/* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland * All rights reserved * Created: Fri Mar 17 17:09:28 1995 ylo * This program is the ssh daemon. It listens for connections from clients, and * performs authentication, executes use commands or shell, and forwards * information to/from the application to the user client over an encrypted * connection. This can also handle forwarding of X11, TCP/IP, and authentication * agent connections. * * SSH2 implementation, * Copyright (c) 2000 Markus Friedl. All rights reserved. */ #include "includes.h" RCSID("$OpenBSD: sshd.c,v 1.104 2000/04/12 09:39:10 markus Exp $"); #include "xmalloc.h" #include "rsa.h" #include "ssh.h" #include "pty.h" #include "packet.h" #include "cipher.h" #include "mpaux.h" #include "servconf.h" #include "uidswap.h" #include "compat.h" #include "buffer.h" #include "ssh2.h" #ifdef HAVE_OPENSSL # include # include # include # include # include #endif #ifdef HAVE_SSL # include # include # include # include # include #endif #include "kex.h" #include "key.h" #include "dsa.h" #include "auth.h" #include "myproposal.h" #ifdef LIBWRAP #include #include int allow_severity = LOG_INFO; int deny_severity = LOG_WARNING; #endif /* LIBWRAP */ #ifndef O_NOCTTY #define O_NOCTTY 0 #endif /* Server configuration options. */ ServerOptions options; /* Name of the server configuration file. */ char *config_file_name = SERVER_CONFIG_FILE; /* * Flag indicating whether IPv4 or IPv6. This can be set on the command line. * Default value is AF_UNSPEC means both IPv4 and IPv6. */ #ifdef IPV4_DEFAULT int IPv4or6 = AF_INET; #else int IPv4or6 = AF_UNSPEC; #endif /* * Debug mode flag. This can be set on the command line. If debug * mode is enabled, extra debugging output will be sent to the system * log, the daemon will not go to background, and will exit after processing * the first connection. */ int debug_flag = 0; /* Flag indicating that the daemon is being started from inetd. */ int inetd_flag = 0; /* debug goes to stderr unless inetd_flag is set */ int log_stderr = 0; /* argv[0] without path. */ char *av0; /* Saved arguments to main(). */ char **saved_argv; /* * The sockets that the server is listening; this is used in the SIGHUP * signal handler. */ #define MAX_LISTEN_SOCKS 16 int listen_socks[MAX_LISTEN_SOCKS]; int num_listen_socks = 0; /* * the client's version string, passed by sshd2 in compat mode. if != NULL, * sshd will skip the version-number exchange */ char *client_version_string = NULL; char *server_version_string = NULL; /* * Any really sensitive data in the application is contained in this * structure. The idea is that this structure could be locked into memory so * that the pages do not get written into swap. However, there are some * problems. The private key contains BIGNUMs, and we do not (in principle) * have access to the internals of them, and locking just the structure is * not very useful. Currently, memory locking is not implemented. */ struct { RSA *private_key; /* Private part of server key. */ RSA *host_key; /* Private part of host key. */ } sensitive_data; /* * Flag indicating whether the current session key has been used. This flag * is set whenever the key is used, and cleared when the key is regenerated. */ int key_used = 0; /* This is set to true when SIGHUP is received. */ int received_sighup = 0; /* Public side of the server key. This value is regenerated regularly with the private key. */ RSA *public_key; /* session identifier, used by RSA-auth */ unsigned char session_id[16]; /* Prototypes for various functions defined later in this file. */ void do_ssh1_kex(); void do_ssh2_kex(); /* * Close all listening sockets */ void close_listen_socks(void) { int i; for (i = 0; i < num_listen_socks; i++) close(listen_socks[i]); num_listen_socks = -1; } /* * Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP; * the effect is to reread the configuration file (and to regenerate * the server key). */ void sighup_handler(int sig) { received_sighup = 1; signal(SIGHUP, sighup_handler); } /* * Called from the main program after receiving SIGHUP. * Restarts the server. */ void sighup_restart() { log("Received SIGHUP; restarting."); close_listen_socks(); execv(saved_argv[0], saved_argv); log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno)); exit(1); } /* * Generic