/* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland * All rights reserved * Code to connect to a remote host, and to perform the client side of the * login (authentication) dialog. * * As far as I am concerned, the code I have written for this software * can be used freely for any purpose. Any derived versions of this * software must be clearly marked as such, and if the derived work is * incompatible with the protocol description in the RFC file, it must be * called by a name other than "ssh" or "Secure Shell". */ #include "includes.h" RCSID("$OpenBSD: sshconnect.c,v 1.94 2001/02/08 10:47:04 itojun Exp $"); #include #include "ssh.h" #include "xmalloc.h" #include "rsa.h" #include "buffer.h" #include "packet.h" #include "uidswap.h" #include "compat.h" #include "key.h" #include "sshconnect.h" #include "hostfile.h" #include "log.h" #include "readconf.h" #include "atomicio.h" #include "misc.h" char *client_version_string = NULL; char *server_version_string = NULL; extern Options options; extern char *__progname; /* AF_UNSPEC or AF_INET or AF_INET6 */ extern int IPv4or6; /* * Connect to the given ssh server using a proxy command. */ int ssh_proxy_connect(const char *host, u_short port, uid_t original_real_uid, const char *proxy_command) { Buffer command; const char *cp; char *command_string; int pin[2], pout[2]; pid_t pid; char strport[NI_MAXSERV]; /* Convert the port number into a string. */ snprintf(strport, sizeof strport, "%hu", port); /* Build the final command string in the buffer by making the appropriate substitutions to the given proxy command. */ buffer_init(&command); for (cp = proxy_command; *cp; cp++) { if (cp[0] == '%' && cp[1] == '%') { buffer_append(&command, "%", 1); cp++; continue; } if (cp[0] == '%' && cp[1] == 'h') { buffer_append(&command, host, strlen(host)); cp++; continue; } if (cp[0] == '%' && cp[1] == 'p') { buffer_append(&command, strport, strlen(strport)); cp++; continue; } buffer_append(&command, cp, 1); } buffer_append(&command, "\0", 1); /* Get the final command string. */ command_string = buffer_ptr(&command); /* Create pipes for communicating with the proxy. */ if (pipe(pin) < 0 || pipe(pout) < 0) fatal("Could not create pipes to communicate with the proxy: %.100s", strerror(errno)); debug("Executing proxy command: %.500s", command_string); /* Fork and execute the proxy command. */ if ((pid = fork()) == 0) { char *argv[10]; /* Child. Permanently give up superuser privileges. */ permanently_set_uid(original_real_uid); /* Redirect stdin and stdout. */ close(pin[1]); if (pin[0] != 0) { if (dup2(pin[0], 0) < 0) perror("dup2 stdin"); close(pin[0]); } close(pout[0]); if (dup2(pout[1], 1) < 0) perror("dup2 stdout"); /* Cannot be 1 because pin allocated two descriptors. */ close(pout[1]); /* Stderr is left as it is so that error messages get printed on the user's terminal. */ argv[0] = _PATH_BSHELL; argv[1] = "-c"; argv[2] = command_string; argv[3] = NULL; /* Execute the proxy command. Note that we gave up any extra privileges above. */ execv(argv[0], argv); perror(argv[0]); exit(1); } /* Parent. */ if (pid < 0) fatal("fork failed: %.100s", strerror(errno)); /* Close child side of the descriptors. */ close(pin[0]); close(pout[1]); /* Free the command name. */ buffer_free(&command); /* Set the connection file descriptors. */ packet_set_connection(pout[0], pin[1]); return 1; } /* * Creates a (possibly privileged) socket for use as the ssh connection. */ int ssh_create_socket(uid_t original_real_uid, int privileged, int family) { int sock; /* * If we are running as root and want to connect to a privileged * port, bind our own socket to a privileged port. */ if (privileged) { int p = IPPORT_RESERVED - 1; sock = rresvport_af(&p, family); if (sock < 0) error("rresvport: af=%d %.100s", family, strerror(errno)); else debug("Allocated local port %d.", p); } else { /* * Just create an ordinary socket on arbitrary port. We use * the user's uid to create the socket. */ temporarily_use_uid(original_real_uid); sock = socket(family, SOCK_STREAM, 0); if (sock < 0) error("socket: %.100s", strerror(errno)); restore_uid(); } return sock; } /* * Opens a TCP/IP connection to the remote