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nmap/ncat/ncat_listen.c

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/***************************************************************************
* ncat_listen.c -- --listen mode. *
***********************IMPORTANT NMAP LICENSE TERMS************************
* *
* The Nmap Security Scanner is (C) 1996-2017 Insecure.Com LLC ("The Nmap *
* Project"). Nmap is also a registered trademark of the Nmap Project. *
* This program is free software; you may redistribute and/or modify it *
* under the terms of the GNU General Public License as published by the *
* Free Software Foundation; Version 2 ("GPL"), BUT ONLY WITH ALL OF THE *
* CLARIFICATIONS AND EXCEPTIONS DESCRIBED HEREIN. This guarantees your *
* right to use, modify, and redistribute this software under certain *
* conditions. If you wish to embed Nmap technology into proprietary *
* software, we sell alternative licenses (contact sales@nmap.com). *
* Dozens of software vendors already license Nmap technology such as *
* host discovery, port scanning, OS detection, version detection, and *
* the Nmap Scripting Engine. *
* *
* Note that the GPL places important restrictions on "derivative works", *
* yet it does not provide a detailed definition of that term. To avoid *
* misunderstandings, we interpret that term as broadly as copyright law *
* allows. For example, we consider an application to constitute a *
* derivative work for the purpose of this license if it does any of the *
* following with any software or content covered by this license *
* ("Covered Software"): *
* *
* o Integrates source code from Covered Software. *
* *
* o Reads or includes copyrighted data files, such as Nmap's nmap-os-db *
* or nmap-service-probes. *
* *
* o Is designed specifically to execute Covered Software and parse the *
* results (as opposed to typical shell or execution-menu apps, which will *
* execute anything you tell them to). *
* *
* o Includes Covered Software in a proprietary executable installer. The *
* installers produced by InstallShield are an example of this. Including *
* Nmap with other software in compressed or archival form does not *
* trigger this provision, provided appropriate open source decompression *
* or de-archiving software is widely available for no charge. For the *
* purposes of this license, an installer is considered to include Covered *
* Software even if it actually retrieves a copy of Covered Software from *
* another source during runtime (such as by downloading it from the *
* Internet). *
* *
* o Links (statically or dynamically) to a library which does any of the *
* above. *
* *
* o Executes a helper program, module, or script to do any of the above. *
* *
* This list is not exclusive, but is meant to clarify our interpretation *
* of derived works with some common examples. Other people may interpret *
* the plain GPL differently, so we consider this a special exception to *
* the GPL that we apply to Covered Software. Works which meet any of *
* these conditions must conform to all of the terms of this license, *
* particularly including the GPL Section 3 requirements of providing *
* source code and allowing free redistribution of the work as a whole. *
* *
* As another special exception to the GPL terms, the Nmap Project grants *
* permission to link the code of this program with any version of the *
* OpenSSL library which is distributed under a license identical to that *
* listed in the included docs/licenses/OpenSSL.txt file, and distribute *
* linked combinations including the two. *
* *
* The Nmap Project has permission to redistribute Npcap, a packet *
* capturing driver and library for the Microsoft Windows platform. *
* Npcap is a separate work with it's own license rather than this Nmap *
* license. Since the Npcap license does not permit redistribution *
* without special permission, our Nmap Windows binary packages which *
* contain Npcap may not be redistributed without special permission. *
