Novell APPARMOR - AND User manual

This document helps you understand the main concepts behind Novell® AppArmor—the content of AppArmor
proles. Learn how to create or modify AppArmor proles. You can create and manage AppArmor proles 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 if you just edit the proles in a text editor.
AppArmor Modes
complain/learning
In complain or learning mode, violations of AppArmor
prole rules, such as the proled program accessing les
not permitted by the prole, are detected. The violations
are permitted, but also logged. This mode is convenient
for developing proles and is used by the AppArmor
tools for generating proles.
enforce
Loading a prole in enforcement mode enforces the
policy dened in the prole as well as reports policy vi-
olation attempts to syslogd.
Starting and Stopping AppArmor
Use the rcapparmor command with one of the following
parameters:
start
Load the kernel module, mount securityfs, parse and
load proles. Proles and connement are applied to
any application started after this command was executed.
Processes already running at the time AppArmor is
started continue to run unconned.
stop
Unmount securityfs, and invalidate proles.
reload
Reload proles.
status
If AppArmor is enabled, output how many proles 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 the
status.
AppArmor Command Line Tools
autodep
Guess basic AppArmor prole requirements. autodep
creates a stub prole for the program or application
examined. The resulting prole is called “approximate”
because it does not necessarily contain all of the prole
entries that the program needs to be conned properly.
complain
Set an AppArmor prole to complain mode.
Manually activating complain mode (using the command
line) adds a ag to the top of the prole so that
/bin/foo becomes /bin/foo flags=(complain).
enforce
Set an AppArmor prole to enforce mode from complain
mode.
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Quick Start
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Manually activiating enforce mode (using the command
line) removes mode ags from the top of the prole
/bin/foo flags=(complain) becomes /bin/foo.
genprof
Generate or update a prole. When running, you must
specify a program to prole. If the specied program is
not an absolute path, genprof searches the $PATH vari-
able. If a prole does not exist, genprof creates one using
autodep.
logprof
Manage AppArmor proles. 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 proles.
unconned
Output a list of processes with open tcp or udp ports
that do not have AppArmor proles loaded.
Methods of Proling
Stand-Alone Proling
Using genprof. Suitable for proling small applications.
Systemic Proling
Suitable for proling large numbers of programs all at
once and for proling applications that may run “forev-
er.”
To apply systemic proling, proceed as follows:
1. Create proles for the individual programs that make
up your application (autodep).
2. Put relevant proles into learning or complain mode.
3. Exercise your application.
4. Analyze the log (logprof).
5. Repeat Steps 3-4.
6. Edit the proles.
7. Return to enforce mode.
8. Reload all proles (rcapparmor restart).
Learning Mode
When using genprof, logprof, or YaST in learning mode,
you get several options for how to proceed:
Allow
Grant access.
Deny
Prevent access.
Glob
Modify the directory path to include all les in the sug-
gested directory.
Glob w/Ext
Modify the original directory path while retaining the
lename extension. This allows the program to access
all les in the suggested directories that end with the
specied extension.
Edit
Enable editing of the highlighted line. The new (edited)
line appears at the bottom of the list. This option is called
New in the logprof and genprof command line tools.
Abort
Abort logprof or YaST, losing all rule changes entered
so far and leaving all proles unmodied.
Finish
Close logprof or YaST, saving all rule changes entered
so far and modifying all proles.
Example Prole
# a variable definition
@{HOME} = /home/*/ /root/
# a comment about foo.
/usr/bin/foo {
/bin/mount ux,
/dev/{,u}random r,
/etc/ld.so.cache r,
/etc/foo.conf 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 w,
# a comment about foo's subprofile, bar.
^bar {
/lib/ld-*.so* mr,
/usr/bin/bar px,
/var/spool/* rwl,
}
}
Structure of a Prole
Proles are simple text les in the /etc/apparmor.d di-
rectory. They consist of several parts: #include, capability
entries, rules, and “hats.”
#include
This is the section of an AppArmor prole that refers to an
include le, which mediates access permissions for pro-
grams. By using an include, you can give the program access
to directory paths or les that are also required by other
programs. Using includes can reduce the size of a prole.
It is good practice to select includes when suggested.
