Novell APPARMOR - AND Manuale utente

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.

Novell AppArmor (for SLE 10 SP2)

Quick Start

NOVELL® QUICK START CARD

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.

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-

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

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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