The most secure way to manage privileges for users and roles is to confine use of privilege to commands in a rights profile. The rights profile is then included in a role. The role is assigned to a user. When the user assumes the assigned role, the privileged commands are available to be run in a profile shell. The following procedures show how to assign privileges, remove privileges, and debug privilege use.
How to Determine the Privileges on a Process
Example 11-1 Determining the Privileges in Your Current Shell
In the following example, the privileges in the parent process of the user's shell process are listed. In the second example, the full names of the privileges are listed. The single letters in the output refer to the following privilege sets:
% ppriv $$ 1200: -csh flags = <none> E: basic I: basic P: basic L: all % ppriv -v $$ 1200: -csh flags = <none> E: file_link_any,proc_exec,proc_fork,proc_info,proc_session I: file_link_any,proc_exec,proc_fork,proc_info,proc_session P: file_link_any,proc_exec,proc_fork,proc_info,proc_session L: cpc_cpu,dtrace_kernel,dtrace_proc,dtrace_user,…,sys_time
Example 11-2 Determining the Privileges of a Role That You Can Assume
Roles use an administrative shell, or profile shell. You must assume a role and use the role's shell to list the privileges that have been directly assigned to the role. In the following example, the role sysadmin has no directly assigned privileges.
% su - sysadmin Password: <Type sysadmin password> $ /usr/ucb/whoami sysadmin $ ppriv -v $$ 1400: pfksh flags = <none> E: file_link_any,proc_exec,proc_fork,proc_info,proc_session I: file_link_any,proc_exec,proc_fork,proc_info,proc_session P: file_link_any,proc_exec,proc_fork,proc_info,proc_session L: cpc_cpu,dtrace_kernel,dtrace_proc,dtrace_user,…,sys_time
How to Determine Which Privileges a Program Requires
Before You Begin
The command or process must have failed for this procedure to work.
Example 11-3 Using the truss Command to Examine Privilege Use
The truss command can debug privilege use in a regular shell. For example, the following command debugs the failing touch process:
% truss -t creat touch /etc/acct/yearly creat64("/etc/acct/yearly", 0666) Err#13 EACCES [file_dac_write] touch: /etc/acct/yearly cannot create
The extended /proc interfaces report the missing privilege after the error code in truss output.
Example 11-4 Using the ppriv Command to Examine Privilege Use in a Profile Shell
The ppriv command can debug privilege use in a profile shell. If you assign a rights profile to a user, and the rights profile includes commands with privileges, the commands must be typed in a profile shell. When the privileged commands are typed in a regular shell, the commands do not execute with privilege.
In this example, the jdoe user can assume the role objadmin. The objadmin role includes the Object Access Management rights profile. This rights profile allows the objadmin role to change permissions on files that objadmin does not own.
In the following excerpt, jdoe fails to change the permissions on the useful.script file:
jdoe% ls -l useful.script -rw-r--r-- 1 aloe staff 2303 Mar 11 05:29 useful.script jdoe% chown objadmin useful.script chown: useful.script: Not owner jdoe% ppriv -eD chown objadmin useful.script chown: missing privilege "file_chown" (euid = 130, syscall = 16) needed at ufs_setattr+0x258 chown: useful.script: Not owner
When jdoe assumes the objadmin role, the permissions on the file are changed:
jdoe% su - objadmin Password: <Type objadmin password> $ ls -l useful.script -rw-r--r-- 1 aloe staff 2303 Mar 11 05:29 useful.script $ chown objadmin useful.script $ ls -l useful.script -rw-r--r-- 1 objadmin staff 2303 Mar 11 05:29 useful.script $ chgrp admin useful.script $ ls -l objadmin.script -rw-r--r-- 1 objadmin admin 2303 Mar 11 05:31 useful.script
Example 11-5 Changing a File Owned by the root User
This example illustrates the protections against privilege escalation. For a discussion, see Prevention of Privilege Escalation. The file is owned by the root user. The less powerful role, objadmin role needs all privileges to change the file's ownership, so the operation fails.
jdoe% su - objadmin Password: <Type objadmin password> $ cd /etc; ls -l system -rw-r--r-- 1 root sys 1883 Mar 20 14:04 system $ chown objadmin system chown: system: Not owner $ ppriv -eD chown objadmin system chown: missing privilege "ALL" (euid = 101, syscall = 16) needed at ufs_setattr+0x258 chown: system: Not owner
How to Add Privileges to a Command
You add privileges to a command when you are adding the command to a rights profile. The privileges enable the role that includes the rights profile to run the administrative command, while not gaining any other superuser capabilities.
Before You Begin
The command or program must be privilege-aware. For a fuller discussion, see How Processes Get Privileges.
How to Assign Privileges to a User or Role
You might trust some users with a particular privilege all the time. Very specific privileges that affect a small part of the system are good candidates for assigning to a user. For a discussion of the implications of directly assigned privileges, see Security Considerations When Directly Assigning Security Attributes.
The following procedure enables user jdoe to use high resolution timers.
Example 11-6 Creating a Role With Privileges to Configure System Time
$ /usr/sadm/bin/smrole -D nisplus:/examplehost/example.domain \ -r primaryadm -l <Type primaryadm password> \ add -- -n clockmgr \ -c "Role that sets system time" \ -F "Clock Manager" \ -s /bin/pfksh \ -u 108 \ -P <Type clockmgr password> \ -K defaultpriv=basic,proc_priocntl,sys_cpu_config, proc_clock_highres,sys_time
The -K line is wrapped for display purposes.
If the role was created locally, the user_attr entry for the role would appear similar to the following:
clockmgr:::Role that sets system time: type=role;defaultpriv=basic,proc_priocntl,sys_cpu_config, proc_clock_highres,sys_time
How to Limit a User's or Role's Privileges
You can limit the privileges that are available to a user or role by reducing the basic set, or by reducing the limit set. You should have good reason to limit the user's privileges in this way, because such limitations can have unintended side effects.
Caution - You should thoroughly test any user's capabilities where the basic set or the limit set has been modified for a user.
Example 11-7 Removing Privileges From a User's Limit Set
In the following example, all sessions that originate from jdoe's initial login are prevented from using the sys_linkdir privilege. That is, the user cannot make hard links to directories, nor can the user unlink directories, even after the user runs the su command.
$ usermod -K limitpriv=all,!sys_linkdir jdoe $ grep jdoe /etc/user_attr jdoe::::type=normal;defaultpriv=basic;limitpriv=all,!sys_linkdir
Example 11-8 Removing Privileges From a User's Basic Set
In the following example, all sessions that originate from jdoe's initial login are prevented from using the proc_session privilege. That is, the user cannot examine any processes outside the user's session, even after the user runs the su command.
$ usermod -K defaultpriv=basic,!proc_session jdoe
$ grep jdoe /etc/user_attr jdoe::::type=normal;defaultpriv=basic,!proc_session;limitpriv=all
How to Run a Shell Script With Privileged Commands
Note - When you create a shell script that runs commands with inherited privileges, the appropriate rights profile must contain the commands with privileges assigned to them.