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

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

1 files changed, 856 insertions, 0 deletions

diff --git a/auth.c b/auth.c
new file mode 100644
index 0000000..3b380d9
--- /dev/null
+++ b/auth.c
@@ -0,0 +1,856 @@
+/* $OpenBSD: auth.c,v 1.160 2023/03/05 05:34:09 dtucker Exp $ */
+/*
+ * Copyright (c) 2000 Markus Friedl.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+
+#include <netinet/in.h>
+
+#include <stdlib.h>
+#include <errno.h>
+#include <fcntl.h>
+#ifdef HAVE_PATHS_H
+# include <paths.h>
+#endif
+#include <pwd.h>
+#ifdef HAVE_LOGIN_H
+#include <login.h>
+#endif
+#ifdef USE_SHADOW
+#include <shadow.h>
+#endif
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <limits.h>
+#include <netdb.h>
+#include <time.h>
+
+#include "xmalloc.h"
+#include "match.h"
+#include "groupaccess.h"
+#include "log.h"
+#include "sshbuf.h"
+#include "misc.h"
+#include "servconf.h"
+#include "sshkey.h"
+#include "hostfile.h"
+#include "auth.h"
+#include "auth-options.h"
+#include "canohost.h"
+#include "uidswap.h"
+#include "packet.h"
+#include "loginrec.h"
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+#include "authfile.h"
+#include "monitor_wrap.h"
+#include "ssherr.h"
+#include "channels.h"
+
+/* import */
+extern ServerOptions options;
+extern struct include_list includes;
+extern int use_privsep;
+extern struct sshbuf *loginmsg;
+extern struct passwd *privsep_pw;
+extern struct sshauthopt *auth_opts;
+
+/* Debugging messages */
+static struct sshbuf *auth_debug;
+
+/*
+ * Check if the user is allowed to log in via ssh. If user is listed
+ * in DenyUsers or one of user's groups is listed in DenyGroups, false
+ * will be returned. If AllowUsers isn't empty and user isn't listed
+ * there, or if AllowGroups isn't empty and one of user's groups isn't
+ * listed there, false will be returned.
+ * If the user's shell is not executable, false will be returned.
+ * Otherwise true is returned.
+ */
+int
+allowed_user(struct ssh *ssh, struct passwd * pw)
+{
+	struct stat st;
+	const char *hostname = NULL, *ipaddr = NULL;
+	u_int i;
+	int r;
+
+	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
+	if (!pw || !pw->pw_name)
+		return 0;
+
+	if (!options.use_pam && platform_locked_account(pw)) {
+		logit("User %.100s not allowed because account is locked",
+		    pw->pw_name);
+		return 0;
+	}
+
+	/*
+	 * Deny if shell does not exist or is not executable unless we
+	 * are chrooting.
+	 */
+	if (options.chroot_directory == NULL ||
+	    strcasecmp(options.chroot_directory, "none") == 0) {
+		char *shell = xstrdup((pw->pw_shell[0] == '\0') ?
