apparmor.d(5)
SECCIÓN: 5 - Formatos de archivo
APPARMOR.D(5) AppArmor APPARMOR.D(5)
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
AppArmor policy is written in a declarative language, in which the order
of rules within a given section or block does not matter. Policy is by
convention written so that it is contained in multiple files, but this
is not a requirement. It could just as easily be written in a single
file. The policy language is compiled to a architecture independent
binary format that is loaded into the kernel for enforcement.
The base unit of AppArmor confinement is the profile. It contains a set
of rules which are enforced when the profile is associated with a
running program. The rules within the profile provide a whitelist of
different permission that are allowed, along with a few other special
rules.
The text in AppArmor policy is split into two sections, the preamble and
the profile definitions. The preamble must occur at the head of the file
and once profile definitions begin, no more preamble rules are allowed
(even in files that are included into the profile). When AppArmor policy
(set of profiles) is split across multiple files, each file can have its
own preamble section, which may be the same or different from other
files preamble. Files included within a profile section can not have a
preamble section.
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).
PROFILE FILE = ( [ PREAMBLE ] [ PROFILE ] )*
PREAMBLE = ( COMMENT | VARIABLE ASSIGNMENT | ALIAS RULE | INCLUDE |
ABI )*
Variable assignment and alias rules must come before the profile.
VARIABLE ASSIGNMENT = VARIABLE (’=’ | ’+=’) (space separated values)
VARIABLE = ’@{’ ALPHA [ ( ALPHANUMERIC | ’_’ ) ... ] ’}’
ALIAS RULE = ’alias’ ABS PATH ’->’ REWRITTEN ABS PATH ’,’
INCLUDE = ( ’#include’ | ’include’ ) [ ’if exists’ ] ( ABS PATH |
MAGIC PATH )
ABI = ( ’abi’ ) ( 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 [ ’\r’ ] ’\n’
TEXT = any characters
PROFILE = ( PROFILE HEAD ) [ ATTACHMENT SPECIFICATION ] [ PROFILE
FLAG CONDS ] ’{’ ( RULES )* ’}’
PROFILE HEAD = [ ’profile’ ] FILEGLOB | ’profile’ PROFILE NAME
PROFILE NAME ( UNQUOTED PROFILE NAME | QUOTED PROFILE NAME )
QUOTED PROFILE NAME = ’"’ UNQUOTED PROFILE NAME ’"’
UNQUOTED PROFILE NAME = (must start with alphanumeric character
(after variable expansion), or ’/’ AARE have special meanings; see
below. May include VARIABLE. Rules with embedded spaces or tabs must
be quoted.)
ATTACHMENT SPECIFICATION = [ PROFILE_EXEC_COND ] [ PROFILE XATTR
CONDS ]
PROFILE_EXEC_COND = FILEGLOB
PROFILE XATTR CONDS = [ ’xattrs=’ ] ’(’ comma or white space
separated list of PROFILE XATTR ’)’
PROFILE XATTR = extended attribute name ’=’ XATTR VALUE FILEGLOB
XATTR VALUE FILEGLOB = FILEGLOB
PROFILE FLAG CONDS = [ ’flags=’ ] ’(’ comma or white space
separated list of PROFILE FLAGS ’)’
PROFILE FLAGS = PROFILE MODE | AUDIT_MODE | ’mediate_deleted’ |
’attach_disconnected’ | ’chroot_relative’
PROFILE MODE = ’enforce’ | ’complain’ | ’kill’ | ’unconfined’
AUDIT MODE = ’audit’
RULES = [ ( LINE RULES | COMMA RULES ’,’ | BLOCK RULES )
LINE RULES = ( COMMENT | INCLUDE ) [ ’\r’ ] ’\n’
COMMA RULES = ( CAPABILITY RULE | NETWORK RULE | MOUNT RULE | PIVOT
ROOT RULE | UNIX RULE | FILE RULE | LINK RULE | CHANGE_PROFILE RULE
| RLIMIT RULE | DBUS RULE )
BLOCK RULES = ( SUBPROFILE | HAT | QUALIFIER BLOCK )
SUBPROFILE = ’profile’ PROFILE NAME [ ATTACHMENT SPECIFICATION ] [
PROFILE FLAG CONDS ] ’{’ ( RULES )* ’}’
HAT = (’hat’ | ’ˆ’) HATNAME [ PROFILE FLAG CONDS ] ’{’ ( RULES )*
’}’
HATNAME = (must start with alphanumeric character. See
aa_change_hat(2) for a description of how this "hat" is used. If ’ˆ’
is used to start a hat then there is no space between the ’ˆ’ and
HATNAME)
QUALIFIER BLOCK = QUALIFIERS BLOCK
ACCESS TYPE = ( ’allow’ | ’deny’ )
QUALIFIERS = [ ’audit’ ] [ ACCESS TYPE ]
CAPABILITY RULE = [ QUALIFIERS ] ’capability’ [ CAPABILITY LIST ]
CAPABILITY LIST = ( CAPABILITY )+
CAPABILITY = (lowercase capability name without ’CAP_’ prefix; see
capabilities(7))
NETWORK RULE = [ QUALIFIERS ] ’network’ [ DOMAIN ] [ TYPE | PROTOCOL
]
DOMAIN = ( ’unix’ | ’inet’ | ’ax25’ | ’ipx’ | ’appletalk’ | ’netrom’
| ’bridge’ | ’atmpvc’ | ’x25’ | ’inet6’ | ’rose’ | ’netbeui’ |
’security’ | ’key’ | ’netlink’ | ’packet’ | ’ash’ | ’econet’ |
’atmsvc’ | ’rds’ | ’sna’ | ’irda’ | ’pppox’ | ’wanpipe’ | ’llc’ |
’ib’ | ’mpls’ | ’can’ | ’tipc’ | ’bluetooth’ | ’iucv’ | ’rxrpc’ |
’isdn’ | ’phonet’ | ’ieee802154’ | ’caif’ | ’alg’ | ’nfc’ | ’vsock’
| ’kcm’ | ’qipcrtr’ | ’smc’ | ’xdp’ | ’mctp’ ) ’,’
TYPE = ( ’stream’ | ’dgram’ | ’seqpacket’ | ’rdm’ | ’raw’ |
’packet’ )
PROTOCOL = ( ’tcp’ | ’udp’ | ’icmp’ )
MOUNT RULE = ( MOUNT | REMOUNT | UMOUNT )
MOUNT = [ QUALIFIERS ] ’mount’ [ MOUNT CONDITIONS ] [ SOURCE
FILEGLOB ] [ ’->’ [ MOUNTPOINT FILEGLOB ]
REMOUNT = [ QUALIFIERS ] ’remount’ [ MOUNT CONDITIONS ] MOUNTPOINT
FILEGLOB
UMOUNT = [ QUALIFIERS ] ’umount’ [ MOUNT CONDITIONS ] MOUNTPOINT
FILEGLOB
MOUNT CONDITIONS = [ ( ’fstype’ | ’vfstype’ ) ( ’=’ | ’in’ ) MOUNT
FSTYPE EXPRESSION ] [ ’options’ ( ’=’ | ’in’ ) MOUNT FLAGS
EXPRESSION ]
MOUNT FSTYPE EXPRESSION = ( MOUNT FSTYPE LIST | MOUNT EXPRESSION )
MOUNT FSTYPE LIST = Comma separated list of valid filesystem and
virtual filesystem types (eg ext4, debugfs, devfs, etc)
MOUNT FLAGS EXPRESSION = ( MOUNT FLAGS LIST | MOUNT EXPRESSION )
MOUNT FLAGS LIST = Comma separated list of MOUNT FLAGS.
