path: root/src/util/hijack.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdarg.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <signal.h>
#include <net/if.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <syslog.h>
#include <getopt.h>
#include <pcap.h>

#define SNAPLEN 1600

struct hijack {
	pcap_t *pcap;
	int fd;
};

struct hijack_listener {
	struct sockaddr_un sun;
	int fd;
};

struct hijack_options {
	char interface[IF_NAMESIZE];
	int daemonise;
};

static int daemonised = 0;

/**
 * Log error message
 *
 */
static void logmsg ( int level, const char *format, ... ) {
	va_list ap;

	va_start ( ap, format );
	if ( daemonised ) {
		vsyslog ( ( LOG_DAEMON | level ), format, ap );
	} else {
		vfprintf ( stderr, format, ap );
	}
	va_end ( ap );
}

/**
 * Open pcap device
 *
 */
static int hijack_open ( const char *interface, struct hijack *hijack ) {
	char errbuf[PCAP_ERRBUF_SIZE];

	/* Open interface via pcap */
	errbuf[0] = '\0';
	hijack->pcap = pcap_open_live ( interface, SNAPLEN, 1, 0, errbuf );
	if ( ! hijack->pcap ) {
		logmsg ( LOG_ERR, "Failed to open %s: %s\n",
			 interface, errbuf );
		goto err;
	}
	if ( errbuf[0] )
		logmsg ( LOG_WARNING, "Warning: %s\n", errbuf );

	/* Set capture interface to non-blocking mode */
	if ( pcap_setnonblock ( hijack->pcap, 1, errbuf ) < 0 ) {
		logmsg ( LOG_ERR, "Could not make %s non-blocking: %s\n",
			 interface, errbuf );
		goto err;
	}

	/* Get file descriptor for select() */
	hijack->fd = pcap_get_selectable_fd ( hijack->pcap );
	if ( hijack->fd < 0 ) {
		logmsg ( LOG_ERR, "Cannot get selectable file descriptor "
			 "for %s\n", interface );
		goto err;
	}

	return 0;

 err:
	if ( hijack->pcap )
		pcap_close ( hijack->pcap );
	return -1;
}

/**
 * Close pcap device
 *
 */
static void hijack_close ( struct hijack *hijack ) {
	pcap_close ( hijack->pcap );
}

/**
 * Forward data from hijacker
 *
 */
static ssize_t forward_from_hijacker ( struct hijack *hijack, int fd ) {
	char buf[SNAPLEN];
	ssize_t len;

	len = read ( fd, buf, sizeof ( buf ) );
	if ( len < 0 ) {
		logmsg ( LOG_ERR, "read from hijacker failed: %s\n",
			 strerror ( errno ) );
		return -1;
	}

	if ( len == 0 )
		return 0;

	if ( write ( hijack->fd, buf, len ) != len ) {
		logmsg ( LOG_ERR, "write to hijacked port failed: %s\n",
			 strerror ( errno ) );
		return -1;
	}

	logmsg ( LOG_INFO, "forwarded %zd bytes from hijacker\n", len );

	return len;
};

/**
 * Forward data to hijacker
 *
 */
static ssize_t forward_to_hijacker ( int fd, struct hijack *hijack ) {
	char buf[SNAPLEN];
	ssize_t len;

	len = read ( hijack->fd, buf, sizeof ( buf ) );
	if ( len < 0 ) {
		logmsg ( LOG_ERR, "read from hijacked port failed: %s\n",
			 strerror ( errno ) );
		return -1;
	}

	if ( len == 0 )
		return 0;

	if ( write ( fd, buf, len ) != len ) {
		logmsg ( LOG_ERR, "write to hijacker failed: %s\n",
			 strerror ( errno ) );
		return -1;
	}

	logmsg ( LOG_INFO, "forwarded %zd bytes to hijacker\n", len );

	return len;
};


/**
 * Run hijacker
 *
 */
static int run_hijacker ( const char *interface, int fd ) {
	struct hijack hijack;
	fd_set fdset;
	int max_fd;
	ssize_t len;

	memset ( &hijack, 0, sizeof ( hijack ) );

	logmsg ( LOG_INFO, "new connection for %s\n", interface );

	if ( hijack_open ( interface, &hijack ) < 0 )
		goto err;
	
