maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Aleksey!

On Oct 20, Aleksey Midenkov wrote:
> revision-id: 0cd5377e9ff (mariadb-10.2.31-357-g0cd5377e9ff)
> parent(s): dc716da4571
> author: Aleksey Midenkov <midenok@xxxxxxxxx>
> committer: Aleksey Midenkov <midenok@xxxxxxxxx>
> timestamp: 2020-08-17 00:52:35 +0300
> message:
> 
> MDEV-18734 ASAN heap-use-after-free in my_strnxfrm_simple_internal upon update on versioned partitioned table
> 
> update_virtual_fields() may reallocate Field_blob::value buffer due to
> different reasons (f.ex. different types, see
> Field_str::memcpy_field_possible()). But the buffer address may be
> already in m_ordered_rec_buffer which is then used in ordered index
> scan queue.
> 
> The patch updates blob virtual fields when the ordered index scan
> queue is sorted as well as the top record is restored from the queue.
> 
> New VCOL_UPDATE_BLOBS mode is introduced to update only blobs. Swap is
> not needed as it was already done if it was needed.
> 
> Related to ea1b2504

No, I think we need to go deeper here.
The bug is not only not caused by system versioning, it is also not
caused by virtual columns.

The problem is that partitioning copies record[0] out and then back to
save and restore values. This does not work for blobs, because record[0]
may store the pointer to the memory that Field_blob owns and can free or
reallocate as needed.

Normally it's not the problem because typically after row reads the
engine owns the memory, not Field_blob. When a virtual column is set to
a calculated value - then Field_blob owns the memory and we have this
bug.

But there are engines that use field->store() to set values - in this
case Field_blob will own the memory too. Here's a test case with
FederatedX:

=============================================================
source include/have_partition.inc;
source include/have_sequence.inc;
source have_federatedx.inc;
source include/federated.inc;
connection slave;
use federated;
create table t1_1 (x int, b text, key(x));
create table t1_2 (x int, b text, key(x));
connection master;
eval create table t1 (x int, b text, key(x)) engine=federated
  partition by range columns (x) (
  partition p1 values less than (40) connection='mysql://root@127.0.0.1:$SLAVE_MYPORT/federated/t1_1',
  partition pn values less than (maxvalue) connection='mysql://root@127.0.0.1:$SLAVE_MYPORT/federated/t1_2'
);
insert t1 select seq, seq from seq_1_to_35;
insert t1 select seq, repeat(seq, 100) from seq_50_to_90;
flush tables;
select x, b from t1 where x > 30 and x < 60 order by x;
select x, b from t1 where x > 30 and x < 60 order by b;
drop table t1;
connection slave;
drop table t1_1, t1_2;
source include/federated_cleanup.inc;
=============================================================

first select doesn't trigger ASAN error, but it produces incorrect
results (I'm showing it here, so that you could create a non-ASAN test
that could be run on all builders).

the second select gets the same ASAN error as your test below.

> diff --git a/mysql-test/suite/vcol/r/partition.result b/mysql-test/suite/vcol/r/partition.result
> index bd1353fa145..74c3c3394dc 100644
> --- a/mysql-test/suite/vcol/r/partition.result
> +++ b/mysql-test/suite/vcol/r/partition.result
> @@ -28,3 +28,26 @@ set statement sql_mode= '' for update t1 set i= 1, v= 2;
>  Warnings:
>  Warning	1906	The value specified for generated column 'v' in table 't1' has been ignored
>  drop table t1;
> +#
> +# MDEV-18734 ASAN heap-use-after-free in my_strnxfrm_simple_internal upon update on versioned partitioned table
> +#
> +# Cover queue_fix() in ha_partition::handle_ordered_index_scan()
> +create table t1 (
> +x int auto_increment primary key,
> +b text, v mediumtext as (b) virtual,
> +index (v(10))
> +) partition by range columns (x) (
> +partition p1 values less than (3),
> +partition p2 values less than (6),
> +partition pn values less than (maxvalue));
> +insert into t1 (b) values ('q'), ('a'), ('b');
> +update t1 set b= 'bar' where v > 'a';
> +drop table t1;

this test above doesn't cause ASAN failures for me without your fix.
the test below fails all right.

> +# Cover return_top_record() in ha_partition::handle_ordered_index_scan()
> +create table t1 (x int primary key, b tinytext, v text as (b) virtual)
> +partition by range columns (x) (
> +partition p1 values less than (4),
> +partition pn values less than (maxvalue));
> +insert into t1 (x, b) values (1, ''), (2, ''), (3, 'a'), (4, 'b');
> +update t1 set b= 'bar' where x > 0 order by v limit 2;
> +drop table t1;

Regards,
Sergei
VP of MariaDB Server Engineering
and security@xxxxxxxxxxx