Sssd: sssd: nss responder uninitialized heap disclosure in initgroups reply

A flaw was found in SSSD. The sss_nss_protocol_fill_initgr() function in the NSS responder pre-allocates reply space for all group entries but does not shrink the packet when groups are skipped, causing uninitialized heap bytes to be transmitted to the client. A local attacker can exploit this to disclose cached directory data and heap layout information from the sssd_nss process.