Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Managing System Security

Managing Access to Files and Directories

Chapter 8 773

• Protect all disk special ﬁles:

❏ Write-protect all disk special ﬁles from general users, to prevent

inadvertent data corruption. Turn off write access for group and

other.

❏ Read-protect disk special ﬁles to prevent disclosure. Turn off

read access for other.

The directory entries should look like:

brw-r----- 1 bin sys 31 0x002000 Feb 18 1998 /dev/dsk/c0t2d0

crw-r----- 1 bin sys 188 0x002000 Aug 3 1998 /dev/rdsk/c0t2d0

brw-r----- 1 root sys 64 0x000002 Jun 11 1996 /dev/vg00/lvol2

crw-r----- 1 root sys 64 0x000002 Jun 11 1996 /dev/vg00/rlvol2

• Terminal ports on UNIX systems may be writable by anyone, if you

are allowing users to communicate by using the write or talk

programs. Only the owner, however, should have read permission.

• Individual users should never own a device ﬁle other than a terminal

device or personal printer.

• Before putting a disk or other mountable device of unknown origin

into service, check its ﬁles for special ﬁles and setuid programs. See

“Guidelines for Mounting and Unmounting a File System” on

page 779.

Protecting Disk Partitions and Logical Volumes

• The device ﬁles for disk partitions and logical volumes should be

readable only by root and perhaps by an account used for disk

backups. See “Security Considerations for Device Files” on page 772.

• Since ownership and permissions are stored in the inode, anyone

with write permission to a mounted partition can set the user ID for

any ﬁle in that partition, regardless of the owner, bypassing the

chmod() system call and other security checks.

• If a program, such as a database, requires direct access to the

partition, that partition should be reserved exclusively for the

program and never mounted. Program users should be informed that

the ﬁle’s security is enforced by its permission settings, rather than

by the UNIX ﬁle system.