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, 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:
o 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.
o 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) 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.
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 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 /var/log/audit/audit.log or
/var/log/messages, depending upon local configuration.
FILES
/etc/init.d/apparmor
/etc/apparmor.d/
/var/lib/apparmor/
/var/log/audit/audit.log
/var/log/messages
SEE ALSO
apparmor_parser(8), change_hat(2), apparmor.d(5), subdomain.conf(5),
autodep(1), clean(1), auditd(8), unconfined(8), enforce(1),
complain(1), and
<http://forge.novell.com/modules/xfmod/project/?apparmor>.