* *
* Any redistribution of Covered Software, including any derived works, *
* must obey and carry forward all of the terms of this license, including *
* obeying all GPL rules and restrictions. For example, source code of *
* the whole work must be provided and free redistribution must be *
* allowed. All GPL references to "this License", are to be treated as *
* including the terms and conditions of this license text as well. *
* *
* Because this license imposes special exceptions to the GPL, Covered *
* Work may not be combined (even as part of a larger work) with plain GPL *
* software. The terms, conditions, and exceptions of this license must *
* be included as well. This license is incompatible with some other open *
* source licenses as well. In some cases we can relicense portions of *
* Nmap or grant special permissions to use it in other open source *
* software. Please contact fyodor@nmap.org with any such requests. *
* Similarly, we don't incorporate incompatible open source software into *
* Covered Software without special permission from the copyright holders. *
* *
* If you have any questions about the licensing restrictions on using *
* Nmap in other works, are happy to help. As mentioned above, we also *
* offer alternative license to integrate Nmap into proprietary *
* applications and appliances. These contracts have been sold to dozens *
* of software vendors, and generally include a perpetual license as well *
* as providing for priority support and updates. They also fund the *
* continued development of Nmap. Please email sales@nmap.com for further *
* information. *
* *
* If you have received a written license agreement or contract for *
* Covered Software stating terms other than these, you may choose to use *
* and redistribute Covered Software under those terms instead of these. *
* *
* Source is provided to this software because we believe users have a *
* right to know exactly what a program is going to do before they run it. *
* This also allows you to audit the software for security holes. *
* *
* Source code also allows you to port Nmap to new platforms, fix bugs, *
* and add new features. You are highly encouraged to send your changes *
* to the dev@nmap.org mailing list for possible incorporation into the *
* main distribution. By sending these changes to Fyodor or one of the *
* Insecure.Org development mailing lists, or checking them into the Nmap *
* source code repository, it is understood (unless you specify *
* otherwise) that you are offering the Nmap Project the unlimited, *
* non-exclusive right to reuse, modify, and relicense the code. Nmap *
* will always be available Open Source, but this is important because *
* the inability to relicense code has caused devastating problems for *
* other Free Software projects (such as KDE and NASM). We also *
* occasionally relicense the code to third parties as discussed above. *
* If you wish to specify special license conditions of your *
* contributions, just say so when you send them. *
* *
* This program is distributed in the hope that it will be useful, but *
* WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Nmap *
* license file for more details (it's in a COPYING file included with *
* Nmap, and also available from https://svn.nmap.org/nmap/COPYING) *
* *
***************************************************************************/
/* $Id$ */
#include "ncat.h"
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <limits.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
#if HAVE_SYS_UN_H
#include <sys/un.h>
#endif
#ifdef HAVE_OPENSSL
#include <openssl/ssl.h>
#include <openssl/err.h>
#endif
#ifdef WIN32
/* Define missing constant for shutdown(2).
* See:
* http://msdn.microsoft.com/en-us/library/windows/desktop/ms740481%28v=vs.85%29.aspx
*/
#define SHUT_WR SD_SEND
#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.
write_fds is the list of clients that are waiting for some kind of response
from us, like a pending ssl negotiation. */
