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Diffstat (limited to 'ssh.c')
| -rw-r--r-- | ssh.c | 809 |
1 files changed, 809 insertions, 0 deletions
@@ -0,0 +1,809 @@ +/* + +ssh.c + +Author: Tatu Ylonen <ylo@cs.hut.fi> + +Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland + All rights reserved + +Created: Sat Mar 18 16:36:11 1995 ylo + +Ssh client program. This program can be used to log into a remote machine. +The software supports strong authentication, encryption, and forwarding +of X11, TCP/IP, and authentication connections. + +Modified to work with SSL by Niels Provos <provos@citi.umich.edu> in Canada. + +*/ + +#include "includes.h" +RCSID("$Id: ssh.c,v 1.1 1999/10/27 03:42:45 damien Exp $"); + +#include "xmalloc.h" +#include "ssh.h" +#include "packet.h" +#include "buffer.h" +#include "authfd.h" +#include "readconf.h" +#include "uidswap.h" + +/* Flag indicating whether debug mode is on. This can be set on the + command line. */ +int debug_flag = 0; + +/* Flag indicating whether quiet mode is on. */ +int quiet_flag = 0; + +/* Flag indicating whether to allocate a pseudo tty. This can be set on the + command line, and is automatically set if no command is given on the command + line. */ +int tty_flag = 0; + +/* Flag indicating that nothing should be read from stdin. This can be set + on the command line. */ +int stdin_null_flag = 0; + +/* Flag indicating that ssh should fork after authentication. This is useful + so that the pasphrase can be entered manually, and then ssh goes to the + background. */ +int fork_after_authentication_flag = 0; + +/* General data structure for command line options and options configurable + in configuration files. See readconf.h. */ +Options options; + +/* Name of the host we are connecting to. This is the name given on the + command line, or the HostName specified for the user-supplied name + in a configuration file. */ +char *host; + +/* socket address the host resolves to */ +struct sockaddr_in hostaddr; + +/* Flag to indicate that we have received a window change signal which has + not yet been processed. This will cause a message indicating the new + window size to be sent to the server a little later. This is volatile + because this is updated in a signal handler. */ +volatile int received_window_change_signal = 0; + +/* Value of argv[0] (set in the main program). */ +char *av0; + +/* Flag indicating whether we have a valid host private key loaded. */ +int host_private_key_loaded = 0; + +/* Host private key. */ +RSA *host_private_key = NULL; + +/* Original real UID. */ +uid_t original_real_uid; + +/* Prints a help message to the user. This function never returns. */ + +void +usage() +{ + fprintf(stderr, "Usage: %s [options] host [command]\n", av0); + fprintf(stderr, "Options:\n"); + fprintf(stderr, " -l user Log in using this user name.\n"); + fprintf(stderr, " -n Redirect input from /dev/null.\n"); + fprintf(stderr, " -a Disable authentication agent forwarding.\n"); +#ifdef AFS + fprintf(stderr, " -k Disable Kerberos ticket and AFS token forwarding.\n"); +#endif /* AFS */ + fprintf(stderr, " -x Disable X11 connection forwarding.\n"); + fprintf(stderr, " -i file Identity for RSA authentication (default: ~/.ssh/identity).\n"); + fprintf(stderr, " -t Tty; allocate a tty even if command is given.\n"); + fprintf(stderr, " -v Verbose; display verbose debugging messages.\n"); + fprintf(stderr, " -V Display version number only.\n"); + fprintf(stderr, " -P Don't allocate a privileged port.\n"); + fprintf(stderr, " -q Quiet; don't display any warning messages.\n"); + fprintf(stderr, " -f Fork into background after authentication.\n"); + fprintf(stderr, " -e char Set escape character; ``none'' = disable (default: ~).\n"); + + fprintf(stderr, " -c cipher Select encryption algorithm: " + "``3des'', " + "``blowfish''\n"); + fprintf(stderr, " -p port Connect to this port. Server must be on the same port.