vishalmishra434 / rpms / openssh

Forked from rpms/openssh a month ago
Clone
Blob Blame History Raw
diff -up openssh-5.8p1/HOWTO.ldap-keys.ldap2 openssh-5.8p1/HOWTO.ldap-keys
--- openssh-5.8p1/HOWTO.ldap-keys.ldap2	2011-03-10 21:45:52.706855323 +0100
+++ openssh-5.8p1/HOWTO.ldap-keys	2011-03-10 19:35:50.000000000 +0100
@@ -1,14 +1,108 @@
 
+HOW TO START
+
 1) configure LDAP server
-2) add appropriate schema
+  * Use LDAP server documentation
+2) add appropriate LDAP schema
+  * For OpenLDAP or SunONE Use attached schema, otherwise you have to create it. 
+  * LDAP user entry
+        User entry:
+	- attached to the 'ldapPublicKey' objectclass
+	- attached to the 'posixAccount' objectclass
+	- with a filled 'sshPublicKey' attribute 
 3) insert users into LDAP
+  * Use LDAP Tree management tool as useful
+  * Entry in the LDAP server must respect 'posixAccount' and 'ldapPublicKey' which are defined in core.schema and the additionnal lpk.schema.
+  * Example:
+	dn: uid=captain,ou=commanders,dc=enterprise,dc=universe
+	objectclass: top
+	objectclass: person
+	objectclass: organizationalPerson
+	objectclass: posixAccount
+	objectclass: ldapPublicKey
+	description: Jonathan Archer
+	userPassword: Porthos
+	cn: onathan Archer
+	sn: onathan Archer
+	uid: captain
+	uidNumber: 1001
+	gidNumber: 1001
+	homeDirectory: /home/captain
+	sshPublicKey: ssh-rss AAAAB3.... =captain@universe
+	sshPublicKey: command="kill -9 1" ssh-rss AAAAM5...
 4) on the ssh side set in sshd_config
-AuthorizedKeysCommand "/usr/libexec/openssh/ssh-ldap-wrapper"
-AuthorizedKeysCommandRunAs <appropriate user to run LDAP>
-5) do not forget to set
-PubkeyAuthentication yes
+  * Set up the backend
+	AuthorizedKeysCommand "/usr/libexec/openssh/ssh-ldap-wrapper"
+	AuthorizedKeysCommandRunAs <appropriate user to run LDAP>
+  * Do not forget to set
+	PubkeyAuthentication yes
+  * Swith off unnecessary auth methods
+5) confugure ldap.conf
+  * Default ldap.conf is placed in /etc/ssh
+  * The configuration style is the same as other ldap based aplications
+6) if necessary edit ssh-ldap-wrapper
+  * There is a possibility to change ldap.conf location
+  * There are some debug options
+  * Example
+	/usr/libexec/openssh -s -f /etc/ldap.conf -w -d >> /tmp/ldapdebuglog.txt
+
+HOW TO MIGRATE FROM LPK
+
+1) goto HOW TO START 4) .... the ldap schema is the same
+
+2) convert the group requests to the appropriate LDAP requests
+
+HOW TO SOLVE PROBLEMS
+
+1) use debug in sshd
+  * /usr/sbin/sshd -d -d -d -d
+2) use debug in ssh-ldap-helper
+  * ssh-ldap-helper -d -d -d -d -s <username>
+3) use tcpdump ... other ldap client etc.
+
+ADVANTAGES
+
+1) Blocking an user account can be done directly from LDAP (if sshd is using PubkeyAuthentication + AuthorizedKeysCommand with ldap only).
+
+DISADVANTAGES
+
+1)  LDAP must be well configured, getting the public key of some user is not a problem, but if anonymous LDAP 
+  allows write to users dn, somebody could replace some user's public key by his own and impersonate some 
+  of your users in all your server farm -- be VERY CAREFUL.
+2) With incomplete PKI the MITM attack when sshd is requesting the public key, could lead to a compromise of your servers allowing login 
+  as the impersonated user.
+3) If LDAP server is down there may be no fallback on passwd auth.