signal handler for terminating signals in the master daemon. * These close the listen socket; not closing it seems to cause "Address * already in use" problems on some machines, which is inconvenient. */ void sigterm_handler(int sig) { log("Received signal %d; terminating.", sig); close_listen_socks(); exit(255); } /* * SIGCHLD handler. This is called whenever a child dies. This will then * reap any zombies left by exited c. */ void main_sigchld_handler(int sig) { int save_errno = errno; int status; while (waitpid(-1, &status, WNOHANG) > 0) ; signal(SIGCHLD, main_sigchld_handler); errno = save_errno; } /* * Signal handler for the alarm after the login grace period has expired. */ void grace_alarm_handler(int sig) { /* Close the connection. */ packet_close(); /* Log error and exit. */ fatal("Timeout before authentication for %s.", get_remote_ipaddr()); } /* * Signal handler for the key regeneration alarm. Note that this * alarm only occurs in the daemon waiting for connections, and it does not * do anything with the private key or random state before forking. * Thus there should be no concurrency control/asynchronous execution * problems. */ void key_regeneration_alarm(int sig) { int save_errno = errno; /* Check if we should generate a new key. */ if (key_used) { /* This should really be done in the background. */ log("Generating new %d bit RSA key.", options.server_key_bits); if (sensitive_data.private_key != NULL) RSA_free(sensitive_data.private_key); sensitive_data.private_key = RSA_new(); if (public_key != NULL) RSA_free(public_key); public_key = RSA_new(); rsa_generate_key(sensitive_data.private_key, public_key, options.server_key_bits); arc4random_stir(); key_used = 0; log("RSA key generation complete."); } /* Reschedule the alarm. */ signal(SIGALRM, key_regeneration_alarm); alarm(options.key_regeneration_time); errno = save_errno; } char * chop(char *s) { char *t = s; while (*t) { if(*t == '\n' || *t == '\r') { *t = '\0'; return s; } t++; } return s; } void sshd_exchange_identification(int sock_in, int sock_out) { int i, mismatch; int remote_major, remote_minor; int major, minor; char *s; char buf[256]; /* Must not be larger than remote_version. */ char remote_version[256]; /* Must be at least as big as buf. */ if ((options.protocol & SSH_PROTO_1) && (options.protocol & SSH_PROTO_2)) { major = PROTOCOL_MAJOR_1; minor = 99; } else if (options.protocol & SSH_PROTO_2) { major = PROTOCOL_MAJOR_2; minor = PROTOCOL_MINOR_2; } else { major = PROTOCOL_MAJOR_1; minor = PROTOCOL_MINOR_1; } snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", major, minor, SSH_VERSION); server_version_string = xstrdup(buf); if (client_version_string == NULL) { /* Send our protocol version identification. */ if (atomicio(write, sock_out, server_version_string, strlen(server_version_string)) != strlen(server_version_string)) { log("Could not write ident string to %s.", get_remote_ipaddr()); fatal_cleanup(); } /* Read other side\'s version identification. */ for (i = 0; i < sizeof(buf) - 1; i++) { if (read(sock_in, &buf[i], 1) != 1) { log("Did not receive ident string from %s.", get_remote_ipaddr()); fatal_cleanup(); } if (buf[i] == '\r') { buf[i] = '\n'; buf[i + 1] = 0; continue; } if (buf[i] == '\n') { /* buf[i] == '\n' */ buf[i + 1] = 0; break; } } buf[sizeof(buf) - 1] = 0; client_version_string = xstrdup(buf); } /* * Check that the versions match. In future this might accept * several versions and set appropriate flags to handle them. */ if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor, remote_version) != 3) { s = "Protocol mismatch.\n"; (void) atomicio(write, sock_out, s, strlen(s)); close(sock_in); close(sock_out); log("Bad protocol version identification '%.100s' from %s", client_version_string, get_remote_ipaddr()); fatal_cleanup(); } debug("Client protocol version %d.%d; client software version %.100s", remote_major, remote_minor, remote_version); compat_datafellows(remote_version); mismatch = 0; switch(remote_major) { case 1: if (!