MOUNT FLAGS = ( ’ro’ | ’rw’ | ’nosuid’ | ’suid’ | ’nodev’ | ’dev’ |
’noexec’ | ’exec’ | ’sync’ | ’async’ | ’remount’ | ’mand’ | ’nomand’
| ’dirsync’ | ’noatime’ | ’atime’ | ’nodiratime’ | ’diratime’ |
’bind’ | ’rbind’ | ’move’ | ’verbose’ | ’silent’ | ’loud’ | ’acl’ |
’noacl’ | ’unbindable’ | ’runbindable’ | ’private’ | ’rprivate’ |
’slave’ | ’rslave’ | ’shared’ | ’rshared’ | ’relatime’ |
’norelatime’ | ’iversion’ | ’noiversion’ | ’strictatime’ |
’nostrictatime’ | ’lazytime’ | ’nolazytime’ | ’nouser’ | ’user’ |
’symfollow’ | ’nosymfollow’ )
MOUNT EXPRESSION = ( ALPHANUMERIC | AARE ) ...
PIVOT ROOT RULE = [ QUALIFIERS ] pivot_root [ oldroot=OLD PUT
FILEGLOB ] [ NEW ROOT FILEGLOB ] [ ’->’ PROFILE NAME ]
SOURCE FILEGLOB = FILEGLOB
MOUNTPOINT FILEGLOB = FILEGLOB
OLD PUT FILEGLOB = FILEGLOB
PTRACE_RULE = [ QUALIFIERS ] ’ptrace’ [ PTRACE ACCESS PERMISSIONS ]
[ PTRACE PEER ]
PTRACE ACCESS PERMISSIONS = PTRACE ACCESS | PTRACE ACCESS LIST
PTRACE ACCESS LIST = ’(’ Comma or space separated list of PTRACE
ACCESS ’)’
PTRACE ACCESS = ( ’r’ | ’w’ | ’rw’ | ’read’ | ’readby’ | ’trace’ |
’tracedby’ )
PTRACE PEER = ’peer’ ’=’ AARE
SIGNAL_RULE = [ QUALIFIERS ] ’signal’ [ SIGNAL ACCESS PERMISSIONS ]
[ SIGNAL SET ] [ SIGNAL PEER ]
SIGNAL ACCESS PERMISSIONS = SIGNAL ACCESS | SIGNAL ACCESS LIST
SIGNAL ACCESS LIST = ’(’ Comma or space separated list of SIGNAL
ACCESS ’)’
SIGNAL ACCESS = ( ’r’ | ’w’ | ’rw’ | ’read’ | ’write’ | ’send’ |
’receive’ )
SIGNAL SET = ’set’ ’=’ ’(’ SIGNAL LIST ’)’
SIGNAL LIST = Comma or space separated list of SIGNALS
SIGNALS = ( ’hup’ | ’int’ | ’quit’ | ’ill’ | ’trap’ | ’abrt’ | ’bus’
| ’fpe’ | ’kill’ | ’usr1’ | ’segv’ | ’usr2’ | ’pipe’ | ’alrm’ |
’term’ | ’stkflt’ | ’chld’ | ’cont’ | ’stop’ | ’stp’ | ’ttin’ |
’ttou’ | ’urg’ | ’xcpu’ | ’xfsz’ | ’vtalrm’ | ’prof’ | ’winch’ |
’io’ | ’pwr’ | ’sys’ | ’emt’ | ’exists’ | ’rtmin+0’ ... ’rtmin+32’ )
SIGNAL PEER = ’peer’ ’=’ AARE
DBUS RULE = ( DBUS MESSAGE RULE | DBUS SERVICE RULE | DBUS EAVESDROP
RULE | DBUS COMBINED RULE )
DBUS MESSAGE RULE = [ QUALIFIERS ] ’dbus’ [ DBUS ACCESS EXPRESSION ]
[ DBUS BUS ] [ DBUS PATH ] [ DBUS INTERFACE ] [ DBUS MEMBER ] [ DBUS
PEER ]
DBUS SERVICE RULE = [ QUALIFIERS ] ’dbus’ [ DBUS ACCESS EXPRESSION ]
[ DBUS BUS ] [ DBUS NAME ]
DBUS EAVESDROP RULE = [ QUALIFIERS ] ’dbus’ [ DBUS ACCESS EXPRESSION
] [ DBUS BUS ]
DBUS COMBINED RULE = [ QUALIFIERS ] ’dbus’ [ DBUS ACCESS EXPRESSION
] [ DBUS BUS ]
DBUS ACCESS EXPRESSION = ( DBUS ACCESS | ’(’ DBUS ACCESS LIST ’)’ )
DBUS BUS = ’bus’ ’=’ ’(’ ’system’ | ’session’ | ’"’ AARE ’"’ | AARE
’)’
DBUS PATH = ’path’ ’=’ ’(’ ’"’ AARE ’"’ | AARE ’)’
DBUS INTERFACE = ’interface’ ’=’ ’(’ ’"’ AARE ’"’ | AARE ’)’
DBUS MEMBER = ’member’ ’=’ ’(’ ’"’ AARE ’"’ | AARE ’)’
DBUS PEER = ’peer’ ’=’ ’(’ [ DBUS NAME ] [ DBUS LABEL ] ’)’
DBUS NAME = ’name’ ’=’ ’(’ ’"’ AARE ’"’ | AARE ’)’
DBUS LABEL = ’label’ ’=’ ’(’ ’"’ AARE ’"’ | AARE ’)’
DBUS ACCESS LIST = Comma separated list of DBUS ACCESS
DBUS ACCESS = ( ’send’ | ’receive’ | ’bind’ | ’eavesdrop’ | ’r’ |
’read’ | ’w’ | ’write’ | ’rw’ )
Some accesses are incompatible with some rules; see below.