server on the given host. * The address of the remote host will be returned in hostaddr. * If port is 0, the default port will be used. If anonymous is zero, * a privileged port will be allocated to make the connection. * This requires super-user privileges if anonymous is false. * Connection_attempts specifies the maximum number of tries (one per * second). If proxy_command is non-NULL, it specifies the command (with %h * and %p substituted for host and port, respectively) to use to contact * the daemon. */ int ssh_connect(const char *host, struct sockaddr_storage * hostaddr, u_short port, int connection_attempts, int anonymous, uid_t original_real_uid, const char *proxy_command) { int gaierr; int on = 1; int sock = -1, attempt; char ntop[NI_MAXHOST], strport[NI_MAXSERV]; struct addrinfo hints, *ai, *aitop; struct linger linger; struct servent *sp; debug("ssh_connect: getuid %u geteuid %u anon %d", (u_int) getuid(), (u_int) geteuid(), anonymous); /* Get default port if port has not been set. */ if (port == 0) { sp = getservbyname(SSH_SERVICE_NAME, "tcp"); if (sp) port = ntohs(sp->s_port); else port = SSH_DEFAULT_PORT; } /* If a proxy command is given, connect using it. */ if (proxy_command != NULL) return ssh_proxy_connect(host, port, original_real_uid, proxy_command); /* No proxy command. */ memset(&hints, 0, sizeof(hints)); hints.ai_family = IPv4or6; hints.ai_socktype = SOCK_STREAM; snprintf(strport, sizeof strport, "%d", port); if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0) fatal("%s: %.100s: %s", __progname, host, gai_strerror(gaierr)); /* * Try to connect several times. On some machines, the first time * will sometimes fail. In general socket code appears to behave * quite magically on many machines. */ for (attempt = 0; attempt < connection_attempts; attempt++) { if (attempt > 0) debug("Trying again..."); /* Loop through addresses for this host, and try each one in sequence until the connection succeeds. */ for (ai = aitop; ai; ai = ai->ai_next) { if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6) continue; if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop), strport, sizeof(strport), NI_NUMERICHOST|NI_NUMERICSERV) != 0) { error("ssh_connect: getnameinfo failed"); continue; } debug("Connecting to %.200s [%.100s] port %s.", host, ntop, strport); /* Create a socket for connecting. */ sock = ssh_create_socket(original_real_uid, !anonymous && geteuid() == 0, ai->ai_family); if (sock < 0) continue; /* Connect to the host. We use the user's uid in the * hope that it will help with tcp_wrappers showing * the remote uid as root. */ temporarily_use_uid(original_real_uid); if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) { /* Successful connection. */ memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen); restore_uid(); break; } else { debug("connect: %.100s", strerror(errno)); restore_uid(); /* * Close the failed socket; there appear to * be some problems when reusing a socket for * which connect() has already returned an * error. */ shutdown(sock, SHUT_RDWR); close(sock); } } if (ai) break; /* Successful connection. */ /* Sleep a moment before retrying. */ sleep(1); } freeaddrinfo(aitop); /* Return failure if we didn't get a successful connection. */ if (attempt >= connection_attempts) return 0; debug("Connection established."); /* * Set socket options. We would like the socket to disappear as soon * as it has been closed for whatever reason. */ /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */ linger.l_onoff = 1; linger.l_linger = 5; setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger)); /* Set keepalives if requested. */ if (options.keepalives && setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on, sizeof(on)) < 0) error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno)); /* Set the connection. */ packet_set_connection(sock, sock); return 1; } /* * Waits for the server identification string, and sends our own * identification string. */ void ssh_exchange_identification() { char buf[256], remote_version[256]; /* must be same size! */ int remote_major, remote_minor, i, mismatch; int connection_in = packet_get_connection_in(); int