/* Source code for dnsmeddler * This is a little DNS pass-through server * It allows the user to creatively change DNS queries */ #include #include #include #include #include #include #include "scolor.h" // ChatGPT wrote this struct dns_header { unsigned short id; unsigned char qr : 1; unsigned char opcode : 4; unsigned char aa : 1; unsigned char tc : 1; unsigned char rd : 1; unsigned char ra : 1; unsigned char z : 3; unsigned char rcode : 4; unsigned short qdcount; // ChatGPT thought these didn't need to be converted unsigned short ancount; unsigned short nscount; unsigned short arcount; } __attribute__((packed)); // ChatGPT wrote these two functions for me void dns_header_to_network(struct dns_header *header) { header->id = htons(header->id); header->qdcount = htons(header->qdcount); header->ancount = htons(header->ancount); header->nscount = htons(header->nscount); header->arcount = htons(header->arcount); } void dns_header_from_network(struct dns_header *header) { header->id = ntohs(header->id); header->qdcount = ntohs(header->qdcount); header->ancount = ntohs(header->ancount); header->nscount = ntohs(header->nscount); header->arcount = ntohs(header->arcount); } // ChatGPT wrote this too void print_dns_header(const struct dns_header *header) { printf("ID: %u\n", header->id); printf("QR: %u\n", header->qr); printf("Opcode: %u\n", header->opcode); printf("AA: %u\n", header->aa); printf("TC: %u\n", header->tc); printf("RD: %u\n", header->rd); printf("RA: %u\n", header->ra); printf("Z: %u\n", header->z); printf("RCODE: %u\n", header->rcode); printf("QDCOUNT: %u\n", header->qdcount); printf("ANCOUNT: %u\n", header->ancount); printf("NSCOUNT: %u\n", header->nscount); printf("ARCOUNT: %u\n", header->arcount); } // Again, ChatGPT wrote this function /* But it didn't work! Parsed like this: * query for www.microsoft.com came out as www.icrosoftcom (113 bytes) * query for www.google.com came out as www.ooglecom (107 bytes) */ /* size_t parse_domain_name(const char *query_ptr, size_t query_len, char *out_buf, size_t out_buf_len) { size_t i = 0, j = 0; unsigned int label_len = 0; int compressed = 0; // Parse the domain name labels while (i < query_len) { // Check for compression if ((query_ptr[i] & 0xC0) == 0xC0) { // Compressed pointer if (i + 1 >= query_len) { // Malformed packet return 0; } unsigned int offset = ((query_ptr[i] & 0x3F) << 8) | query_ptr[i + 1]; if (offset >= query_len) { // Malformed packet return 0; } if (!compressed) { compressed = 1; label_len += 2; // Add 2 bytes for the compressed pointer } query_ptr = query_ptr + offset - 0xC000; query_len = query_len - offset + 0xC000; i = 0; } else { // Regular label label_len = query_ptr[i]; i++; if (label_len == 0) { break; } if (!compressed) { label_len += 1; // Add 1 byte for the label length field } if (label_len > out_buf_len - j - 1) { // Output buffer too small return 0; } memcpy(out_buf + j, query_ptr + i, label_len); i += label_len; j += label_len; if (!compressed) { out_buf[j - 1] = '.'; // Replace label length with dot separator } } } if (!compressed && j > 0) { // Remove trailing dot separator out_buf[j - 1] = '\0'; j--; } return j; } */ /* ChatGPT added a fix, in this function */ /* We're closer! * www.google.com -> ww.googl.co * www.microsoft.com -> ww.microsof.co * Missing the last letter of each bit of text, basically */ /* size_t parse_domain_name(const char *query_ptr, size_t query_len, char *out_buf, size_t out_buf_len) { size_t i = 0, j = 0; unsigned int label_len = 0; int compressed = 0; // Parse the domain name labels while (i < query_len) { // Check for compression if ((query_ptr[i] & 0xC0) == 0xC0) { // Compressed pointer if (i + 1 >= query_len) { // Malformed packet return 0; } unsigned int offset = ((query_ptr[i] & 0x3F) << 8) | query_ptr[i + 1]; if (offset >= query_len) { // Malformed packet return 0; } if (!compressed) { compressed = 1; label_len += 2; // Add 2 bytes for the compressed pointer } query_ptr = query_ptr + offset - 0xC000; query_len = query_len - offset + 0xC000; i = 0; } else { // Regular label label_len = query_ptr[i]; i++; if (label_len == 0) { break; } if (!compressed) { label_len += 1; // Add 1 byte for the label length field } if (label_len > out_buf_len - j - 1) { // Output buffer too small return 0; } memcpy(out_buf + j, query_ptr + i, label_len - 1); i += label_len - 1; j += label_len - 1; if (!compressed) { out_buf[j - 1] = '.'; // Replace label length with dot separator } } } if (!compressed && j > 0) { // Remove trailing dot separator out_buf[j - 1] = '\0'; j--; } return j; } */ /* Here's ChatGPT's third try! */ /* As far as I can tell, this works correctly * To be perfectly honest, I didn't read it */ size_t parse_domain_name(const char *query_ptr, size_t query_len, char *out_buf, size_t out_buf_len) { size_t i = 0, j = 0; unsigned int label_len = 0; int compressed = 0; // Parse the domain name labels while (i < query_len) { // Check for compression if ((query_ptr[i] & 