UNIX RULE = [ QUALIFIERS ] ’unix’ [ UNIX ACCESS EXPR ] [ UNIX RULE
CONDS ] [ UNIX LOCAL EXPR ] [ UNIX PEER EXPR ]
UNIX ACCESS EXPR = ( UNIX ACCESS | UNIX ACCESS LIST )
UNIX ACCESS = ( ’create’ | ’bind’ | ’listen’ | ’accept’ | ’connect’
| ’shutdown’ | ’getattr’ | ’setattr’ | ’getopt’ | ’setopt’ | ’send’
| ’receive’ | ’r’ | ’w’ | ’rw’ )
Some access modes are incompatible with some rules or require
additional parameters.
UNIX ACCESS LIST = ’(’ UNIX ACCESS ( [’,’] UNIX ACCESS )* ’)’
UNIX RULE CONDS = ( TYPE COND | PROTO COND )
Each cond can appear at most once.
TYPE COND = ’type’ ’=’ ( AARE | ’(’ ( ’"’ AARE ’"’ | AARE )+ ’)’ )
PROTO COND = ’protocol’ ’=’ ( AARE | ’(’ ( ’"’ AARE ’"’ | AARE )+
’)’ )
UNIX LOCAL EXPR = ( UNIX ADDRESS COND | UNIX LABEL COND | UNIX ATTR
COND | UNIX OPT COND )*
Each cond can appear at most once.
UNIX PEER EXPR = ’peer’ ’=’ ( UNIX ADDRESS COND | UNIX LABEL COND )+
Each cond can appear at most once.
UNIX ADDRESS COND ’addr’ ’=’ ( AARE | ’(’ ’"’ AARE ’"’ | AARE ’)’ )
UNIX LABEL COND ’label’ ’=’ ( AARE | ’(’ ’"’ AARE ’"’ | AARE ’)’ )
UNIX ATTR COND ’attr’ ’=’ ( AARE | ’(’ ’"’ AARE ’"’ | AARE ’)’ )
UNIX OPT COND ’opt’ ’=’ ( AARE | ’(’ ’"’ AARE ’"’ | AARE ’)’ )
RLIMIT RULE = ’set’ ’rlimit’ [RLIMIT ’<=’ RLIMIT VALUE ]
RLIMIT = ( ’cpu’ | ’fsize’ | ’data’ | ’stack’ | ’core’ | ’rss’ |
’nofile’ | ’ofile’ | ’as’ | ’nproc’ | ’memlock’ | ’locks’ |
’sigpending’ | ’msgqueue’ | ’nice’ | ’rtprio’ | ’rttime’ )
RLIMIT VALUE = ( RLIMIT SIZE | RLIMIT NUMBER | RLIMIT TIME | RLIMIT
NICE )
RLIMIT SIZE = NUMBER ( ’K’ | ’M’ | ’G’ )
Only applies to RLIMIT of ’fsize’, ’data’, ’stack’, ’core’, ’rss’,
’as’, ’memlock’, ’msgqueue’.
RLIMIT NUMBER = number from 0 to max rlimit value.
Only applies to RLIMIT of ’ofile’, ’nofile’, ’locks’,
’sigpending’, ’nproc’, ’rtprio’.
RLIMIT TIME = NUMBER ( ’us’ | ’microsecond’ | ’microseconds’ | ’ms’
| ’millisecond’ | ’milliseconds’ | ’s’ | ’sec’ | ’second’ |
’seconds’ | ’min’ | ’minute’ | ’minutes’ | ’h’ | ’hour’ | ’hours’ |
’d’ | ’day’ | ’days’ | ’week’ | ’weeks’ )
Only applies to RLIMIT of ’cpu’ and ’rttime’. RLIMIT ’cpu’ only
allows units >= ’seconds’.
RLIMIT NICE = a number between -20 and 19.
Only applies to RLIMIT of ’nice’.
FILE RULE = [ QUALIFIERS ] [ ’owner’ ] ( ’file’ | [ ’file’ ] (
FILEGLOB ACCESS | ACCESS FILEGLOB ) [ ’->’ EXEC TARGET ] )
FILEGLOB = ( QUOTED FILEGLOB | UNQUOTED FILEGLOB )
QUOTED FILEGLOB = ’"’ UNQUOTED FILEGLOB ’"’
UNQUOTED FILEGLOB = (must start with ’/’ (after variable expansion),
AARE 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.)
AARE = ?*[]{}ˆ
See section "Globbing (AARE)" below for meanings.
ACCESS = ( ’r’ | ’w’ | ’a’ | ’l’ | ’k’ | ’m’ | EXEC TRANSITION )+
(not all combinations are allowed; see below.)
EXEC TRANSITION = ( ’ix’ | ’ux’ | ’Ux’ | ’px’ | ’Px’ | ’cx’ | ’Cx’
| ’pix’ | ’Pix’ | ’cix’ | ’Cix’ | ’pux’ | ’PUx’ | ’cux’ | ’CUx’ |
’x’ )
A bare ’x’ is only allowed in rules with the deny qualifier,
everything else only without the deny qualifier.
EXEC TARGET = name
Requires EXEC TRANSITION specified.
LINK RULE = QUALIFIERS [ ’owner’ ] ’link’ [ ’subset’ ] FILEGLOB ’->’
FILEGLOB
ALPHA = (’a’, ’b’, ’c’, ... ’z’, ’A’, ’B’, ... ’Z’)
ALPHANUMERIC = (’0’, ’1’, ’2’, ... ’9’, ’a’, ’b’, ’c’, ... ’z’, ’A’,
’B’, ... ’Z’)
CHANGE_PROFILE RULE = ’change_profile’ [ [ EXEC MODE ] EXEC COND ] [
’->’ PROFILE NAME ]
EXEC_MODE = ( ’safe’ | ’unsafe’ )
EXEC COND = FILEGLOB
All resources and programs need a full path. There may be any number of
subprofiles (aka child profiles) in a profile, limited only by kernel
memory. Subprofile names are limited to 974 characters. Child profiles
can be used to confine an application in a special way, or when you want
the child to be unconfined on the system, but confined when called from
the parent. Hats are a special child profile that can be used with the
aa_change_hat(2) API call. Applications written or modified to use
aa_change_hat(2) can take advantage of subprofiles to run under
different confinements, dependent on program logic. Several
aa_change_hat(2)-aware applications exist, including an Apache module,
mod_apparmor(5); a PAM module, pam_apparmor; and a Tomcat valve,
tomcat_apparmor. Applications written or modified to use
change_profile(2) transition permanently to the specified profile.
libvirt is one such application.
