CVE-2022-32744 s4:kpasswd: Ensure we pass the kpasswd server principal into krb5_rd_r...

To ensure that, when decrypting the kpasswd ticket, we look up the
correct principal and don't trust the sname from the ticket, we should
pass the principal name of the kpasswd service into krb5_rd_req_ctx().
However, gensec_krb5_update_internal() will pass in NULL unless the
principal in our credentials is CRED_SPECIFIED.

At present, our principal will be considered obtained as CRED_SMB_CONF
(from the cli_credentials_set_conf() a few lines up), so we explicitly
set the realm again, but this time as CRED_SPECIFIED. Now the value of
server_in_keytab that we provide to smb_krb5_rd_req_decoded() will not
be NULL.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15074

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>

diff --git a/selftest/knownfail_mit_kdc b/selftest/knownfail_mit_kdc
index e1315ed71ac32fdccad74e8ee02de34a0f895cfd..8601da3d79acd46cc7a25a4f6b34686d7aeeff84 100644 (file)
--- a/selftest/knownfail_mit_kdc
+++ b/selftest/knownfail_mit_kdc
@@ -439,5 +439,3 @@ samba.tests.krb5.as_canonicalization_tests.samba.tests.krb5.as_canonicalization_
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_canonicalize_realm_case.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_no_canonicalize_realm_case.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_ticket_requester_sid_tgs.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_wrong_key_server.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_wrong_key_service.ad_dc

diff --git a/source4/kdc/kpasswd-service.c b/source4/kdc/kpasswd-service.c
index aec3085017328961a127919a2d51a1f85062f472..d2f1bb02906c96b93767f9de43f7fff684ee1240 100644 (file)
--- a/source4/kdc/kpasswd-service.c
+++ b/source4/kdc/kpasswd-service.c
@@ -29,6 +29,7 @@
 #include "kdc/kdc-server.h"
 #include "kdc/kpasswd-service.h"
 #include "kdc/kpasswd-helper.h"
+#include "param/param.h"
 
 #define HEADER_LEN 6
 #ifndef RFC3244_VERSION
@@ -161,6 +162,20 @@ kdc_code kpasswd_process(struct kdc_server *kdc,
                goto done;
        }
 
+       /*
+        * After calling cli_credentials_set_conf(), explicitly set the realm
+        * with CRED_SPECIFIED. We need to do this so the result of
+        * principal_from_credentials() called from the gensec layer is
+        * CRED_SPECIFIED rather than CRED_SMB_CONF, avoiding a fallback to
+        * match-by-key (very undesirable in this case).
+        */
+       ok = cli_credentials_set_realm(server_credentials,
+                                      lpcfg_realm(kdc->task->lp_ctx),
+                                      CRED_SPECIFIED);
+       if (!ok) {
+               goto done;
+       }
+
        ok = cli_credentials_set_username(server_credentials,
                                          "kadmin/changepw",
                                          CRED_SPECIFIED);
@@ -168,6 +183,21 @@ kdc_code kpasswd_process(struct kdc_server *kdc,
                goto done;
        }
 
+       /* Check that the server principal is indeed CRED_SPECIFIED. */
+       {
+               char *principal = NULL;
+               enum credentials_obtained obtained;
+
+               principal = cli_credentials_get_principal_and_obtained(server_credentials,
+                                                                      tmp_ctx,
+                                                                      &obtained);
+               if (obtained < CRED_SPECIFIED) {
+                       goto done;
+               }
+
+               TALLOC_FREE(principal);
+       }
+
        rv = cli_credentials_set_keytab_name(server_credentials,
                                             kdc->task->lp_ctx,
                                             kdc->kpasswd_keytab_name,