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To assist you in proling your applications, AppArmor pro-
vides three classes of #includes: abstractions, program
chunks, and variables.
Abstractions are #includes that are grouped by common
application tasks. These tasks include access to authentica-
tion 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 specic 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 proles to be portable
to different environments. Changes in the variable's content
are just made in the variable denition while the prole
containing the variable can remain untouched.
Capability Entries (POSIX.1e)
Capabilities statements are simply the word “capability”
followed by the name of the POSIX.1e capability as dened
in the capabilities(7) man page.
Rules: General Options for Files and
Directories
FileOption
rread
wwrite
llink
Rules: Dening Execute Permissions
For executables that may be called from the conned pro-
grams, the prole creating tools ask you for an appropriate
mode, which is also reected directly in the prole itself:
DescriptionFileOption
Stay in the same (parent's) prole.ixInherit
Requires that a separate prole ex-
ists for the executed program. No
environment scrubbing.
pxProle
Requires that a separate prole ex-
ists for the executed program. Uses
environment scrubbing.
PxProle
Executes the program without a
prole. Avoid running programs in
uxUncon-
strained
unconstrained or unconned mode
for security reasons. No environ-
ment scrubbing.
Executes the program without a
prole. Avoid running programs in
UxUncon-
strained
unconstrained or unconned mode
DescriptionFileOption
for security reasons. This mode
makes use of environment scrub-
bing.
allow PROT_EXEC with mmap(2)
calls
mAllow Exe-
cutable Map-
ping
WARNING: 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 process-
es inherit certain environment variables from the
parent that might inuence the child's execution
behavior and create possible security risks.
For more information about the different le 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.
Rules: Paths and Globbing
DescriptionGlob
Substitutes for any number of characters,
except /.
*
Substitutes for any number of characters,
including /.
**
Substitutes for any single character, ex-
cept /.
?
Substitutes for the single character a,b,
or c.
[ abc ]
Substitutes for the single character a,b,
or c.
[ a-c ]
Expand to one rule to match ab and an-
other to match cd.
{ ab,cd }
Hats
An AppArmor prole represents a security policy for an
individual program instance or process. It applies to an ex-
ecutable program, but if a portion of the program needs
different access permissions than other portions, the pro-
gram can “change hats” to use a different security context,
distinctive from the access of the main program. This is
known as a hat or subprole.
A prole can have an arbitrary number of subproles, but
there are only two levels: a subprole cannot have further
sub-subproles.
The AppArmor ChangeHat feature can be used by applica-
tions to access hats or subproles during execution. Current-
ly the packages apache2-mod_apparmor and tom-
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cat_apparmor utilize ChangeHat to provide sub-process
connement for the Apache Web server and the Tomcat
servlet container.
Helpful Additions
Autodocumentation
The tool “sitar” gathers all system conguration information
available from your system and creates comprehensive
system documentation. It can be used to document all new
and changed proles.
Logging and Auditing
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 notication can
be congured. Congure this feature using YaST. It is based
on severity levels according to /etc/apparmor/
severity.db. Notication frequency and type of noti-
cation (such as e-mail) can be congured.
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.
Directories and Files
/sys/kernel/security/apparmor/profiles
Virtualized le representing the currently loaded set of
proles.
/etc/apparmor/
Location of AppArmor conguration les.
/etc/apparmor.d/
Location of proles, named with the convention of re-
placing the /in pathnames with .(not for the root /)
so proles are easier to manage. For example, the prole
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 connement status of a process and the
prole that is used to conne the process. The ps auxZ
command retrieves this information automatically.
For More Information
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
conguration of AppArmor in the Novell AppArmor Admin-
istration Guide.
Legal Notice
Copyright© 2006-2008 Novell, Inc. All rights reserved. No
part of this publication may be reproduced, photocopied,
stored on a retrieval system, or transmitted without the
express written consent of the publisher. For Novell trade-
marks, see the Novell Trademark and Service Mark list
[http://www.novell.com/company/legal/
trademarks/tmlist.html]. All third-party trademarks
are the property of their respective owners. A trademark
symbol (® , ™, etc.) denotes a Novell trademark; an asterisk
(*) denotes a third-party trademark.
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