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=pod

=head1 NAME

mod_apparmor - fine-grained AppArmor confinement for Apache

=head1 DESCRIPTION

An AppArmor profile applies to an executable program; if a portion of

the program needs different access permissions than other portions,

the program can "change hats" via aa_change_hat(2) to a different role,

also known as a subprofile.  The mod_apparmor Apache module uses the

aa_change_hat(2) mechanism to offer more fine-grained confinement of dynamic

elements within Apache such as individual php and perl scripts, while

still allowing the performance benefits of using mod_php and mod_perl.

To use mod_apparmor with Apache, ensure that mod_apparmor is configured to

be loaded into Apache, either via a2enmod, yast or manual editing of the

apache2(8)/httpd(8) configuration files, and restart Apache. Make sure that

apparmor is also functioning.

Once mod_apparmor is loaded within Apache, all requests to Apache will

cause mod_apparmor to attempt to change into a hat named by the URI

(e.g. /app/some.cgi). If no such hat is found, it will fall back to

attempting to use the hat DEFAULT_URI; if that also does not exist,

it will fall back to using the global Apache profile. Most static web

pages can simply make use of the DEFAULT_URI hat.

Additionally, before any requests come in to Apache, mod_apparmor

will attempt to change hat into the HANDLING_UNTRUSTED_INPUT hat.

mod_apparmor will attempt to use this hat while Apache is doing the

initial parsing of a given http request, before its given to a specific

handler (like mod_php) for processing.

Because defining hats for every URI/URL often becomes tedious, mod_apparmor

provides the AAHatName and AADefaultHatName Apache configuration options.

=over 4

=item B<AAHatName>

AAHatName allows you to specify a hat to be used for a given Apache

E<lt>DirectoryE<gt>, E<lt>DirectoryMatch>, E<lt>LocationE<gt> or

E<lt>LocationMatchE<gt> directive (see the Apache documenation for more

details). Note that mod_apparmor behavior can become confused if

E<lt>Directory*E<gt> and E<lt>Location*E<gt> directives are intermingled

and it is recommended to use one type of directive. If the hat specified by

AAHatName does not exist in the Apache profile, then it falls back to the

behavior described above.

=item B<AADefaultHatName>

AADefaultHatName allows you to specify a default hat to be used for

virtual hosts and other Apache server directives, so that you can have

different defaults for different virtual hosts. This can be overridden by

the AAHatName directive and is checked for only if there isn't a matching

AAHatName or hat named by the URI. If the AADefaultHatName hat does not

exist, it falls back to the DEFAULT_URI hat if it exists (as described

above).

=back

=head1 URI REQUEST SUMMARY

When profiling with mod_apparmor, it is helpful to keep the following order

of operations in mind:

On each URI request, mod_apparmor will first aa_change_hat(2) into

^HANDLING_UNTRUSTED_INPUT, if it exists.

Then, after performing the initial parsing of the request, mod_apparmor

will:

=over 2

1. try to aa_change_hat(2) into a matching AAHatName hat if it exists and

applies, otherwise it will

2. try to aa_change_hat(2) into the URI itself, otherwise it will

3. try to aa_change_hat(2) into an AADefaultHatName hat if it has been defined

for the server/vhost, otherwise it will

4. try to aa_change_hat(2) into the DEFAULT_URI hat, if it exists, otherwise it

will

5. fall back to the global Apache policy

=back

=head1 BUGS

mod_apparmor() currently only supports apache2, and has only been tested

with the prefork MPM configuration -- threaded configurations of Apache

may not work correctly.

There are likely other bugs lurking about; if you find any, please report

them at L<http://https://bugs.launchpad.net/apparmor/+filebug>.

=head1 SEE ALSO

apparmor(7), subdomain.conf(5), apparmor_parser(8), aa_change_hat(2) and

L<http://wiki.apparmor.net>.

=cut