	/* Do the forwarding */
	max_fd = ( ( fd > hijack.fd ) ? fd : hijack.fd );
	while ( 1 ) {
		/* Wait for available data */
		FD_ZERO ( &fdset );
		FD_SET ( fd, &fdset );
		FD_SET ( hijack.fd, &fdset );
		if ( select ( ( max_fd + 1 ), &fdset, NULL, NULL, 0 ) < 0 ) {
			logmsg ( LOG_ERR, "select failed: %s\n",
				 strerror ( errno ) );
			goto err;
		}
		if ( FD_ISSET ( fd, &fdset ) ) {
			len = forward_from_hijacker ( &hijack, fd );
			if ( len < 0 )
				goto err;
			if ( len == 0 )
				break;
		}
		if ( FD_ISSET ( hijack.fd, &fdset ) ) {
			len = forward_to_hijacker ( fd, &hijack );
			if ( len < 0 )
				goto err;
			if ( len == 0 )
				break;
		}
	}

	hijack_close ( &hijack );
	logmsg ( LOG_INFO, "closed connection for %s\n", interface );

	return 0;

 err:
	if ( hijack.pcap )
		hijack_close ( &hijack );
	return -1;
}

/**
 * Open listener socket
 *
 */
static int open_listener ( const char *interface,
			   struct hijack_listener *listener ) {
	
	/* Create socket */
	listener->fd = socket ( PF_UNIX, SOCK_SEQPACKET, 0 );
	if ( listener->fd < 0 ) {
		logmsg ( LOG_ERR, "Could not create socket: %s\n",
			 strerror ( errno ) );
		goto err;
	}

	/* Bind to local filename */
	listener->sun.sun_family = AF_UNIX,
	snprintf ( listener->sun.sun_path, sizeof ( listener->sun.sun_path ),
		   "/var/run/hijack-%s", interface );
	if ( bind ( listener->fd, ( struct sockaddr * ) &listener->sun,
		    sizeof ( listener->sun ) ) < 0 ) {
		logmsg ( LOG_ERR, "Could not bind socket to %s: %s\n",
			 listener->sun.sun_path, strerror ( errno ) );
		goto err;
	}

	/* Set as a listening socket */
	if ( listen ( listener->fd, 0 ) < 0 ) {
		logmsg ( LOG_ERR, "Could not listen to %s: %s\n",
			 listener->sun.sun_path, strerror ( errno ) );
		goto err;
	}

	return 0;
	
 err:
	if ( listener->fd >= 0 )
		close ( listener->fd );
	return -1;
}

/**
 * Listen on listener socket
 *
 */
static int listen_for_hijackers ( struct hijack_listener *listener,
				  const char *interface ) {
	int fd;
	pid_t child;
	int rc;

	logmsg ( LOG_INFO, "Listening on %s\n", listener->sun.sun_path );

	while ( 1 ) {
		/* Accept new connection */
		fd = accept ( listener->fd, NULL, 0 );
		if ( fd < 0 ) {
			logmsg ( LOG_ERR, "accept failed: %s\n",
				 strerror ( errno ) );
			goto err;
		}

		/* Fork child process */
		child = fork();
		if ( child < 0 ) {
			logmsg ( LOG_ERR, "fork failed: %s\n",
				 strerror ( errno ) );
			goto err;
		}
		if ( child == 0 ) {
			/* I am the child; run the hijacker */
			rc = run_hijacker ( interface, fd );
			close ( fd );
			exit ( rc );
		}
		
		close ( fd );
	}

	return 0;

 err:
	return -1;
}

/**
 * Close listener socket
 *
 */
static void close_listener ( struct hijack_listener *listener ) {
	close ( listener->fd );
	unlink ( listener->sun.sun_path );
}

/**
 * Print usage
 *
 */
static void usage ( char **argv ) {
	logmsg ( LOG_ERR,
		 "Usage: %s [options]\n"
		 "\n"
		 "Options:\n"
		 "  -h|--help               Print this help message\n"
		 "  -i|--interface intf     Use specified network interface\n"
		 "  -n|--nodaemon           Run in foreground\n",
		 argv[0] );
}