static fd_set master_readfds, master_writefds, master_broadcastfds;
#ifdef HAVE_OPENSSL
/* sslpending_fds contains the list of ssl sockets that are waiting to complete
the ssl handshake */
static fd_set sslpending_fds;
#endif
/* These are bookkeeping data structures that are parallel to read_fds and
broadcast_fds. */
static fd_list_t client_fdlist, broadcast_fdlist;
static int listen_socket[NUM_LISTEN_ADDRS];
/* Has stdin seen EOF? */
static int stdin_eof = 0;
static int crlf_state = 0;
static void handle_connection(int socket_accept);
static int read_stdin(void);
static int read_socket(int recv_fd);
static void post_handle_connection(struct fdinfo sinfo);
static void read_and_broadcast(int recv_socket);
static void shutdown_sockets(int how);
static int chat_announce_connect(int fd, const union sockaddr_u *su);
static int chat_announce_disconnect(int fd);
static char *chat_filter(char *buf, size_t size, int fd, int *nwritten);
/* 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);
ncat_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, i, fds_ready;
fd_set listen_fds;
struct timeval tv;
struct timeval *tvp = NULL;
unsigned int num_sockets;
/* clear out structs */
FD_ZERO(&master_readfds);
FD_ZERO(&master_writefds);
FD_ZERO(&master_broadcastfds);
FD_ZERO(&listen_fds);
#ifdef HAVE_OPENSSL
FD_ZERO(&sslpending_fds);
#endif
zmem(&client_fdlist, sizeof(client_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)
{
if (o.sslalpn)
bye("ALPN is not supported in listen mode\n");
setup_ssl_listen();
}
#endif
/* Not sure if this problem exists on Windows, but fcntl and /dev/null don't */
#ifndef WIN32
/* Check whether stdin is closed. Because we treat this fd specially, we
* can't risk it being reopened for an incoming connection, so we'll hold
* it open instead. */
if (fcntl(STDIN_FILENO, F_GETFD) == -1 && errno == EBADF) {
logdebug("stdin is closed, attempting to reserve STDIN_FILENO\n");
rc = open("/dev/null", O_RDONLY);
if (rc >= 0 && rc != STDIN_FILENO) {
/* Oh well, we tried */
logdebug("Couldn't reserve STDIN_FILENO\n");
close(rc);
}
}
#endif
/* We need a list of fds to keep current fdmax. The second parameter is a
number added to the supplied connection limit, that will compensate
maxfds for the added by default listen and stdin sockets. */
init_fdlist(&client_fdlist, sadd(o.conn_limit, num_listenaddrs + 1));
for (i = 0; i < NUM_LISTEN_ADDRS; i++)
listen_socket[i] = -1;
num_sockets = 0;
for (i = 0; i < num_listenaddrs; i++) {
/* setup the main listening socket */
listen_socket[num_sockets] = do_listen(SOCK_STREAM, proto, &listenaddrs[i]);
if (listen_socket[num_sockets] == -1) {
if (o.debug > 0)
logdebug("do_listen(\"%s\"): %s\n", inet_ntop_ez(&listenaddrs[i].storage, sizeof(listenaddrs[i].storage)), socket_strerror(socket_errno()));
continue;
}
/* 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[num_sockets]);
/* setup select sets and max fd */
FD_SET(listen_socket[num_sockets], &master_readfds);
add_fd(&client_fdlist, listen_socket[num_sockets]);
FD_SET(listen_socket[num_sockets], &listen_fds);
num_sockets++;
}
if (num_sockets == 0) {
if (num_listenaddrs == 1)
bye("Unable to open listening socket on %s: %s", inet_ntop_ez(&listenaddrs[0].storage, sizeof(listenaddrs[0].storage)), socket_strerror(socket_errno()));
else
bye("Unable to open any listening sockets.");
}
add_fd(&client_fdlist, STDIN_FILENO);
init_fdlist(&broadcast_fdlist, o.conn_limit);
if (o.idletimeout > 0)
tvp = &tv;
while (1) {
/* We pass these temporary descriptor sets to fselect, since fselect
modifies the sets it receives. */
fd_set readfds = master_readfds, writefds = master_writefds;
if (o.debug > 1)
logdebug("selecting, fdmax %d\n", client_fdlist.fdmax);
if (o.debug > 1 && o.broker)
logdebug("Broker connection count is %d\n", get_conn_count());
if (o.idletimeout > 0)
ms_to_timeval(tvp, o.idletimeout);
/* The idle timer should only be running when there are active connections */
if (get_conn_count())