(options.protocol & SSH_PROTO_1)) { mismatch = 1; break; } if (remote_minor < 3) { packet_disconnect("Your ssh version is too old and" "is no longer supported. Please install a newer version."); } else if (remote_minor == 3) { /* note that this disables agent-forwarding */ enable_compat13(); } if (remote_minor == 99) { if (options.protocol & SSH_PROTO_2) enable_compat20(); else mismatch = 1; } break; case 2: if (options.protocol & SSH_PROTO_2) { enable_compat20(); break; } /* FALLTHROUGH */ default: mismatch = 1; break; } chop(server_version_string); chop(client_version_string); debug("Local version string %.200s", server_version_string); if (mismatch) { s = "Protocol major versions differ.\n"; (void) atomicio(write, sock_out, s, strlen(s)); close(sock_in); close(sock_out); log("Protocol major versions differ for %s: %.200s vs. %.200s", get_remote_ipaddr(), server_version_string, client_version_string); fatal_cleanup(); } } /* * Main program for the daemon. */ int main(int ac, char **av) { extern char *optarg; extern int optind; int opt, sock_in = 0, sock_out = 0, newsock, i, fdsetsz, pid, on = 1; socklen_t fromlen; int silentrsa = 0; fd_set *fdset; struct sockaddr_storage from; const char *remote_ip; int remote_port; char *comment; FILE *f; struct linger linger; struct addrinfo *ai; char ntop[NI_MAXHOST], strport[NI_MAXSERV]; int listen_sock, maxfd; /* Save argv[0]. */ saved_argv = av; if (strchr(av[0], '/')) av0 = strrchr(av[0], '/') + 1; else av0 = av[0]; /* Initialize configuration options to their default values. */ initialize_server_options(&options); /* Parse command-line arguments. */ while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ46")) != EOF) { switch (opt) { case '4': IPv4or6 = AF_INET; break; case '6': IPv4or6 = AF_INET6; break; case 'f': config_file_name = optarg; break; case 'd': debug_flag = 1; options.log_level = SYSLOG_LEVEL_DEBUG; break; case 'i': inetd_flag = 1; break; case 'Q': silentrsa = 1; break; case 'q': options.log_level = SYSLOG_LEVEL_QUIET; break; case 'b': options.server_key_bits = atoi(optarg); break; case 'p': options.ports_from_cmdline = 1; if (options.num_ports >= MAX_PORTS) fatal("too many ports.\n"); options.ports[options.num_ports++] = atoi(optarg); break; case 'g': options.login_grace_time = atoi(optarg); break; case 'k': options.key_regeneration_time = atoi(optarg); break; case 'h': options.host_key_file = optarg; break; case 'V': client_version_string = optarg; /* only makes sense with inetd_flag, i.e. no listen() */ inetd_flag = 1; break; case '?': default: fprintf(stderr, "sshd version %s\n", SSH_VERSION); fprintf(stderr, "Usage: %s [options]\n", av0); fprintf(stderr, "Options:\n"); fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE); fprintf(stderr, " -d Debugging mode\n"); fprintf(stderr, " -i Started from inetd\n"); fprintf(stderr, " -q Quiet (no logging)\n"); fprintf(stderr, " -p port Listen on the specified port (default: 22)\n"); fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n"); fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n"); fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n"); fprintf(stderr, " -h file File from which to read host key (default: %s)\n", HOST_KEY_FILE); fprintf(stderr, " -4 Use IPv4 only\n"); fprintf(stderr, " -6 Use IPv6 only\n"); exit(1); } } /* * Force logging to stderr until we have loaded the private host * key (unless started from inetd) */ log_init(av0, options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level, options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility, !inetd_flag); /* check if RSA support exists */ if (rsa_alive() == 0) { if (silentrsa == 0) printf("sshd: no RSA support in libssl and libcrypto -- exiting. See ssl(8)\n"); log("no RSA support in libssl and libcrypto -- exiting. See ssl(8)"); exit(1); } /* Read server configuration options from the configuration file. */ read_server_config(&options, config_file_name); /* Fill in default values for those options not explicitly set. */ fill_default_server_options(&options); /* Check certain values for sanity. */ if (options.server_key_bits < 512 || options.server_key_bits > 32768) { fprintf(stderr, "Bad server key size.\n"); exit(1); } /* Check that there are no remaining arguments. */ if (optind < ac) { fprintf(stderr, "Extra argument %s.