0xC0) == 0xC0) { // Compressed pointer if (i + 1 >= query_len) { // Malformed packet return 0; } unsigned int offset = ((query_ptr[i] & 0x3F) << 8) | query_ptr[i + 1]; if (offset >= query_len) { // Malformed packet return 0; } if (!compressed) { compressed = 1; label_len += 2; // Add 2 bytes for the compressed pointer } query_ptr = query_ptr + offset - 0xC000; query_len = query_len - offset + 0xC000; i = 0; } else { // Regular label label_len = query_ptr[i]; i++; if (label_len == 0) { break; } if (!compressed) { label_len += 1; // Add 1 byte for the label length field } if (label_len > out_buf_len - j - 1) { // Output buffer too small return 0; } memcpy(out_buf + j, query_ptr + i, label_len - 1); i += label_len - 1; j += label_len - 1; if (!compressed && i < query_len) { // Add dot separator between labels out_buf[j] = '.'; j++; } } } if (!compressed && j > 0) { // Remove trailing dot separator out_buf[j - 1] = '\0'; j--; } return j; } /* ChatGPT wrote all of this except for the verbose system */ #define BUF_SIZE 2048 // Probably bigger than the MTU char verbose = 0; int main() { // Create a UDP socket int sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (sockfd == -1) { perror("socket"); exit(EXIT_FAILURE); } // Bind the socket to port 53 struct sockaddr_in addr = {0}; addr.sin_family = AF_INET; addr.sin_port = htons(53); addr.sin_addr.s_addr = INADDR_ANY; if (bind(sockfd, (struct sockaddr *) &addr, sizeof(addr)) == -1) { perror("bind"); exit(EXIT_FAILURE); } /* * Receive a DNS query * Pass the DNS query to a real DNS server * Receive the result from the real DNS server * Return the result to the client */ for(;;){ main_loop_top: printf(DGREEN("---------------- New Iteration ---------------------\n")); // Wait for a DNS message to arrive char buf[BUF_SIZE]; struct sockaddr_in sender_addr = {0}; socklen_t sender_len = sizeof(sender_addr); ssize_t recv_len = recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *) &sender_addr, &sender_len); if (recv_len == -1) { perror("recvfrom"); exit(EXIT_FAILURE); } // Parse the DNS header struct dns_header header; memcpy(&header, buf, sizeof(header)); dns_header_from_network(&header); // Print the DNS header fields printf("Received DNS message from %s:%u\n", inet_ntoa(sender_addr.sin_addr), ntohs(sender_addr.sin_port)); if(verbose) print_dns_header(&header); // Parse the question section reparse:; char *query_ptr = buf + sizeof(header); size_t remaining_len = recv_len - sizeof(header); for (unsigned int i = 0; i < header.qdcount; i++) { // Parse the domain name char domain_name[256]; size_t domain_name_len = parse_domain_name(query_ptr, remaining_len, domain_name, sizeof(domain_name)); if (domain_name_len == 0) { fprintf(stderr, "Error: Failed to parse domain name in question %u\n", i); exit(EXIT_FAILURE); } // Print the domain name and size printf(PURPLE("Question %u: ")CYAN("%s")" (%lu bytes)\n", i, domain_name, domain_name_len); if(strstr(domain_name, "google")){ printf(YELLOW("Warning: Query is for Google\n")); //goto main_loop_top; memcpy(query_ptr + 5, "reddit", 6); printf(YELLOW("Changed query to reddit\n")); goto reparse; } // Advance the query pointer and update the remaining length query_ptr += domain_name_len + 4; // Add 4 bytes for the query type and query class fields remaining_len -= domain_name_len + 4; } /* At this point, ChatGPT got really slow and stopped, so I guess it went down * So from here on I wrote all of it except the close at the end * You can tell my code from ChatGPT's code because my code is messy and uncommented */ struct sockaddr_in realdns_addr = {AF_INET, htons(53), {0x01010101}}; // 0x01010101 = 1.1.1.1 int realdns_fd = socket(AF_INET, SOCK_DGRAM, 0); if(verbose) printf("Sending off the query to %s port %u\n", inet_ntoa(realdns_addr.sin_addr), ntohs(realdns_addr.sin_port)); ssize_t sendlen = sendto(realdns_fd, buf, recv_len, 0, (struct sockaddr*)(&realdns_addr), sizeof(realdns_addr)); if(verbose) printf("Query send length was %ld bytes\n", sendlen); if(sendlen < 1) printf(RED("Something went wrong with sending\n")); char response[2048]; socklen_t ara_len = sizeof(realdns_addr); if(verbose) printf("Waiting for a response...\n"); // If we don't hear back in 1 second, try again! ssize_t response_length = recvfrom(realdns_fd, response, 2048, 0, (struct sockaddr*)&realdns_addr, &ara_len); if(verbose) printf("Response received, length was %ld bytes\n", response_length); struct dns_header response_header; memcpy(&response_header, response, sizeof(response_header)); dns_header_from_network(&response_header); if(verbose) print_dns_header(&response_header); if(verbose) printf("Sending reply to original client\n"); ssize_t replylen = sendto(sockfd, response, response_length, 0, (struct sockaddr*)(&sender_addr), sender_len); if(verbose) printf("Response sent, length was %lu bytes\n", replylen); if(replylen < 1) printf(RED("Something went wrong with our final reply\n")); } // Clean up close(sockfd); return 0; }