\n"); + fprintf(stderr, " -L listen-port:host:port Forward local port to remote address\n"); + fprintf(stderr, " -R listen-port:host:port Forward remote port to local address\n"); + fprintf(stderr, " These cause %s to listen for connections on a port, and\n", av0); + fprintf(stderr, " forward them to the other side by connecting to host:port.\n"); + fprintf(stderr, " -C Enable compression.\n"); + fprintf(stderr, " -g Allow remote hosts to connect to forwarded ports.\n"); + fprintf(stderr, " -o 'option' Process the option as if it was read from a configuration file.\n"); + exit(1); +} + +/* Connects to the given host using rsh (or prints an error message and exits + if rsh is not available). This function never returns. */ + +void +rsh_connect(char *host, char *user, Buffer *command) +{ + char *args[10]; + int i; + + log("Using rsh. WARNING: Connection will not be encrypted."); + /* Build argument list for rsh. */ + i = 0; + args[i++] = _PATH_RSH; + args[i++] = host; /* may have to come after user on some systems */ + if (user) + { + args[i++] = "-l"; + args[i++] = user; + } + if (buffer_len(command) > 0) + { + buffer_append(command, "\0", 1); + args[i++] = buffer_ptr(command); + } + args[i++] = NULL; + if (debug_flag) + { + for (i = 0; args[i]; i++) + { + if (i != 0) + fprintf(stderr, " "); + fprintf(stderr, "%s", args[i]); + } + fprintf(stderr, "\n"); + } + execv(_PATH_RSH, args); + perror(_PATH_RSH); + exit(1); +} + +/* Main program for the ssh client. */ + +uid_t original_real_uid; + +int +main(int ac, char **av) +{ + int i, opt, optind, type, exit_status, ok, fwd_port, fwd_host_port, authfd; + char *optarg, *cp, buf[256]; + Buffer command; + struct winsize ws; + struct stat st; + struct passwd *pw, pwcopy; + int interactive = 0, dummy; + uid_t original_effective_uid; + int plen; + + /* Save the original real uid. It will be needed later (uid-swapping may + clobber the real uid). */ + original_real_uid = getuid(); + original_effective_uid = geteuid(); + + /* If we are installed setuid root be careful to not drop core. */ + if (original_real_uid != original_effective_uid) + { + struct rlimit rlim; + rlim.rlim_cur = rlim.rlim_max = 0; + if (setrlimit(RLIMIT_CORE, &rlim) < 0) + fatal("setrlimit failed: %.100s", strerror(errno)); + } + + /* Use uid-swapping to give up root privileges for the duration of option + processing. We will re-instantiate the rights when we are ready to + create the privileged port, and will permanently drop them when the + port has been created (actually, when the connection has been made, as + we may need to create the port several times). */ + temporarily_use_uid(original_real_uid); + + /* Set our umask to something reasonable, as some files are created with + the default umask. This will make them world-readable but writable + only by the owner, which is ok for all files for which we don't set + the modes explicitly. */ + umask(022); + + /* Save our own name. */ + av0 = av[0]; + + /* Initialize option structure to indicate that no values have been set. */ + initialize_options(&options); + + /* Parse command-line arguments. */ + host = NULL; + + /* If program name is not one of the standard names, use it as host name. */ + if (strchr(av0, '/')) + cp = strrchr(av0, '/') + 1; + else + cp = av0; + if (strcmp(cp, "rsh") != 0 && strcmp(cp, "ssh") != 0 && + strcmp(cp, "rlogin") != 0 && strcmp(cp, "slogin") != 0) + host = cp; + + for (optind = 1; optind < ac; optind++) + { + if (av[optind][0] != '-') + { + if (host) + break; + if ((cp = strchr(av[optind], '@'))) { + options.user = av[optind]; + *cp = '\0'; + host = ++cp; + } + else + host = av[optind]; + continue; + } + opt = av[optind][1]; + if (!opt) + usage(); + if (strchr("eilcpLRo", opt)) /* options