connection_out = packet_get_connection_out(); int minor1 = PROTOCOL_MINOR_1; /* Read other side\'s version identification. */ for (;;) { for (i = 0; i < sizeof(buf) - 1; i++) { int len = atomicio(read, connection_in, &buf[i], 1); if (len < 0) fatal("ssh_exchange_identification: read: %.100s", strerror(errno)); if (len != 1) fatal("ssh_exchange_identification: Connection closed by remote host"); if (buf[i] == '\r') { buf[i] = '\n'; buf[i + 1] = 0; continue; /**XXX wait for \n */ } if (buf[i] == '\n') { buf[i + 1] = 0; break; } } buf[sizeof(buf) - 1] = 0; if (strncmp(buf, "SSH-", 4) == 0) break; debug("ssh_exchange_identification: %s", buf); } server_version_string = xstrdup(buf); /* * Check that the versions match. In future this might accept * several versions and set appropriate flags to handle them. */ if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor, remote_version) != 3) fatal("Bad remote protocol version identification: '%.100s'", buf); debug("Remote protocol version %d.%d, remote software version %.100s", remote_major, remote_minor, remote_version); compat_datafellows(remote_version); mismatch = 0; switch(remote_major) { case 1: if (remote_minor == 99 && (options.protocol & SSH_PROTO_2) && !(options.protocol & SSH_PROTO_1_PREFERRED)) { enable_compat20(); break; } if (!(options.protocol & SSH_PROTO_1)) { mismatch = 1; break; } if (remote_minor < 3) { fatal("Remote machine has too old SSH software version."); } else if (remote_minor == 3 || remote_minor == 4) { /* We speak 1.3, too. */ enable_compat13(); minor1 = 3; if (options.forward_agent) { log("Agent forwarding disabled for protocol 1.3"); options.forward_agent = 0; } } break; case 2: if (options.protocol & SSH_PROTO_2) { enable_compat20(); break; } /* FALLTHROUGH */ default: mismatch = 1; break; } if (mismatch) fatal("Protocol major versions differ: %d vs. %d", (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1, remote_major); if (compat20) packet_set_ssh2_format(); /* Send our own protocol version identification. */ snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1, compat20 ? PROTOCOL_MINOR_2 : minor1, SSH_VERSION); if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf)) fatal("write: %.100s", strerror(errno)); client_version_string = xstrdup(buf); chop(client_version_string); chop(server_version_string); debug("Local version string %.100s", client_version_string); } int read_yes_or_no(const char *prompt, int defval) { char buf[1024]; FILE *f; int retval = -1; if (isatty(STDIN_FILENO)) f = stdin; else f = fopen("/dev/tty", "rw"); if (f == NULL) return 0; fflush(stdout); while (1) { fprintf(stderr, "%s", prompt); if (fgets(buf, sizeof(buf), f) == NULL) { /* Print a newline (the prompt probably didn\'t have one). */ fprintf(stderr, "\n"); strlcpy(buf, "no", sizeof buf); } /* Remove newline from response. */ if (strchr(buf, '\n')) *strchr(buf, '\n') = 0; if (buf[0] == 0) retval = defval; if (strcmp(buf, "yes") == 0) retval = 1; else if (strcmp(buf, "no") == 0) retval = 0; else fprintf(stderr, "Please type 'yes' or 'no'.\n"); if (retval != -1) { if (f != stdin) fclose(f); return retval; } } } /* * check whether the supplied host key is valid, return only if ok. */ void check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key, const char *user_hostfile, const char *system_hostfile) { Key *file_key; char *type = key_type(host_key); char *ip = NULL; char hostline[1000], *hostp; HostStatus host_status; HostStatus ip_status; int local = 0, host_ip_differ = 0; char ntop[NI_MAXHOST]; int host_line, ip_line; const char *host_file = NULL, *ip_file = NULL; /* * Force accepting of the host key for loopback/localhost. The * problem is that if the home directory is NFS-mounted to multiple * machines, localhost will refer to a different machine in each of * them, and the user will get bogus HOST_CHANGED warnings. This * essentially disables host authentication for localhost; however, * this is probably not a real problem. */ /** hostaddr == 0! */ switch (hostaddr->sa_family) { case AF_INET: local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET; break; case AF_INET6: local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr)); break; default: local = 0; break; } if (local && options.host_key_alias == NULL) { debug("Forcing accepting of host key for " "loopback/localhost."); return; } /* * We don't have the remote ip-address for connections * using a proxy command */ if (options.proxy_command == NULL) { if (getnameinfo(hostaddr, hostaddr->sa_len, ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0) fatal("check_host_key: getnameinfo failed"); ip = xstrdup(ntop); } else { ip = xstrdup(""); } /* * Turn off check_host_ip if the connection is to localhost, via proxy * command or if we don't have a hostname to compare with */ if (options.check_host_ip && (local || strcmp(host, ip) == 0 || options.proxy_command != NULL)) options.check_host_ip = 0; /* * Allow the user to record the key under a different name. This is * useful for ssh tunneling over forwarded connections or if you run * multiple sshd's on different ports on the same machine. */ if (options.host_key_alias != NULL) { host = options.host_key_alias; debug("using hostkeyalias: %s", host); } /* * Store the host key from the known host file in here so that we can * compare it with the key for the IP address. */ file_key = key_new(host_key->type); /* * Check if the host key is present in the user\'s list of known * hosts or in the systemwide list. */ host_file = user_hostfile; host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line); if (host_status == HOST_NEW) { host_file = system_hostfile; host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line); } /* * Also perform check for the ip address, skip the check if we are * localhost or the hostname was an ip address to begin with */ if (options.check_host_ip) { Key *ip_key = key_new(host_key->type); ip_file = user_hostfile; ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line); if (ip_status == HOST_NEW) { ip_file = system_hostfile; ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line); } if (host_status == HOST_CHANGED && (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key))) host_ip_differ = 1; key_free(ip_key); } else ip_status = host_status; key_free(file_key); switch (host_status) { case HOST_OK: /* The host is known and the key matches. */ debug("Host '%.200s' is known and matches the %s host key.", host, type); debug("Found key in %s:%d", host_file, host_line); if (options.check_host_ip && ip_status == HOST_NEW) { if (!add_host_to_hostfile(user_hostfile, ip, host_key)) log("Failed to add the %s host key for IP address '%.128s' to the list of known hosts (%.30s).", type, ip, user_hostfile); else log("Warning: Permanently added the %s host key for IP address '%.128s' to the list of known hosts.", type, ip); } break; case HOST_NEW: /* The host is new. */ if (options.strict_host_key_checking == 1) { /* User has requested strict host key checking. We will not add the host key automatically. The only alternative left is to abort. */ fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host); } else if (options.strict_host_key_checking == 2) { /* The default */ char prompt[1024]; snprintf(prompt, sizeof(prompt), "The authenticity of host '%.200s (%s)' can't be established.\n" "%s key fingerprint is %s.\n" "Are you sure you want to continue connecting (yes/no)? ", host, ip, type, key_fingerprint(host_key)); if (!read_yes_or_no(prompt, -1)) fatal("Aborted by user!\n"); } if (options.check_host_ip && ip_status == HOST_NEW) { snprintf(hostline, sizeof(hostline), "%s,%s", host, ip); hostp = hostline; } else hostp = host; /* If not in strict mode, add the key automatically to the local known_hosts file. */ if (!add_host_to_hostfile(user_hostfile, hostp, host_key)) log("Failed to add the host to the list of known hosts (%.500s).", user_hostfile); else log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.", hostp, type); break; case HOST_CHANGED: if (options.check_host_ip && host_ip_differ) { char *msg; if (ip_status == HOST_NEW) msg = "is unknown"; else if (ip_status == HOST_OK) msg = "is unchanged"; else msg = "has a different value"; error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @"); error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); error("The %s host key for %s has changed,", type, host); error("and the key for the according IP address %s", ip); error("%s. This could either mean that", msg); error("DNS SPOOFING is happening or the IP address for the host"); error("and its host key have changed at the same time."); if (ip_status != HOST_NEW) error("Offending key for IP in %s:%d", ip_file, ip_line); } /* The host key has changed. */ error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @"); error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!"); error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!"); error("It is also possible that the %s host key has just been changed.", type); error("The fingerprint for the %s key sent by the remote host is\n%s.", type, key_fingerprint(host_key)); error("Please contact your system administrator."); error("Add correct host key in %.100s to get rid of this message.", user_hostfile); error("Offending key in %s:%d", host_file, host_line); /* * If strict host key checking is in use, the user will have * to edit the key manually and we can only abort. */ if (options.strict_host_key_checking) fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host); /* * If strict host key checking has not been requested, allow * the connection but without password authentication or * agent forwarding. */ if (options.password_authentication) { error("Password authentication is disabled to avoid trojan horses."); options.password_authentication = 0; } if (options.forward_agent) { error("Agent forwarding is disabled to avoid trojan horses."); options.forward_agent = 0; } if (options.forward_x11) { error("X11 forwarding is disabled to avoid trojan horses."); options.forward_x11 = 0; } if (options.num_local_forwards > 0 || options.num_remote_forwards > 0) { error("Port forwarding is disabled to avoid trojan horses."); options.num_local_forwards = options.num_remote_forwards = 0; } /* * XXX Should permit the user to change to use the new id. * This could be done by converting the host key to an * identifying sentence, tell that the host identifies itself * by that sentence, and ask the user if he/she whishes to * accept the authentication. */ break; } if (options.check_host_ip && host_status != HOST_CHANGED && ip_status == HOST_CHANGED) { log("Warning: the %s host key for '%.200s' " "differs from the key for the IP address '%.128s'", type, host, ip); if (host_status == HOST_OK) log("Matching host key in %s:%d", host_file, host_line); log("Offending key for IP in %s:%d", ip_file, ip_line); if (options.strict_host_key_checking == 1) { fatal("Exiting, you have requested strict checking."); } else if (options.strict_host_key_checking == 2) { if (!read_yes_or_no("Are you sure you want " \ "to continue connecting (yes/no)? ", -1)) fatal("Aborted by user!\n"); } } xfree(ip); } /* * Starts a dialog with the server, and authenticates the current user on the * server. This does not need any extra privileges. The basic connection * to the server must already have been established before this is called. * If login fails, this function prints an error and never returns. * This function does not require super-user privileges. */ void ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost, struct sockaddr *hostaddr, uid_t original_real_uid) { struct passwd *pw; char *host, *cp; char *server_user, *local_user; /* Get local user name. Use it as server user if no user name was given. */ pw = getpwuid(original_real_uid); if (!pw) fatal("User id %u not found from user database.", original_real_uid); local_user = xstrdup(pw->pw_name); server_user = options.user ? options.user : local_user; /* Convert the user-supplied hostname into all lowercase. */ host = xstrdup(orighost); for (cp = host; *cp; cp++) if (isupper(*cp)) *cp = tolower(*cp); /* Exchange protocol version identification strings with the server. */ ssh_exchange_identification(); /* Put the connection into non-blocking mode. */ packet_set_nonblocking(); /* key exchange */ /* authenticate user */ if (compat20) { ssh_kex2(host, hostaddr); ssh_userauth2(server_user, host); } else { ssh_kex(host, hostaddr); ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key); } }