ipa-kdb: add UPN_DNS_INFO PAC structure

UPN_DNS_INFO structure contains the client's user principal name (UPN)
and a fully qualified domain name. It is used to provide the UPN and the
FQDN that corresponds to the client of the ticket.

The structure is defined in MS-PAC section 2.10. MS-KILE specification
says in the section 3.3.5.6.4.5 that KDCs should return this buffer. It
further clarifies in section 3.3.5.2 that if the user account object has no
userPrincipalName attribute, UPN_DNS_INFO should be constructed by
concatenating user name, the "@" symbol, and the DNS name of the domain.

IPA users don't really have userPrincipalName attribute. Instead, we
always construct their account names in LOGON Info3 structure by
unparsing the canonical principal name without realm, meaning that user
principal can be recovered by concatenating the account name and the
realm (domain).

Unless the account name and unparsed client principal name are different
or the primary Info3 gid (group RID) is the one for machine accounts,
mark the UPN as constructed.

Related: https://pagure.io/freeipa/issue/8319

Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Isaac Boukris <iboukris@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>

daemons/ipa-kdb/ipa_kdb_mspac.c

@@ -805,6 +805,8 @@ static krb5_error_code ipadb_get_pac(krb5_context kcontext,
     union PAC_INFO pac_info;
     krb5_error_code kerr;
     enum ndr_err_code ndr_err;
+    union PAC_INFO pac_upn;
+    char *principal = NULL;
 
     /* When no client entry is there, we cannot generate MS-PAC */
     if (!client) {
@@ -879,6 +881,46 @@ static krb5_error_code ipadb_get_pac(krb5_context kcontext,
 
     kerr = krb5_pac_add_buffer(kcontext, *pac, KRB5_PAC_LOGON_INFO, &data);
 
+    /* == Package UPN_DNS_LOGON_INFO == */
+    memset(&pac_upn, 0, sizeof(pac_upn));
+    kerr = krb5_unparse_name(kcontext, client->princ, &principal);
+    if (kerr) {
+        goto done;
+    }
+
+    pac_upn.upn_dns_info.upn_name = talloc_strdup(tmpctx, principal);
+    krb5_free_unparsed_name(kcontext, principal);
+    if (pac_upn.upn_dns_info.upn_name == NULL) {
+        kerr = KRB5_KDB_INTERNAL_ERROR;
+        goto done;
+    }
+
+    pac_upn.upn_dns_info.dns_domain_name = talloc_strdup(tmpctx, ipactx->realm);
+    if (pac_upn.upn_dns_info.dns_domain_name == NULL) {
+            kerr = KRB5_KDB_INTERNAL_ERROR;
+            goto done;
+    }
+
+    /* IPA user principals are all constructed */
+    if ((pac_info.logon_info.info->info3.base.rid != 515) ||
+        (pac_info.logon_info.info->info3.base.rid != 516)) {
+        pac_upn.upn_dns_info.flags |= PAC_UPN_DNS_FLAG_CONSTRUCTED;
+    }
+
+    ndr_err = ndr_push_union_blob(&pac_data, tmpctx, &pac_upn,
+                                  PAC_TYPE_UPN_DNS_INFO,
+                                  (ndr_push_flags_fn_t)ndr_push_PAC_INFO);
+    if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
+        kerr = KRB5_KDB_INTERNAL_ERROR;
+        goto done;
+    }
+
+    data.magic = KV5M_DATA;
+    data.data = (char *)pac_data.data;
+    data.length = pac_data.length;
+
+    kerr = krb5_pac_add_buffer(kcontext, *pac, KRB5_PAC_UPN_DNS_INFO, &data);
+
 done:
     ldap_msgfree(results);
     talloc_free(tmpctx);