diff options
Diffstat (limited to 'sshconnect.c')
| -rw-r--r-- | sshconnect.c | 1581 |
1 files changed, 1581 insertions, 0 deletions
diff --git a/sshconnect.c b/sshconnect.c new file mode 100644 index 0000000..6d81927 --- /dev/null +++ b/sshconnect.c @@ -0,0 +1,1581 @@ +/* $OpenBSD: sshconnect.c,v 1.305 2018/09/20 03:30:44 djm Exp $ */ +/* + * Author: Tatu Ylonen <ylo@cs.hut.fi> + * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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" + +#include <sys/types.h> +#include <sys/wait.h> +#include <sys/stat.h> +#include <sys/socket.h> +#ifdef HAVE_SYS_TIME_H +# include <sys/time.h> +#endif + +#include <net/if.h> +#include <netinet/in.h> +#include <arpa/inet.h> + +#include <ctype.h> +#include <errno.h> +#include <fcntl.h> +#include <netdb.h> +#ifdef HAVE_PATHS_H +#include <paths.h> +#endif +#include <pwd.h> +#ifdef HAVE_POLL_H +#include <poll.h> +#endif +#include <signal.h> +#include <stdarg.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#ifdef HAVE_IFADDRS_H +# include <ifaddrs.h> +#endif + +#include "xmalloc.h" +#include "hostfile.h" +#include "ssh.h" +#include "sshbuf.h" +#include "packet.h" +#include "compat.h" +#include "sshkey.h" +#include "sshconnect.h" +#include "hostfile.h" +#include "log.h" +#include "misc.h" +#include "readconf.h" +#include "atomicio.h" +#include "dns.h" +#include "monitor_fdpass.h" +#include "ssh2.h" +#include "version.h" +#include "authfile.h" +#include "ssherr.h" +#include "authfd.h" + +char *client_version_string = NULL; +char *server_version_string = NULL; +struct sshkey *previous_host_key = NULL; + +static int matching_host_key_dns = 0; + +static pid_t proxy_command_pid = 0; + +/* import */ +extern Options options; +extern char *__progname; + +static int show_other_keys(struct hostkeys *, struct sshkey *); +static void warn_changed_key(struct sshkey *); + +/* Expand a proxy command */ +static char * +expand_proxy_command(const char *proxy_command, const char *user, + const char *host, int port) +{ + char *tmp, *ret, strport[NI_MAXSERV]; + + snprintf(strport, sizeof strport, "%d", port); + xasprintf(&tmp, "exec %s", proxy_command); + ret = percent_expand(tmp, "h", host, "p", strport, + "r", options.user, (char *)NULL); + free(tmp); + return ret; +} + +/* + * Connect to the given ssh server using a proxy command that passes a + * a connected fd back to us. + */ +static int +ssh_proxy_fdpass_connect(struct ssh *ssh, const char *host, u_short port, + const char *proxy_command) +{ + char *command_string; + int sp[2], sock; + pid_t pid; + char *shell; + + if ((shell = getenv("SHELL")) == NULL) + shell = _PATH_BSHELL; + + if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) < 0) + fatal("Could not create socketpair to communicate with " + "proxy dialer: %.100s", strerror(errno)); + + command_string = expand_proxy_command(proxy_command, options.user, + host, port); + debug("Executing proxy dialer command: %.500s", command_string); + + /* Fork and execute the proxy command. */ + if ((pid = fork()) == 0) { + char *argv[10]; + + close(sp[1]); + /* Redirect stdin and stdout. */ + if (sp[0] != 0) { + if (dup2(sp[0], 0) < 0) + perror("dup2 stdin"); + } + if (sp[0] != 1) { + if (dup2(sp[0], 1) < 0) + perror("dup2 stdout"); + } + if (sp[0] >= 2) + close(sp[0]); + + /* + * Stderr is left as it is so that error messages get + * printed on the user's terminal. + */ + argv[0] = shell; + 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(sp[0]); + free(command_string); + + if ((sock = mm_receive_fd(sp[1])) == -1) + fatal("proxy dialer did not pass back a connection"); + close(sp[1]); + + while (waitpid(pid, NULL, 0) == -1) + if (errno != EINTR) + fatal("Couldn't wait for child: %s", strerror(errno)); + + /* Set the connection file descriptors. */ + if (ssh_packet_set_connection(ssh, sock, sock) == NULL) + return -1; /* ssh_packet_set_connection logs error */ + + return 0; +} + +/* + * Connect to the given ssh server using a proxy command. + */ +static int +ssh_proxy_connect(struct ssh *ssh, const char *host, u_short port, + const char *proxy_command) +{ + char *command_string; + int pin[2], pout[2]; + pid_t pid; + char *shell; + + if ((shell = getenv("SHELL")) == NULL || *shell == '\0') + shell = _PATH_BSHELL; + + /* 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)); + + command_string = expand_proxy_command(proxy_command, options.user, + host, port); + debug("Executing proxy command: %.500s", command_string); + + /* Fork and execute the proxy command. */ + if ((pid = fork()) == 0) { + char *argv[10]; + + /* 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] = shell; + argv[1] = "-c"; + argv[2] = command_string; + argv[3] = NULL; + + /* Execute the proxy command. Note that we gave up any + extra privileges above. */ + signal(SIGPIPE, SIG_DFL); + execv(argv[0], argv); + perror(argv[0]); + exit(1); + } + /* Parent. */ + if (pid < 0) + fatal("fork failed: %.100s", strerror(errno)); + else + proxy_command_pid = pid; /* save pid to clean up later */ + + /* Close child side of the descriptors. */ + close(pin[0]); + close(pout[1]); + + /* Free the command name. */ + free(command_string); + + /* Set the connection file descriptors. */ + if (ssh_packet_set_connection(ssh, pout[0], pin[1]) == NULL) + return -1; /* ssh_packet_set_connection logs error */ + + return 0; +} + +void +ssh_kill_proxy_command(void) +{ + /* + * Send SIGHUP to proxy command if used. We don't wait() in + * case it hangs and instead rely on init to reap the child + */ + if (proxy_command_pid > 1) + kill(proxy_command_pid, SIGHUP); +} + +#ifdef HAVE_IFADDRS_H +/* + * Search a interface address list (returned from getifaddrs(3)) for an + * address that matches the desired address family on the specified interface. + * Returns 0 and fills in *resultp and *rlenp on success. Returns -1 on failure. + */ +static int +check_ifaddrs(const char *ifname, int af, const struct ifaddrs *ifaddrs, + struct sockaddr_storage *resultp, socklen_t *rlenp) +{ + struct sockaddr_in6 *sa6; + struct sockaddr_in *sa; + struct in6_addr *v6addr; + const struct ifaddrs *ifa; + int allow_local; + + /* + * Prefer addresses that are not loopback or linklocal, but use them + * if nothing else matches. + */ + for (allow_local = 0; allow_local < 2; allow_local++) { + for (ifa = ifaddrs; ifa != NULL; ifa = ifa->ifa_next) { + if (ifa->ifa_addr == NULL || ifa->ifa_name == NULL || + (ifa->ifa_flags & IFF_UP) == 0 || + ifa->ifa_addr->sa_family != af || + strcmp(ifa->ifa_name, options.bind_interface) != 0) + continue; + switch (ifa->ifa_addr->sa_family) { + case AF_INET: + sa = (struct sockaddr_in *)ifa->ifa_addr; + if (!allow_local && sa->sin_addr.s_addr == + htonl(INADDR_LOOPBACK)) + continue; + if (*rlenp < sizeof(struct sockaddr_in)) { + error("%s: v4 addr doesn't fit", + __func__); + return -1; + } + *rlenp = sizeof(struct sockaddr_in); + memcpy(resultp, sa, *rlenp); + return 0; + case AF_INET6: + sa6 = (struct sockaddr_in6 *)ifa->ifa_addr; + v6addr = &sa6->sin6_addr; + if (!allow_local && + (IN6_IS_ADDR_LINKLOCAL(v6addr) || + IN6_IS_ADDR_LOOPBACK(v6addr))) + continue; + if (*rlenp < sizeof(struct sockaddr_in6)) { + error("%s: v6 addr doesn't fit", + __func__); + return -1; + } + *rlenp = sizeof(struct sockaddr_in6); + memcpy(resultp, sa6, *rlenp); + return 0; + } + } + } + return -1; +} +#endif + +/* + * Creates a socket for use as the ssh connection. + */ +static int +ssh_create_socket(struct addrinfo *ai) +{ + int sock, r; + struct sockaddr_storage bindaddr; + socklen_t bindaddrlen = 0; + struct addrinfo hints, *res = NULL; +#ifdef HAVE_IFADDRS_H + struct ifaddrs *ifaddrs = NULL; +#endif + char ntop[NI_MAXHOST]; + + sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol); + if (sock < 0) { + error("socket: %s", strerror(errno)); + return -1; + } + fcntl(sock, F_SETFD, FD_CLOEXEC); + + /* Bind the socket to an alternative local IP address */ + if (options.bind_address == NULL && options.bind_interface == NULL) + return sock; + + if (options.bind_address != NULL) { + memset(&hints, 0, sizeof(hints)); + hints.ai_family = ai->ai_family; + hints.ai_socktype = ai->ai_socktype; + hints.ai_protocol = ai->ai_protocol; + hints.ai_flags = AI_PASSIVE; + if ((r = getaddrinfo(options.bind_address, NULL, + &hints, &res)) != 0) { + error("getaddrinfo: %s: %s", options.bind_address, + ssh_gai_strerror(r)); + goto fail; + } + if (res == NULL) { + error("getaddrinfo: no addrs"); + goto fail; + } + if (res->ai_addrlen > sizeof(bindaddr)) { + error("%s: addr doesn't fit", __func__); + goto fail; + } + memcpy(&bindaddr, res->ai_addr, res->ai_addrlen); + bindaddrlen = res->ai_addrlen; + } else if (options.bind_interface != NULL) { +#ifdef HAVE_IFADDRS_H + if ((r = getifaddrs(&ifaddrs)) != 0) { + error("getifaddrs: %s: %s", options.bind_interface, + strerror(errno)); + goto fail; + } + bindaddrlen = sizeof(bindaddr); + if (check_ifaddrs(options.bind_interface, ai->ai_family, + ifaddrs, &bindaddr, &bindaddrlen) != 0) { + logit("getifaddrs: %s: no suitable addresses", + options.bind_interface); + goto fail; + } +#else + error("BindInterface not supported on this platform."); +#endif + } + if ((r = getnameinfo((struct sockaddr *)&bindaddr, bindaddrlen, + ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST)) != 0) { + error("%s: getnameinfo failed: %s", __func__, + ssh_gai_strerror(r)); + goto fail; + } + if (bind(sock, (struct sockaddr *)&bindaddr, bindaddrlen) != 0) { + error("bind %s: %s", ntop, strerror(errno)); + goto fail; + } + debug("%s: bound to %s", __func__, ntop); + /* success */ + goto out; +fail: + close(sock); + sock = -1; + out: + if (res != NULL) + freeaddrinfo(res); +#ifdef HAVE_IFADDRS_H + if (ifaddrs != NULL) + freeifaddrs(ifaddrs); +#endif + return sock; +} + +/* + * Wait up to *timeoutp milliseconds for fd to be readable. Updates + * *timeoutp with time remaining. + * Returns 0 if fd ready or -1 on timeout or error (see errno). + */ +static int +waitrfd(int fd, int *timeoutp) +{ + struct pollfd pfd; + struct timeval t_start; + int