Giving Users Privileges
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Some system activities are limited to users who hold specific privileges. These restrictions protect the integrity of the operating system's performance and, thus, the integrity of service provided to users. Grant privileges to each user on the basis of two factors: (a) whether the user has a legitimate need for the privilege and (b) whether the user has the skill and experience to use the privilege without disrupting the system.
A user's privileges are recorded in the user's UAF record in two privilege vectors. One vector stores the authorized privileges, and the other vector stores the default privileges. The default privileges are the subset of authorized privileges that a user process receives at login.
When a user logs in to the system, the user's privilege vector is stored in the header of the user's process. In this way, the user's privileges are passed on to the process created for the user. Users can use the DCL command SET PROCESS/PRIVILEGES to enable and disable privileges for which they are authorized.
The operating system monitors and audits the use of privilege. You can enable auditing for specific privileges and examine the audit log file to see what privileges were used to execute DCL commands or system services. See Chapter 9 “Security Auditing” for further information.
Privileges are divided into the following seven categories according to the damage that the user possessing them could cause the system:
None: No privileges
Normal: Minimum privileges to effectively use the system
Group: Potential to interfere with members of the same group
Devour: Potential to consume noncritical systemwide resources
System: Potential to interfere with normal system operation
Objects: Potential to compromise object security
All: Potential to control the system
Table 8-2 “OpenVMS Privileges” categorizes the privileges and includes a brief definition of the powers associated with each privilege.
Table 8-2 OpenVMS Privileges
| Category | Privilege | Activity Permitted |
|---|---|---|
None | None | Deny activities requiring privileges |
Normal | NETMBX TMPMBX | Create network connections Create temporary mailbox |
Group | GROUP GRPPRV | Control processes in the same group Gain access through the system protection field of the group's objects |
Devour | ACNT ALLSPOOL BUGCHK EXQUOTA GRPNAM PRMCEB PRMGBL PRMMBX SHMEM | Disable accounting Allocate spooled devices Make bugcheck error log entries Exceed disk quotas Insert group logical names in the name table Create/delete permanent common event flag clusters Create permanent global sections Create permanent mailboxes Create/delete structures in shared memory |
System | ALTPRI AUDIT OPER PSWAPM WORLD SECURITY SYSLCK | Set base priority higher than allotment Generate audit records Perform operator functions Change process swap mode Control any process Perform security-related functions Lock systemwide resources |
Objects | DIAGNOSE IMPORT MOUNT READALL SYSGBL VOLPRO | Diagnose devices Mount a nonlabeled tape volume Execute mount volume QIO Possess read access to all system objects Create systemwide global sections Override volume protection |
All | BYPASS CMEXEC CMKRNL IMPERSONATE DOWNGRADE LOG_IO PFNMAP PHY_IO SETPRV SHARE SYSNAM SYSPRV UPGRADE | Disregard protection Change to executive mode Change to kernel mode Create detached processes of arbitrary UIC Write to a lower secrecy object or lower an object's classification Issue logical I/O requests Map to specific physical pages Issue physical I/O requests Enable any privilege Access devices allocated to other users Insert system logical names in the name table Access objects through the system protection field Write to a higher integrity object or raise an object's integrity level |
Appendix A “Assigning Privileges” lists all user privileges and includes recommendations on when to grant them. When allocating user privileges, be conservative.
The summary guidelines in Table 8-3 “Minimum Privileges for System Users” indicate the minimum privilege requirements for common classes of system users.
Table 8-3 Minimum Privileges for System Users
| Type of User | Minimum Privileges |
|---|---|
General | TMPMBX, NETMBX |
Operator | OPER |
Group manager | GROUP, GRPPRV |
System manager/administrator | SYSPRV, OPER, SYSNAM, CMKRNL[1] |
Security administrator | SECURITY, AUDIT, READALL |
[1] The general purpose system manager often needs an authorized privilege set consisting of all privileges except BYPASS. | |
Granting privileges allows users those privileges until you remove them. To avoid such blanket permission, you may want to grant privileges on an as-needed basis. For example, certain users may need to run a program requiring one of the more powerful privileges. You can install the program with the necessary privilege by using the Install utility (INSTALL). “Installing Images with Privilege” discusses installing privileged images in more detail.
An alternative to granting blanket privileges is to set up emergency or specialized privileged accounts. Users would log in to these privileged accounts only to perform specific functions. You have two options with this technique:
Establish a limited group of users who know about the account and are informed how to use it.
Create two accounts for the user, giving the privileges to one account but not to the other. In this case, the user would have the same UIC and the same default directory in each account. (This is the only case where HP recommends shared UICs, because there is still only one actual user.) If you decide to adopt this dual account practice, avoid obvious user names that reveal which account is the privileged account.
With both options, you can place special restrictions on the privileged account, such as long passwords, brief password lifetimes, restricted hours, and limited modes of operation (no dialup, network, remote, or batch logins). In addition, limited account durations would force frequent consideration of privilege requirements.
Yet another alternative is to use protected subsystems, which are described in Chapter 13 “Using Protected Subsystems”, and thereby eliminate the need for any system privileges.
A user cannot execute an image that requires a privilege the user does not possess unless the image is installed as a known image with the privilege in question. (See the HP OpenVMS System Management Utilities Reference Manual for instructions on installing known images.) Execution of a known image with privileges grants those privileges to the user process executing the image for the duration of the image's execution. Thus, you should install images with amplified privileges (other than the normal HP-supplied configuration) only after ensuring that the privileges are required by the image's function and that the image operates safely. Also consider restricting access to the image to a selected set of users.
Images installed with privileges are activated with all amplified privileges enabled. For maximum safety, images designed to run with amplified privilege should use the $SETPRV system service to disable all amplified privileges immediately on activation, and enable them only when they are needed.
Following is an example of installing an image with privilege. The System Dump Analyzer utility (SDA) requires CMKRNL privilege to analyze the running system.
Install SDA.EXE with the CMKRNL privilege, as follows:
$ INSTALL SDA.EXE /PRIVILEGED=CMKRNLPlace an ACL on SDA.EXE, and also set the UIC-based protection to deny all access to the world category of users, as follows:
$ SET SECURITY/ACL=(IDENTIFIER=SDA,ACCESS=EXECUTE)-
_$ SYS$SYSTEM:SDA.EXE
$ SET SECURITY/PROTECTION=(WORLD) SYS$SYSTEM:SDA.EXEUse the AUTHORIZE command to confirm that the users who hold the SDA identifier are those intended to run the program. If necessary, make adjustments to this list of users.
Some DCL commands behave differently depending on the privileges that the user holds.
For example, unless a user holds the GROUP or WORLD privilege, the SHOW PROCESS command limits the display of process information to the user's process. A user with GROUP privilege can display other processes in the user's UIC group; a user with WORLD privilege can display any process on the system.