/*************************************************************************** * 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 * * 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 docs/licenses/OpenSSL.txt 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 /* 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; }