Protecting Files (Tasks)

The following procedures protect files with UNIX permissions, locate files with security risks, and protect the system from compromise by these files.

Protecting Files With UNIX Permissions (Task Map)

The following task map points to procedures that list file permissions, change file permissions, and protect files with special file permissions.

Task	For Instructions
Display file information.	How to Display File Information
Change local file ownership.	How to Change the Owner of a File How to Change Group Ownership of a File
Change local file permissions.	How to Change File Permissions in Symbolic Mode How to Change File Permissions in Absolute Mode How to Change Special File Permissions in Absolute Mode

How to Display File Information

Display information about all the files in a directory by using the ls command.

Type the following command to display a long listing of all files in the current directory.
```
% ls -la
```
-l

Displays the long format that includes user ownership, group ownership, and file permissions.

-a

Displays all files, including hidden files that begin with a dot (.).

For all options to the ls command, see the ls(1) man page.

Example 7-1 Displaying File Information

In the following example, a partial list of the files in the /sbin directory is displayed.

% cd /sbin
% ls -la
total 4960
drwxr-xr-x   2 root     sys           64 Dec  8 11:57 ./
drwxr-xr-x  39 root     root          41 Dec  8 15:20 ../
-r-xr-xr-x   1 root     bin        21492 Dec  1 20:55 autopush*
-r-xr-xr-x   1 root     bin        33680 Oct  1 11:36 beadm*
-r-xr-xr-x   1 root     bin       184360 Dec  1 20:55 bootadm*
lrwxrwxrwx   1 root     root          21 Jun  7  2010 bpgetfile -> ...
-r-xr-xr-x   1 root     bin        86048 Dec  1 20:55 cryptoadm*
-r-xr-xr-x   1 root     bin        12828 Dec  1 20:55 devprop*
-r-xr-xr-x   1 root     bin       130132 Dec  1 20:55 dhcpagent*
-r-xr-xr-x   1 root     bin        13076 Dec  1 20:55 dhcpinfo*

   .
   .
   .

Each line displays information about a file in the following order:

Type of file – For example, d. For list of file types, see File and Directory Ownership.
Permissions – For example, r-xr-xr-x. For description, see File and Directory Ownership.
Number of hard links – For example, 2.
Owner of the file – For example, root.
Group of the file – For example, bin.
Size of the file, in bytes – For example, 13076.
Date the file was created or the last date that the file was changed – For example, Dec 1 20:55.
Name of the file – For example, dhcpinfo.

How to Change the Owner of a File

Before You Begin

If you are not the owner of the file or directory, you must be assigned the Object Access Management rights profile. To change a file that is a public object, you must assume the root role.

For more information, see How to Use Your Assigned Administrative Rights.

Display the permissions on a local file.

% ls -l example-file
-rw-r--r--   1 janedoe   staff   112640 May 24 10:49 example-file

Change the owner of the file.
```
# chown stacey example-file
```
Verify that the owner of the file has changed.
```
# ls -l example-file
-rw-r--r--   1 stacey   staff   112640 May 26 08:50 example-file 
```
To change permissions on NFS-mounted files, see Chapter 3, Accessing Network File Systems (Reference), in Managing Network File Systems in Oracle Solaris 11.1.

Example 7-2 Enabling Users to Change the Ownership of Their Own Files

Security Consideration – You need a good reason to change the setting of the rstchown variable to zero. The default setting prevents users from listing their files as belonging to others so as to bypass space quotas.

In this example, the value of the rstchown variable is set to zero in the /etc/system file. This setting enables the owner of a file to use the chown command to change the file's ownership to another user. This setting also enables the owner to use the chgrp command to set the group ownership of a file to a group that the owner does not belong to. The change goes into effect when the system is rebooted.

set rstchown = 0

For more information, see the chown(1) and chgrp(1) man pages.

How to Change Group Ownership of a File

Before You Begin

If you are not the owner of the file or directory, you must be assigned the Object Access Management rights profile. To change a file that is a public object, you must assume the root role.

For more information, see How to Use Your Assigned Administrative Rights.

