Novell APPARMOR 2.0.1 Instruction Manual

Novell AppArmor
www.novell.com2.0.1
November29,2006 Novell AppArmor Administration Guide

Novell AppArmor Administration Guide
Copyright © 2006 Novell, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU
Free Documentation License, Version 1.2 or any later version published by the Free Software Foun-
dation; with the Invariant Section being this copyright notice and license. A copy of the license is in-
cluded in the section entitled “GNU Free Documentation License”.
Novell, the Novell logo, the N logo, openSUSE, SUSE, and the SUSE “geeko” logo are registered
trademarks of Novell, Inc. in the United States and other countries. * Linux is a registered trademark
of Linus Torvalds. All other third party trademarks are the property of their respective owners.
All information found in this book has been compiled with utmost attention to detail. However, this
does not guarantee complete accuracy. Neither Novell, Inc., SUSE LINUX Products GmbH, the authors,
nor the translators shall be held liable for possible errors or the consequences thereof.

Contents
About This Guide v
1Immunizing Programs 9
1.1 Introducing the AppArmor Framework . . . . . . . . . . . . . . . . 10
1.2 Determining Programs to Immunize . . . . . . . . . . . . . . . . . 12
1.3 Immunizing Cron Jobs . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 Immunizing Network Applications . . . . . . . . . . . . . . . . . . 13
2Prole Components and Syntax 19
2.1 Breaking a Novell AppArmor Prole into Its Parts . . . . . . . . . . . 19
2.2 #include Statements ...................... 21
2.3 Capability Entries (POSIX.1e) . . . . . . . . . . . . . . . . . . . . 22
3Building and Managing Proles With YaST 23
3.1 Adding a Prole Using the Wizard . . . . . . . . . . . . . . . . . . 25
3.2 Manually Adding a Prole . . . . . . . . . . . . . . . . . . . . . 32
3.3 EditingProles.......................... 33
3.4 DeletingaProle......................... 38
3.5 Updating Proles from Log Entries . . . . . . . . . . . . . . . . . . 39
3.6 Managing Novell AppArmor and Security Event Status . . . . . . . . . 40
4Building Proles via the Command Line 45
4.1 Checking the AppArmor Module Status . . . . . . . . . . . . . . . 45
4.2 Building Novell AppArmor Proles . . . . . . . . . . . . . . . . . . 47
4.3 Adding or Creating a Novell AppArmor Prole . . . . . . . . . . . . 48
4.4 Editing a Novell AppArmor Prole . . . . . . . . . . . . . . . . . . 48

4.5 Deleting a Novell AppArmor Prole . . . . . . . . . . . . . . . . . 48
4.6 Two Methods of Proling . . . . . . . . . . . . . . . . . . . . . . 49
4.7 Pathnames and Globbing . . . . . . . . . . . . . . . . . . . . . . 68
4.8 File Permission Access Modes . . . . . . . . . . . . . . . . . . . . 69
4.9 Important Filenames and Directories . . . . . . . . . . . . . . . . . 73
5Proling Your Web Applications Using ChangeHat 75
5.1 ApacheChangeHat........................ 76
5.2 Conguring Apache for mod_apparmor . . . . . . . . . . . . . . . 83
6Managing Proled Applications 87
6.1 Monitoring Your Secured Applications . . . . . . . . . . . . . . . . 87
6.2 Conguring Security Event Notication . . . . . . . . . . . . . . . . 88
6.3 Conguring Reports . . . . . . . . . . . . . . . . . . . . . . . . 91
6.4 Reacting to Security Event Rejections . . . . . . . . . . . . . . . . 110
6.5 Maintaining Your Security Proles . . . . . . . . . . . . . . . . . 111
7Support 113
7.1 Updating Novell AppArmor Online . . . . . . . . . . . . . . . . . 113
7.2 Using the Man Pages . . . . . . . . . . . . . . . . . . . . . . . 113
7.3 For More Information . . . . . . . . . . . . . . . . . . . . . . 115
7.4 Troubleshooting......................... 116
7.5 Reporting Bugs for AppArmor . . . . . . . . . . . . . . . . . . . 117
ABackground Information on AppArmor Proling 119
BGNU Licenses 121
B.1 GNU General Public License . . . . . . . . . . . . . . . . . . . . 121
B.2 GNU Free Documentation License . . . . . . . . . . . . . . . . . 129
Glossary 139

