nrelease - fix/improve livecd

[dragonfly.git] / crypto / openssh / sshconnect.c

/* $OpenBSD: sshconnect.c,v 1.358 2022/08/26 08:16:27 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 <limits.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 <stdio.h>
#include <stdlib.h>
#include <stdarg.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 "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"
#include "kex.h"

struct sshkey *previous_host_key = NULL;

static int matching_host_key_dns = 0;

static pid_t proxy_command_pid = 0;

/* import */
extern int debug_flag;
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, const char *host_arg, int port)
{
        char *tmp, *ret, strport[NI_MAXSERV];
        const char *keyalias = options.host_key_alias ?
            options.host_key_alias : host_arg;

        snprintf(strport, sizeof strport, "%d", port);
        xasprintf(&tmp, "exec %s", proxy_command);
        ret = percent_expand(tmp,
            "h", host,
            "k", keyalias,
            "n", host_arg,
            "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,
    const char *host_arg, 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) == -1)
                fatal("Could not create socketpair to communicate with "
                    "proxy dialer: %.100s", strerror(errno));

        command_string = expand_proxy_command(proxy_command, options.user,
            host, host_arg, 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) == -1)
                                perror("dup2 stdin");
                }
                if (sp[0] != 1) {
                        if (dup2(sp[0], 1) == -1)
                                perror("dup2 stdout");
                }
                if (sp[0] >= 2)
                        close(sp[0]);

                /*
                 * Stderr is left for non-ControlPersist connections is so
                 * error messages may be printed on the user's terminal.
                 */
                if (!debug_flag && options.control_path != NULL &&
                    options.control_persist && stdfd_devnull(0, 0, 1) == -1)
                        error_f("stdfd_devnull failed");

                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 == -1)
                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, const char *host_arg,
    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) == -1 || pipe(pout) == -1)
                fatal("Could not create pipes to communicate with the proxy: %.100s",
                    strerror(errno));

        command_string = expand_proxy_command(proxy_command, options.user,
            host, host_arg, 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) == -1)
                                perror("dup2 stdin");
                        close(pin[0]);
                }
                close(pout[0]);
                if (dup2(pout[1], 1) == -1)
                        perror("dup2 stdout");
                /* Cannot be 1 because pin allocated two descriptors. */
                close(pout[1]);

                /*
                 * Stderr is left for non-ControlPersist connections is so
                 * error messages may be printed on the user's terminal.
                 */
                if (!debug_flag && options.control_path != NULL &&
                    options.control_persist && stdfd_devnull(0, 0, 1) == -1)
                        error_f("stdfd_devnull failed");

                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.
                 */
                ssh_signal(SIGPIPE, SIG_DFL);
                execv(argv[0], argv);
                perror(argv[0]);
                exit(1);
        }
        /* Parent. */
        if (pid == -1)
                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_f("v4 addr doesn't fit");
                                        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_f("v6 addr doesn't fit");
                                        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 == -1) {
                error("socket: %s", strerror(errno));
                return -1;
        }
        fcntl(sock, F_SETFD, FD_CLOEXEC);

        /* Use interactive QOS (if specified) until authentication completed */
        if (options.ip_qos_interactive != INT_MAX)
                set_sock_tos(sock, options.ip_qos_interactive);

        /* 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;
                }
                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_f("getnameinfo failed: %s", ssh_gai_strerror(r));
                goto fail;
        }
        if (bind(sock, (struct sockaddr *)&bindaddr, bindaddrlen) != 0) {
                error("bind %s: %s", ntop, strerror(errno));
                goto fail;
        }
        debug_f("bound to %s", 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;
}

/*
 * 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 connection_attempts,
    int *timeout_ms, int want_keepalive)
{
        int on = 1, saved_timeout_ms = *timeout_ms;
        int oerrno, sock = -1, attempt;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        struct addrinfo *ai;

        debug3_f("entering");
        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_f("getnameinfo failed");
                                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;
                        }

                        *timeout_ms = saved_timeout_ms;
                        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)) == -1)
                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, const char *host_arg,
    struct addrinfo *addrs, struct sockaddr_storage *hostaddr, u_short port,
    int connection_attempts, int *timeout_ms, int want_keepalive)
{
        int in, out;

        if (options.proxy_command == NULL) {
                return ssh_connect_direct(ssh, host, addrs, hostaddr, port,
                    connection_attempts, timeout_ms, want_keepalive);
        } else if (strcmp(options.proxy_command, "-") == 0) {
                if ((in = dup(STDIN_FILENO)) == -1 ||
                    (out = dup(STDOUT_FILENO)) == -1) {
                        if (in >= 0)
                                close(in);
                        error_f("dup() in/out failed");
                        return -1; /* ssh_packet_set_connection logs error */
                }
                if ((ssh_packet_set_connection(ssh, in, out)) == NULL)
                        return -1; /* ssh_packet_set_connection logs error */
                return 0;
        } else if (options.proxy_use_fdpass) {
                return ssh_proxy_fdpass_connect(ssh, host, host_arg, port,
                    options.proxy_command);
        }
        return ssh_proxy_connect(ssh, host, host_arg, port,
            options.proxy_command);
}

