MDEV-24827: MariaDB 10.5.5 crash (sig 11) during a SELECT

Running a query using cursor could lead to a server crash on
building a temporary table used for handling the query.

For example, the following cursor

DECLARE cur1 CURSOR FOR
  SELECT t2.c1 AS c1 FROM t1 LEFT JOIN t2 ON t1.c1 = t2.c1
  WHERE EXISTS (SELECT 1 FROM t1 WHERE c2 = -1) ORDER BY c1;

declared and executed inside a stored routine could result in server
crash on creating a temporary table used for handling the ORDER BY clause.

Crash occurred on attempt to create the temporary table's fields based
on fields whose data located in a memory root that already freed.

It happens inside the function return_zero_rows() where the method
Select_materialize::send_result_set_metadata() is invoked for cursor case.
This method calls the st_select_lex_unit::get_column_types() in order to
get a list of items with types of columns for the temporary table being created.
The method st_select_lex_unit::get_column_types() returns
  first_select()->join->fields
in case it is invoked for a cursor. Unfortunately, this memory has been already
deallocated bit earlier by calling
  join->join_free();
inside the function return_zero_rows().

In case the query listed in the example is run in conventional way (without
using cursor) the method st_select_lex_unit::get_column_types()
returns first_select()->item_list that is not touched by invocation
of the method join->join_free() so everything is fine for that.

So, to fix the issue the resources allocated for the JOIN class should be
released after any activities with the JOIN class has been completed,
that is as the last statement before returning from the function
return_zero_rows().

This patch includes tests both for the case when a cursor is run explicitly
from within a stored routine and for the case when a cursor is opened
implicitly as prescribed by the STMT_ATTR_CURSOR_TYPE attribute of
binary protocol (the case of prepared statement).

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/mysql_client_test.c b/tests/mysql_client_test.c
index ac9c06ac94b..acd9b61327b 100644
--- a/tests/mysql_client_test.c
+++ b/tests/mysql_client_test.c
@@ -19962,6 +19962,58 @@ static void test_mdev_26145()
   myquery(rc);
 }
 
+static void test_mdev24827()
+{
+  int rc;
+  MYSQL_STMT *stmt;
+  unsigned long cursor = CURSOR_TYPE_READ_ONLY;
+
+  myheader("test_mdev24827");
+
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t1");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t2");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT)");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "CREATE TABLE t2 (c1 INT PRIMARY KEY, c2 INT, "
+                  "KEY idx_c2(c2))");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "INSERT INTO t1 (c1, c2) "
+                  "SELECT seq, seq FROM seq_1_to_10000");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "INSERT INTO t2 (c1, c2) "
+                  "SELECT seq, seq FROM seq_1_to_20000");
+  myquery(rc);
+
+  const char* query=
+      "SELECT t2.c1 AS c1 FROM t1 LEFT JOIN t2 ON t1.c1 = t2.c1 "
+      "WHERE EXISTS (SELECT 1 FROM t1 WHERE c2 = -1) ORDER BY c1";
+
+  stmt= mysql_stmt_init(mysql);
+  check_stmt(stmt);
+
+  rc= mysql_stmt_prepare(stmt, query, strlen(query));
+  check_execute(stmt, rc);
+
+  rc= mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, &cursor);
+  check_execute(stmt, rc);
+
+  rc= mysql_stmt_execute(stmt);
+  check_execute(stmt, rc);
+
+  rc= mysql_query(mysql, "DROP TABLE t1");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "DROP TABLE t2");
+  myquery(rc);
+}
+
 #ifndef EMBEDDED_LIBRARY
 #define MDEV19838_MAX_PARAM_COUNT 32
 #define MDEV19838_FIELDS_COUNT 17
@@ -20112,6 +20164,7 @@ static void test_mdev19838()
 #endif // EMBEDDED_LIBRARY
 
 static struct my_tests_st my_tests[]= {
+  { "test_mdev24827", test_mdev24827 },
   { "test_mdev_26145", test_mdev_26145 },
   { "disable_query_logs", disable_query_logs },
   { "test_view_sp_list_fields", test_view_sp_list_fields },