in slapd.conf add
164:
165: passsword-hash {SSHA}
166:
167:
168: And of course you'll need to change the secret for the rootpw into something encrypted.
169:
170: Note that the traffic between the ldap client and the server is still not (that is if you've been following this document) encrypted so this might be best to perform locally.
171:
172: This user will be used for ACL filtering later.
173:
1.3 tron 174: Next we'll need to configure the LDAP part of the plugins, a convenience here is that since both the plugins are made by the same people, they can share a configuration file. They will look for ${PKG_SYSCONFBASE}/nss_ldap.conf and ${PKG_SYSCONFBASE}/pam_ldap.conf, but linking them to the same file will let you have just one place to configure (and protect for your ldap user password)
1.2 schmonz 175:
176: The important bits in this file is the base setting and the uri for your ldap server:
177:
178: base dc=example,dc=org
179:
180:
181: uri ldap://my.server/
182:
183:
184: Next we need to tell it who it should contact the ldap database as:
185:
186: binddn cn=nss,dc=example,dc=org
187:
188:
189: And if you want to be able to change passwords as root without knowing the user's password in advance (with passwd, using ldapmodify you can still just set it, if you bind with the credentials to do it (see ACLs).)
190:
191: I haven't mentioned this user before, it's the database's root user, allowed to do anything;
192:
193: rootbinddn cn=root,dc=example,dc=org
194:
195:
1.3 tron 196: The password for this will not be in this file, but in a separate file called ${PKG_SYSCONFBASE}/nss_ldap.secret or for pam; ${PKG_SYSCONFBASE}/pam_ldap.secret
1.2 schmonz 197:
198: * ) not sure about this, but my system has both, linked together
199:
200: Finally we will set the password exchange method to exop;
201:
202: pam_password exop
203:
204:
205: This is the OpenLDAP extended method and while the passwords will still be sent in the clear, they are encrypted with the database's scheme in the database.
206:
207: So while you can use ldapsearch to get the data (though ACLs can prevent this if properly set up) it will still only be a hash.
208:
209: That's it for configuring the plugins so far.
210:
211: # NSS
212:
213: The next change we will need to do is to enable the ldap module in nsswitch.conf:
214:
215: Change
216:
217: group: files
218: ...
219: passwd: files
220:
221:
222: To
223:
224: group: files ldap
225: ...
226: passwd: files ldap
1.3 tron 227: ...
228: netgroup: files ldap
1.2 schmonz 229:
1.3 tron 230: This will enable you to have local accounts as well as LDAP users. You could test this out now, by running the getent program;
1.2 schmonz 231:
232: % getent group
233:
234:
235: Will present you with a list of all the groups in the system, with the ldap group 'ldapusers' we created earlier tacked on to the end of the list.
236:
237: % getent passwd
238:
239:
240: And this will show you the user list, with the ldap user 'test' at the end.
241:
242: # PAM
243:
244: PAM keeps it's configuration files in /etc/pam.d/, these are divided into individual files per each pam service in the system; most are just including system but some need special attention.
245:
246: On my system I have the following changes from the stock netbsd setup:
247:
248: ## /etc/pam.d/sshd
249:
250: #
251: # PAM configuration for the "sshd" service
252: #
253:
254: # auth
255: auth required pam_nologin.so no_warn
256: auth sufficient pam_krb5.so no_warn try_first_pass
1.3 tron 257: auth sufficient pam_ldap.so no_warn try_first_pass
1.2 schmonz 258: # pam_ssh has potential security risks. See pam_ssh(8).
259: #auth sufficient pam_ssh.so no_warn try_first_pass
260: auth required pam_unix.so no_warn try_first_pass
261:
262: # account
263: account required pam_krb5.so
264: account required pam_login_access.so
265: account required pam_unix.so
266:
267: # session
268: # pam_ssh has potential security risks. See pam_ssh(8).
269: #session optional pam_ssh.so
270: session required pam_permit.so
271:
272: # password
273: password sufficient pam_krb5.so no_warn try_first_pass
1.3 tron 274: password sufficient pam_ldap.so no_warn try_first_pass
1.2 schmonz 275: password required pam_unix.so no_warn try_first_pass
276:
277:
278: ## /etc/pam.d/su
279:
280: #
281: # PAM configuration for the "su" service
282: #
283:
284: # auth
285: auth sufficient pam_rootok.so no_warn
286: auth sufficient pam_self.so no_warn
287: auth sufficient pam_ksu.so no_warn try_first_pass
1.3 tron 288: #auth sufficient pam_group.so no_warn group=rootauth root_only fail_safe authenticate
1.2 schmonz 289: auth requisite pam_group.so no_warn group=wheel root_only fail_safe
1.3 tron 290: auth sufficient pam_ldap.so no_warn try_first_pass
1.2 schmonz 291: auth required pam_unix.so no_warn try_first_pass nullok
292:
293: # account
294: account required pam_login_access.so
295: account include system
296:
297: # session
298: session required pam_permit.so
299:
300:
301: ## /etc/pam.d/system
302:
1.5 ! tron 303: # $NetBSD: openldap_authentication_on_netbsd.mdwn,v 1.4 2014/06/04 20:56:19 tron Exp $
1.2 schmonz 304: #
305: # System-wide defaults
306: #
307:
308: # auth
309: auth sufficient pam_krb5.so no_warn try_first_pass
1.3 tron 310: auth sufficient pam_ldap.so no_warn try_first_pass
1.2 schmonz 311: auth required pam_unix.so no_warn try_first_pass nullok
312:
313: # account
314: account required pam_krb5.so
315: account required pam_unix.so
316:
317: # session
318: session required pam_lastlog.so no_fail no_nested
319:
320: # password
1.3 tron 321: password sufficient pam_krb5.so no_warn try_first_pass
322: password sufficient pam_ldap.so no_warn try_first_pass
323: password sufficient pam_unix.so no_warn try_first_pass
1.2 schmonz 324: password required pam_deny.so prelim_ignore
325:
326:
327: The last bit here with pam_deny, is a bit special, it is what enables you to change passwords for both local users and those in the ldap database with the passwd command. pam_deny with the prelim_ignore flag is needed, else pam will will fail in the preliminary phase (it is always run trough twice) and you will not be able to change passwords.
