/gs option causing program to throw exception

Question

Recently, I've been trying to make a little test program to communicate with a MySQL server in C++. I'm currently using MySQL Connector/C++ as my API to connect to my database server. It took me a very long time to get it running, because oracle/mysql has little to no documentation of how to use connector/c++ with Visual Studio 10+.

Finally after getting everything working, there seems to be some issue when the application tries to exit. It throws the following unhandled exception:

Unhandled exception at 0x00C62291 in mysql2.exe: Stack cookie instrumentation code detected a stack-based buffer overrun.

After researching about the error, I figured out it was due to the "security check" option (/gs compiler option). When I disable this compiler option, the application exits gracefully.

I have a feeling that I should not turn it off, as it is the default option in Visual Studio 2012 (and possibly other versions?)

My questions are:

• Why is this /gs compiler option causing the unhandled exception?
• Is it safe or okay to turn off the /gs compiler option?

Here is the piece of code the unhandled exception points to (inside a file, called: gs_report.c):

#if defined (_M_IX86) || defined (_M_X64)
    if (IsProcessorFeaturePresent(PF_FASTFAIL_AVAILABLE))
#endif  /* defined (_M_IX86) || defined (_M_X64) */
    __fastfail(FAST_FAIL_STACK_COOKIE_CHECK_FAILURE);

Here is my application code:

/* Standard C++ includes */
#include <stdlib.h>
#include <iostream>

/*
Include directly the different
headers from cppconn/ and mysql_driver.h + mysql_util.h
(and mysql_connection.h). This will reduce your build time!
*/
#include "mysql_connection.h"
#include "mysql_driver.h"

#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/prepared_statement.h>

using namespace std;

int main(void)
{
    cout << endl;
    cout << "Let's have MySQL count from 10 to 1..." << endl;

    try {
        sql::Driver *driver;
        sql::Connection *con;
        sql::Statement *stmt;
        sql::ResultSet *res;
        sql::PreparedStatement *pstmt;

        /* Create a connection */
        driver = sql::mysql::get_driver_instance();
        con = driver->connect("tcp://127.0.0.1:3306", "root", "MSxa5y");
        /* Connect to the MySQL test database */
        con->setSchema("test");

        stmt = con->createStatement();
        stmt->execute("DROP TABLE IF EXISTS test");
        stmt->execute("CREATE TABLE test(id INT)");
        delete stmt;

        /* '?' is the supported placeholder syntax */
        pstmt = con->prepareStatement("INSERT INTO test(id) VALUES (?)");
        for (int i = 1; i <= 10; i++) {
            pstmt->setInt(1, i);
            pstmt->executeUpdate();
        }
        delete pstmt;

        /* Select in ascending order */
        pstmt = con->prepareStatement("SELECT id FROM test ORDER BY id ASC");
        res = pstmt->executeQuery();

        /* Fetch in reverse = descending order! */
        res->afterLast();
        while (res->previous())
            cout << "\t... MySQL counts: " << res->getInt("id") << endl;
        delete res;

        delete pstmt;
        delete con;

    } catch (sql::SQLException &e) {
        cout << "# ERR: SQLException in " << __FILE__;
        cout << "() on line " << __LINE__ << endl;
        cout << "# ERR: " << e.what();
        cout << " (MySQL error code: " << e.getErrorCode();
        cout << ", SQLState: " << e.getSQLState() << " )" << endl;
    }

    cout << endl;

    return EXIT_SUCCESS;
}

Answer 1

The /gs option is allowing the runtime to detect an error in your program. Removing the option allows the program to exit without detecting it, but the error is still there. Somewhere in your code or the libraries, memory on the stack is being overwritten. I'd try a binary search on the code to see which statement is leading to the error. You may also want to always check the return value from all of your database calls.

You definitely should not disable this option. Doing so will hide real errors and may leave your program open to hacking.