fds_ready = fselect(client_fdlist.fdmax + 1, &readfds, &writefds, NULL, tvp);
else
fds_ready = fselect(client_fdlist.fdmax + 1, &readfds, &writefds, NULL, NULL);
if (o.debug > 1)
logdebug("select returned %d fds ready\n", fds_ready);
if (fds_ready == 0)
bye("Idle timeout expired (%d ms).", o.idletimeout);
/*
* 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 <= client_fdlist.fdmax && fds_ready > 0; i++) {
/* Loop through descriptors until there's something to read */
if (!FD_ISSET(i, &readfds) && !FD_ISSET(i, &writefds))
continue;
if (o.debug > 1)
logdebug("fd %d is ready\n", i);
#ifdef HAVE_OPENSSL
/* Is this an ssl socket pending a handshake? If so handle it. */
if (o.ssl && FD_ISSET(i, &sslpending_fds)) {
struct fdinfo *fdi = NULL;
FD_CLR(i, &master_readfds);
FD_CLR(i, &master_writefds);
fdi = get_fdinfo(&client_fdlist, i);
ncat_assert(fdi != NULL);
switch (ssl_handshake(fdi)) {
case NCAT_SSL_HANDSHAKE_COMPLETED:
/* Clear from sslpending_fds once ssl is established */
FD_CLR(i, &sslpending_fds);
post_handle_connection(*fdi);
break;
case NCAT_SSL_HANDSHAKE_PENDING_WRITE:
FD_SET(i, &master_writefds);
break;
case NCAT_SSL_HANDSHAKE_PENDING_READ:
FD_SET(i, &master_readfds);
break;
case NCAT_SSL_HANDSHAKE_FAILED:
default:
SSL_free(fdi->ssl);
Close(fdi->fd);
FD_CLR(i, &sslpending_fds);
FD_CLR(i, &master_readfds);
rm_fd(&client_fdlist, i);
/* Are we in single listening mode(without -k)? If so
then we should quit also. */
if (!o.keepopen && !o.broker)
return 1;
--conn_inc;
break;
}
} else
#endif
if (FD_ISSET(i, &listen_fds)) {
/* we have a new connection request */
handle_connection(i);
} else if (i == STDIN_FILENO) {
if (o.broker) {
read_and_broadcast(i);
} else {
/* Read from stdin and write to all clients. */
rc = read_stdin();
if (rc == 0) {
if (o.proto != IPPROTO_TCP || (o.proto == IPPROTO_TCP && o.sendonly)) {
/* There will be nothing more to send. If we're not
receiving anything, we can quit here. */
return 0;
}
if (!o.noshutdown) shutdown_sockets(SHUT_WR);
}
if (rc < 0)
return 1;
}
} else if (!o.sendonly) {
if (o.broker) {
read_and_broadcast(i);
} else {
/* 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(int socket_accept)
{
union sockaddr_u remoteaddr;
socklen_t ss_len;
struct fdinfo s = { 0 };
int conn_count;
zmem(&s, sizeof(s));
zmem(&remoteaddr, sizeof(remoteaddr.storage));
ss_len = sizeof(remoteaddr.storage);
errno = 0;
s.fd = accept(socket_accept, &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) {
#if HAVE_SYS_UN_H
if (remoteaddr.sockaddr.sa_family == AF_UNIX)
loguser("Connection from a client on Unix domain socket.\n");
else
#endif
if (o.chat)
loguser("Connection from %s on file descriptor %d.\n", inet_socktop(&remoteaddr), s.fd);
else
loguser("Connection from %s.\n", inet_socktop(&remoteaddr));
}
if (!o.keepopen && !o.broker) {
int i;
for (i = 0; i < num_listenaddrs; i++) {
Close(listen_socket[i]);
FD_CLR(listen_socket[i], &master_readfds);
rm_fd(&client_fdlist, listen_socket[i]);
}
}
if (o.verbose) {
#if HAVE_SYS_UN_H
if (remoteaddr.sockaddr.sa_family == AF_UNIX)
loguser("Connection from %s.\n", remoteaddr.un.sun_path);
else
#endif
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;
}
s.remoteaddr = remoteaddr;
conn_inc++;
unblock_socket(s.fd);
#ifdef HAVE_OPENSSL
if (o.ssl) {
/* Add the socket to the necessary descriptor lists. */
FD_SET(s.fd, &sslpending_fds);
FD_SET(s.fd, &master_readfds);
FD_SET(s.fd, &master_writefds);
/* Add it to our list of fds too for maintaining maxfd. */
if (add_fdinfo(&client_fdlist, &s) < 0)
bye("add_fdinfo() failed.");
} else
#endif
post_handle_connection(s);
}
/* This function handles the post connection specific actions that are needed
* after a socket has been initialized(normal socket or ssl socket). */
static void post_handle_connection(struct fdinfo sinfo)
{
/*
* Are we executing a command? If so then don't add this guy
* to our descriptor list or set.
*/
if (o.cmdexec) {
#ifdef HAVE_OPENSSL
/* We added this in handle_connection, but at this point the ssl
* connection has taken over. Stop tracking.