+  
+MISC.
+  
+1) todo
+  * Possibility to reuse the ssh-ldap-helper.
+  * Tune the LDAP part to accept  all possible LDAP configurations.
+
+2) differences from original lpk
+  * No LDAP code in sshd.
+  * Support for various LDAP platforms and configurations.
+  * LDAP is configured in separate ldap.conf file.
+
+3) docs/link 
+  * http://pacsec.jp/core05/psj05-barisani-en.pdf
+  * http://fritz.potsdam.edu/projects/openssh-lpk/
+  * http://fritz.potsdam.edu/projects/sshgate/
+  * http://dev.inversepath.com/trac/openssh-lpk
+  * http://lam.sf.net/ ( http://lam.sourceforge.net/documentation/supportedSchemas.htm )
 
+4) contributors/ideas/greets
+  - Eric AUGE <eau@phear.org>
+  - Andrea Barisani <andrea@inversepath.com>
+  - Falk Siemonsmeier.
+  - Jacob Rief.
+  - Michael Durchgraf.
+  - frederic peters.
+  - Finlay dobbie.
+  - Stefan Fisher.
+  - Robin H. Johnson.
+  - Adrian Bridgett.
 
-To debug the ssh-ldap-helper is possible to set
-the necessary flags in the ssh-ldap-wrapper.
+5) Author
+    Jan F. Chadima <jchadima@redhat.com>
 
diff -up openssh-5.8p1/ldap-helper.c.ldap2 openssh-5.8p1/ldap-helper.c
--- openssh-5.8p1/ldap-helper.c.ldap2	2011-03-10 21:45:52.872854838 +0100
+++ openssh-5.8p1/ldap-helper.c	2011-03-10 21:45:53.342855061 +0100
@@ -138,6 +138,7 @@ main(int ac, char **av)
 	if (config_single_user) {
 		process_user (config_single_user, outfile);
 	} else {
+		usage();
 		fatal ("Not yet implemented");
 /* TODO
  * open unix socket a run the loop on it
diff -up openssh-5.8p1/lpk-user-example.txt.ldap2 openssh-5.8p1/lpk-user-example.txt
--- openssh-5.8p1/lpk-user-example.txt.ldap2	2011-03-10 21:45:52.986980339 +0100
+++ openssh-5.8p1/lpk-user-example.txt	2011-03-10 21:45:53.379854929 +0100
@@ -1,117 +0,0 @@
-
-Post to ML -> User Made Quick Install Doc.
-Contribution from John Lane <john@lane.uk.net>
-
-++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
-
-OpenSSH LDAP keystore Patch
-===========================
-
-NOTE: these notes are a transcript of a specific installation
-      they work for me, your specifics may be different!
-      from John Lane March 17th 2005         john@lane.uk.net
-
-This is a patch to OpenSSH 4.0p1 to allow it to obtain users' public keys
-from their LDAP record as an alternative to ~/.ssh/authorized_keys.
-
-(Assuming here that necessary build stuff is in $BUILD)
-
-cd $BUILD/openssh-4.0p1
-patch -Np1 -i $BUILD/openssh-lpk-4.0p1-0.3.patch
-mkdir -p /var/empty &&
-./configure --prefix=/usr --sysconfdir=/etc/ssh \
-    --libexecdir=/usr/sbin --with-md5-passwords --with-pam \
-    --with-libs="-lldap" --with-cppflags="-DWITH_LDAP_PUBKEY"
-Now do.
-make &&
-make install
-
-Add the following config to /etc/ssh/ssh_config
-UseLPK yes
-LpkServers ldap://myhost.mydomain.com
-LpkUserDN  ou=People,dc=mydomain,dc=com
-
-We need to tell sshd about the SSL keys during boot, as root's
-environment does not exist at that time. Edit /etc/rc.d/init.d/sshd.
-Change the startup code from this:
-                echo "Starting SSH Server..."
-                loadproc /usr/sbin/sshd
-                ;;
-to this:
-                echo "Starting SSH Server..."
