/***************************************************************************
* ncat_listen.c -- --listen mode. *
***********************IMPORTANT NMAP LICENSE TERMS************************
* *
* The Nmap Security Scanner is (C) 1996-2011 Insecure.Com LLC. Nmap is *
* also a registered trademark of Insecure.Com LLC. This program is free *
* software; you may redistribute and/or modify it under the terms of the *
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***************************************************************************/
/* $Id$ */
#include "ncat.h"
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#ifndef WIN32
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#else
#include <fcntl.h>
#endif
#ifdef HAVE_OPENSSL
#include <openssl/ssl.h>
#include <openssl/err.h>
#endif
/* read_fds is the clients we are accepting data from. broadcast_fds is the
clients were are sending data to. broadcast_fds doesn't include the listening
socket and stdin. Network clients are not added to read_fds when --send-only
is used, because they would be always selected without having data read. */
static fd_set read_fds, broadcast_fds;
/* These are bookkeeping data structures that are parallel to read_fds and
broadcast_fds. */
static fd_list_t read_fdlist, broadcast_fdlist;
static int listen_socket;
/* Has stdin seen EOF? */
static int stdin_eof = 0;
static int crlf_state = 0;
static void handle_connection(void);
static int read_stdin(void);
static int read_socket(int recv_fd);
/* The number of connected clients is the difference of conn_inc and conn_dec.
It is split up into two variables for signal safety. conn_dec is modified
(asynchronously) only in signal handlers and conn_inc is modified
(synchronously) only in the main program. get_conn_count loops while conn_dec
is being modified. */
static unsigned int conn_inc = 0;
static volatile unsigned int conn_dec = 0;
static volatile sig_atomic_t conn_dec_changed;
static void decrease_conn_count(void) {
conn_dec_changed = 1;
conn_dec++;
}
static int get_conn_count(void)
{
unsigned int count;
/* conn_dec is modified in a signal handler, so loop until it stops
changing. */
do {
conn_dec_changed = 0;
count = conn_inc - conn_dec;
} while (conn_dec_changed);
assert(count <= INT_MAX);
return count;
}
#ifndef WIN32
static void sigchld_handler(int signum)
{
while (waitpid(-1, NULL, WNOHANG) > 0)
decrease_conn_count();
}
#endif
static int ncat_listen_stream(int proto)
{
int rc;
#ifdef HAVE_OPENSSL
SSL_CTX *ctx;
#endif
/* clear out structs */
FD_ZERO(&read_fds);
FD_ZERO(&broadcast_fds);
zmem(&read_fdlist, sizeof(read_fdlist));
zmem(&broadcast_fdlist, sizeof(broadcast_fdlist));
#ifdef WIN32
set_pseudo_sigchld_handler(decrease_conn_count);
#else
/* Reap on SIGCHLD */
Signal(SIGCHLD, sigchld_handler);
/* Ignore the SIGPIPE that occurs when a client disconnects suddenly and we
send data to it before noticing. */
Signal(SIGPIPE, SIG_IGN);
#endif
#ifdef HAVE_OPENSSL
if (o.ssl)
ctx = setup_ssl_listen();
#endif
/* setup the main listening socket */
listen_socket = do_listen(SOCK_STREAM, proto);
/* Make our listening socket non-blocking because there are timing issues
* which could cause us to block on accept() even though select() says it's
* readable. See UNPv1 2nd ed, p422 for more.
*/
unblock_socket(listen_socket);
/* setup select sets and max fd */
FD_SET(listen_socket, &read_fds);
/* we need a list of fds to keep current fdmax */
init_fdlist(&read_fdlist, sadd(o.conn_limit, 2));
add_fd(&read_fdlist, listen_socket);
add_fd(&read_fdlist, STDIN_FILENO);
init_fdlist(&broadcast_fdlist, o.conn_limit);
while (1) {
fd_set fds;
int i, fds_ready;
if(o.debug > 1)
logdebug("selecting, fdmax %d\n", read_fdlist.fdmax);
fds = read_fds;
fds_ready = fselect(read_fdlist.fdmax + 1, &fds, NULL, NULL, NULL);
if(o.debug > 1)
logdebug("select returned %d fds ready\n", fds_ready);
/*
* FIXME: optimize this loop to look only at the fds in the fd list,
* doing it this way means that if you have one descriptor that is very
* large, say 500, and none close to it, that you'll loop many times for
* nothing.
*/
for (i = 0; i <= read_fdlist.fdmax && fds_ready > 0; i++) {
/* Loop through descriptors until there's something to read */
if (!FD_ISSET(i, &fds))
continue;
if (o.debug > 1)
logdebug("fd %d is ready\n", i);
if (i == listen_socket) {
/* we have a new connection request */
handle_connection();
} else if(i == STDIN_FILENO) {
/* Read from stdin and write to all clients. */
rc = read_stdin();
if (rc == 0 && o.sendonly)
/* There will be nothing more to send. If we're not
receiving anything, we can quit here. */
return 0;
if (rc < 0)
return 1;
} else if (!o.sendonly) {
/* Read from a client and write to stdout. */
rc = read_socket(i);
if (rc <= 0 && !o.keepopen)
return rc == 0 ? 0 : 1;
}
fds_ready--;
}
}
return 0;
}
/* Accept a connection on a listening socket. Allow or deny the connection.