with arguments */ + { + optarg = av[optind] + 2; + if (strcmp(optarg, "") == 0) + { + if (optind >= ac - 1) + usage(); + optarg = av[++optind]; + } + } + else + { + if (av[optind][2]) + usage(); + optarg = NULL; + } + switch (opt) + { + case 'n': + stdin_null_flag = 1; + break; + + case 'f': + fork_after_authentication_flag = 1; + stdin_null_flag = 1; + break; + + case 'x': + options.forward_x11 = 0; + break; + + case 'X': + options.forward_x11 = 1; + break; + + case 'g': + options.gateway_ports = 1; + break; + + case 'P': + options.use_privileged_port = 0; + break; + + case 'a': + options.forward_agent = 0; + break; +#ifdef AFS + case 'k': + options.kerberos_tgt_passing = 0; + options.afs_token_passing = 0; + break; +#endif + case 'i': + if (stat(optarg, &st) < 0) + { + fprintf(stderr, "Warning: Identity file %s does not exist.\n", + optarg); + break; + } + if (options.num_identity_files >= SSH_MAX_IDENTITY_FILES) + fatal("Too many identity files specified (max %d)", + SSH_MAX_IDENTITY_FILES); + options.identity_files[options.num_identity_files++] = + xstrdup(optarg); + break; + + case 't': + tty_flag = 1; + break; + + case 'v': + case 'V': + debug_flag = 1; + fprintf(stderr, "SSH Version %s, protocol version %d.%d.\n", + SSH_VERSION, PROTOCOL_MAJOR, PROTOCOL_MINOR); + fprintf(stderr, "Compiled with SSL.\n"); + if (opt == 'V') + exit(0); + break; + + case 'q': + quiet_flag = 1; + break; + + case 'e': + if (optarg[0] == '^' && optarg[2] == 0 && + (unsigned char)optarg[1] >= 64 && (unsigned char)optarg[1] < 128) + options.escape_char = (unsigned char)optarg[1] & 31; + else + if (strlen(optarg) == 1) + options.escape_char = (unsigned char)optarg[0]; + else + if (strcmp(optarg, "none") == 0) + options.escape_char = -2; + else + { + fprintf(stderr, "Bad escape character '%s'.\n", optarg); + exit(1); + } + break; + + case 'c': + options.cipher = cipher_number(optarg); + if (options.cipher == -1) + { + fprintf(stderr, "Unknown cipher type '%s'\n", optarg); + exit(1); + } + break; + + case 'p': + options.port = atoi(optarg); + if (options.port < 1 || options.port > 65535) + { + fprintf(stderr, "Bad port %s.\n", optarg); + exit(1); + } + break; + + case 'l': + options.user = optarg; + break; + + case 'R': + if (sscanf(optarg, "%d:%255[^:]:%d", &fwd_port, buf, + &fwd_host_port) != 3) + { + fprintf(stderr, "Bad forwarding specification '%s'.\n", optarg); + usage(); + /*NOTREACHED*/ + } + add_remote_forward(&options, fwd_port, buf, fwd_host_port); + break; + + case 'L': + if (sscanf(optarg, "%d:%255[^:]:%d", &fwd_port, buf, + &fwd_host_port) != 3) + { + fprintf(stderr, "Bad forwarding specification '%s'.\n", optarg); + usage(); + /*NOTREACHED*/ + } + add_local_forward(&options, fwd_port, buf, fwd_host_port); + break; + + case 'C': + options.compression = 1; + break; + + case 'o': + dummy = 1; + process_config_line(&options, host ? host : "", optarg, + "command-line", 0, &dummy); + break; + + default: + usage(); + } + } + + /* Check that we got a host name. */ + if (!host) + usage(); + + /* check if RSA support exists */ + if (rsa_alive() == 0) { + extern char *__progname; + + fprintf(stderr, + "%s: no RSA support in libssl and libcrypto. See ssl(8).\n", + __progname); + exit(1); + } + + /* Initialize the command to execute on remote host. */ + buffer_init(&command); + + /* Save the command to execute on the remote host in a buffer. There is + no limit on the length of the command, except by the maximum packet + size. Also sets the tty flag if there is no command. */ + if (optind == ac) + { + /* No command specified - execute shell on a tty. */ + tty_flag = 1; + } + else + { + /* A command has been specified. Store it into the buffer. */ + for (i = optind; i < ac; i++) + { + if (i > optind) + buffer_append(&command, " ", 1); + buffer_append(&command, av[i], strlen(av[i])); + } + } + + /* Cannot fork to background if no command. */ + if (fork_after_authentication_flag && buffer_len(&command) == 0) + fatal("Cannot fork into background without a command to execute."); + + /* Allocate a tty by default if no command specified. */ + if (buffer_len(&command) == 0) + tty_flag = 1; + + /* Do not allocate a tty if stdin is not a tty. */ + if (!isatty(fileno(stdin))) + { + if (tty_flag) + fprintf(stderr, "Pseudo-terminal will not be allocated because stdin is not a terminal.