/* * 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. */ #include "includes.h" RCSID("$Id: sshd.c,v 1.71 1999/12/08 00:08:09 provos Exp $"); #include "xmalloc.h" #include "rsa.h" #include "ssh.h" #include "pty.h" #include "packet.h" #include "buffer.h" #include "cipher.h" #include "mpaux.h" #include "servconf.h" #include "uidswap.h" #include "compat.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 /* Local Xauthority file. */ static char *xauthfile = NULL; /* Server configuration options. */ ServerOptions options; /* Name of the server configuration file. */ char *config_file_name = SERVER_CONFIG_FILE; /* * 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; /* * This is set to the socket that the server is listening; this is used in * the SIGHUP signal handler. */ int listen_sock; /* * 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; /* Flags set in auth-rsa from authorized_keys flags. These are set in auth-rsa.c. */ int no_port_forwarding_flag = 0; int no_agent_forwarding_flag = 0; int no_x11_forwarding_flag = 0; int no_pty_flag = 0; /* RSA authentication "command=" option. */ char *forced_command = NULL; /* RSA authentication "environment=" options. */ struct envstring *custom_environment = NULL; /* Session id for the current session. */ unsigned char session_id[16]; /* * 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; /* Prototypes for various functions defined later in this file. */ void do_connection(); void do_authentication(char *user); void do_authloop(struct passwd * pw); void do_fake_authloop(char *user); void do_authenticated(struct passwd * pw); void do_exec_pty(const char *command, int ptyfd, int ttyfd, const char *ttyname, struct passwd * pw, const char *term, const char *display, const char *auth_proto, const char *auth_data); void do_exec_no_pty(const char *command, struct passwd * pw, const char *display, const char *auth_proto, const char *auth_data); void do_child(const char *command, struct passwd * pw, const char *term, const char *display, const char *auth_proto, const char *auth_data, const char *ttyname); /* * 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_sock); 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_sock); 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()); } /* * convert ssh auth msg type into description */ char * get_authname(int type) { switch (type) { case SSH_CMSG_AUTH_PASSWORD: return "password"; case SSH_CMSG_AUTH_RSA: return "rsa"; case SSH_CMSG_AUTH_RHOSTS_RSA: return "rhosts-rsa"; case SSH_CMSG_AUTH_RHOSTS: return "rhosts"; #ifdef KRB4 case SSH_CMSG_AUTH_KERBEROS: return "kerberos"; #endif #ifdef SKEY case SSH_CMSG_AUTH_TIS_RESPONSE: return "s/key"; #endif } fatal("get_authname: unknown auth %d: internal error", type); return NULL; } /* * 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; } /* * Main program for the daemon. */ int main(int ac, char **av) { extern char *optarg; extern int optind; int opt, aux, sock_in, sock_out, newsock, i, pid, on = 1; int remote_major, remote_minor; int silentrsa = 0; struct pollfd fds; struct sockaddr_in sin; char buf[100]; /* Must not be larger than remote_version. */ char remote_version[100]; /* Must be at least as big as buf. */ const char *remote_ip; int remote_port; char *comment; FILE *f; struct linger linger; /* 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:diqQ")) != EOF) { switch (opt) { 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.port = 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); exit(1); } } /* 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); } if (options.port < 1 || options.port > 65535) { fprintf(stderr, "Bad port number.\n"); exit(1); } /* Check that there are no remaining arguments. */ if (optind < ac) { fprintf(stderr, "Extra argument %s.\n", av[optind]); exit(1); } /* Force logging to stderr while loading the private host key unless started from inetd */ log_init(av0, options.log_level, options.log_facility, !inetd_flag); 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("/"); /* Close connection cleanly after attack. */ cipher_attack_detected = packet_disconnect; /* 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(); 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 { /* Create socket for listening. */ listen_sock = socket(AF_INET, SOCK_STREAM, 0); if (listen_sock < 0) fatal("socket: %.100s", strerror(errno)); /* 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)); memset(&sin, 0, sizeof(sin)); sin.sin_family = AF_INET; sin.sin_addr = options.listen_addr; sin.sin_port = htons(options.port); if (bind(listen_sock, (struct sockaddr *) & sin, sizeof(sin)) < 0) { error("bind: %.100s", strerror(errno)); shutdown(listen_sock, SHUT_RDWR); close(listen_sock); fatal("Bind to port %d failed.", options.port); } 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); } } log("Server listening on port %d.", options.port); if (listen(listen_sock, 5) < 0) fatal("listen: %.100s", strerror(errno)); 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); /* * Stay listening for connections until the system crashes or * the daemon is killed with a signal. */ for (;;) { if (received_sighup) sighup_restart(); /* Wait in poll until there is a connection. */ memset(&fds, 0, sizeof(fds)); fds.fd = listen_sock; fds.events = POLLIN; if (poll(&fds, 1, -1) == -1) { if (errno == EINTR) continue; fatal("poll: %.100s", strerror(errno)); /*NOTREACHED*/ } if (fds.revents == 0) continue; aux = sizeof(sin); newsock = accept(listen_sock, (struct sockaddr *) & sin, &aux); if (received_sighup) sighup_restart(); if (newsock < 0) { if (errno == EINTR) continue; error("accept: %.100s", 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_sock); 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_sock); 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); } } /* 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 { 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); } verbose("Connection