+		    _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */
+
+		if (stat(shell, &st) == -1) {
+			logit("User %.100s not allowed because shell %.100s "
+			    "does not exist", pw->pw_name, shell);
+			free(shell);
+			return 0;
+		}
+		if (S_ISREG(st.st_mode) == 0 ||
+		    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
+			logit("User %.100s not allowed because shell %.100s "
+			    "is not executable", pw->pw_name, shell);
+			free(shell);
+			return 0;
+		}
+		free(shell);
+	}
+
+	if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
+	    options.num_deny_groups > 0 || options.num_allow_groups > 0) {
+		hostname = auth_get_canonical_hostname(ssh, options.use_dns);
+		ipaddr = ssh_remote_ipaddr(ssh);
+	}
+
+	/* Return false if user is listed in DenyUsers */
+	if (options.num_deny_users > 0) {
+		for (i = 0; i < options.num_deny_users; i++) {
+			r = match_user(pw->pw_name, hostname, ipaddr,
+			    options.deny_users[i]);
+			if (r < 0) {
+				fatal("Invalid DenyUsers pattern \"%.100s\"",
+				    options.deny_users[i]);
+			} else if (r != 0) {
+				logit("User %.100s from %.100s not allowed "
+				    "because listed in DenyUsers",
+				    pw->pw_name, hostname);
+				return 0;
+			}
+		}
+	}
+	/* Return false if AllowUsers isn't empty and user isn't listed there */
+	if (options.num_allow_users > 0) {
+		for (i = 0; i < options.num_allow_users; i++) {
+			r = match_user(pw->pw_name, hostname, ipaddr,
+			    options.allow_users[i]);
+			if (r < 0) {
+				fatal("Invalid AllowUsers pattern \"%.100s\"",
+				    options.allow_users[i]);
+			} else if (r == 1)
+				break;
+		}
+		/* i < options.num_allow_users iff we break for loop */
+		if (i >= options.num_allow_users) {
+			logit("User %.100s from %.100s not allowed because "
+			    "not listed in AllowUsers", pw->pw_name, hostname);
+			return 0;
+		}
+	}
+	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
+		/* Get the user's group access list (primary and supplementary) */
+		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
+			logit("User %.100s from %.100s not allowed because "
+			    "not in any group", pw->pw_name, hostname);
+			return 0;
+		}
+
+		/* Return false if one of user's groups is listed in DenyGroups */
+		if (options.num_deny_groups > 0)
+			if (ga_match(options.deny_groups,
+			    options.num_deny_groups)) {
+				ga_free();
+				logit("User %.100s from %.100s not allowed "
+				    "because a group is listed in DenyGroups",
+				    pw->pw_name, hostname);
+				return 0;
+			}
+		/*
+		 * Return false if AllowGroups isn't empty and one of user's groups
+		 * isn't listed there
+		 */
+		if (options.num_allow_groups > 0)
+			if (!ga_match(options.allow_groups,
+			    options.num_allow_groups)) {
+				ga_free();
+				logit("User %.100s from %.100s not allowed "
+				    "because none of user's groups are listed "
+				    "in AllowGroups", pw->pw_name, hostname);
+				return 0;
+			}
+		ga_free();
+	}
+
+#ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
+	if (!sys_auth_allowed_user(pw, loginmsg))
+		return 0;
+#endif
+
+	/* We found no reason not to let this user try to log on... */
+	return 1;
+}
+
+/*
+ * Formats any key left in authctxt->auth_method_key for inclusion in
+ * auth_log()'s message. Also includes authxtct->auth_method_info if present.
+ */
+static char *
+format_method_key(Authctxt *authctxt)
+{
+	const struct sshkey *key = authctxt->auth_method_key;
+	const char *methinfo = authctxt->auth_method_info;
+	char *fp, *cafp, *ret = NULL;
+
+	if (key == NULL)
+		return NULL;
+
+	if (sshkey_is_cert(key)) {
+		fp = sshkey_fingerprint(key,
+		    options.fingerprint_hash, SSH_FP_DEFAULT);
+		cafp = sshkey_fingerprint(key->cert->signature_key,
+		    options.fingerprint_hash, SSH_FP_DEFAULT);
+		xasprintf(&ret, "%s %s ID %s (serial %llu) CA %s %s%s%s",
+		    sshkey_type(key), fp == NULL ? "(null)" : fp,