-                LDAPRC="/root/.ldaprc" loadproc /usr/sbin/sshd
-                ;;
-
-Re-start the sshd daemon:
-/etc/rc.d/init.d/sshd restart
-
-Install the additional LDAP schema
-cp $BUILD/openssh-lpk-0.2.schema  /etc/openldap/schema/openssh.schema
-
-Now add the openSSH LDAP schema to /etc/openldap/slapd.conf:
-Add the following to the end of the existing block of schema includes
-include         /etc/openldap/schema/openssh.schema
-
-Re-start the LDAP server:
-/etc/rc.d/init.d/slapd restart
-
-To add one or more public keys to a user, eg "testuser" :
-ldapsearch -x -W -Z -LLL -b "uid=testuser,ou=People,dc=mydomain,dc=com" -D
-"uid=testuser,ou=People,dc=mydomain,dc=com" > /tmp/testuser
-
-append the following to this /tmp/testuser file
-objectclass: ldapPublicKey
-sshPublicKey: ssh-rsa
-AAAAB3NzaC1yc2EAAAABJQAAAIB3dsrwqXqD7E4zYYrxwdDKBUQxKMioXy9pxFVai64kAPxjU9KS
-qIo7QfkjslfsjflksjfldfkjsldfjLX/5zkzRmT28I5piGzunPv17S89z8XwSsuAoR1t86t+5dlI
-7eZE/gVbn2UQkQq7+kdDTS2yXV6VnC52N/kKLG3ciBkBAw== General Purpose RSA Key
-
-Then do a modify:
-ldapmodify -x -D "uid=testuser,ou=People,dc=mydomain,dc=com" -W -f
-/tmp/testuser -Z
-Enter LDAP Password:
-modifying entry "uid=testuser,ou=People,dc=mydomain,dc=com"
-And check the modify is ok:
-ldapsearch -x -W -Z -b "uid=testuser,ou=People,dc=mydomain,dc=com" -D
-"uid=testuser,ou=People,dc=mydomain,dc=com"
-Enter LDAP Password:
-# extended LDIF
-#
-# LDAPv3
-# base <uid=testuser,ou=People,dc=mydomain,dc=com> with scope sub
-# filter: (objectclass=*)
-# requesting: ALL
-#
-
-# testuser, People, mydomain.com
-dn: uid=testuser,ou=People,dc=mydomain,dc=com
-uid: testuser
-cn: testuser
-objectClass: account
-objectClass: posixAccount
-objectClass: top
-objectClass: shadowAccount
-objectClass: ldapPublicKey
-shadowLastChange: 12757
-shadowMax: 99999
-shadowWarning: 7
-loginShell: /bin/bash
-uidNumber: 9999
-gidNumber: 501
-homeDirectory: /home/testuser
-userPassword:: e1NTSEF9UDgwV1hnM1VjUDRJK0k1YnFiL1d4ZUJObXlZZ3Z3UTU=
-sshPublicKey: ssh-rsa
-AAAAB3NzaC1yc2EAAAABJQAAAIB3dsrwqXqD7E4zYYrxwdDKBUQxKMioXy9pxFVai64kAPxjU9KSqIo7QfkjslfsjflksjfldfkjsldfjLX/5zkzRmT28I5piGzunPv17S89z
-8XwSsuAoR1t86t+5dlI7eZE/gVbn2UQkQq7+kdDTS2yXV6VnC52N/kKLG3ciBkBAw== General Purpose RSA Key
-
-# search result
-search: 3
-result: 0 Success
-
-# numResponses: 2
-# numEntries: 1
-
-Now start a ssh session to user "testuser" from usual ssh client (e.g.
-puTTY). Login should succeed.
-
-++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
diff -up openssh-5.8p1/README.lpk.ldap2 openssh-5.8p1/README.lpk
--- openssh-5.8p1/README.lpk.ldap2	2011-03-10 21:45:53.112979980 +0100
+++ openssh-5.8p1/README.lpk	2011-03-10 21:45:53.416856007 +0100
@@ -1,274 +0,0 @@
-OpenSSH LDAP PUBLIC KEY PATCH 
-Copyright (c) 2003 Eric AUGE (eau@phear.org)
-All rights reserved.