/**
 * Parse command-line options
 *
 */
static int parse_options ( int argc, char **argv,
			   struct hijack_options *options ) {
	static struct option long_options[] = {
		{ "interface", 1, NULL, 'i' },
		{ "nodaemon", 0, NULL, 'n' },
		{ "help", 0, NULL, 'h' },
		{ },
	};
	int c;

	/* Set default options */
	memset ( options, 0, sizeof ( *options ) );
	strncpy ( options->interface, "eth0", sizeof ( options->interface ) );
	options->daemonise = 1;

	/* Parse command-line options */
	while ( 1 ) {
		int option_index = 0;
		
		c = getopt_long ( argc, argv, "i:hn", long_options,
				  &option_index );
		if ( c < 0 )
			break;

		switch ( c ) {
		case 'i':
			strncpy ( options->interface, optarg,
				  sizeof ( options->interface ) );
			break;
		case 'n':
			options->daemonise = 0;
			break;
		case 'h':
			usage( argv );
			return -1;
		case '?':
			/* Unrecognised option */
			return -1;
		default:
			logmsg ( LOG_ERR, "Unrecognised option '-%c'\n", c );
			return -1;
		}
	}

	/* Check there's nothing left over on the command line */
	if ( optind != argc ) {
		usage ( argv );
		return -1;
	}

	return 0;
}

/**
 * Daemonise
 *
 */
static int daemonise ( const char *interface ) {
	char pidfile[16 + IF_NAMESIZE + 4]; /* "/var/run/hijack-<intf>.pid" */
	char pid[16];
	int pidlen;
	int fd = -1;

	/* Daemonise */
	if ( daemon ( 0, 0 ) < 0 ) {
		logmsg ( LOG_ERR, "Could not daemonise: %s\n",
			 strerror ( errno ) );
		goto err;
	}
	daemonised = 1; /* Direct messages to syslog now */

	/* Open pid file */
	snprintf ( pidfile, sizeof ( pidfile ), "/var/run/hijack-%s.pid",
		   interface );
	fd = open ( pidfile, ( O_WRONLY | O_CREAT | O_TRUNC ),
		    ( S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH ) );
	if ( fd < 0 ) {
		logmsg ( LOG_ERR, "Could not open %s for writing: %s\n",
			 pidfile, strerror ( errno ) );
		goto err;
	}

	/* Write pid to file */
	pidlen = snprintf ( pid, sizeof ( pid ), "%d\n", getpid() );
	if ( write ( fd, pid, pidlen ) != pidlen ) {
		logmsg ( LOG_ERR, "Could not write %s: %s\n",
			 pidfile, strerror ( errno ) );
		goto err;
	}

	close ( fd );
	return 0;

 err:
	if ( fd >= 0 )
		close ( fd );
	return -1;
}

int main ( int argc, char **argv ) {
	struct hijack_options options;
	struct hijack_listener listener;
	struct sigaction sigchld;

	/* Parse command-line options */
	if ( parse_options ( argc, argv, &options ) < 0 )
		exit ( 1 );

	/* Set up syslog connection */
	openlog ( basename ( argv[0] ), LOG_PID, LOG_DAEMON );

	/* Set up listening socket */
	if ( open_listener ( options.interface, &listener ) < 0 )
		exit ( 1 );

	/* Daemonise on demand */
	if ( options.daemonise ) {
		if ( daemonise ( options.interface ) < 0 )
			exit ( 1 );
	}

	/* Avoid creating zombies */
	memset ( &sigchld, 0, sizeof ( sigchld ) );
	sigchld.sa_handler = SIG_IGN;
	sigchld.sa_flags = SA_NOCLDWAIT;
	if ( sigaction ( SIGCHLD, &sigchld, NULL ) < 0 ) {
		logmsg ( LOG_ERR, "Could not set signal handler: %s",
			 strerror ( errno ) );
		exit ( 1 );
	}

	/* Listen for hijackers */
	if ( listen_for_hijackers ( &listener, options.interface ) < 0 )
		exit ( 1 );

	close_listener ( &listener );
	
	return 0;
}