+		    key->cert->key_id,
+		    (unsigned long long)key->cert->serial,
+		    sshkey_type(key->cert->signature_key),
+		    cafp == NULL ? "(null)" : cafp,
+		    methinfo == NULL ? "" : ", ",
+		    methinfo == NULL ? "" : methinfo);
+		free(fp);
+		free(cafp);
+	} else {
+		fp = sshkey_fingerprint(key, options.fingerprint_hash,
+		    SSH_FP_DEFAULT);
+		xasprintf(&ret, "%s %s%s%s", sshkey_type(key),
+		    fp == NULL ? "(null)" : fp,
+		    methinfo == NULL ? "" : ", ",
+		    methinfo == NULL ? "" : methinfo);
+		free(fp);
+	}
+	return ret;
+}
+
+void
+auth_log(struct ssh *ssh, int authenticated, int partial,
+    const char *method, const char *submethod)
+{
+	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
+	int level = SYSLOG_LEVEL_VERBOSE;
+	const char *authmsg;
+	char *extra = NULL;
+
+	if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
+		return;
+
+	/* Raise logging level */
+	if (authenticated == 1 ||
+	    !authctxt->valid ||
+	    authctxt->failures >= options.max_authtries / 2 ||
+	    strcmp(method, "password") == 0)
+		level = SYSLOG_LEVEL_INFO;
+
+	if (authctxt->postponed)
+		authmsg = "Postponed";
+	else if (partial)
+		authmsg = "Partial";
+	else
+		authmsg = authenticated ? "Accepted" : "Failed";
+
+	if ((extra = format_method_key(authctxt)) == NULL) {
+		if (authctxt->auth_method_info != NULL)
+			extra = xstrdup(authctxt->auth_method_info);
+	}
+
+	do_log2(level, "%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s",
+	    authmsg,
+	    method,
+	    submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod,
+	    authctxt->valid ? "" : "invalid user ",
+	    authctxt->user,
+	    ssh_remote_ipaddr(ssh),
+	    ssh_remote_port(ssh),
+	    extra != NULL ? ": " : "",
+	    extra != NULL ? extra : "");
+
+	free(extra);
+
+#if defined(CUSTOM_FAILED_LOGIN) || defined(SSH_AUDIT_EVENTS)
+	if (authenticated == 0 && !(authctxt->postponed || partial)) {
+		/* Log failed login attempt */
+# ifdef CUSTOM_FAILED_LOGIN
+		if (strcmp(method, "password") == 0 ||
+		    strncmp(method, "keyboard-interactive", 20) == 0 ||
+		    strcmp(method, "challenge-response") == 0)
+			record_failed_login(ssh, authctxt->user,
+			    auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
+# endif
+# ifdef SSH_AUDIT_EVENTS
+		audit_event(ssh, audit_classify_auth(method));
+# endif
+	}
+#endif
+#if defined(CUSTOM_FAILED_LOGIN) && defined(WITH_AIXAUTHENTICATE)
+	if (authenticated)
+		sys_auth_record_login(authctxt->user,
+		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
+		    loginmsg);
+#endif
+}
+
+void
+auth_maxtries_exceeded(struct ssh *ssh)
+{
+	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
+
+	error("maximum authentication attempts exceeded for "
+	    "%s%.100s from %.200s port %d ssh2",
+	    authctxt->valid ? "" : "invalid user ",
+	    authctxt->user,
+	    ssh_remote_ipaddr(ssh),
+	    ssh_remote_port(ssh));
+	ssh_packet_disconnect(ssh, "Too many authentication failures");
+	/* NOTREACHED */
+}
+
+/*
+ * Check whether root logins are disallowed.
+ */
+int
+auth_root_allowed(struct ssh *ssh, const char *method)
+{
+	switch (options.permit_root_login) {
+	case PERMIT_YES:
+		return 1;
+	case PERMIT_NO_PASSWD:
+		if (strcmp(method, "publickey") == 0 ||
+		    strcmp(method, "hostbased") == 0 ||
+		    strcmp(method, "gssapi-with-mic") == 0)
+			return 1;
+		break;
+	case PERMIT_FORCED_ONLY:
+		if (auth_opts->force_command != NULL) {
+			logit("Root login accepted for forced command.");
+			return 1;
+		}
+		break;
+	}
+	logit("ROOT LOGIN REFUSED FROM %.200s port %d",
+	    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
+	return 0;
+}
+
+
+/*
+ * Given a template and a passwd structure, build a filename
+ * by substituting % tokenised options. Currently, %% becomes '%',
+ * %h becomes the home directory and %u the username.
+ *
+ * This returns a buffer allocated by xmalloc.