*/
if (o.ssl) {
rm_fd(&client_fdlist, sinfo.fd);
}
#endif
if (o.keepopen)
netrun(&sinfo, o.cmdexec);
else
netexec(&sinfo, o.cmdexec);
} else {
/* Now that a client is connected, pay attention to stdin. */
if (!stdin_eof)
FD_SET(STDIN_FILENO, &master_readfds);
if (!o.sendonly) {
/* add to our lists */
FD_SET(sinfo.fd, &master_readfds);
/* add it to our list of fds for maintaining maxfd */
#ifdef HAVE_OPENSSL
/* Don't add it twice (see handle_connection above) */
if (!o.ssl) {
#endif
if (add_fdinfo(&client_fdlist, &sinfo) < 0)
bye("add_fdinfo() failed.");
#ifdef HAVE_OPENSSL
}
#endif
}
FD_SET(sinfo.fd, &master_broadcastfds);
if (add_fdinfo(&broadcast_fdlist, &sinfo) < 0)
bye("add_fdinfo() failed.");
if (o.chat)
chat_announce_connect(sinfo.fd, &sinfo.remoteaddr);
}
}
/* 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, &master_readfds);
/* 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(&master_broadcastfds, &broadcast_fdlist, tempbuf, nbytes);
free(tempbuf);
tempbuf = NULL;
} else {
ncat_broadcast(&master_broadcastfds, &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;
#ifdef HAVE_OPENSSL
int err = SSL_ERROR_NONE;
#endif
fdn = get_fdinfo(&client_fdlist, recv_fd);
ncat_assert(fdn != NULL);
nbytes = 0;
do {
int n;
n = ncat_recv(fdn, buf, sizeof(buf), &pending);
#ifdef HAVE_OPENSSL
/* SSL_read returns <0 in some cases like renegotiation. In these
* cases, SSL_get_error gives SSL_ERROR_WANT_{READ,WRITE}, and we
* should try the SSL_read again. */
if (n < 0 && o.ssl && fdn->ssl) {
err = SSL_get_error(fdn->ssl, n);
if (err == SSL_ERROR_WANT_READ || err == SSL_ERROR_WANT_WRITE) {
pending = 1;
}
}
#endif
/* If return value is 0, it's a clean shutdown from the other side, SSL
* or plain. If <0, it's an error. If pending, the error may be
* recoverable with a second SSL_read, so don't shut down yet. */
if (n <= 0 && !pending) {
if (o.debug)
logdebug("Closing fd %d.\n", recv_fd);
#ifdef HAVE_OPENSSL
if (o.ssl && fdn->ssl) {
if (n < 0 && o.debug) {
logdebug("SSL error on %d: %s\n", recv_fd, ERR_error_string(err, NULL));;
}
if (nbytes == 0)
SSL_shutdown(fdn->ssl);
SSL_free(fdn->ssl);
}
#endif
close(recv_fd);
FD_CLR(recv_fd, &master_readfds);
rm_fd(&client_fdlist, recv_fd);
FD_CLR(recv_fd, &master_broadcastfds);
rm_fd(&broadcast_fdlist, recv_fd);
conn_inc--;
if (get_conn_count() == 0)
FD_CLR(STDIN_FILENO, &master_readfds);
return n;
}
else if (n > 0) {
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)
{
struct {
int fd;
union sockaddr_u addr;
} sockfd[NUM_LISTEN_ADDRS];
int i, fdn = -1;
int fdmax, nbytes, n, 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);
struct timeval tv;
struct timeval *tvp = NULL;
unsigned int num_sockets;
#ifdef HAVE_OPENSSL
if(o.ssl)
bye("DTLS is not supported in listen mode\n");
#endif
for (i = 0; i < NUM_LISTEN_ADDRS; i++) {
sockfd[i].fd = -1;
sockfd[i].addr.storage.ss_family = AF_UNSPEC;
}
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
/* Not sure if this problem exists on Windows, but fcntl and /dev/null don't */
#ifndef WIN32
/* Check whether stdin is closed. Because we treat this fd specially, we
* can't risk it being reopened for an incoming connection, so we'll hold
