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Sun Nov 20 21:35:54 2011 UTC (8 years, 11 months ago) by mspo
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    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: 
   22: These are (in pkgsrc-2008Q2) 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. 
   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: 
   28: Options you'll be using alot like -b (base) and -H (host URI) can conveninently be stuck in a client configuration file, ${LOCALBASE}/etc/openldap/ldap.conf, which will save you time and aggravation from having to type them all the time. 
   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:     
  134: 
  135: Once these are installed, you can either link them, copy or use in place from ${LOCALBASE}/lib and ${LOCALBASE}/lib/security into /usr/lib and /usr/lib/security respectively. I prefer to use symbolic links because then any upgrade I make will automatically have the latest version already in place. 
  136: 
  137: 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. 
  138: 
  139: XXX can anonymous binds actually write to a db without ACLs? 
  140: 
  141: 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) 
  142: 
  143: So we'll create a user called nss 
  144:     
  145:     dn: cn=nss,dc=example,dc=org
  146:     objectClass: top
  147:     objectClass: inetOrgPerson
  148:     o: Example Organisation
  149:     cn: nss
  150:     sn: manager
  151:     
  152: 
  153: 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. 
  154:     
  155:     userPassword: {SSHA}w5aocfmGgZqq3h8AjvaZiw8WKdrRTjTi
  156:     
  157: 
  158: To generate this password I use (bundled with openldap-server) slapdpasswd 
  159:     
  160:     % slappasswd -h "{SSHA}"
  161:     
  162:     
  163: 
  164: And in slapd.conf add 
  165:     
  166:     passsword-hash {SSHA}
  167:     
  168: 
  169: And of course you'll need to change the secret for the rootpw into something encrypted. 
  170: 
  171: 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. 
  172: 
  173: This user will be used for ACL filtering later. 
  174: 
  175: 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 ${LOCALBASE}/etc/nss_ldap.conf and ${LOCALBASE}/etc/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) 
  176: 
  177: The important bits in this file is the base setting and the uri for your ldap server: 
  178:     
  179:     base dc=example,dc=org
  180:     
  181:     
  182:     uri ldap://my.server/
  183:     
  184: 
  185: Next we need to tell it who it should contact the ldap database as: 
  186:     
  187:     binddn cn=nss,dc=example,dc=org
  188:     
  189:     
  190:     bindpw unencrypted-password
  191:     
  192: 
  193: 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).) 
  194: 
  195: I haven't mentioned this user before, it's the database's root user, allowed to do anything; 
  196:     
  197:     rootbinddn cn=root,dc=example,dc=org
  198:     
  199: 
  200: The password for this will not be in this file, but in a separate file called ${LOCALBASE}/etc/nss_ldap.secret or for pam; ${LOCALBASE}/etc/pam_ldap.secret 
  201: 
  202:   * ) not sure about this, but my system has both, linked together 
  203: 
  204: Finally we will set the password exchange method to exop; 
  205:     
  206:     pam_password exop
  207:     
  208: 
  209: 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. 
  210: 
  211: 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. 
  212: 
  213: That's it for configuring the plugins so far. 
  214: 
  215: #  NSS 
  216: 
  217: The next change we will need to do is to enable the ldap module in nsswitch.conf: 
  218: 
  219: Change 
  220:     
  221:     group:	files
  222:     ...
  223:     passwd:	files
  224:     
  225: 
  226: To 
  227:     
  228:     group:	files ldap
  229:     ...
  230:     passwd:	files ldap
  231:     
  232: 
  233: This will enable you to have local accounts as well as ldap users. You could test this out now, by running the getent program; 
  234:     
  235:     % getent group
  236:     
  237: 
  238: 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. 
  239:     
  240:     % getent passwd
  241:     
  242: 
  243: And this will show you the user list, with the ldap user 'test' at the end. 
  244: 
  245: #  PAM 
  246: 
  247: 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. 
  248: 
  249: On my system I have the following changes from the stock netbsd setup: 
  250: 
  251: ##  /etc/pam.d/sshd 
  252:     
  253:     # $NetBSD: openldap_authentication_on_netbsd.mdwn,v 1.1 2011/11/20 21:35:54 mspo Exp $
  254:     #
  255:     # PAM configuration for the "sshd" service
  256:     #
  257:      
  258:     # auth
  259:     auth            required        pam_nologin.so  no_warn
  260:     auth            sufficient      pam_ldap.so
  261:     auth            sufficient      pam_krb5.so     no_warn try_first_pass
  262:     # pam_ssh has potential security risks.  See pam_ssh(8).
  263:     #auth           sufficient      pam_ssh.so      no_warn try_first_pass
  264:     auth            required        pam_unix.so     no_warn try_first_pass
  265:      
  266:     # account
  267:     account         required        pam_krb5.so
  268:     account         sufficient      pam_ldap.so
  269:     account         required        pam_login_access.so
  270:     account         required        pam_unix.so
  271:      
  272:     # session
  273:     # pam_ssh has potential security risks.  See pam_ssh(8).