oerrno, r; + + monotime_tv(&t_start); + pfd.fd = fd; + pfd.events = POLLIN; + for (; *timeoutp >= 0;) { + r = poll(&pfd, 1, *timeoutp); + oerrno = errno; + ms_subtract_diff(&t_start, timeoutp); + errno = oerrno; + if (r > 0) + return 0; + else if (r == -1 && errno != EAGAIN) + return -1; + else if (r == 0) + break; + } + /* timeout */ + errno = ETIMEDOUT; + return -1; +} + +static int +timeout_connect(int sockfd, const struct sockaddr *serv_addr, + socklen_t addrlen, int *timeoutp) +{ + int optval = 0; + socklen_t optlen = sizeof(optval); + + /* No timeout: just do a blocking connect() */ + if (*timeoutp <= 0) + return connect(sockfd, serv_addr, addrlen); + + set_nonblock(sockfd); + if (connect(sockfd, serv_addr, addrlen) == 0) { + /* Succeeded already? */ + unset_nonblock(sockfd); + return 0; + } else if (errno != EINPROGRESS) + return -1; + + if (waitrfd(sockfd, timeoutp) == -1) + return -1; + + /* Completed or failed */ + if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval, &optlen) == -1) { + debug("getsockopt: %s", strerror(errno)); + return -1; + } + if (optval != 0) { + errno = optval; + return -1; + } + unset_nonblock(sockfd); + return 0; +} + +/* + * 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. + * 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. + */ +static int +ssh_connect_direct(struct ssh *ssh, const char *host, struct addrinfo *aitop, + struct sockaddr_storage *hostaddr, u_short port, int family, + int connection_attempts, int *timeout_ms, int want_keepalive) +{ + int on = 1; + int oerrno, sock = -1, attempt; + char ntop[NI_MAXHOST], strport[NI_MAXSERV]; + struct addrinfo *ai; + + debug2("%s", __func__); + memset(ntop, 0, sizeof(ntop)); + memset(strport, 0, sizeof(strport)); + + for (attempt = 0; attempt < connection_attempts; attempt++) { + if (attempt > 0) { + /* Sleep a moment before retrying. */ + sleep(1); + 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) { + errno = EAFNOSUPPORT; + continue; + } + if (getnameinfo(ai->ai_addr, ai->ai_addrlen, + ntop, sizeof(ntop), strport, sizeof(strport), + NI_NUMERICHOST|NI_NUMERICSERV) != 0) { + oerrno = errno; + error("%s: getnameinfo failed", __func__); + errno = oerrno; + continue; + } + debug("Connecting to %.200s [%.100s] port %s.", + host, ntop, strport); + + /* Create a socket for connecting. */ + sock = ssh_create_socket(ai); + if (sock < 0) { + /* Any error is already output */ + errno = 0; + continue; + } + + if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen, + timeout_ms) >= 0) { + /* Successful connection. */ + memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen); + break; + } else { + oerrno = errno; + debug("connect to address %s port %s: %s", + ntop, strport, strerror(errno)); + close(sock); + sock = -1; + errno = oerrno; + } + } + if (sock != -1) + break; /* Successful connection. */ + } + + /* Return failure if we didn't get a successful connection. */ + if (sock == -1) { + error("ssh: connect to host %s port %s: %s", + host, strport, errno == 0 ? "failure" : strerror(errno)); + return -1; + } + + debug("Connection established."); + + /* Set SO_KEEPALIVE if requested. */ + if (want_keepalive && + setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on, + sizeof(on)) < 0) + error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno)); + + /* Set the connection. */ + if (ssh_packet_set_connection(ssh, sock, sock) == NULL) + return -1; /* ssh_packet_set_connection logs error */ + + return 0; +} + +int +ssh_connect(struct ssh *ssh, const char *host, struct addrinfo *addrs, + struct sockaddr_storage *hostaddr, u_short port, int family, + int connection_attempts, int *timeout_ms, int want_keepalive) +{ + if (options.proxy_command == NULL) { + return ssh_connect_direct(ssh, host, addrs, hostaddr, port, + family, connection_attempts, timeout_ms, want_keepalive); + } else if (strcmp(options.proxy_command, "-") == 0) { + if ((ssh_packet_set_connection(ssh, + STDIN_FILENO, STDOUT_FILENO)) == NULL) + return -1; /* ssh_packet_set_connection logs error */ + return 0; + } else if (options.proxy_use_fdpass) { + return ssh_proxy_fdpass_connect(ssh, host, port, + options.proxy_command); + } + return ssh_proxy_connect(ssh, host, port, options.proxy_command); +} + +static void +send_client_banner(int connection_out, int minor1) +{ + /* Send our own protocol version identification. */ + xasprintf(&client_version_string, "SSH-%d.