* it open instead. */
if (fcntl(STDIN_FILENO, F_GETFD) == -1 && errno == EBADF) {
logdebug("stdin is closed, attempting to reserve STDIN_FILENO\n");
i = open("/dev/null", O_RDONLY);
if (i >= 0 && i != STDIN_FILENO) {
/* Oh well, we tried */
logdebug("Couldn't reserve STDIN_FILENO\n");
close(i);
}
}
#endif
/* set for selecting udp listening sockets */
fd_set listen_fds;
fd_list_t listen_fdlist;
FD_ZERO(&listen_fds);
init_fdlist(&listen_fdlist, num_listenaddrs);
num_sockets = 0;
for (i = 0; i < num_listenaddrs; i++) {
/* create the UDP listen sockets */
sockfd[num_sockets].fd = do_listen(SOCK_DGRAM, proto, &listenaddrs[i]);
if (sockfd[num_sockets].fd == -1) {
if (o.debug > 0)
logdebug("do_listen(\"%s\"): %s\n", inet_ntop_ez(&listenaddrs[i].storage, sizeof(listenaddrs[i].storage)), socket_strerror(socket_errno()));
continue;
}
FD_SET(sockfd[num_sockets].fd, &listen_fds);
add_fd(&listen_fdlist, sockfd[num_sockets].fd);
sockfd[num_sockets].addr = listenaddrs[i];
num_sockets++;
}
if (num_sockets == 0) {
if (num_listenaddrs == 1)
bye("Unable to open listening socket on %s: %s", inet_ntop_ez(&listenaddrs[0].storage, sizeof(listenaddrs[0].storage)), socket_strerror(socket_errno()));
else
bye("Unable to open any listening sockets.");
}
if (o.idletimeout > 0)
tvp = &tv;
while (1) {
int i, j, conn_count, socket_n;
if (fdn != -1) {
/*remove socket descriptor which is burnt */
FD_CLR(sockfd[fdn].fd, &listen_fds);
rm_fd(&listen_fdlist, sockfd[fdn].fd);
/* Rebuild the udp socket which got burnt */
sockfd[fdn].fd = do_listen(SOCK_DGRAM, proto, &sockfd[fdn].addr);
if (sockfd[fdn].fd == -1)
bye("do_listen: %s", socket_strerror(socket_errno()));
FD_SET(sockfd[fdn].fd, &listen_fds);
add_fd(&listen_fdlist, sockfd[fdn].fd);
}
fdn = -1;
socket_n = -1;
fd_set fds;
FD_ZERO(&fds);
while (1) {
/*
* We just select to get a list of sockets which we can talk to
*/
if (o.debug > 1)
logdebug("selecting, fdmax %d\n", listen_fdlist.fdmax);
fds = listen_fds;
if (o.idletimeout > 0)
ms_to_timeval(tvp, o.idletimeout);
/* The idle timer should only be running when there are active connections */
if (get_conn_count())
fds_ready = fselect(listen_fdlist.fdmax + 1, &fds, NULL, NULL, tvp);
else
fds_ready = fselect(listen_fdlist.fdmax + 1, &fds, NULL, NULL, NULL);
if (o.debug > 1)
logdebug("select returned %d fds ready\n", fds_ready);
if (fds_ready == 0)
bye("Idle timeout expired (%d ms).", o.idletimeout);
/*
* Figure out which listening socket got a connection. This loop should
* really call a function for each ready socket instead of breaking on
* the first one.
*/
for (i = 0; i <= listen_fdlist.fdmax && fds_ready > 0; i++) {
/* Loop through descriptors until there is something ready */
if (!FD_ISSET(i, &fds))
continue;
/* Check each listening socket */
for (j = 0; j < num_sockets; j++) {
if (i == sockfd[j].fd) {
if (o.debug > 1)
logdebug("Valid descriptor %d \n", i);
fdn = j;
socket_n = i;
break;
}
}
/* if we found a valid socket break */
if (fdn != -1) {
fds_ready--;
break;
}
}
/* Make sure someone connected */
if (fdn == -1)
continue;
/*
* We just peek so we can get the client connection details without
* removing anything from the queue. Sigh.
