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Troubleshooting SELinux

Mandatory access control (MAC) is an essential element to modern system security. SELinux is a common implementation of MAC that must be well understood by engineers in order to incorporate the most ideal security practices into production systems. This exercise delves into a common occurrence relating to MAC; troubleshooting a system that is experiencing errors as a consequence of SELinux. *This course is not approved or sponsored by Red Hat.*

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Path Info

Clock icon Advanced
Clock icon 30m
Clock icon Nov 05, 2018

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Table of Contents

  1. Challenge

    Verify there is an error by trying to access `localhost:80/index.html` using curl on the `www` host and check the audit log using sealert. Direct the output from sealert to `/home/cloud_user/seinfo.txt`.

    • Run curl localhost:80/index.html to confirm the error.
    • Run sealert -a /var/log/audit/audit.log > /home/cloud_user/seinfo.txt.
  2. Challenge

    Examine `/home/cloud_user/seinfo.txt` to figure out what is wrong and fix the error regarding `/var/www/html/index.html`.

    • Reviewing the seinfo.txt file should indicate the context for /var/www/html/index.html is incorrect.
    • Run restorecon /var/www/html/index.html to fix the issue.
  3. Challenge

    Restart `httpd` to check for other possible issues and correct any issues you might find.

    • Run systemctl restart httpd (note: httpd should fail to restart).
    • Based on journalctl --xe or by re-examining the audit log with sealert, you will see the file context is incorrect on /etc/httpd/conf/httpd.conf.
    • Run restorecon /etc/httpd/conf/httpd.conf to fix the context on httpd.conf.
    • Run systemctl start httpd and service should be restored.
  4. Challenge

    Confirm `localhost:80/index.html` loads correctly with curl on the `www` host.

    Run curl localhost:80/index.html and verify that you get the message "The website is up".

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