-
-Rewriten by Jan F. Chadima (jchadima@redhat.com)
-Copyright (c) 2010 Red Hat, Inc.
-The new PKA-LDAP patch is rewritten from the scratch.
-LDAP schema and part of the documentation is based on original
-LPK project (http://code.google.com/p/openssh-lpk),
-copyright (c) 2003 Eric AUGE
-The new openssh configuration is different from the original LPK one.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions
-are met:
-1. Redistributions of source code must retain the above copyright
-   notice, this list of conditions and the following disclaimer.
-2. Redistributions in binary form must reproduce the above copyright
-   notice, this list of conditions and the following disclaimer in the
-   documentation and/or other materials provided with the distribution.
-3. The name of the author may not be used to endorse or promote products
-   derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
-IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
-OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
-IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
-INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
-NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
-THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-purposes of this patch:
-
-This patch would help to have authentication centralization policy
-using ssh public key authentication.
-This patch could be an alternative to other "secure" authentication system
-working in a similar way (Kerberos, SecurID, etc...), except the fact 
-that it's based on OpenSSH and its public key abilities.
-
->> FYI: <<
-'uid': means unix accounts existing on the current server
-'ServerGroup:' mean server group configured on the current server by the SSH_Filter option in the ldap.conf.
-
-example schema:
-
-
-                                  server1 (uid: eau,rival,toto) (ServerGroup: unix)
-                ___________      /
-               /           \ --- - server3 (uid: eau, titi) (ServerGroup: unix)
-              | LDAP Server |    \
-	      | eau  ,rival |     server2 (uid: rival, eau) (ServerGroup: unix)
-	      | titi ,toto  |
-	      | userx,....  |         server5 (uid: eau)  (ServerGroup: mail)
-               \___________/ \       /
-	                       ----- - server4 (uid: eau, rival)  (no group configured)
-			             \
-				        etc...
-
-- WHAT WE NEED :
-
-  * configured LDAP server somewhere on the network (i.e. OpenLDAP)
-  * patched sshd (with this patch ;)
-  * LDAP user(/group) entry (look at users.ldif (& groups.ldif)):
-        User entry:
-	- attached to the 'ldapPublicKey' objectclass
-	- attached to the 'posixAccount' objectclass
-	- with a filled 'sshPublicKey' attribute 
-	Example:
-		dn: uid=eau,ou=users,dc=cuckoos,dc=net
-		objectclass: top
-		objectclass: person
-		objectclass: organizationalPerson
-		objectclass: posixAccount
-		objectclass: ldapPublicKey
-		description: Eric AUGE Account
-		userPassword: blah
-		cn: Eric AUGE
-		sn: Eric AUGE
-		uid: eau
-		uidNumber: 1034
-		gidNumber: 1
-		homeDirectory: /export/home/eau
-		sshPublicKey: ssh-dss AAAAB3...
-		sshPublicKey: ssh-dss AAAAM5...
-
-	Group entry:
-	- attached to the 'posixGroup' objectclass
-	- with a 'cn' groupname attribute
-	- with multiple 'memberUid' attributes filled with usernames allowed in this group
-	Example:
-		# few members
-		dn: cn=unix,ou=groups,dc=cuckoos,dc=net
-		objectclass: top
-		objectclass: posixGroup
-		description: Unix based servers group
-		cn: unix
-		gidNumber: 1002
-		memberUid: eau
-		memberUid: user1
-		memberUid: user2
-
-
-- HOW IT WORKS :
-
-  * without patch
-  If a user wants to authenticate to log in a server the sshd, will first look for authentication method allowed (RSAauth,kerberos,etc..)
-  and if RSAauth and tickets based auth fails, it will fallback to standard password authentication (if enabled).
-
-  * with the patch
-  If a user want to authenticate to log in a server, the sshd will first look for auth method including LDAP pubkey, if the ldappubkey options is enabled.
-  It will do an ldapsearch to get the public key directly from the LDAP instead of reading it from the server filesystem. 
