Elysian Shadows

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// Send and receive the DNSRequest message
void Send_Receive_DNSRequest(struct DNS_BEGIN* bmsg, unsigned char* buffer, char* argvone)
{
    int res, size, sockfd, sizeof_serv_addr;
    struct sockaddr_in serv_addr;
    struct hostent* server;
    unsigned char* url;

    // allocate memory for the buffer
    buffer = (unsigned char*) malloc( sizeof(unsigned char) * BUFFER_SIZE);

    // clear buffer
    bzero(buffer, BUFFER_SIZE);

    // set bmsg to point to the beginning of the buffer
    bmsg = (struct DNS_BEGIN*)buffer;

    // add to size
    // The size of the struct DNS_BEGIN is 24
    size =  sizeof(struct DNS_BEGIN); 

    // set the url to point to the correct spot in the buffer
    // This sets the url to point 12 bytes into buffer
    url = (unsigned char*)(buffer + size/2);

    // The size of the struct DNS_BEGIN is 24
    ...
}

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    // Convert the address the user provided to the format expected by DNS protocol.
    ConvertHostName_DNSFormat(argvone, (char*)url);

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    // allocate memory for the buffer
    unsigned char* buffer = (unsigned char*) malloc( sizeof(unsigned char) * BUFFER_SIZE);
    unsigned char* url;

    bzero(buffer, BUFFER_SIZE);

    struct myType
    {
       short a;
	    short b;
	    short c;
	    short d;
    };
    // assuming short is 2 bytes on your architecture, sizeof(struct myType) = 8

    struct myType* ptr;

    // set ptr to beginning of buffer pointer
    ptr = (struct myType*) buffer;
    
    // set url to 4 bytes in
    url = &buffer[4];
    
    // attempt to copy "lala" to buffer[4] (buffer[4] is obviously within the first 8 bytes of buffer
    // this will fail to write anything
    strcpy((char*)url, "lala");

Code: Select all

    // allocate memory for the buffer
    unsigned char* buffer = (unsigned char*) malloc( sizeof(unsigned char) * BUFFER_SIZE);
    unsigned char* url;

    bzero(buffer, BUFFER_SIZE);

    struct myType
    {
       short a;
	    short b;
	    short c;
	    short d;
    };
    // assuming short is 2 bytes on your architecture, sizeof(struct myType) = 8

    struct myType* ptr;

    // set ptr to beginning of buffer pointer
    // the only change here is to comment out setting the ptr pointer
    //ptr = (struct myType*) buffer;
    
    // set url to 4 bytes in
    url = &buffer[4];
    
    // attempt to copy "lala" to buffer[4] (buffer[4] is obviously within the first 8 bytes of buffer
    // this will NOT fail since i commented out setting the ptr pointer
    strcpy((char*)url, "lala");