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Fixed bug#17366: Unchecked Item_int results in server crash

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When there is conjunction of conds, the substitute_for_best_equal_field()
will call the eliminate_item_equal() function in loop to build final
expression. But if eliminate_item_equal() finds that some cond will always
evaluate to 0, then that cond will be substituted by Item_int with value ==
0. In this case on the next iteration eliminate_item_equal() will get that 
Item_int and treat it as Item_cond. This is leads to memory corruption and
server crash on cleanup phase.

To the eliminate_item_equal() function was added DBUG_ASSERT for checking
that all items treaten as Item_cond are really Item_cond.
The substitute_for_best_equal_field() now checks that if
eliminate_item_equal() returns Item_int and it's value is 0 then this 
value is returned as the result of whole conjunction.
This commit is contained in:
evgen@sunlight.local
2006-03-13 21:11:15 +03:00
parent f47ed62fb0
commit af660df0ef
3 changed files with 22 additions and 0 deletions
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7
mysql-test/r/subselect.result
View File

@@ -3157,3 +3157,10 @@ id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 9 Using where 1 PRIMARY t1 ALL NULL NULL NULL NULL 9 Using where
2 DEPENDENT SUBQUERY t1 index NULL a 8 NULL 9 Using filesort 2 DEPENDENT SUBQUERY t1 index NULL a 8 NULL 9 Using filesort
DROP TABLE t1; DROP TABLE t1;
create table t1( f1 int,f2 int);
insert into t1 values (1,1),(2,2);
select tt.t from (select 'crash1' as t, f2 from t1) as tt left join t1 on tt.t = 'crash2' and tt.f2 = t1.f2 where tt.t = 'crash1';
t
crash1
crash1
drop table t1;

7
mysql-test/t/subselect.test
View File

@@ -2073,3 +2073,10 @@ SELECT * FROM t1 WHERE (a,b) = ANY (SELECT a, max(b) FROM t1 GROUP BY a);
DROP TABLE t1; DROP TABLE t1;
#
# Bug#17366: Unchecked Item_int results in server crash
#
create table t1( f1 int,f2 int);
insert into t1 values (1,1),(2,2);
select tt.t from (select 'crash1' as t, f2 from t1) as tt left join t1 on tt.t = 'crash2' and tt.f2 = t1.f2 where tt.t = 'crash1';
drop table t1;

8
sql/sql_select.cc
View File

@@ -7066,7 +7066,10 @@ static Item *eliminate_item_equal(COND *cond, COND_EQUAL *upper_levels,
if (!cond) if (!cond)
cond= new Item_cond_and(eq_list); cond= new Item_cond_and(eq_list);
else else
{
DBUG_ASSERT(cond->type() == Item::COND_ITEM);
((Item_cond *) cond)->add_at_head(&eq_list); ((Item_cond *) cond)->add_at_head(&eq_list);
}
cond->quick_fix_field(); cond->quick_fix_field();
cond->update_used_tables(); cond->update_used_tables();
@@ -7151,6 +7154,11 @@ static COND* substitute_for_best_equal_field(COND *cond,
while ((item_equal= it++)) while ((item_equal= it++))
{ {
cond= eliminate_item_equal(cond, cond_equal->upper_levels, item_equal); cond= eliminate_item_equal(cond, cond_equal->upper_levels, item_equal);
// This occurs when eliminate_item_equal() founds that cond is
// always false and substitues it with Item_int 0.
// Due to this, value of item_equal will be 0, so just return it.
if (cond->type() != Item::ITEM_COND)
break;
} }
} }
} }