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Troubleshooting SELinux on Files and Directories

Understanding how to fix potential SELinux issues is important. This lab will present an SELinux problem and allow us to work through the solution, getting us familiar with where to look and how to fix problems.

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Path Info

Level
Clock icon Intermediate
Duration
Clock icon 30m
Published
Clock icon Jan 24, 2020

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Table of Contents

  1. Challenge

    Identify and Fix the Problem on Startup

    Trying to run systemctl start httpd will error. Running journalctl -xe will show lines similar to this:

    Jan 09 20:32:46 Server1 httpd[7107]: (13)Permission denied: AH00091: httpd: could not open error log file /etc/httpd/l>
    Jan 09 20:32:46 Server1 httpd[7107]: AH00015: Unable to open logs
    

    It looks like a problem with the error log file, which is /var/log/httpd/error_log.

    ls -lZ /var/log/httpd/error_log shows:

    -rw-r--r--. 1 root root unconfined_u:object_r:admin_home_t:s0 0 Jan  9 20:17 /var/log/httpd/error_log
    

    So let's use restorecon.

    restorecon /var/log/httpd/error_log
    systemctl start httpd
    

    The service starts!

  2. Challenge

    Fix the Problem with Home Directories

    Based on /etc/httpd/conf.d/userdir.conf we should have a public_html directory in the developer's home directory. Since we don't, let's create it, set the permissions to 755, set the home directory permissions to 711, and see what happens with a test file:

    mkdir /home/developer/public_html
    chmod 0755 /home/developer/public_html
    chmod 0711 /home/developer
    touch /home/developer/public_html/file
    curl localhost/~developer/file
    

    We're still getting an error. Looking at /var/log/audit/audit.log, we see an AVC denial for the file we're trying to load, so it's SELinux related.

    The contexts are correct, but the enable homedir boolean defaults to off.

    setsebool httpd_enable_homedirs on

    Now the curl should work correctly.

  3. Challenge

    Make Sure the index.html in the Developer's Home Directory public_html is Able to be Displayed

    The instructions say to move the index page, so let's do it:

    mv /home/developer/index.html /home/developer/public_html/index.html
    curl localhost/~developer/index.html
    

    That failed. Let's look at SELinux contexts.

The Cloud Content team comprises subject matter experts hyper focused on services offered by the leading cloud vendors (AWS, GCP, and Azure), as well as cloud-related technologies such as Linux and DevOps. The team is thrilled to share their knowledge to help you build modern tech solutions from the ground up, secure and optimize your environments, and so much more!

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