SELinux

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General

  • ls -Z
  • sestatus - to get status, e.g., whether in enforcing or not
    • also setenforce and getenforce
  • getsebool -a | grep httpd
  • semanage boolean -l | sort | less
  • SE Control programs: getsebool, setsebool, booleans, togglesebool, semanage
  • CentOS6 SELinux troubleshooting
    • "SELinux decisions, such as allowing or disallowing access, are cached. This cache is known as the Access Vector Cache (AVC). Denial messages are logged when SELinux denies access. These denials are also known as "AVC denials""
  • CentOS7 SELinux troubleshooting

SELinux and webservers

semanage

  • SELinux Policy Management tool
  • semanage fcontext -a -t httpd_sys_content_t "/var/www/lgorders/admin(/.*)?
  • semanage port -l - List all the ports and contexts known to SELinux

restorecon

  • restore file(s) default SELinux security contexts.
  • passively check whether the file contexts are all set as specified by the active policy
  • restorecon -Rv .
    • -n is dry-run (passive-check)
  1. When you cp files from one location to another, they keep their original context
  2. If you scp (from another machine?) directly into place, they get the context corresponding to the receiving location.
  3. Every time you copy (cp) new/modified files into /var/www/lgorders you’ll have to run sudo restorecon -R /var/www/lgorders to allow httpd to use them.

auditd

  • If Linux audit daemon (see below) is turned on, SELinux problems should be written to file /var/log/audit/audit.log
  • audit2allow and audit2why
  • man auditd
  • /etc/audit/auditd.conf
  • service auditd status
  • dumps infos to /var/log/audit/audit.log
  • aureport -a
  • ausearch -m avc -ts recent - denials from the last 10 minutes

auditctl

  • a utility to assist controlling the kernel's audit system
  • -a always,exit = append action always to syscall exit list
  • -S open = any open call made by a program
  • -F success!=0 = create a rule field evaluating on the exit value

examples

  • auditctl -a always,exit -S all -F pid=1005
    • To see all syscalls made by a specific program
  • auditctl -a always,exit -S openat -F auid=510
    • To see files opened by a specific user
  • auditctl -a always,exit -S openat -F success=0
    • To see unsuccessful openat calls
  • auditctl -w /etc/shadow -p wa or auditctl -a always,exit -F path=/etc/shadow -F perm=wa
    • To watch a file for changes
  • auditctl -w /etc/ -p wa or auditctl -a always,exit -F dir=/etc/ -F perm=wa
    • To recursively watch a directory for changes
  • auditctl -a always,exit -F dir=/home/ -F uid=0 -C auid!=obj_uid
    • To see if an admin is accessing other user's files