\n"); + tty_flag = 0; + } + + /* Get user data. */ + pw = getpwuid(original_real_uid); + if (!pw) + { + fprintf(stderr, "You don't exist, go away!\n"); + exit(1); + } + + /* 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; + + /* Initialize "log" output. Since we are the client all output actually + goes to the terminal. */ + log_init(av[0], 1, debug_flag, quiet_flag, SYSLOG_FACILITY_USER); + + /* Read per-user configuration file. */ + snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir, SSH_USER_CONFFILE); + read_config_file(buf, host, &options); + + /* Read systemwide configuration file. */ + read_config_file(HOST_CONFIG_FILE, host, &options); + + /* Fill configuration defaults. */ + fill_default_options(&options); + if (options.user == NULL) + options.user = xstrdup(pw->pw_name); + + if (options.hostname != NULL) + host = options.hostname; + + /* Find canonic host name. */ + if (strchr(host, '.') == 0) + { + struct hostent *hp = gethostbyname(host); + if (hp != 0) + { + if (strchr(hp->h_name, '.') != 0) + host = xstrdup(hp->h_name); + else if (hp->h_aliases != 0 + && hp->h_aliases[0] != 0 + && strchr(hp->h_aliases[0], '.') != 0) + host = xstrdup(hp->h_aliases[0]); + } + } + + /* Disable rhosts authentication if not running as root. */ + if (original_effective_uid != 0) + { + options.rhosts_authentication = 0; + options.rhosts_rsa_authentication = 0; + } + + /* If using rsh has been selected, exec it now (without trying anything + else). Note that we must release privileges first. */ + if (options.use_rsh) + { + /* Restore our superuser privileges. This must be done before + permanently setting the uid. */ + restore_uid(); + + /* Switch to the original uid permanently. */ + permanently_set_uid(original_real_uid); + + /* Execute rsh. */ + rsh_connect(host, options.user, &command); + fatal("rsh_connect returned"); + } + + /* Restore our superuser privileges. */ + restore_uid(); + + /* Open a connection to the remote host. This needs root privileges if + rhosts_{rsa_}authentication is true. */ + + if (!options.use_privileged_port) + { + options.rhosts_authentication = 0; + options.rhosts_rsa_authentication = 0; + } + + ok = ssh_connect(host, &hostaddr, options.port, options.connection_attempts, + !options.rhosts_authentication && + !options.rhosts_rsa_authentication, + original_real_uid, options.proxy_command); + + /* If we successfully made the connection, load the host private key in + case we will need it later for combined rsa-rhosts authentication. + This must be done before releasing extra privileges, because the file + is only readable by root. */ + if (ok) + { + host_private_key = RSA_new(); + if (load_private_key(HOST_KEY_FILE, "", host_private_key, NULL)) + host_private_key_loaded = 1; + } + + /* Get rid of any extra privileges that we may have. We will no longer need + them. Also, extra privileges could make it very hard to read identity + files and other non-world-readable files from the user's home directory + if it happens to be on a NFS volume where root is mapped to nobody. */ + permanently_set_uid(original_real_uid); + + /* Now that we are back to our own permissions, create ~/.ssh directory + if it doesn\'t already exist. */ + snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir, SSH_USER_DIR); + if (stat(buf, &st) < 0) + if (mkdir(buf, 