CVE-2022-2031 s4:kpasswd: Correctly generate error strings

The error_data we create already has an explicit length, and should not
be zero-terminated, so we omit the trailing null byte. Previously,
Heimdal builds would leave a superfluous trailing null byte on error
strings, while MIT builds would omit the final character.

The two bytes added to the string's length are for the prepended error
code.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15047
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15049
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>

[jsutton@samba.org Removed MIT KDC 1.20-specific knownfails]

3 files changed, 6 insertions, 34 deletions

diff --git a/selftest/knownfail_heimdal_kdc b/selftest/knownfail_heimdal_kdc
index 54e69a48bc1..40e24f3155b 100644
--- a/selftest/knownfail_heimdal_kdc
+++ b/selftest/knownfail_heimdal_kdc
@@ -276,24 +276,12 @@
 #
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_canonicalize.ad_dc
 ^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_change.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_change_expired_password.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_empty.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_from_rodc.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_initial.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_no_canonicalize.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_no_seq_number.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_non_initial.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_expired_password.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_and_realm_access.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_and_realm_no_access.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_only.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_realm_only.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_ticket_lifetime.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_too_weak.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_wrong_key.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/selftest/knownfail_mit_kdc b/selftest/knownfail_mit_kdc
index 53638afc17a..a914c4d3492 100644
--- a/selftest/knownfail_mit_kdc
+++ b/selftest/knownfail_mit_kdc
@@ -578,26 +578,11 @@ samba.tests.krb5.as_canonicalization_tests.samba.tests.krb5.as_canonicalization_
 #
 # Kpasswd tests
 #
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_canonicalize.ad_dc
 ^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_change.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_change_expired_password.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_empty.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_from_rodc.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_initial.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_no_canonicalize.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_no_seq_number.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_non_initial.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_expired_password.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_and_realm_access.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_and_realm_no_access.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_princ_only.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_set_target_realm_only.ad_dc
 ^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_ticket_lifetime.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_too_weak.ad_dc
-^samba.tests.krb5.kpasswd_tests.samba.tests.krb5.kpasswd_tests.KpasswdTests.test_kpasswd_wrong_key.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-helper.c b/source4/kdc/kpasswd-helper.c
index 995f54825b5..55a2f5b3bf6 100644
--- a/source4/kdc/kpasswd-helper.c
+++ b/source4/kdc/kpasswd-helper.c
@@ -48,17 +48,16 @@ bool kpasswd_make_error_reply(TALLOC_CTX *mem_ctx,
 	}
 
 	/*
-	 * The string 's' has two terminating nul-bytes which are also
-	 * reflected by 'slen'. Normally Kerberos doesn't expect that strings
-	 * are nul-terminated, but Heimdal does!
+	 * The string 's' has one terminating nul-byte which is also
+	 * reflected by 'slen'. We subtract it from the length.
 	 */
-#ifndef SAMBA4_USES_HEIMDAL
-	if (slen < 2) {
+	if (slen < 1) {
 		talloc_free(s);
 		return false;
 	}
-	slen -= 2;
-#endif
+	slen--;
+
+	/* Two bytes are added to the length to account for the error code. */
 	if (2 + slen < slen) {
 		talloc_free(s);
 		return false;