sajingeo · September 2, 2021 15:45 · May 29, 2016
diff --git a/dns.c b/dns.c
@@ -0,0 +1,417 @@
+//DNS Query Program on Linux
+//Author : Silver Moon (m00n.silv3r@gmail.com)
+//Dated : 29/4/2009
+
+//Header Files
+#include<stdio.h> //printf
+#include<string.h>    //strlen
+#include<stdlib.h>    //malloc
+#include<sys/socket.h>    //you know what this is for
+#include<arpa/inet.h> //inet_addr , inet_ntoa , ntohs etc
+#include<netinet/in.h>
+#include<unistd.h>    //getpid
+
+//List of DNS Servers registered on the system
+char dns_servers[10][100];
+int dns_server_count = 0;
+//Types of DNS resource records :)
+
+#define T_A 1 //Ipv4 address
+#define T_NS 2 //Nameserver
+#define T_CNAME 5 // canonical name
+#define T_SOA 6 /* start of authority zone */
+#define T_PTR 12 /* domain name pointer */
+#define T_MX 15 //Mail server
+
+//Function Prototypes
+void ngethostbyname (unsigned char* , int);
+void ChangetoDnsNameFormat (unsigned char*,unsigned char*);
+unsigned char* ReadName (unsigned char*,unsigned char*,int*);
+void get_dns_servers();
+
+//DNS header structure
+struct DNS_HEADER
+{
+    unsigned short id; // identification number
+
+    unsigned char rd :1; // recursion desired
+    unsigned char tc :1; // truncated message
+    unsigned char aa :1; // authoritive answer
+    unsigned char opcode :4; // purpose of message
+    unsigned char qr :1; // query/response flag
+
+    unsigned char rcode :4; // response code
+    unsigned char cd :1; // checking disabled
+    unsigned char ad :1; // authenticated data
+    unsigned char z :1; // its z! reserved
+    unsigned char ra :1; // recursion available
+
+    unsigned short q_count; // number of question entries
+    unsigned short ans_count; // number of answer entries
+    unsigned short auth_count; // number of authority entries
+    unsigned short add_count; // number of resource entries
+};
+
+//Constant sized fields of query structure
+struct QUESTION
+{
+    unsigned short qtype;
+    unsigned short qclass;
+};
+
+//Constant sized fields of the resource 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 resource record contents
+struct RES_RECORD
+{
+    unsigned char *name;
+    struct R_DATA *resource;
+    unsigned char *rdata;
+};
+
+//Structure of a Query
+typedef struct
+{
+    unsigned char *name;
+    struct QUESTION *ques;
+} QUERY;
+
+int main( int argc , char *argv[])
+{
+    unsigned char hostname[100];
+
+    //Get the DNS servers from the resolv.conf file
+    get_dns_servers();
+
+    //Get the hostname from the terminal
+    printf("Enter Hostname to Lookup : ");
+    scanf("%s" , hostname);
+
+    //Now get the ip of this hostname , A record
+    ngethostbyname(hostname , T_A);
+
+    return 0;
+}
+
+/*
+ * Perform a DNS query by sending a packet
+ * */
+void ngethostbyname(unsigned char *host , int query_type)
+{
+    unsigned char buf[65536],*qname,*reader;
+    int i , j , stop , s;
+
+    struct sockaddr_in a;
+
+    struct RES_RECORD answers[20],auth[20],addit[20]; //the replies from the DNS server
+    struct sockaddr_in dest;
+
+    struct DNS_HEADER *dns = NULL;
+    struct QUESTION *qinfo = NULL;
+
+    printf("Resolving %s" , host);
+
+    s = socket(AF_INET , SOCK_DGRAM , IPPROTO_UDP); //UDP packet for DNS queries
+
+    dest.sin_family = AF_INET;
+    dest.sin_port = htons(53);
+    dest.sin_addr.s_addr = inet_addr(dns_servers[0]); //dns servers
+
+    //Set the DNS structure to standard queries
+    dns = (struct DNS_HEADER *)&buf;
+
+    dns->id = (unsigned short) htons(getpid());
+    dns->qr = 0; //This is a query
+    dns->opcode = 0; //This is a standard query
+    dns->aa = 0; //Not Authoritative
+    dns->tc = 0; //This message is not truncated
+    dns->rd = 1; //Recursion Desired
+    dns->ra = 0; //Recursion not available! hey we dont have it (lol)
+    dns->z = 0;
+    dns->ad = 0;
+    dns->cd = 0;
+    dns->rcode = 0;
+    dns->q_count = htons(1); //we have only 1 question
+    dns->ans_count = 0;
+    dns->auth_count = 0;
+    dns->add_count = 0;
+
+    //point to the query portion
+    qname =(unsigned char*)&buf[sizeof(struct DNS_HEADER)];
+
+    ChangetoDnsNameFormat(qname , host);
+    qinfo =(struct QUESTION*)&buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1)]; //fill it
+
+    qinfo->qtype = htons( query_type ); //type of the query , A , MX , CNAME , NS etc
+    qinfo->qclass = htons(1); //its internet (lol)
+
+    printf("\nSending Packet...");
+    if( sendto(s,(char*)buf,sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0)
+    {
+        perror("sendto failed");
+    }
+    printf("Done");
+
+    //Receive the answer
+    i = sizeof dest;
+    printf("\nReceiving answer...");
+    if(recvfrom (s,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0)
+    {
+        perror("recvfrom failed");
+    }
+    printf("Done");
+
+    dns = (struct DNS_HEADER*) buf;
+
+    //move ahead of the dns header and the query field
+    reader = &buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION)];
+
+    printf("\nThe response contains : ");
+    printf("\n %d Questions.",ntohs(dns->q_count));
+    printf("\n %d Answers.",ntohs(dns->ans_count));
+    printf("\n %d Authoritative Servers.",ntohs(dns->auth_count));
