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Manual Section... (5) - page: apparmor.d

 

NAME

apparmor.d - syntax of security profiles for AppArmor.  

DESCRIPTION

AppArmor profiles describe mandatory access rights granted to given programs and are fed to the AppArmor policy enforcement module using apparmor_parser(8). This man page describes the format of the AppArmor configuration files; see apparmor(7) for an overview of AppArmor.  

FORMAT

The following is a BNF-style description of AppArmor policy configuration files; see below for an example AppArmor policy file. AppArmor configuration files are line-oriented; # introduces a comment, similar to shell scripting languages. The exception to this rule is that #include will include the contents of a file inline to the policy; this behaviour is modelled after cpp(1).

INCLUDE = '#include' ( ABS PATH | MAGIC PATH )

ABS PATH = '``' path '''' (the path is passed to open(2))

MAGIC PATH = '<' relative path '>' (the path is relative to /etc/apparmor.d/)

COMMENT = '#' TEXT

TEXT = any characters

PROFILE = [ COMMENT ... ] [ VARIABLE ASSIGNMENT ... ] ( '"' PROGRAM '"' | PROGRAM ) [ 'flags=(complain)' ]'{' [ ( RESOURCE RULE | COMMENT | INCLUDE | SUBPROFILE | 'capability ' CAPABILITY | NETWORK RULE ) ... ] '}'

SUBPROFILE = [ COMMENT ... ] PROGRAMHAT '{' [ ( FILE RULE | COMMENT | INCLUDE ) ... ] '}'

CAPABILITY = (lowercase capability name without 'CAP_' prefix; see capabilities(7))

NETWORK RULE = 'network' [ [ DOMAIN ] [ TYPE ] [ I <PROTOCOL> ] ] ','

DOMAIN = ( 'inet' | 'ax25' | 'ipx' | 'appletalk' | 'netrom' | 'bridge' | 'atmpvc' | 'x25' | 'inet6' | 'rose' | 'netbeui' | 'security' | 'key' | 'packet' | 'ash' | 'econet' | 'atmsvc' | 'sna' | 'irda' | 'pppox' | 'wanpipe' | 'bluetooth' ) ','

TYPE = ( 'stream' | 'dgram' | 'seqpacket' | 'rdm' | 'raw' | 'packet' )

PROTOCOL = ( 'tcp' | 'udp' | 'icmp' )

PROGRAM = (non-whitespace characters except for '^', must start with '/'. Embedded spaces or tabs must be quoted.)

PROGRAMHAT = '^' (non-whitespace characters; see change_hat(2) for a description of how this ``hat'' is used.)

FILE RULE = ( '"' FILEGLOB '"' | FILEGLOB ) ACCESS ','

FILEGLOB = (must start with '/' (after variable expansion), ?*[]{}^ have special meanings; see below. May include VARIABLE. Rules with embedded spaces or tabs must be quoted. Rules must end with '/' to apply to directories.)

ACCESS = ( 'r' | 'w' | 'l' | 'ix' | 'ux' | 'Ux' | 'px' | 'Px' | 'm' ) [ ACCESS ... ] (not all combinations are allowed; see below.)

VARIABLE = '@{' ALPHA [ ALPHANUMERIC ... ] '}'

VARIABLE ASSIGNMENT = VARIABLE ('=' | '+=') (space separated values)

ALPHA = ('a', 'b', 'c', ... 'z', 'A', 'B', ... 'Z')

ALPHANUMERIC = ('1', '2', '3', ... '9', 'a', 'b', 'c', ... 'z', 'A', 'B', ... 'Z')

All resources and programs need a full path. There may be any number of subprofiles (``hats'') in a profile, limited only by kernel memory. Subprofile names are limited to 974 characters. Not all profiles benefit from subprofiles --- applications must either be written or modified to use change_hat(2) to take advantage of subprofiles. Several change_hat(2)-aware applications exist, including an Apache module, mod_apparmor(5); a PAM module, pam_apparmor; and a Tomcat valve, tomcat_apparmor.  

Access Modes

File permission access modes consists of combinations of the following modes:
r      - read

w    - write --- conflicts with append

a     - append --- conflicts with write

ux    - unconfined execute

Ux    - unconfined execute --- scrub the environment

px    - discrete profile execute

Px    - discrete profile execute --- scrub the environment

ix    - inherit execute

m     - allow PROT_EXEC with mmap(2) calls

l     - link

k     - lock

 

Access Modes Details

r - Read mode
Allows the program to have read access to the file or directory listing. Read access is required for shell scripts and other interpreted content.
w - Write mode
Allows the program to have write access to the file. Files and directories must have this permission if they are to be unlinked (removed.) Write mode is not required on a directory to rename or create files within the directory.

This mode conflicts with append mode.

a - Append mode
Allows the program to have a limited appending only write access to the file. Append mode will prevent an application from opening the file for write unless it passes the O_APPEND parameter flag on open.

The mode conflicts with Write mode.

ux - Unconfined execute mode
Allows the program to execute the program without any AppArmor profile being applied to the program.

