- (djm) Release OpenSSH 4.0p1

[openssh-git.git] / sshconnect.c

/*
 * 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"
RCSID("$OpenBSD: sshconnect.c,v 1.161 2005/03/02 01:00:06 djm Exp $");

#include <openssl/bn.h>

#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"

#include "dns.h"

char *client_version_string = NULL;
char *server_version_string = NULL;

int matching_host_key_dns = 0;

/* import */
extern Options options;
extern char *__progname;
extern uid_t original_real_uid;
extern uid_t original_effective_uid;
extern pid_t proxy_command_pid;

#ifndef INET6_ADDRSTRLEN                /* for non IPv6 machines */
#define INET6_ADDRSTRLEN 46
#endif

static int show_other_keys(const char *, Key *);
static void warn_changed_key(Key *);

/*
 * Connect to the given ssh server using a proxy command.
 */
static int
ssh_proxy_connect(const char *host, u_short port, 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.
         *
         * Use "exec" to avoid "sh -c" processes on some platforms
         * (e.g. Solaris)
         */
        buffer_init(&command);
        buffer_append(&command, "exec ", 5);

        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. */
                seteuid(original_real_uid);
                setuid(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));
        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. */
        buffer_free(&command);

        /* Set the connection file descriptors. */
        packet_set_connection(pout[0], pin[1]);

        /* Indicate OK return */
        return 0;
}

/*
 * Creates a (possibly privileged) socket for use as the ssh connection.
 */
static int
ssh_create_socket(int privileged, struct addrinfo *ai)
{
        int sock, gaierr;
        struct addrinfo hints, *res;

        /*
         * 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;
                PRIV_START;
                sock = rresvport_af(&p, ai->ai_family);
                PRIV_END;
                if (sock < 0)
                        error("rresvport: af=%d %.100s", ai->ai_family,
                            strerror(errno));
                else
                        debug("Allocated local port %d.", p);
                return sock;
        }
        sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
        if (sock < 0)
                error("socket: %.100s", strerror(errno));

        /* Bind the socket to an alternative local IP address */
        if (options.bind_address == NULL)
                return sock;

        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;
        gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
        if (gaierr) {
                error("getaddrinfo: %s: %s", options.bind_address,
                    gai_strerror(gaierr));
                close(sock);
                return -1;
        }
        if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
                error("bind: %s: %s", options.bind_address, strerror(errno));
                close(sock);
                freeaddrinfo(res);
                return -1;
        }
        freeaddrinfo(res);
        return sock;
}

static int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
    socklen_t addrlen, int timeout)
{
        fd_set *fdset;
        struct timeval tv;
        socklen_t optlen;
        int fdsetsz, optval, rc, result = -1;

        if (timeout <= 0)
                return (connect(sockfd, serv_addr, addrlen));

        set_nonblock(sockfd);
        rc = connect(sockfd, serv_addr, addrlen);
        if (rc == 0) {
                unset_nonblock(sockfd);
                return (0);
        }
        if (errno != EINPROGRESS)
                return (-1);

        fdsetsz = howmany(sockfd + 1, NFDBITS) * sizeof(fd_mask);
        fdset = (fd_set *)xmalloc(fdsetsz);

        memset(fdset, 0, fdsetsz);
        FD_SET(sockfd, fdset);
        tv.tv_sec = timeout;
        tv.tv_usec = 0;

        for(;;) {
                rc = select(sockfd + 1, NULL, fdset, NULL, &tv);
                if (rc != -1 || errno != EINTR)
                        break;
        }

        switch(rc) {
        case 0:
                /* Timed out */
                errno = ETIMEDOUT;
                break;
        case -1:
                /* Select error */
                debug("select: %s", strerror(errno));
                break;
        case 1:
                /* Completed or failed */
                optval = 0;
                optlen = sizeof(optval);
                if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval,
                    &optlen) == -1) {
                        debug("getsockopt: %s", strerror(errno));
                        break;
                }
                if (optval != 0) {
                        errno = optval;
                        break;
                }
                result = 0;
                unset_nonblock(sockfd);
                break;
        default:
                /* Should not occur */
                fatal("Bogus return (%d) from select()", rc);
        }

        xfree(fdset);
        return (result);
}

/*
 * 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 needpriv is true,
 * a privileged port will be allocated to make the connection.
 * This requires super-user privileges if needpriv is true.
 * 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 family, int connection_attempts,
    int needpriv, 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 servent *sp;

        debug2("ssh_connect: needpriv %d", needpriv);

        /* 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, proxy_command);

