Sample Code–Lilt
The following two source files comprise the Lilt codebase. To preserve readability, we richly comment the code but do not display book-text inside the code. You can download the full source files from this book's companion Web site at http://www.wiley.com/compbooks/schiffman.
Lilt.h
/*
* $Id: lilt.h,v 1.7 2002/01/02 02:43:02 route Exp $
*
* Building Open Source Network Security Tools
* lilt.h - libnids example code
*
* Copyright (c) 2002 Mike D. Schiffman <mike@infonexus.com>
* All rights reserved.
*
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <termios.h>
#include <ctype.h>
#include <time.h>
#include <nids.h>
/*
* The following two structures taken from libnids sources to be used
* in the reporting function.
*/
struct scan
{
u_int addr;
unsigned short port;
u_char flags;
};
struct host
{
struct host *next;
struct host *prev;
u_int addr;
int modtime;
int n_packets;
struct scan *packets;
};
struct lilt_pack
{
#define M_LEN 128 /* this should be more than enough */
u_short mon[M_LEN]; /* list of TCP WKP to monitor */
u_char flags; /* control flags */
#define LP_CONN Ox1 /* there is a connection to watch */
#define LP_WATCH 0x2 /* watch this connection */
#define LP_KILL 0x4 /* kill this connection */
#define LP_DISCARD 0x8 /* discard this connection */
struct tuple4 t; /* four tuple of the connection in question */
int tcp_count; /* number of TCP connections seen */
int tcp_killed; /* number of TCP connections killed */
int ps_count; /* number of port scans seen */
};
char *cull_address (struct tuple4);
char *get_time ();
int set_ports (char *);
void monitor_tcp (struct tcp_stream *, void *);
void report (int, int, void *, void *);
void command_summary ();
void usage (char *);
int interesting (u_short);
void lock_tuple (struct tuple4);
int our_tuple (struct tuple4);
void process_command ();
/* EOF */
Lilt.c
/*
* $Id: lilt.c,v 1.10 2002/01/02 03:21:27 route Exp $
*
* Building Open Source Network Security Tools
* lilt.c - libnids example code
*
* Copyright (c) 2002 Mike D. Schiffman <mike@infonexus.com>
* All rights reserved.
*
*/
#include "./lilt.h"
struct lilt_pack lp;
int
main(int argc, char **argv)
{
int c, fd;
fd_set read_set;
struct termios term;
memset (&1p, 0, sizeof (lp));
while ((c = getopt (argc, argv, "m:")) != EOF)
{
switch (c)
{
case 'm':
/*
* Set the ports to be monitored. We want them to be
* of the format x,y,z. If we wanted, we could use
* libnet's port list chaining functionality here to
* be more robust.
*/
if (set_ports (optarg) == -1)
{
fprintf (stderr, "set_ports (): bad port list\n");
exit (EXIT_FAILURE);
}
break;
default:
usage (argv[0]);
exit (EXIT_FAILURE);
}
}
printf ("Lilt 1.0 [the littlest network watcher]\n");
if (lp.mon[0] == 0)
{
/* if the user specified no ports to look for, use these */
lp.mon[0] = 23;
lp.mon[1] = 6667;
}
/*
* Change the following libnids defaults:
* scan_num_ports: 7
* Slightly more sensitive than the default of 10.
* syslog: report
* Use our own function rather than syslog to report portscans.
* pcap_filter: "tcp"
* Limit libnids to capturing TCP packets only.
*/
nids_params.scan_num_ports = 7;
nids_params.syslog = report;
nids_params.pcap_filter = "tcp";
/* initialize the library */
if (nids_init () == 0)
{
fprintf (stderr, "nids_init() failed: %s\n", nids_errbuf);
exit (EXIT_FAILURE);
}
/*
* Register the TCP callback. We could stack more TCP callback
* functions here but in this sample program we only have one.
*/
nids_register_tcp(monitor_tcp);
printf("TCP monitoring callback registered\n");
printf("Monitoring connections to the following ports: ");
for (c = 0; 1p.mon[c]; C++)
{
printf("%d", 1p.mon[c]);
}
printf("\nLibnids engine initialized, waiting for events...\n");
/*
* We want to change the behavior of stdin to not echo characters
* typed and more importantly we want each character to be handed
* off as soon as it is pressed (not waiting for \r). To do this
* we have to manipulate the termios structure and change the
* normal behavior of stdin. First we get the current terminal
* state of stdin. If any of this fails, we'll warn, but not quit.
*/
c = tcgetattr(STDIN_FILENO, &term);
if (c == -1)
{
perror("main(): tcgetattr():");
/* nonfatal */
}
else
{
/* disable canonical mode and terminal echo */
term.c_lflag ~= $ICANON;
term.c_lflag ~= $ECHO;
/* set our changed state "NOW" */
c = tcsetattr (STDIN_FILENO, TCSANOW, &term);
if (c == -1)
{
perror("main(): tcsetattr():");
/* nonfatal */
}
}
/*
* Lilt is driven by commands from the user and input from the
* network. Since we want to monitor for both at the "same time"
* we need to do synchronous I/O multiplexing across these two
* input streams. We'll watch the libnids descriptor to see if
* there is any network traffic we need to pay attention to and
* also we monitor stdin to see if the user hits a key we need to
* process. To do this, we call nids_getfd() to get the underlying
* network file descriptor (which is really a wrapper to
* pcap_fileno()). Then we call nids_next () in conjunction with
* select ().