This mode is useful when a confined program needs to be able to perform a privileged operation, such as rebooting the machine. By placing the privileged section in another executable and granting unconfined execution rights, it is possible to bypass the mandatory constraints imposed on all confined processes. For more information on what is constrained, see the apparmor(7) man page.

WARNING 'ux' should only be used in very special cases. It enables the designated child processes to be run without any AppArmor protection. 'ux' does not scrub the environment of variables such as LD_PRELOAD; as a result, the calling domain may have an undue amount of influence over the callee. Use this mode only if the child absolutely must be run unconfined and LD_PRELOAD must be used. Any profile using this mode provides negligible security. Use at your own risk.

Incompatible with 'Ux', 'px', 'Px', 'ix'.

Ux - unconfined execute --- scrub the environment
'Ux' allows the named program to run in 'ux' mode, but AppArmor will invoke the Linux Kernel's unsafe_exec routines to scrub the environment, similar to setuid programs. (See ld.so(8) for some information on setuid/setgid environment scrubbing.)

WARNING 'Ux' should only be used in very special cases. It enables the designated child processes to be run without any AppArmor protection. Use this mode only if the child absolutely must be run unconfined. Use at your own risk.

Incompatible with 'ux', 'px', 'Px', 'ix'.

px - Discrete Profile execute mode
This mode requires that a discrete security profile is defined for a program executed and forces an AppArmor domain transition. If there is no profile defined then the access will be denied.

WARNING 'px' does not scrub the environment of variables such as LD_PRELOAD; as a result, the calling domain may have an undue amount of influence over the callee.

Incompatible with 'Ux', 'ux', 'Px', 'ix'.

Px - Discrete Profile execute mode --- scrub the environment
'Px' allows the named program to run in 'px' mode, but AppArmor will invoke the Linux Kernel's unsafe_exec routines to scrub the environment, similar to setuid programs. (See ld.so(8) for some information on setuid/setgid environment scrubbing.)

Incompatible with 'Ux', 'ux', 'px', 'ix'.

ix - Inherit execute mode
Prevent the normal AppArmor domain transition on execve(2) when the profiled program executes the named program. Instead, the executed resource will inherit the current profile.

This mode is useful when a confined program needs to call another confined program without gaining the permissions of the target's profile, or losing the permissions of the current profile. There is no version to scrub the environment because 'ix' executions don't change privileges.

Incompatible with 'Ux', 'ux', 'Px', 'px'. Implies 'm'.

m - Allow executable mapping
This mode allows a file to be mapped into memory using mmap(2)'s PROT_EXEC flag. This flag marks the pages executable; it is used on some architectures to provide non-executable data pages, which can complicate exploit attempts. AppArmor uses this mode to limit which files a well-behaved program (or all programs on architectures that enforce non-executable memory access controls) may use as libraries, to limit the effect of invalid -L flags given to ld(1) and LD_PRELOAD, LD_LIBRARY_PATH, given to ld.so(8).
l - Link mode
Allows the program to be able to create a link with this name. When a link is created, the new link MUST have a subset of permissions as the original file (with the exception that the destination does not have to have link access.) If there is an 'x' rule on the new link, it must match the original file exactly.
k - lock mode
Allows the program to be able lock a file with this name. This permission covers both advisory and mandatory locking.
 

Comments

Comments start with # and may begin at any place within a line. The comment ends when the line ends. This is the same comment style as shell scripts.  

Capabilities

The only capabilities a confined process may use may be enumerated; for the complete list, please refer to capabilities(7). Note that granting some capabilities renders AppArmor confinement for that domain advisory; while open(2), read(2), write(2), etc., will still return error when access is not granted, some capabilities allow loading kernel modules, arbitrary access to IPC, ability to bypass discretionary access controls, and other operations that are typically reserved for the root user.

The only operations that cannot be controlled in this manner are mount(2), umount(2), and loading new AppArmor policy into the kernel, which are always denied to confined processes.  

Network Rules

AppArmor supports simple coarse grained network mediation. The network rule restrict all socket(2) based operations. The mediation done is a course grained check on whether a socket of a given type and family can be created, read, or written. There is no mediation based of port number or protocol beyond tcp, udp, and raw.

AppArmor network rules are accumulated so that the granted network permissions are the union of all the listed network rule permissions.

AppArmor network rules are broad and general and become more restrictive as further information is specified.

eg.

network,               #allow access to all networking
network tcp,            #allow access to tcp
network inet tcp,       #allow access to tcp only for inet4 addresses
network inet6 tcp,      #allow access to tcp only for inet6 addresses
 

Variables

AppArmor's policy language allows embedding variables into file rules to enable easier configuration for some common (and pervasive) setups. Variables may have multiple values assigned, but any variable assignments must be made before the start of the profile.

The parser will automatically expand variables to include all values that they have been assigned; it is an error to reference a variable without setting at least one value.

