/*************************************************************************** * ncat_listen.c -- --listen mode. * ***********************IMPORTANT NMAP LICENSE TERMS************************ * * * The Nmap Security Scanner is (C) 1996-2009 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 * * GNU General Public License as published by the Free Software * * Foundation; Version 2 with the clarifications and exceptions described * * below. 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@insecure.com). Dozens of software vendors already * * license Nmap technology such as host discovery, port scanning, OS * * detection, and version detection. * * * * Note that the GPL places important restrictions on "derived works", yet * * it does not provide a detailed definition of that term. To avoid * * misunderstandings, we consider an application to constitute a * * "derivative work" for the purpose of this license if it does any of the * * following: * * o Integrates source code from Nmap * * o Reads or includes Nmap copyrighted data files, such as * * nmap-os-db or nmap-service-probes. * * o Executes Nmap and parses the results (as opposed to typical shell or * * execution-menu apps, which simply display raw Nmap output and so are * * not derivative works.) * * o Integrates/includes/aggregates Nmap into a proprietary executable * * installer, such as those produced by InstallShield. * * o Links to a library or executes a program that does any of the above * * * * The term "Nmap" should be taken to also include any portions or derived * * works of Nmap. This list is not exclusive, but is meant to clarify our * * interpretation of derived works with some common examples. Our * * interpretation applies only to Nmap--we don't speak for other people's * * GPL works. * * * * If you have any questions about the GPL licensing restrictions on using * * Nmap in non-GPL works, we would be 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 as well as helping to * * fund the continued development of Nmap technology. Please email * * sales@insecure.com for further information. * * * * As a special exception to the GPL terms, Insecure.Com LLC 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 COPYING.OpenSSL file, and distribute linked * * combinations including the two. You must obey the GNU GPL in all * * respects for all of the code used other than OpenSSL. If you modify * * this file, you may extend this exception to your version of the file, * * but you are not obligated to do so. * * * * If you received these files with a written license agreement or * * contract stating terms other than the terms above, then that * * alternative license agreement takes precedence over these comments. * * * * 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 (none * * have been found so far). * * * * 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 nmap-dev@insecure.org for possible incorporation into the main * * distribution. By sending these changes to Fyodor or one of the * * Insecure.Org development mailing lists, it is assumed that you are * * offering the Nmap Project (Insecure.Com LLC) 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 GNU * * General Public License v2.0 for more details at * * http://www.gnu.org/licenses/gpl-2.0.html , or in the COPYING file * * included with Nmap. * * * ***************************************************************************/ /* $Id$ */ #include "ncat.h" #include #include #include #include #include #include #include #ifndef WIN32 #include #include #include #include #include #else #include #endif #ifdef HAVE_OPENSSL #include #include #endif static fd_set master, read_fds; static fd_list_t fdlist; static int listen_socket; static int conn_count = 0; /* Has stdin seen EOF? */ static int stdin_eof = 0; static void handle_connection(void); static int read_stdin(void); static int read_socket(int recv_fd); /* reap child processes */ static void sig_chld(int signo) { while (Waitpid(-1, NULL, WNOHANG) > 0) conn_count--; } static int ncat_listen_tcp() { #ifdef HAVE_OPENSSL SSL_CTX *ctx; #endif /* clear out structs */ FD_ZERO(&master); FD_ZERO(&read_fds); zmem(&fdlist, sizeof(fdlist)); #ifndef WIN32 /* Reap on SIGCHLD */ Signal(SIGCHLD, sig_chld); /* 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); /* 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, &master); /* we need a list of fds to keep current fdmax and send data to clients */ init_fdlist(&fdlist, sadd(o.conn_limit, 2)); add_fd(&fdlist, listen_socket, NULL); add_fd(&fdlist, STDIN_FILENO, NULL); while (1) { int i, fds_ready; if(o.debug > 1) logdebug("selecting, fdmax %d\n", fdlist.fdmax); read_fds = master; fds_ready = fselect(fdlist.fdmax + 1, &read_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 <= fdlist.fdmax && fds_ready > 0; i++) { /* Loop through descriptors until there's something to read */ if (!FD_ISSET(i, &read_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. */ if (read_stdin() <= 0) { /* There will be nothing more to send. If we're not receiving anything, we can quit here. */ if (o.sendonly) goto quit; } } else if (!o.sendonly) { /* Read from a client and write to stdout. */ if (read_socket(i) <= 0) { if (!o.keepopen) goto quit; } } fds_ready--; } } quit: 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) { struct sockaddr_storage remoteaddr; socklen_t ss_len; int fd; #ifdef HAVE_OPENSSL SSL *tmpssl = NULL; #else void *tmpssl = NULL; #endif ss_len = sizeof(remoteaddr); errno = 0; fd = accept(listen_socket, (struct sockaddr *) &remoteaddr, &ss_len); if (fd < 0) { if (o.debug) logdebug("Error in accept: %s\n", strerror(errno)); close(fd); return; } if (o.verbose) loguser("Connection from %s.\n", inet_socktop(&remoteaddr)); /* Check conditions that might cause us to deny the connection. */ if (conn_count >= o.conn_limit) { if (o.verbose) loguser("New connection denied: connection limit reached (%d)\n", conn_count); Close(fd); return; } if (!allow_access(&remoteaddr)) { if (o.verbose) loguser("New connection denied: not allowed\n"); Close(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(fd); #ifdef HAVE_OPENSSL if (o.ssl) { tmpssl = new_ssl(fd); if (SSL_accept(tmpssl) != 1) { if (o.verbose) { loguser("Failed SSL connection from %s: %s\n", inet_socktop(&remoteaddr), ERR_error_string(ERR_get_error(), NULL)); } SSL_free(tmpssl); Close(fd); return; } } #endif conn_count++; /* * are we executing a command? if so then don't add this guy * to our descriptor list or set. */ if (o.cmdexec) { netrun(fd, o.cmdexec); } else { /* add to our lists */ FD_SET(fd, &master); /* Now that a client is connected, pay attention to stdin. */ if (!stdin_eof) FD_SET(STDIN_FILENO, &master); /* add it to our list of fds for maintaining maxfd */ if (add_fd(&fdlist, fd, tmpssl) < 0) bye("add_fd() 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; fd_set 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)); 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); /* 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); if(o.linedelay) ncat_delay_timer(o.linedelay); /* Write to everything in the master set, except the listener, sender, and stdin. */ fds = master; FD_CLR(STDIN_FILENO, &fds); FD_CLR(listen_socket, &fds); if (tempbuf != NULL) { broadcast(&fds, &fdlist, tempbuf, nbytes); free(tempbuf); tempbuf = NULL; } else broadcast(&fds, &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 = get_fdinfo(&fdlist, recv_fd); ssize_t nbytes; assert(fdn); #ifdef HAVE_OPENSSL readagain: if (o.ssl && fdn->ssl) nbytes = SSL_read(fdn->ssl, buf, sizeof(buf)); else #endif nbytes = recv(recv_fd, buf, sizeof(buf), 0); if (nbytes <= 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, &master); rm_fd(&fdlist, recv_fd); conn_count--; if (conn_count == 0) FD_CLR(STDIN_FILENO, &master); return nbytes; } if(o.linedelay) ncat_delay_timer(o.linedelay); if (o.telnet) dotelnet(recv_fd, (unsigned char *) buf, nbytes); Write(STDOUT_FILENO, buf, nbytes); ncat_log_recv(buf, nbytes); #ifdef HAVE_OPENSSL /* SSL can buffer our input, so doing another select() * won't necessarily work for us. We jump back up to * read any more data we can grab now */ if (o.ssl && fdn->ssl && SSL_pending(fdn->ssl)) goto readagain; #endif 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_udp() { int sockfd, fdmax, nbytes, fds_ready; char buf[DEFAULT_UDP_BUF_LEN] = {0}; char* tempbuf = NULL; fd_set master, read_fds; struct sockaddr_storage remotess; socklen_t sslen = sizeof(remotess); FD_ZERO(&master); read_fds = master; /* Initialize remotess struct so recvfrom() doesn't hit the fan.. */ zmem(&remotess, sizeof(remotess)); remotess.ss_family = o.af; #ifndef WIN32 /* Reap on SIGCHLD */ Signal(SIGCHLD, sig_chld); #endif while (1) { /* create the UDP listen socket */ sockfd = do_listen(SOCK_DGRAM); while (1) { /* * 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, (struct sockaddr *) &remotess, &sslen); /* Check conditions that might cause us to deny the connection. */ 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_count++; /* * We're using connected udp. This has the down side of only * being able to handle one udp client at a time */ Connect(sockfd, (struct sockaddr *) &remotess, sslen); /* clean slate for buf */ zmem(buf, sizeof(buf)); /* are we executing a command? then do it */ if (o.cmdexec) { netrun(sockfd, o.cmdexec); continue; } FD_SET(sockfd, &master); FD_SET(STDIN_FILENO, &master); fdmax = sockfd; /* stdin -> socket and socket -> stdout */ while (1) { read_fds = master; if(o.debug > 1) logdebug("udp select'ing\n"); fds_ready = fselect(fdmax + 1, &read_fds, NULL, NULL, NULL); if (FD_ISSET(STDIN_FILENO, &read_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); 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, &read_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_udp(); else return ncat_listen_tcp(); /* unreached */ return 1; }