CVE-2020-25717 auth_sam: use pdb_get_domain_info to look up DNS forest information

When Samba is used as a part of FreeIPA domain controller, Windows
clients for a trusted AD forest may try to authenticate (perform logon
operation) as a REALM\name user account.

Fix auth_sam plugins to accept DNS forest name if we are running on a DC
with PASSDB module providing domain information (e.g. pdb_get_domain_info()
returning non-NULL structure). Right now, only FreeIPA or Samba AD DC
PASSDB backends return this information but Samba AD DC configuration is
explicitly ignored by the two auth_sam (strict and netlogon3) modules.

Detailed logs below:

[2020/11/11 09:23:53.281296,  1, pid=42677, effective(65534, 65534), real(65534, 0), class=rpc_parse] ../../librpc/ndr/ndr.c:482(ndr_print_function_debug)
       netr_LogonSamLogonWithFlags: struct netr_LogonSamLogonWithFlags
          in: struct netr_LogonSamLogonWithFlags
              server_name              : *
                  server_name              : '\\master.ipa.test'
              computer_name            : *
                  computer_name            : 'AD1'
              credential               : *
                  credential: struct netr_Authenticator
                      cred: struct netr_Credential
                          data                     : 529f4b087c5f6546
                      timestamp                : Wed Nov 11 09:23:55 AM 2020 UTC
              return_authenticator     : *
                  return_authenticator: struct netr_Authenticator
                      cred: struct netr_Credential
                          data                     : 204f28f622010000
                      timestamp                : Fri May  2 06:37:50 AM 1986 UTC
              logon_level              : NetlogonNetworkTransitiveInformation (6)
              logon                    : *
                  logon                    : union netr_LogonLevel(case 6)
                  network                  : *
                      network: struct netr_NetworkInfo
                          identity_info: struct netr_IdentityInfo
                              domain_name: struct lsa_String
                                  length                   : 0x0010 (16)
                                  size                     : 0x01fe (510)
                                  string                   : *
                                      string                   : 'IPA.TEST'
                              parameter_control        : 0x00002ae0 (10976)
                                     0: MSV1_0_CLEARTEXT_PASSWORD_ALLOWED
                                     0: MSV1_0_UPDATE_LOGON_STATISTICS
                                     0: MSV1_0_RETURN_USER_PARAMETERS
                                     0: MSV1_0_DONT_TRY_GUEST_ACCOUNT
                                     1: MSV1_0_ALLOW_SERVER_TRUST_ACCOUNT
                                     1: MSV1_0_RETURN_PASSWORD_EXPIRY
                                     1: MSV1_0_USE_CLIENT_CHALLENGE
                                     0: MSV1_0_TRY_GUEST_ACCOUNT_ONLY
                                     1: MSV1_0_RETURN_PROFILE_PATH
                                     0: MSV1_0_TRY_SPECIFIED_DOMAIN_ONLY
                                     1: MSV1_0_ALLOW_WORKSTATION_TRUST_ACCOUNT
                                     0: MSV1_0_DISABLE_PERSONAL_FALLBACK
                                     1: MSV1_0_ALLOW_FORCE_GUEST
                                     0: MSV1_0_CLEARTEXT_PASSWORD_SUPPLIED
                                     0: MSV1_0_USE_DOMAIN_FOR_ROUTING_ONLY
                                     0: MSV1_0_ALLOW_MSVCHAPV2
                                     0: MSV1_0_S4U2SELF
                                     0: MSV1_0_CHECK_LOGONHOURS_FOR_S4U
                                     0: MSV1_0_SUBAUTHENTICATION_DLL_EX
                              logon_id                 : 0x0000000000884ef2 (8933106)
                              account_name: struct lsa_String
                                  length                   : 0x000e (14)
                                  size                     : 0x000e (14)
                                  string                   : *
                                      string                   : 'idmuser'
                              workstation: struct lsa_String
                                  length                   : 0x0000 (0)
                                  size                     : 0x0000 (0)
                                  string                   : *
                                      string                   : ''
                         challenge                : 417207867bd33c74
                          nt: struct netr_ChallengeResponse
                              length                   : 0x00c0 (192)
                              size                     : 0x00c0 (192)
                              data                     : *
                                  data: ARRAY(192)
  [0000] A5 24 62 6E 31 DF 69 66   9E DC 54 D6 63 4C D6 2F   .$bn1.if ..T.cL./
  [0010] 01 01 00 00 00 00 00 00   50 37 D7 60 0C B8 D6 01   ........ P7.`....
  [0020] 15 1B 38 4F 47 95 4D 62   00 00 00 00 02 00 0E 00   ..8OG.Mb ........
  [0030] 57 00 49 00 4E 00 32 00   30 00 31 00 36 00 01 00   W.I.N.2. 0.1.6...
  [0040] 06 00 41 00 44 00 31 00   04 00 18 00 77 00 69 00   ..A.D.1. ....w.i.
  [0050] 6E 00 32 00 30 00 31 00   36 00 2E 00 74 00 65 00   n.2.0.1. 6...t.e.
  [0060] 73 00 74 00 03 00 20 00   61 00 64 00 31 00 2E 00   s.t... . a.d.1...
  [0070] 77 00 69 00 6E 00 32 00   30 00 31 00 36 00 2E 00   w.i.n.2. 0.1.6...
  [0080] 74 00 65 00 73 00 74 00   05 00 18 00 77 00 69 00   t.e.s.t. ....w.i.
  [0090] 6E 00 32 00 30 00 31 00   36 00 2E 00 74 00 65 00   n.2.0.1. 6...t.e.
  [00A0] 73 00 74 00 07 00 08 00   50 37 D7 60 0C B8 D6 01   s.t..... P7.`....
  [00B0] 06 00 04 00 02 00 00 00   00 00 00 00 00 00 00 00   ........ ........
                          lm: struct netr_ChallengeResponse
                              length                   : 0x0018 (24)
                              size                     : 0x0018 (24)
                              data                     : *
                                  data                     : 000000000000000000000000000000000000000000000000
              validation_level         : 0x0006 (6)
              flags                    : *
                  flags                    : 0x00000000 (0)
                         0: NETLOGON_SAMLOGON_FLAG_PASS_TO_FOREST_ROOT
                         0: NETLOGON_SAMLOGON_FLAG_PASS_CROSS_FOREST_HOP
                         0: NETLOGON_SAMLOGON_FLAG_RODC_TO_OTHER_DOMAIN
                         0: NETLOGON_SAMLOGON_FLAG_RODC_NTLM_REQUEST