Fork a command if o.cmdexec is set. Otherwise, add the new socket to the
watch set. */
static void handle_connection(void)
{
union sockaddr_u remoteaddr;
socklen_t ss_len;
struct fdinfo s = { 0 };
int conn_count;
ss_len = sizeof(remoteaddr.storage);
errno = 0;
s.fd = accept(listen_socket, &remoteaddr.sockaddr, &ss_len);
if (s.fd < 0) {
if (o.debug)
logdebug("Error in accept: %s\n", strerror(errno));
close(s.fd);
return;
}
if (o.verbose)
loguser("Connection from %s:%hu.\n", inet_socktop(&remoteaddr), inet_port(&remoteaddr));
/* Check conditions that might cause us to deny the connection. */
conn_count = get_conn_count();
if (conn_count >= o.conn_limit) {
if (o.verbose)
loguser("New connection denied: connection limit reached (%d)\n", conn_count);
Close(s.fd);
return;
}
if (!allow_access(&remoteaddr)) {
if (o.verbose)
loguser("New connection denied: not allowed\n");
Close(s.fd);
return;
}
/* On Linux the new socket will be blocking, but on BSD it inherits the
non-blocking status of the listening socket. The socket must be blocking
for operations like SSL_accept to work in the way that we use them. */
block_socket(s.fd);
#ifdef HAVE_OPENSSL
if (o.ssl) {
s.ssl = new_ssl(s.fd);
if (SSL_accept(s.ssl) != 1) {
if (o.verbose) {
loguser("Failed SSL connection from %s: %s\n",
inet_socktop(&remoteaddr), ERR_error_string(ERR_get_error(), NULL));
}
SSL_free(s.ssl);
Close(s.fd);
return;
}
}
#endif
conn_inc++;
/*
* are we executing a command? if so then don't add this guy
* to our descriptor list or set.
*/
if (o.cmdexec) {
if (o.keepopen)
netrun(&s, o.cmdexec);
else
netexec(&s, o.cmdexec);
} else {
/* Now that a client is connected, pay attention to stdin. */
if (!stdin_eof)
FD_SET(STDIN_FILENO, &read_fds);
if (!o.sendonly) {
/* add to our lists */
FD_SET(s.fd, &read_fds);
/* add it to our list of fds for maintaining maxfd */
if (add_fdinfo(&read_fdlist, &s) < 0)
bye("add_fdinfo() failed.");
}
FD_SET(s.fd, &broadcast_fds);
if (add_fdinfo(&broadcast_fdlist, &s) < 0)
bye("add_fdinfo() failed.");
}
}
/* Read from stdin and broadcast to all client sockets. Return the number of
bytes read, or -1 on error. */
int read_stdin(void)
{
int nbytes;
char buf[DEFAULT_TCP_BUF_LEN];
char* tempbuf = NULL;
nbytes = read(STDIN_FILENO, buf, sizeof(buf));
if (nbytes <= 0) {
if (nbytes < 0 && o.verbose)
logdebug("Error reading from stdin: %s\n", strerror(errno));
if (nbytes == 0 && o.debug)
logdebug("EOF on stdin\n");
/* Don't close the file because that allows a socket to be fd 0. */
FD_CLR(STDIN_FILENO, &read_fds);
/* Buf mark that we've seen EOF so it doesn't get re-added to the
select list. */
stdin_eof = 1;
return nbytes;
}
if (o.crlf)
fix_line_endings((char *) buf, &nbytes, &tempbuf, &crlf_state);
if(o.linedelay)
ncat_delay_timer(o.linedelay);
/* Write to everything in the broadcast set. */
if (tempbuf != NULL) {
ncat_broadcast(&broadcast_fds, &broadcast_fdlist, tempbuf, nbytes);
free(tempbuf);
tempbuf = NULL;
} else {
ncat_broadcast(&broadcast_fds, &broadcast_fdlist, buf, nbytes);
}
return nbytes;
}
/* Read from a client socket and write to stdout. Return the number of bytes
read from the socket, or -1 on error. */
int read_socket(int recv_fd)
{
char buf[DEFAULT_TCP_BUF_LEN];
struct fdinfo *fdn;
int nbytes, pending;
fdn = get_fdinfo(&read_fdlist, recv_fd);
assert(fdn != NULL);
nbytes = 0;
do {
int n;
n = ncat_recv(fdn, buf, sizeof(buf), &pending);
if (n <= 0) {
if (o.debug)
logdebug("Closing connection.\n");
#ifdef HAVE_OPENSSL
if (o.ssl && fdn->ssl) {
if (nbytes == 0)