About This Guide
Novell® AppArmor is designed to provide easy-to-use application security for both
servers and workstations. Novell AppArmor is an access control system that lets you
specify per program which les the program may read, write, and execute. AppArmor
secures applications by enforcing good application behavior without relying on attack
signatures, so can prevent attacks even if they are exploiting previously unknown vul-
nerabilities.
Novell AppArmor consists of:
• A library of AppArmor proles for common Linux* applications describing what
les the program needs to access.
• A library of AppArmor prole foundation classes (prole building blocks) needed
for common application activities, such as DNS lookup and user authentication.
• A tool suite for developing and enhancing AppArmor proles, so that you can
change the existing proles to suit your needs and create new proles for your own
local and custom applications.
• Several specially modied applications that are AppArmor enabled to provide en-
hanced security in the form of unique subprocess connement, including Apache
and Tomcat.
• The Novell AppArmor–loadable kernel module and associated control scripts to
enforce AppArmor policies on your openSUSE™ system.
This guide covers the following topics:
Immunizing Programs
Describes the operation of Novell AppArmor and describes the types of programs
that should have Novell AppArmor proles created for them.
Prole Components and Syntax
Introduces the prole components and syntax.
Building and Managing Proles With YaST
Describes how to use the AppArmor YaST modules to build, maintain and update
proles.

Building Proles via the Command Line
Describes how to use the AppArmor command line tools to build, maintain and
update proles.
Proling Your Web Applications Using ChangeHat
Enables you to create subproles for the Apache Web server that allow you to
tightly conne small sections of Web application processing.
Managing Proled Applications
Describes how to perform Novell AppArmor prole maintenance, which involves
tracking common issues and concerns.
Support
Indicates support options for this product.
Glossary
Provides a list of terms and their denitions.
1 Feedback
We want to hear your comments and suggestions about this manual and the other doc-
umentation included with this product. Please use the User Comments feature at the
bottom of each page of the online documentation and enter your comments there.
2 Documentation Conventions
The following typographical conventions are used in this manual:
•/etc/passwd: lenames and directory names
•placeholder: replace placeholder with the actual value
•PATH: the environment variable PATH
•ls,--help: commands, options, and parameters
•user: users or groups
vi Novell AppArmor Administration Guide

•Alt,Alt +F1: a key to press or a key combination; keys are shown in uppercase as
on a keyboard
•File,File →Save As: menu items, buttons
•Dancing Penguins (Chapter Penguins, ↑Reference): This is a reference to a chapter
in another book.
3 Source Code
The source code of openSUSE is publicly available. To download the source code,
proceed as outlined under http://www.novell.com/products/suselinux/
source_code.html. If requested we send you the source code on a DVD. We need
to charge a $15 or €15 fee for creation, handling and postage. To request a DVD of the
source code, send an e-mail to [email protected] [mailto:sourcedvd@suse
.de] or mail the request to:
SUSE Linux Products GmbH
Product Management openSUSE
Maxfeldstr. 5
D-90409 Nürnberg
Germany
About This Guide vii

