#include #include #include #include #include //#include //#include //#include #include "dns.h" #include #include void change_to_DNS_name_format(unsigned char* dns, unsigned char* host); char* read_name(unsigned char* reader, unsigned char* buffer, int* count); // DNS code copied from // https://gist.github.com/fffaraz/9d9170b57791c28ccda9255b48315168 /* DNS header struct */ struct DNS_HEADER { unsigned short id; // ID number unsigned char rd : 1; // recursion unsigned char tc : 1; // truncated message unsigned char aa : 1; // authoritive answer unsigned char opcode : 4; // message purpose unsigned char qr : 1; // query response unsigned char rcode : 4; // response code unsigned char cd : 1; // checking disabled unsigned char ad : 1; // authenticated data unsigned char z : 1; // reserved for future use unsigned char ra : 1; // recursion available unsigned short q_count; // number of question entrise unsigned short ans_count; // number of answer entries unsigned short auth_count; // number of authority entries unsigned short add_count; // number of resource entries }; /* structured for query structure */ struct QUESTION { unsigned short qtype; unsigned short qclass; }; /* Query structure */ struct QUERY { unsigned char* name; struct QUESTION* ques; }; /* Constant sized fields of record structure */ #pragma pack(push, 1) struct R_DATA { unsigned short type; unsigned short _class; unsigned int ttl; unsigned short data_len; }; #pragma pack(pop) /* Pointers to record components */ struct RES_RECORD { char* name; struct R_DATA resource; char* rdata; }; // Test server dns_ip as IPv4 string for hostname // Writes received packet to buf, which is supplied and returns time for request struct timespec resolve(unsigned char* buf, char* hostname, char* dns_ip, int query_type) { int s, i; struct sockaddr_in dest; unsigned char* qname; struct DNS_HEADER* dns = (struct DNS_HEADER*)buf; struct QUESTION* qinfo; struct timespec start, end, total, timeout; timeout.tv_nsec = 0; timeout.tv_sec = 1; s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); setsockopt( s, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(struct timespec)); // use a 1 second timeout for receiving, // should be more than enough and anything // more is really bad dest.sin_family = AF_INET; dest.sin_port = htons(53); dest.sin_addr.s_addr = inet_addr(dns_ip); // dns packet header dns->id = (unsigned short)htons(getpid()); dns->qr = 0; // make query dns->opcode = 0; // standard query dns->aa = 0; // not authoritive dns->tc = 0; // not trucated dns->rd = 1; // want recursion dns->ra = 0; // recursion not available dns->z = 0; dns->ad = 0; dns->cd = 0; dns->rcode = 0; dns->q_count = htons(1); // one question dns->ans_count = 0; dns->auth_count = 0; dns->add_count = 0; // dns packet query qname = (unsigned char*)&buf[sizeof(struct DNS_HEADER)]; change_to_DNS_name_format(qname, (unsigned char*)hostname); qinfo = (struct QUESTION*)&buf[sizeof(struct DNS_HEADER) + strlen((const char*)qname) + 1]; qinfo->qtype = htons( query_type); // type of query from argument (A,AAAA,MX,CNAME,NS,...) qinfo->qclass = htons(1); // internet class // send request // return less than 0 is a fail clock_gettime(CLOCK_MONOTONIC, &start); i = sendto(s, (char*)buf, sizeof(struct DNS_HEADER) + strlen((const char*)qname) + 1 + sizeof(struct QUESTION), 0, (struct sockaddr*)&dest, sizeof(dest)); if (i >= 0) { // receive response // negative return is a fail i = sizeof(dest); i = recvfrom(s, (char*)buf, 65536, 0, (struct sockaddr*)&dest, (socklen_t*)&i); clock_gettime(CLOCK_MONOTONIC, &end); } // Make sure packet was returned if (i == -1) total.tv_nsec = -1; else total.tv_sec = end.tv_sec - start.tv_sec; if ((end.tv_nsec - start.tv_nsec) < 0) total.tv_nsec = start.tv_nsec - end.tv_nsec; else total.tv_nsec = end.tv_nsec - start.tv_nsec; close(s); return total; } // Print dns packet content, not terribly reliable but works for testing resolve // with A requests void print_packet(unsigned char* buf) { struct RES_RECORD answers[20], auth[20], addit[20]; struct DNS_HEADER* dns; struct sockaddr_in a; unsigned char *qname = buf + sizeof(struct DNS_HEADER), *reader; int stop, i, j; dns = (struct DNS_HEADER*)buf; reader = &buf[sizeof(struct DNS_HEADER) + strlen((const char*)qname) + 1 + sizeof(struct QUESTION)]; printf("Response contains %d Qs, %d ans, %d auth serv, %d add reconds\n", ntohs(dns->q_count), ntohs(dns->ans_count), ntohs(dns->auth_count), ntohs(dns->add_count)); stop = 0; // read answers for (i = 0; i < ntohs(dns->ans_count); i++) { answers[i].name = read_name(reader, buf, &stop); reader = reader + stop; memcpy(&(answers[i].resource), reader, sizeof(struct R_DATA)); reader = reader + sizeof(struct R_DATA); if (ntohs(answers[i].resource.type) == T_A) { // IPv4 address answers[i].rdata = (char*)malloc(ntohs(answers[i].resource.data_len)); for (j = 0; j < ntohs(answers[i].resource.data_len); j++) { answers[i].rdata[j] = reader[j]; } answers[i].rdata[ntohs(answers[i].resource.data_len)] = '\0'; reader = reader + ntohs(answers[i].resource.data_len); } else { answers[i].rdata = read_name(reader, buf, &stop); reader = reader + stop; } } // read authorities for (i = 0; i < ntohs(dns->auth_count); i++) { auth[i].name = read_name(reader, buf, &stop); reader += stop; memcpy(&(auth[i].resource), reader, sizeof(struct R_DATA)); reader += sizeof(struct R_DATA); auth[i].rdata = read_name(reader, buf, &stop); reader += stop; } // read additional for (i = 0; i < ntohs(dns->add_count); i++) { addit[i].name = read_name(reader, buf, &stop); reader += stop; memcpy(&(addit[i].resource), reader, sizeof(struct R_DATA)); reader += sizeof(struct R_DATA); if (ntohs(addit[i].resource.type) == 1) { addit[i].rdata = malloc(ntohs(addit[i].resource.data_len)); for (j = 0; j < ntohs(addit[i].resource.data_len); j++) addit[i].rdata[j] = reader[j]; addit[i].rdata[ntohs(addit[i].resource.data_len)] = '\0'; reader += ntohs(addit[i].resource.data_len); } else { addit[i].rdata = read_name(reader, buf, &stop); reader += stop; } } // print answers printf("ans recs: %d\n", ntohs(dns->ans_count)); for (i = 0; i < ntohs(dns->ans_count); i++) { printf("name: %s ", answers[i].name); if (ntohs(answers[i].resource.type) == T_A) { // IPv4 long* p; p = (long*)answers[i].rdata; a.sin_addr.s_addr = (*p); printf("has IPv4 addresss: %s", inet_ntoa(a.sin_addr)); } else if (ntohs(answers[i].resource.type) == T_CNAME) { // CNAME printf("has alias: %s", answers[i].rdata); } free(answers[i].name); free(answers[i].rdata); putc('\n', stdout); } // print authorities printf("Auth recs: %d\n", ntohs(dns->auth_count)); for (i = 0; i < ntohs(dns->auth_count); i++) { printf("name: %s ", auth[i].name); if (ntohs(auth[i].resource.type) == 1) { long* p; p = (long*)auth[i].rdata; a.sin_addr.s_addr = *p; printf("has IPv4 address: %s", inet_ntoa(a.sin_addr)); } free(answers[i].name); free(auth[i].rdata); putc('\n', stdout); } printf("Addit recs: %d\n", ntohs(dns->add_count)); for (i = 0; i < ntohs(dns->add_count); i++) { printf("name; %s", addit[i].name); if (ntohs(auth[i].resource.type) == 1) { long* p; p = (long*)addit[i].rdata; a.sin_addr.s_addr = *p; printf("has IPv4 address: %s", inet_ntoa(a.sin_addr)); } else { printf("has %s", addit[i].rdata); } free(answers[i].name); free(addit[i].rdata); putc('\n', stdout); } } // convert from dot format to dns format // eg google.com to 6google3com void change_to_DNS_name_format(unsigned char* dns, unsigned char* host) { int lock = 0; char h[300]; strcpy(h, (char*)host); strcat((char*)h, "."); for (int i = 0; i < strlen(h); i++) { if (h[i] == '.') { *dns++ = i - lock; for (; lock < i; lock++) { *dns++ = h[lock]; } lock++; } } *dns++ = '\0'; } // Convert from dns to dot format char* read_name(unsigned char* reader, unsigned char* buffer, int* count) { char* name; unsigned int p = 0, jumped = 0, offset; int i, j; *count = 1; name = (char*)malloc(256); name[0] = '\0'; while (*reader != 0) { if (*reader >= 192) { offset = (*reader) * 256 + *(reader + 1) - 49152; reader = buffer + offset - 1; jumped = 1; } else { name[p++] = *reader; } reader = reader + 1; if (jumped == 0) { *count = *count + 1; } } name[p] = '\0'; if (jumped == 1) { *count = *count + 1; } // convert from dns format to normal for (i = 0; i < strlen((const char*)name); i++) { p = name[i]; for (j = 0; j < p; j++) { name[i] = name[i + 1]; i++; } name[i] = '.'; } name[i - 1] = '\0'; return name; }