Profile Head
The profile head consists of a required name that is unique and optional
attachment conditionals and control flags.
Name
The name of the profile is its identifier. It is what is displayed
during introspection (eg. ps -Z), and defines how the profile is
referenced by policy rules for any policy interaction via ipc or domain
changes. It is recommended that the name be kept short and have meaning
for the application it is being applied eg. firefox for the firefox web
browser or its functional role eg. log_admin.
If the name is an applications full absolute path name eg.
/usr/bin/firefox and an exec attachment conditional is not specified the
name is also used as the profile’s exec attachment conditional. This use
however has been deprecated and is discouraged as it makes for long
names that can make profile rules difficult to understand, and may not
be fully displayed by some introspection tools.
Attachment Conditionals
The attachment conditionals are used during profile changes to determine
whether a profile is a match for the proposed profile transition. The
attachment conditionals are optional, how and when they are applied is
determined by the specific condition(s) used.
When attachment conditionals are used, the attachment conditionals for
all profiles in the namespace will be evaluated. The profile with the
set of attachments that result in the best match will become the new
profile after a transition operation. Attachments that don’t match will
result in the profile not being available for transition.
If no conditionals are specified the profile will only be used if a
transition explicitly specifies the profile name.
Exec Attachment Conditional
The exec attachment conditional governs how closely the profile matches
an executable program. This conditional is only used during an exec
operation when the matching exec rule specifies either a px or cx (or
their derivatives) transition type. The exec attachment conditional will
also be used by tasks that are unconfined as they use a pix transition
rule.
If there are no attachment matches then it is up to the exec rule to
determine what happens (fail or a fallback option).
Note: see profile Name for information around using the profile name as
an attachment conditional.
Exec attachment conditionals can contain variable names and pattern
matching. They use a longest left match heuristic to deterime the
winner in the case of multiple matches at run time. The exact
implementation of this resolution is kernel specific and has improved
over time, while retaining backwards compatibility. If the heuristic can
not determine a winner between multiple matches the exec will be denied.
Extended Attributes Attachment Conditional
AppArmor profiles have the ability to target files based on their
xattr(7) values in addition to their path. For example, the following
profile matches files in /usr/bin with the attribute "security.apparmor"
and value "trusted":
/usr/bin/* xattrs(security.apparmor="trusted") {
# ...
}
See apparmor_xattrs(7) for further details.
Flags
The profile flags allow modifying the behavior of the profile. If a
profile flag is specified it takes priority over any conflicting flags
that have been specified by rules in the profile body.
Profile Mode
The profile mode allow controlling the enforcement behavior of the
profile rules.
If no mode is specified the profile defaults to enforce mode.
enforce For a given action, if the profile rules do not grant permission
the action will be denied, with an EACCES or EPERM error code returned
to userspace, and the violation will be logged with a tag of the access
being DENIED.
kill This is a variant of enforce mode where in addition to returning
EACCES or EPERM for a violation, the task is also sent a signal to kill
it.
complain For a given action, if the profile rules do not grant
permission the action will be allowed, but the violation will be logged
with a tag of the access being ALLOWED.
unconfined This mode allows a task confined by the profile to behave as
though they are unconfined. This mode allow for an unconfined behavior
that can be later changed to confinement by using profile replacement.
This mode is should not be used under regular deployment but can be
useful during debugging and some system initialization scenarios.
Audit Mode
The audit mode allows control of how AppArmor messages are are logged to
the audit system.
audit This flag causes all actions whether allowed or denied to be
logged.
Misc modes
mediate_deleted This forces AppArmor to mediate deleted files as if they
still exist in the file system.
attach_disconnected This forces AppArmor to attach disconnected objects
to the task’s namespace and mediate them as though they are part of the
namespace. WARNING this mode is unsafe and can result in aliasing and
access to objects that should not be allowed. Its intent is a debug and
policy development tool.
chroot_relative This forces file names to be relative to a chroot and
behave as if the chroot is a mount namespace.
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
cx - transition to subprofile on execute
Cx - transition to subprofile on execute ‐‐ scrub the environment
ix - inherit execute
pix - discrete profile execute with inherit fallback
Pix - discrete profile execute with inherit fallback ‐‐ scrub the
environment
cix - transition to subprofile on execute with inherit fallback
Cix - transition to subprofile on execute with inherit fallback ‐‐
scrub the environment
pux - discrete profile execute with fallback to unconfined
PUx - discrete profile execute with fallback to unconfined ‐‐ scrub
the environment
cux - transition to subprofile on execute with fallback to
unconfined
CUx - transition to subprofile on execute with fallback to
unconfined ‐‐ scrub the environment
deny x - disallow execute (in rules with the deny qualifier)
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 other exec transition modes and the deny
qualifier.
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 other exec transition modes and the deny
qualifier.
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 other exec transition modes and the deny
qualifier.
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 other exec transition modes and the deny
qualifier.
cx - Transition to Subprofile execute mode
This mode requires that a local security profile is defined and
forces an AppArmor domain transition to the named profile. If there
is no profile defined then the access will be denied.
WARNING ’cx’ 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 other exec transition modes and the deny
qualifier.
Cx - Transition to Subprofile execute mode ‐‐ scrub the environment
’Cx’ allows the named program to run in ’cx’ 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 other exec transition modes and the deny
qualifier.
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 other exec transition modes and the deny
qualifier.
Profile transition with inheritance fallback execute mode
These modes attempt to perform a domain transition as specified by
the matching permission (shown below) and if that transition fails
to find the matching profile the domain transition proceeds using
the ’ix’ transition mode.
'Pix' == 'Px' with fallback to 'ix'
'pix' == 'px' with fallback to 'ix'
'Cix' == 'Cx' with fallback to 'ix'
'cix' == 'cx' with fallback to 'ix'
Incompatible with other exec transition modes and the deny
qualifier.
Profile transition with unconfined fallback execute mode
These modes attempt to perform a domain transition as specified by
the matching permission (shown below) and if that transition fails
to find the matching profile the domain transition proceeds using
the ’ux’ transition mode if ’pux’, ’cux’ or the ’Ux’ transition mode
if ’PUx’, ’CUx’ is used.
'PUx' == 'Px' with fallback to 'Ux'
'pux' == 'px' with fallback to 'ux'
'CUx' == 'Cx' with fallback to 'Ux'
'cux' == 'cx' with fallback to 'ux'
Incompatible with other exec transition modes and the deny
qualifier.
deny x - Deny execute
For rules including the deny modifier, only ’x’ is allowed to deny
execute.