*/
for (fd = nids_getfd();;)
{
FD_ZERO(&read_set);
FD_SET(fd, &read_set);
FD_SET(STDIN_FILENO, &read_set);
/* check the status of our file descriptors */
c = select (fd + 1, &read_set, 0, 0, NULL);
if (c > 0)
{
/* input from libnids? */
if (FD_ISSET(fd, &read_set))
{
/*
* nids_next() handles the calling of our callback
* function.
*/
if (nids_next() == 0)
{
/* non-fatal, pcap_next() probably returned NULL */
continue;
}
}
/* input from the user? */
if (FD_ISSET(STDIN_FILENO, &read_set))
{
/* hand the keypress off be processed */
process_command(argv[0]);
}
}
if (c == -1)
{
perror("select:");
}
}
/* NOT REACHED */
return (EXIT_SUCCESS);
}
int
set_ports(char *list)
{
u_short p;
u_char *q;
int i;
q = list;
/* pull out ports and stick them in our port list array */
for (i = 0; q; i++)
{
if (i > M_LEN)
{
/* list too long */
return (-1);
}
p = atoi(q);
if (p == 0)
{
return (-1);
}
else
{
lp.mon[i] = p;
}
if ((q = strchr(q, (char)',')))
{
*q = NULL;
q++;
}
}
return (1);
}
void
report (int type, int err, void *unused, void *data)
{
int i;
char buf[BUFSIZ];
struct host *offender;
/* port scan warning? */
if (type == NIDS_WARN_SCAN)
{
lp.ps_count++;
offender = (struct host *)data;
fprintf(stderr, "\n-[%s: portscan detected from %s]-\n",
get_time(),
inet_ntoa(*((struct in_addr *)&offender->addr)));
/* pull out IPs and ports scanned */
for (memset (buf, 0, BUFSIZ), i = 0; i < offender->n_packets; i++)
{
sprintf(buf + strlen(buf), "%s",
inet_ntoa(*((struct in_addr *)
&offender->packets[i].addr)));
sprintf(buf + strlen(buf), ":%hi",
offender->packets[i].port);
strcat(buf, "\n");
}
fprintf(stderr, "%s", buf);
}
}
void
monitor_tcp(struct tcp_stream *stream, void *unused)
{
int i;
struct half_stream *half;
/*
* First check to see if we have a connection we're watching
* and the user presses 'D' to discard it.
*/
if (lp.flags & LP_DISCARD)
{
/* clear out all the state for this connection */
lp.flags &= ~LP_DISCARD;
lp.flags &= ~LP_WATCH;
lp.flags &= ~LP_KILL;
memset (&lp.t, 0, sizeof(lp.t));
}
/* TCP SYN packet */
if (stream->nids_state == NIDS_JUST_EST)
{
/* if we already have a connection in scope, ignore this one */
if (lp.flags & LP_CONN)
{
return;
}
/* see if this connection is to a port we're monitoring */
if (!interesting(stream->addr.dest))
{
return;
}
/* lock this connection in scope */
lock_tuple(stream->addr);
lp.flags |= LP_CONN;
lp.tcp_count++;
fprintf(stderr, "\n-[%s: TCP connection: %s]-\n",
get_time(),
cull_address(stream->addr));
/* we want data from both ends of the connection */
stream->client.collect++;
stream->server.collect++;
return;
}
/* TCP FIN or RST packet */
if (stream->nids_state == NIDS_CLOSE ||
stream->nids_state == NIDS_RESET)
{
/* if this isn't data from our locked connection return */
if (!our_tuple(stream->addr))
{
return;
}
fprintf(stderr, "\n-[%s: TCP connection terminated]-\n",
get_time());
if (lp.flags & LP_KILL)
{
/* we were set to kill this connection, increment counter */
lp.tcp_killed++;
}
/* clear out all the state for this connection */
lp.flags &= ~LP_CONN;
lp.flags &= ~LP_WATCH;
lp.flags &= ~LP_KILL;
memset(&lp.t, 0, sizeof(lp.t));
return;
}
/* TCP data packet */
if (stream->nids_state == NIDS_DATA)
{
/* if this isn't data from our locked connection return */
if (!our_tuple(stream->addr))
{
return;
}
if (stream->client.count_new)
{
half = &stream->client;
}
else
{
half = &stream->server;
}
/* if we're not set to watch the connection, return */
if (!(lp.flags & LP_WATCH))
{
return;
}
if (lp.flags & LP_KILL)
{
/* kill the connection */
nids_killtcp(stream);
/* dump the rest of the data */
nids_discard(stream, half->count_new);
return;
}
for (i = 0; i < half->count_new; i++)
{
/* we only want to print characters that are printable! */
if (isascii(half->data[i]))
