82347f4 IPA: handle searches by SID in apply_subdomain_homedir

Authored and Committed by jhrozek 9 years ago
    IPA: handle searches by SID in apply_subdomain_homedir
    
    https://fedorahosted.org/sssd/ticket/2391
    
    apply_subdomain_homedir() didn't handle the situation where an entity
    that doesn't match was requested from the cache. For user and group
    lookups this wasn't a problem because the negative match was caught
    sooner.
    
    But SID lookups can match either user or group. When a group SID was
    requested, the preceding LDAP request matched the SID and stored the
    group in the cache. Then apply_subdomain_homedir() only tried to search
    user by SID, didn't find the entry and accessed a NULL pointer.
    
    A simple reproducer is:
    $ python
    >>> import pysss_nss_idmap
    >>> pysss_nss_idmap.getnamebysid(group_sid)
    
    The group_sid can be anything, including Domain Users (XXX-513)
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>