The ’ix’, ’Px’, ’px’, ’Cx’, ’cx’ and the fallback modes conflict
with the deny modifier.
Directed profile transitions
The directed (’px’, ’Px’, ’pix’, ’Pix’, ’pux’, ’PUx’) profile and
subprofile (’cx’, ’Cx’, ’cix’, ’Cix’, ’cux’, ’CUx’) transitions
normally determine the profile to transition to from the executable
name. It is however possible to specify the name of the profile that
the transition should use.
The name of the profile to transition to is specified using the ’->’
followed by the name of the profile to transition to. Eg.
/bin/** px -> profile,
Incompatible with other exec transition modes.
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.
leading OR trailing access permissions
File rules can be specified with the access permission either
leading or trailing the file glob. Eg.
rw /**, # leading permissions
/** rw, # trailing permissions
When leading permissions are used further rule options and context
may be allowed, Eg.
l /foo -> /bar, # lead 'l' link permission is equivalent to link rules
Link rules
Link rules allow specifying permission to form a hard link as a link
target pair. If the subset condition is specified then the permissions
to access the link file must be a subset of the profiles permissions to
access the target file. If there is an ’x’ rule on the new link, it must
match the original file exactly.
Eg.
/file1 r,
/file2 rwk,
/link* rw,
link subset /link* -> /**,
The link rule allows linking of /link to both /file1 or /file2 by name
however because the /link file has ’rw’ permissions it is not allowed to
link to /file1 because that would grant an access path to /file1 with
more permissions than the ’r’ permissions the profile specifies.
A link of /link to /file2 would be allowed because the ’rw’ permissions
of /link are a subset of the ’rwk’ permissions for /file1.
The link rule is equivalent to specifying the ’l’ link permission as a
leading permission with no other file access permissions. When this is
done the link rule options can be specified.
The following link rule is equivalent to the ’l’ permission file rule
link /foo -> bar,
l /foo -> /bar,
File rules that specify the ’l’ permission and don’t specify the extend
link permissions map to link rules as follows.
/foo l,
l /foo,
link subset /foo -> /**,
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.
Network Rules
AppArmor supports simple coarse grained network mediation. The network
rule restrict all socket(2) based operations. The mediation done is a
coarse‐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. Network netlink(7) rules
may only specify type ’dgram’ 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
network netlink raw, #allow access to AF_NETLINK SOCK_RAW
Mount Rules
AppArmor supports mount mediation and allows specifying filesystem types
and mount flags. The syntax of mount rules in AppArmor is based on the
mount(8) command syntax. Mount rules must contain one of the mount,
remount or umount keywords, but all mount conditions are optional.
Unspecified optional conditionals are assumed to match all entries (eg,
not specifying fstype means all fstypes are matched). Due to the
complexity of the mount command and how options may be specified,
AppArmor allows specifying conditionals three different ways:
1. If a conditional is specified using ’=’, then the rule only grants
permission for mounts matching the exactly specified options. For
example, an AppArmor policy with the following rule:
mount options=ro /dev/foo -E<gt> /mnt/,
Would match:
$ mount -o ro /dev/foo /mnt
but not either of these:
$ mount -o ro,atime /dev/foo /mnt
$ mount -o rw /dev/foo /mnt
2. If a conditional is specified using ’in’, then the rule grants
permission for mounts matching any combination of the specified
options. For example, if an AppArmor policy has the following rule:
mount options in (ro,atime) /dev/foo -> /mnt/,
all of these mount commands will match:
$ mount -o ro /dev/foo /mnt
$ mount -o ro,atime /dev/foo /mnt
$ mount -o atime /dev/foo /mnt
but none of these will:
$ mount -o ro,sync /dev/foo /mnt
$ mount -o ro,atime,sync /dev/foo /mnt
$ mount -o rw /dev/foo /mnt
$ mount -o rw,noatime /dev/foo /mnt
$ mount /dev/foo /mnt
3. If multiple conditionals are specified in a single mount rule, then
the rule grants permission for each set of options. This provides a
shorthand when writing mount rules which might help to logically
break up a conditional. For example, if an AppArmor policy has the
following rule:
mount options=ro options=atime
both of these mount commands will match:
$ mount -o ro /dev/foo /mnt
$ mount -o atime /dev/foo /mnt
but this one will not:
$ mount -o ro,atime /dev/foo /mnt
Note that separate mount rules are distinct and the options do not
accumulate. For example, these AppArmor mount rules:
mount options=ro,
mount options=atime,
are not equivalent to either of these mount rules:
mount options=(ro,atime),
mount options in (ro,atime),
To help clarify the flexibility and complexity of mount rules, here are
some example rules with accompanying matching commands:
mount,
the ’mount’ rule without any conditionals is the most generic and
allows any mount. Equivalent to ’mount fstype=** options=** ** ->
/**’.
mount /dev/foo,
allow mounting of /dev/foo anywhere with any options. Some matching
mount commands:
$ mount /dev/foo /mnt
$ mount -t ext3 /dev/foo /mnt
$ mount -t vfat /dev/foo /mnt
$ mount -o ro,atime,noexec,nodiratime /dev/foo /srv/some/mountpoint
mount options=ro /dev/foo,
allow mounting of /dev/foo anywhere, as read only. Some matching
mount commands:
$ mount -o ro /dev/foo /mnt
$ mount -o ro /dev/foo /some/where/else
mount options=(ro,atime) /dev/foo,
allow mount of /dev/foo anywhere, as read only and using inode
access times. Some matching mount commands:
$ mount -o ro,atime /dev/foo /mnt
$ mount -o ro,atime /dev/foo /some/where/else
mount options in (ro,atime) /dev/foo,
allow mount of /dev/foo anywhere using some combination of ’ro’ and
’atime’ (see above). Some matching mount commands:
$ mount -o ro /dev/foo /mnt
$ mount -o atime /dev/foo /some/where/else
$ mount -o ro,atime /dev/foo /some/other/place
mount options=ro /dev/foo, mount options=atime /dev/foo,
allow mount of /dev/foo anywhere as read only, and allow mount of
/dev/foo anywhere using inode access times. Note this is expressed
as two different rules. Matches:
$ mount -o ro /dev/foo /mnt/1
$ mount -o atime /dev/foo /mnt/2
mount -> /mnt/**,
allow mounting anything under a directory in /mnt/**. Some matching
mount commands:
$ mount /dev/foo1 /mnt/1
$ mount -o ro,atime,noexec,nodiratime /dev/foo2 /mnt/deep/path/foo2
mount options=ro -> /mnt/**,
allow mounting anything under /mnt/**, as read only. Some matching
mount commands:
$ mount -o ro /dev/foo1 /mnt/1
$ mount -o ro /dev/foo2 /mnt/deep/path/foo2
mount fstype=ext3 options=(rw,atime) /dev/sdb1 -> /mnt/stick/,
allow mounting an ext3 filesystem in /dev/sdb1 on /mnt/stick as
read/write and using inode access times. Matches only:
$ mount -o rw,atime /dev/sdb1 /mnt/stick
mount options=(ro, atime) options in (nodev, user) /dev/foo -> /mnt/,
allow mounting /dev/foo on /mmt/ read only and using inode access
times or allow mounting /dev/foo on /mnt/ with some combination of
’nodev’ and ’user’. Matches only:
$ mount -o ro,atime /dev/foo /mnt
$ mount -o nodev /dev/foo /mnt
$ mount -o user /dev/foo /mnt
$ mount -o nodev,user /dev/foo /mnt
Pivot Root Rules
AppArmor mediates changing of the root filesystem through the
pivot_root(2) system call. The syntax of ’pivot_root’ rules in AppArmor
is based on the pivot_root(2) system call parameters with the notable
exception that the ordering is reversed. The path corresponding to the
put_old parameter of pivot_root(2) is optionally specified in the
’pivot_root’ rule using the ’oldroot=’ prefix.