/* defaults to 'no' */
static int
confirm(const char *prompt, const char *fingerprint)
{
        const char *msg, *again = "Please type 'yes' or 'no': ";
        const char *again_fp = "Please type 'yes', 'no' or the fingerprint: ";
        char *p, *cp;
        int ret = -1;

        if (options.batch_mode)
                return 0;
        for (msg = prompt;;msg = fingerprint ? again_fp : again) {
                cp = p = read_passphrase(msg, RP_ECHO);
                if (p == NULL)
                        return 0;
                p += strspn(p, " \t"); /* skip leading whitespace */
                p[strcspn(p, " \t\n")] = '\0'; /* remove trailing whitespace */
                if (p[0] == '\0' || strcasecmp(p, "no") == 0)
                        ret = 0;
                else if (strcasecmp(p, "yes") == 0 || (fingerprint != NULL &&
                    strcmp(p, fingerprint) == 0))
                        ret = 1;
                free(cp);
                if (ret != -1)
                        return ret;
        }
}

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_f("getnameinfo failed");
                        *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);
                }
        }
}

/* returns non-zero if path appears in hostfiles, or 0 if not. */
static int
path_in_hostfiles(const char *path, char **hostfiles, u_int num_hostfiles)
{
        u_int i;

        for (i = 0; i < num_hostfiles; i++) {
                if (strcmp(path, hostfiles[i]) == 0)
                        return 1;
        }
        return 0;
}

struct find_by_key_ctx {
        const char *host, *ip;
        const struct sshkey *key;
        char **names;
        u_int nnames;
};

/* Try to replace home directory prefix (per $HOME) with a ~/ sequence */
static char *
try_tilde_unexpand(const char *path)
{
        char *home, *ret = NULL;
        size_t l;

        if (*path != '/')
                return xstrdup(path);
        if ((home = getenv("HOME")) == NULL || (l = strlen(home)) == 0)
                return xstrdup(path);
        if (strncmp(path, home, l) != 0)
                return xstrdup(path);
        /*
         * ensure we have matched on a path boundary: either the $HOME that
         * we just compared ends with a '/' or the next character of the path
         * must be a '/'.
         */
        if (home[l - 1] != '/' && path[l] != '/')
                return xstrdup(path);
        if (path[l] == '/')
                l++;
        xasprintf(&ret, "~/%s", path + l);
        return ret;
}

static int
hostkeys_find_by_key_cb(struct hostkey_foreach_line *l, void *_ctx)
{
        struct find_by_key_ctx *ctx = (struct find_by_key_ctx *)_ctx;
        char *path;

        /* we are looking for keys with names that *do not* match */
        if ((l->match & HKF_MATCH_HOST) != 0)
                return 0;
        /* not interested in marker lines */
        if (l->marker != MRK_NONE)
                return 0;
        /* we are only interested in exact key matches */
        if (l->key == NULL || !sshkey_equal(ctx->key, l->key))
                return 0;
        path = try_tilde_unexpand(l->path);
        debug_f("found matching key in %s:%lu", path, l->linenum);
        ctx->names = xrecallocarray(ctx->names,
            ctx->nnames, ctx->nnames + 1, sizeof(*ctx->names));
        xasprintf(&ctx->names[ctx->nnames], "%s:%lu: %s", path, l->linenum,
            strncmp(l->hosts, HASH_MAGIC, strlen(HASH_MAGIC)) == 0 ?
            "[hashed name]" : l->hosts);
        ctx->nnames++;
        free(path);
        return 0;
}

static int
hostkeys_find_by_key_hostfile(const char *file, const char *which,
    struct find_by_key_ctx *ctx)
{
        int r;

        debug3_f("trying %s hostfile \"%s\"", which, file);
        if ((r = hostkeys_foreach(file, hostkeys_find_by_key_cb, ctx,
            ctx->host, ctx->ip, HKF_WANT_PARSE_KEY, 0)) != 0) {
                if (r == SSH_ERR_SYSTEM_ERROR && errno == ENOENT) {
                        debug_f("hostkeys file %s does not exist", file);
                        return 0;
                }
                error_fr(r, "hostkeys_foreach failed for %s", file);
                return r;
        }
        return 0;
}