SSL_shutdown(fdn->ssl);
SSL_free(fdn->ssl);
}
#endif
close(recv_fd);
FD_CLR(recv_fd, &read_fds);
rm_fd(&read_fdlist, recv_fd);
FD_CLR(recv_fd, &broadcast_fds);
rm_fd(&broadcast_fdlist, recv_fd);
conn_inc--;
if (get_conn_count() == 0)
FD_CLR(STDIN_FILENO, &read_fds);
return n;
}
Write(STDOUT_FILENO, buf, n);
nbytes += n;
} while (pending);
return nbytes;
}
/* This is sufficiently different from the TCP code (wrt SSL, etc) that it
* resides in its own simpler function
*/
static int ncat_listen_dgram(int proto)
{
int sockfd, fdmax, nbytes, fds_ready;
char buf[DEFAULT_UDP_BUF_LEN] = {0};
char* tempbuf = NULL;
fd_set read_fds;
union sockaddr_u remotess;
socklen_t sslen = sizeof(remotess.storage);
FD_ZERO(&read_fds);
/* Initialize remotess struct so recvfrom() doesn't hit the fan.. */
zmem(&remotess.storage, sizeof(remotess.storage));
remotess.storage.ss_family = o.af;
#ifdef WIN32
set_pseudo_sigchld_handler(decrease_conn_count);
#else
/* Reap on SIGCHLD */
Signal(SIGCHLD, sigchld_handler);
/* Ignore the SIGPIPE that occurs when a client disconnects suddenly and we
send data to it before noticing. */
Signal(SIGPIPE, SIG_IGN);
#endif
while (1) {
/* create the UDP listen socket */
sockfd = do_listen(SOCK_DGRAM, proto);
while (1) {
int conn_count;
/*
* We just peek so we can get the client connection details without
* removing anything from the queue. Sigh.
*/
nbytes = Recvfrom(sockfd, buf, sizeof(buf), MSG_PEEK,
&remotess.sockaddr, &sslen);
/* Check conditions that might cause us to deny the connection. */
conn_count = get_conn_count();
if (conn_count >= o.conn_limit) {
if (o.verbose)
loguser("New connection denied: connection limit reached (%d)\n", conn_count);
} else if (!allow_access(&remotess)) {
if (o.verbose)
loguser("New connection denied: not allowed\n");
} else {
/* Good to go. */
break;
}
/* Dump the current datagram */
Recv(sockfd, buf, sizeof(buf), 0);
}
conn_inc++;
/*
* We're using connected udp. This has the down side of only
* being able to handle one udp client at a time
*/
Connect(sockfd, &remotess.sockaddr, sslen);
/* clean slate for buf */
zmem(buf, sizeof(buf));
/* are we executing a command? then do it */
if (o.cmdexec) {
struct fdinfo info = { 0 };
info.fd = sockfd;
if (o.keepopen)
netrun(&info, o.cmdexec);
else
netexec(&info, o.cmdexec);
continue;
}
FD_SET(sockfd, &read_fds);
FD_SET(STDIN_FILENO, &read_fds);
fdmax = sockfd;
/* stdin -> socket and socket -> stdout */
while (1) {
fd_set fds;
fds = read_fds;
if(o.debug > 1)
logdebug("udp select'ing\n");
fds_ready = fselect(fdmax + 1, &fds, NULL, NULL, NULL);
if (FD_ISSET(STDIN_FILENO, &fds)) {
nbytes = Read(STDIN_FILENO, buf, sizeof(buf));
if (nbytes < 0) {
loguser("%s.\n", strerror(errno));
return 1;
} else if (nbytes == 0) {
return 0;
}
if (o.crlf)
fix_line_endings((char *) buf, &nbytes, &tempbuf, &crlf_state);
if (!o.recvonly) {
if (tempbuf != NULL)
send(sockfd, tempbuf, nbytes, 0);
else
send(sockfd, buf, nbytes, 0);
}
if (tempbuf != NULL) {
free(tempbuf);
tempbuf = NULL;
}
}
if (FD_ISSET(sockfd, &fds)) {
nbytes = recv(sockfd, buf, sizeof(buf), 0);
if (nbytes < 0) {
loguser("%s.\n", socket_strerror(socket_errno()));
close(sockfd);
return 1;
}
if (!o.sendonly)
Write(STDOUT_FILENO, buf, nbytes);
}
zmem(buf, sizeof(buf));
}
}
return 0;
}
int ncat_listen()
{
if (o.httpserver)
return ncat_http_server();
else if (o.udp)
return ncat_listen_dgram(IPPROTO_UDP);
else if (o.sctp)
return ncat_listen_stream(IPPROTO_SCTP);
else
return ncat_listen_stream(IPPROTO_TCP);
/* unreached */
return 1;
}