-  (usually in $HOME/.ssh/authorized_keys)
-
-  2 tokens are added to sshd_config :
-  # here is the new patched ldap related tokens
-  AuthorizedKeysCommand "/usr/libexec/openssh/ssh-ldap-wrapper"
-  AuthorizedKeysCommandRunAs nobody
-
-  The LDAP configuratin is read from common /etc/ldap.conf configuration file.
-There is also one optional parameter in the LDAP configuration file, SSH_Filter, which is a LDAP filter limiting keys to be searched.
-
-- HOW TO INSERT A USER/KEY INTO AN LDAP ENTRY
-
-  * my way (there is plenty :)
-  - create ldif file (i.e. users.ldif)
-  - cat ~/.ssh/id_dsa.pub OR cat ~/.ssh/id_rsa.pub OR cat ~/.ssh/identity.pub
-  - my way in 4 steps :
-  Example:
-
-  # you add this to the user entry in the LDIF file :
-  [...]
-  objectclass: posixAccount
-  objectclass: ldapPublicKey
-  [...]
-  sshPubliKey: ssh-dss AAAABDh12DDUR2...
-  [...]
-
-  # insert your entry and you're done :)
-  ldapadd -D balblabla -w bleh < file.ldif 
-  
-  all standard options can be present in the 'sshPublicKey' attribute.
-
-- WHY :
-
-  Simply because, i was looking for a way to centralize all sysadmins authentication, easily,  without completely using LDAP 
-  as authentication method (like pam_ldap etc..).  
-  
-  After looking into Kerberos, SecurID, and other centralized secure authentications systems, the use of RSA and LDAP to get 
-  public key for authentication allows us to control who has access to which server (the user needs an account and to be in 'strongAuthenticationUser'
-  objectclass within LDAP and part of the group the SSH server is in). 
-
-  Passwords update are no longer a nightmare for a server farm (key pair passphrase is stored on each user's box and private key is locally encrypted using his passphrase 
-  so each user can change it as much as he wants). 
-
-  Blocking a user account can be done directly from the LDAP (if sshd is using RSAAuth + ldap only).
-
-- RULES :  
-  Entry in the LDAP server must respect 'posixAccount' and 'ldapPublicKey' which are defined in core.schema. 
-  and the additionnal lpk.schema.
-
-  This patch could allow a smooth transition between standard auth (/etc/passwd) and complete LDAP based authentication 
-  (pamldap, nss_ldap, etc..).
-
-  This can be an alternative to other (old?/expensive?) authentication methods (Kerberos/SecurID/..).
-  
-  Referring to schema at the beginning of this file if user 'eau' is only in group 'unix'
-  'eau' would ONLY access 'server1', 'server2', 'server3' AND 'server4' BUT NOT 'server5'.
-  If you then modify the LDAP 'mail' group entry to add 'memberUid: eau' THEN user 'eau' would be able
-  to log in 'server5' (i hope you got the idea, my english is bad :).
-
-  Each server's sshd is patched and configured to ask the public key and the group infos in the LDAP
-  server.
-  When you want to allow a new user to have access to the server parc, you just add him an account on 
-  your servers, you add his public key into his entry on the LDAP server, it's done. 
-
-  Because sshds are looking public keys into the LDAP directly instead of a file ($HOME/.ssh/authorized_keys).
-
-  When the user needs to change his passphrase he can do it directly from his workstation by changing 
-  his own key set lock passphrase, and all servers are automatically aware.
- 
-  With a CAREFUL LDAP server configuration you could allow a user to add/delete/modify his own entry himself
-  so he can add/modify/delete himself his public key when needed.
-
-­ FLAWS :
-  LDAP must be well configured, getting the public key of some user is not a problem, but if anonymous LDAP 
-  allow write to users dn, somebody could replace someuser's public key by its own and impersonate some 
-  of your users in all your server farm be VERY CAREFUL.
-  
-  MITM attack when sshd is requesting the public key, could lead to a compromise of your servers allowing login 
-  as the impersonnated user.
