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Unit 8: Sudo rule management

Prerequisites:

Sudo is a program that allows users to run programs as another user with different privileges (possibly root). Sudo rules provide fine-grained control over who can execute which processes, as which users. FreeIPA allows centralised management of Sudo rules. To simplify management, Sudo rules can refer to User Groups, Host Groups and Command Groups as well as individual users, hosts and commands.

Older versions of sudo did not require pam access for passwordless rules (e.g. rules with the NOPASSWD keyword). sudo-1.8.23 and newer require pam access for all rules.

The goal of this unit is to allow alice (being a sysadmin) to run any command on any FreeIPA-enrolled machine, and to allow bob (who is merely a web server administrator) to control httpd on hosts that are webservers.

As of FreeIPA 4.6.90.pre2, you should enable SSSD's sudo responder by running:

[client]$ sudo authselect enable-feature with-sudo

Restart SSSD:

[client]$ sudo systemctl restart sssd

Permitting alice to run all commmands

Let's deal with alice first. Before we do anything else, log in as alice and attempt to run the id command as root. Observe that the action is denied:

[client]$ su -l alice
Password:

[alice@client]$ sudo id
[sudo] password for alice:
alice is not allowed to run sudo on client.  This incident will be reported.

[alice@client]$ exit
logout

Now define the sysadmin_sudo rule, which allows members of the sysadmin User Group to to run any command on any host:

[client]$ ipa sudorule-add sysadmin_sudo \
    --hostcat=all --runasusercat=all --runasgroupcat=all --cmdcat=all
-------------------------------
Added Sudo Rule "sysadmin_sudo"
-------------------------------
  Rule name: sysadmin_sudo
  Enabled: TRUE
  Host category: all
  Command category: all
  RunAs User category: all
  RunAs Group category: all

Next add the sysadmin User Group to the Sudo rule:

[client]$ ipa sudorule-add-user sysadmin_sudo --group sysadmin
  Rule name: sysadmin_sudo
  Enabled: TRUE
  Host category: all
  Command category: all
  RunAs User category: all
  RunAs Group category: all
  User Groups: sysadmin
-------------------------
Number of members added 1
-------------------------

Now attempt to sudo id as alice again:

[client]$ su -l alice
Password:

[alice@client]$ sudo id
[sudo] password for alice:
uid=0(root) gid=0(root) groups=0(root) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

This time the action was allowed, and we can see from the output that alice indeed executed the id command as root.

Note: if the command is prevented there may be some stale cache entries. Move on with the workshop and try again in 5 minutes.

Permitting bob to run web administration commands

Now let us turn our attention to bob. The goal is to allow bob and other web servers administrators to run commands related to web server administration (and only such commands).

First, create a new User Group named webadmin and add bob as a member. Add an hbacrule that allows bob to log into hosts that are members of the webservers Host Group using the sshd service.

Once this is done you should be able to login, but not use su -l:

[client]$ su -l bob
Password:

[bob@client]$ su -l bob
Password:
su: Permission denied

Then, let's observe that bob currently cannot restart Apache:

[bob@client]$ sudo systemctl restart httpd
[sudo] password for bob:
sudo: PAM account management error: Permission denied

Take note that the error is different from the one alice got, which was:

alice is not allowed to run sudo on client.  This incident will be reported.

While the HBAC rule alice uses (sysadmin_webservers) was created with "--servicecat=all", the HBAC rule for bob was created with sshd in mind, like this:

[server]$ ipa hbacrule-add-service webadmin_webservers --hbacsvcs=sshd

As bob needs to run both su -l and sudo, add both commands to the list of allowed services in your access control rule, for instance:

[server]$ ipa hbacrule-add-service webadmin_webservers \
    --hbacsvcs=sudo --hbacsvcs=su-l

Now login and logout as bob. Not only bob should now be able to use su -l, but the error message from sudo should change:

[bob@client]$ sudo systemctl restart httpd
[sudo] password for bob:
Sorry, user bob is not allowed to execute '/bin/systemctl restart httpd' as root on client.ipademo.local.

Now define the webadmin_sudo rule. Note that we do not use --hostcat=all or cmdcat=all this time.

[client]$ ipa sudorule-add webadmin_sudo \
    --runasusercat=all --runasgroupcat=all
-------------------------------
Added Sudo Rule "webadmin_sudo"
-------------------------------
  Rule name: webadmin_sudo
  Enabled: TRUE
  RunAs User category: all
  RunAs Group category: all

Add the webadmin User Group and webservers Host Group to the rule:

[client]$ ipa sudorule-add-user webadmin_sudo --group webadmin
  Rule name: webadmin_sudo
  Enabled: TRUE
  RunAs User category: all
  RunAs Group category: all
  User Groups: webadmin
-------------------------
Number of members added 1
-------------------------

[client]$ ipa sudorule-add-host webadmin_sudo --hostgroup webservers
  Rule name: webadmin_sudo
  Enabled: TRUE
  RunAs User category: all
  RunAs Group category: all
  User Groups: webadmin
  Host Groups: webservers
-------------------------
Number of members added 1
-------------------------

Next, define Sudo Commands and a Sudo Command Group for web server administration:

[client]$ ipa sudocmd-add "/usr/bin/systemctl start httpd"
---------------------------------------------------
Added Sudo Command "/usr/bin/systemctl start httpd"
---------------------------------------------------
  Sudo Command: /usr/bin/systemctl start httpd

[client]$ ipa sudocmd-add "/usr/bin/systemctl restart httpd"
-----------------------------------------------------
Added Sudo Command "/usr/bin/systemctl restart httpd"
-----------------------------------------------------
  Sudo Command: /usr/bin/systemctl restart httpd

[client]$ ipa sudocmdgroup-add webadmin_cmds
----------------------------------------
Added Sudo Command Group "webadmin_cmds"
----------------------------------------
  Sudo Command Group: webadmin_cmds

[client]$ ipa sudocmdgroup-add-member webadmin_cmds \
    --sudocmds "/usr/bin/systemctl start httpd" \
    --sudocmds "/usr/bin/systemctl restart httpd"
  Sudo Command Group: webadmin_cmds
  Member Sudo commands: /usr/bin/systemctl start httpd, /usr/bin/systemctl restart httpd
-------------------------
Number of members added 2
-------------------------

Finally, add this new command group to the Sudo rule:

[client]$ ipa sudorule-add-allow-command webadmin_sudo \
    --sudocmdgroups webadmin_cmds
  Rule name: webadmin_sudo
  Enabled: TRUE
  RunAs User category: all
  RunAs Group category: all
  User Groups: webadmin
  Host Groups: webservers
  Sudo Allow Command Groups: webadmin_cmds
-------------------------
Number of members added 1
-------------------------

Now log in again as bob and observe that we have reached our goal: he can restart (or start) Apache, but not run other commands via sudo:

[client]$ su -l bob
Password:

[bob@client]$ sudo systemctl restart httpd
[sudo] password for bob:

[bob@client]$ sudo id
Sorry, user bob is not allowed to execute '/bin/id' as root on client.ipademo.local.

This concludes the unit. Now that you have Sudo rules working, proceed to Unit 9: SELinux User Maps.