\n", av[optind]); exit(1); } debug("sshd version %.100s", SSH_VERSION); sensitive_data.host_key = RSA_new(); errno = 0; /* Load the host key. It must have empty passphrase. */ if (!load_private_key(options.host_key_file, "", sensitive_data.host_key, &comment)) { error("Could not load host key: %.200s: %.100s", options.host_key_file, strerror(errno)); exit(1); } xfree(comment); /* Initialize the log (it is reinitialized below in case we forked). */ if (debug_flag && !inetd_flag) log_stderr = 1; log_init(av0, options.log_level, options.log_facility, log_stderr); /* If not in debugging mode, and not started from inetd, disconnect from the controlling terminal, and fork. The original process exits. */ if (!debug_flag && !inetd_flag) { #ifdef TIOCNOTTY int fd; #endif /* TIOCNOTTY */ if (daemon(0, 0) < 0) fatal("daemon() failed: %.200s", strerror(errno)); /* Disconnect from the controlling tty. */ #ifdef TIOCNOTTY fd = open("/dev/tty", O_RDWR | O_NOCTTY); if (fd >= 0) { (void) ioctl(fd, TIOCNOTTY, NULL); close(fd); } #endif /* TIOCNOTTY */ } /* Reinitialize the log (because of the fork above). */ log_init(av0, options.log_level, options.log_facility, log_stderr); /* Check that server and host key lengths differ sufficiently. This is necessary to make double encryption work with rsaref. Oh, I hate software patents. I dont know if this can go? Niels */ if (options.server_key_bits > BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED && options.server_key_bits < BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) { options.server_key_bits = BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED; debug("Forcing server key to %d bits to make it differ from host key.", options.server_key_bits); } /* Do not display messages to stdout in RSA code. */ rsa_set_verbose(0); /* Initialize the random number generator. */ arc4random_stir(); /* Chdir to the root directory so that the current disk can be unmounted if desired. */ chdir("/"); /* Start listening for a socket, unless started from inetd. */ if (inetd_flag) { int s1, s2; s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */ s2 = dup(s1); sock_in = dup(0); sock_out = dup(1); /* We intentionally do not close the descriptors 0, 1, and 2 as our code for setting the descriptors won\'t work if ttyfd happens to be one of those. */ debug("inetd sockets after dupping: %d, %d", sock_in, sock_out); public_key = RSA_new(); sensitive_data.private_key = RSA_new(); /* XXX check options.protocol */ log("Generating %d bit RSA key.", options.server_key_bits); rsa_generate_key(sensitive_data.private_key, public_key, options.server_key_bits); arc4random_stir(); log("RSA key generation complete."); } else { for (ai = options.listen_addrs; ai; ai = ai->ai_next) { if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6) continue; if (num_listen_socks >= MAX_LISTEN_SOCKS) fatal("Too many listen sockets. " "Enlarge MAX_LISTEN_SOCKS"); if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop), strport, sizeof(strport), NI_NUMERICHOST|NI_NUMERICSERV) != 0) { error("getnameinfo failed"); continue; } /* Create socket for listening. */ listen_sock = socket(ai->ai_family, SOCK_STREAM, 0); if (listen_sock < 0) { /* kernel may not support ipv6 */ verbose("socket: %.100s", strerror(errno)); continue; } if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) { error("listen_sock O_NONBLOCK: %s", strerror(errno)); close(listen_sock); continue; } /* * Set socket options. We try to make the port * reusable and have it close as fast as possible * without waiting in unnecessary wait states on * close. */ setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, (void *) &on, sizeof(on)); linger.l_onoff = 1; linger.l_linger = 5; setsockopt(listen_sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger)); debug("Bind to port %s on %s.", strport, ntop); /* Bind the socket to the desired port. */ if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) && (!ai->ai_next)) { error("Bind to port %s on %s failed: %.200s.", strport, ntop, strerror(errno)); close(listen_sock); continue; } listen_socks[num_listen_socks] = listen_sock; num_listen_socks++; /* Start listening on the port. */ log("Server listening on %s port %s.", ntop, strport); if (listen(listen_sock, 5) < 0) fatal("listen: %.100s", strerror(errno)); } freeaddrinfo(options.listen_addrs); if (!num_listen_socks) fatal("Cannot bind any address."); if (!debug_flag) { /* * Record our pid in /etc/sshd_pid to make it easier * to kill the correct sshd. We don\'t want to do * this before the bind above because the bind will * fail if there already is a daemon, and this will * overwrite any old pid in the file. */ f = fopen(SSH_DAEMON_PID_FILE, "w"); if (f) { fprintf(f, "%u\n", (unsigned int) getpid()); fclose(f); } } public_key = RSA_new(); sensitive_data.private_key = RSA_new(); log("Generating %d bit RSA key.", options.server_key_bits); rsa_generate_key(sensitive_data.private_key, public_key, options.server_key_bits); arc4random_stir(); log("RSA key generation complete."); /* Schedule server key regeneration alarm. */ signal(SIGALRM, key_regeneration_alarm); alarm(options.key_regeneration_time); /* Arrange to restart on SIGHUP. The handler needs listen_sock. */ signal(SIGHUP, sighup_handler); signal(SIGTERM, sigterm_handler); signal(SIGQUIT, sigterm_handler); /* Arrange SIGCHLD to be caught. */ signal(SIGCHLD, main_sigchld_handler); /* setup fd set for listen */ maxfd = 0; for (i = 0; i < num_listen_socks; i++) if (listen_socks[i] > maxfd) maxfd = listen_socks[i]; fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask); fdset = (fd_set *)xmalloc(fdsetsz); /* * Stay listening for connections until the system crashes or * the daemon is killed with a signal. */ for (;;) { if (received_sighup) sighup_restart(); /* Wait in select until there is a connection. */ memset(fdset, 0, fdsetsz); for (i = 0; i < num_listen_socks; i++) FD_SET(listen_socks[i], fdset); if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) { if (errno != EINTR) error("select: %.100s", strerror(errno)); continue; } for (i = 0; i < num_listen_socks; i++) { if (!FD_ISSET(listen_socks[i], fdset)) continue; fromlen = sizeof(from); newsock = accept(listen_socks[i], (struct sockaddr *)&from, &fromlen); if (newsock < 0) { if (errno != EINTR && errno != EWOULDBLOCK) error("accept: %.100s", strerror(errno)); continue; } if (fcntl(newsock, F_SETFL, 0) < 0) { error("newsock del O_NONBLOCK: %s", strerror(errno)); continue; } /* * Got connection. Fork a child to handle it, unless * we are in debugging mode. */ if (debug_flag) { /* * In debugging mode. Close the listening * socket, and start processing the * connection without forking. */ debug("Server will not fork when running in debugging mode."); close_listen_socks(); sock_in = newsock; sock_out = newsock; pid = getpid(); break; } else { /* * Normal production daemon. Fork, and have * the child process the connection. The * parent continues listening. */ if ((pid = fork()) == 0) { /* * Child. Close the listening socket, and start using the * accepted socket. Reinitialize logging (since our pid has * changed). We break out of the loop to handle the connection. */ close_listen_socks(); sock_in = newsock; sock_out = newsock; log_init(av0, options.log_level, options.log_facility, log_stderr); break; } } /* Parent. Stay in the loop. */ if (pid < 0) error("fork: %.100s", strerror(errno)); else debug("Forked child %d.", pid); /* Mark that the key has been used (it was "given" to the child). */ key_used = 1; arc4random_stir(); /* Close the new socket (the child is now taking care of it). */ close(newsock); } /* for (i = 0; i < num_listen_socks; i++) */ /* child process check (or debug mode) */ if (num_listen_socks < 0) break; } } /* This is the child processing a new connection. */ /* * Disable the key regeneration alarm. We will not regenerate the * key since we are no longer in a position to give it to anyone. We * will not restart on SIGHUP since it no longer makes sense. */ alarm(0); signal(SIGALRM, SIG_DFL); signal(SIGHUP, SIG_DFL); signal(SIGTERM, SIG_DFL); signal(SIGQUIT, SIG_DFL); signal(SIGCHLD, SIG_DFL); /* * Set socket options for the connection. We want the socket to * close as fast as possible without waiting for anything. If the * connection is not a socket, these will do nothing. */ /* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */ linger.l_onoff = 1; linger.l_linger = 5; setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger)); /* * Register our connection. This turns