AppArmor ’pivot_root’ rules can specify a profile transition to occur
during the pivot_root(2) system call. Note that AppArmor will only
transition the process calling pivot_root(2) to the new profile.
The paths specified in ’pivot_root’ rules must end with ’/’ since they
are directories.
Here are some example ’pivot_root’ rules:
# Allow any pivot
pivot_root,
# Allow pivoting to any new root directory and putting the old root
# directory at /mnt/root/old/
pivot_root oldroot=/mnt/root/old/,
# Allow pivoting the root directory to /mnt/root/
pivot_root /mnt/root/,
# Allow pivoting to /mnt/root/ and putting the old root directory at
# /mnt/root/old/
pivot_root oldroot=/mnt/root/old/ /mnt/root/,
# Allow pivoting to /mnt/root/, putting the old root directory at
# /mnt/root/old/ and transition to the /mnt/root/sbin/init profile
pivot_root oldroot=/mnt/root/old/ /mnt/root/ -> /mnt/root/sbin/init,
PTrace rules
AppArmor supports mediation of ptrace(2). AppArmor PTrace rules are
accumulated so that the granted PTrace permissions are the union of all
the listed PTrace rule permissions.
AppArmor PTrace permissions are implied when a rule does not explicitly
state an access list. By default, all PTrace permissions are implied.
The trace and tracedby permissions govern ptrace(2) while read and
readby govern certain proc(5) filesystem accesses, kcmp(2), futexes
(get_robust_list(2)) and perf trace events.
For a ptrace operation to be allowed the profile of the tracing process
and the profile of the target task must both have the correct
permissions. For example, the profile of the process attaching to
another task must have the trace permission for the target task’s
profile, and the task being traced must have the tracedby permission for
the tracing process’ profile.
Example AppArmor PTrace rules:
# Allow all PTrace access
ptrace,
# Explicitly allow all PTrace access,
ptrace (read, readby, trace, tracedby),
# Explicitly deny use of ptrace(2)
deny ptrace (trace),
# Allow unconfined processes (eg, a debugger) to ptrace us
ptrace (readby, tracedby) peer=unconfined,
# Allow ptrace of a process running under the /usr/bin/foo profile
ptrace (trace) peer=/usr/bin/foo,
Signal rules
AppArmor supports mediation of signal(7). AppArmor signal rules are
accumulated so that the granted signal permissions are the union of all
the listed signal rule permissions.
AppArmor signal permissions are implied when a rule does not explicitly
state an access list. By default, all signal permissions are implied.
For the sending of a signal to be allowed, the profile of the sending
process and the profile of the target task must both have the correct
permissions. For example, the profile of a process sending a signal to
another task must have the send permission for the target task’s
profile, and the task receiving the signal must have a receive
permission for the sending process’ profile.
Example AppArmor signal rules:
# Allow all signal access
signal,
# Explicitly deny sending the HUP and INT signals
deny signal (send) set=(hup, int),
# Allow unconfined processes to send us signals
signal (receive) peer=unconfined,
# Allow sending of signals to a process running under the /usr/bin/foo
# profile
signal (send) peer=/usr/bin/foo,
# Allow checking for PID existence
signal (receive, send) set=("exists"),
# Allow us to signal ourselves using the built-in @{profile_name} variable
signal peer=@{profile_name},
# Allow two real-time signals
signal set=(rtmin+0 rtmin+32),
DBus rules
AppArmor supports DBus mediation. The mediation is performed in
conjunction with the DBus daemon. The DBus daemon verifies that
communications over the bus are permitted by AppArmor policy.
AppArmor DBus rules are accumulated so that the granted DBus permissions
are the union of all the listed DBus rule permissions.
AppArmor DBus rules are broad and general and become more restrictive as
further information is specified. Policy may be specified down to the
interface member level (method or signal name), however the contents of
messages are not examined.
Some AppArmor DBus permissions are not compatible with all AppArmor DBus
rules. The ’bind’ permission cannot be used in message rules. The
’send’ and ’receive’ permissions cannot be used in service rules. The
’eavesdrop’ permission cannot be used in rules containing any
conditionals outside of the ’bus’ conditional.
’r’ and ’read’ are synonyms for ’receive’. ’w’ and ’write’ are synonyms
for ’send’. ’rw’ is a synonym for both ’send’ and ’receive’.
AppArmor DBus permissions are implied when a rule does not explicitly
state an access list. By default, all DBus permissions are implied. Only
message permissions are implied for message rules and only service
permissions are implied for service rules.
Example AppArmor DBus rules:
# Allow all DBus access
dbus,
# Explicitly allow all DBus access,
dbus (send, receive, bind),
# Deny send/receive/bind access to the session bus
deny dbus bus=session,
# Allow bind access for a particular name on any bus
dbus bind name=com.example.ExampleName,
# Allow receive access for a particular path and interface
dbus receive path=/com/example/path interface=com.example.Interface,
# Deny send/receive access to the system bus for a particular interface
deny dbus bus=system interface=com.example.ExampleInterface,
# Allow send access for a particular path, interface, member, and pair of
# peer names:
dbus send
bus=session
path=/com/example/path
interface=com.example.Interface
member=ExampleMethod
peer=(name=(com.example.ExampleName1|com.example.ExampleName2)),
# Allow receive access for all unconfined peers
dbus receive peer=(label=unconfined),
# Allow eavesdropping on the system bus
dbus eavesdrop bus=system,
# Allow and audit all eavesdropping
audit dbus eavesdrop,
Unix socket rules
AppArmor supports fine grained mediation of unix domain abstract and
anonymous sockets. Unix domain sockets with file system paths are
mediated via file access rules.
