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#include
#include
#include
#include
#include
#include
#include
#include
#define DNS_SVR "211.68.71.4"
#define DNS_HOST 0x01
#define DNS_CNAME 0x05
int socketfd;
struct sockaddr_in dest;
static void
send_dns_request(const char *dns_name);
static void
parse_dns_response();
/**
* Generate DNS question chunk
*/
static void
generate_question(const char *dns_name
, unsigned char *buf , int *len);
/**
* Check whether the current byte is
* a dns pointer or a length
*/
static int
is_pointer(int in);
/**
* Parse data chunk into dns name
* @param chunk The complete response chunk
* @param ptr The pointer points to data
* @param out This will be filled with dns name
* @param len This will be filled with the length of dns name
*/
static void
parse_dns_name(unsigned char *chunk , unsigned char *ptr
, char *out , int *len);
int main(int argc , char *argv[]){
if(argc != 2){
printf("Usage : %s /n" , argv[0]);
exit(-1);
}
socketfd = socket(AF_INET , SOCK_DGRAM , 0);
if(socketfd < 0){
perror("create socket failed");
exit(-1);
}
bzero(&dest , sizeof(dest));
dest.sin_family = AF_INET;
dest.sin_port = htons(53);
dest.sin_addr.s_addr = inet_addr(DNS_SVR);
send_dns_request(argv[1]);
parse_dns_response();
return 0;
}
static void parse_dns_response(){
unsigned char buf[1024];
unsigned char *ptr = buf;
struct sockaddr_in addr;
char *src_ip;
int n , i , flag , querys , answers;
int type , ttl , datalen , len;
char cname[128] , aname[128] , ip[20] , *cname_ptr;
unsigned char netip[4];
size_t addr_len = sizeof(struct sockaddr_in);
n = recvfrom(socketfd , buf , sizeof(buf) , 0
, (struct sockaddr*)&addr , &addr_len);
ptr += 4; /* move ptr to Questions */
querys = ntohs(*((unsigned short*)ptr));
ptr += 2; /* move ptr to Answer RRs */
answers = ntohs(*((unsigned short*)ptr));
ptr += 6; /* move ptr to Querys */
/* move over Querys */
for(i= 0 ; i < querys ; i ++){
for(;;){
flag = (int)ptr[0];
ptr += (flag + 1);
if(flag == 0)
break;
}
ptr += 4;
}
printf("-------------------------------/n");
/* now ptr points to Answers */
for(i = 0 ; i < answers ; i ++){
bzero(aname , sizeof(aname));
len = 0;
parse_dns_name(buf , ptr , aname , &len);
ptr += 2; /* move ptr to Type*/
type = htons(*((unsigned short*)ptr));
ptr += 4; /* move ptr to Time to live */
ttl = htonl(*((unsigned int*)ptr));
ptr += 4; /* move ptr to Data lenth */
datalen = ntohs(*((unsigned short*)ptr));
ptr += 2; /* move ptr to Data*/
if(type == DNS_CNAME){
bzero(cname , sizeof(cname));
len = 0;
parse_dns_name(buf , ptr , cname , &len);
printf("%s is an alias for %s/n" , aname , cname);
ptr += datalen;
}
if(type == DNS_HOST){
bzero(ip , sizeof(ip));
if(datalen == 4){
memcpy(netip , ptr , datalen);
inet_ntop(AF_INET , netip , ip , sizeof(struct sockaddr));
printf("%s has address %s/n" , aname , ip);
printf("/tTime to live: %d minutes , %d seconds/n"
, ttl / 60 , ttl % 60);
}
ptr += datalen;
}
}
ptr += 2;
}
static void
parse_dns_name(unsigned char *chunk
, unsigned char *ptr , char *out , int *len){
int n , alen , flag;
char *pos = out + (*len);
for(;;){
flag = (int)ptr[0];
if(flag == 0)
break;
if(is_pointer(flag)){
n = (int)ptr[1];
ptr = chunk + n;
parse_dns_name(chunk , ptr , out , len);
break;
}else{
ptr ++;
memcpy(pos , ptr , flag);
pos += flag;
ptr += flag;
*len += flag;
if((int)ptr[0] != 0){
memcpy(pos , "." , 1);
pos += 1;
(*len) += 1;
}
}
}
}
static int is_pointer(int in){
return ((in & 0xc0) == 0xc0);
}
static void send_dns_request(const char *dns_name){
unsigned char request[256];
unsigned char *ptr = request;
unsigned char question[128];
int question_len;
generate_question(dns_name , question , &question_len);
*((unsigned short*)ptr) = htons(0xff00);
ptr += 2;
*((unsigned short*)ptr) = htons(0x0100);
ptr += 2;
*((unsigned short*)ptr) = htons(1);
ptr += 2;
*((unsigned short*)ptr) = 0;
ptr += 2;
*((unsigned short*)ptr) = 0;
ptr += 2;
*((unsigned short*)ptr) = 0;
ptr += 2;
memcpy(ptr , question , question_len);
ptr += question_len;
sendto(socketfd , request , question_len + 12 , 0
, (struct sockaddr*)&dest , sizeof(struct sockaddr));
}
static void
generate_question(const char *dns_name , unsigned char *buf , int *len){
char *pos;
unsigned char *ptr;
int n;
*len = 0;
ptr = buf;
pos = (char*)dns_name;
for(;;){
n = strlen(pos) - (strstr(pos , ".") ? strlen(strstr(pos , ".")) : 0);
*ptr ++ = (unsigned char)n;
memcpy(ptr , pos , n);
*len += n + 1;
ptr += n;
if(!strstr(pos , ".")){
*ptr = (unsigned char)0;
ptr ++;
*len += 1;
break;
}
pos += n + 1;
}
*((unsigned short*)ptr) = htons(1);
*len += 2;
ptr += 2;
*((unsigned short*)ptr) = htons(1);
*len += 2;
} |