from %.500s port %d", eval_client(&req), remote_port); } #else /* Log the connection. */ verbose("Connection from %.500s port %d", remote_ip, remote_port); #endif /* LIBWRAP */ /* * 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); if (client_version_string != NULL) { /* we are exec'ed by sshd2, so skip exchange of protocol version */ strlcpy(buf, client_version_string, sizeof(buf)); } else { /* Send our protocol version identification. */ snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION); if (atomicio(write, sock_out, buf, strlen(buf)) != strlen(buf)) fatal("Could not write ident string to %s.", get_remote_ipaddr()); /* Read other side\'s version identification. */ for (i = 0; i < sizeof(buf) - 1; i++) { if (read(sock_in, &buf[i], 1) != 1) fatal("Did not receive ident string from %s.", get_remote_ipaddr()); if (buf[i] == '\r') { buf[i] = '\n'; buf[i + 1] = 0; break; } if (buf[i] == '\n') { /* buf[i] == '\n' */ buf[i + 1] = 0; break; } } buf[sizeof(buf) - 1] = 0; } /* * Check that the versions match. In future this might accept * several versions and set appropriate flags to handle them. */ if (sscanf(buf, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor, remote_version) != 3) { char *s = "Protocol mismatch.\n"; (void) atomicio(write, sock_out, s, strlen(s)); close(sock_in); close(sock_out); fatal("Bad protocol version identification '%.100s' from %s", buf, get_remote_ipaddr()); } debug("Client protocol version %d.%d; client software version %.100s", remote_major, remote_minor, remote_version); if (remote_major != PROTOCOL_MAJOR) { char *s = "Protocol major versions differ.\n"; (void) atomicio(write, sock_out, s, strlen(s)); close(sock_in); close(sock_out); fatal("Protocol major versions differ for %s: %d vs. %d", get_remote_ipaddr(), PROTOCOL_MAJOR, remote_major); } /* Check that the client has sufficiently high software version. */ if (remote_major == 1 && remote_minor < 3) packet_disconnect("Your ssh version is too old and is no longer supported. Please install a newer version."); if (remote_major == 1 && remote_minor == 3) { enable_compat13(); if (strcmp(remote_version, "OpenSSH-1.1") != 0) { debug("Agent forwarding disabled, remote version is not compatible."); no_agent_forwarding_flag = 1; } } /* * 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; } packet_set_nonblocking(); /* Handle the connection. */ do_connection(); #ifdef KRB4 /* Cleanup user's ticket cache file. */ if (options.kerberos_ticket_cleanup) (void) dest_tkt(); #endif /* KRB4 */ /* Cleanup user's local Xauthority file. */ if (xauthfile) unlink(xauthfile); /* The connection has been terminated. */ verbose("Closing connection to %.100s", remote_ip); packet_close(); exit(0); } /* * Process an incoming connection. Protocol version identifiers have already * been exchanged. This sends server key and performs the key exchange. * Server and host keys will no longer be needed after this functions. */ void do_connection() { int i, len; BIGNUM *session_key_int; unsigned char session_key[SSH_SESSION_KEY_LENGTH]; unsigned char check_bytes[8]; char *user; unsigned int cipher_type, auth_mask, protocol_flags; int plen, slen; 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(); check_bytes[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(check_bytes[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_mask()); /* 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 (check_bytes[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, check_bytes, sensitive_data.host_key->n, sensitive_data.private_key->n); /* * 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); /* 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]; /* Destroy the decrypted integer. It is no longer needed. */ BN_clear_free(session_key_int); /* 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(); /* Get the name of the user that we wish to log in as. */ packet_read_expect(&plen, SSH_CMSG_USER); /* Get the user name. */ { int ulen; user = packet_get_string(&ulen); packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER); } /* 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); setproctitle("%s", user); /* Do the authentication. */ do_authentication(user); } /* * Check if the user is allowed to log in via ssh. If user is listed in * DenyUsers or user's primary group is listed in DenyGroups, false will * be returned. If AllowUsers isn't empty and user isn't listed there, or * if AllowGroups isn't empty and user isn't listed there, false will be * returned. Otherwise true is returned. * XXX This function should also check if user has a valid shell */ static int allowed_user(struct passwd * pw) { struct group *grp; int i; /* Shouldn't be called if pw is NULL, but better safe than sorry... */ if (!pw) return 0; /* XXX Should check for valid login shell */ /* Return false if user is listed in DenyUsers */ if (options.num_deny_users > 0) { if (!pw->pw_name) return 0; for (i = 0; i < options.num_deny_users; i++) if (match_pattern(pw->pw_name, options.deny_users[i])) return 0; } /* Return false if AllowUsers isn't empty and user isn't listed there */ if (options.num_allow_users > 0) { if (!pw->pw_name) return 0; for (i = 0; i < options.num_allow_users; i++) if (match_pattern(pw->pw_name, options.allow_users[i])) break; /* i < options.num_allow_users iff we break for loop */ if (i >= options.num_allow_users) return 0; } /* Get the primary group name if we need it. Return false if it fails */ if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { grp = getgrgid(pw->pw_gid); if (!grp) return 0; /* Return false if user's group is listed in DenyGroups */ if (options.num_deny_groups > 0) { if (!grp->gr_name) return 0; for (i = 0; i < options.num_deny_groups; i++) if (match_pattern(grp->gr_name, options.deny_groups[i])) return 0; } /* * Return false if AllowGroups isn't empty and user's group * isn't listed there */ if (options.num_allow_groups > 0) { if (!grp->gr_name) return 0; for (i = 0; i < options.num_allow_groups; i++) if (match_pattern(grp->gr_name, options.allow_groups[i])) break; /* i < options.num_allow_groups iff we break for loop */ if (i >= options.num_allow_groups) return 0; } } /* We found no reason not to let this user try to log on... */ return 1; } /* * Performs authentication of an incoming connection. Session key has already * been exchanged and encryption is enabled. User is the user name to log * in as (received from the client). */ void do_authentication(char *user) { struct passwd *pw, pwcopy; #ifdef AFS /* If machine has AFS, set process authentication group. */ if (k_hasafs()) { k_setpag(); k_unlog(); } #endif /* AFS */ /* Verify that the user is a valid user. */ pw = getpwnam(user); if (!pw || !allowed_user(pw)) do_fake_authloop(user); /* Take a copy of the returned structure. */ memset(&pwcopy, 0, sizeof(pwcopy)); pwcopy.pw_name = xstrdup(pw->pw_name); pwcopy.pw_passwd = xstrdup(pw->pw_passwd); pwcopy.pw_uid = pw->pw_uid; pwcopy.pw_gid = pw->pw_gid; pwcopy.pw_dir = xstrdup(pw->pw_dir); pwcopy.pw_shell = xstrdup(pw->pw_shell); pw = &pwcopy; /* * If we are not running as root, the user must have the same uid as * the server. */ if (getuid() != 0 && pw->pw_uid != getuid()) packet_disconnect("Cannot change user when server not running as root."); debug("Attempting authentication for %.100s.", user); /* If the user has no password, accept authentication immediately. */ if (options.password_authentication && #ifdef KRB4 (!options.kerberos_authentication || options.kerberos_or_local_passwd) && #endif /* KRB4 */ auth_password(pw, "")) { /* Authentication with empty password succeeded. */ log("Login for user %s from %.100s, accepted without authentication.", pw->pw_name, get_remote_ipaddr()); } else { /* Loop until the user has been authenticated or the connection is closed, do_authloop() returns only if authentication is successfull */ do_authloop(pw); } /* Check if the user is logging in as root and root logins are disallowed. */ if (pw->pw_uid == 0 && !options.permit_root_login) { if (forced_command) log("Root login accepted for forced command."); else packet_disconnect("ROOT LOGIN REFUSED FROM %.200s", get_canonical_hostname()); } /* The user has been authenticated and accepted. */ packet_start(SSH_SMSG_SUCCESS); packet_send(); packet_write_wait(); /* Perform session preparation. */ do_authenticated(pw); } #define AUTH_FAIL_MAX 6 #define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2) #define AUTH_FAIL_MSG "Too many authentication failures for %.100s" /* * read packets and try to authenticate local user *pw. * return if authentication is successfull */ void do_authloop(struct passwd * pw) { int attempt = 0; unsigned int bits; BIGNUM *client_host_key_e, *client_host_key_n; BIGNUM *n; char *client_user, *password; char user[1024]; int plen, dlen, nlen, ulen, elen; int type = 0; void (*authlog) (const char *fmt,...) = verbose; /* Indicate that authentication is needed. */ packet_start(SSH_SMSG_FAILURE); packet_send(); packet_write_wait(); for (attempt = 1;; attempt++) { int authenticated = 0; strlcpy(user, "", sizeof user); /* Get a packet from the client. */ type = packet_read(&plen); /* Process the packet. */ switch (type) { #ifdef AFS case SSH_CMSG_HAVE_KERBEROS_TGT: if (!options.kerberos_tgt_passing) { /* packet_get_all(); */ verbose("Kerberos tgt passing disabled."); break; } else { /* Accept Kerberos tgt. */ char *tgt = packet_get_string(&dlen); packet_integrity_check(plen, 4 + dlen, type); if (!auth_kerberos_tgt(pw, tgt)) verbose("Kerberos tgt REFUSED for %s", pw->pw_name); xfree(tgt); } continue; case SSH_CMSG_HAVE_AFS_TOKEN: if (!options.afs_token_passing || !k_hasafs()) { /* packet_get_all(); */ verbose("AFS token passing disabled."); break; } else { /* Accept AFS token. */ char *token_string = packet_get_string(&dlen); packet_integrity_check(plen, 4 + dlen, type); if (!auth_afs_token(pw, token_string)) verbose("AFS token REFUSED for %s", pw->pw_name); xfree(token_string); } continue; #endif /* AFS */ #ifdef KRB4 case SSH_CMSG_AUTH_KERBEROS: if (!options.kerberos_authentication) { /* packet_get_all(); */ verbose("Kerberos authentication disabled."); break; } else { /* Try Kerberos v4 authentication. */ KTEXT_ST auth; char *tkt_user = NULL; char *kdata = packet_get_string((unsigned int *) &auth.length); packet_integrity_check(plen, 4 + auth.length, type); if (auth.length < MAX_KTXT_LEN) memcpy(auth.dat, kdata, auth.length); xfree(kdata); authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user); if (authenticated) { snprintf(user, sizeof user, " tktuser %s", tkt_user); xfree(tkt_user); } } break; #endif /* KRB4 */ case SSH_CMSG_AUTH_RHOSTS: if (!options.rhosts_authentication) { verbose("Rhosts authentication disabled."); break; } /* * Get client user name. Note that we just have to * trust the client; this is one reason why rhosts * authentication is insecure. (Another is * IP-spoofing on a local network.) */ client_user = packet_get_string(&ulen); packet_integrity_check(plen, 4 + ulen, type); /* Try to authenticate using /etc/hosts.equiv and .rhosts. */ authenticated = auth_rhosts(pw, client_user); snprintf(user, sizeof user, " ruser %s", client_user); xfree(client_user); break; case SSH_CMSG_AUTH_RHOSTS_RSA: if (!options.rhosts_rsa_authentication) { verbose("Rhosts with RSA authentication disabled."); break; } /* * Get client user name. Note that we just have to * trust the client; root on the client machine can * claim to be any user. */ client_user = packet_get_string(&ulen); /* Get the client host key. */ client_host_key_e = BN_new(); client_host_key_n = BN_new(); bits = packet_get_int(); packet_get_bignum(client_host_key_e, &elen); packet_get_bignum(client_host_key_n, &nlen); if (bits != BN_num_bits(client_host_key_n)) error("Warning: keysize mismatch for client_host_key: " "actual %d, announced %d", BN_num_bits(client_host_key_n), bits); packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type); authenticated = auth_rhosts_rsa(pw, client_user, client_host_key_e, client_host_key_n); BN_clear_free(client_host_key_e); BN_clear_free(client_host_key_n); snprintf(user, sizeof user, " ruser %s", client_user); xfree(client_user); break; case SSH_CMSG_AUTH_RSA: if (!options.rsa_authentication) { verbose("RSA authentication disabled."); break; } /* RSA authentication requested. */ n = BN_new(); packet_get_bignum(n, &nlen); packet_integrity_check(plen, nlen, type); authenticated = auth_rsa(pw, n); BN_clear_free(n); break; case SSH_CMSG_AUTH_PASSWORD: if (!options.password_authentication) { verbose("Password authentication disabled."); break; } /* * Read user password. It is in plain text, but was * transmitted over the encrypted channel so it is * not visible to an outside observer. */ password = packet_get_string(&dlen); packet_integrity_check(plen, 4 + dlen, type); /* Try authentication with the password. */ authenticated = auth_password(pw, password); memset(password, 0, strlen(password)); xfree(password); break; #ifdef SKEY case SSH_CMSG_AUTH_TIS: debug("rcvd SSH_CMSG_AUTH_TIS"); if (options.skey_authentication == 1) { char *skeyinfo = skey_keyinfo(pw->pw_name); if (skeyinfo == NULL) { debug("generating fake skeyinfo for %.100s.", pw->pw_name); skeyinfo = skey_fake_keyinfo(pw->pw_name); } if (skeyinfo != NULL) { /* we send our s/key- in tis-challenge messages */ debug("sending challenge '%s'", skeyinfo); packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE); packet_put_string(skeyinfo, strlen(skeyinfo)); packet_send(); packet_write_wait(); continue; } } break; case SSH_CMSG_AUTH_TIS_RESPONSE: debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE"); if (options.skey_authentication == 1) { char *response = packet_get_string(&dlen); debug("skey response == '%s'", response); packet_integrity_check(plen, 4 + dlen, type); authenticated = (skey_haskey(pw->pw_name) == 0 && skey_passcheck(pw->pw_name, response) != -1); xfree(response); } break; #else case SSH_CMSG_AUTH_TIS: /* TIS Authentication is unsupported */ log("TIS authentication unsupported."); break; #endif default: /* * Any unknown messages will be ignored (and failure * returned) during authentication. */ log("Unknown message during authentication: type %d", type); break; } /* Raise logging level */ if (authenticated || attempt == AUTH_FAIL_LOG || type == SSH_CMSG_AUTH_PASSWORD) authlog = log; authlog("%s %s for %.200s from %.200s port %d%s", authenticated ? "Accepted" : "Failed", get_authname(type), pw->pw_uid == 0 ? "ROOT" : pw->pw_name, get_remote_ipaddr(), get_remote_port(), user); if (authenticated) return; if (attempt > AUTH_FAIL_MAX) packet_disconnect(AUTH_FAIL_MSG, pw->pw_name); /* Send a message indicating that the authentication attempt failed. */ packet_start(SSH_SMSG_FAILURE); packet_send(); packet_write_wait(); } } /* * The user does not exist or access is denied, * but fake indication that authentication is needed. */ void do_fake_authloop(char *user) { int attempt = 0; log("Faking authloop for illegal user %.200s from %.200s port %d", user, get_remote_ipaddr(), get_remote_port()); /* Indicate that authentication is needed. */ packet_start(SSH_SMSG_FAILURE); packet_send(); packet_write_wait(); /* * Keep reading packets, and always respond with a failure. This is * to avoid disclosing whether such a user really exists. */ for (attempt = 1;; attempt++) { /* Read a packet. This will not return if the client disconnects. */ int plen; int type = packet_read(&plen); #ifdef SKEY int dlen; char *password, *skeyinfo; if (options.password_authentication && options.skey_authentication == 1 && type == SSH_CMSG_AUTH_PASSWORD && (password = packet_get_string(&dlen)) != NULL && dlen == 5 && strncasecmp(password, "s/key", 5) == 0 && (skeyinfo = skey_fake_keyinfo(user)) != NULL) { /* Send a fake s/key challenge. */ packet_send_debug(skeyinfo); } #endif if (attempt > AUTH_FAIL_MAX) packet_disconnect(AUTH_FAIL_MSG, user); /* * Send failure. This should be indistinguishable from a * failed authentication. */ packet_start(SSH_SMSG_FAILURE); packet_send(); packet_write_wait(); } /* NOTREACHED */ abort(); } /* * Remove local Xauthority file. */ static void xauthfile_cleanup_proc(void *ignore) { debug("xauthfile_cleanup_proc called"); if (xauthfile != NULL) { unlink(xauthfile); xfree(xauthfile); xauthfile = NULL; } } /* * Prepares for an interactive session. This is called after the user has * been successfully authenticated. During this message exchange, pseudo * terminals are allocated, X11, TCP/IP, and authentication agent forwardings * are requested, etc. */ void do_authenticated(struct passwd * pw) { int type; int compression_level = 0, enable_compression_after_reply = 0; int have_pty = 0, ptyfd = -1, ttyfd = -1, xauthfd = -1; int row, col, xpixel, ypixel, screen; char ttyname[64]; char *command, *term = NULL, *display = NULL, *proto = NULL, *data = NULL; struct group *grp; gid_t tty_gid; mode_t tty_mode; int n_bytes; /* * Cancel the alarm we set to limit the time taken for * authentication. */ alarm(0); /* * Inform the channel mechanism that we are the server side and that * the client may request to connect to any port at all. (The user * could do it anyway, and we wouldn\'t know what is permitted except * by the client telling us, so we can equally well trust the client * not to request anything bogus.) */ channel_permit_all_opens(); /* * We stay in this loop until the client requests to execute a shell * or a command. */ while (1) { int plen, dlen; /* Get a packet from the client. */ type = packet_read(&plen); /* Process the packet. */ switch (type) { case SSH_CMSG_REQUEST_COMPRESSION: packet_integrity_check(plen, 4, type); compression_level = packet_get_int(); if (compression_level < 1 || compression_level > 9) { packet_send_debug("Received illegal compression level %d.", compression_level); goto fail; } /* Enable