In such case checks for a workgroup name will not match the DNS forest
name used in the username specification:

[2020/11/11 09:23:53.283055,  3, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth.c:200(auth_check_ntlm_password)
  check_ntlm_password:  Checking password for unmapped user [IPA.TEST]\[idmuser]@[] with the new password interface
[2020/11/11 09:23:53.283073,  3, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth.c:203(auth_check_ntlm_password)
  check_ntlm_password:  mapped user is: [IPA.TEST]\[idmuser]@[]
[2020/11/11 09:23:53.283082, 10, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth.c:213(auth_check_ntlm_password)
  check_ntlm_password: auth_context challenge created by fixed
[2020/11/11 09:23:53.283091, 10, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth.c:216(auth_check_ntlm_password)
  challenge is:
[2020/11/11 09:23:53.283099,  5, pid=42677, effective(65534, 65534), real(65534, 0)] ../../lib/util/util.c:678(dump_data)
  [0000] 41 72 07 86 7B D3 3C 74                             Ar..{.<t
[2020/11/11 09:23:53.283113, 10, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth_sam.c:209(auth_sam_netlogon3_auth)
  auth_sam_netlogon3_auth: Check auth for: [IPA.TEST]\[idmuser]
[2020/11/11 09:23:53.283123,  5, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth_sam.c:234(auth_sam_netlogon3_auth)
  auth_sam_netlogon3_auth: IPA.TEST is not our domain name (DC for IPA)
[2020/11/11 09:23:53.283131, 10, pid=42677, effective(65534, 65534), real(65534, 0), class=auth] ../../source3/auth/auth.c:249(auth_check_ntlm_password)
  auth_check_ntlm_password: sam_netlogon3 had nothing to say

and overall authentication attempt will fail: auth_winbind will complain
that this domain is not a trusted one and refuse operating on it:

[2020/11/11 09:23:53.283784, 10, pid=42663, effective(0, 0), real(0, 0), class=winbind] ../../source3/winbindd/winbindd.c:742(process_request_send)
  process_request_send: process_request: Handling async request smbd(42677):PAM_AUTH_CRAP
[2020/11/11 09:23:53.283796,  3, pid=42663, effective(0, 0), real(0, 0), class=winbind] ../../source3/winbindd/winbindd_pam_auth_crap.c:110(winbindd_pam_auth_crap_send)
  [42677]: pam auth crap domain: [IPA.TEST] user: idmuser
[2020/11/11 09:23:53.283810,  3, pid=42663, effective(0, 0), real(0, 0), class=winbind] ../../source3/winbindd/winbindd_pam.c:409(find_auth_domain)
  Authentication for domain [IPA.TEST] refused as it is not a trusted domain
[2020/11/11 09:23:53.283825, 10, pid=42663, effective(0, 0), real(0, 0), class=winbind] ../../source3/winbindd/winbindd.c:810(process_request_done)
  process_request_done: [smbd(42677):PAM_AUTH_CRAP]: NT_STATUS_NO_SUCH_USER
[2020/11/11 09:23:53.283844, 10, pid=42663, effective(0, 0), real(0, 0), class=winbind] ../../source3/winbindd/winbindd.c:855(process_request_written)
  process_request_written: [smbd(42677):PAM_AUTH_CRAP]: delivered response to client

Signed-off-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14556

(cherry picked from commit 2a8b672652dcbcf55ec59be537773d76f0f14d0a)

diff --git a/source3/auth/auth_sam.c b/source3/auth/auth_sam.c
index 3c12f959fafedf527b9364e1fefb30f3e6b53c42..e8e0d543f8c36903e7ff2420c71f551bddbaae1f 100644 (file)
--- a/source3/auth/auth_sam.c
+++ b/source3/auth/auth_sam.c
@@ -22,6 +22,7 @@
 
 #include "includes.h"
 #include "auth.h"
+#include "passdb.h"
 
 #undef DBGC_CLASS
 #define DBGC_CLASS DBGC_AUTH
@@ -142,10 +143,28 @@ static NTSTATUS auth_samstrict_auth(const struct auth_context *auth_context,
                        break;
                case ROLE_DOMAIN_PDC:
                case ROLE_DOMAIN_BDC:
-                       if ( !is_local_name && !is_my_domain ) {
-                               DEBUG(6,("check_samstrict_security: %s is not one of my local names or domain name (DC)\n",
-                                       effective_domain));
-                               return NT_STATUS_NOT_IMPLEMENTED;
+                       if (!is_local_name && !is_my_domain) {
+                              /* If we are running on a DC that has PASSDB module with domain
+                               * information, check if DNS forest name is matching the domain
+                               * name. This is the case of FreeIPA domain controller when
+                               * trusted AD DCs attempt to authenticate FreeIPA users using
+                               * the forest root domain (which is the only domain in FreeIPA).
+                               */
+                               struct pdb_domain_info *dom_info = NULL;
+
+                               dom_info = pdb_get_domain_info(mem_ctx);
+                               if ((dom_info != NULL) && (dom_info->dns_forest != NULL)) {
+                                       is_my_domain = strequal(user_info->mapped.domain_name,
+                                                               dom_info->dns_forest);
+                               }
+
+                               TALLOC_FREE(dom_info);
+                               if (!is_my_domain) {
+                                       DEBUG(6,("check_samstrict_security: %s is not one "
+                                                "of my local names or domain name (DC)\n",
+                                                effective_domain));
+                                       return NT_STATUS_NOT_IMPLEMENTED;
+                               }
                        }
 
                        break;
@@ -230,6 +249,24 @@ static NTSTATUS auth_sam_netlogon3_auth(const struct auth_context *auth_context,
        }
 
        is_my_domain = strequal(user_info->mapped.domain_name, lp_workgroup());
+       if (!is_my_domain) {
+              /* If we are running on a DC that has PASSDB module with domain
+               * information, check if DNS forest name is matching the domain
+               * name. This is the case of FreeIPA domain controller when
+               * trusted AD DCs attempt to authenticate FreeIPA users using
+               * the forest root domain (which is the only domain in FreeIPA).
+               */
+               struct pdb_domain_info *dom_info = NULL;
+               dom_info = pdb_get_domain_info(mem_ctx);
+
+               if ((dom_info != NULL) && (dom_info->dns_forest != NULL)) {
+                       is_my_domain = strequal(user_info->mapped.domain_name,
+                                               dom_info->dns_forest);
+               }
+
+               TALLOC_FREE(dom_info);
+       }
+
        if (!is_my_domain) {
                DBG_INFO("%s is not our domain name (DC for %s)\n",
                         effective_domain, lp_workgroup());