+ */
+char *
+expand_authorized_keys(const char *filename, struct passwd *pw)
+{
+	char *file, uidstr[32], ret[PATH_MAX];
+	int i;
+
+	snprintf(uidstr, sizeof(uidstr), "%llu",
+	    (unsigned long long)pw->pw_uid);
+	file = percent_expand(filename, "h", pw->pw_dir,
+	    "u", pw->pw_name, "U", uidstr, (char *)NULL);
+
+	/*
+	 * Ensure that filename starts anchored. If not, be backward
+	 * compatible and prepend the '%h/'
+	 */
+	if (path_absolute(file))
+		return (file);
+
+	i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
+	if (i < 0 || (size_t)i >= sizeof(ret))
+		fatal("expand_authorized_keys: path too long");
+	free(file);
+	return (xstrdup(ret));
+}
+
+char *
+authorized_principals_file(struct passwd *pw)
+{
+	if (options.authorized_principals_file == NULL)
+		return NULL;
+	return expand_authorized_keys(options.authorized_principals_file, pw);
+}
+
+/* return ok if key exists in sysfile or userfile */
+HostStatus
+check_key_in_hostfiles(struct passwd *pw, struct sshkey *key, const char *host,
+    const char *sysfile, const char *userfile)
+{
+	char *user_hostfile;
+	struct stat st;
+	HostStatus host_status;
+	struct hostkeys *hostkeys;
+	const struct hostkey_entry *found;
+
+	hostkeys = init_hostkeys();
+	load_hostkeys(hostkeys, host, sysfile, 0);
+	if (userfile != NULL) {
+		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
+		if (options.strict_modes &&
+		    (stat(user_hostfile, &st) == 0) &&
+		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+		    (st.st_mode & 022) != 0)) {
+			logit("Authentication refused for %.100s: "
+			    "bad owner or modes for %.200s",
+			    pw->pw_name, user_hostfile);
+			auth_debug_add("Ignored %.200s: bad ownership or modes",
+			    user_hostfile);
+		} else {
+			temporarily_use_uid(pw);
+			load_hostkeys(hostkeys, host, user_hostfile, 0);
+			restore_uid();
+		}
+		free(user_hostfile);
+	}
+	host_status = check_key_in_hostkeys(hostkeys, key, &found);
+	if (host_status == HOST_REVOKED)
+		error("WARNING: revoked key for %s attempted authentication",
+		    host);
+	else if (host_status == HOST_OK)
+		debug_f("key for %s found at %s:%ld",
+		    found->host, found->file, found->line);
+	else
+		debug_f("key for host %s not found", host);
+
+	free_hostkeys(hostkeys);
+
+	return host_status;
+}
+
+struct passwd *
+getpwnamallow(struct ssh *ssh, const char *user)
+{
+#ifdef HAVE_LOGIN_CAP
+	extern login_cap_t *lc;
+#ifdef BSD_AUTH
+	auth_session_t *as;
+#endif
+#endif
+	struct passwd *pw;
+	struct connection_info *ci;
+	u_int i;
+
+	ci = get_connection_info(ssh, 1, options.use_dns);
+	ci->user = user;
+	parse_server_match_config(&options, &includes, ci);
+	log_change_level(options.log_level);
+	log_verbose_reset();
+	for (i = 0; i < options.num_log_verbose; i++)
+		log_verbose_add(options.log_verbose[i]);
+	process_permitopen(ssh, &options);
+
+#if defined(_AIX) && defined(HAVE_SETAUTHDB)
+	aix_setauthdb(user);
+#endif
+
+	pw = getpwnam(user);
+
+#if defined(_AIX) && defined(HAVE_SETAUTHDB)
+	aix_restoreauthdb();
+#endif
+	if (pw == NULL) {
+		logit("Invalid user %.100s from %.100s port %d",
+		    user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
+#ifdef CUSTOM_FAILED_LOGIN
+		record_failed_login(ssh, user,
+		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
+#endif
+#ifdef SSH_AUDIT_EVENTS
