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ssh-add side of destination constraints

Have ssh-add accept a list of "destination constraints" that allow
restricting where keys may be used in conjunction with a ssh-agent/ssh
that supports session ID/hostkey binding.

Constraints are specified as either "[user@]host-pattern" or
"host-pattern>[user@]host-pattern".

The first form permits a key to be used to authenticate as the
specified user to the specified host.

The second form permits a key that has previously been permitted
for use at a host to be available via a forwarded agent to an
additional host.

For example, constraining a key with "user1@host_a" and
"host_a>host_b". Would permit authentication as "user1" at
"host_a", and allow the key to be available on an agent forwarded
to "host_a" only for authentication to "host_b". The key would not
be visible on agent forwarded to other hosts or usable for
authentication there.

Internally, destination constraints use host keys to identify hosts.
The host patterns are used to obtain lists of host keys for that
destination that are communicated to the agent. The user/hostkeys are
encoded using a new restrict-destination-v00@openssh.com key
constraint.

host keys are looked up in the default client user/system known_hosts
files. It is possible to override this set on the command-line.

feedback Jann Horn & markus@
ok markus@

/* $OpenBSD: sshconnect.c,v 1.356 2021/12/19 22:10:24 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 <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <net/if.h>
#include <netinet/in.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <limits.h>
#include <paths.h>
#include <signal.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <ifaddrs.h>

#include "xmalloc.h"
#include "ssh.h"
#include "sshbuf.h"
#include "packet.h"
#include "compat.h"
#include "sshkey.h"
#include "sshconnect.h"
#include "hostfile.h"
#include "log.h"
#include "misc.h"
#include "readconf.h"
#include "atomicio.h"
#include "dns.h"
#include "monitor_fdpass.h"
#include "ssh2.h"
#include "version.h"
#include "authfile.h"
#include "ssherr.h"
#include "authfd.h"
#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);
}

/*
 * 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;
}

/*
 * 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;
	struct ifaddrs *ifaddrs = NULL;
	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) {
		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;
		}
	}
	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);
	if (ifaddrs != NULL)
		freeifaddrs(ifaddrs);
	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];

	/*
	 * 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, hostaddr->sa_len,
			    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);
}