Issue 6417 - If an entry RDN is identical to the suffix, then Entryrd…

…n gets broken during a reindex (#6418)

Bug description:
        During a reindex, the entryrdn index is built at the end from
        each entry in the suffix.
        If one entry has a RDN that is identical to the suffix DN,
        then entryrdn_lookup_dn may erroneously return the suffix DN
        as the DN of the entry.

Fix description:
        When the lookup entry has no parent (because index is under
        work) the loop lookup the entry using the RDN.
        If this RDN matches the suffix DN, then it exits from the loop
        with the suffix DN.
        Before exiting it checks that the original lookup entryID
        is equal to suffix entryID. If it does not match
        the function fails and then the DN from the entry will be
        built from id2enty

fixes: #6417

Reviewed by: Pierre Rogier, Simon Pichugin (Thanks !!!)

ldap/servers/slapd/back-ldbm/ldbm_entryrdn.c

@@ -1224,7 +1224,16 @@ entryrdn_lookup_dn(backend *be,
                     }
                     goto bail;
                 }
-                maybesuffix = 1;
+                if (workid == 1) {
+                    /* The loop (workid) iterates from the starting 'id'
+                     * up to the suffix ID (i.e. '1').
+                     * A corner case (#6417) is if an entry, on the path
+                     * 'id' -> suffix, has the same RDN than the suffix.
+                     * In order to erroneously believe the loop hits the suffix
+                     * we need to check that 'workid' is '1' (suffix)
+                     */
+                    maybesuffix = 1;
+                }
             } else {
                 _entryrdn_cursor_print_error("entryrdn_lookup_dn",
                                              key.data, data.size, data.ulen, rc);