1
Immunizing Programs
Novell® AppArmor provides immunization technologies that protect applications from
the inherent vulnerabilities they possess. After installing Novell AppArmor, setting up
Novell AppArmor proles, and rebooting the computer, your system becomes immu-
nized because it begins to enforce the Novell AppArmor security policies. Protecting
programs with Novell AppArmor is referred to as immunizing.
Novell AppArmor sets up a collection of default application proles to protect standard
Linux services. In order to protect other applications, use the Novell AppArmor tools
to create proles for the applications that you want protected. This chapter introduces
the philosophy of immunizing programs. Proceed to Chapter 2, Prole Components
and Syntax (page 19), Chapter 3, Building and Managing Proles With YaST (page 23),
or Chapter 4, Building Proles via the Command Line (page 45) if you are ready to
build and manage Novell AppArmor proles.
Novell AppArmor provides streamlined access control for network services by specifying
which les each program is allowed to read, write, and execute. This ensures that each
program does what it is supposed to do and nothing else. Novell AppArmor quarantines
programs to protect the rest of the system from being damaged by a compromised
process.
Novell AppArmor is a host intrusion prevention, or mandatory access control scheme.
Previously, access control schemes were centered around users because they were built
for large timeshare systems. Alternatively, modern network servers largely do not permit
users to log in, but instead provide a variety of network services for users, such as Web,
mail, le, and print. Novell AppArmor controls the access given to network services
and other programs to prevent weaknesses from being exploited.
Immunizing Programs 9

TIP: Background Information for Novell AppArmor
To get a more in-depth overview of AppArmor and the overall concept behind
it, refer to Appendix A, Background Information on AppArmor Proling
(page 119).
1.1 Introducing the AppArmor
Framework
The following section provides you with a very basic understanding of what is happening
“behind the scenes” (and under the hood of the YaST interface) when you run App-
Armor.
An AppArmor prole is a plain text le containing path entries and access permissions,
see Section 2.1, “Breaking a Novell AppArmor Prole into Its Parts” (page 19) for a
detailed reference prole. The directives contained in this text le are then enforced
by the AppArmor routines to quarantine the process/program.
The following tools interact in the building and enforcement of AppArmor proles and
policies:
aa-unconned
aa-unconned detects any application running on your system that listens for net-
work connections and is not protected by an AppArmor prole. Refer to Section
“aa-unconned—Identifying Unprotected Processes” (page 67) for detailed infor-
mation on this tool.
aa-autodep
aa-autodep creates a basic skeleton of a prole that needs to be eshed out before
it is put to productive use. The resulting prole is loaded and put into complain
mode, reporting any behavior of the application that is not (yet) covered by App-
Armor rules. Refer to Section “aa-autodep—Creating Approximate Proles”
(page 52) for detailed information on this tool.
aa-genprof
aa-genprof generates a basic prole and asks you to rene this prole by executing
the application and thus generating log events that need to be taken care of by
10 Novell AppArmor Administration Guide

AppArmor policies. You will be guided through a series of questions to deal with
the log events that have been triggered during the application's execution. After
the prole has been generated, it gets loaded and put into enforce mode. Refer to
Section “aa-genprof—Generating Proles” (page 55) for detailed information on
this tool.
aa-logprof
aa-logprof interactively scans and reviews the log entries generated by an application
that is conned by an AppArmor prole in complain mode. It assists you in gener-
ating new entries in the prole concerned. Refer to Section “aa-logprof—Scanning
the System Log” (page 61) for detailed information on this tool.
aa-complain
aa-complain toggles the mode of an AppArmor prole from enforce to complain.
Exceptions to rules set in a prole are logged, but the prole is not enforced. Refer
to Section “aa-complain—Entering Complain or Learning Mode” (page 53) for
detailed information on this tool.
aa-enforce
aa-enforce toggles the mode of an AppArmor prole form complain to enforce.
Exceptions to rules set in a prole are logged, but not permitted—the prole is
enforced. Refer to Section “aa-enforce—Entering Enforce Mode” (page 54) for
detailed information on this tool.
Once a prole has been built and is loaded, there are two ways in which it can get pro-
cessed:
complain
In complain mode, violations of AppArmor prole rules, such as the proled pro-
gram accessing les not permitted by the prole, are detected. The violations are
permitted, but also logged. To improve the prole, turn complain mode on, run the
program through a suite of tests to generate log events that characterize the program's
access needs, then postprocess the log with the AppArmor tools (YaST or aa-log-
prof) to transform log events into improved proles.
enforce
In enforce 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 logged
and not permitted. The default is for enforce mode to be enabled. To log the viola-
tions only, but still permit them, use complain mode. Enforce toggles with complain
mode.
Immunizing Programs 11