compression after we have responded with SUCCESS. */ enable_compression_after_reply = 1; break; case SSH_CMSG_REQUEST_PTY: if (no_pty_flag) { debug("Allocating a pty not permitted for this authentication."); goto fail; } if (have_pty) packet_disconnect("Protocol error: you already have a pty."); debug("Allocating pty."); /* Allocate a pty and open it. */ if (!pty_allocate(&ptyfd, &ttyfd, ttyname, sizeof(ttyname))) { error("Failed to allocate pty."); goto fail; } /* Determine the group to make the owner of the tty. */ grp = getgrnam("tty"); if (grp) { tty_gid = grp->gr_gid; tty_mode = S_IRUSR | S_IWUSR | S_IWGRP; } else { tty_gid = pw->pw_gid; tty_mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH; } /* Change ownership of the tty. */ if (chown(ttyname, pw->pw_uid, tty_gid) < 0) fatal("chown(%.100s, %d, %d) failed: %.100s", ttyname, pw->pw_uid, tty_gid, strerror(errno)); if (chmod(ttyname, tty_mode) < 0) fatal("chmod(%.100s, 0%o) failed: %.100s", ttyname, tty_mode, strerror(errno)); /* Get TERM from the packet. Note that the value may be of arbitrary length. */ term = packet_get_string(&dlen); packet_integrity_check(dlen, strlen(term), type); /* packet_integrity_check(plen, 4 + dlen + 4*4 + n_bytes, type); */ /* Remaining bytes */ n_bytes = plen - (4 + dlen + 4 * 4); if (strcmp(term, "") == 0) term = NULL; /* Get window size from the packet. */ row = packet_get_int(); col = packet_get_int(); xpixel = packet_get_int(); ypixel = packet_get_int(); pty_change_window_size(ptyfd, row, col, xpixel, ypixel); /* Get tty modes from the packet. */ tty_parse_modes(ttyfd, &n_bytes); packet_integrity_check(plen, 4 + dlen + 4 * 4 + n_bytes, type); /* Indicate that we now have a pty. */ have_pty = 1; break; case SSH_CMSG_X11_REQUEST_FORWARDING: if (!options.x11_forwarding) { packet_send_debug("X11 forwarding disabled in server configuration file."); goto fail; } #ifdef XAUTH_PATH if (no_x11_forwarding_flag) { packet_send_debug("X11 forwarding not permitted for this authentication."); goto fail; } debug("Received request for X11 forwarding with auth spoofing."); if (display) packet_disconnect("Protocol error: X11 display already set."); { int proto_len, data_len; proto = packet_get_string(&proto_len); data = packet_get_string(&data_len); packet_integrity_check(plen, 4 + proto_len + 4 + data_len + 4, type); } if (packet_get_protocol_flags() & SSH_PROTOFLAG_SCREEN_NUMBER) screen = packet_get_int(); else screen = 0; display = x11_create_display_inet(screen); if (!display) goto fail; /* Setup to always have a local .Xauthority. */ xauthfile = xmalloc(MAXPATHLEN); snprintf(xauthfile, MAXPATHLEN, "/tmp/XauthXXXXXX"); if ((xauthfd = mkstemp(xauthfile)) != -1) { fchown(xauthfd, pw->pw_uid, pw->pw_gid); close(xauthfd); fatal_add_cleanup(xauthfile_cleanup_proc, NULL); } else { xfree(xauthfile); xauthfile = NULL; } break; #else /* XAUTH_PATH */ packet_send_debug("No xauth program; cannot forward with spoofing."); goto fail; #endif /* XAUTH_PATH */ case SSH_CMSG_AGENT_REQUEST_FORWARDING: if (no_agent_forwarding_flag) { debug("Authentication agent forwarding not permitted for this authentication."); goto fail; } debug("Received authentication agent forwarding request."); auth_input_request_forwarding(pw); break; case SSH_CMSG_PORT_FORWARD_REQUEST: if (no_port_forwarding_flag) { debug("Port forwarding not permitted for this authentication."); goto fail; } debug("Received TCP/IP port forwarding request."); channel_input_port_forward_request(pw->pw_uid == 0); break; case SSH_CMSG_MAX_PACKET_SIZE: if (packet_set_maxsize(packet_get_int()) < 0) goto fail; break; case SSH_CMSG_EXEC_SHELL: /* Set interactive/non-interactive mode. */ packet_set_interactive(have_pty || display != NULL, options.keepalives); if (forced_command != NULL) goto do_forced_command; debug("Forking shell."); packet_integrity_check(plen, 0, type); if (have_pty) do_exec_pty(NULL, ptyfd, ttyfd, ttyname, pw, term, display, proto, data); else do_exec_no_pty(NULL, pw, display, proto, data); return; case SSH_CMSG_EXEC_CMD: /* Set interactive/non-interactive mode. */ packet_set_interactive(have_pty || display != NULL, options.keepalives); if (forced_command != NULL) goto do_forced_command; /* Get command from the packet. */ { int dlen; command = packet_get_string(&dlen); debug("Executing command '%.500s'", command); packet_integrity_check(plen, 4 + dlen, type); } if (have_pty) do_exec_pty(command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data); else do_exec_no_pty(command, pw, display, proto, data); xfree(command); return; default: /* * Any unknown messages in this phase are ignored, * and a failure message is returned. */ log("Unknown packet type received after authentication: %d", type); goto fail; } /* The request was successfully processed. */ packet_start(SSH_SMSG_SUCCESS); packet_send(); packet_write_wait(); /* Enable compression now that we have replied if appropriate. */ if (enable_compression_after_reply) { enable_compression_after_reply = 0; packet_start_compression(compression_level); } continue; fail: /* The request failed. */ packet_start(SSH_SMSG_FAILURE); packet_send(); packet_write_wait(); continue; do_forced_command: /* * There is a forced command specified for this login. * Execute it. */ debug("Executing forced command: %.900s", forced_command); if (have_pty) do_exec_pty(forced_command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data); else do_exec_no_pty(forced_command, pw, display, proto, data); return; } } /* * This is called to fork and execute a command when we have no tty. This * will call do_child from the child, and server_loop from the parent after * setting up file descriptors and such. */ void do_exec_no_pty(const char *command, struct passwd * pw, const char *display, const char *auth_proto, const char *auth_data) { int pid; #ifdef USE_PIPES int pin[2], pout[2], perr[2]; /* Allocate pipes for communicating with the program. */ if (pipe(pin) < 0 || pipe(pout) < 