Fix for bug #42803: Field_bit does not have unsigned_flag field,

can lead to bad memory access

Problem: Field_bit is the only field which returns INT_RESULT
and doesn't have unsigned flag. As it's not a descendant of the 
Field_num, so using ((Field_num *) field_bit)->unsigned_flag may lead
to unpredictable results.

Fix: check the field type before casting.

mysql-test/r/type_bit.result

@@ -749,4 +749,14 @@ bin(a1)
 110000111111111
 110001011111111
 drop table t1bit7, t2bit7;
+#
+# Bug42803: Field_bit does not have unsigned_flag field, 
+# can lead to bad memory access
+#
+CREATE TABLE t1 (a BIT(7), b BIT(9), KEY(a, b));
+INSERT INTO t1 VALUES(0, 0), (5, 3), (5, 6), (6, 4), (7, 0);
+EXPLAIN SELECT a+0, b+0 FROM t1 WHERE a > 4 and b < 7 ORDER BY 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	a	a	2	NULL	4	Using where; Using index; Using filesort
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/type_bit.test

@@ -397,4 +397,15 @@ insert into t2bit7 values (b'110011011111111');
 select bin(a1) from t1bit7, t2bit7 where t1bit7.a1=t2bit7.b1; 
 drop table t1bit7, t2bit7; 
 
+
+--echo #
+--echo # Bug42803: Field_bit does not have unsigned_flag field, 
+--echo # can lead to bad memory access
+--echo #
+CREATE TABLE t1 (a BIT(7), b BIT(9), KEY(a, b));
+INSERT INTO t1 VALUES(0, 0), (5, 3), (5, 6), (6, 4), (7, 0);
+EXPLAIN SELECT a+0, b+0 FROM t1 WHERE a > 4 and b < 7 ORDER BY 2;
+DROP TABLE t1;
+
+
 --echo End of 5.0 tests

sql/opt_range.cc

@@ -4536,6 +4536,7 @@ get_mm_leaf(PARAM *param, COND *conf_func, Field *field, KEY_PART *key_part,
       if (type == Item_func::LT_FUNC && (value->val_int() > 0))
         type = Item_func::LE_FUNC;
       else if (type == Item_func::GT_FUNC &&
+               (field->type() != FIELD_TYPE_BIT) &&
                !((Field_num*)field)->unsigned_flag &&
                !((Item_int*)value)->unsigned_flag &&
                (value->val_int() < 0))
@@ -4572,7 +4573,9 @@ get_mm_leaf(PARAM *param, COND *conf_func, Field *field, KEY_PART *key_part,
    */
   if (field->result_type() == INT_RESULT &&
       value->result_type() == INT_RESULT &&
-      ((Field_num*)field)->unsigned_flag && !((Item_int*)value)->unsigned_flag)
+      ((field->type() == FIELD_TYPE_BIT || 
+       ((Field_num *) field)->unsigned_flag) && 
+       !((Item_int*) value)->unsigned_flag))
   {
     longlong item_val= value->val_int();
     if (item_val < 0)