        /* No proxy command. */

        memset(&hints, 0, sizeof(hints));
        hints.ai_family = family;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%u", 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; ;) {
                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(needpriv, ai);
                        if (sock < 0)
                                /* Any error is already output */
                                continue;

                        if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
                            options.connection_timeout) >= 0) {
                                /* Successful connection. */
                                memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
                                break;
                        } else {
                                debug("connect to address %s port %s: %s",
                                    ntop, strport, strerror(errno));
                                /*
                                 * Close the failed socket; there appear to
                                 * be some problems when reusing a socket for
                                 * which connect() has already returned an
                                 * error.
                                 */
                                close(sock);
                        }
                }
                if (ai)
                        break;  /* Successful connection. */

                attempt++;
                if (attempt >= connection_attempts)
                        break;
                /* Sleep a moment before retrying. */
                sleep(1);
        }

        freeaddrinfo(aitop);

        /* Return failure if we didn't get a successful connection. */
        if (attempt >= connection_attempts) {
                error("ssh: connect to host %s port %s: %s",
                    host, strport, strerror(errno));
                return (-1);
        }

        debug("Connection established.");

        /* Set SO_KEEPALIVE if requested. */
        if (options.tcp_keep_alive &&
            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 0;
}

/*
 * Waits for the server identification string, and sends our own
 * identification string.
 */
static void
ssh_exchange_identification(void)
{
        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) {
                                logit("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);
        /* 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(vwrite, 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);
}

/* 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 ||
                    (p[0] == '\0') || (p[0] == '\n') ||
                    strncasecmp(p, "no", 2) == 0)
                        ret = 0;
                if (p && strncasecmp(p, "yes", 3) == 0)
                        ret = 1;
                if (p)
                        xfree(p);
                if (ret != -1)
                        return ret;
        }
}

/*
 * check whether the supplied host key is valid, return -1 if the key
 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
 */
static int
check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
    int readonly, const char *user_hostfile, const char *system_hostfile)
{
        Key *file_key;
        const char *type = key_type(host_key);
        char *ip = NULL;
        char hostline[1000], *hostp, *fp;
        HostStatus host_status;
        HostStatus ip_status;
        int r, local = 0, host_ip_differ = 0;
        int salen;
        char ntop[NI_MAXHOST];
        char msg[1024];
        int len, 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;
                salen = sizeof(struct sockaddr_in);
                break;
        case AF_INET6:
                local = IN6_IS_ADDR_LOOPBACK(
                    &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
                salen = sizeof(struct sockaddr_in6);
                break;
        default:
                local = 0;
                salen = sizeof(struct sockaddr_storage);
                break;
        }
        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;
        }

        /*
         * We don't have the remote ip-address for connections
         * using a proxy command
         */
        if (options.proxy_command == NULL) {
                if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
                    NULL, 0, NI_NUMERICHOST) != 0)
                        fatal("check_host_key: getnameinfo failed");
                ip = xstrdup(ntop);
        } else {
                ip = xstrdup("<no hostip for proxy command>");
        }
        /*
         * 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 (readonly)
                                logit("%s host key for IP address "
                                    "'%.128s' not in list of known hosts.",
                                    type, ip);
                        else if (!add_host_to_hostfile(user_hostfile, 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 (%.30s).", type, ip, user_hostfile);
                        else
                                logit("Warning: Permanently added the %s host "
                                    "key for IP address '%.128s' to the list "
                                    "of known hosts.", type, ip);
                }
                break;
        case HOST_NEW:
                if (readonly)
                        goto fail;
                /* 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.
                         */
                        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 == 2) {
                        char msg1[1024], msg2[1024];

                        if (show_other_keys(host, 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 = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
                        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.\n%s"
                            "Are you sure you want to continue connecting "
                            "(yes/no)? ",
                            host, ip, msg1, type, fp, msg2);
                        xfree(fp);
                        if (!confirm(msg))
                                goto fail;
                }
                /*
                 * If not in 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_hostfile, host,
                                    host_key, options.hash_known_hosts) &&
                                    add_host_to_hostfile(user_hostfile, ip,
                                    host_key, options.hash_known_hosts);
                        } else {
                                /* Add unhashed "host,ip" */
                                r = add_host_to_hostfile(user_hostfile,
                                    hostline, host_key,
                                    options.hash_known_hosts);
                        }
                } else {
                        r = add_host_to_hostfile(user_hostfile, 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_hostfile);
                else
                        logit("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 *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 according 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:%d", ip_file, ip_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_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) {
                        error("%s host key for %.200s has changed and you have "
                            "requested strict checking.", type, host);
                        goto fail;
                }