Abstract unix domain sockets is a nonportable Linux extension of unix
domain sockets, see unix(7) for more information.
Unix socket address paths
The sun_path component (aka the socket address) of a unix domain socket
is specified by the
addr=
conditional. If an address conditional is not specified as part of a
rule then the rule matches both abstract and anonymous sockets.
In apparmor the address of an abstract unix domain socket begins with
the @ character, similar to how they are reported (as paths) by netstat
The address then follows and may contain pattern matching and any
characters including the null character. In apparmor null characters
must be specified by using an escape sequence \000 or \x00. The pattern
matching is the same as is used by file path matching so * will not
match / even though it has no special meaning with in an abstract socket
name. Eg.
unix addr=@*,
Autobound unix domain sockets have a unix sun_path assigned to them by
the kernel, as such specifying a policy based address is not possible.
The autobinding of sockets can be controlled by specifying the special
auto keyword. Eg.
unix addr=auto,
To indicate that the rule only applies to auto binding of unix domain
sockets. It is important to note this only applies to the bind
permission as once the socket is bound to an address it is
indistinguishable from a socket that have an addr bound with a specified
name. When the auto keyword is used with other permissions or as part of
a peer addr it will be replaced with a pattern that can match an
autobound socket. Eg. For some kernels
unix rw addr=auto,
is transformed to
unix rw addr=@[a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9],
It is important to note, this pattern may match abstract sockets that
were not autobound but have an addr that fits what is generated by the
kernel when autobinding a socket.
Anonymous unix domain sockets have no sun_path associated with the
socket address, however it can be specified with the special none
keyword to indicate the rule only applies to anonymous unix domain
sockets. Eg.
unix addr=none,
If the address component of a rule is not specified then the rule
applies to autobind, abstract and anonymous sockets.
Unix socket permissions
Unix domain socket rules are accumulated so that the granted unix socket
permissions are the union of all the listed unix rule permissions.
Unix domain socket rules are broad and general and become more
restrictive as further information is specified. Policy may be specified
down to the socket address (aka sun_path) and label level. The content
of the communication is not examined.
Unix socket rule permissions are implied when a rule does not explicitly
state an access list. By default if a rule does not have an access list
all permissions that are compatible with the specified set of local and
peer conditionals are implied.
The create, bind, listen, shutdown, getattr, setattr, getopt, and setopt
permissions are local socket permissions. They are only applied to the
local socket and can’t be specified in rules that have a peer component.
The accept permission applies to the combination of a local and peer
socket. The connect, send, and receive permissions are peer socket
permissions.
Only the peer socket permissions will be applied to rules that don’t
specify permissions and contain a peer component.
Example Unix domain socket rules:
# Allow all permissions to unix sockets
unix,
# Explicitly allow all unix permissions
unix (create, listen, accept, connect, send, receive, getattr, setattr, setopt, getopt),
# Explicitly deny unix socket access
deny unix,
# Allow create and use of abstract and anonymous sockets for profile_name
unix peer=(label=@{profile_name}),
# Allow receiving via unix sockets from unconfined
unix (receive) peer=(label=unconfined),
# Allow getattr and shutdown on anonymous sockets
unix (getattr, shutdown) addr=none,
# Allow SOCK_STREAM connect, receive and send on an abstract socket @bar
# with peer running under profile '/foo'
unix (connect, receive, send) type=stream peer=(label=/foo,addr="@bar"),
# Allow accepting connections from and receiving from peer running under
# profile '/bar' on abstract socket '@foo'
unix (accept, receive) addr=@foo peer=(label=/bar),
Abstract unix domain sockets autobind
Abstract unix domain sockets can autobind to an address. The autobind
address is a unique 5 digit string of decimal numbers, eg. @00001. There
is nothing that prevents a task from manually binding to addresses with
a similar pattern so it is impossible to reliably identify autobind
addresses from a regular address.
Interaction of network rules and fine grained unix domain socket rules
The coarse grained networking rules can be used to control unix domain
sockets as well. When fine grained unix domain socket mediation is
available the coarse grained network rule is mapped into the equivalent
unix socket rule.
E.G.
network unix, => unix,
network unix stream, => unix stream,
Fine grained mediation rules however can not be losslessly converted
back to the coarse grained network rule; e.g.
unix bind addr=@example,
Has no exact match under coarse grained network rules, the closest match
is the much wider permission rule of
network unix,
change_profile rules
AppArmor supports self directed profile transitions via the
change_profile api. Change_profile rules control which permissions for
which profiles a confined task can transition to. The profile name can
contain apparmor pattern matching to specify different profiles.
change_profile -> **,
The change_profile api allows the transition to be delayed until when a
task executes another application. If an exec rule transition is
specified for the application and the change_profile api is used to make
a transition at exec time, the transition specified by the
change_profile api takes precedence.
The Change_profile permission can restrict which profiles can be
transitioned to based off of the executable name by specifying the exec
condition.
change_profile /bin/bash -> new_profile,
The restricting of the transition profile to a given executable at exec
time is only useful when then current task is allowed to make dynamic
decisions about what confinement should be, but the decision set needs
to be controlled. A list of profiles or multiple rules can be used to
specify the profiles in the set. Eg.
change_profile /bin/bash -> {new_profile1,new_profile2,new_profile3},
An exec rule can be used to specify a transition for the executable, if
the transition should be allowed even if the change_profile api has not
been used to select a transition for those available in the
change_profile rule set. Eg.
/bin/bash Px -> new_profile1,
change_profile /bin/bash -> {new_profile1,new_profile2,new_profile3},
The exec mode dictates whether or not the Linux Kernel’s unsafe_exec
routines should be used to scrub the environment, similar to setuid
programs. (See ld.so(8) for some information on setuid/setgid
environment scrubbing.) The safe mode sets up environment scrubbing to
occur when the new application is executed and unsafe mode disables
AppArmor’s requirement for environment scrubbing (the kernel and/or libc
may still require environment scrubbing). An exec mode can only be
specified when an exec condition is present.
change_profile safe /bin/bash -> new_profile,
Not all kernels support safe mode and the parser will downgrade rules to
unsafe mode in that situation. If no exec mode is specified, the default
is safe mode in kernels that support it.
rlimit rules
AppArmor can set and control the resource limits associated with a
profile as described in the setrlimit(2) man page.
The AppArmor rlimit controls allow setting of limits and restricting
changes of them and these actions can be audited. Enforcement of the set
limits is handled by the standard kernel enforcement mechanism for
rlimits and will not result in an audited apparmor message if the limit
is enforced.