/*
 * Find 'key' in known hosts file(s) that do not match host/ip.
 * Used to display also-known-as information for previously-unseen hostkeys.
 */
static void
hostkeys_find_by_key(const char *host, const char *ip, const struct sshkey *key,
    char **user_hostfiles, u_int num_user_hostfiles,
    char **system_hostfiles, u_int num_system_hostfiles,
    char ***names, u_int *nnames)
{
        struct find_by_key_ctx ctx = {0, 0, 0, 0, 0};
        u_int i;

        *names = NULL;
        *nnames = 0;

        if (key == NULL || sshkey_is_cert(key))
                return;

        ctx.host = host;
        ctx.ip = ip;
        ctx.key = key;

        for (i = 0; i < num_user_hostfiles; i++) {
                if (hostkeys_find_by_key_hostfile(user_hostfiles[i],
                    "user", &ctx) != 0)
                        goto fail;
        }
        for (i = 0; i < num_system_hostfiles; i++) {
                if (hostkeys_find_by_key_hostfile(system_hostfiles[i],
                    "system", &ctx) != 0)
                        goto fail;
        }
        /* success */
        *names = ctx.names;
        *nnames = ctx.nnames;
        ctx.names = NULL;
        ctx.nnames = 0;
        return;
 fail:
        for (i = 0; i < ctx.nnames; i++)
                free(ctx.names[i]);
        free(ctx.names);
}

#define MAX_OTHER_NAMES 8 /* Maximum number of names to list */
static char *
other_hostkeys_message(const char *host, const char *ip,
    const struct sshkey *key,
    char **user_hostfiles, u_int num_user_hostfiles,
    char **system_hostfiles, u_int num_system_hostfiles)
{
        char *ret = NULL, **othernames = NULL;
        u_int i, n, num_othernames = 0;

        hostkeys_find_by_key(host, ip, key,
            user_hostfiles, num_user_hostfiles,
            system_hostfiles, num_system_hostfiles,
            &othernames, &num_othernames);
        if (num_othernames == 0)
                return xstrdup("This key is not known by any other names.");

        xasprintf(&ret, "This host key is known by the following other "
            "names/addresses:");

        n = num_othernames;
        if (n > MAX_OTHER_NAMES)
                n = MAX_OTHER_NAMES;
        for (i = 0; i < n; i++) {
                xextendf(&ret, "\n", "    %s", othernames[i]);
        }
        if (n < num_othernames) {
                xextendf(&ret, "\n", "    (%d additional names omitted)",
                    num_othernames - n);
        }
        for (i = 0; i < num_othernames; i++)
                free(othernames[i]);
        free(othernames);
        return ret;
}

void
load_hostkeys_command(struct hostkeys *hostkeys, const char *command_template,
    const char *invocation, const struct ssh_conn_info *cinfo,
    const struct sshkey *host_key, const char *hostfile_hostname)
{
        int r, i, ac = 0;
        char *key_fp = NULL, *keytext = NULL, *tmp;
        char *command = NULL, *tag = NULL, **av = NULL;
        FILE *f = NULL;
        pid_t pid;
        void (*osigchld)(int);

        xasprintf(&tag, "KnownHostsCommand-%s", invocation);

        if (host_key != NULL) {
                if ((key_fp = sshkey_fingerprint(host_key,
                    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
                        fatal_f("sshkey_fingerprint failed");
                if ((r = sshkey_to_base64(host_key, &keytext)) != 0)
                        fatal_fr(r, "sshkey_to_base64 failed");
        }
        /*
         * NB. all returns later this function should go via "out" to
         * ensure the original SIGCHLD handler is restored properly.
         */
        osigchld = ssh_signal(SIGCHLD, SIG_DFL);

        /* Turn the command into an argument vector */
        if (argv_split(command_template, &ac, &av, 0) != 0) {
                error("%s \"%s\" contains invalid quotes", tag,
                    command_template);
                goto out;
        }
        if (ac == 0) {
                error("%s \"%s\" yielded no arguments", tag,
                    command_template);
                goto out;
        }
        for (i = 1; i < ac; i++) {
                tmp = percent_dollar_expand(av[i],
                    DEFAULT_CLIENT_PERCENT_EXPAND_ARGS(cinfo),
                    "H", hostfile_hostname,
                    "I", invocation,
                    "t", host_key == NULL ? "NONE" : sshkey_ssh_name(host_key),
                    "f", key_fp == NULL ? "NONE" : key_fp,
                    "K", keytext == NULL ? "NONE" : keytext,
                    (char *)NULL);
                if (tmp == NULL)
                        fatal_f("percent_expand failed");
                free(av[i]);
                av[i] = tmp;
        }
        /* Prepare a printable command for logs, etc. */
        command = argv_assemble(ac, av);