+		audit_event(ssh, SSH_INVALID_USER);
+#endif /* SSH_AUDIT_EVENTS */
+		return (NULL);
+	}
+	if (!allowed_user(ssh, pw))
+		return (NULL);
+#ifdef HAVE_LOGIN_CAP
+	if ((lc = login_getpwclass(pw)) == NULL) {
+		debug("unable to get login class: %s", user);
+		return (NULL);
+	}
+#ifdef BSD_AUTH
+	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
+	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
+		debug("Approval failure for %s", user);
+		pw = NULL;
+	}
+	if (as != NULL)
+		auth_close(as);
+#endif
+#endif
+	if (pw != NULL)
+		return (pwcopy(pw));
+	return (NULL);
+}
+
+/* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
+int
+auth_key_is_revoked(struct sshkey *key)
+{
+	char *fp = NULL;
+	int r;
+
+	if (options.revoked_keys_file == NULL)
+		return 0;
+	if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
+	    SSH_FP_DEFAULT)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		error_fr(r, "fingerprint key");
+		goto out;
+	}
+
+	r = sshkey_check_revoked(key, options.revoked_keys_file);
+	switch (r) {
+	case 0:
+		break; /* not revoked */
+	case SSH_ERR_KEY_REVOKED:
+		error("Authentication key %s %s revoked by file %s",
+		    sshkey_type(key), fp, options.revoked_keys_file);
+		goto out;
+	default:
+		error_r(r, "Error checking authentication key %s %s in "
+		    "revoked keys file %s", sshkey_type(key), fp,
+		    options.revoked_keys_file);
+		goto out;
+	}
+
+	/* Success */
+	r = 0;
+
+ out:
+	free(fp);
+	return r == 0 ? 0 : 1;
+}
+
+void
+auth_debug_add(const char *fmt,...)
+{
+	char buf[1024];
+	va_list args;
+	int r;
+
+	va_start(args, fmt);
+	vsnprintf(buf, sizeof(buf), fmt, args);
+	va_end(args);
+	debug3("%s", buf);
+	if (auth_debug != NULL)
+		if ((r = sshbuf_put_cstring(auth_debug, buf)) != 0)
+			fatal_fr(r, "sshbuf_put_cstring");
+}
+
+void
+auth_debug_send(struct ssh *ssh)
+{
+	char *msg;
+	int r;
+
+	if (auth_debug == NULL)
+		return;
+	while (sshbuf_len(auth_debug) != 0) {
+		if ((r = sshbuf_get_cstring(auth_debug, &msg, NULL)) != 0)
+			fatal_fr(r, "sshbuf_get_cstring");
+		ssh_packet_send_debug(ssh, "%s", msg);
+		free(msg);
+	}
+}
+
+void
+auth_debug_reset(void)
+{
+	if (auth_debug != NULL)
+		sshbuf_reset(auth_debug);
+	else if ((auth_debug = sshbuf_new()) == NULL)
+		fatal_f("sshbuf_new failed");
+}
+
+struct passwd *
+fakepw(void)
+{
+	static int done = 0;
+	static struct passwd fake;
+	const char hashchars[] = "./ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	    "abcdefghijklmnopqrstuvwxyz0123456789"; /* from bcrypt.c */
+	char *cp;
+
+	if (done)
+		return (&fake);
+
+	memset(&fake, 0, sizeof(fake));
+	fake.pw_name = "NOUSER";
+	fake.pw_passwd = xstrdup("$2a$10$"
+	    "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
+	for (cp = fake.pw_passwd + 7; *cp != '\0'; cp++)
+		*cp = hashchars[arc4random_uniform(sizeof(hashchars) - 1)];
+#ifdef HAVE_STRUCT_PASSWD_PW_GECOS
+	fake.pw_gecos = "NOUSER";
+#endif
+	fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
+	fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
+#ifdef HAVE_STRUCT_PASSWD_PW_CLASS
+	fake.pw_class = "";
+#endif
+	fake.pw_dir = "/nonexist";
+	fake.pw_shell = "/nonexist";
+	done = 1;
+
+	return (&fake);
+}
+
+/*
+ * Returns the remote DNS hostname as a string. The returned string must not
+ * be freed. NB. this will usually trigger a DNS query the first time it is
+ * called.