1.2 Determining Programs to
Immunize
Now that you have familiarized yourself with AppArmor, start selecting the applications
to build proles for. Programs that need proling are those that mediate privilege. The
following programs have access to resources that the person using the program does
not have, so they grant the privilege to the user when used:
cron Jobs
Programs that are run periodically by cron. Such programs read input from a variety
of sources and can run with special privileges, sometimes with as much as root
privilege. For example, cron can run /usr/sbin/logrotate daily to rotate,
compress or even mail system logs. For instructions for nding these types of
programs, refer to Section 1.3, “Immunizing Cron Jobs” (page 13).
Web Applications
Programs that can be invoked through a Web browser, including CGI Perl scripts,
PHP pages, and more complex Web applications. For instructions for nding these
types of programs, refer to Section 1.4.1, “Immunizing Web Applications”
(page 15).
Network Agents
Programs (servers and clients) that have open network ports. User clients, such as
mail clients and Web browsers mediate privilege. These programs run with the
privilege to write to the user's home directory and they process input from poten-
tially hostile remote sources, such as hostile Web sites and e-mailed malicious
code. For instructions for nding these types of programs, refer to Section 1.4.2,
“Immunizing Network Agents” (page 17).
Conversely, unprivileged programs do not need to be proled. For instance, a shell
script might invoke the cp program to copy a le. Because cp does not have its own
prole, it inherits the prole of the parent shell script, so can copy any les that the
parent shell script's prole can read and write.
12 Novell AppArmor Administration Guide

1.3 Immunizing Cron Jobs
To nd programs that are run by cron, inspect your local cron conguration. Unfortu-
nately, cron conguration is rather complex, so there are numerous les to inspect.
Periodic cron jobs are run from these les:
/etc/crontab
/etc/cron.d/*
/etc/cron.daily/*
/etc/cron.hourly/*
/etc/cron.monthly/*
/etc/cron.weekly/*
For root's cron jobs, edit the tasks with crontab -e and list root's cron tasks
with crontab -l. You must be root for these to work.
Once you nd these programs, you can use the Add Prole Wizard to create proles
for them. Refer to Section 3.1, “Adding a Prole Using the Wizard” (page 25).
1.4 Immunizing Network Applications
An automated method for nding network server daemons that should be proled is to
use the aa-unconned tool. You can also simply view a report of this information in
the YaST module (refer to Section “Application Audit Report” (page 97) for instruc-
tions).
The aa-unconned tool uses the command netstat -nlp to inspect your open ports
from inside your computer, detect the programs associated with those ports, and inspect
the set of Novell AppArmor proles that you have loaded. aa-unconned then reports
these programs along with the Novell AppArmor prole associated with each program
or reports “none” if the program is not conned.
NOTE
If you create a new prole, you must restart the program that has been proled
to have it be effectively conned by AppArmor.
Immunizing Programs 13

Below is a sample aa-unconned output:
2325 /sbin/portmap not confined
3702❶/usr/sbin/sshd❷confined
by '/usr/sbin/sshd❸(enforce)'
4040 /usr/sbin/ntpd confined by '/usr/sbin/ntpd (enforce)'
4373 /usr/lib/postfix/master confined by '/usr/lib/postfix/master (enforce)'
4505 /usr/sbin/httpd2-prefork confined by '/usr/sbin/httpd2-prefork (enforce)'
5274 /sbin/dhcpcd not confined
5592 /usr/bin/ssh not confined
7146 /usr/sbin/cupsd confined by '/usr/sbin/cupsd (complain)'
❶The rst portion is a number. This number is the process ID number (PID) of the
listening program.
❷The second portion is a string that represents the absolute path of the listening
program
❸The nal portion indicates the prole conning the program, if any.
NOTE
aa-unconned requires root privileges and should not be run from a shell
that is conned by an AppArmor prole.
aa-unconned does not distinguish between one network interface and another, so it
reports all unconned processes, even those that might be listening to an internal LAN
interface.
Finding user network client applications is dependent on your user preferences. The
aa-unconned tool detects and reports network ports opened by client applications, but
only those client applications that are running at the time the aa-unconned analysis is
performed. This is a problem because network services tend to be running all the time,
while network client applications tend only to be running when the user is interested
in them.
Applying Novell AppArmor proles to user network client applications is also dependent
on user preferences. Therefore, we leave proling of user network client applications
as an exercise for the user.
To aggressively conne desktop applications, the aa-unconned command supports a
paranoid option, which reports all processes running and the corresponding App-
14 Novell AppArmor Administration Guide