{
fprintf(stderr, "%c", half->data[i]);
}
}
}
}
/* peel off the character and process it */
void
process_command()
{
int i;
char buf[1];
if (read(STDIN_FILENO, buf, 1) == -1)
{
perror("read error:");
return;
}
switch (toupper(buf[0]))
{
case '?':
/* help */
command_summary();
break;
case 'D':
/* if we have a connection, discard it */
if (lp.flags & LP_DISCARD)
{
/* got it the first time you typed it dorkus! */
return;
}
if (lp.flags & LP_CONN)
{
lp.flags |= LP_DISCARD;
lp.flags &= ~LP_CONN;
fprintf(stderr, "\n-[discarded connection]-\n");
}
break;
case 'K':
/* if we have a connection, kill it */
if (lp.flags & LP_KILL)
{
/* got it the first time you typed it dorkus! */
return;
}
if (lp.flags & LP_CONN)
{
lp.flags |= LP_KILL;
fprintf(stderr, "\n-[killing connection]-\n");
}
break;
case 'p':
/* ports we're watching */
fprintf(stderr, "\n-[lilt monitor ports]-\n");
for (i = 0; lp.mon[i]; i++)
{
fprintf(stderr, "%d", lp.mon[i]);
}
fprintf(stderr, "\n");
break;
case 'Q':
/* quit */
fprintf(stderr, "\n-[later dorkus!]-\n");
exit (EXIT_SUCCESS);
case 'S':
/* statistics */
fprintf(stderr, "\n-[lilt statistics]-\n");
fprintf(stderr, "TCP connections:\t%d\n", lp.tcp_count);
fprintf(stderr, "TCP connections killed:\t%d\n",
lp.tcp_killed);
fprintf(stderr, "port scans detected:\t%d\n", lp.ps_count);
break;
case 'W':
/* if we have a connection, watch it */
if (lp.flags & LP_WATCH)
{
/* got it the first time you typed it dorkus! */
return;
}
if (lp.flags & LP_CONN)
{
lp.flags |= LP_WATCH;
fprintf(stderr, "\n-[watching connection]-\n");
}
break;
default:
break;
}
}
/* basically pulled from libnids sample code */
char *
cull_address(struct tuple4 addr)
{
static char buf[256];
strcpy(buf, inet_ntoa(*((struct in_addr *)&addr.saddr)));
sprintf(buf + strlen(buf), ".%d ->", addr.source);
strcat(buf, inet_ntoa(*((struct in_addr *)&addr.daddr)));
sprintf(buf + strlen(buf),".%d", addr.dest);
return (buf);
}
int
interesting(u_short port)
{
int i;
/* check our TCP WKP list for the port in question */
for (i = 0; lp.mon[i]; i++)
{
if (lp.mon[i] == port)
{
return (1);
}
}
return (0);
}
int
our_tuple(struct tuple4 addr)
{
/* check to see if this packet belongs to us */
if (addr.source == lp.t.source && addr.dest == lp.t.dest &&
addr.saddr == lp.t.saddr && addr.daddr == lp.t.daddr)
{
return (1);
}
else if (addr.source == lp.t.dest && addr.dest == lp.t.source &&
addr.daddr == lp.t.saddr && addr.saddr == lp.t.daddr)
{
return (2);
}
else
{
return (0);
}
}
void
lock_tuple(struct tuple4 addr)
{
/* lock this tuple in to our radar */
lp.t.source = addr.source;
lp.t.dest = addr.dest;
lp.t.saddr = addr.saddr;
lp.t.daddr = addr.daddr;
}
char *
get_time()
{
int i;
time_t t;
static char buf[26];
t = time((time_t *)NULL);
strcpy(buf, ctime(&t));
/* cut out the day, year and \n */
for (i = 0; i < 20; i++)
{
buf[i] = buf[i + 4];
}
buf[15] = 0;
return (buf);
}
void
usage(char *name)
{
fprintf(stderr,
"usage: %s:\n"
"-m ports\tList of TCP ports to monitor (x,y,z)\n",
name);
}
void
command_summary ()
{
/* print the commands that are available to the user in brackets */
fprintf(stderr,"\n-[lilt command summary]-\n[?] - this blurb\n");
if (lp.flags & LP_CONN)
{
fprintf(stderr,"[d] - discard connection from scope\n");
fprintf(stderr,"[k] - kill connection in scope\n");
}
else
{'
fprintf(stderr," d - discard connection from scope\n");
fprintf(stderr," k - kill connection in scope\n");
}
fprintf(stderr,"[p] - display ports being monitored\n");
fprintf(stderr,"[q] - quit lilt\n");
fprintf(stderr,"[s] - statistics\n");
if (lp.flags & LP_CONN)
{
fprintf(stderr,"[w] - watch connection in scope\n");
}
else
{
fprintf(stderr," w - watch connection in scope\n");
}
}
/* EOF */
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