+ * This function does additional checks on the hostname to mitigate some
+ * attacks on based on conflation of hostnames and IP addresses.
+ */
+
+static char *
+remote_hostname(struct ssh *ssh)
+{
+	struct sockaddr_storage from;
+	socklen_t fromlen;
+	struct addrinfo hints, *ai, *aitop;
+	char name[NI_MAXHOST], ntop2[NI_MAXHOST];
+	const char *ntop = ssh_remote_ipaddr(ssh);
+
+	/* Get IP address of client. */
+	fromlen = sizeof(from);
+	memset(&from, 0, sizeof(from));
+	if (getpeername(ssh_packet_get_connection_in(ssh),
+	    (struct sockaddr *)&from, &fromlen) == -1) {
+		debug("getpeername failed: %.100s", strerror(errno));
+		return xstrdup(ntop);
+	}
+
+	ipv64_normalise_mapped(&from, &fromlen);
+	if (from.ss_family == AF_INET6)
+		fromlen = sizeof(struct sockaddr_in6);
+
+	debug3("Trying to reverse map address %.100s.", ntop);
+	/* Map the IP address to a host name. */
+	if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
+	    NULL, 0, NI_NAMEREQD) != 0) {
+		/* Host name not found.  Use ip address. */
+		return xstrdup(ntop);
+	}
+
+	/*
+	 * if reverse lookup result looks like a numeric hostname,
+	 * someone is trying to trick us by PTR record like following:
+	 *	1.1.1.10.in-addr.arpa.	IN PTR	2.3.4.5
+	 */
+	memset(&hints, 0, sizeof(hints));
+	hints.ai_socktype = SOCK_DGRAM;	/*dummy*/
+	hints.ai_flags = AI_NUMERICHOST;
+	if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
+		logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
+		    name, ntop);
+		freeaddrinfo(ai);
+		return xstrdup(ntop);
+	}
+
+	/* Names are stored in lowercase. */
+	lowercase(name);
+
+	/*
+	 * Map it back to an IP address and check that the given
+	 * address actually is an address of this host.  This is
+	 * necessary because anyone with access to a name server can
+	 * define arbitrary names for an IP address. Mapping from
+	 * name to IP address can be trusted better (but can still be
+	 * fooled if the intruder has access to the name server of
+	 * the domain).
+	 */
+	memset(&hints, 0, sizeof(hints));
+	hints.ai_family = from.ss_family;
+	hints.ai_socktype = SOCK_STREAM;
+	if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
+		logit("reverse mapping checking getaddrinfo for %.700s "
+		    "[%s] failed.", name, ntop);
+		return xstrdup(ntop);
+	}
+	/* Look for the address from the list of addresses. */
+	for (ai = aitop; ai; ai = ai->ai_next) {
+		if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
+		    sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
+		    (strcmp(ntop, ntop2) == 0))
+				break;
+	}
+	freeaddrinfo(aitop);
+	/* If we reached the end of the list, the address was not there. */
+	if (ai == NULL) {
+		/* Address not found for the host name. */
+		logit("Address %.100s maps to %.600s, but this does not "
+		    "map back to the address.", ntop, name);
+		return xstrdup(ntop);
+	}
+	return xstrdup(name);
+}
+
+/*
+ * Return the canonical name of the host in the other side of the current
+ * connection.  The host name is cached, so it is efficient to call this
+ * several times.
