Wednesday, 19 September 2018

Changing / assigning contexts with SELinux (labelling)

I came accross an SELinux error the other day when I instructed rsyslog to write radius logs to '/var/log/radius'.

The message was as follows:

'SELinux is preventing /usr/sbin/rsyslogd from write access on the directory /var/log/radius.#012#012*****'

After inspecting the SELinux label:

ls -Z /var/log/radius

drwx------. radiusd radiusd system_u:object_r:unlabeled_t:s0 radacct
-rw-r-----. radiusd radiusd system_u:object_r:unlabeled_t:s0 radius.log
-rw-r-----. radiusd radiusd system_u:object_r:unlabeled_t:s0 radius.log-1234567.gz

It was clear that the typical 'var_log_t' context was absent and hence preventing rsyslog from writing logs.

The 'var_log_t' defines common logging directories / files.

In order to assign a context we can issue the following:

chcon system_u:object_r:var_log_t:s0 /var/log/radius && chcon system_u:object_r:var_log_t:s0 /var/log/radius/*

Warning: Using chcon will not make the change of context permanent - we need to use semanage to ensure changes remain in tact after system relabel or the restorecon command.

semanage fcontext -a -t var_log_t "/var/log/radius(/.*)?"

The last part of the command instructs all existing files (and newly created ones) to be of the 'var_log_t' context within the '/var/log/radius' directory.

Finally confirm our changes (using restorecon as well to ensure changes are permanent):

restorecon -R -v /var/log/radius

ls -Z

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