Bug#40281, partitioning the general log table crashes the server

We disallow the partitioning of a log table. You could however
partition a table first, and then point logging to it. This is
not only against the docs, it also crashes the server.

We catch this case now.

mysql-test/r/partition.result:
  results for 40281
mysql-test/t/partition.test:
  test for 40281: show that trying to log to partitioned table fails rather
  to crash the server
sql/ha_partition.cc:
  Signal that we no longer support logging to partitioned tables,
  as per the docs.
sql/sql_partition.cc:
  Some commands like "USE ..." have no select, yet we may try
  to parse partition info after their execution if user set a
  partitioned table as log target. This shouldn't lead to a
  NULL-deref/crash.

mysql-test/r/partition.result

@@ -1991,5 +1991,39 @@ CREATE TABLE t1(id INT,KEY(id)) ENGINE=MYISAM
 PARTITION BY HASH(id) PARTITIONS 2;
 DROP TABLE t1;
 SET SESSION SQL_MODE=DEFAULT;
+
+Bug#40281: partitioning the general log table crashes the server
+
+--- set up partitioned log, and switch to it
+USE mysql;
+SET GLOBAL general_log =0;
+CREATE TABLE gl_partitioned LIKE general_log;
+ALTER TABLE gl_partitioned ENGINE=myisam;
+ALTER TABLE gl_partitioned PARTITION BY HASH (thread_id) PARTITIONS 10;
+ALTER TABLE general_log RENAME TO gl_nonpartitioned;
+ALTER TABLE gl_partitioned RENAME TO general_log;
+SELECT @@global.log_output INTO @old_glo;
+SET GLOBAL log_output='table';
+SET GLOBAL general_log =1;
+--- do some things to be logged to partitioned log, should fail
+USE /* 1 */ test;
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (1);
+SELECT * FROM t1;
+i
+1
+USE mysql;
+SET GLOBAL general_log =0;
+ALTER TABLE general_log RENAME TO gl_partitioned;
+ALTER TABLE gl_nonpartitioned RENAME TO general_log;
+--- show whether we actually logged anything (no) to general_log
+SELECT COUNT(argument) FROM gl_partitioned;
+COUNT(argument)
+0
+DROP TABLE gl_partitioned;
+SET GLOBAL log_output=@old_glo;
+SET GLOBAL general_log =1;
+USE /* 2 */ test;
+DROP TABLE t1;
 End of 5.1 tests
 SET @@global.general_log= @old_general_log;

mysql-test/t/partition.test

@@ -1987,6 +1987,53 @@ CREATE TABLE t1(id INT,KEY(id)) ENGINE=MYISAM
 DROP TABLE t1;
 SET SESSION SQL_MODE=DEFAULT;
 
+--echo
+--echo Bug#40281: partitioning the general log table crashes the server
+--echo
+
+--echo --- set up partitioned log, and switch to it
+
+USE mysql;
+SET GLOBAL general_log =0;
+CREATE TABLE gl_partitioned LIKE general_log;
+ALTER TABLE gl_partitioned ENGINE=myisam;
+ALTER TABLE gl_partitioned PARTITION BY HASH (thread_id) PARTITIONS 10;
+ALTER TABLE general_log RENAME TO gl_nonpartitioned;
+ALTER TABLE gl_partitioned RENAME TO general_log;
+
+SELECT @@global.log_output INTO @old_glo;
+SET GLOBAL log_output='table';
+SET GLOBAL general_log =1;
+
+--echo --- do some things to be logged to partitioned log, should fail
+USE /* 1 */ test;
+
+CREATE TABLE t1 (i INT);
+
+connect (master,127.0.0.1,root,,test,$MASTER_MYPORT,);
+connection master;
+INSERT INTO t1 VALUES (1);
+SELECT * FROM t1;
+disconnect master;
+
+connection default;
+
+USE mysql;
+SET GLOBAL general_log =0;
+ALTER TABLE general_log RENAME TO gl_partitioned;
+ALTER TABLE gl_nonpartitioned RENAME TO general_log;
+
+--echo --- show whether we actually logged anything (no) to general_log
+SELECT COUNT(argument) FROM gl_partitioned;
+
+DROP TABLE gl_partitioned;
+
+SET GLOBAL log_output=@old_glo;
+SET GLOBAL general_log =1;
+
+USE /* 2 */ test;
+DROP TABLE t1;
+
 --echo End of 5.1 tests
 
 SET @@global.general_log= @old_general_log;

sql/ha_partition.cc

@@ -5381,6 +5381,13 @@ int ha_partition::extra(enum ha_extra_function operation)
     /* Currently only NDB use the *_CANNOT_BATCH */
     break;
   }
+  /*
+    http://dev.mysql.com/doc/refman/5.1/en/partitioning-limitations.html
+    says we no longer support logging to partitioned tables, so we fail
+    here.
+  */
+  case HA_EXTRA_MARK_AS_LOG_TABLE:
+    DBUG_RETURN(ER_UNSUPORTED_LOG_ENGINE);
   default:
   {
     /* Temporary crash to discover what is wrong */

sql/sql_partition.cc

@@ -3824,8 +3824,13 @@ bool mysql_unpack_partition(THD *thd,
     Item_field objects.
     This is not a nice solution since if the parser uses current_select
     for anything else it will corrupt the current LEX object.
+    Also, we need to make sure there even is a select -- if the statement
+    was a "USE ...", current_select will be NULL, but we may still end up
+    here if we try to log to a partitioned table. This is currently
+    unsupported, but should still fail rather than crash!
   */
-  thd->lex->current_select= old_lex->current_select; 
+  if (!(thd->lex->current_select= old_lex->current_select))
+    goto end;
   /*
     All Items created is put into a free list on the THD object. This list
     is used to free all Item objects after completing a query. We don't