Difference between revisions of "SELinux Notes"

From Simson Garfinkel
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m (Problem: apache can't access the files)
m (Problem: CGI scripts won't run.)
 
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     $ restorecon -R -v /var/www/html/bin
 
     $ restorecon -R -v /var/www/html/bin
  
 
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See the errors:
 +
    $ journalctl -xe
  
  

Latest revision as of 11:03, 11 September 2019

SELinux is enabled by default on Centos 7 and on RHEL. It's a good thing to enable for internet-facing servers. It makes it far, far more complex to run a web server.


References:


Problem: apache can't access the files

   sudo /sbin/restorecon -R /var/www
   setsebool -P httpd_read_user_content 1

Running a web server:

If you can't run PHP, you may have the files in the wrong SELinux security context. You can change the security

  1. Check the security context:
   ls -lZ /var/www/html/
  1. You can give the web server read/write access to the files with:
   chcon -R -t httpd_sys_rw_content_t /var/www/html/xxx

Problem: CGI scripts won't run.

In order to be able to execute a CGI script under SELinux, the script must be in the httpd_sys_rw_content_t security context. There are two ways to set the security context:

  1. The context can be manually set on a per-file basis with the _chcon_ command
  2. The context can be derrived from a selinux policy. Policies provide regular expressions that match filenames and automatically assign contexts.

The RedHat SELinux installation appears to install rules for the cgi-bin directory, but it does not allow you to use the .cgi extension.

You can see the selinux policies that might possibly apply to cgi-bin with:

   $ semanage fcontext --list | grep cgi-bin

You can explicitly the script the SELinux context cgi-bin directory with:

   $ chcon -t httpd_sys_script_exec_t /var/www/cgi-bin/script.cgi

You can take it away with:

   $ chcon -t unlabeled_t /var/www/cgi-bin/script.cgi

Check the file's SELinux attributes with `ls -laZ`:

   $ ls -laZ /var/www/cgi-bin/script.cgi

Looks like we can add a policy with the semanage command. I tried this to make everything in the bin directory within html executable:

   $ semanage fcontext -a -t httpd_sys_script_exec_t "/var/www/html/bin(/.*)?"
   $ restorecon -R -v /var/www/html/bin

See the errors:

   $ journalctl -xe


References:

Disabling SELinux

Don't do this. People will get angry.

  • edit /etc/selinux/config and change SELINUX from 'enforcing' to 'permissive'

Problem: RHEL doesn't support PHP7.x

You want PHP7 to run mediawiki.

Solution:

  1. Install httpd, httpd-devel and php
  2. Now download PHP7
   ./configure --with-apxs2=/usr/bin/apxs --enable-mbstring --with-mysqli --with-openssl
  1. And let httpd scripts make outbound TCP connections:
   # setsebool -P httpd_can_network_connect 1


For running mediawiki, also see: