python3 stack smashing - python extending with c

Question

I am writing a python extension in C. There is a library for a raspberry hw dev board in C so I'm using that. So I'm exporting a function from C to python and at the end of the call, python falls over saying *** stack smashing detected ***: python3 terminated.

python call:

print("self.handle="+str(self.handle))
ret=dcc.dcc_send(self.handle, d[0], d[1], d[2], d[3], d[4], d[5])
print("returned: "+str(ret)) # never gets here

C python export (finishes):

static PyObject* dcc_send(PyObject* self, PyObject* args) {
    unsigned char handle, count, b1, b2, b3, b4, b5;

    if (!PyArg_ParseTuple(args, "iiiiiii", &handle, &count, &b1, &b2, &b3, &b4, &b5))
            return NULL;

    printf("1234-handle: %d\n", handle);

    int ret = -1;
    ret = send_command(handle, count, b1, b2, b3, b4, b5);

    printf("1235-after-send_command-return: %d\n", ret);

    //Py_RETURN_NONE;
    return Py_BuildValue("i", ret);
}

Another call in the stack:

int send_command(int handle, unsigned char count, unsigned char b1, unsigned char b2, unsigned char b3, unsigned char b4, unsigned char b5) {
    unsigned char message[10];
    message[0] = CMD_START_VAL;
    message[1] = CMD_DCC_MESS;
    message[2] = 0;
    message[3] = 0xF0 | count; //2 byte size
    message[4] = b1;
    message[5] = b2;
    message[6] = b3;
    message[7] = b4;
    message[8] = b5;
    message[9] = CMD_STOP_VAL;
    return write_uart(handle, message,10);
}

Final call in the stack (I didn't write that completely, I just took it from the lib and fixed a few things in it like invalid memory access that used to be there):

int write_uart(int handle, unsigned char *data,int bytes) {
    #ifdef TEST
    int length = bytes;
    printf("handle: %d\n", handle);
    printf("bytes: %d\ndata: ", length);
    for (int i=0; i<length; ++i)
        printf("%d ", (int) data[i]);
    printf("\n---\n");
    #endif
    int txed;
    int offset=0;
    while (length) {
        txed = write(handle, (unsigned char*)data+offset, length);
        if (txed==-1) {
            fprintf(stderr,"UART WRITE ERRROR!!\n");
            return 0;
        }
        length -= txed;
        offset += txed;
    }
    tcdrain(handle);
    return 1;
}

When I run it, I get this:

self.handle=3
1234-handle: 3
handle: 3
bytes: 10
data: 160 25 0 242 47 130 0 0 0 80
---
1235-after-send_command-return: 1
*** stack smashing detected ***: python3 terminated
Aborted

What am I doing wrong? Thanks

Answer 1

As squeamish ossifrage said, the problem was in using 'iiiiiii' for a char type. Then when the function finished and returned the stack pointer, it was way off and the app crashed.