Bug 1238165

+++ This bug was initially created as a clone of Bug #1238163 +++

(this is the original message explaining design and use case, mgrepl@ already has policy in works)

I'm implementing a feature in FreeIPA for which I'll need new SELinux
policy and I'd like to hear your suggestions how to design it.

Sorry in advance for long prelude, it needs to be said to establish the
context.

For FreeIPA 4.2 we are adding support to establish one-way trust to
Active Directory. As a consequence of this, we need to change how
certain operations against AD LDAP are performed. Right now we are
using feature of cross-realm Kerberos trust: we authenticate as
HTTP/ipa.master from within Apache process and then talk to
ldap/ad.dc or to cifs/ad.dc services in AD.

With one-way trust we cannot use this approach anymore because there is
no cross-realm Kerberos trust from IPA to AD, only the other way around.
Instead, there is an object in AD LDAP which represents IPA and we have
to authenticate as this object.

Access to this object is highly regulated (by us) because possession of
the trust domain object (TDO) credentials impersonates whole trust link.
Thus, we want to avoid authenticating as TDO within Apache process.

To achieve this I've implemented a scheme similar to oddjob-mkhomedir,
by providing a helper script which is executed by oddjobd on request
from Apache:

Apache process sends d-bus request to oddjobd daemon. Oddjobd daemon
executes an IPA helper. IPA helper accesses /etc/samba/samba.keytab and
authenticates as cifs/ipa.master. It then fetches TDO
credentials from IPA LDAP and authenticates with them to AD DC. Once
operation is performed, it connects again to IPA LDAP and updates it.

Now, there are several moving parts here:

 1. /etc/samba/samba.keytab is root:root, 0600, unconfined_u:object_r:samba_etc_t:s0
    It is created by /usr/sbin/ipa-adtrust-install

 2. /var/lib/sss/keytabs/ad.test.keytab is root:root, 0600, unconfined_u:object_r:sssd_var_lib_t:s0
    It can be created by IPA helper or by SSSD, whoever runs into need
    of the keytab first. The name is dependent on the AD forest root
    name (ad.test in my case).

 3. /usr/libexec/ipa/com.redhat.idm.trust-fetch-domains is root:root, 0755, uknown label so far.
    It is the IPA helper oddjobd daemon will be calling in response to Apache request.
    The helper is written in Python.

 4. /var/run/ipa/krb5cc_oddjob_trusts{,_fetch} -- credential caches used by the helper.
    They are root:root, 0600, unconfined_u:object_r:ipa_var_run_t:s0

 5. oddjobd daemon runs under system_u:system_r:oddjob_t:s0-s0:c0.c1023 context.


Could you please add SELinux policy that would allow the IPA
helper (3) to be executed by oddjobd, read from (1), read/write to files (2) and (4),
and communicate with LDAP server locally and AD DC remotely.