MySQL Trouble transitioning from Injection to Paramterization - c++

Question

I have the following code here that executes a query. Originally, I used SQL Injection to return row results. Hearing I should use parametrization, I rearranged my code and read the MySQL docs on how to do so. I'm using MySQL's C library in a C++ application.
However, it's not returning the results.
I know my SQL statement is 100% fine. It has been tested. The only thing I changed was changing %d (injection) to ?, which accepts the player's ID.
This returns -1. It's a SELECT statement though, so maybe it's normal?
// Get the number of affected rows
affected_rows = mysql_stmt_affected_rows(m_stmt);
This returns 2. This is correct. I have two fields being returned.
// Store the field count
m_fieldCount = mysql_field_count(&m_conn);
This returns 0 (success)
if (mysql_stmt_store_result(m_stmt))
Finally, this returns null.
m_result = mysql_store_result(&m_conn);
I need m_result so I can read the rows. "mysql_stmt_store_result" sounds similar, but doesn't return MYSQL_RESULT.
m_result = mysql_store_result(&m_conn);
/// <summary>
/// Executes a query.
/// </summary>
/// <param name="query">The query to execute.</param>
/// <returns>Returns true on success, else false.</returns>
bool SQLConnection::executeQuery_New(const char *query)
{
int param_count = 0;
int affected_rows = 0;
// Validate connection.
if (!m_connected)
return false;
// Initialize the statement
m_stmt = mysql_stmt_init(&m_conn);
if (!m_stmt) {
fprintf(stderr, " mysql_stmt_init(), out of memory\n");
return false;
}
// Prepare the statement
if (mysql_stmt_prepare(m_stmt, query, strlen(query))) {
fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n");
fprintf(stderr, " %s\n", mysql_stmt_error(m_stmt));
return false;
}
// Get the parameter count from the statement
param_count = mysql_stmt_param_count(m_stmt);
if (param_count != m_bind.size()) {
fprintf(stderr, " invalid parameter count returned by MySQL\n");
return false;
}
// Bind buffers
// The parameter binds are stored in std::vector<MYSQL_BIND>
// I need to convert std::vector<MYSQL_BIND> m_bind to MYSQL_BIND *bnd
MYSQL_BIND *bind = new MYSQL_BIND[m_bind.size() + 1];
memset(bind, 0, sizeof(bind) * m_bind.size());
for (int i = 0; i < param_count; i++)
bind[i] = m_bind[i];
if (mysql_stmt_bind_param(m_stmt, &bind[0]))
{
fprintf(stderr, " mysql_stmt_bind_param() failed\n");
fprintf(stderr, " %s\n", mysql_stmt_error(m_stmt));
return false;
}
// Execute the query
if (mysql_stmt_execute(m_stmt)) {
fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
fprintf(stderr, " %s\n", mysql_stmt_error(m_stmt));
return false;
}
// Get the number of affected rows
affected_rows = mysql_stmt_affected_rows(m_stmt);
//if (affected_rows == -1) {
// fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
// fprintf(stderr, " %s\n", mysql_stmt_error(m_stmt));
// return false;
//}
// Store the field count
m_fieldCount = mysql_field_count(&m_conn);
// Store the result
if (mysql_stmt_store_result(m_stmt))
{
fprintf(stderr, " failed retrieving result\n");
fprintf(stderr, " %s\n", mysql_error(&m_conn));
int d = mysql_errno(&m_conn);
return false;
}
// This looks similar to the last above statement, but I need m_result. I used mysql_store_result earlier when using injection and it worked fine, but here in this case it returns null.
m_result = mysql_store_result(&m_conn);
// Close the statement
if (mysql_stmt_close(m_stmt)) {
/* mysql_stmt_close() invalidates stmt, so call */
/* mysql_error(mysql) rather than mysql_stmt_error(stmt) */
fprintf(stderr, " failed while closing the statement\n");
fprintf(stderr, " %s\n", mysql_error(&m_conn));
return false;
}
// Delete bind array
if (bind) {
delete[] bind;
bind = NULL;
}
return true;
