APPARMOR(7) AppArmor 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, 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): once a profile is loaded for a program, that
program will be confined on the next exec(3). If a process is already
running under a profile, when one replaces that profile in the kernel,
the updated profile is applied immediately to that process. On the
other hand, a process that is already running unconfined cannot be
confined.
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)
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.
DEBUGGING
AppArmor provides a few facilities to log more information, which can
help debugging profiles.
Enable debug mode
When debug mode is enabled, AppArmor will log a few extra messages to
dmesg (not via the audit subsystem). For example, the logs will tell
whether environment scrubbing has been applied.
To enable debug mode, run:
echo 1 > /sys/module/apparmor/parameters/debug
Turn off deny audit quieting
By default, operations that trigger "deny" rules are not logged. This
is called deny audit quieting.
To turn off deny audit quieting, run:
echo -n noquiet >/sys/module/apparmor/parameters/audit
Force audit mode
AppArmor can log a message for every operation that triggers a rule
configured in the policy. This is called force audit mode.
Warning! Force audit mode can be extremely noisy even for a single
profile, let alone when enabled globally.
To set a specific profile in force audit mode, add the "audit" flag:
profile foo flags=(audit) { ... }
To enable force audit mode globally, run:
echo -n all > /sys/module/apparmor/parameters/audit
If auditd is not running, to avoid losing too many of the extra log
messages, you will likely have to turn off rate limiting by doing:
echo 0 > /proc/sys/kernel/printk_ratelimit
But even then the kernel ring buffer may overflow and you might lose
messages.
Else, if auditd is running, see auditd(8) and auditd.conf(5).
FILES
/etc/init.d/apparmor
/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), aa-autodep(1),
clean(1), auditd(8), aa-unconfined(8), aa-enforce(1), aa-complain(1),
and <https://wiki.apparmor.net>.
AppArmor 2.13.4 2020-06-16 APPARMOR(7)