+    printf("\n %d Additional records.\n\n",ntohs(dns->add_count));
+
+    //Start reading answers
+    stop=0;
+
+    for(i=0;i<ntohs(dns->ans_count);i++)
+    {
+        answers[i].name=ReadName(reader,buf,&stop);
+        reader = reader + stop;
+
+        answers[i].resource = (struct R_DATA*)(reader);
+        reader = reader + sizeof(struct R_DATA);
+
+        if(ntohs(answers[i].resource->type) == 1) //if its an ipv4 address
+        {
+            answers[i].rdata = (unsigned 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 = ReadName(reader,buf,&stop);
+            reader = reader + stop;
+        }
+    }
+
+    //read authorities
+    for(i=0;i<ntohs(dns->auth_count);i++)
+    {
+        auth[i].name=ReadName(reader,buf,&stop);
+        reader+=stop;
+
+        auth[i].resource=(struct R_DATA*)(reader);
+        reader+=sizeof(struct R_DATA);
+
+        auth[i].rdata=ReadName(reader,buf,&stop);
+        reader+=stop;
+    }
+
+    //read additional
+    for(i=0;i<ntohs(dns->add_count);i++)
+    {
+        addit[i].name=ReadName(reader,buf,&stop);
+        reader+=stop;
+
+        addit[i].resource=(struct R_DATA*)(reader);
+        reader+=sizeof(struct R_DATA);
+
+        if(ntohs(addit[i].resource->type)==1)
+        {
+            addit[i].rdata = (unsigned char*)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=ReadName(reader,buf,&stop);
+            reader+=stop;
+        }
+    }
+
+    //print answers
+    printf("\nAnswer Records : %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 address
+        {
+            long *p;
+            p=(long*)answers[i].rdata;
+            a.sin_addr.s_addr=(*p); //working without ntohl
+            printf("has IPv4 address : %s",inet_ntoa(a.sin_addr));
+        }
+
+        if(ntohs(answers[i].resource->type)==5) 
+        {
+            //Canonical name for an alias
+            printf("has alias name : %s",answers[i].rdata);
+        }
+
+        printf("\n");
+    }
+
+    //print authorities
+    printf("\nAuthoritive Records : %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)==2)
+        {
+            printf("has nameserver : %s",auth[i].rdata);
+        }
+        printf("\n");
+    }
+
+    //print additional resource records
+    printf("\nAdditional Records : %d \n" , ntohs(dns->add_count) );
+    for(i=0; i < ntohs(dns->add_count) ; i++)
+    {
+        printf("Name : %s ",addit[i].name);
+        if(ntohs(addit[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));
+        }
+        printf("\n");
+    }
+    return;
+}
+
+/*
+ * 
+ * */
+u_char* ReadName(unsigned char* reader,unsigned char* buffer,int* count)
+{
+    unsigned char *name;
+    unsigned int p=0,jumped=0,offset;
+    int i , j;
+
+    *count = 1;
+    name = (unsigned char*)malloc(256);
+
+    name[0]='\0';
+
+    //read the names in 3www6google3com format
+    while(*reader!=0)
+    {
+        if(*reader>=192)
+        {
+            offset = (*reader)*256 + *(reader+1) - 49152; //49152 = 11000000 00000000 ;)
+            reader = buffer + offset - 1;
+            jumped = 1; //we have jumped to another location so counting wont go up!
+        }
+        else
+        {
+            name[p++]=*reader;
+        }
+
+        reader = reader+1;
+
+        if(jumped==0)
+        {
+            *count = *count + 1; //if we havent jumped to another location then we can count up
+        }
+    }
+
+    name[p]='\0'; //string complete
+    if(jumped==1)
+    {
+        *count = *count + 1; //number of steps we actually moved forward in the packet
+    }
+
+    //now convert 3www6google3com0 to www.google.com
+    for(i=0;i<(int)strlen((const char*)name);i++) 
+    {
+        p=name[i];
+        for(j=0;j<(int)p;j++) 
+        {
+            name[i]=name[i+1];
+            i=i+1;
+        }
+        name[i]='.';
+    }
+    name[i-1]='\0'; //remove the last dot
+    return name;
+}
+
+/*
+ * Get the DNS servers from /etc/resolv.conf file on Linux
+ * */
+void get_dns_servers()
+{
+    FILE *fp;
+    char line[200] , *p;
+    if((fp = fopen("/etc/resolv.conf" , "r")) == NULL)
+    {
+        printf("Failed opening /etc/resolv.conf file \n");
+    }
+
+    while(fgets(line , 200 , fp))
+    {
+        if(line[0] == '#')
+        {
+            continue;
+        }
+        if(strncmp(line , "nameserver" , 10) == 0)
+        {
+            p = strtok(line , " ");
+            p = strtok(NULL , " ");
+
+            //p now is the dns ip :)
+            //????
+        }
+    }
+
+    strcpy(dns_servers[0] , "208.67.222.222");
+    strcpy(dns_servers[1] , "208.67.220.220");
+}
+
+/*
+ * This will convert www.google.com to 3www6google3com 
+ * got it :)
+ * */
+void ChangetoDnsNameFormat(unsigned char* dns,unsigned char* host) 
+{
+    int lock = 0 , i;
+    strcat((char*)host,".");
+
+    for(i = 0 ; i < strlen((char*)host) ; i++) 
+    {
+        if(host[i]=='.') 
+        {
+            *dns++ = i-lock;
+            for(;lock<i;lock++) 
+            {
+                *dns++=host[lock];
+            }
+            lock++; //or lock=i+1;
+        }
+    }
+    *dns++='\0';
+}
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