apparmor/parser/apparmor.pod

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=pod

=head1 NAME

AppArmor - kernel enhancement to confine programs to a limited set of resources.

=head1 DESCRIPTION

AppArmor is a kernel enhancement to confine programs to a limited set
of resources. AppArmor's unique security model is to bind access control
attributes to programs rather than to users.

AppArmor confinement is provided via I<profiles> loaded into the kernel
via apparmor_parser(8), typically through the F</etc/init.d/apparmor>
SysV initscript, which is used like this:

	# /etc/init.d/apparmor start
	# /etc/init.d/apparmor stop
	# /etc/init.d/apparmor restart

AppArmor can operate in two modes: I<enforcement>, and I<complain or learning>:

=over 4

=item *

I<enforcement> -  Profiles loaded in enforcement mode will result 
in enforcement of the policy defined in the profile as well as reporting 
policy violation attempts to syslogd.  

=item *

I<complain> - Profiles loaded in  C<complain> mode will not enforce policy.  
Instead, it will report policy violation attempts. This mode is convenient for 
developing profiles. To manage complain mode for individual profiles the 
utilities aa-complain(8) and aa-enforce(8) can be used. 
These utilities take a program name as an argument. 


=back

Profiles are traditionally stored in files in F</etc/apparmor.d/>
under filenames with the convention of replacing the B</> in pathnames
with B<.> (except for the root B</>) so profiles are easier to manage
(e.g. the F</usr/sbin/nscd> profile would be named F<usr.sbin.nscd>).

Profiles are applied to a process at exec(3) time (as seen through the
execve(2) system call); an already running process cannot be confined.
However, once a profile is loaded for a program, that program will be
confined on the next exec(3).

AppArmor supports the Linux kernel's securityfs filesystem, and makes
available the list of the profiles currently loaded; to mount the
filesystem:

	# mount -tsecurityfs securityfs /sys/kernel/security
	$ cat /sys/kernel/security/apparmor/profiles
	/usr/bin/mutt
	/usr/bin/gpg
	   ...

Normally, the initscript will mount securityfs if it has not already
been done.

AppArmor also restricts what privileged operations a confined process
may execute, even if the process is running as root. A confined process
cannot call the following system calls:

	create_module(2) delete_module(2) init_module(2) ioperm(2)
	iopl(2) mount(2) umount(2) ptrace(2) reboot(2) setdomainname(2)
	sethostname(2) swapoff(2) swapon(2) sysctl(2)

A confined process can not call mknod(2) to create character or block devices.

=head1 ERRORS

When a confined process tries to access a file it does not have permission
to access, the kernel will report a message through audit, similar to:

	audit(1148420912.879:96): REJECTING x access to /bin/uname
	  (sh(6646) profile /tmp/sh active /tmp/sh)

	audit(1148420912.879:97): REJECTING r access to /bin/uname
	  (sh(6646) profile /tmp/sh active /tmp/sh)

	audit(1148420944.837:98): REJECTING access to capability
	  'dac_override' (sh(6641) profile /tmp/sh active /tmp/sh)


The permissions requested by the process are immediately after
REJECTING. The "name" and process id of the running program are reported,
as well as the profile name and any "hat" that may be active. ("Name"
is in quotes, because the process name is limited to 15 bytes; it is the
same as reported through the Berkeley process accounting.) If no hat is
active (see aa_change_hat(2)) then the profile name is printed for "active".

For confined processes running under a profile that has been loaded in 
complain mode, enforcement will not take place and the log messages 
reported to audit will be of the form:

	audit(1146868287.904:237): PERMITTING r access to
	  /etc/apparmor.d/tunables (du(3811) profile /usr/bin/du active
	  /usr/bin/du)

	audit(1146868287.904:238): PERMITTING r access to /etc/apparmor.d
	  (du(3811) profile /usr/bin/du active /usr/bin/du)


If the userland auditd is not running, the kernel will send audit events
to klogd; klogd will send the messages to syslog, which will log the
messages with the KERN facility. Thus, REJECTING and PERMITTING messages
may go to either F</var/log/audit/audit.log> or F</var/log/messages>,
depending upon local configuration.

=head1 FILES

=over 4

=item F</etc/init.d/apparmor>

=item F</etc/apparmor.d/>

=item F</var/lib/apparmor/>

=item F</var/log/audit/audit.log>

=item F</var/log/messages>

=back

=head1 SEE ALSO

apparmor_parser(8), aa_change_hat(2), apparmor.d(5),
subdomain.conf(5), aa-autodep(1), clean(1),
auditd(8),
aa-unconfined(8), aa-enforce(1), aa-complain(1), and
L<http://wiki.apparmor.net>.

=cut