Make password change work without default realm

This fix is not very general or clean, but is suitable for backporting
because it is minimally invasive.  A more comprehensive fix will
follow.

(cherry picked from commit b9ff95a)

ticket: 7177 (new)
version_fixed: 1.8.7
status: resolved

src/lib/krb5/krb/get_in_tkt.c

@@ -992,6 +992,11 @@ build_in_tkt_name(krb5_context context,
     *server = NULL;
 
     if (in_tkt_service) {
+        /* Minimally invasive fix for inability to change password with no
+         * default realm, for backporting. */
+        if (strcmp(in_tkt_service, "kadmin/changepw") == 0)
+            in_tkt_service = "kadmin/changepw@";
+
         /* this is ugly, because so are the data structures involved.  I'm
            in the library, so I'm going to manipulate the data structures
            directly, otherwise, it will be worse. */