s3:libads: Clear previous CLDAP ping flags when reusing the ADS_STRUCT

s3:libads: Clear previous CLDAP ping flags when reusing the ADS_STRUCT

Before commit 1d066f37b9217a475b6b84a935ad51fbec88fe04, when the LDAP
connection wasn't established yet (ads->ldap.ld == NULL), the
ads_current_time() function always allocated and initialized a new
ADS_STRUCT even when ads->ldap.ss had a good address after having called
ads_find_dc().

After that commit, when the ADS_STRUCT is reused and passed to the
ads_connect() call, ads_try_connect() may fail depending on the
contacted DC because ads->config.flags field can contain the flags
returned by the previous CLDAP call. For example, when having 5 DCs:

* 192.168.101.31 has PDC FSMO role
* 192.168.101.32
* 192.168.101.33
* 192.168.101.34
* 192.168.101.35

$> net ads info -S 192.168.101.35

net_ads_info()
  ads_startup_nobind()
    ads_startup_int()
      ads_init()
      ads_connect()
        ads_try_connect(192.168.101.35)
          check_cldap_reply_required_flags(returned=0xF1FC, required=0x0)
  ads_current_time()
    ads_connect()
      ads_try_connect(192.168.101.35)
        check_cldap_reply_required_flags(returned=0xF1FC, required=0xF1FC)

The check_cldap_reply_required_flags() call fails because
ads->config.flags contain the flags returned by the previous CLDAP call,
even when the returned and required values match because they have
different semantics:

  if (req_flags & DS_PDC_REQUIRED)
        RETURN_ON_FALSE(ret_flags & NBT_SERVER_PDC);

  translates to:

  if (0xF1FC & 0x80)
        RETURN_ON_FALSE(0xF1FC & 0x01);

  which returns false because 192.168.101.35 has no PDC FSMO role.

The easiest fix for now is to reset ads->config.flags in
ads_current_time() when reusing an ADS_STRUCT before calling
ads_connect(), but we should consider storing the required and returned
flags in different fields or at least use the same bitmap for them
because check_cldap_reply_required_flags() is checking a
netr_DsRGetDCName_flags value using the nbt_server_type bitmap.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14674

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Mon May 23 19:18:38 UTC 2022 on sn-devel-184