Administrator's Guide

Observe the following precautions when mounting a file system or disk:
• Create a mount point directory (such as /mnt) on which to mount a new file system.
Never mount a file system on a directory that already contains files, because those
files will become inaccessible.
The mount point of a mounted file system acquires the permissions and ownership
of the file system's root directory.
• Set permissions and access control list entries on disk path names to control access
to disks.
• Use the -r option of the mount command to mount the file system as read-only.
You must mount physically write-protected file systems this way.
• When mounting a new or foreign file system, assume that the medium is insecure.
— Make sure that the PATH environment variable does not include “.” (the current
directory); otherwise, you might run a Trojan horse version of ls or some similar
command while examining the new file system.
— Run the fsck command to verify that the file system is not technically corrupted.
See fsck(1M).
— Run the ncheck_hfs -s or ncheck_vxfs -s command to scan for setuid
and setgid programs and device files, and investigate any suspicious findings.
The -s option is intended to discover concealed violations of security policy. For
more information, see ncheck_hfs(1M) and ncheck_vxfs(1M).
— Create a directory restricted to root by setting its permissions at 700
(drwx------).
# mkdir /securefile
# chmod 700 /securefile
— Mount the foreign file system read-only at that location:
# mount -r /dev/disk1 /securefile
— Check all directories for privileged programs, and verify the identity of every
program.
— Remount the system read and write permissions and remove any unnecessary
setuid and setgid permissions from files that you discovered in the previous
step. These precautions are especially important if a user requests that you mount
a personal file system.
Only after performing these tests should you unmount the file system and remount it
in its desired location.
• Be sure to unmount all mounted file systems of a user whose account you are
disabling or removing.
For information on files mounted in an NFS environment, see Section 5.10.2.
5.9 Security Guidelines for Mounting and Unmounting File Systems 105