0755) < 0) + error("Could not create directory '%.200s'.", buf); + + /* Check if the connection failed, and try "rsh" if appropriate. */ + if (!ok) + { + if (options.port != 0) + log("Secure connection to %.100s on port %d refused%.100s.", + host, options.port, + options.fallback_to_rsh ? "; reverting to insecure method" : ""); + else + log("Secure connection to %.100s refused%.100s.", host, + options.fallback_to_rsh ? "; reverting to insecure method" : ""); + + if (options.fallback_to_rsh) + { + rsh_connect(host, options.user, &command); + fatal("rsh_connect returned"); + } + exit(1); + } + + /* Expand ~ in options.identity_files. */ + for (i = 0; i < options.num_identity_files; i++) + options.identity_files[i] = + tilde_expand_filename(options.identity_files[i], original_real_uid); + + /* Expand ~ in known host file names. */ + options.system_hostfile = tilde_expand_filename(options.system_hostfile, + original_real_uid); + options.user_hostfile = tilde_expand_filename(options.user_hostfile, + original_real_uid); + + /* Log into the remote system. This never returns if the login fails. */ + ssh_login(host_private_key_loaded, host_private_key, + host, &hostaddr, &options, original_real_uid); + + /* We no longer need the host private key. Clear it now. */ + if (host_private_key_loaded) + RSA_free(host_private_key); /* Destroys contents safely */ + + /* Close connection cleanly after attack. */ + cipher_attack_detected = packet_disconnect; + + /* If requested, fork and let ssh continue in the background. */ + if (fork_after_authentication_flag) + { + int ret = fork(); + if (ret == -1) + fatal("fork failed: %.100s", strerror(errno)); + if (ret != 0) + exit(0); + setsid(); + } + + /* Enable compression if requested. */ + if (options.compression) + { + debug("Requesting compression at level %d.", options.compression_level); + + if (options.compression_level < 1 || options.compression_level > 9) + fatal("Compression level must be from 1 (fast) to 9 (slow, best)."); + + /* Send the request. */ + packet_start(SSH_CMSG_REQUEST_COMPRESSION); + packet_put_int(options.compression_level); + packet_send(); + packet_write_wait(); + type = packet_read(&plen); + if (type == SSH_SMSG_SUCCESS) + packet_start_compression(options.compression_level); + else if (type == SSH_SMSG_FAILURE) + log("Warning: Remote host refused compression."); + else + packet_disconnect("Protocol error waiting for compression response."); + } + + /* Allocate a pseudo tty if appropriate. */ + if (tty_flag) + { + debug("Requesting pty."); + + /* Start the packet. */ + packet_start(SSH_CMSG_REQUEST_PTY); + + /* Store TERM in the packet. There is no limit on the length of the + string. */ + cp = getenv("TERM"); + if (!cp) + cp = ""; + packet_put_string(cp, strlen(cp)); + + /* Store window size in the packet. */ + if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) < 0) + memset(&ws, 0, sizeof(ws)); + packet_put_int(ws.ws_row); + packet_put_int(ws.ws_col); + packet_put_int(ws.ws_xpixel); + packet_put_int(ws.ws_ypixel); + + /* Store tty modes in the packet. */ + tty_make_modes(fileno(stdin)); + + /* Send the packet, and wait for it to leave. */ + packet_send(); + packet_write_wait(); + + /* Read response from the server. */ + type = packet_read(&plen); + if (type == SSH_SMSG_SUCCESS) + interactive = 1; + else if (type == SSH_SMSG_FAILURE) + log("Warning: Remote host failed or refused to allocate a pseudo tty."); + else + packet_disconnect("Protocol error waiting for pty request response."); + } + + /* Request X11 forwarding if enabled and DISPLAY is set. */ + if (options.forward_x11 && getenv("DISPLAY") != NULL) + { + char line[512], proto[512], data[512]; + FILE *f; + int forwarded = 0, got_data = 0, i; + +#ifdef XAUTH_PATH + /* Try to get Xauthority information for the display. */ + snprintf(line, sizeof