At the time of this writing, only @{HOME} and @{HOMEDIR} are defined in the AppArmor policy provided with SUSE Linux, in the /etc/apparmor.d/tunables/home file; these variables are used in many of the abstractions described later.  

Globbing

File resources may be specified with a globbing syntax similar to that used by popular shells, such as csh(1), bash(1), zsh(1).
*
can substitute for any number of characters, excepting '/'
**
can substitute for any number of characters, including '/'
?
can substitute for any single character excepting '/'
[abc]
will substitute for the single character a, b, or c
[a-c]
will substitute for the single character a, b, or c
{ab,cd}
will expand to one rule to match ab, one rule to match cd

When AppArmor looks up a directory the pathname being looked up will end with a slash (e.g., /var/tmp/); otherwise it will not end with a slash. Only rules that match a trailing slash will match directories. Some examples, none matching the /tmp/ directory itself, are:

/tmp/*
Files directly in /tmp.
/tmp/*/
Directories directly in /tmp.
/tmp/**
Files and directories anywhere underneath /tmp.
/tmp/**/
Directories anywhere underneath /tmp.
 

#include mechanism

AppArmor provides an easy abstraction mechanism to group common file access requirements; this abstraction is an extremely flexible way to grant site-specific rights and makes writing new AppArmor profiles very simple by assembling the needed building blocks for any given program.

The use of '#include' is modelled directly after cpp(1); its use will replace the '#include' statement with the specified file's contents. #include ``/absolute/path'' specifies that /absolute/path should be used. #include ``relative/path'' specifies that relative/path should be used, where the path is relative to the current working directory. #include <magic/path> is the most common usage; it will load magic/path relative to a directory specified to apparmor_parser(8). /etc/apparmor.d/ is the AppArmor default.

The supplied AppArmor profiles follow several conventions; the abstractions stored in /etc/apparmor.d/abstractions/ are some large clusters that are used in most profiles. What follows are short descriptions of how some of the abstractions are used.

abstractions/audio
Includes accesses to device files used for audio applications.
abstractions/authentication
Includes access to files and services typically necessary for services that perform user authentication.
abstractions/base
Includes files that should be readable and writable in all profiles.
abstractions/bash
Includes many files used by bash; useful for interactive shells and programs that call system(3).
abstractions/consoles
Includes read and write access to the device files controlling the virtual console, sshd(8), xterm(1), etc. This abstraction is needed for many programs that interact with users.
abstractions/fonts
Includes access to fonts and the font libraries.
abstractions/gnome
Includes read and write access to GNOME configuration files, as well as read access to GNOME libraries.
abstractions/kde
Includes read and write access to KDE configuration files, as well as read access to KDE libraries.
abstractions/kerberosclient
Includes file access rules needed for common kerberos clients.
abstractions/nameservice
Includes file rules to allow DNS, LDAP, NIS, SMB, user and group password databases, services, and protocols lookups.
abstractions/perl
Includes read access to perl modules.
abstractions/user-download
abstractions/user-mail
abstractions/user-manpages
abstractions/user-tmp
abstractions/user-write
Some profiles for typical ``user'' programs will use these include files to describe rights that users have in the system.
abstractions/wutmp
Includes write access to files used to maintain wtmp(5) and utmp(5) databases, used with the w(1) and associated commands.
abstractions/X
Includes read access to libraries, configuration files, X authentication files, and the X socket.

The abstractions stored in /etc/apparmor.d/program-chunks/ are intended for use by specific program suites, and are not generally useful.

Some of the abstractions rely on variables that are set in files in the /etc/apparmor.d/tunables/ directory. These variables are currently @{HOME} and @{HOMEDIR}. Variables cannot be set in profile scope; they can only be set before the profile. Therefore, any profiles that use abstractions should either #include <tunables/global> or otherwise ensure that @{HOME} and @{HOMEDIR} are set before starting the profile definition. The autodep(8) and genprof(8) utilities will automatically emit #include <tunables/global> in generated profiles.  

EXAMPLE

An example AppArmor profile:

        # 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*       rmix,
          /lib/lib*.so*       r,
          /proc/[0-9]**       r,
          /usr/lib/**         r,
          /tmp/foo.pid        wr,
          /tmp/foo.*          lrw,
          /@{HOME}/.foo_file  rw,

          # a comment about foo's subprofile, bar.
          ^bar {
            /lib/ld-*.so*       rmix,
            /usr/bin/bar        rmix,
            /var/spool/*        rwl,
          }
        }

 

FILES

/etc/init.d/boot.apparmor
/etc/apparmor.d/
 

SEE ALSO

apparmor(7), apparmor_parser(8), complain(1), enforce(1), change_hat(2), mod_apparmor(5), and <http://forge.novell.com/modules/xfmod/project/?apparmor>.


 

Index

NAME
DESCRIPTION
FORMAT
Access Modes
Access Modes Details
Comments
Capabilities
Network Rules
Variables
Globbing
#include mechanism
EXAMPLE
FILES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 15:27:46 GMT, June 11, 2010

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