Contents
Abstract
This document helps you understand the main concepts behind Novell® AppArmor—the content of AppArmor profiles. Learn how to create or modify AppArmor profiles. You can create and manage AppArmor profiles in three different ways. The most convenient interface to AppArmor is provided by means of the AppArmor YaST modules, which can be used either in graphical or ncurses mode. The same functionality is provided by the AppArmor command line tools or by editing the profiles in a text editor.
In complain or learning mode, violations of AppArmor profile rules, such as the profiled program accessing files not permitted by the profile, are detected. The violations are permitted, but also logged. This mode is convenient for developing profiles and is used by the AppArmor tools for generating profiles.
Loading a profile in enforcement mode enforces the policy defined in the profile as well as reports policy violation attempts to syslogd.
Use the rcapparmor command with one of the following parameters:
start
Load the kernel module, mount securityfs, parse and load profiles. Profiles and confinement are applied to any application started after this command was executed. Processes already running at the time AppArmor is started continue to run unconfined.
stop
Unmount securityfs, and invalidate profiles.
reload
Reload profiles.
status
If AppArmor is enabled, output how many profiles are loaded in complain or enforce mode.
Use the rcaaeventd command to control event logging
with aa-eventd. Use the start
and stop
options to toggle the status of the aa-eventd and check its status using
status
.
Guess basic AppArmor profile requirements. autodep creates a stub profile for the program or application examined. The resulting profile is called “approximate” because it does not necessarily contain all of the profile entries that the program needs in order to be confined properly.
Set an AppArmor profile to complain mode.
Manually activating complain mode (using the command line) adds a flag to the top of the profile so that /bin/foo becomes /bin/foo flags=(complain).
Set an AppArmor profile to enforce mode from complain mode.
Manually activating enforce mode (using the command line) removes mode flags from the top of the profile /bin/foo flags=(complain) becomes /bin/foo.
Generate or update a profile. When running, you must specify a program
to profile. If the specified program is not an absolute path, genprof
searches the $PATH
variable. If a profile does not
exist, genprof creates one using autodep.
Manage AppArmor profiles. logprof is an interactive tool used to review the learning or complain mode output found in the AppArmor syslog entries and to generate new entries in AppArmor profiles.
Output a list of processes with open tcp or udp ports that do not have AppArmor profiles loaded.
Using genprof. Suitable for profiling small applications.
Suitable for profiling large numbers of programs all at once and for profiling applications that may run “forever.”
To apply systemic profiling, proceed as follows:
Create profiles for the individual programs that make up your application (autodep).
Put relevant profiles into learning or complain mode.
Exercise your application.
Analyze the log (logprof).
Repeat Steps 3-4.
Edit the profiles.
Return to enforce mode.
Reload all profiles (rcapparmor restart).
When using genprof, logprof, or YaST in learning mode, you get several options for how to proceed:
Grant access.
Prevent access.
Modify the directory path to include all files in the suggested directory.
Modify the original directory path while retaining the filename extension. This allows the program to access all files in the suggested directories that end with the specified extension.
Enable editing of the highlighted line. The new (edited) line appears at the bottom of the list. This option is called
in the logprof and genprof command line tools.Abort logprof or YaST, losing all rule changes entered so far and leaving all profiles unmodified.
Close logprof or YaST, saving all rule changes entered so far and modifying all profiles.
#include<tunables/global> @{HOME} = /home/*/ /root/ # variable /usr/bin/foo { #include <abstractions/base> network inet tcp, capability setgid, /bin/mount ux, /dev/{,u}random r, /etc/ld.so.cache r, /etc/foo/* r, /lib/ld-*.so* mr, /lib/lib*.so* mr, /proc/[0-9]** r, /usr/lib/** mr, /tmp/ r, /tmp/foo.pid wr, /tmp/foo.* lrw, /@{HOME}/.foo_file rw, /@{HOME}/.foo_lock kw, link /etc/sysconfig/foo -> /etc/foo.conf, deny /etc/shadow w, owner /home/*/** rw, /usr/bin/foobar cx, /bin/** px -> bin_generic # comment on foo's local profile, foobar. foobar { /bin/bash rmix, /bin/cat rmix, /bin/more rmix, /var/log/foobar* rwl, /etc/foobar r, } }
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 tunables.
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.
Tunables are global variable definitions. When used in a profile, these variables expand to a value that can be changed without changing the entire profile. Therefore your profiles become portable to different environments.
Local variables are defined at the head of a profile. Use local variables to create shortcuts for paths, for example to provide the base for a chrooted path:
@{CHROOT_BASE}=/tmp/foo /sbin/syslog-ng { ... # chrooted applications @{CHROOT_BASE}/var/lib/*/dev/log w, @{CHROOT_BASE}/var/log/** w, ... }
Alias rules provide an alternative form of path rewriting to using variables, and are done post variable resolution:
alias /home/ -> /mnt/users/
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 Part “Confining Privileges with Novell AppArmor” (↑Security Guide).
