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apparmor.d

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apparmor.d: syntax of security profiles for AppArmor.

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 | 'change_profile -> ' PROGRAMCHILD ) ... ] '}' SUBPROFILE = [ COMMENT ... ] ( PROGRAMHAT | 'profile ' PROGRAMCHILD ) '{' [ ( 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 aa_change_hat(2) for a description of how this "hat" is used.) PROGRAMCHILD = SUBPROFILE name FILE RULE = RULE QUALIFIER ( '"' FILEGLOB '"' | FILEGLOB ) ACCESS ',' RULE QUALIFIER = [ 'audit' ] [ 'deny' ] [ 'owner' ] 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' | 'cx -> ' PROGRAMCHILD | 'Cx -> ' PROGRAMCHILD | 'm' ) [ ACCESS ... ] (not all combinations are allowed; see below.) VARIABLE = '@{' ALPHA [ ALPHANUMERIC ... ] '}' VARIABLE ASSIGNMENT = VARIABLE ('=' | '+=') (space separated values) ALIAS RULE = ABS PATH '->' REWRITTEN ABS PATH ',' 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 (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. 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 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', 'cx', 'Cx', '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', 'cx', 'Cx', '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', 'cx', 'Cx', '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', 'cx', 'Cx', 'ix'. 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 'Ux', 'ux', 'px', 'Px', 'Cx', 'ix'. 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 'Ux', 'ux', 'px', 'Px', 'cx', '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', 'cx', 'Cx'. 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 @{HOMEDIRS} are defined in the AppArmor policy provided, in the /etc/apparmor.d/tunables/home file; these variables 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}. 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 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 [^a-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 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. 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. owner Specifies that the task must have the same euid/fsuid as the object being referenced by the permission check. #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 @{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.

EXAMPLE

An example AppArmor profile: # 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. ^bar { /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/

SEE ALSO

apparmor(7), apparmor_parser(8), aa-complain(1), aa-enforce(1), aa_change_hat(2), mod_apparmor(5), and <//wiki.apparmor.net>. APPARMOR.D(5)
 
 
 

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