328:
329: In order to use this you need to patch your pam_deny (/usr/src/lib/libpam/modules/pam_deny.c) with the patch by Edgar Fuß <ef@math.uni-bonn.de>:
330:
331: <http://mail-index.netbsd.org/tech-userlevel/2007/08/29/0001.html>
332:
333: The original message describing the problem is here:
334:
335: <http://mail-index.netbsd.org/tech-userlevel/2007/08/25/0006.html>
336:
337:
1.5 ! tron 338: ## /etc/pam.d/sudo
1.4 tron 339:
340: #
341: # PAM configuration for the "sudo" service
342: #
343:
344: # auth
345: auth sufficient pam_ldap.so no_warn try_first_pass
346: auth required pam_unix.so no_warn try_first_pass nullok use_uid
347:
348: # account
349: account required pam_login_access.so
350: account include system
351:
352: # session
353: session required pam_permit.so
354:
355: This file is only required if you want to use the "sudo" package from "pkgsrc".
356: You will have to compile this package manually with "PKG_OPTIONS.sudo" set to
357: "pam" because it doesn't support PAM by default.
358:
1.2 schmonz 359: # Securing your system
360:
361: As far as the document goes now, this setup is unprotected in that anyone listening in to the packets travelling trough your network would be able to find the unencrypted messages of your ldap users. Not a happy thought.
362:
363: So we'll want to enable SSL encryption of the traffic between your clients and the server.
364:
365: In order to do this you will need to create an SSL certificate for your server and also distribute it to the client machines, so that they will be able to certify the authenticity of the server.
366:
367: We'll also need to configure slapd to use it, I put my keys in the /etc/openssl hierachy, since it seemed made for it.
368:
1.3 tron 369: TLSCipherSuite HIGH
1.2 schmonz 370: TLSCertificateFile /etc/openssl/certs/openldap.pem
371: TLSCertificateKeyFile /etc/openssl/private/openldap.pem
372: TLSCACertificateFile /etc/openssl/certs/openldap.pem
373:
374:
1.3 tron 375: Next we'll need to change the clients setup so that they will use encryption. Enable ssl in ${PKG_SYSCONFBASE}/{nss_,pam_}ldap.conf;
1.2 schmonz 376:
1.3 tron 377: ssl start_tls
1.2 schmonz 378:
1.3 tron 379: Next if you're like me using the ${PKG_SYSCONFBASE}/openldap/ldap.conf file, telling the client libs where to find the cert file is enough, we don't have to put it in the nss/pam config:
1.2 schmonz 380:
381: TLS_CACERT /etc/openssl/certs/openldap.pem
382:
383:
384: If you can still use getent, encryption is happening. You can of course also tcpdump your network traffic to see what's going on.
385:
386: # ACL
387:
388: I left access control lists of the server to the last, because they are the easiest to get wrong and often cause problems that you might attribute to other things in the various setups.
389:
390: The syntax is fairly straightforward;
391:
392: acceess to [something] by [someone] [access]
393:
394:
395: The order is important; if something matches, later tests will not be run.
396:
397: The one I use looks like this:
398:
399: #
400: # Protect passwords from prying eyes
401: #
402: access to attrs=userPassword
403: by dn="cn=nss,dc=example,dc=org" write
404: by anonymous auth
405: by self write
406: by * none
407:
408: #
409: # set read-only attributes
410: #
411: access to attrs=uidNumber,gidNumber,uid,homeDirectory
412: by dn="cn=nss,dc=example,dc=org" write
413: by self read
414: by * read
415:
416: #
417: # For all else, let the user edit his own entry and everyone else watch
418: #
419: access to *
420: by dn="cn=nss,dc=example,dc=org" write
421: by self write
422: by * read
423:
424:
425:
426: Note that access to the user password can be set to auth; so that the database can authenticate a user without letting them see the password hash using an anonymous bind.
427:
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