%d-%.100s\r\n", + PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION); + if (atomicio(vwrite, connection_out, client_version_string, + strlen(client_version_string)) != strlen(client_version_string)) + fatal("write: %.100s", strerror(errno)); + chop(client_version_string); + debug("Local version string %.100s", client_version_string); +} + +/* + * Waits for the server identification string, and sends our own + * identification string. + */ +void +ssh_exchange_identification(int timeout_ms) +{ + char buf[256], remote_version[256]; /* must be same size! */ + int remote_major, remote_minor, mismatch; + int connection_in = packet_get_connection_in(); + int connection_out = packet_get_connection_out(); + u_int i, n; + size_t len; + int rc; + + send_client_banner(connection_out, 0); + + /* Read other side's version identification. */ + for (n = 0;;) { + for (i = 0; i < sizeof(buf) - 1; i++) { + if (timeout_ms > 0) { + rc = waitrfd(connection_in, &timeout_ms); + if (rc == -1 && errno == ETIMEDOUT) { + fatal("Connection timed out during " + "banner exchange"); + } else if (rc == -1) { + fatal("%s: %s", + __func__, strerror(errno)); + } + } + + len = atomicio(read, connection_in, &buf[i], 1); + if (len != 1 && errno == EPIPE) + fatal("ssh_exchange_identification: " + "Connection closed by remote host"); + else if (len != 1) + fatal("ssh_exchange_identification: " + "read: %.100s", strerror(errno)); + 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; + } + if (++n > 65536) + fatal("ssh_exchange_identification: " + "No banner received"); + } + 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); + + active_state->compat = compat_datafellows(remote_version); + mismatch = 0; + + switch (remote_major) { + case 2: + break; + case 1: + if (remote_minor != 99) + mismatch = 1; + break; + default: + mismatch = 1; + break; + } + if (mismatch) + fatal("Protocol major versions differ: %d vs. %d", + PROTOCOL_MAJOR_2, remote_major); + if ((datafellows & SSH_BUG_RSASIGMD5) != 0) + logit("Server version \"%.100s\" uses unsafe RSA signature " + "scheme; disabling use of RSA keys", remote_version); + chop(server_version_string); +} + +/* defaults to 'no' */ +static int +confirm(const char *prompt) +{ + const char *msg, *again = "Please type 'yes' or 'no': "; + char *p; + int ret = -1; + + if (options.batch_mode) + return 0; + for (msg = prompt;;msg = again) { + p = read_passphrase(msg, RP_ECHO); + if (p == NULL) + return 0; + p[strcspn(p, "\n")] = '\0'; + if (p[0] == '\0' || strcasecmp(p, "no") == 0) + ret = 0; + else if (strcasecmp(p, "yes") == 0) + ret = 1; + free(p); + if (ret != -1) + return ret; + } +} + +static int +check_host_cert(const char *host, const struct sshkey *key) +{ + const char *reason; + int r; + + if (sshkey_cert_check_authority(key, 1, 0, host, &reason) != 0) { + error("%s", reason); + return 0; + } + if (sshbuf_len(key->cert->critical) != 0) { + error("Certificate for %s contains unsupported " + "critical options(s)", host); + return 0; + } + if ((r = sshkey_check_cert_sigtype(key, + options.ca_sign_algorithms)) != 0) { + logit("%s: certificate signature algorithm %s: %s", __func__, + (key->cert == NULL || key->cert->signature_type == NULL) ? + "(null)" : key->cert->signature_type, ssh_err(r)); + return 0; + } + + return 1; +} + +static int +sockaddr_is_local(struct sockaddr *hostaddr) +{ + switch (hostaddr->sa_family) { + case AF_INET: + return (ntohl(((struct sockaddr_in *)hostaddr)-> + sin_addr.s_addr) >> 24) == IN_LOOPBACKNET; + case AF_INET6: + return IN6_IS_ADDR_LOOPBACK( + &(((struct sockaddr_in6 *)hostaddr)->sin6_addr)); + default: + return 0; + } +} + +/* + * Prepare the hostname and ip address strings that are used to lookup + * host keys in known_hosts files. These may have a port number appended. + */ +void +get_hostfile_hostname_ipaddr(char *hostname, struct sockaddr *hostaddr, + u_short port, char **hostfile_hostname, char **hostfile_ipaddr) +{ + char ntop[NI_MAXHOST]; + socklen_t addrlen; + + switch (hostaddr == NULL ? -1 : hostaddr->sa_family) { + case -1: + addrlen = 0; + break; + case AF_INET: + addrlen = sizeof(struct sockaddr_in); + break; + case AF_INET6: + addrlen = sizeof(struct sockaddr_in6); + break; + default: + addrlen = sizeof(struct sockaddr); + break; + } + + /* + * We don't have the remote ip-address for connections + * using a proxy command + */ + if (hostfile_ipaddr != NULL) { + if (options.proxy_command == NULL) { + if (getnameinfo(hostaddr, addrlen, + ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0) + fatal("%s: getnameinfo failed", __func__); + *hostfile_ipaddr = put_host_port(ntop, port); + } else { + *hostfile_ipaddr = xstrdup("<no hostip for proxy " + "command>"); + } + } + + /* + * Allow the user to record the key under a different name or + * differentiate a non-standard port. This is useful for ssh + * tunneling over forwarded connections or if you run multiple + * sshd's on different ports on the same machine. + */ + if (hostfile_hostname != NULL) { + if (options.host_key_alias != NULL) { + *hostfile_hostname = xstrdup(options.host_key_alias); + debug("using hostkeyalias: %s", *hostfile_hostname); + } else { + *hostfile_hostname = put_host_port(hostname, port); + } + } +} + +/* + * check whether the supplied host key is valid, return -1 if the key + * is not valid. user_hostfile[0] will not be updated if 'readonly' is true. + */ +#define RDRW 0 +#define RDONLY 1 +#define ROQUIET 2 +static int +check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port, + struct sshkey *host_key, int readonly, + char **user_hostfiles, u_int num_user_hostfiles, + char **system_hostfiles, u_int num_system_hostfiles) +{ + HostStatus host_status; + HostStatus ip_status; + struct sshkey *raw_key = NULL; + char *ip = NULL, *host = NULL; + char hostline[1000], *hostp, *fp, *ra; + char msg[1024]; + const char *type; + const struct hostkey_entry *host_found, *ip_found; + int len, cancelled_forwarding = 0; + int local = sockaddr_is_local(hostaddr); + int r, want_cert = sshkey_is_cert(host_key), host_ip_differ = 0; + int hostkey_trusted = 0; /* Known or explicitly accepted by user */ + struct hostkeys *host_hostkeys, *ip_hostkeys; + u_int i; + + /* + * 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. + */ + if (options.no_host_authentication_for_localhost == 1 && local && + options.host_key_alias == NULL) { + debug("Forcing accepting of host key for " + "loopback/localhost."); + return 0; + } + + /* + * Prepare the hostname and address strings used for hostkey lookup. + * In some cases, these will have a port number appended. + */ + get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip); + + /* + * 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(hostname, ip) == 0 || options.proxy_command != NULL)) + options.check_host_ip = 0; + + host_hostkeys = init_hostkeys(); + for (i = 0; i < num_user_hostfiles; i++) + load_hostkeys(host_hostkeys, host, user_hostfiles[i]); + for (i = 0; i < num_system_hostfiles; i++) + load_hostkeys(host_hostkeys, host, system_hostfiles[i]); + + ip_hostkeys = NULL; + if (!want_cert && options.check_host_ip) { + ip_hostkeys = init_hostkeys(); + for (i = 0; i < num_user_hostfiles; i++) + load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]); + for (i = 0; i < num_system_hostfiles; i++) + load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]); + } + + retry: + /* Reload these as they may have changed on cert->key downgrade */ + want_cert = sshkey_is_cert(host_key); + type = sshkey_type(host_key); + + /* + * Check if the host key is present in the user's list of known + * hosts or in the systemwide list. + */ + host_status = check_key_in_hostkeys(host_hostkeys, host_key, + &host_found); + + /* + * Also perform check for the ip address, skip the check if we are + * localhost, looking for a certificate, or the hostname was an ip + * address to begin with. + */ + if (!want_cert && ip_hostkeys != NULL) { + ip_status = check_key_in_hostkeys(ip_hostkeys, host_key, + &ip_found); + if (host_status == HOST_CHANGED && + (ip_status != HOST_CHANGED || + (ip_found != NULL && + !sshkey_equal(ip_found->key, host_found->key)))) + host_ip_differ = 1; + } else + ip_status = host_status; + + switch (host_status) { + case HOST_OK: + /* The host is known and the key matches. */ + debug("Host '%.200s' is known and matches the %s host %s.", + host, type, want_cert ? "certificate" : "key"); + debug("Found %s in %s:%lu", want_cert ? "CA key" : "key", + host_found->file, host_found->line); + if (want_cert && + !check_host_cert(options.host_key_alias == NULL ? + hostname : options.host_key_alias, host_key)) + goto fail; + if (options.check_host_ip && ip_status == HOST_NEW) { + if (readonly || want_cert) + logit("%s host key for IP address " + "'%.128s' not in list of known hosts.", + type, ip); + else if (!add_host_to_hostfile(user_hostfiles[0], ip, + host_key, options.hash_known_hosts)) + logit("Failed to add the %s host key for IP " + "address '%.128s' to the list of known " + "hosts (%.500s).", type, ip, + user_hostfiles[0]); + else + logit("Warning: Permanently added the %s host " + "key for IP address '%.128s' to the list " + "of known hosts.", type, ip); + } else if (options.visual_host_key) { + fp = sshkey_fingerprint(host_key, + options.fingerprint_hash, SSH_FP_DEFAULT); + ra = sshkey_fingerprint(host_key, + options.fingerprint_hash, SSH_FP_RANDOMART); + if (fp == NULL || ra == NULL) + fatal("%s: sshkey_fingerprint fail", __func__); + logit("Host key fingerprint is %s\n%s", fp, ra); + free(ra); + free(fp); + } + hostkey_trusted = 1; + break; + case HOST_NEW: + if (options.host_key_alias == NULL && port != 0 && + port != SSH_DEFAULT_PORT) { + debug("checking without port identifier"); + if (check_host_key(hostname, hostaddr, 0, host_key, + ROQUIET, user_hostfiles, num_user_hostfiles, + system_hostfiles, num_system_hostfiles) == 0) { + debug("found matching key w/out port"); + break; + } + } + if (readonly || want_cert) + goto fail; + /* The host is new. */ + if (options.strict_host_key_checking == + SSH_STRICT_HOSTKEY_YES) { + /* + * User has requested strict host key checking. We + * will not add the host key automatically. The only + * alternative left is to abort. + */ + error("No %s host key is known for %.200s and you " + "have requested strict checking.", type, host); + goto fail; + } else if (options.strict_host_key_checking == + SSH_STRICT_HOSTKEY_ASK) { + char msg1[1024], msg2[1024]; + + if (show_other_keys(host_hostkeys, host_key)) + snprintf(msg1, sizeof(msg1), + "\nbut keys of different type are already" + " known for this host."); + else + snprintf(msg1, sizeof(msg1), "."); + /* The default */ + fp = sshkey_fingerprint(host_key, + options.fingerprint_hash, SSH_FP_DEFAULT); + ra = sshkey_fingerprint(host_key, + options.fingerprint_hash, SSH_FP_RANDOMART); + if (fp == NULL || ra == NULL) + fatal("%s: sshkey_fingerprint fail", __func__); + msg2[0] = '\0'; + if (options.verify_host_key_dns) { + if (matching_host_key_dns) + snprintf(msg2, sizeof(msg2), + "Matching host key fingerprint" + " found in DNS.