After using a default set of directories to watch, and allowing admins to mark other types as such as well, let's consider another approach for making the policy more flexible: booleans. The idea now is that a boolean called incron_notify_non_security_files enables incrond to be notified on changes on all possible non-security related files (the latter is merely an approach, you can define other sets as well if you want, including all possible files).

Booleans in SELinux policy can be generated in the incron.te file as follows:

## <desc>
## <p>
##      Determine whether incron can watch all non-security
##      file types
## </p>
## </desc>
gen_tunable(incron_notify_non_security_files, false)

With this boolean in place, the policy can be enhanced with code like the following:

tunable_policy(`incron_notify_non_security_files',`
        files_read_non_security_files(incrond_t)
        files_read_all_dirs_except(incrond_t)
')

This code tells SELinux that, if the incron_notify_non_security_files boolean is set (which by default is not the case), then incrond_t is able to read non security files.

Let's try to watch for changes in the AIDE log directory:

# tail audit.log
type=AVC msg=audit(1368777675.597:28611): avc:  denied  { search } for  pid=11704 comm="incrond" name="log" dev="dm-4" ino=13 scontext=system_u:system_r:incrond_t tcontext=system_u:object_r:var_log_t tclass=dir
type=AVC msg=audit(1368777675.597:28612): avc:  denied  { search } for  pid=11704 comm="incrond" name="log" dev="dm-4" ino=13 scontext=system_u:system_r:incrond_t tcontext=system_u:object_r:var_log_t tclass=dir

# tail cron.log
May 17 10:01:15 test incrond[11704]: access denied on /var/log/aide - events will be discarded silently

# getsebool incron_notify_non_security_files
incron_notify_non_security_files --> off

Let's enable the boolean and try again:

# setsebool incron_notify_non_security_files on

Reloading the incrontab tables now works, and the notifications work as well.

As you can see, once a policy is somewhat working, policy developers are considering the various "use cases" of an application, trying to write down policies that can be used by the majority of users, without granting too many rights automatically.


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