diff options
Diffstat (limited to 'sshd.c')
| -rw-r--r-- | sshd.c | 2445 |
1 files changed, 2445 insertions, 0 deletions
@@ -0,0 +1,2445 @@ +/* + +sshd.c + +Author: Tatu Ylonen <ylo@cs.hut.fi> + +Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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 1.1 1999/10/27 03:42:46 damien 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 <tcpd.h> +#include <syslog.h> +int allow_severity = LOG_INFO; +int deny_severity = LOG_WARNING; +#endif /* LIBWRAP */ + +#ifndef O_NOCTTY +#define O_NOCTTY 0 +#endif + +#ifdef KRB4 +char *ticket = NULL; +#endif /* KRB4 */ + +#ifdef HAVE_PAM +#include <security/pam_appl.h> +struct pam_handle_t *pamh=NULL; +char *pampasswd=NULL; +int retval; +int origretval; +#endif /* HAVE_PAM */ + +/* Local Xauthority file. */ +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; + +/* 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; + +/* 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; +char *forced_command = NULL; /* RSA authentication "command=" option. */ +struct envstring *custom_environment = NULL; + /* RSA authentication "environment=" options. */ + +/* 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 +{ + /* Private part of server key. */ + RSA *private_key; + + /* Private part of host key. */ + RSA *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(int privileged_port); +void do_authentication(char *user, int privileged_port); +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); +#ifdef HAVE_PAM +static int pamconv(int num_msg, const struct pam_message **msg, + struct pam_response **resp, void *appdata_ptr); + +static struct pam_conv conv = { + pamconv, + NULL +}; + +static int pamconv(int num_msg, const struct pam_message **msg, + struct pam_response **resp, void *appdata_ptr) +{ + int count = 0; + int replies = 0; + struct pam_response *reply = NULL; + int size = sizeof(struct pam_response); + + for(count = 0; count < num_msg; count++) + { + switch (msg[count]->msg_style) + { + case PAM_PROMPT_ECHO_ON: + case PAM_PROMPT_ECHO_OFF: + if (reply == NULL) + reply = xmalloc(size); + else + reply = realloc(reply, size); + + if (reply == NULL) + return PAM_CONV_ERR; + + size += sizeof(struct pam_response); + + reply[replies].resp_retcode = PAM_SUCCESS; + + reply[replies++].resp = xstrdup(pampasswd); + /* PAM frees resp */ + break; + + case PAM_TEXT_INFO: + /* ignore it... */ + break; + + case PAM_ERROR_MSG: + default: + /* Must be an error of some sort... */ + if (reply != NULL) + free(reply); + + return PAM_CONV_ERR; + } + } + + if (reply != NULL) + *resp = reply; + + return PAM_SUCCESS; +} + +void pam_cleanup_proc(void *context) +{ + if (retval == PAM_SUCCESS) + retval = pam_close_session((pam_handle_t *)pamh, 0); + + if (pam_end((pam_handle_t *)pamh, retval) != PAM_SUCCESS) + log("Cannot release PAM authentication."); +} +#endif /* HAVE_PAM */ + +/* 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; + wait(&status); + 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."); +} + +/* 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 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. */ + 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:diqQ")) != EOF) + { + switch (opt) + { + case 'f': + config_file_name = optarg; + break; + case 'd': + debug_flag = 1; + break; + case 'i': + inetd_flag = 1; + break; + case 'Q': + silentrsa = 1; + break; + case 'q': + options.quiet_mode = 1; + 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 '?': + 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/sshd_config)\n", ETCDIR); + 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); + } + + /* Initialize the log (it is reinitialized below in case we forked). */ + log_init(av0, debug_flag && !inetd_flag, + debug_flag || options.fascist_logging, + options.quiet_mode, options.log_facility); + + debug("sshd version %.100s", SSH_VERSION); + + sensitive_data.host_key = RSA_new(); + /* Load the host key. It must have empty passphrase. */ + if (!load_private_key(options.host_key_file, "", + sensitive_data.host_key, &comment)) + { + if (debug_flag) + fprintf(stderr, "Could not load host key: %s: %s\n", + options.host_key_file, strerror(errno)); + else + { + int err = errno; + log_init(av0, !inetd_flag, 1, 0, options.log_facility); + error("Could not load host key: %.200s: %.100s", + options.host_key_file, strerror(err)); + } + exit(1); + } + xfree(comment); + + /* 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, debug_flag && !inetd_flag, + debug_flag || options.fascist_logging, + options.quiet_mode, options.log_facility); + + /* 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(); + /* Generate an rsa key. */ + 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)); + + /* Initialize the socket address. */ + memset(&sin, 0, sizeof(sin)); + sin.sin_family = AF_INET; + sin.sin_addr = options.listen_addr; + sin.sin_port = htons(options.port); + + /* Bind the socket to the desired 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); + } + } + + /* Start listening on the port. */ + 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(); + /* Generate an rsa key. */ + 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 accept until there is a connection. */ + 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, debug_flag && !inetd_flag, + options.fascist_logging || debug_flag, + options.quiet_mode, options.log_facility); + 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); + + /* 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); + } + log("Connection from %.500s port %d", + eval_client(&req), get_remote_port()); + } +#else + /* Log the connection. */ + log("Connection from %.100s port %d", + get_remote_ipaddr(), get_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); + + /* Send our protocol version identification. */ + snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", + PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION); + if (write(sock_out, buf, strlen(buf)) != strlen(buf)) + fatal("Could not write ident string."); + + /* 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."); + 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) + { + const char *s = "Protocol mismatch.\n"; + (void) write(sock_out, s, strlen(s)); + close(sock_in); + close(sock_out); + fatal("Bad protocol version identification: %.100s", buf); + } + debug("Client protocol version %d.%d; client software version %.100s", + remote_major, remote_minor, remote_version); + if (remote_major != PROTOCOL_MAJOR) + { + const char *s = "Protocol major versions differ.\n"; + (void) write(sock_out, s, strlen(s)); + close(sock_in); + close(sock_out); + fatal("Protocol major versions differ: %d vs. %d", + 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; + } + } + + packet_set_nonblocking(); + + /* Handle the connection. We pass as argument whether the connection + came from a privileged port. */ + do_connection(get_remote_port() < IPPORT_RESERVED); + +#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. */ + log("Closing connection to %.100s", inet_ntoa(sin.sin_addr)); + +#ifdef HAVE_PAM + if (retval == PAM_SUCCESS) + retval = pam_close_session((pam_handle_t *)pamh, 0); + + if (pam_end((pam_handle_t *)pamh, retval) != PAM_SUCCESS) + log("Cannot release PAM authentication."); + + fatal_remove_cleanup(&pam_cleanup_proc, NULL); +#endif /* HAVE_PAM */ + + 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 privileged_port) +{ + int i; + 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 + 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. */ + cipher_type = packet_get_char(); + + /* 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); + + /* Get protocol flags. */ + 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. */ + assert(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). */ + assert(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 for this session. */ + compute_session_id(session_id, check_bytes, + BN_num_bits(sensitive_data.host_key->n), + sensitive_data.host_key->n, + BN_num_bits(sensitive_data.private_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); + assert(BN_num_bytes(session_key_int) == sizeof(session_key)); + BN_bn2bin(session_key_int, session_key); + + /* 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, 0); + + /* 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, privileged_port); +} + +/* 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 (receive |