Change the group ownership of a file.
```
$ chgrp scifi example-file
```
For information about setting up groups, see Chapter 1, Managing User Accounts and User Environments (Overview), in Managing User Accounts and User Environments in Oracle Solaris 11.1.

Verify that the group ownership of the file has changed.

$ ls -l example-file
 -rw-r--r--   1 stacey   scifi   112640 June 20 08:55  example-file

Also see Example 7-2.

How to Change File Permissions in Symbolic Mode

In the following procedure, a user changes permissions on a file that the user owns.

Change permissions in symbolic mode.
```
% chmod who operator permissions filename
```
who

Specifies whose permissions are to be changed.

operator

Specifies the operation to be performed.

permissions

Specifies what permissions are to be changed. For the list of valid symbols, see Table 7-5.

filename

Specifies the file or directory.
Verify that the permissions of the file have changed.
```
% ls -l filename
```
Note - If you are not the owner of the file or directory, you must be assigned the Object Access Management rights profile. To change a file that is a public object, you must assume the root role.

Example 7-3 Changing Permissions in Symbolic Mode

In the following example, read permission is taken away from others.

% chmod o-r example-file1

In the following example, read and execute permissions are added to a local file for user, group, and others.

$ chmod a+rx example-file2

In the following example, read, write, and execute permissions for group are assigned to a local file.

$ chmod g=rwx example-file3

How to Change File Permissions in Absolute Mode

In the following procedure, a user changes permissions on a file that the user owns.

Change permissions in absolute mode.
```
% chmod nnn filename
```
nnn

Specifies the octal values that represent the permissions for the file owner, file group, and others, in that order. For the list of valid octal values, see Table 7-4.

filename

Specifies the file or directory.

Note - If you use the chmod command to change file or directory permissions on objects that have existing ACL entries, the ACL entries might change as well. The exact changes are dependent upon the chmod permission operation changes and the file system's aclmode and aclinherit property values.
For more information, see Chapter 7, Using ACLs and Attributes to Protect Oracle Solaris ZFS Files, in Oracle Solaris 11.1 Administration: ZFS File Systems.
Verify that the permissions of the file have changed.
```
% ls -l filename
```
Note - If you are not the owner of the file or directory, you must be assigned the Object Access Management rights profile. To change a file that is a public object, you must assume the root role.

Example 7-4 Changing Permissions in Absolute Mode

In the following example, the permissions of a directory that is open to the public are changed from 744 (read, write, execute; read-only; and read-only) to 755 (read, write, execute; read and execute; and read and execute).

# ls -ld public_dir
drwxr--r--  1 jdoe   staff    6023 Aug  5 12:06 public_dir
# chmod 755 public_dir
# ls -ld public_dir
drwxr-xr-x  1 jdoe   staff    6023 Aug  5 12:06 public_dir

In the following example, the permissions of an executable shell script are changed from read and write to read, write, and execute.

% ls -l my_script
-rw------- 1 jdoe   staff    6023 Aug  5 12:06 my_script
% chmod 700 my_script
% ls -l my_script
-rwx------ 1 jdoe   staff    6023 Aug  5 12:06 my_script

How to Change Special File Permissions in Absolute Mode

Before You Begin

If you are not the owner of the file or directory, you must be assigned the Object Access Management rights profile. To change a file that is a public object, you must assume the root role.

For more information, see How to Use Your Assigned Administrative Rights.

Change special permissions in absolute mode.
```
% chmod nnnn filename
```
nnnn

Specifies the octal values that change the permissions on the file or directory. The leftmost octal value sets the special permissions on the file. For the list of valid octal values for special permissions, see Table 7-6.

filename

Specifies the file or directory.

Note - When you use the chmod command to change the file group permissions on a file with ACL entries, both the file group permissions and the ACL mask are changed to the new permissions. Be aware that the new ACL mask permissions can change the permissions for additional users and groups who have ACL entries on the file. Use the getfacl command to make sure that the appropriate permissions are set for all ACL entries. For more information, see the getfacl(1) man page.
Verify that the permissions of the file have changed.
```
% ls -l filename
```

Example 7-5 Setting Special File Permissions in Absolute Mode

In the following example, the setuid permission is set on the dbprog file.

