apparmor(7)
NAME
AppArmor - kernel enhancement to confine programs to a limited set of
resources.
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 profiles loaded into the kernel
via apparmor_parser(8), typically through the /etc/init.d/apparmor SysV
initscript (on Ubuntu, see UBUNTU POLICY LOAD, below), 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: enforcement, and complain or
learning:
* 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.
* complain - Profiles loaded in "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.
Profiles are traditionally stored in files in /etc/apparmor.d/ under
filenames with the convention of replacing the / in pathnames with .
(except for the root /) so profiles are easier to manage (e.g. the
/usr/sbin/nscd profile would be named 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) ptrace(2) reboot(2) setdomainname(2)
sethostname(2) swapoff(2) swapon(2) sysctl(2)
UBUNTU POLICY LOAD
Ubuntu systems use upstart(8) instead of a traditional SysV init
system. Because upstart is an event-driven init system and
understanding that policy must be loaded before execution, Ubuntu loads
policy in two ways:
1. via upstart jobs for services started during the boot process
2. via the AppArmor upstart job for any remaining policy
The AppArmor upstart job is configured to make sure all policy is
loaded before any user sessions start. When developing policy it is
important to know how your application is started and if policy load
should be handled specially.
The upstart job may be call with or without arguments, like so:
$ sudo start apparmor
$ sudo start apparmor ACTION=clear # clear policy cache
$ sudo start apparmor ACTION=teardown # unload all policy
$ sudo start apparmor ACTION=reload # reload policy
$ sudo start apparmor ACTION=force-reload # same as 'reload'
Because the job is an upstart(8) task, use 'start apparmor
ACTION=teardown' to unload all policy.
In general, nothing extra has to be done for applications not started
during boot or those that start after AppArmor's upstart job.
If the confined application has an Upstart job, adjust the job to call
/lib/init/apparmor-profile-load with the filename of the policy file
(relative to /etc/apparmor.d/). For example:
pre-start script
/lib/init/apparmor-profile-load usr.bin.foo
end script
If the confined application does not have an Upstart job but it starts
before AppArmor's second stage initscript, then add a symlink from the
policy file in /etc/apparmor.d to
/etc/apparmor/init/network-interface-security/. For example:
$ cd /etc/apparmor/init/network-interface-security/
$ sudo ln -s /etc/apparmor.d/usr.bin.foo .
The network-interface-security Upstart job will load all the symlinked
policy files in /etc/apparmor/init/network-interface-security/ before
any network interfaces come up. Because network interfaces come up very
early in the boot process, this will help ensure that AppArmor policy
is loaded before the confined application starts.
In addition, AppArmor on Ubuntu stores policy in two places:
1. /etc/apparmor.d for system policy
2. /var/lib/apparmor/profiles for click policy
See apparmor_parser(8) and aa-clickhook(1) for details.
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(1386511672.612:238): apparmor="DENIED" operation="exec"
parent=7589 profile="/tmp/sh" name="/bin/uname" pid=7605
comm="sh" requested_mask="x" denied_mask="x" fsuid=0 ouid=0
audit(1386511672.613:239): apparmor="DENIED" operation="open"
parent=7589 profile="/tmp/sh" name="/bin/uname" pid=7605
comm="sh" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
audit(1386511772.804:246): apparmor="DENIED" operation="capable"
parent=7246 profile="/tmp/sh" pid=7589 comm="sh" pid=7589
comm="sh" capability=2 capname="dac_override"
The permissions requested by the process are described in the
operation= and denied_mask= (for files - capabilities etc. use a
slightly different log format). The "name" and process id of the
running program are reported, as well as the profile name including any
"hat" that may be active, separated by "//". ("Name" is in quotes,
because the process name is limited to 15 bytes; it is the same as
reported through the Berkeley process accounting.)
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(1386512577.017:275): apparmor="ALLOWED" operation="open"
parent=8012 profile="/usr/bin/du" name="/etc/apparmor.d/tunables/"
pid=8049 comm="du" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
audit(1386512577.017:276): apparmor="ALLOWED" operation="open"
parent=8012 profile="/usr/bin/du" name="/etc/apparmor.d/tunables/"
pid=8049 comm="du" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
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 /var/log/audit/audit.log or
/var/log/messages, depending upon local configuration.
FILES
/etc/init.d/apparmor
/etc/apparmor/init/network-interface-security/
/etc/apparmor.d/
/var/lib/apparmor/
/var/log/audit/audit.log
/var/log/messages
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 <http://wiki.apparmor.net>.
Free and Open Source Software