                /*
                 * If strict host key checking has not been requested, allow
                 * the connection but without MITM-able authentication or
                 * agent forwarding.
                 */
                if (options.password_authentication) {
                        error("Password authentication is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.password_authentication = 0;
                }
                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;
                }
                if (options.challenge_response_authentication) {
                        error("Challenge/response authentication is disabled"
                            " to avoid man-in-the-middle attacks.");
                        options.challenge_response_authentication = 0;
                }
                if (options.forward_agent) {
                        error("Agent forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.forward_agent = 0;
                }
                if (options.forward_x11) {
                        error("X11 forwarding is disabled to avoid "
                            "man-in-the-middle attacks.");
                        options.forward_x11 = 0;
                }
                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;
                }
                /*
                 * 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;
        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:%d",
                    type, host, ip, ip_file, ip_line);
                if (host_status == HOST_OK) {
                        len = strlen(msg);
                        snprintf(msg + len, sizeof(msg) - len,
                            "\nMatching host key in %s:%d",
                            host_file, host_line);
                }
                if (options.strict_host_key_checking == 1) {
                        logit("%s", msg);
                        error("Exiting, you have requested strict checking.");
                        goto fail;
                } else if (options.strict_host_key_checking == 2) {
                        strlcat(msg, "\nAre you sure you want "
                            "to continue connecting (yes/no)? ", sizeof(msg));
                        if (!confirm(msg))
                                goto fail;
                } else {
                        logit("%s", msg);
                }
        }

        xfree(ip);
        return 0;

fail:
        xfree(ip);
        return -1;
}

/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
        struct stat st;
        int flags = 0;

        if (options.verify_host_key_dns &&
            verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {

                if (flags & DNS_VERIFY_FOUND) {

                        if (options.verify_host_key_dns == 1 &&
                            flags & DNS_VERIFY_MATCH &&
                            flags & DNS_VERIFY_SECURE)
                                return 0;

                        if (flags & DNS_VERIFY_MATCH) {
                                matching_host_key_dns = 1;
                        } else {
                                warn_changed_key(host_key);
                                error("Update the SSHFP RR in DNS with the new "
                                    "host key to get rid of this message.");
                        }
                }
        }

        /* return ok if the key can be found in an old keyfile */
        if (stat(options.system_hostfile2, &st) == 0 ||
            stat(options.user_hostfile2, &st) == 0) {
                if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
                    options.user_hostfile2, options.system_hostfile2) == 0)
                        return 0;
        }
        return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
            options.user_hostfile, options.system_hostfile);
}

/*
 * 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, struct passwd *pw)
{
        char *host, *cp;
        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);
        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(local_user, server_user, host, sensitive);
        } else {
                ssh_kex(host, hostaddr);
                ssh_userauth1(local_user, server_user, host, sensitive);
        }
}

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 = xmalloc(size);
        memset(padded, 0, size);
        strlcpy(padded, password, size);
        packet_put_string(padded, size);
        memset(padded, 0, size);
        xfree(padded);
}

static int
show_key_from_file(const char *file, const char *host, int keytype)
{
        Key *found;
        char *fp;
        int line, ret;

        found = key_new(keytype);
        if ((ret = lookup_key_in_hostfile_by_type(file, host,
            keytype, found, &line))) {
                fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
                logit("WARNING: %s key found for host %s\n"
                    "in %s:%d\n"
                    "%s key fingerprint %s.",
                    key_type(found), host, file, line,
                    key_type(found), fp);
                xfree(fp);
        }
        key_free(found);
        return (ret);
}

/* print all known host keys for a given host, but skip keys of given type */
static int
show_other_keys(const char *host, Key *key)
{
        int type[] = { KEY_RSA1, KEY_RSA, KEY_DSA, -1};
        int i, found = 0;

        for (i = 0; type[i] != -1; i++) {
                if (type[i] == key->type)
                        continue;
                if (type[i] != KEY_RSA1 &&
                    show_key_from_file(options.user_hostfile2, host, type[i])) {
                        found = 1;
                        continue;
                }
                if (type[i] != KEY_RSA1 &&
                    show_key_from_file(options.system_hostfile2, host, type[i])) {
                        found = 1;
                        continue;
                }
                if (show_key_from_file(options.user_hostfile, host, type[i])) {
                        found = 1;
                        continue;
                }
                if (show_key_from_file(options.system_hostfile, host, type[i])) {
                        found = 1;
                        continue;
                }
                debug2("no key of type %d for host %s", type[i], host);
        }
        return (found);
}

static void
warn_changed_key(Key *host_key)
{
        char *fp;
        const char *type = key_type(host_key);

        fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);

        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, fp);
        error("Please contact your system administrator.");

        xfree(fp);
}