  274:     #session        optional        pam_ssh.so
  275:     session         sufficient      pam_ldap.so
  276:     session         required        pam_permit.so
  277:      
  278:     # password
  279:     password        sufficient      pam_krb5.so     no_warn try_first_pass
  280:     password        sufficient      pam_ldap.so
  281:     password        required        pam_unix.so     no_warn try_first_pass
  282:     
  283: 
  284: ##  /etc/pam.d/su 
  285:     
  286:     # $NetBSD: openldap_authentication_on_netbsd.mdwn,v 1.1 2011/11/20 21:35:54 mspo Exp $
  287:     #
  288:     # PAM configuration for the "su" service
  289:     #
  290:      
  291:     # auth
  292:     auth            sufficient      pam_ldap.so
  293:     auth            sufficient      pam_rootok.so           no_warn
  294:     auth            sufficient      pam_self.so             no_warn
  295:     auth            sufficient      pam_ksu.so              no_warn try_first_pass
  296:     auth            requisite       pam_group.so            no_warn group=wheel root_only fail_safe
  297:     #auth           sufficient      pam_group.so            no_warn group=rootauth root_only fail_safe authenticate
  298:     auth            required        pam_unix.so             no_warn try_first_pass nullok
  299:      
  300:     # account
  301:     account         required        pam_login_access.so
  302:     account         include         system
  303:      
  304:     # session
  305:     session         required        pam_permit.so
  306:     
  307: 
  308: ##  /etc/pam.d/system 
  309:     
  310:     # $NetBSD: openldap_authentication_on_netbsd.mdwn,v 1.1 2011/11/20 21:35:54 mspo Exp $
  311:     #
  312:     # System-wide defaults
  313:     #
  314:      
  315:     # auth
  316:     auth            sufficient      pam_ldap.so
  317:     auth            sufficient      pam_krb5.so             no_warn try_first_pass
  318:     auth            required        pam_unix.so             no_warn try_first_pass nullok
  319:      
  320:     # account
  321:     account         sufficient      pam_ldap.so
  322:     account         required        pam_krb5.so
  323:     account         required        pam_unix.so
  324:     
  325:     # session
  326:     session         sufficient      pam_ldap.so
  327:     session         required        pam_lastlog.so          no_fail no_nested
  328:      
  329:     # password
  330:     password        sufficient      pam_ldap.so
  331:     password        sufficient      pam_krb5.so             try_first_pass
  332:     password        sufficient      pam_unix.so             try_first_pass
  333:     password        required        pam_deny.so             prelim_ignore
  334:     
  335: 
  336: 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. 
  337: 
  338: 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>: 
  339: 
  340: <http://mail-index.netbsd.org/tech-userlevel/2007/08/29/0001.html>
  341: 
  342: The original message describing the problem is here: 
  343: 
  344: <http://mail-index.netbsd.org/tech-userlevel/2007/08/25/0006.html>
  345: 
  346: 
  347: #  Securing your system 
  348: 
  349: 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. 
  350: 
  351: So we'll want to enable SSL encryption of the traffic between your clients and the server. 
  352: 
  353: 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. 
  354: 
  355: 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. 
  356:     
  357:     TLSCipherSuite          HIGH:MEDIUM:+SSLv2
  358:     TLSCertificateFile      /etc/openssl/certs/openldap.pem
  359:     TLSCertificateKeyFile   /etc/openssl/private/openldap.pem
  360:     TLSCACertificateFile    /etc/openssl/certs/openldap.pem
  361:     
  362: 
  363: And we'll also have to change the way slapd is started, so add this to your /etc/rc.conf 
  364:     
  365:     slapd_flags="-h ldaps://"
  366:     
  367: 
  368: Note that this will make slapd answer only to ldaps! 
  369: 
  370: Next we'll need to change the clients setup so that they will use ldaps. Enable ssl in ${LOCALBASE}/etc/{nss_,pam_}ldap.conf; 
  371:     
  372:     ssl on
  373:     
  374: 
  375: Next if you're like me using the ${LOCALBASE}/etc/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: 
  376:     
  377:     URI		ldaps://my.server
  378:     TLS_CACERT	/etc/openssl/certs/openldap.pem
  379:     
  380: 
  381: If you can still use getent, encryption is happening. You can of course also tcpdump your network traffic to see what's going on. 
  382: 
  383: #  ACL 
  384: 
  385: 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. 
  386: 
  387: The syntax is fairly straightforward; 
  388:     
  389:     acceess to [something] by [someone] [access]
  390:     
  391: 
  392: The order is important; if something matches, later tests will not be run. 
  393: 
  394: The one I use looks like this: 
  395:     
  396:      #
  397:      # Protect passwords from prying eyes
  398:      #
  399:      access to attrs=userPassword
  400:      	by dn="cn=nss,dc=example,dc=org" write
  401:      	by anonymous auth
  402:      	by self write
  403:      	by * none
  404:      
  405:      #
  406:      # set read-only attributes
  407:      #
  408:      access to attrs=uidNumber,gidNumber,uid,homeDirectory
  409:      	by dn="cn=nss,dc=example,dc=org" write
  410:      	by self read
  411:      	by * read
  412:      
  413:      #
  414:      # For all else, let the user edit his own entry and everyone else watch
  415:      #
  416:      access to *
  417:      	by dn="cn=nss,dc=example,dc=org" write
  418:      	by self write
  419:      	by * read
  420:      
  421:     
  422: 
  423: 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. 
  424: 

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