        if ((pid = subprocess(tag, command, ac, av, &f,
            SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_UNSAFE_PATH|
            SSH_SUBPROCESS_PRESERVE_ENV, NULL, NULL, NULL)) == 0)
                goto out;

        load_hostkeys_file(hostkeys, hostfile_hostname, tag, f, 1);

        if (exited_cleanly(pid, tag, command, 0) != 0)
                fatal("KnownHostsCommand failed");

 out:
        if (f != NULL)
                fclose(f);
        ssh_signal(SIGCHLD, osigchld);
        for (i = 0; i < ac; i++)
                free(av[i]);
        free(av);
        free(tag);
        free(command);
        free(key_fp);
        free(keytext);
}

/*
 * 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, const struct ssh_conn_info *cinfo,
    struct sockaddr *hostaddr, u_short port,
    struct sshkey *host_key, int readonly, int clobber_port,
    char **user_hostfiles, u_int num_user_hostfiles,
    char **system_hostfiles, u_int num_system_hostfiles,
    const char *hostfile_command)
{
        HostStatus host_status = -1, ip_status = -1;
        struct sshkey *raw_key = NULL;
        char *ip = NULL, *host = NULL;
        char hostline[1000], *hostp, *fp, *ra;
        char msg[1024];
        const char *type, *fail_reason;
        const struct hostkey_entry *host_found = NULL, *ip_found = NULL;
        int len, cancelled_forwarding = 0, confirmed;
        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.");
                options.update_hostkeys = 0;
                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,
            clobber_port ? 0 : 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], 0);
        for (i = 0; i < num_system_hostfiles; i++)
                load_hostkeys(host_hostkeys, host, system_hostfiles[i], 0);
        if (hostfile_command != NULL && !clobber_port) {
                load_hostkeys_command(host_hostkeys, hostfile_command,
                    "HOSTNAME", cinfo, host_key, host);
        }

        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], 0);
                for (i = 0; i < num_system_hostfiles; i++)
                        load_hostkeys(ip_hostkeys, ip, system_hostfiles[i], 0);
                if (hostfile_command != NULL && !clobber_port) {
                        load_hostkeys_command(ip_hostkeys, hostfile_command,
                            "ADDRESS", cinfo, host_key, ip);
                }
        }

 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);

        /*
         * If there are no hostfiles, or if the hostkey was found via
         * KnownHostsCommand, then don't try to touch the disk.
         */
        if (!readonly && (num_user_hostfiles == 0 ||
            (host_found != NULL && host_found->note != 0)))
                readonly = RDONLY;

        /*
         * 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) {
                        if (sshkey_cert_check_host(host_key,
                            options.host_key_alias == NULL ?
                            hostname : options.host_key_alias, 0,
                            options.ca_sign_algorithms, &fail_reason) != 0) {
                                error("%s", fail_reason);
                                goto fail;
                        }
                        /*
                         * Do not attempt hostkey update if a certificate was
                         * successfully matched.
                         */
                        if (options.update_hostkeys != 0) {
                                options.update_hostkeys = 0;
                                debug3_f("certificate host key in use; "
                                    "disabling UpdateHostkeys");
                        }
                }
                /* Turn off UpdateHostkeys if key was in system known_hosts */
                if (options.update_hostkeys != 0 &&
                    (path_in_hostfiles(host_found->file,
                    system_hostfiles, num_system_hostfiles) ||
                    (ip_status == HOST_OK && ip_found != NULL &&
                    path_in_hostfiles(ip_found->file,
                    system_hostfiles, num_system_hostfiles)))) {
                        options.update_hostkeys = 0;
                        debug3_f("host key found in GlobalKnownHostsFile; "
                            "disabling UpdateHostkeys");
                }
                if (options.update_hostkeys != 0 && host_found->note) {
                        options.update_hostkeys = 0;
                        debug3_f("host key found via KnownHostsCommand; "
                            "disabling UpdateHostkeys");
                }
                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_f("sshkey_fingerprint failed");
                        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 && !clobber_port) {
                        debug("checking without port identifier");
                        if (check_host_key(hostname, cinfo, hostaddr, 0,
                            host_key, ROQUIET, 1,
                            user_hostfiles, num_user_hostfiles,
                            system_hostfiles, num_system_hostfiles,
                            hostfile_command) == 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 = NULL, *msg2 = NULL;