*/
nbytes = recvfrom(socket_n, buf, sizeof(buf), MSG_PEEK,
&remotess.sockaddr, &sslen);
if (nbytes < 0) {
loguser("%s.\n", socket_strerror(socket_errno()));
close(socket_n);
return 1;
}
/* 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 */
nbytes = recv(socket_n, buf, sizeof(buf), 0);
if (nbytes < 0) {
loguser("%s.\n", socket_strerror(socket_errno()));
close(socket_n);
return 1;
}
ncat_log_recv(buf, nbytes);
}
if (o.debug > 1)
logdebug("Valid Connection from %d\n", socket_n);
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(socket_n, &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 = socket_n;
if (o.keepopen)
netrun(&info, o.cmdexec);
else
netexec(&info, o.cmdexec);
continue;
}
FD_SET(socket_n, &read_fds);
FD_SET(STDIN_FILENO, &read_fds);
fdmax = socket_n;
/* stdin -> socket and socket -> stdout */
while (1) {
fd_set fds;
fds = read_fds;
if (o.debug > 1)
logdebug("udp select'ing\n");
if (o.idletimeout > 0)
ms_to_timeval(tvp, o.idletimeout);
fds_ready = fselect(fdmax + 1, &fds, NULL, NULL, tvp);
if (fds_ready == 0)
bye("Idle timeout expired (%d ms).", o.idletimeout);
if (FD_ISSET(STDIN_FILENO, &fds)) {
nbytes = Read(STDIN_FILENO, buf, sizeof(buf));
if (nbytes <= 0) {
if (nbytes < 0 && o.verbose) {
logdebug("Error reading from stdin: %s\n", strerror(errno));
} else if (nbytes == 0 && o.debug) {
logdebug("EOF on stdin\n");
}
FD_CLR(STDIN_FILENO, &read_fds);
if (nbytes < 0)
return 1;
continue;
}
if (o.crlf)
fix_line_endings((char *) buf, &nbytes, &tempbuf, &crlf_state);
if (!o.recvonly) {
if (tempbuf != NULL)
n = send(socket_n, tempbuf, nbytes, 0);
else
n = send(socket_n, buf, nbytes, 0);
if (n < nbytes) {
loguser("%s.\n", socket_strerror(socket_errno()));
close(socket_n);
return 1;
}
ncat_log_send(buf, nbytes);
}
if (tempbuf != NULL) {
free(tempbuf);
tempbuf = NULL;
}
}
if (FD_ISSET(socket_n, &fds)) {
nbytes = recv(socket_n, buf, sizeof(buf), 0);
if (nbytes < 0) {
loguser("%s.\n", socket_strerror(socket_errno()));
close(socket_n);
return 1;
}
ncat_log_recv(buf, nbytes);
if (!o.sendonly)
Write(STDOUT_FILENO, buf, nbytes);
}
zmem(buf, sizeof(buf));
}
}
return 0;
}
int ncat_listen()
{
#if HAVE_SYS_UN_H
if (o.af == AF_UNIX)
if (o.proto == IPPROTO_UDP)
return ncat_listen_dgram(0);
else
return ncat_listen_stream(0);
else
#endif
if (o.httpserver)
return ncat_http_server();
else if (o.proto == IPPROTO_UDP)
return ncat_listen_dgram(o.proto);
else if (o.proto == IPPROTO_SCTP)
return ncat_listen_stream(o.proto);
else if (o.proto == IPPROTO_TCP)
return ncat_listen_stream(o.proto);
else
bye("Unknown o.proto %d\n", o.proto);
/* unreached */
return 1;
}
//---------------
/* Read from recv_fd and broadcast whatever is read to all other descriptors in
read_fds, with the exception of stdin, listen_socket, and recv_fd itself.
Handles EOL translation and chat mode. On read error or end of stream,
closes the socket and removes it from the read_fds list. */
static void read_and_broadcast(int recv_fd)
{
struct fdinfo *fdn;
int pending;
fdn = get_fdinfo(&client_fdlist, recv_fd);
ncat_assert(fdn != NULL);
/* Loop while ncat_recv indicates data is pending. */
do {
char buf[DEFAULT_TCP_BUF_LEN];
char *chatbuf, *outbuf;
char *tempbuf = NULL;
fd_set broadcastfds;
int n;
/* Behavior differs depending on whether this is stdin or a socket. */
if (recv_fd == STDIN_FILENO) {
n = read(recv_fd, buf, sizeof(buf));
if (n <= 0) {
if (n < 0 && o.verbose)
logdebug("Error reading from stdin: %s\n", strerror(errno));
if (n == 0 && o.debug)
logdebug("EOF on stdin\n");
/* Don't close the file because that allows a socket to be
fd 0. */
FD_CLR(recv_fd, &master_readfds);
/* But mark that we've seen EOF so it doesn't get re-added to
the select list. */
stdin_eof = 1;
return;
}
if (o.crlf)
fix_line_endings((char *) buf, &n, &tempbuf, &crlf_state);
pending = 0;