Armor proles that might or might not be associated with each process. The user can
then decide whether each of these programs needs an AppArmor prole.
If you have new or modied proles, you can submit them to the apparmor-gener-
[e-mail] [mailto:[email protected]]
mailing list along with a use case for the application behavior that you exercised. The
AppArmor team reviews and may submit the work into openSUSE. We cannot guarantee
that every prole will be included, but we make a sincere effort to include as much as
possible so that end users can contribute to the security proles that ship in openSUSE.
1.4.1 Immunizing Web Applications
To nd Web applications, investigate your Web server conguration. The Apache Web
server is highly congurable and Web applications can be stored in many directories,
depending on your local conguration. openSUSE, by default, stores Web applications
in /srv/www/cgi-bin/. To the maximum extent possible, each Web application
should have an Novell AppArmor prole.
Once you nd these programs, you can use the AppArmor Add Prole Wizard to create
proles for them. Refer to Section 3.1, “Adding a Prole Using the Wizard” (page 25).
Because CGI programs are executed by the Apache Web server, the prole for Apache
itself, usr.sbin.httpd2-prefork for Apache2 on openSUSE, must be modied
to add execute permissions to each of these programs. For instance, adding the line
/srv/www/cgi-bin/my_hit_counter.pl rpx grants Apache permission to
execute the Perl script my_hit_counter.pl and requires that there be a dedicated
prole for my_hit_counter.pl. If my_hit_counter.pl does not have a ded-
icated prole associated with it, the rule should say
/srv/www/cgi-bin/my_hit_counter.pl rix to cause my_hit_counter
.pl to inherit the usr.sbin.httpd2-prefork prole.
Some users might nd it inconvenient to specify execute permission for every CGI
script that Apache might invoke. Instead, the administrator can grant controlled access
to collections of CGI scripts. For instance, adding the line
/srv/www/cgi-bin/*.{pl,py,pyc} rix allows Apache to execute all les
in /srv/www/cgi-bin/ ending in .pl (Perl scripts) and .py or .pyc (Python
scripts). As above, the ix part of the rule causes Python scripts to inherit the Apache
prole, which is appropriate if you do not want to write individual proles for each
Python script.
Immunizing Programs 15

NOTE
If you want the subprocess connement module (apache2-mod-apparmor)
functionality when Web applications handle Apache modules (mod_perl and
mod_php), use the ChangeHat features when you add a prole in YaST or at
the command line. To take advantage of the subprocess connement, refer to
Section 5.1, “Apache ChangeHat” (page 76).
Proling Web applications that use mod_perl and mod_php requires slightly different
handling. In this case, the “program” is a script interpreted directly by the module
within the Apache process, so no exec happens. Instead, the Novell AppArmor version
of Apache calls change_hat() using a subprole (a “hat”) corresponding to the
name of the URI requested.
NOTE
The name presented for the script to execute might not be the URI, depending
on how Apache has been congured for where to look for module scripts. If
you have congured your Apache to place scripts in a different place, the dif-
ferent names appear in log le when Novell AppArmor complains about access
violations. See Chapter 6, Managing Proled Applications (page 87).
For mod_perl and mod_php scripts, this is the name of the Perl script or the PHP
page requested. For example, adding this subprole allows the localtime.php page
to execute and access the local system time:
/usr/bin/httpd2-prefork {
# ...
^/cgi-bin/localtime.php {
/etc/localtime r,
/srv/www/cgi-bin/localtime.php r,
/usr/lib/locale/** r,
}
}
If no subprole has been dened, the Novell AppArmor version of Apache applies the
DEFAULT_URI hat. This subprole is basically sufcient to display an HTML Web
page. The DEFAULT_URI hat that Novell AppArmor provides by default is the follow-
ing:
16 Novell AppArmor Administration Guide

