Lines below which were added in the patch for Bug#56814 cause this crash:

+      if (table->table)
+        table->table->maybe_null= FALSE;

Consider following test case:
--
CREATE TABLE t1(f1 INT NOT NULL);
INSERT INTO t1 VALUES (16777214),(0);

SELECT COUNT(*) FROM t1 LEFT JOIN t1 t2
ON 1 WHERE t2.f1 > 1 GROUP BY t2.f1;

DROP TABLE t1;
--

We set TABLE::maybe_null to FALSE for t2 table
and in create_tmp_field() we create appropriate tmp table field
using create_tmp_field_from_item() function instead of
create_tmp_field_from_field. As a result we have
LONGLONG field. As we have GROUP BY clause we calculate
group buffer length, see calc_group_buffer().
Item from group list which is used for calculation
refer to the field from real tables and have LONG type.
So group buffer length become insufficient for storing of
LONGLONG value. It leads to overwriting of wrong memory
area in do_field_int() function which is called from
end_update().
After some investigation I found out that
create_tmp_field_from_item() is used only for OLAP
grouping and can not be used for common grouping
as it could be an incompatibility between tmp
table fields and group buffer length.
We can not remove create_tmp_field_from_item() call from
create_tmp_field as OLAP needs it and we can not use this
function for common grouping. So we should remove setting
TABLE::maybe_null to FALSE from simplify_joins().
In this case we'll get wrong behaviour of
list_contains_unique_index() back. To fix it we
could use Field::real_maybe_null() check instead of
Field::maybe_null() and add addition check of
TABLE_LIST::outer_join.

The problem is caused by bug49487 fix and became visible
after after bug56679 fix.
Items are cleaned up and set to unfixed state after filling derived table.
So we can not rely on item::fixed state in Item_func_group_concat::print
and we can not use 'args' array as items there may be cleaned up.
The fix is always to use orig_args array of items as it
always should contain the correct data.

The problem is dividing by const value when
the result is out of supported range.
The fix:
-return LONGLONG_MIN if the result is out of supported range for DIV operator.
-return 0 if divisor is -1 for MOD operator.

Approved by Sunny Bains

or foreign key

Fix approved by Sunny Bains

create_sort_index() function overwrites original JOIN_TAB::type field.
At re-execution of subquery overwritten JOIN_TAB::type(JT_ALL) is
used instead of JT_FT. It misleads test_if_skip_sort_order() and
the function tries to find suitable key for the order that should
not be allowed for FULLTEXT(JT_FT) table.
The fix is to restore JOIN_TAB strucures for subselect on re-execution
for EXPLAIN.
Additional fix:
Update TABLE::maybe_null field which
affects list_contains_unique_index() behaviour as it
could have the value(maybe_null==TRUE) based on the
assumption that this join is outer
(see setup_table_map() func).

Subquery executes twice, at top level JOIN::optimize and ::execute stages.
At first execution create_sort_index() function is called and
FT_SELECT object is created and destroyed. HANDLER::ft_handler is cleaned up
in the object destructor and at second execution FT_SELECT::get_next() method
returns error.
The fix is to reinit HANDLER::ft_handler field before re-execution of subquery.

Where realpath(3) is used in Linux, mf_load_path is
used for Windows. This function doesn't however
correspond to the functionality of realpath.
This patch attempts to do better by using 
the Windows function GetFullPathName() instead.

Problem: some call of INET_NTOA() function may lead 
to a crash due to missing its character set initialization.

Fix: explicitly set the character set.

Problem: if multibyte and binary string arguments passed to 
RPAD(), LPAD() or INSERT() functions, they might return 
wrong results or even lead to a server crash due to missed
character set convertion.

Fix: perform the convertion if necessary.

with concurrent lock/unlock tables

Approved by Marko

row_create_table_for_mysql(): When the table creation fails,
free the dict_table_t object.

row_create_table_for_mysql(): When the table creation fails,
free the dict_table_t object.

No mysql-test case. Tested by creating a table, removing a *.frm file and
attempting to create the table again. Code coverage tested by
instrumentation. Tested with Valgrind.

Print an error message to stderr an get rid of the assertion.

Approved by: Jimmy Yang (over IM)

linked with foreign keys at once" from mysql-5.1-security to
mysql-5.5-security again.

rb://391 approved by Heikki

rb://477 approved by Marko