                        xasprintf(&msg1, "The authenticity of host "
                            "'%.200s (%s)' can't be established", host, ip);

                        if (show_other_keys(host_hostkeys, host_key)) {
                                xextendf(&msg1, "\n", "but keys of different "
                                    "type are already known for this host.");
                        } else
                                xextendf(&msg1, "", ".");

                        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_f("sshkey_fingerprint failed");
                        xextendf(&msg1, "\n", "%s key fingerprint is %s.",
                            type, fp);
                        if (options.visual_host_key)
                                xextendf(&msg1, "\n", "%s", ra);
                        if (options.verify_host_key_dns) {
                                xextendf(&msg1, "\n",
                                    "%s host key fingerprint found in DNS.",
                                    matching_host_key_dns ?
                                    "Matching" : "No matching");
                        }
                        /* msg2 informs for other names matching this key */
                        if ((msg2 = other_hostkeys_message(host, ip, host_key,
                            user_hostfiles, num_user_hostfiles,
                            system_hostfiles, num_system_hostfiles)) != NULL)
                                xextendf(&msg1, "\n", "%s", msg2);

                        xextendf(&msg1, "\n",
                            "Are you sure you want to continue connecting "
                            "(yes/no/[fingerprint])? ");

                        confirmed = confirm(msg1, fp);
                        free(ra);
                        free(fp);
                        free(msg1);
                        free(msg2);
                        if (!confirmed)
                                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("Host key for %.200s has changed and you have "
                            "requested strict checking.", 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;
                        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.update_hostkeys != 0) {
                        error("UpdateHostkeys is disabled because the host "
                            "key is not trusted.");
                        options.update_hostkeys = 0;
                }
                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 they wish 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, NULL))
                                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_f("hostkey not known or explicitly trusted: "
                    "disabling UpdateHostkeys");
                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_fr(r, "decode key");
                if ((r = sshkey_drop_cert(raw_key)) != 0)
                        fatal_r(r, "Couldn't drop certificate");
                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,
    const struct ssh_conn_info *cinfo)
{
        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_fr(r, "fingerprint host key");
                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_fr(r, "fingerprint CA key");
                        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_f("server host key %s %s matches cached key",
                    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_r(r, "Error checking host key %s %s in "
                            "revoked keys file %s", sshkey_type(host_key),
                            fp, options.revoked_host_keys);
                        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, cinfo, hostaddr, options.port, host_key,
            RDRW, 0, options.user_hostfiles, options.num_user_hostfiles,
            options.system_hostfiles, options.num_system_hostfiles,
            options.known_hosts_command);

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(struct ssh *ssh, Sensitive *sensitive, const char *orighost,
    struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms,
    const struct ssh_conn_info *cinfo)
{
        char *host;
        char *server_user, *local_user;
        int r;

        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. */
        if ((r = kex_exchange_identification(ssh, timeout_ms, NULL)) != 0)
                sshpkt_fatal(ssh, r, "banner exchange");

        /* Put the connection into non-blocking mode. */
        ssh_packet_set_nonblocking(ssh);

        /* key exchange */
        /* authenticate user */
        debug("Authenticating to %s:%d as '%s'", host, port, server_user);
        ssh_kex2(ssh, host, hostaddr, port, cinfo);
        ssh_userauth2(ssh, local_user, server_user, host, sensitive);
        free(local_user);
        free(host);
}

/* 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],
                    -1, &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_f("sshkey_fingerprint fail");
                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_f("sshkey_fingerprint fail");

        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 = ssh_signal(SIGCHLD, SIG_DFL);
        pid = fork();
        if (pid == 0) {
                ssh_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));
        ssh_signal(SIGCHLD, osighand);

        if (!WIFEXITED(status))
                return (1);

        return (WEXITSTATUS(status));
}

void
maybe_add_key_to_agent(const char *authfile, struct sshkey *private,
    const char *comment, const char *passphrase)
{
        int auth_sock = -1, r;
        const char *skprovider = NULL;

        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 (sshkey_is_sk(private))
                skprovider = options.sk_provider;
        if ((r = ssh_add_identity_constrained(auth_sock, private,
            comment == NULL ? authfile : comment,
            options.add_keys_to_agent_lifespan,
            (options.add_keys_to_agent == 3), 0, skprovider, NULL, 0)) == 0)
                debug("identity added to agent: %s", authfile);
        else
                debug("could not add identity to agent: %s (%d)", authfile, r);
        close(auth_sock);
}