}
How I'm adding an int parameter (player's id):
void SQLConnection::addParam(int buffer, enum_field_types type, unsigned long length)
{
MYSQL_BIND bind;
memset(&bind, 0, sizeof(bind));
bind.buffer = (char *)&buffer;
bind.buffer_type = type;
bind.is_null = 0;
bind.length = &length;
m_bind.push_back(bind);
}
My variables and their types:
class SQLConnection
{
private:
MYSQL m_conn;
MYSQL_ROW m_row;
MYSQL_RES *m_result;
char m_errorMessage[ERROR_MSG_MAX];
bool m_connected;
MYSQL_STMT *m_stmt;
std::vector<MYSQL_BIND> m_bind;
int m_fieldCount;
// ...
And finally its calling function at the end of the SQL statement:
...WHERE player_id = ?;");
conn.addParam(m_id, MYSQL_TYPE_LONGLONG, 0);
if (!conn.executeQuery_New(buffer)) {
conn.close();
return "";
}
// Close the connection.
conn.close();
std::string s = conn.getField("max_value_column_name");
The error code I get is 2014:
https://dev.mysql.com/doc/refman/5.7/en/commands-out-of-sync.html
Just for the sake of interest, this is a prior function I used. This worked fine for injection. Using the new function above with parameterization is the one causing the issues.
bool SQLConnection::executeQuery(const char *query)
{
// Validate connection.
if (!m_connected)
return false;
// Execute the query
int status = mysql_query(&m_conn, query);
if (status != 0) {
sprintf(m_errorMessage, "Error: %s", mysql_error(&m_conn));
return false;
}
// Store the result
m_result = mysql_store_result(&m_conn);
return true;
}
After I started having language religious wars in my head about using C# over C++, I thought I'd give one last attempt here. Any help is appreciated.
Edit:
This is how I read in column names prior to parameterization (maybe this code needs to be updated after calling mysql_stmt_store_result(m_stmt)?
std::string SQLConnection::getField(const char *fieldName)
{
MYSQL_FIELD *field = NULL;
unsigned int name_field = 0;
mysql_stmt_data_seek(m_stmt, 0);
mysql_stmt_fetch_column(m_stmt, &bind, 0, 0);
//mysql_data_seek(m_result, 0);
//mysql_field_seek(m_result, 0);
const unsigned int num_fields = mysql_stmt_field_count(m_stmt);
// const unsigned int num_fields = mysql_num_fields(m_result);
std::vector<char *> headers(num_fields);
for (unsigned int i = 0; (field = mysql_fetch_field(m_result)); i++)
{
headers[i] = field->name;
if (strcmp(fieldName, headers[i]) == 0)
name_field = i;
}
while ((m_row = mysql_fetch_row(m_result))) {
return std::string(m_row[name_field]);
}
return "";
}
Edit:
What I'm finding is in this last function there are equivalent functions for statements, like mysql_num_fields() is mysql_stmt_field_count(). I'm thinking these need to be updated because it's using m_stmt and not m_result anymore, which gives reason to update the functions so m_stmt is used. It's not very apparent how to update the second half of the function though.

Answer 1

You may need a better understanding of how stmt works.You can't get the final results by mysql_store_result() when you're using stmt.
You shoud bind several buffers for the statement you're using to accept the result set. You can finish this by mysql_stmt_bind_result(), just like mysql_stmt_bind_param().
Then you can use the buffers bound by mysql_stmt_bind_result() to return row data. You can finish this by mysql_stmt_fetch().
Do the fetch method repeatedly, so you can get the whole result set row by row.
The basic sequence of calls:
mysql_stmt_init
mysql_stmt_prepare
mysql_stmt_bind_param
mysql_stmt_execute
mysql_stmt_bind_result
mysql_stmt_store_result
mysql_stmt_fetch (repeatedly, row by row)
mysql_stmt_free_result
It works for me.
It's a long time since I finished this part of my project, you'd better read the manual carefully and find more examples of stmt.
Sorry for my poor English. Good luck!