If a profile does not have an rlimit rule associated with a given rlimit
then the rlimit is left alone and regular access, including changing the
limit, is allowed. However if the profile sets an rlimit then the
current limit is checked and if greater than the limit specified in the
rule it will be changed to the specified limit.
AppArmor rlimit rules control the hard limit of an application and
ensure that if the hard limit is lowered that the soft limit does not
exceed the hard limit value.
Eg.
set rlimit data <= 100M,
set rlimit nproc <= 10,
set rlimit nice <= 5,
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. You can use empty quotes ("") to
explicitly add an empty value.
At the time of this writing, the following variables are defined in the
provided AppArmor policy:
@{HOME}
@{HOMEDIRS}
@{multiarch}
@{pid}
@{pids}
@{PROC}
@{securityfs}
@{apparmorfs}
@{sys}
@{tid}
@{run}
@{XDG_DESKTOP_DIR}
@{XDG_DOWNLOAD_DIR}
@{XDG_TEMPLATES_DIR}
@{XDG_PUBLICSHARE_DIR}
@{XDG_DOCUMENTS_DIR}
@{XDG_MUSIC_DIR}
@{XDG_PICTURES_DIR}
@{XDG_VIDEOS_DIR}
These are defined in files in /etc/apparmor.d/tunables and are used in
many of the abstractions described later.
You may also add files in /etc/apparmor.d/tunables/home.d for site‐
specific customization of @{HOMEDIRS},
/etc/apparmor.d/tunables/multiarch.d for @{multiarch} and
/etc/apparmor.d/tunables/xdg-user-dirs.d for @{XDG_*}.
The special @{profile_name} variable is set to the profile name and may
be used in all policy.
Alias rules
AppArmor also provides alias rules for remapping paths for site‐specific
layouts. They are an alternative form of path rewriting to using
variables, and are done after variable resolution. Alias rules must
occur within the preamble of the profile. System‐wide aliases are found
in /etc/apparmor.d/tunables/alias, which is included by
/etc/apparmor.d/tunables/global. /etc/apparmor.d/tunables/global is
typically included at the beginning of an AppArmor profile.
Globbing (AARE)
File resources and other parameters accepting an AARE 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
[ˆa-c]
will substitute for any single character not matching a, b or c
{ab,cd}
will expand to one rule to match ab, one rule to match cd
Can also include variables.
@{variable}
will expand to all values assigned to the given variable.
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.
Rule Qualifiers
There are several rule qualifiers that can be applied to permission
rules. Rule qualifiers can modify the rule and/or permissions within
the rule.
allow
Specifies that permissions requests that match the rule are allowed.
This is the default value for rules and does not need to be
specified. Conflicts with the deny qualifier.
audit
Specifies that permissions requests that match the rule should be
recorded to the audit log.
deny
Specifies that permissions requests that match the rule should be
denied without logging. Can be combined with ’audit’ to enable
logging. Conflicts with the allow qualifier.
owner
Specifies that the task must have the same euid/fsuid as the object
being referenced by the permission check.
Qualifier Blocks
Rule Qualifiers can be applied to multiple rules at a time by grouping
the rules into a rule block.
audit {
/foo r,
network,
}
#include mechanism
AppArmor provides an easy abstraction mechanism to group common 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.
The leading ’#’ is optional, and the ’#include’ keyword can be followed
by an option conditional ’if exists’ that specifies profile compilation
should continue if the specified file or directory is not found.
#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.
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 @{HOMEDIRS}. 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 @{HOMEDIRS} are set before starting the profile
definition. The aa-autodep(8) and aa-genprof(8) utilities will
automatically emit #include <tunables/global> in generated profiles.
Feature ABI
The feature abi tells AppArmor which feature set the policy was
developed under. This is important to ensure that kernels with a
different feature set don’t enforce features that the policy doesn’t
support, which can result in unexpected application failures.
When policy is compiled both the kernel feature abi and policy feature
abi are consulted to build a policy that will work for the system’s
kernel.
If the kernel supports a feature not supported by the policy then policy
will be built so that the kernel does NOT enforce that feature.
If the policy supports a feature not supported by the kernel the compile
may downgrade the rule with the feature to something the kernel
supports, drop the rule completely, or fail the compile.
If the policy abi is specified as kernel then the running kernel’s abi
will be used. This should never be used in shipped policy as it can
cause system breakage when a new kernel is installed.
ABI compatibility with AppArmor 2.x
AppArmor 3 remains compatible with AppArmor 2.x by detecting when a
profile does not have a feature ABI specified. In this case the policy
compile will either apply the pinned feature ABI as specified by the
config file or the command line, or if neither of those are applied by
using a default feature ABI.
It is important to note that the default feature ABI does not support
new features added in AppArmor 3 or later.
EXAMPLE
An example AppArmor profile:
# which feature abi the policy was developed with
abi <abi/3.0>,
# a variable definition in the preamble
@{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,
/usr/bin/baz Cx -> baz,
# a comment about foo's hat (subprofile), bar.
ˆbar {
/lib/ld-*.so* rmix,
/usr/bin/bar rmix,
/var/spool/* rwl,
}
# a comment about foo's subprofile, baz.
profile baz {
#include <abstractions/bash>
owner /proc/[0-9]*/stat r,
/bin/bash ixr,
/var/lib/baz/ r,
owner /var/lib/baz/* rw,
}
}
FILES
/etc/init.d/boot.apparmor
/etc/apparmor.d/
KNOWN BUGS
• Mount options support the use of pattern matching but mount flags
are not correctly intersected against specified patterns. Eg, ’mount
options=**,’ should be equivalent to ’mount,’, but it is not. (LP:
#965690)
• The fstype may not be matched against when certain mount command
flags are used. Specifically fstype matching currently only works
when creating a new mount and not remount, bind, etc.
• Mount rules with multiple ’options’ conditionals are not applied as
documented but instead merged such that ’options in (ro,nodev)
options in (atime)’ is equivalent to ’options in (ro,nodev,atime)’.
• When specifying mount options with the ’in’ conditional, both the
positive and negative values match when specifying one or the other.
Eg, ’rw’ matches when ’ro’ is specified and ’dev’ matches when
’nodev’ is specified such that ’options in (ro,nodev)’ is equivalent
to ’options in (rw,dev)’.
SEE ALSO
apparmor(7), apparmor_parser(8), apparmor_xattrs(7), aa-complain(1),
aa-enforce(1), aa_change_hat(2), mod_apparmor(5), and
<https://wiki.apparmor.net>.
AppArmor 3.1.7 2024‐02‐02 APPARMOR.D(5)
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