\n"); + else + snprintf(msg2, sizeof(msg2), + "No matching host key fingerprint" + " found in DNS.\n"); + } + snprintf(msg, sizeof(msg), + "The authenticity of host '%.200s (%s)' can't be " + "established%s\n" + "%s key fingerprint is %s.%s%s\n%s" + "Are you sure you want to continue connecting " + "(yes/no)? ", + host, ip, msg1, type, fp, + options.visual_host_key ? "\n" : "", + options.visual_host_key ? ra : "", + msg2); + free(ra); + free(fp); + if (!confirm(msg)) + goto fail; + hostkey_trusted = 1; /* user explicitly confirmed */ + } + /* + * If in "new" or "off" strict mode, add the key automatically + * to the local known_hosts file. + */ + if (options.check_host_ip && ip_status == HOST_NEW) { + snprintf(hostline, sizeof(hostline), "%s,%s", host, ip); + hostp = hostline; + if (options.hash_known_hosts) { + /* Add hash of host and IP separately */ + r = add_host_to_hostfile(user_hostfiles[0], + host, host_key, options.hash_known_hosts) && + add_host_to_hostfile(user_hostfiles[0], ip, + host_key, options.hash_known_hosts); + } else { + /* Add unhashed "host,ip" */ + r = add_host_to_hostfile(user_hostfiles[0], + hostline, host_key, + options.hash_known_hosts); + } + } else { + r = add_host_to_hostfile(user_hostfiles[0], host, + host_key, options.hash_known_hosts); + hostp = host; + } + + if (!r) + logit("Failed to add the host to the list of known " + "hosts (%.500s).", user_hostfiles[0]); + else + logit("Warning: Permanently added '%.200s' (%s) to the " + "list of known hosts.", hostp, type); + break; + case HOST_REVOKED: + error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); + error("@ WARNING: REVOKED HOST KEY DETECTED! @"); + error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); + error("The %s host key for %s is marked as revoked.", type, host); + error("This could mean that a stolen key is being used to"); + error("impersonate this host."); + + /* + * 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 != + SSH_STRICT_HOSTKEY_OFF) { + error("%s host key for %.200s was revoked and you have " + "requested strict checking.", type, host); + goto fail; + } + goto continue_unsafe; + + case HOST_CHANGED: + if (want_cert) { + /* + * This is only a debug() since it is valid to have + * CAs with wildcard DNS matches that don't match + * all hosts that one might visit. + */ + debug("Host certificate authority does not " + "match %s in %s:%lu", CA_MARKER, + host_found->file, host_found->line); + goto fail; + } + if (readonly == ROQUIET) + goto fail; + if (options.check_host_ip && host_ip_differ) { + char *key_msg; + if (ip_status == HOST_NEW) + key_msg = "is unknown"; + else if (ip_status == HOST_OK) + key_msg = "is unchanged"; + else + key_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 corresponding IP address %s", ip); + error("%s. This could either mean that", key_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:%lu", + ip_found->file, ip_found->line); + } + /* The host key has changed. */ + warn_changed_key(host_key); + error("Add correct host key in %.100s to get rid of this message.", + user_hostfiles[0]); + error("Offending %s key in %s:%lu", + sshkey_type(host_found->key), + host_found->file, host_found->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 != + SSH_STRICT_HOSTKEY_OFF) { + error("%s host key for %.200s has changed and you have " + "requested strict checking.", type, host); + goto fail; + } + + continue_unsafe: + /* + * If strict host key checking has not been requested, allow + * the connection but without MITM-able authentication or + * forwarding. + */ + if (options.password_authentication) { + error("Password authentication is disabled to avoid " + "man-in-the-middle attacks."); + options.password_authentication = 0; + cancelled_forwarding = 1; + } + if (options.kbd_interactive_authentication) { + error("Keyboard-interactive authentication is disabled" + " to avoid man-in-the-middle attacks."); + options.kbd_interactive_authentication = 0; + options.challenge_response_authentication = 0; + cancelled_forwarding = 1; + } + if (options.challenge_response_authentication) { + error("Challenge/response authentication is disabled" + " to avoid man-in-the-middle attacks."); + options.challenge_response_authentication = 0; + cancelled_forwarding = 1; + } + if (options.forward_agent) { + error("Agent forwarding is disabled to avoid " + "man-in-the-middle attacks."); + options.forward_agent = 0; + cancelled_forwarding = 1; + } + if (options.forward_x11) { + error("X11 forwarding is disabled to avoid " + "man-in-the-middle attacks."); + options.forward_x11 = 