line, "%.100s list %.200s 2>/dev/null", + XAUTH_PATH, getenv("DISPLAY")); + f = popen(line, "r"); + if (f && fgets(line, sizeof(line), f) && + sscanf(line, "%*s %s %s", proto, data) == 2) + got_data = 1; + if (f) + pclose(f); +#endif /* XAUTH_PATH */ + /* If we didn't get authentication data, just make up some data. The + forwarding code will check the validity of the response anyway, and + substitute this data. The X11 server, however, will ignore this + fake data and use whatever authentication mechanisms it was using + otherwise for the local connection. */ + if (!got_data) + { + u_int32_t rand = 0; + + strlcpy(proto, "MIT-MAGIC-COOKIE-1", sizeof proto); + for (i = 0; i < 16; i++) { + if (i % 4 == 0) + rand = arc4random(); + snprintf(data + 2 * i, sizeof data - 2 * i, "%02x", rand & 0xff); + rand >>= 8; + } + } + + /* Got local authentication reasonable information. Request forwarding + with authentication spoofing. */ + debug("Requesting X11 forwarding with authentication spoofing."); + x11_request_forwarding_with_spoofing(proto, data); + + /* Read response from the server. */ + type = packet_read(&plen); + if (type == SSH_SMSG_SUCCESS) + { + forwarded = 1; + interactive = 1; + } + else if (type == SSH_SMSG_FAILURE) + log("Warning: Remote host denied X11 forwarding."); + else + packet_disconnect("Protocol error waiting for X11 forwarding"); + } + + /* Tell the packet module whether this is an interactive session. */ + packet_set_interactive(interactive, options.keepalives); + + /* Clear agent forwarding if we don\'t have an agent. */ + authfd = ssh_get_authentication_socket(); + if (authfd < 0) + options.forward_agent = 0; + else + ssh_close_authentication_socket(authfd); + + /* Request authentication agent forwarding if appropriate. */ + if (options.forward_agent) + { + debug("Requesting authentication agent forwarding."); + auth_request_forwarding(); + + /* Read response from the server. */ + type = packet_read(&plen); + packet_integrity_check(plen, 0, type); + if (type != SSH_SMSG_SUCCESS) + log("Warning: Remote host denied authentication agent forwarding."); + } + + /* Initiate local TCP/IP port forwardings. */ + for (i = 0; i < options.num_local_forwards; i++) + { + debug("Connections to local port %d forwarded to remote address %.200s:%d", + options.local_forwards[i].port, options.local_forwards[i].host, + options.local_forwards[i].host_port); + channel_request_local_forwarding(options.local_forwards[i].port, + options.local_forwards[i].host, + options.local_forwards[i].host_port); + } + + /* Initiate remote TCP/IP port forwardings. */ + for (i = 0; i < options.num_remote_forwards; i++) + { + debug("Connections to remote port %d forwarded to local address %.200s:%d", + options.remote_forwards[i].port, options.remote_forwards[i].host, + options.remote_forwards[i].host_port); + channel_request_remote_forwarding(options.remote_forwards[i].port, + options.remote_forwards[i].host, + options.remote_forwards[i].host_port); + } + + /* If a command was specified on the command line, execute the command now. + Otherwise request the server to start a shell. */ + if (buffer_len(&command) > 0) + { + int len = buffer_len(&command); + if (len > 900) + len = 900; + debug("Sending command: %.*s", len, buffer_ptr(&command)); + packet_start(SSH_CMSG_EXEC_CMD); + packet_put_string(buffer_ptr(&command), buffer_len(&command)); + packet_send(); + packet_write_wait(); + } + else + { + debug("Requesting shell."); + packet_start(SSH_CMSG_EXEC_SHELL); + packet_send(); + packet_write_wait(); + } + + /* Enter the interactive session. */ + exit_status = client_loop(tty_flag, tty_flag ? options.escape_char : -1); + + /* Close the connection to the remote host. */ + packet_close(); + + /* Exit with the status returned by the program on the remote side. */ + exit(exit_status); +} |