A fix and test case for Bug#8330 "mysql_stmt_execute crashes" (libmysql).

libmysql/libmysql.c:
  Fix for bug#8330 "mysql_stmt_execute crashes": we need to bail out
  from mysql_stmt_execute if mysql->net is occupied with a result set of
  another statement. Otherwise on the next attempt to use net we get
  a crash, as it's freed in case of error.
tests/mysql_client_test.c:
  A test case for Bug#8330 "mysql_stmt_execute craches" (libmysql)

libmysql/libmysql.c

@@ -2467,6 +2467,11 @@ int cli_stmt_execute(MYSQL_STMT *stmt)
       set_stmt_error(stmt, CR_PARAMS_NOT_BOUND, unknown_sqlstate);
       DBUG_RETURN(1);
     }
+    if (stmt->mysql->status != MYSQL_STATUS_READY)
+    {
+      set_stmt_error(stmt, CR_COMMANDS_OUT_OF_SYNC, unknown_sqlstate);
+      DBUG_RETURN(1);
+    }
 
     net_clear(net);				/* Sets net->write_pos */
     /* Reserve place for null-marker bytes */

tests/mysql_client_test.c

@@ -24,6 +24,7 @@
 #include <my_global.h>
 #include <my_sys.h>
 #include <mysql.h>
+#include <errmsg.h>
 #include <my_getopt.h>
 #include <m_string.h>
 
@@ -11532,6 +11533,58 @@ static void test_bug6761(void)
   myquery(rc);
 }
 
+
+/* Bug#8330 - Bug #8330   mysql_stmt_execute crashes (libmysql) */
+
+static void test_bug8330()
+{
+  const char *stmt_text;
+  MYSQL_STMT *stmt[2];
+  int i, rc;
+  char *query= "select a,b from t1 where a=?";
+  MYSQL_BIND bind[2];
+  long lval[2];
+
+  myheader("test_bug8330");
+
+  stmt_text= "drop table if exists t1";
+  /* in case some previos test failed */
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+  stmt_text= "create table t1 (a int, b int)";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  bzero(bind, sizeof(bind));
+  for (i=0; i < 2; i++)
+  {
+    stmt[i]= mysql_stmt_init(mysql);
+    rc= mysql_stmt_prepare(stmt[i], query, strlen(query));
+    check_execute(stmt[i], rc);
+
+    bind[i].buffer_type= MYSQL_TYPE_LONG;
+    bind[i].buffer= (void*) &lval[i];
+    bind[i].is_null= 0;
+    mysql_stmt_bind_param(stmt[i], &bind[i]);
+  }
+
+  rc= mysql_stmt_execute(stmt[0]);
+  check_execute(stmt[0], rc);
+
+  rc= mysql_stmt_execute(stmt[1]);
+  DIE_UNLESS(rc && mysql_stmt_errno(stmt[1]) == CR_COMMANDS_OUT_OF_SYNC);
+  rc= mysql_stmt_execute(stmt[0]);
+  check_execute(stmt[0], rc);
+
+  mysql_stmt_close(stmt[0]);
+  mysql_stmt_close(stmt[1]);
+
+  stmt_text= "drop table t1";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+}
+
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -11739,6 +11792,7 @@ static struct my_tests_st my_tests[]= {
   { "test_conversion", test_conversion },
   { "test_rewind", test_rewind },
   { "test_bug6761", test_bug6761 },
+  { "test_bug8330", test_bug8330 },
   { 0, 0 }
 };