+ */
+
+const char *
+auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
+{
+	static char *dnsname;
+
+	if (!use_dns)
+		return ssh_remote_ipaddr(ssh);
+	else if (dnsname != NULL)
+		return dnsname;
+	else {
+		dnsname = remote_hostname(ssh);
+		return dnsname;
+	}
+}
+
+/* These functions link key/cert options to the auth framework */
+
+/* Log sshauthopt options locally and (optionally) for remote transmission */
+void
+auth_log_authopts(const char *loc, const struct sshauthopt *opts, int do_remote)
+{
+	int do_env = options.permit_user_env && opts->nenv > 0;
+	int do_permitopen = opts->npermitopen > 0 &&
+	    (options.allow_tcp_forwarding & FORWARD_LOCAL) != 0;
+	int do_permitlisten = opts->npermitlisten > 0 &&
+	    (options.allow_tcp_forwarding & FORWARD_REMOTE) != 0;
+	size_t i;
+	char msg[1024], buf[64];
+
+	snprintf(buf, sizeof(buf), "%d", opts->force_tun_device);
+	/* Try to keep this alphabetically sorted */
+	snprintf(msg, sizeof(msg), "key options:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
+	    opts->permit_agent_forwarding_flag ? " agent-forwarding" : "",
+	    opts->force_command == NULL ? "" : " command",
+	    do_env ?  " environment" : "",
+	    opts->valid_before == 0 ? "" : "expires",
+	    opts->no_require_user_presence ? " no-touch-required" : "",
+	    do_permitopen ?  " permitopen" : "",
+	    do_permitlisten ?  " permitlisten" : "",
+	    opts->permit_port_forwarding_flag ? " port-forwarding" : "",
+	    opts->cert_principals == NULL ? "" : " principals",
+	    opts->permit_pty_flag ? " pty" : "",
+	    opts->require_verify ? " uv" : "",
+	    opts->force_tun_device == -1 ? "" : " tun=",
+	    opts->force_tun_device == -1 ? "" : buf,
+	    opts->permit_user_rc ? " user-rc" : "",
+	    opts->permit_x11_forwarding_flag ? " x11-forwarding" : "");
+
+	debug("%s: %s", loc, msg);
+	if (do_remote)
+		auth_debug_add("%s: %s", loc, msg);
+
+	if (options.permit_user_env) {
+		for (i = 0; i < opts->nenv; i++) {
+			debug("%s: environment: %s", loc, opts->env[i]);
+			if (do_remote) {
+				auth_debug_add("%s: environment: %s",
+				    loc, opts->env[i]);
+			}
+		}
+	}
+
+	/* Go into a little more details for the local logs. */
+	if (opts->valid_before != 0) {
+		format_absolute_time(opts->valid_before, buf, sizeof(buf));
+		debug("%s: expires at %s", loc, buf);
+	}
+	if (opts->cert_principals != NULL) {
+		debug("%s: authorized principals: \"%s\"",
+		    loc, opts->cert_principals);
+	}
+	if (opts->force_command != NULL)
+		debug("%s: forced command: \"%s\"", loc, opts->force_command);
+	if (do_permitopen) {
+		for (i = 0; i < opts->npermitopen; i++) {
+			debug("%s: permitted open: %s",
+			    loc, opts->permitopen[i]);
+		}
+	}
+	if (do_permitlisten) {
+		for (i = 0; i < opts->npermitlisten; i++) {
+			debug("%s: permitted listen: %s",
+			    loc, opts->permitlisten[i]);
+		}
+	}
+}
+
+/* Activate a new set of key/cert options; merging with what is there. */
+int
+auth_activate_options(struct ssh *ssh, struct sshauthopt *opts)
+{
+	struct sshauthopt *old = auth_opts;
+	const char *emsg = NULL;
+
+	debug_f("setting new authentication options");
+	if ((auth_opts = sshauthopt_merge(old, opts, &emsg)) == NULL) {
+		error("Inconsistent authentication options: %s", emsg);
+		return -1;
+	}
+	return 0;
+}
+
+/* Disable forwarding, etc for the session */
+void
+auth_restrict_session(struct ssh *ssh)
+{
+	struct sshauthopt *restricted;
+
+	debug_f("restricting session");
+
+	/* A blank sshauthopt defaults to permitting nothing */
+	if ((restricted = sshauthopt_new()) == NULL)
+		fatal_f("sshauthopt_new failed");
+	restricted->permit_pty_flag = 1;
+	restricted->restricted = 1;
+
+	if (auth_activate_options(ssh, restricted) != 0)
+		fatal_f("failed to restrict session");
+	sshauthopt_free(restricted);
+}