Bug #5960 A consistent read of an updated row with BLOB or TEXT col can return garbage

Description:
Hi!

If one updates a row so that the size of some column value changes, but the value of a BLOB or a TEXT column does not change, then a consistent read of the previous version of the BLOB or TEXT will bring at most 532 bytes of data, of which 512 bytes is good data, and the remaining 20 bytes the 'external storage header', that is, nonprintable characters.

This bug was found by a user.

Will be fixed in 4.0.22.

Regards,

Heikki

How to repeat:
See above.

Suggested fix:
Do not forget columns with the external bit set in the original row:

        if (row_upd_changes_field_size_or_external(rec, index, update)) {

                entry = row_rec_to_index_entry(ROW_COPY_DATA, index, rec,
                                                                     heap);
                row_upd_index_replace_new_col_vals(entry, index, update, heap);

                buf = mem_heap_alloc(heap, rec_get_converted_size(entry));

                *old_vers = rec_convert_dtuple_to_rec(buf, entry);
        } else {
                buf = mem_heap_alloc(heap, rec_get_size(rec));

                *old_vers = rec_copy(buf, rec);

                row_upd_rec_in_place(*old_vers, update);
        }

        for (i = 0; i < upd_get_n_fields(update); i++) {

                if (upd_get_nth_field(update, i)->extern_storage) {

                        rec_set_nth_field_extern_bit(*old_vers,
                                upd_get_nth_field(update, i)->field_no,
                                TRUE, NULL);
                }
        }

        return(DB_SUCCESS);

This bug is only in InnoDB.

Fixed in 4.0.22.