Profiles are simple text files in the
/etc/apparmor.d
directory. They consist of several
parts: #include, capability entries, rules,
and “hats.”
This is the section of an AppArmor profile that refers to an include file, which mediates access permissions for programs. By using an include, you can give the program access to directory paths or files that are also required by other programs. Using includes can reduce the size of a profile. It is good practice to select includes when suggested.
To assist you in profiling your applications, AppArmor
provides three classes of #includes
: abstractions,
program chunks, and variables.
Abstractions are #includes
that are grouped by common
application tasks. These tasks include access to authentication
mechanisms, access to name service routines, common graphics requirements,
and system accounting, for example, base, consoles, kerberosclient, perl,
user-mail, user-tmp, authentication, bash, nameservice.
Program chunks are access controls for specific programs that a system administrator might want to control based on local site policy. Each chunk is used by a single program.
Using variables, you can design your profiles to be portable to different environments. Changes in the variable's content are just made in the variable definition while the profile containing the variable can remain untouched.
Capabilities statements are simply the word “capability” followed by the name of the POSIX.1e capability as defined in the capabilities(7) man page.
Option |
File |
---|---|
read |
|
write |
|
link |
|
file locking |
|
file append (mutually exclusive to |
|
For executables that may be called from the confined programs, the profile creating tools ask you for an appropriate mode, which is also reflected directly in the profile itself:
Option |
File |
Description |
---|---|---|
Inherit |
|
Stay in the same (parent's) profile. |
Profile |
|
Requires that a separate profile exists for the executed program. No environment scrubbing. |
Profile |
|
Requires that a separate profile exists for the executed program. Uses environment scrubbing. |
Unconstrained |
|
Executes the program without a profile. Avoid running programs in unconstrained or unconfined mode for security reasons. No environment scrubbing. |
Unconstrained |
|
Executes the program without a profile. Avoid running programs in unconstrained or unconfined mode for security reasons. This mode makes use of environment scrubbing. |
Allow Executable Mapping |
|
allow |
![]() | Running in ux Mode |
---|---|
Avoid running programs in ux mode as much as possible. A program running in ux mode is not only totally unprotected by AppArmor, but child processes inherit certain environment variables from the parent that might influence the child's execution behavior and create possible security risks. |
For more information about the different file execute modes, refer to the apparmor.d(5) man page. For more information about setgid and setuid environment scrubbing, refer to the ld.so(8) man page.
AppArmor provides network access mediation based on network domain and type:
/bin/ping { network inet dgram, network inet raw, ... }
The example would allow IPv4 network access of the datagram and raw type for the ping command. For details on the network rule syntax, refer to the Novell AppArmor Administration Guide.
AppArmor supports explicit handling of directories. Use a trailing
/
for any directory path that needs to be explicitly
distinguished:
/some/random/example/* r
Allow read access to files in the
/some/random/example
directory.
/some/random/example/ r
Allow read access to the directory only.
/some/**/ r
Give read access to any directories below
/some
.
/some/random/example/** r
Give read access to files and directories under
/some/random/example
.
/some/random/example/**[^/] r
Give read access to files under
/some/random/example
. Explicitly exclude
directories ([^/]
).
To spare users from specifying similar paths all over again, AppArmor supports basic globbing:
Glob |
Description |
---|---|
|
Substitutes for any number of characters, except |
|
Substitutes for any number of characters, including |
|
Substitutes for any single character, except |
|
Substitutes for the single character |
|
Substitutes for the single character |
|
Expand to one rule to match |
|
Substitutes for any character except |
![]() | Updating Profiles to AppArmor 2.1 |
---|---|
If you have been using prior versions of AppArmor, many of the old profiles may trigger unexpected behavior of the profiled applications. In this case, update your profiles as outlined in the Troubleshooting section of the Novell AppArmor Administration Guide. |
An AppArmor profile represents a security policy for an individual program instance or process. It applies to an executable program, but if a portion of the program needs different access permissions than other portions, the program can “change hats” to use a different security context, distinctive from the access of the main program. This is known as a hat or subprofile.
A profile can have an arbitrary number of subprofiles, but there are only two levels: a subprofile cannot have further sub-subprofiles.
The AppArmor ChangeHat feature can be used by applications to access hats
or subprofiles during execution. Currently the packages apache2-mod_apparmor
and tomcat_apparmor
utilize ChangeHat to provide
sub-process confinement for the Apache Web server and the Tomcat servlet
container.