/usr/sbin/suexec2 ixr,
/var/log/apache2/** rwl,
/home/*/public_html/** r,
/srv/www/htdocs/** r,
/srv/www/icons/*.{gif,jpg,png} r,
/usr/share/apache2/** r,
To use a single Novell AppArmor prole for all Web pages and CGI scripts served by
Apache, a good approach is to edit the DEFAULT_URI subprole.
1.4.2 Immunizing Network Agents
To nd network server daemons and network clients (such as fetchmail, Firefox, amaroK
or Banshee) that should be proled, you should inspect the open ports on your machine,
consider the programs that are answering on those ports, and provide proles for as
many of those programs as possible. If you provide proles for all programs with open
network ports, an attacker cannot get to the le system on your machine without passing
through a Novell AppArmor prole policy.
Scan your server for open network ports manually from outside the machine using a
scanner, such as nmap, or from inside the machine using the netstat --inet -n
-p command. Then inspect the machine to determine which programs are answering
on the discovered open ports.
TIP
Refer to the man page of the netstat command for a detailed reference of
all possible options.
Immunizing Programs 17

2
Prole Components and
Syntax
This chapter explains the components and syntax of Novell® AppArmor proles. You
are ready to build Novell AppArmor proles after you select the programs to prole.
For help with this, refer to Section 1.2, “Determining Programs to Immunize” (page 12).
To start building AppArmor proles with YaST, proceed to Chapter 3, Building and
Managing Proles With YaST (page 23). To build proles using the AppArmor com-
mand line interface, proceed to Chapter 4, Building Proles via the Command Line
(page 45).
2.1 Breaking a Novell AppArmor
Prole into Its Parts
Novell AppArmor prole components are called Novell AppArmor rules. Currently
there are two main types of Novell AppArmor rules, path entries and capability entries.
Path entries specify what the process can access in the le system and capability entries
provide a more ne-grained control over what a conned process is allowed to do
through other system calls that require privileges. Includes are a type of meta rule or
directives that pull in path and capability entries from other les.
The easiest way of explaining what a prole consists of and how to create one is to
show the details of a sample prole. Consider, for example, the following shortened
prole for the program /usr/lib/postfix/flush (for the complete version, refer
to /etc/apparmor.d/usr.lib.postfix.flush):
Prole Components and Syntax 19

# profile to confine postfix/flush❶
#include <tunables/global>❷
/usr/lib/postfix/flush❸
{❹
#include <abstractions/base>❺
...
capability setgid❻,
...
/usr/lib/postfix/flush rix,
/{var/spool/postfix/,}❼deferred r,
...
/{var/spool/postfix/,}flush rwl,
...
/{var/spool/postfix/,}incoming r,
...
/{var/spool/postfix/,}public/qmgr w,
/etc/mtab❽r,
/etc/postfix/main.cf r,
/etc/postfix/virtual.db r,
@{HOME}❾/.forward r,
/proc/stat r,
/proc/sys/kernel/ngroups_max r,
/var/spool/postfix/pid/unix.flush rw,
}
❶A comment naming the program that is conned by this prole. Always precede
comments like this with the #sign.
❷This loads a le containing variable denitions.
❸The absolute path to the program that is conned.
❹The curly braces ({}) serve as a container for include statements of other proles
as well as for path and capability entries.
❺This directive pulls in components of Novell AppArmor proles to simplify pro-
les.
❻Capability entry statements enable each of the 29 POSIX.1e draft capabilities.
❼The curly braces ({}) make this rule apply to the path both with and without the
content enclosed by the braces.
❽A path entry specifying what areas of the le system the program can access. The
rst part of a path entry species the absolute path of a le (including regular
expression globbing) and the second part indicates permissible access modes (r
for read, wfor write, and xfor execute). A whitespace of any kind (spaces or tabs)
can precede pathnames or separate the pathname from the access modes. Spaces
20 Novell AppArmor Administration Guide