Hi, Sachin!

Great work!

On Mar 27, Sachin Setiya wrote:
> revision-id: 710756527ec8589bce33bc834a1d8e6604266b6d (mariadb-10.1.31-47-g7107565)
> parent(s): 8152c52e1af608da5d288a4e6fc82e2d804e64cd
> author: Sachin Setiya
> committer: Sachin Setiya
> timestamp: 2018-03-27 04:24:57 +0530
> message:
>
> MDEV-10259 mysqld crash with certain statement length and...
> order with Galera and encrypt-tmp-files=1
>
> Problem:- If trans_cache (IO_CACHE) uses encrypted tmp file
> then on next DML server will crash.
>
> Case:-
>  Lets take a case , we have a table t1 , We try to do 2 inserts in t1
>   1. A really long insert so that trans_cache has to use temp_file
>   2. Just a small insert
>
> Analysis:- Actually server crashes from inside of galera
> library.
> /lib64/libc.so.6(abort+0x175)[0x7fb5ba779dc5]
> /usr/lib64/galera/libgalera_smm.so(_ZN6galera3FSMINS_9TrxHandle5State...
> mysys/stacktrace.c:247(my_print_stacktrace)[0x7fb5a714940e]
> sql/signal_handler.cc:160(handle_fatal_signal)[0x7fb5a715c1bd]
> sql/wsrep_hton.cc:257(wsrep_rollback)[0x7fb5bcce923a]
> sql/wsrep_hton.cc:268(wsrep_rollback)[0x7fb5bcce9368]
> sql/handler.cc:1658(ha_rollback_trans(THD*, bool))[0x7fb5bcd4f41a]
> sql/handler.cc:1483(ha_commit_trans(THD*, bool))[0x7fb5bcd4f804]
>
> but actual issue is not in galera but in mariadb, because for 2nd
> insert we should never call rollback. We are calling rollback because
> log_and_order fails it fails because write_cache fails , It fails
> because after reinit_io_cache(trans_cache) , my_b_tell says 0 so we
> look into tmp_file for data , which is obviously wrong since temp
> was used for previous insert and it no longer exist.

Add here something like:

  wsrep_write_cache_inc() reads the IO_CACHE in a loop, filling it with
  my_b_fill() until it returns "0 bytes read". Later
  MYSQL_BIN_LOG::write_cache() does the same.  wsrep_write_cache_inc()
  assumes that reading a zero bytes past EOF leaves the old data in the
  cache. Let's do that.

> diff --git a/sql/mf_iocache_encr.cc b/sql/mf_iocache_encr.cc
> index 149e6fe..41e1333 100644
> --- a/sql/mf_iocache_encr.cc
> +++ b/sql/mf_iocache_encr.cc
> @@ -49,8 +49,7 @@ static int my_b_encr_read(IO_CACHE *info, uchar *Buffer, size_t Count)
> 
>    if (pos_in_file == info->end_of_file)
>    {

here, a comment: /* reading past EOF should not empty the cache */

> -    info->read_pos= info->read_end= info->buffer;
> -    info->pos_in_file= pos_in_file;
> +    info->read_pos= info->read_end;
>      info->error= 0;
>      DBUG_RETURN(MY_TEST(Count));
>    }

and add a test for it into unittest/sql/mf_iocache-t.cc. Something
simple, like, write into a cache, reinit to READ, fill, fill, reinit to
READ, verify the data is still there.

Regards,
Sergei
Chief Architect MariaDB
and security@mariadb.org