[Tarantool-patches] [PATCH 2/6] sql: fix possible null dereference in sql_expr_coll()
Nikita Pettik
korablev at tarantool.org
Fri Dec 6 15:48:29 MSK 2019
On 06 Dec 00:59, Vladislav Shpilevoy wrote:
> On 05/12/2019 12:40, Nikita Pettik wrote:
> > On 28 Nov 23:42, Vladislav Shpilevoy wrote:
> >> Thanks for the patch!
> >>
> >> Is it possible to test this?
> >
> > As a pure test case - I've failed to come up with it.
> > But the next patch (which adds collation to metadata) definitely fails
> > without this fix (when TRIM() or REPLACE() are called without args).
>
> Why does not it fail right after finding that there are no
> arguments? TRIM looks strange, but REPLACE expects 3 arguments.
>
> > I can dive into details, but I guess it's not so important here (since
> > this is obviously buggy place).
>
> Is it? As I pointed above, maybe the bug is really in another
> place? I see, that REPLACE checks argument count. But somewhy
> too late:
>
> tarantool> box.execute('SELECT REPLACE()')
> ---
> - null
> - 'Wrong number of arguments is passed to REPLACE(): expected 3, got 0'
> ...
>
> > If you want further investigation, let me
> > know and I will do it.
Sorry, in fact I mean SUBSTR() function. It can take 1 or 2 arguments.
But the check of arguments count is delayed till function execution (see
substrFunc in sql/func.c).
To generate collation for metadata we should call sql_expr_coll()
(without such necessity we avoid call of this function). And it leads
to null-dereference.
Finally, I've come up with example which results in null-dereference on
master branch as well (added it to the current patch):
box.execute("CREATE TABLE t (id INT PRIMARY KEY, a TEXT, b TEXT COLLATE \"binary\", c TEXT COLLATE \"unicode_ci\");")
box.execute("SELECT * FROM t WHERE a COLLATE \"binary\" = substr();")
Here we have to call sql_expr_coll() with expression representing
substr() in order to verify that collations of LHS and RHS are
compatible. So we eventually we get in the same situation.
> Yeah. I think we need to understand the bug before fixing
> it.
New patch:
sql: fix possible null dereference in sql_expr_coll()
Some built-in functions can accept different number of arguments.
Check of argument count for such functions takes place right before
its execution. So it is possible that expression-list representing
arguments for built-in function is NULL. On the other hand, in
sql_expr_coll() (which returns collation of expression) it is assumed
that if function features SQL_FUNC_DERIVEDCOLL flag (it implies that
resulting collation depends on collation of arguments) then it has at
least one argument. The last assumption is wrong considering for example
SUBSTR() function: it may have 1 or 2 arguments, so check of argument
count doesn't occur during compilation. Hence, if it is required to
calculate collation for SUBSTR() function and there's no arguments,
Tarantool crashes due to null-dereference.
This patch fixes this bug with one additional check in sql_expr_coll().
diff --git a/src/box/sql/expr.c b/src/box/sql/expr.c
index 648b7170e..0bdcfe576 100644
--- a/src/box/sql/expr.c
+++ b/src/box/sql/expr.c
@@ -332,7 +332,8 @@ sql_expr_coll(Parse *parse, Expr *p, bool *is_explicit_coll, uint32_t *coll_id,
sql_func_by_signature(p->u.zToken, arg_count);
if (func == NULL)
break;
- if (sql_func_flag_is_set(func, SQL_FUNC_DERIVEDCOLL)) {
+ if (sql_func_flag_is_set(func, SQL_FUNC_DERIVEDCOLL) &&
+ arg_count > 0) {
/*
* Now we use quite straightforward
* approach assuming that resulting
diff --git a/test/sql/collation.result b/test/sql/collation.result
index 11962ef47..fbc7ce9aa 100644
--- a/test/sql/collation.result
+++ b/test/sql/collation.result
@@ -292,6 +292,15 @@ box.execute("SELECT * FROM t WHERE a COLLATE \"binary\" = c COLLATE \"unicode\";
- null
- Illegal mix of collations
...
+-- Make sure that using function featuring variable arguemnts
+-- length and resulting collation which depends on arguments
+-- is processed correctly.
+--
+box.execute("SELECT * FROM t WHERE a COLLATE \"binary\" = substr();")
+---
+- null
+- 'Wrong number of arguments is passed to SUBSTR(): expected 1 or 2, got 0'
+...
-- Compound queries perform implicit comparisons between values.
-- Hence, rules for collations compatibilities are the same.
--
diff --git a/test/sql/collation.test.lua b/test/sql/collation.test.lua
index 1be28b3ff..a013253cd 100644
--- a/test/sql/collation.test.lua
+++ b/test/sql/collation.test.lua
@@ -80,6 +80,11 @@ box.execute("SELECT * FROM t WHERE b = c;")
box.execute("SELECT * FROM t WHERE b COLLATE \"binary\" = c;")
box.execute("SELECT * FROM t WHERE a = c;")
box.execute("SELECT * FROM t WHERE a COLLATE \"binary\" = c COLLATE \"unicode\";")
+-- Make sure that using function featuring variable arguemnts
+-- length and resulting collation which depends on arguments
+-- is processed correctly.
+--
+box.execute("SELECT * FROM t WHERE a COLLATE \"binary\" = substr();")
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