0; + cancelled_forwarding = 1; + } + if (options.num_local_forwards > 0 || + options.num_remote_forwards > 0) { + error("Port forwarding is disabled to avoid " + "man-in-the-middle attacks."); + options.num_local_forwards = + options.num_remote_forwards = 0; + cancelled_forwarding = 1; + } + if (options.tun_open != SSH_TUNMODE_NO) { + error("Tunnel forwarding is disabled to avoid " + "man-in-the-middle attacks."); + options.tun_open = SSH_TUNMODE_NO; + cancelled_forwarding = 1; + } + if (options.exit_on_forward_failure && cancelled_forwarding) + fatal("Error: forwarding disabled due to host key " + "check failure"); + + /* + * 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 wishes to + * accept the authentication. + */ + break; + case HOST_FOUND: + fatal("internal error"); + break; + } + + if (options.check_host_ip && host_status != HOST_CHANGED && + ip_status == HOST_CHANGED) { + snprintf(msg, sizeof(msg), + "Warning: the %s host key for '%.200s' " + "differs from the key for the IP address '%.128s'" + "\nOffending key for IP in %s:%lu", + type, host, ip, ip_found->file, ip_found->line); + if (host_status == HOST_OK) { + len = strlen(msg); + snprintf(msg + len, sizeof(msg) - len, + "\nMatching host key in %s:%lu", + host_found->file, host_found->line); + } + if (options.strict_host_key_checking == + SSH_STRICT_HOSTKEY_ASK) { + strlcat(msg, "\nAre you sure you want " + "to continue connecting (yes/no)? ", sizeof(msg)); + if (!confirm(msg)) + goto fail; + } else if (options.strict_host_key_checking != + SSH_STRICT_HOSTKEY_OFF) { + logit("%s", msg); + error("Exiting, you have requested strict checking."); + goto fail; + } else { + logit("%s", msg); + } + } + + if (!hostkey_trusted && options.update_hostkeys) { + debug("%s: hostkey not known or explicitly trusted: " + "disabling UpdateHostkeys", __func__); + options.update_hostkeys = 0; + } + + free(ip); + free(host); + if (host_hostkeys != NULL) + free_hostkeys(host_hostkeys); + if (ip_hostkeys != NULL) + free_hostkeys(ip_hostkeys); + return 0; + +fail: + if (want_cert && host_status != HOST_REVOKED) { + /* + * No matching certificate. Downgrade cert to raw key and + * search normally. + */ + debug("No matching CA found. Retry with plain key"); + if ((r = sshkey_from_private(host_key, &raw_key)) != 0) + fatal("%s: sshkey_from_private: %s", + __func__, ssh_err(r)); + if ((r = sshkey_drop_cert(raw_key)) != 0) + fatal("Couldn't drop certificate: %s", ssh_err(r)); + host_key = raw_key; + goto retry; + } + sshkey_free(raw_key); + free(ip); + free(host); + if (host_hostkeys != NULL) + free_hostkeys(host_hostkeys); + if (ip_hostkeys != NULL) + free_hostkeys(ip_hostkeys); + return -1; +} + +/* returns 0 if key verifies or -1 if key does NOT verify */ +int +verify_host_key(char *host, struct sockaddr *hostaddr, struct sshkey *host_key) +{ + u_int i; + int r = -1, flags = 0; + char valid[64], *fp = NULL, *cafp = NULL; + struct sshkey *plain = NULL; + + if ((fp = sshkey_fingerprint(host_key, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { + error("%s: fingerprint host key: %s", __func__, ssh_err(r)); + r = -1; + goto out; + } + + if (sshkey_is_cert(host_key)) { + if ((cafp = sshkey_fingerprint(host_key->cert->signature_key, + options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { + error("%s: fingerprint CA key: %s", + __func__, ssh_err(r)); + r = -1; + goto out; + } + sshkey_format_cert_validity(host_key->cert, + valid, sizeof(valid)); + debug("Server host certificate: %s %s, serial %llu " + "ID \"%s\" CA %s %s valid %s", + sshkey_ssh_name(host_key), fp, + (unsigned long long)host_key->cert->serial, + host_key->cert->key_id, + sshkey_ssh_name(host_key->cert->signature_key), cafp, + valid); + for (i = 0; i < host_key->cert->nprincipals; i++) { + debug2("Server host certificate hostname: %s", + host_key->cert->principals[i]); + } + } else { + debug("Server host key: %s %s", sshkey_ssh_name(host_key), fp); + } + + if (sshkey_equal(previous_host_key, host_key)) { + debug2("%s: server host key %s %s matches cached key", + __func__, sshkey_type(host_key), fp); + r = 0; + goto out; + } + + /* Check in RevokedHostKeys file if specified */ + if (options.revoked_host_keys != NULL) { + r = sshkey_check_revoked(host_key, options.revoked_host_keys); + switch (r) { + case 0: + break; /* not revoked */ + case SSH_ERR_KEY_REVOKED: + error("Host key %s %s revoked by file %s", + sshkey_type(host_key), fp, + options.revoked_host_keys); + r = -1; + goto out; + default: + error("Error checking host key %s %s in " + "revoked keys file %s: %s", sshkey_type(host_key), + fp, options.revoked_host_keys, ssh_err(r)); + r = -1; + goto out; + } + } + + if (options.verify_host_key_dns) { + /* + * XXX certs are not yet supported for DNS, so downgrade + * them and try the plain key. + */ + if ((r = sshkey_from_private(host_key, &plain)) != 0) + goto out; + if (sshkey_is_cert(plain)) + sshkey_drop_cert(plain); + if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) { + if (flags & DNS_VERIFY_FOUND) { + if (options.verify_host_key_dns == 1 && + flags & DNS_VERIFY_MATCH && + flags & DNS_VERIFY_SECURE) { + r = 0; + goto out; + } + if (flags & DNS_VERIFY_MATCH) { + matching_host_key_dns = 1; + } else { + warn_changed_key(plain); + error("Update the SSHFP RR in DNS " + "with the new host key to get rid " + "of this message."); + } + } + } + } + r = check_host_key(host, hostaddr, options.port, host_key, RDRW, + options.user_hostfiles, options.num_user_hostfiles, + options.system_hostfiles, options.num_system_hostfiles); + +out: + sshkey_free(plain); + free(fp); + free(cafp); + if (r == 0 && host_key != NULL) { + sshkey_free(previous_host_key); + r = sshkey_from_private(host_key, &previous_host_key); + } + + return r; +} + +/* + * 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(Sensitive *sensitive, const char *orighost, + struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms) +{ + char *host; + char *server_user, *local_user; + + 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); + lowercase(host); + + /* Exchange protocol version identification strings with the server. */ + ssh_exchange_identification(timeout_ms); + + /* Put the connection into non-blocking mode. */ + packet_set_nonblocking(); + + /* key exchange */ + /* authenticate user */ + debug("Authenticating to %s:%d as '%s'", host, port, server_user); + ssh_kex2(host, hostaddr, port); + ssh_userauth2(local_user, server_user, host, sensitive); + free(local_user); +} + +void +ssh_put_password(char *password) +{ + int size; + char *padded; + + if (datafellows & SSH_BUG_PASSWORDPAD) { + packet_put_cstring(password); + return; + } + size = ROUNDUP(strlen(password) + 1, 32); + padded = xcalloc(1, size); + strlcpy(padded, password, size); + packet_put_string(padded, size); + explicit_bzero(padded, size); + free(padded); +} + +/* print all known host keys for a given host, but skip keys of given type */ +static int +show_other_keys(struct hostkeys *hostkeys, struct sshkey *key) +{ + int type[] = { + KEY_RSA, + KEY_DSA, + KEY_ECDSA, + KEY_ED25519, + KEY_XMSS, + -1 + }; + int i, ret = 0; + char *fp, *ra; + const struct hostkey_entry *found; + + for (i = 0; type[i] != -1; i++) { + if (type[i] == key->type) + continue; + if (!lookup_key_in_hostkeys_by_type(hostkeys, type[i], &found)) + continue; + fp = sshkey_fingerprint(found->key, + options.fingerprint_hash, SSH_FP_DEFAULT); + ra = sshkey_fingerprint(found->key, + options.fingerprint_hash, SSH_FP_RANDOMART); + if (fp == NULL || ra == NULL) + fatal("%s: sshkey_fingerprint fail", __func__); + logit("WARNING: %s key found for host %s\n" + "in %s:%lu\n" + "%s key fingerprint %s.", + sshkey_type(found->key), + found->host, found->file, found->line, + sshkey_type(found->key), fp); + if (options.visual_host_key) + logit("%s", ra); + free(ra); + free(fp); + ret = 1; + } + return ret; +} + +static void +warn_changed_key(struct sshkey *host_key) +{ + char *fp; + + fp = sshkey_fingerprint(host_key, options.fingerprint_hash, + SSH_FP_DEFAULT); + if (fp == NULL) + fatal("%s: sshkey_fingerprint fail", __func__); + + 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 a host key has just been changed."); + error("The fingerprint for the %s key sent by the remote host is\n%s.", + sshkey_type(host_key), fp); + error("Please contact your system administrator."); + + free(fp); +} + +/* + * Execute a local command + */ +int +ssh_local_cmd(const char *args) +{ + char *shell; + pid_t pid; + int status; + void (*osighand)(int); + + if (!options.permit_local_command || + args == NULL || !*args) + return (1); + + if ((shell = getenv("SHELL")) == NULL || *shell == '\0') + shell = _PATH_BSHELL; + + osighand = signal(SIGCHLD, SIG_DFL); + pid = fork(); + if (pid == 0) { + signal(SIGPIPE, SIG_DFL); + debug3("Executing %s -c \"%s\"", shell, args); + execl(shell, shell, "-c", args, (char *)NULL); + error("Couldn't execute %s -c \"%s\": %s", + shell, args, strerror(errno)); + _exit(1); + } else if (pid == -1) + fatal("fork failed: %.100s", strerror(errno)); + while (waitpid(pid, &status, 0) == -1) + if (errno != EINTR) + fatal("Couldn't wait for child: %s", strerror(errno)); + signal(SIGCHLD, osighand); + + if (!WIFEXITED(status)) + return (1); + + return (WEXITSTATUS(status)); +} + +void +maybe_add_key_to_agent(char *authfile, const struct sshkey *private, + char *comment, char *passphrase) +{ + int auth_sock = -1, r; + + if (options.add_keys_to_agent == 0) + return; + + if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) { + debug3("no authentication agent, not adding key"); + return; + } + + if (options.add_keys_to_agent == 2 && + !ask_permission("Add key %s (%s) to agent?", authfile, comment)) { + debug3("user denied adding this key"); + close(auth_sock); + return; + } + + if ((r = ssh_add_identity_constrained(auth_sock, private, comment, 0, + (options.add_keys_to_agent == 3), 0)) == 0) + debug("identity added to agent: %s", authfile); + else + debug("could not add identity to agent: %s (%d)", authfile, r); + close(auth_sock); +} |