s4:password_hash LDB module - allow empty ("") passwords

This seems to have been broken some time ago - till someone on the
mailing list noticed it.

I've also added a testsuite (and some additional SamDB python helpers) which
should prove this.

2 files changed, 50 insertions, 22 deletions

diff --git a/source4/dsdb/samdb/ldb_modules/password_hash.c b/source4/dsdb/samdb/ldb_modules/password_hash.c
index 35d2729297..4e2e96fa65 100644
--- a/source4/dsdb/samdb/ldb_modules/password_hash.c
+++ b/source4/dsdb/samdb/ldb_modules/password_hash.c
@@ -1298,18 +1298,22 @@ static int setup_given_passwords(struct setup_password_fields_io *io,
 					   (void *)&cleartext_utf16_blob->data,
 					   &cleartext_utf16_blob->length,
 					   false)) {
-			talloc_free(cleartext_utf16_blob);
-			ldb_asprintf_errstring(ldb,
-					       "setup_password_fields: "
-					       "failed to generate UTF16 password from cleartext UTF8 password for user %s", io->u.sAMAccountName);
-			return LDB_ERR_CONSTRAINT_VIOLATION;
-		} else {
-			g->cleartext_utf16 = cleartext_utf16_blob;
+			if (g->cleartext_utf8->length != 0) {
+				talloc_free(cleartext_utf16_blob);
+				ldb_asprintf_errstring(ldb,
+						       "setup_password_fields: "
+						       "failed to generate UTF16 password from cleartext UTF8 one for user '%s'!",
+						       io->u.sAMAccountName);
+				return LDB_ERR_CONSTRAINT_VIOLATION;
+			} else {
+				/* passwords with length "0" are valid! */
+				cleartext_utf16_blob->data = NULL;
+				cleartext_utf16_blob->length = 0;
+			}
 		}
+		g->cleartext_utf16 = cleartext_utf16_blob;
 	} else if (g->cleartext_utf16) {
-		char *cleartext_utf8_str;
 		struct ldb_val *cleartext_utf8_blob;
-		size_t converted_pw_len;
 
 		cleartext_utf8_blob = talloc(io->ac, struct ldb_val);
 		if (!cleartext_utf8_blob) {
@@ -1319,20 +1323,25 @@ static int setup_given_passwords(struct setup_password_fields_io *io,
 					   CH_UTF16MUNGED, CH_UTF8,
 					   g->cleartext_utf16->data,
 					   g->cleartext_utf16->length,
-					   (void *)&cleartext_utf8_str,
-					   &converted_pw_len, false)) {
-			/* We must bail out here, the input wasn't even a
-			 * multiple of 2 bytes */
-			talloc_free(cleartext_utf8_blob);
-			ldb_asprintf_errstring(ldb,
-					       "setup_password_fields: "
-					       "UTF16 password for user %s had odd length (length must be a multiple of 2)", io->u.sAMAccountName);
-			return LDB_ERR_CONSTRAINT_VIOLATION;
-		} else {
-			*cleartext_utf8_blob = data_blob_const(cleartext_utf8_str,
-							       converted_pw_len);
-			g->cleartext_utf8 = cleartext_utf8_blob;
+					   (void *)&cleartext_utf8_blob->data,
+					   &cleartext_utf8_blob->length,
+					   false)) {
+			if (g->cleartext_utf16->length != 0) {
+				/* We must bail out here, the input wasn't even
+				 * a multiple of 2 bytes */
+				talloc_free(cleartext_utf8_blob);
+				ldb_asprintf_errstring(ldb,
+						       "setup_password_fields: "
+						       "failed to generate UTF8 password from cleartext UTF 16 one for user '%s' - the latter had odd length (length must be a multiple of 2)!",
+						       io->u.sAMAccountName);
+				return LDB_ERR_CONSTRAINT_VIOLATION;
+			} else {
+				/* passwords with length "0" are valid! */
+				cleartext_utf8_blob->data = NULL;
+				cleartext_utf8_blob->length = 0;
+			}
 		}
+		g->cleartext_utf8 = cleartext_utf8_blob;
 	}
 
 	if (g->cleartext_utf16) {
diff --git a/source4/dsdb/tests/python/passwords.py b/source4/dsdb/tests/python/passwords.py
index 198b314cc0..e43298e34d 100755
--- a/source4/dsdb/tests/python/passwords.py
+++ b/source4/dsdb/tests/python/passwords.py
@@ -887,6 +887,25 @@ userPassword: thatsAcomplPASS4
         # Reset the test "dSHeuristics" (reactivate "userPassword" pwd changes)
         ldb.set_dsheuristics("000000001")
 
+    def test_zero_length(self):
+        # Get the old "minPwdLength"
+        minPwdLength = ldb.get_minPwdLength()
+        # Set it temporarely to "0"
+        ldb.set_minPwdLength("0")
+
+        # Get the old "pwdProperties"
+        pwdProperties = ldb.get_pwdProperties()
+        # Set them temporarely to "0" (to deactivate eventually the complexity)
+        ldb.set_pwdProperties("0")
+
+        ldb.setpassword("(sAMAccountName=testuser)", "")
+
+        # Reset the "pwdProperties" as they were before
+        ldb.set_pwdProperties(pwdProperties)
+
+        # Reset the "minPwdLength" as it was before
+        ldb.set_minPwdLength(minPwdLength)
+
     def tearDown(self):
         super(PasswordTests, self).tearDown()
         delete_force(self.ldb, "cn=testuser,cn=users," + self.base_dn)