} else {
/* From a connected socket, not stdin. */
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 (n == 0)
SSL_shutdown(fdn->ssl);
SSL_free(fdn->ssl);
}
#endif
close(recv_fd);
FD_CLR(recv_fd, &master_readfds);
rm_fd(&client_fdlist, recv_fd);
FD_CLR(recv_fd, &master_broadcastfds);
rm_fd(&broadcast_fdlist, recv_fd);
conn_inc--;
if (conn_inc == 0)
FD_CLR(STDIN_FILENO, &master_readfds);
if (o.chat)
chat_announce_disconnect(recv_fd);
return;
}
}
if (o.debug > 1)
logdebug("Handling data from client %d.\n", recv_fd);
chatbuf = NULL;
/* tempbuf is in use if we read from STDIN and fixed EOL */
if (tempbuf == NULL)
outbuf = buf;
else
outbuf = tempbuf;
if (o.chat) {
chatbuf = chat_filter(outbuf, n, recv_fd, &n);
if (chatbuf == NULL) {
if (o.verbose)
logdebug("Error formatting chat message from fd %d\n", recv_fd);
} else {
outbuf = chatbuf;
}
}
/* Send to everyone except the one who sent this message. */
broadcastfds = master_broadcastfds;
FD_CLR(recv_fd, &broadcastfds);
ncat_broadcast(&broadcastfds, &broadcast_fdlist, outbuf, n);
free(chatbuf);
free(tempbuf);
tempbuf = NULL;
} while (pending);
}
static void shutdown_sockets(int how)
{
struct fdinfo *fdn;
int i;
for (i = 0; i <= broadcast_fdlist.fdmax; i++) {
if (!FD_ISSET(i, &master_broadcastfds))
continue;
fdn = get_fdinfo(&broadcast_fdlist, i);
ncat_assert(fdn != NULL);
shutdown(fdn->fd, how);
}
}
/* Announce the new connection and who is already connected. */
static int chat_announce_connect(int fd, const union sockaddr_u *su)
{
char *buf = NULL;
size_t size = 0, offset = 0;
int i, count, ret;
strbuf_sprintf(&buf, &size, &offset,
"<announce> %s is connected as <user%d>.\n", inet_socktop(su), fd);
strbuf_sprintf(&buf, &size, &offset, "<announce> already connected: ");
count = 0;
for (i = 0; i < client_fdlist.fdmax; i++) {
union sockaddr_u su;
socklen_t len = sizeof(su.storage);
if (i == fd || !FD_ISSET(i, &master_broadcastfds))
continue;
if (getpeername(i, &su.sockaddr, &len) == -1)
bye("getpeername for sd %d failed: %s.", i, strerror(errno));
if (count > 0)
strbuf_sprintf(&buf, &size, &offset, ", ");
strbuf_sprintf(&buf, &size, &offset, "%s as <user%d>", inet_socktop(&su), i);
count++;
}
if (count == 0)
strbuf_sprintf(&buf, &size, &offset, "nobody");
strbuf_sprintf(&buf, &size, &offset, ".\n");
ret = ncat_broadcast(&master_broadcastfds, &broadcast_fdlist, buf, offset);
free(buf);
return ret;
}
static int chat_announce_disconnect(int fd)
{
char buf[128];
int n;
n = Snprintf(buf, sizeof(buf),
"<announce> <user%d> is disconnected.\n", fd);
if (n >= sizeof(buf) || n < 0)
return -1;
return ncat_broadcast(&master_broadcastfds, &broadcast_fdlist, buf, n);
}
/*
* This is stupid. But it's just a bit of fun.
*
* The file descriptor of the sender is prepended to the
* message sent to clients, so you can distinguish
* each other with a degree of sanity. This gives a
* similar effect to an IRC session. But stupider.
*/
static char *chat_filter(char *buf, size_t size, int fd, int *nwritten)
{
char *result = NULL;
size_t n = 0;
const char *p;
int i;
n = 32;
result = (char *) safe_malloc(n);
i = Snprintf(result, n, "<user%d> ", fd);
/* Escape control characters. */
for (p = buf; p - buf < size; p++) {
char repl[32];
int repl_len;
if (isprint((int) (unsigned char) *p) || *p == '\r' || *p == '\n' || *p == '\t') {
repl[0] = *p;
repl_len = 1;
} else {
repl_len = Snprintf(repl, sizeof(repl), "\\%03o", (unsigned char) *p);
}
if (i + repl_len > n) {
n = (i + repl_len) * 2;
result = (char *) safe_realloc(result, n + 1);
}
memcpy(result + i, repl, repl_len);
i += repl_len;
}
/* Trim to length. (Also does initial allocation when str is empty.) */
result = (char *) safe_realloc(result, i + 1);
result[i] = '\0';
*nwritten = i;
return result;
}
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