0 || pipe(perr) < 0) packet_disconnect("Could not create pipes: %.100s", strerror(errno)); #else /* USE_PIPES */ int inout[2], err[2]; /* Uses socket pairs to communicate with the program. */ if (socketpair(AF_UNIX, SOCK_STREAM, 0, inout) < 0 || socketpair(AF_UNIX, SOCK_STREAM, 0, err) < 0) packet_disconnect("Could not create socket pairs: %.100s", strerror(errno)); #endif /* USE_PIPES */ setproctitle("%s@notty", pw->pw_name); /* Fork the child. */ if ((pid = fork()) == 0) { /* Child. Reinitialize the log since the pid has changed. */ log_init(av0, options.log_level, options.log_facility, log_stderr); /* * Create a new session and process group since the 4.4BSD * setlogin() affects the entire process group. */ if (setsid() < 0) error("setsid failed: %.100s", strerror(errno)); #ifdef USE_PIPES /* * Redirect stdin. We close the parent side of the socket * pair, and make the child side the standard input. */ close(pin[1]); if (dup2(pin[0], 0) < 0) perror("dup2 stdin"); close(pin[0]); /* Redirect stdout. */ close(pout[0]); if (dup2(pout[1], 1) < 0) perror("dup2 stdout"); close(pout[1]); /* Redirect stderr. */ close(perr[0]); if (dup2(perr[1], 2) < 0) perror("dup2 stderr"); close(perr[1]); #else /* USE_PIPES */ /* * Redirect stdin, stdout, and stderr. Stdin and stdout will * use the same socket, as some programs (particularly rdist) * seem to depend on it. */ close(inout[1]); close(err[1]); if (dup2(inout[0], 0) < 0) /* stdin */ perror("dup2 stdin"); if (dup2(inout[0], 1) < 0) /* stdout. Note: same socket as stdin. */ perror("dup2 stdout"); if (dup2(err[0], 2) < 0) /* stderr */ perror("dup2 stderr"); #endif /* USE_PIPES */ /* Do processing for the child (exec command etc). */ do_child(command, pw, NULL, display, auth_proto, auth_data, NULL); /* NOTREACHED */ } if (pid < 0) packet_disconnect("fork failed: %.100s", strerror(errno)); #ifdef USE_PIPES /* We are the parent. Close the child sides of the pipes. */ close(pin[0]); close(pout[1]); close(perr[1]); /* Enter the interactive session. */ server_loop(pid, pin[1], pout[0], perr[0]); /* server_loop has closed pin[1], pout[1], and perr[1]. */ #else /* USE_PIPES */ /* We are the parent. Close the child sides of the socket pairs. */ close(inout[0]); close(err[0]); /* * Enter the interactive session. Note: server_loop must be able to * handle the case that fdin and fdout are the same. */ server_loop(pid, inout[1], inout[1], err[1]); /* server_loop has closed inout[1] and err[1]. */ #endif /* USE_PIPES */ } struct pty_cleanup_context { const char *ttyname; int pid; }; /* * Function to perform cleanup if we get aborted abnormally (e.g., due to a * dropped connection). */ void pty_cleanup_proc(void *context) { struct pty_cleanup_context *cu = context; debug("pty_cleanup_proc called"); /* Record that the user has logged out. */ record_logout(cu->pid, cu->ttyname); /* Release the pseudo-tty. */ pty_release(cu->ttyname); } /* * This is called to fork and execute a command when we have a tty. This * will call do_child from the child, and server_loop from the parent after * setting up file descriptors, controlling tty, updating wtmp, utmp, * lastlog, and other such operations. */ void do_exec_pty(const char *command, int ptyfd, int ttyfd, const char *ttyname, struct passwd * pw, const char *term, const char *display, const char *auth_proto, const char *auth_data) { int pid, fdout; const char *hostname; time_t last_login_time; char buf[100], *time_string; FILE *f; char line[256]; struct stat st; int quiet_login; struct sockaddr_in from; int fromlen; struct pty_cleanup_context cleanup_context; /* Get remote host name. */ hostname = get_canonical_hostname(); /* * Get the time when the user last logged in. Buf will be set to * contain the hostname the last login was from. */ if (!options.use_login) { last_login_time = get_last_login_time(pw->pw_uid, pw->pw_name, buf, sizeof(buf)); } setproctitle("%s@%s", pw->pw_name, strrchr(ttyname, '/') + 1); /* Fork the child. */ if ((pid = fork()) == 0) { pid = getpid(); /* Child. Reinitialize the log because the pid has changed. */ log_init(av0, options.log_level, options.log_facility, log_stderr); /* Close the master side of the pseudo tty. */ close(ptyfd); /* Make the pseudo tty our controlling tty. */ pty_make_controlling_tty(&ttyfd, ttyname); /* Redirect stdin from the pseudo tty. */ if (dup2(ttyfd, fileno(stdin)) < 0) error("dup2 stdin failed: %.100s", strerror(errno)); /* Redirect stdout to the pseudo tty. */ if (dup2(ttyfd, fileno(stdout)) < 0) error("dup2 stdin failed: %.100s", strerror(errno)); /* Redirect stderr to the pseudo tty. */ if (dup2(ttyfd, fileno(stderr)) < 0) error("dup2 stdin failed: %.100s", strerror(errno)); /* Close the extra descriptor for the pseudo tty. */ close(ttyfd); /* * Get IP address of client. This is needed because we want * to record where the user logged in from. If the * connection is not a socket, let the ip address be 0.0.0.0. */ memset(&from, 0, sizeof(from)); if (packet_get_connection_in() == packet_get_connection_out()) { fromlen = sizeof(from); if (getpeername(packet_get_connection_in(), (struct sockaddr *) & from, &fromlen) < 0) { debug("getpeername: %.100s", strerror(errno)); fatal_cleanup(); } } /* Record that there was a login on that terminal. */ record_login(pid, ttyname, pw->pw_name, pw->pw_uid, hostname, &from); /* Check if .hushlogin exists. */ snprintf(line, sizeof line, "%.200s/.hushlogin", pw->pw_dir); quiet_login = stat(line, &st) >= 0; /* * If the user has logged in before, display the time of last * login. However, don't display anything extra if a command * has been specified (so that ssh can be used to execute * commands on a remote machine without users knowing they * are going to another machine). Login(1) will do this for * us as well, so check if login(1) is used */ if (command == NULL && last_login_time != 0 && !quiet_login && !options.use_login) { /* Convert the date to a string. */ time_string = ctime(&last_login_time); /* Remove the trailing newline. */ if (strchr(time_string, '\n')) *strchr(time_string, '\n') = 0; /* Display the last login time. Host if displayed if known. */ if (strcmp(buf, "") == 0) printf("Last login: %s\r\n", time_string); else printf("Last login: %s from %s\r\n", time_string, buf); } /* * Print /etc/motd unless a command was specified or printing * it was disabled in server options or login(1) will be * used. Note that some machines appear to print it in * /etc/profile or similar. */ if (command == NULL && options.print_motd && !quiet_login && !options.use_login) { /* Print /etc/motd if it exists. */ f = fopen("/etc/motd", "r"); if (f) { while (fgets(line, sizeof(line), f)) fputs(line, stdout); fclose(f); } } /* Do common processing for the child, such as execing the command. */ do_child(command, pw, term, display, auth_proto, auth_data, ttyname); /* NOTREACHED */ } if (pid < 0) packet_disconnect("fork failed: %.100s", strerror(errno)); /* Parent. Close the slave side of the pseudo tty. */ close(ttyfd); /* * Create another descriptor of the pty master side for use as the * standard input. We could use the original descriptor, but this * simplifies code in server_loop. The descriptor is bidirectional. */ fdout = dup(ptyfd); if (fdout < 0) packet_disconnect("dup failed: %.100s", strerror(errno)); /* * Add a cleanup function to clear the utmp entry and record logout * time in case we call fatal() (e.g., the connection gets closed). */ cleanup_context.pid = pid; cleanup_context.ttyname = ttyname; fatal_add_cleanup(pty_cleanup_proc, (void *) &cleanup_context); /* Enter interactive session. */ server_loop(pid, ptyfd, fdout, -1); /* server_loop has not closed ptyfd and fdout. */ /* Cancel the cleanup function. */ fatal_remove_cleanup(pty_cleanup_proc, (void *) &cleanup_context); /* Record that the user has logged out. */ record_logout(pid, ttyname); /* Release the pseudo-tty. */ pty_release(ttyname); /* * Close the server side of the socket pairs. We must do this after * the pty cleanup, so that another process doesn't get this pty * while we're still cleaning up. */ close(ptyfd); close(fdout); } /* * Sets the value of the given variable in the environment. If the variable * already exists, its value is overriden. */ void child_set_env(char ***envp, unsigned int *envsizep, const char *name, const char *value) { unsigned int i, namelen; char **env; /* * Find the slot where the value should be stored. If the variable * already exists, we reuse the slot; otherwise we append a new slot * at the end of the array, expanding if necessary. */ env = *envp; namelen = strlen(name); for (i = 0; env[i]; i++) if (strncmp(env[i], name, namelen) == 0 && env[i][namelen] == '=') break; if (env[i]) { /* Reuse the slot. */ xfree(env[i]); } else { /* New variable. Expand if necessary. */ if (i >= (*envsizep) - 1) { (*envsizep) += 50; env = (*envp) = xrealloc(env, (*envsizep) * sizeof(char *)); } /* Need to set the NULL pointer at end of array beyond the new slot. */ env[i + 1] = NULL; } /* Allocate space and format the variable in the appropriate slot. */ env[i] = xmalloc(strlen(name) + 1 + strlen(value) + 1); snprintf(env[i], strlen(name) + 1 + strlen(value) + 1, "%s=%s", name, value); } /* * Reads environment variables from the given file and adds/overrides them * into the environment. If the file does not exist, this does nothing. * Otherwise, it must consist of empty lines, comments (line starts with '#') * and assignments of the form name=value. No other forms are allowed. */ void read_environment_file(char ***env, unsigned int *envsize, const char *filename) { FILE *f; char buf[4096]; char *cp, *value; f = fopen(filename, "r"); if (!f) return; while (fgets(buf, sizeof(buf), f)) { for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) ; if (!*cp || *cp == '#' || *cp == '\n') continue; if (strchr(cp, '\n')) *strchr(cp, '\n') = '\0'; value = strchr(cp, '='); if (value == NULL) { fprintf(stderr, "Bad line in %.100s: %.200s\n", filename, buf); continue; } /* Replace the equals sign by nul, and advance value to the value string. */ *value = '\0'; value++; child_set_env(env, envsize, cp, value); } fclose(f); } /* * Performs common processing for the child, such as setting up the * environment, closing extra file descriptors, setting the user and group * ids, and executing the command or shell. */ void do_child(const char *command, struct passwd * pw, const char *term, const char *display, const char *auth_proto, const char *auth_data, const char *ttyname) { const char *shell, *cp = NULL; char buf[256]; FILE *f; unsigned int envsize, i; char **env; extern char **environ; struct stat st; char *argv[10]; f = fopen("/etc/nologin", "r"); if (f) { /* /etc/nologin exists. Print its contents and exit. */ while (fgets(buf, sizeof(buf), f)) fputs(buf, stderr); fclose(f); if (pw->pw_uid != 0) exit(254); } /* Set login name in the kernel. */ if (setlogin(pw->pw_name) < 0) error("setlogin failed: %s", strerror(errno)); /* Set uid, gid, and groups. */ /* Login(1) does this as well, and it needs uid 0 for the "-h" switch, so we let login(1) to this for us. */ if (!options.use_login) { if (getuid() == 0 || geteuid() == 0) { if (setgid(pw->pw_gid) < 0) { perror("setgid"); exit(1); } /* Initialize the group list. */ if (initgroups(pw->pw_name, pw->pw_gid) < 0) { perror("initgroups"); exit(1); } endgrent(); /* Permanently switch to the desired uid. */ permanently_set_uid(pw->pw_uid); } if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) fatal("Failed to set uids to %d.", (int) pw->pw_uid); } /* * Get the shell from the password data. An empty shell field is * legal, and means /bin/sh. */ shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; #ifdef AFS /* Try to get AFS tokens for the local cell. */ if (k_hasafs()) { char cell[64]; if (k_afs_cell_of_file(pw->pw_dir, cell, sizeof(cell)) == 0) krb_afslog(cell, 0); krb_afslog(0, 0); } #endif /* AFS */ /* Initialize the environment. */ envsize = 100; env = xmalloc(envsize * sizeof(char *)); env[0] = NULL; if (!options.use_login) { /* Set basic environment. */ child_set_env(&env, &envsize, "USER", pw->pw_name); child_set_env(&env, &envsize, "LOGNAME", pw->pw_name); child_set_env(&env, &envsize, "HOME", pw->pw_dir); child_set_env(&env, &envsize, "PATH", _PATH_STDPATH); snprintf(buf, sizeof buf, "%.200s/%.50s", _PATH_MAILDIR, pw->pw_name); child_set_env(&env, &envsize, "MAIL", buf); /* Normal systems set SHELL by default. */ child_set_env(&env, &envsize, "SHELL", shell); } if (getenv("TZ")) child_set_env(&env, &envsize, "TZ", getenv("TZ")); /* Set custom environment options from RSA authentication. */ while (custom_environment) { struct envstring *ce = custom_environment; char *s = ce->s; int i; for (i = 0; s[i] != '=' && s[i]; i++); if (s[i] == '=') { s[i] = 0; child_set_env(&env, &envsize, s, s + i + 1); } custom_environment = ce->next; xfree(ce->s); xfree(ce); } snprintf(buf, sizeof buf, "%.50s %d %d", get_remote_ipaddr(), get_remote_port(), options.port); child_set_env(&env, &envsize, "SSH_CLIENT", buf); if (ttyname) child_set_env(&env, &envsize, "SSH_TTY", ttyname); if (term) child_set_env(&env, &envsize, "TERM", term); if (display) child_set_env(&env, &envsize, "DISPLAY", display); #ifdef KRB4 { extern char *ticket; if (ticket) child_set_env(&env, &envsize, "KRBTKFILE", ticket); } #endif /* KRB4 */ if (xauthfile) child_set_env(&env, &envsize, "XAUTHORITY", xauthfile); if (auth_get_socket_name() != NULL) child_set_env(&env, &envsize, SSH_AUTHSOCKET_ENV_NAME, auth_get_socket_name()); /* read $HOME/.ssh/environment. */ if (!options.use_login) { snprintf(buf, sizeof buf, "%.200s/.ssh/environment", pw->pw_dir); read_environment_file(&env, &envsize, buf); } if (debug_flag) { /* dump the environment */ fprintf(stderr, "Environment:\n"); for (i = 0; env[i]; i++) fprintf(stderr, " %.200s\n", env[i]); } /* * Close the connection descriptors; note that this is the child, and * the server will still have the socket open, and it is important * that we do not shutdown it. Note that the descriptors cannot be * closed before building the environment, as we call * get_remote_ipaddr there. */ if (packet_get_connection_in() == packet_get_connection_out()) close(packet_get_connection_in()); else { close(packet_get_connection_in()); close(packet_get_connection_out()); } /* * Close all descriptors related to channels. They will still remain * open in the parent. */ /* XXX better use close-on-exec? -markus */ channel_close_all(); /* * Close any extra file descriptors. Note that there may still be * descriptors left by system functions. They will be closed later. */ endpwent(); endhostent(); /* * Close any extra open file descriptors so that we don\'t have them * hanging around in clients. Note that we want to do this after * initgroups, because at least on Solaris 2.3 it leaves file * descriptors open. */ for (i = 3; i < 64; i++) close(i); /* Change current directory to the user\'s home directory. */ if (chdir(pw->pw_dir) < 0) fprintf(stderr, "Could not chdir to home directory %s: %s\n", pw->pw_dir, strerror(errno)); /* * Must take new environment into use so that .ssh/rc, /etc/sshrc and * xauth are run in the proper environment. */ environ = env; /* * Run $HOME/.ssh/rc, /etc/sshrc, or xauth (whichever is found first * in this order). */ if (!options.use_login) { if (stat(SSH_USER_RC, &st) >= 0) { if (debug_flag) fprintf(stderr, "Running /bin/sh %s\n", SSH_USER_RC); f = popen("/bin/sh " SSH_USER_RC, "w"); if (f) { if (auth_proto != NULL && auth_data != NULL) fprintf(f, "%s %s\n", auth_proto, auth_data); pclose(f); } else fprintf(stderr, "Could not run %s\n", SSH_USER_RC); } else if (stat(SSH_SYSTEM_RC, &st) >= 0) { if (debug_flag) fprintf(stderr, "Running /bin/sh %s\n", SSH_SYSTEM_RC); f = popen("/bin/sh " SSH_SYSTEM_RC, "w"); if (f) { if (auth_proto != NULL && auth_data != NULL) fprintf(f, "%s %s\n", auth_proto, auth_data); pclose(f); } else fprintf(stderr, "Could not run %s\n", SSH_SYSTEM_RC); } #ifdef XAUTH_PATH else { /* Add authority data to .Xauthority if appropriate. */ if (auth_proto != NULL && auth_data != NULL) { if (debug_flag) fprintf(stderr, "Running %.100s add %.100s %.100s %.100s\n", XAUTH_PATH, display, auth_proto, auth_data); f = popen(XAUTH_PATH " -q -", "w"); if (f) { fprintf(f, "add %s %s %s\n", display, auth_proto, auth_data); fclose(f); } else fprintf(stderr, "Could not run %s -q -\n", XAUTH_PATH); } } #endif /* XAUTH_PATH */ /* Get the last component of the shell name. */ cp = strrchr(shell, '/'); if (cp) cp++; else cp = shell; } /* * If we have no command, execute the shell. In this case, the shell * name to be passed in argv[0] is preceded by '-' to indicate that * this is a login shell. */ if (!command) { if (!options.use_login) { char buf[256]; /* * Check for mail if we have a tty and it was enabled * in server options. */ if (ttyname && options.check_mail) { char *mailbox; struct stat mailstat; mailbox = getenv("MAIL"); if (mailbox != NULL) { if (stat(mailbox, &mailstat) != 0 || mailstat.st_size == 0) printf("No mail.\n"); else if (mailstat.st_mtime < mailstat.st_atime) printf("You have mail.\n"); else printf("You have new mail.\n"); } } /* Start the shell. Set initial character to '-'. */ buf[0] = '-'; strncpy(buf + 1, cp, sizeof(buf) - 1); buf[sizeof(buf) - 1] = 0; /* Execute the shell. */ argv[0] = buf; argv[1] = NULL; execve(shell, argv, env); /* Executing the shell failed. */ perror(shell); exit(1); } else { /* Launch login(1). */ execl("/usr/bin/login", "login", "-h", get_remote_ipaddr(), "-p", "-f", "--", pw->pw_name, NULL); /* Login couldn't be executed, die. */ perror("login"); exit(1); } } /* * Execute the command using the user's shell. This uses the -c * option to execute the command. */ argv[0] = (char *) cp; argv[1] = "-c"; argv[2] = (char *) command; argv[3] = NULL; execve(shell, argv, env); perror(shell); exit(1); }