Adding upstream version 1:9.6p1.upstream/1%9.6p1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1729 insertions, 0 deletions

diff --git a/sshconnect.c b/sshconnect.c
new file mode 100644
index 0000000..bd077c7
--- /dev/null
+++ b/sshconnect.c
@@ -0,0 +1,1729 @@
+/* $OpenBSD: sshconnect.c,v 1.365 2023/11/20 02:50:00 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 "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;
+	}
+	(void)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;
+			}
+			if (options.address_family != AF_UNSPEC &&
+			    ai->ai_family != options.address_family) {
+				debug2_f("skipping address [%s]:%s: "
+				    "wrong address family", ntop, strport);
+				errno = EAFNOSUPPORT;
+				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 = NULL;
+	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;
+	}
+
+	/*
+	 * Don't ever try to write an invalid name to a known hosts file.
+	 * Note: do this before get_hostfile_hostname_ipaddr() to catch
+	 * '[' or ']' in the name before they are added.
+	 */
+	if (strcspn(hostname, "@?*#[]|'\'\"\\") != strlen(hostname)) {
+		debug_f("invalid hostname \"%s\"; will not record: %s",
+		    hostname, fail_reason);
+		readonly = RDONLY;
+	}
+
+	/*
+	 * 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);
+		if (num_user_hostfiles > 0 || num_system_hostfiles > 0) {
+			error("Add correct host key in %.100s to get rid "
+			    "of this message.", num_user_hostfiles > 0 ?
+			    user_hostfiles[0] : system_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);
+}