# chmod 4555 dbprog
# ls -l dbprog
-r-sr-xr-x   1 db     staff        12095 May  6 09:29 dbprog

In the following example, the setgid permission is set on the dbprog2 file.

# chmod 2551 dbprog2
# ls -l dbprog2
-r-xr-s--x   1 db     staff       24576 May  6 09:30 dbprog2

In the following example, the sticky bit permission is set on the public_dir directory.

# chmod 1777 public_dir
# ls -ld public_dir
drwxrwxrwt   2 jdoe   staff          512 May 15 15:27 public_dir

Protecting Against Programs With Security Risk (Task Map)

The following task map points to procedures that find risky executables on the system, and that prevent programs from exploiting an executable stack.

Task	Description	For Instructions
Find files with special permissions.	Locates files with the `setuid` bit set, but that are not owned by the `root` user.	How to Find Files With Special File Permissions
Prevent executable stack from overflowing.	Prevents programs from exploiting an executable stack.	How to Disable Programs From Using Executable Stacks
Prevent logging of executable stack messages.	Turns off logging of executable stack messages.	Example 7-7

How to Find Files With Special File Permissions

This procedure locates potentially unauthorized use of the setuid and setgid permissions on programs. A suspicious executable file grants ownership to a user rather than to root or bin.

Before You Begin

You must assume the root role. For more information, see How to Use Your Assigned Administrative Rights.

Find files with setuid permissions by using the find command.
```
# find directory -user root -perm -4000 -exec ls -ldb {} \; >/tmp/filename
```
find directory

Checks all mounted paths starting at the specified directory, which can be root (/), sys, bin, or mail.

-user root

Displays files owned only by root.

-perm -4000

Displays files only with permissions set to 4000.

-exec ls -ldb

Displays the output of the find command in ls -ldb format.

/tmp/filename

Is the file that contains the results of the find command.
Display the results in /tmp/filename.
```
# more /tmp/filename
```
For background information about setuid permissions, see setuid Permission.

Example 7-6 Finding Files With setuid Permissions

The output from the following example shows that a user in a group called rar has made a personal copy of /usr/bin/sh, and has set the permissions as setuid to root. As a result, the /usr/rar/bin/sh program runs with root permissions.

This output was saved for future reference by moving the /var/tmp/chkprm file to an archive.

# find / -user root -perm -4000 -exec ls -ldb {} \; > /var/tmp/ckprm
# cat /var/tmp/ckprm
-r-sr-xr-x 1 root bin 38836 Aug 10 16:16 /usr/bin/at
-r-sr-xr-x 1 root bin 19812 Aug 10 16:16 /usr/bin/crontab
---s--x--x 1 root sys 46040 Aug 10 15:18 /usr/bin/ct
-r-sr-xr-x 1 root sys 12092 Aug 11 01:29 /usr/lib/mv_dir
-r-sr-sr-x 1 root bin 33208 Aug 10 15:55 /usr/lib/lpadmin
-r-sr-sr-x 1 root bin 38696 Aug 10 15:55 /usr/lib/lpsched
---s--x--- 1 root rar 45376 Aug 18 15:11 /usr/rar/bin/sh
-r-sr-xr-x 1 root bin 12524 Aug 11 01:27 /usr/bin/df
-rwsr-xr-x 1 root sys 21780 Aug 11 01:27 /usr/bin/newgrp
-r-sr-sr-x 1 root sys 23000 Aug 11 01:27 /usr/bin/passwd
-r-sr-xr-x 1 root sys 23824 Aug 11 01:27 /usr/bin/su
# mv /var/tmp/ckprm /export/sysreports/ckprm

How to Disable Programs From Using Executable Stacks

For a description of the security risks of 32-bit executable stacks, see Protecting Executable Files From Compromising Security.

Before You Begin

You must assume the root role. For more information, see How to Use Your Assigned Administrative Rights.

Edit the /etc/system file, and add the following line:
```
set noexec_user_stack=1
```
Reboot the system.
```
# reboot
```

Example 7-7 Disabling the Logging of Executable Stack Messages

In this example, the logging of executable stack messages is disabled, and then the system is rebooted.

# cat /etc/system
set noexec_user_stack=1
set noexec_user_stack_log=0
# reboot

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