Tuesday, October 28, 2014

CentOS / RHEL 6 - Setup SELinux to work with Apache

By default SeLinux is enabled and it will mark some labeling on each and every file and ports on OS based on Service.

SeLinux work on following parameters:

1) Context
2) Boolean

1) Context, we can say label. Commands chcon and semanage
2) Boolean, SeLinux having properties for each service like need to enable read or write access to directory, enable http with ftp or not etc.. Commands semanage, getseboolean, setseboolean

In our case we are going to setup SeLinux to work with Apache

Context

Port Settings

As per SeLinux, services can work on only assigned specific ports like

semanage port -l|grep -i mysql

mysqld_port_t                  tcp      1186, 3306, 63132-63164

semanage port -l|grep -i http_port_t

http_port_t                    tcp      80, 81, 443, 488, 8008, 8009, 8443, 9000

So, port given in above output, by default allowed for mysql and apache services

Lets, take an example and change following line in /etc/httpd/conf/httpd.conf

Listen *:2222

Save and restart httpd service

While httpd restart, this will show following:

service httpd restart
Stopping httpd:                                            [FAILED]
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using 192.168.56.103 for ServerName
(13)Permission denied: make_sock: could not bind to address [::]:2222
(13)Permission denied: make_sock: could not bind to address 0.0.0.0:2222
no listening sockets available, shutting down
Unable to open logs
                                                           [FAILED]

It's showing Permission denied: make_sock, that means SeLinux not allowing to create sock on 2222 port

As we want run Apache / httpd on 2222 port, execute following command to enable 2222 port for httpd service

semanage port -a -t http_port_t -p tcp 2222

semanage port -l|grep -i http_port_t

http_port_t                    tcp      2222, 80, 81, 443, 488, 8008, 8009, 8443, 9000

Now 2222 port has been assigned to http_port i.e.; http/apache service

Start http/apache service, you should not get any error this time

service httpd start
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using 192.168.56.103 for ServerName
                                                           [  OK  ]

netstat -antp|grep http
tcp        0      0 :::2222                     :::*                        LISTEN      1403/httpd

File/Folder Labeling

SeLinux keep labeling on each and every file which is as per service

ls -ldZ /var/www/

drwxr-xr-x. root root system_u:object_r:httpd_sys_content_t:s0 /var/www/

ls -ldZ /var/www/html/

drwxr-xr-x. root root system_u:object_r:httpd_sys_content_t:s0 /var/www/html/

ls -ldZ /etc/httpd/

drwxr-xr-x. root root system_u:object_r:httpd_config_t:s0 /etc/httpd/

ls -ldZ /etc/httpd/conf

drwxr-xr-x. root root system_u:object_r:httpd_config_t:s0 /etc/httpd/conf

ls -lZ /usr/sbin/httpd

-rwxr-xr-x. root root system_u:object_r:httpd_exec_t:s0 /usr/sbin/httpd

Here (starting with http means its Domain for only httpd service):

httpd_config_t                          # http configuration
httpd_sys_content_t                 # http system content
httpd_exec_t                            # http executable

So, each and every called by httpd/apache service should have proper label.

Lets try to run httpd with different DocumentRoot with im-proper labeling on files and folders

mkdir /data/www -p

ls -ldZ /data/

drwxr-xr-x. root root unconfined_u:object_r:default_t:s0 /data/

ls -ldZ /data/www/

drwxr-xr-x. root root unconfined_u:object_r:default_t:s0 /data/www/


cat > /data/www/index.html
this is test

ctrl+D

ls -lZ /data/www/index.html

-rw-r--r--. root root unconfined_u:object_r:default_t:s0 /data/www/index.html


Restart httpd service and access through your web browser http://server-IP:2222

You should get following error in web broweser:

Forbidden

You don't have permission to access / on this server.


and following in apache/httpd service error logs:

[Tue Oct 28 21:17:07 2014] [error] [client 192.168.56.1] (13)Permission denied: access to /index.html denied


How to recover from above error:

Change label of DocumentRoot i.e.; /data/www and its files

As this is going to be http content directory, we should change label to httpd_sys_content_t

chcon -t httpd_sys_content_t /data -R

for permanent changes

semanage fcontext -t httpd_sys_content_t /data
semanage fcontext -t httpd_sys_content_t /data/www

Now you should be able to access server pages without any error

Command to see running process context

ps auxZ         # will provide process context too

Boolean

Commands to get or set Boolean variables

getsebool
setsebool

Some of the http/apache boolean variables

getsebool -a|grep http

httpd_enable_cgi --> on
httpd_enable_homedirs --> off
httpd_unified --> on
httpd_use_cifs --> off
httpd_use_fusefs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off

If you do not want to disable apache/http to serve cgi files

setsebool httpd_enable_cgi off

Enable user's home directory to be used for data/pages serving for apache/http

setsebool httpd_enable_homedirs on

Enable Apache/http to use CIFS/NFS directory to serve pages

setsebool httpd_use_cifs off
setsebool httpd_use_nfs off


Other commands to use

Disable SeLinux

setenforce 0

modify /etc/sysconfig/selinux file and set
SELINUX=disabled

Reboot machine

Command to restore context

restorecon -Rv /data

Create /.autorelabel for allow OS to relabel complete system at next boot time

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