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 |
|
The link mode grants permission to create links to arbitrary files, provided the link has a subset of the permissions granted by the target (subset permission test). By specifying origin and destination, the link pair rule provides greater control over how hard links are created. Link pair rules by, default, do not enforce the link subset permission test that the standard rules link permission requires. To force the rule to require the test the subset keyword is used. The following rules are equivalent:
/link l, link subset /link -> /**,
AppArmor provides deny
rules which are standard rules but
with the keyword deny
prepended. They are used to
remember known rejects, and quiet them so the reject messages don't fill
up the log files. For more information see
Part “Confining Privileges with Novell AppArmor” (↑Security Guide).
The file rules can be extended so that they can be conditional upon the
the user being the owner of the file. by prepending the keyword
owner
to the rule. Owner conditional rules accumulate
just as regular file rules and are considered a subset of regular file
rules. If a regular file rule overlaps with an owner conditional file
rule, the resulting permissions will be that of the regular file rule.
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.
Use |
Local profile |
|
Requires that a local profile exists for the executed program. Use
|
Unconstrained |
|
Executes the program without a profile. Avoid running programs in
unconstrained or unconfined mode for security reasons. Use
|
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 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 |
AppArmor provides the user with the ability to audit given rules so that when they are matched, an audit message will appear in the audit log. To enable audit messages for a given rule the audit keyword is prepended to the rule:
audit /etc/foo/* rw,
Normally, AppArmor only restricts existing native Linux controls and does not grant additional privileges. The only exception from this strict rule is the set capability rule. For security reasons, set capability rules will not be inherited. Once a program leaves the profile, it loses the elevated privilege. Setting a capability also implicitly adds a capability rule allowing that capability. Since this rule gives processes root privileges, it should be used with extreme caution and only in exceptional cases.
set capabilty cap_chown,
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 hats, but there are only two levels: a hat cannot have further hats.
The AppArmor ChangeHat feature can be used by applications to access hats
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.
The pam_apparmor PAM module allows applications to confine authenticated users into subprofiles based on group names, user names, or default profile. To accomplish this, pam_apparmor needs to be registered as a PAM session module.
Details about how to set up and configure pam_apparmor can be found in
/usr/share/doc/packages/pam_apparmor/README
. A HOWTO
on setting up role-based access control (RBAC) with pam_apparmor is
available at
http://developer.novell.com/wiki/index.php/Apparmor_RBAC_in_version_2.3.
All AppArmor events are logged using the system's audit interface (the auditd
logging to /var/log/audit/audit.log
). On top of this
infrastructure, event notification can be configured. Configure this
feature using YaST. It is based on severity levels according to
/etc/apparmor/severity.db
. Notification frequency
and type of notification (such as e-mail) can be configured.
If auditd is not running, AppArmor logs to the system log located under
/var/log/messages
using the LOG_KERN
facility.
Use YaST for generating reports in CSV or HTML format.
The Linux audit framework contains a dispatcher that can send AppArmor events
to any consumer application via dbus. The GNOME AppArmor Desktop Monitor
applet is one example of an application that gathers AppArmor events via
dbus. To configure audit to use the dbus dispatcher, set the dispatcher
in your audit configuration in
/etc/audit/auditd.conf
to
apparmor-dbus
and restart auditd:
dispatcher=/usr/bin/apparmor-dbus
Once the dbus dispatcher is configured correctly, add the AppArmor Desktop
Monitor to the GNOME panel. As soon as a REJECT
event
is logged, the applet's panel icon changes appearance and you can click
the applet to see the number of reject events per confined application.
To view the exact log messages, refer to the audit log under
/var/log/audit/audit.log
. Use the YaST Update
Profile Wizard to adjust the respective profile.
/sys/kernel/security/apparmor/profiles
Virtualized file representing the currently loaded set of profiles.
/etc/apparmor/
Location of AppArmor configuration files.
/etc/apparmor/profiles/extras/
A local repository of profiles shipped with AppArmor, but not enabled by default.
/etc/apparmor.d/
Location of profiles, named with the convention of replacing the
/
in pathnames with .
(not for
the root /
) so profiles are easier to manage. For
example, the profile for the program
/usr/sbin/ntpd
is named
usr.sbin.ntpd
.
/etc/apparmor.d/abstractions/
Location of abstractions.
/etc/apparmor.d/program-chunks/
Location of program chunks.
/proc/*/attr/current
Review the confinement status of a process and the profile that is
used to confine the process. The ps
auxZ
command retrieves this information
automatically.
To learn more about the AppArmor project, check out the project's home page under http://en.opensuse.org/AppArmor. Find more information on the concept and the configuration of AppArmor in Part “Confining Privileges with Novell AppArmor” (↑Security Guide).
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If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.