-
-  If LDAP server is down then, no fallback on passwd auth.
-  
-  the ldap code part has not been well audited yet.
-
-- LDAP USER ENTRY EXAMPLES (LDIF Format, look in users.ldif)
-    --- CUT HERE ---
-    dn: uid=jdoe,ou=users,dc=foobar,dc=net
-    objectclass: top
-    objectclass: person
-    objectclass: organizationalPerson
-    objectclass: posixAccount
-    objectclass: ldapPublicKey
-    description: My account
-    cn: John Doe
-    sn: John Doe
-    uid: jdoe
-    uidNumber: 100
-    gidNumber: 100
-    homeDirectory: /home/jdoe
-    sshPublicKey: ssh-dss AAAAB3NzaC1kc3MAAAEBAOvL8pREUg9wSy/8+hQJ54YF3AXkB0OZrXB....
-    [...]
-    --- CUT HERE ---
-
-- LDAP GROUP ENTRY EXAMPLES (LDIF Format, look in groups.ldif)
-    --- CUT HERE ---
-    dn: cn=unix,ou=groups,dc=cuckoos,dc=net
-    objectclass: top
-    objectclass: posixGroup
-    description: Unix based servers group
-    cn: unix
-    gidNumber: 1002
-    memberUid: jdoe
-    memberUid: user1
-    memberUid: user2
-    [...]
-    --- CUT HERE ---
-
->> FYI: << 
-Multiple 'sshPublicKey' in a user entry are allowed, as well as multiple 'memberUid' attributes in a group entry
-
-- COMPILING:
-  1. Apply the patch
-  2. ./configure --with-your-options --with-ldap=/prefix/to/ldap_libs_and_includes
-  3. make
-  4. it's done.
-
-- BLA :
-  I hope this could help, and i hope to be clear enough,, or give ideas.  questions/comments/improvements are welcome.
-  
-- TODO :
-  Possibility to reuse the ssh-ldap-helper.
-  Tune the LDAP part to all possible LDAP configurations.
-
-- DIFFERENCES FROM ORIGINAL lpk
-  No LDAP code in sshd.
-  Support for various LDAP platforms and configurations.
-  LDAP is configured in separate ldap.conf file.
-
-- DOCS/LINK :
-  http://pacsec.jp/core05/psj05-barisani-en.pdf
-  http://fritz.potsdam.edu/projects/openssh-lpk/
-  http://fritz.potsdam.edu/projects/sshgate/
-  http://dev.inversepath.com/trac/openssh-lpk
-  http://lam.sf.net/ ( http://lam.sourceforge.net/documentation/supportedSchemas.htm )
-
-- CONTRIBUTORS/IDEAS/GREETS :
-  - Eric AUGE <eau@phear.org>
-  - Andrea Barisani <andrea@inversepath.com>
-  - Falk Siemonsmeier.
-  - Jacob Rief.
-  - Michael Durchgraf.
-  - frederic peters.
-  - Finlay dobbie.
-  - Stefan Fisher.
-  - Robin H. Johnson.
-  - Adrian Bridgett.
-
-- CONTACT :
-    Jan F. Chadima <jchadima@redhat.com>
-
diff -up openssh-5.8p1/ssh-ldap-helper.8.ldap2 openssh-5.8p1/ssh-ldap-helper.8
--- openssh-5.8p1/ssh-ldap-helper.8.ldap2	2011-03-10 21:45:53.170854817 +0100
+++ openssh-5.8p1/ssh-ldap-helper.8	2011-03-10 21:45:53.454980272 +0100
@@ -37,11 +37,12 @@ sshd configuration file
 by setting
 .Cm AuthorizedKeysCommand
 to
-.Dq /usr/libexec/ssh-ldap-helper -s %u .
+.Dq /usr/libexec/ssh-ldap-wrapper .
 .Pp
 .Nm
 is not intended to be invoked by the user, but from
-.Xr sshd 8 .
+.Xr sshd 8 via
+.Xr ssh-ldap-wrapper .
 .Pp
 The options are as follows:
 .Bl -tag -width Ds