encryption off because we do * not have a key. */ packet_set_connection(sock_in, sock_out); remote_port = get_remote_port(); remote_ip = get_remote_ipaddr(); /* Check whether logins are denied from this host. */ #ifdef LIBWRAP /* XXX LIBWRAP noes not know about IPv6 */ { struct request_info req; request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL); fromhost(&req); if (!hosts_access(&req)) { close(sock_in); close(sock_out); refuse(&req); } /*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */ } #endif /* LIBWRAP */ /* Log the connection. */ verbose("Connection from %.500s port %d", remote_ip, remote_port); /* * We don\'t want to listen forever unless the other side * successfully authenticates itself. So we set up an alarm which is * cleared after successful authentication. A limit of zero * indicates no limit. Note that we don\'t set the alarm in debugging * mode; it is just annoying to have the server exit just when you * are about to discover the bug. */ signal(SIGALRM, grace_alarm_handler); if (!debug_flag) alarm(options.login_grace_time); sshd_exchange_identification(sock_in, sock_out); /* * Check that the connection comes from a privileged port. Rhosts- * and Rhosts-RSA-Authentication only make sense from priviledged * programs. Of course, if the intruder has root access on his local * machine, he can connect from any port. So do not use these * authentication methods from machines that you do not trust. */ if (remote_port >= IPPORT_RESERVED || remote_port < IPPORT_RESERVED / 2) { options.rhosts_authentication = 0; options.rhosts_rsa_authentication = 0; } #ifdef KRB4 if (!packet_connection_is_ipv4() && options.kerberos_authentication) { debug("Kerberos Authentication disabled, only available for IPv4."); options.kerberos_authentication = 0; } #endif /* KRB4 */ packet_set_nonblocking(); /* perform the key exchange */ /* authenticate user and start session */ if (compat20) { do_ssh2_kex(); do_authentication2(); } else { do_ssh1_kex(); do_authentication(); } #ifdef KRB4 /* Cleanup user's ticket cache file. */ if (options.kerberos_ticket_cleanup) (void) dest_tkt(); #endif /* KRB4 */ /* The connection has been terminated. */ verbose("Closing connection to %.100s", remote_ip); #ifdef USE_PAM finish_pam(); #endif /* USE_PAM */ packet_close(); exit(0); } /* * SSH1 key exchange */ void do_ssh1_kex() { int i, len; int plen, slen; BIGNUM *session_key_int; unsigned char session_key[SSH_SESSION_KEY_LENGTH]; unsigned char cookie[8]; unsigned int cipher_type, auth_mask, protocol_flags; u_int32_t rand = 0; /* * Generate check bytes that the client must send back in the user * packet in order for it to be accepted; this is used to defy ip * spoofing attacks. Note that this only works against somebody * doing IP spoofing from a remote machine; any machine on the local * network can still see outgoing packets and catch the random * cookie. This only affects rhosts authentication, and this is one * of the reasons why it is inherently insecure. */ for (i = 0; i < 8; i++) { if (i % 4 == 0) rand = arc4random(); cookie[i] = rand & 0xff; rand >>= 8; } /* * Send our public key. We include in the packet 64 bits of random * data that must be matched in the reply in order to prevent IP * spoofing. */ packet_start(SSH_SMSG_PUBLIC_KEY); for (i = 0; i < 8; i++) packet_put_char(cookie[i]); /* Store our public server RSA key. */ packet_put_int(BN_num_bits(public_key->n)); packet_put_bignum(public_key->e); packet_put_bignum(public_key->n); /* Store our public host RSA key. */ packet_put_int(BN_num_bits(sensitive_data.host_key->n)); packet_put_bignum(sensitive_data.host_key->e); packet_put_bignum(sensitive_data.host_key->n); /* Put protocol flags. */ packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN); /* Declare which ciphers we support. */ packet_put_int(cipher_mask1()); /* Declare supported authentication types. */ auth_mask = 0; if (options.rhosts_authentication) auth_mask |= 1 << SSH_AUTH_RHOSTS; if (options.rhosts_rsa_authentication) auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA; if (options.rsa_authentication) auth_mask |= 1 << SSH_AUTH_RSA; #ifdef KRB4 if (options.kerberos_authentication) auth_mask |= 1 << SSH_AUTH_KERBEROS; #endif #ifdef AFS if (options.kerberos_tgt_passing) auth_mask |= 1 << SSH_PASS_KERBEROS_TGT; if (options.afs_token_passing) auth_mask |= 1 << SSH_PASS_AFS_TOKEN; #endif #ifdef SKEY if (options.skey_authentication == 1) auth_mask |= 1 << SSH_AUTH_TIS; #endif if (options.password_authentication) auth_mask |= 1 << SSH_AUTH_PASSWORD; packet_put_int(auth_mask); /* Send the packet and wait for it to be sent. */ packet_send(); packet_write_wait(); debug("Sent %d bit public key and %d bit host key.", BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n)); /* Read clients reply (cipher type and session key). */ packet_read_expect(&plen, SSH_CMSG_SESSION_KEY); /* Get cipher type and check whether we accept this. */ cipher_type = packet_get_char(); if (!(cipher_mask() & (1 << cipher_type))) packet_disconnect("Warning: client selects unsupported cipher."); /* Get check bytes from the packet. These must match those we sent earlier with the public key packet. */ for (i = 0; i < 8; i++) if (cookie[i] != packet_get_char()) packet_disconnect("IP Spoofing check bytes do not match."); debug("Encryption type: %.200s", cipher_name(cipher_type)); /* Get the encrypted integer. */ session_key_int = BN_new(); packet_get_bignum(session_key_int, &slen); protocol_flags = packet_get_int(); packet_set_protocol_flags(protocol_flags); packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY); /* * Decrypt it using our private server key and private host key (key * with larger modulus first). */ if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) { /* Private key has bigger modulus. */ if (BN_num_bits(sensitive_data.private_key->n) < BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) { fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d", get_remote_ipaddr(), BN_num_bits(sensitive_data.private_key->n), BN_num_bits(sensitive_data.host_key->n), SSH_KEY_BITS_RESERVED); } rsa_private_decrypt(session_key_int, session_key_int, sensitive_data.private_key); rsa_private_decrypt(session_key_int, session_key_int, sensitive_data.host_key); } else { /* Host key has bigger modulus (or they are equal). */ if (BN_num_bits(sensitive_data.host_key->n) < BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) { fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d", get_remote_ipaddr(), BN_num_bits(sensitive_data.host_key->n), BN_num_bits(sensitive_data.private_key->n), SSH_KEY_BITS_RESERVED); } rsa_private_decrypt(session_key_int, session_key_int, sensitive_data.host_key); rsa_private_decrypt(session_key_int, session_key_int, sensitive_data.private_key); } compute_session_id(session_id, cookie, sensitive_data.host_key->n, sensitive_data.private_key->n); /* Destroy the private and public keys. They will no longer be needed. */ RSA_free(public_key); RSA_free(sensitive_data.private_key); RSA_free(sensitive_data.host_key); /* * Extract session key from the decrypted integer. The key is in the * least significant 256 bits of the integer; the first byte of the * key is in the highest bits. */ BN_mask_bits(session_key_int, sizeof(session_key) * 8); len = BN_num_bytes(session_key_int); if (len < 0 || len > sizeof(session_key)) fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d", get_remote_ipaddr(), len, sizeof(session_key)); memset(session_key, 0, sizeof(session_key)); BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len); /* Destroy the decrypted integer. It is no longer needed. */ BN_clear_free(session_key_int); /* Xor the first 16 bytes of the session key with the session id. */ for (i = 0; i < 16; i++) session_key[i] ^= session_id[i]; /* Set the session key. From this on all communications will be encrypted. */ packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type); /* Destroy our copy of the session key. It is no longer needed. */ memset(session_key, 0, sizeof(session_key)); debug("Received session key; encryption turned on."); /* Send an acknowledgement packet. Note that this packet is sent encrypted. */ packet_start(SSH_SMSG_SUCCESS); packet_send(); packet_write_wait(); } /* * SSH2 key exchange: diffie-hellman-group1-sha1 */ void do_ssh2_kex() { Buffer *server_kexinit; Buffer *client_kexinit; int payload_len, dlen; int slen; unsigned int klen, kout; char *ptr; unsigned char *signature = NULL; unsigned char *server_host_key_blob = NULL; unsigned int sbloblen; DH *dh; BIGNUM *dh_client_pub = 0; BIGNUM *shared_secret = 0; int i; unsigned char *kbuf; unsigned char *hash; Kex *kex; Key *server_host_key; char *cprop[PROPOSAL_MAX]; char *sprop[PROPOSAL_MAX]; /* KEXINIT */ if (options.ciphers != NULL) { myproposal[PROPOSAL_ENC_ALGS_CTOS] = myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers; } debug("Sending KEX init."); for (i = 0; i < PROPOSAL_MAX; i++) sprop[i] = xstrdup(myproposal[i]); server_kexinit = kex_init(sprop); packet_start(SSH2_MSG_KEXINIT); packet_put_raw(buffer_ptr(server_kexinit), buffer_len(server_kexinit)); packet_send(); packet_write_wait(); debug("done"); packet_read_expect(&payload_len, SSH2_MSG_KEXINIT); /* * save raw KEXINIT payload in buffer. this is used during * computation of the session_id and the session keys. */ client_kexinit = xmalloc(sizeof(*client_kexinit)); buffer_init(client_kexinit); ptr = packet_get_raw(&payload_len); buffer_append(client_kexinit, ptr, payload_len); /* skip cookie */ for (i = 0; i < 16; i++) (void) packet_get_char(); /* save kex init proposal strings */ for (i = 0; i < PROPOSAL_MAX; i++) { cprop[i] = packet_get_string(NULL); debug("got kexinit string: %s", cprop[i]); } i = (int) packet_get_char(); debug("first kex follow == %d", i); i = packet_get_int(); debug("reserved == %d", i); debug("done read kexinit"); kex = kex_choose_conf(cprop, sprop, 1); /* KEXDH */ debug("Wait SSH2_MSG_KEXDH_INIT."); packet_read_expect(&payload_len, SSH2_MSG_KEXDH_INIT); /* key, cert */ dh_client_pub = BN_new(); if (dh_client_pub == NULL) fatal("dh_client_pub == NULL"); packet_get_bignum2(dh_client_pub, &dlen); #ifdef DEBUG_KEXDH fprintf(stderr, "\ndh_client_pub= "); bignum_print(dh_client_pub); fprintf(stderr, "\n"); debug("bits %d", BN_num_bits(dh_client_pub)); #endif /* generate DH key */ dh = dh_new_group1(); /* XXX depends on 'kex' */ #ifdef DEBUG_KEXDH fprintf(stderr, "\np= "); bignum_print(dh->p); fprintf(stderr, "\ng= "); bignum_print(dh->g); fprintf(stderr, "\npub= "); bignum_print(dh->pub_key); fprintf(stderr, "\n"); #endif if (!dh_pub_is_valid(dh, dh_client_pub)) packet_disconnect("bad client public DH value"); klen = DH_size(dh); kbuf = xmalloc(klen); kout = DH_compute_key(kbuf, dh_client_pub, dh); #ifdef DEBUG_KEXDH debug("shared secret: len %d/%d", klen, kout); fprintf(stderr, "shared secret == "); for (i = 0; i< kout; i++) fprintf(stderr, "%02x", (kbuf[i])&0xff); fprintf(stderr, "\n"); #endif shared_secret = BN_new(); BN_bin2bn(kbuf, kout, shared_secret); memset(kbuf, 0, klen); xfree(kbuf); server_host_key = dsa_get_serverkey(options.dsa_key_file); dsa_make_serverkey_blob(server_host_key, &server_host_key_blob, &sbloblen); /* calc H */ /* XXX depends on 'kex' */ hash = kex_hash( client_version_string, server_version_string, buffer_ptr(client_kexinit), buffer_len(client_kexinit), buffer_ptr(server_kexinit), buffer_len(server_kexinit), (char *)server_host_key_blob, sbloblen, dh_client_pub, dh->pub_key, shared_secret ); buffer_free(client_kexinit); buffer_free(server_kexinit); xfree(client_kexinit); xfree(server_kexinit); #ifdef DEBUG_KEXDH fprintf(stderr, "hash == "); for (i = 0; i< 20; i++) fprintf(stderr, "%02x", (hash[i])&0xff); fprintf(stderr, "\n"); #endif /* sign H */ dsa_sign(server_host_key, &signature, &slen, hash, 20); /* hashlen depends on KEX */ key_free(server_host_key); /* send server hostkey, DH pubkey 'f' and singed H */ packet_start(SSH2_MSG_KEXDH_REPLY); packet_put_string((char *)server_host_key_blob, sbloblen); packet_put_bignum2(dh->pub_key); // f packet_put_string((char *)signature, slen); packet_send(); packet_write_wait(); kex_derive_keys(kex, hash, shared_secret); packet_set_kex(kex); /* have keys, free DH */ DH_free(dh); debug("send SSH2_MSG_NEWKEYS."); packet_start(SSH2_MSG_NEWKEYS); packet_send(); packet_write_wait(); debug("done: send SSH2_MSG_NEWKEYS."); debug("Wait SSH2_MSG_NEWKEYS."); packet_read_expect(&payload_len, SSH2_MSG_NEWKEYS); debug("GOT SSH2_MSG_NEWKEYS."); #ifdef DEBUG_KEXDH /* send 1st encrypted/maced/compressed message */ packet_start(SSH2_MSG_IGNORE); packet_put_cstring("markus"); packet_send(); packet_write_wait(); #endif debug("done: KEX2."); }