Adding upstream version 1:9.2p1.upstream/1%9.2p1upstream

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

1 files changed, 815 insertions, 0 deletions

diff --git a/auth2-pubkey.c b/auth2-pubkey.c
new file mode 100644
index 0000000..5d59feb
--- /dev/null
+++ b/auth2-pubkey.c
@@ -0,0 +1,815 @@
+/* $OpenBSD: auth2-pubkey.c,v 1.117 2022/09/17 10:34:29 djm Exp $ */
+/*
+ * Copyright (c) 2000 Markus Friedl.  All rights reserved.
+ * Copyright (c) 2010 Damien Miller.  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 <stdlib.h>
+#include <errno.h>
+#ifdef HAVE_PATHS_H
+# include <paths.h>
+#endif
+#include <pwd.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <limits.h>
+
+#include "xmalloc.h"
+#include "ssh.h"
+#include "ssh2.h"
+#include "packet.h"
+#include "kex.h"
+#include "sshbuf.h"
+#include "log.h"
+#include "misc.h"
+#include "servconf.h"
+#include "compat.h"
+#include "sshkey.h"
+#include "hostfile.h"
+#include "auth.h"
+#include "pathnames.h"
+#include "uidswap.h"
+#include "auth-options.h"
+#include "canohost.h"
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+#include "monitor_wrap.h"
+#include "authfile.h"
+#include "match.h"
+#include "ssherr.h"
+#include "channels.h" /* XXX for session.h */
+#include "session.h" /* XXX for child_set_env(); refactor? */
+#include "sk-api.h"
+
+/* import */
+extern ServerOptions options;
+
+static char *
+format_key(const struct sshkey *key)
+{
+	char *ret, *fp = sshkey_fingerprint(key,
+	    options.fingerprint_hash, SSH_FP_DEFAULT);
+
+	xasprintf(&ret, "%s %s", sshkey_type(key), fp);
+	free(fp);
+	return ret;
+}
+
+static int
+userauth_pubkey(struct ssh *ssh, const char *method)
+{
+	Authctxt *authctxt = ssh->authctxt;
+	struct passwd *pw = authctxt->pw;
+	struct sshbuf *b = NULL;
+	struct sshkey *key = NULL, *hostkey = NULL;
+	char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
+	u_char *pkblob = NULL, *sig = NULL, have_sig;
+	size_t blen, slen;
+	int hostbound, r, pktype;
+	int req_presence = 0, req_verify = 0, authenticated = 0;
+	struct sshauthopt *authopts = NULL;
+	struct sshkey_sig_details *sig_details = NULL;
+
+	hostbound = strcmp(method, "publickey-hostbound-v00@openssh.com") == 0;
+
+	if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
+	    (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
+	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
+		fatal_fr(r, "parse %s packet", method);
+
+	/* hostbound auth includes the hostkey offered at initial KEX */
+	if (hostbound) {
+		if ((r = sshpkt_getb_froms(ssh, &b)) != 0 ||
+		    (r = sshkey_fromb(b, &hostkey)) != 0)
+			fatal_fr(r, "parse %s hostkey", method);
+		if (ssh->kex->initial_hostkey == NULL)
+			fatal_f("internal error: initial hostkey not recorded");
+		if (!sshkey_equal(hostkey, ssh->kex->initial_hostkey))
+			fatal_f("%s packet contained wrong host key", method);
+		sshbuf_free(b);
+		b = NULL;
+	}
+
+	if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
+		char *keystring;
+		struct sshbuf *pkbuf;
+
+		if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL)
+			fatal_f("sshbuf_from failed");
+		if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL)
+			fatal_f("sshbuf_dtob64 failed");
+		debug2_f("%s user %s %s public key %s %s",
+		    authctxt->valid ? "valid" : "invalid", authctxt->user,
+		    have_sig ? "attempting" : "querying", pkalg, keystring);
+		sshbuf_free(pkbuf);
+		free(keystring);
+	}
+
+	pktype = sshkey_type_from_name(pkalg);
+	if (pktype == KEY_UNSPEC) {
+		/* this is perfectly legal */
+		verbose_f("unsupported public key algorithm: %s", pkalg);
+		goto done;
+	}
+	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
+		error_fr(r, "parse key");
+		goto done;
+	}
+	if (key == NULL) {
+		error_f("cannot decode key: %s", pkalg);
+		goto done;
+	}
+	if (key->type != pktype) {
+		error_f("type mismatch for decoded key "
+		    "(received %d, expected %d)", key->type, pktype);
+		goto done;
+	}
+	if (sshkey_type_plain(key->type) == KEY_RSA &&
+	    (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
+		logit("Refusing RSA key because client uses unsafe "
+		    "signature scheme");
+		goto done;
+	}
+	if (auth2_key_already_used(authctxt, key)) {
+		logit("refusing previously-used %s key", sshkey_type(key));
+		goto done;
+	}
+	if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
+		logit_f("signature algorithm %s not in "
+		    "PubkeyAcceptedAlgorithms", pkalg);
+		goto done;
+	}
+	if ((r = sshkey_check_cert_sigtype(key,
+	    options.ca_sign_algorithms)) != 0) {
+		logit_fr(r, "certificate signature algorithm %s",
+		    (key->cert == NULL || key->cert->signature_type == NULL) ?
+		    "(null)" : key->cert->signature_type);
+		goto done;
+	}
+	if ((r = sshkey_check_rsa_length(key,
+	    options.required_rsa_size)) != 0) {
+		logit_r(r, "refusing %s key", sshkey_type(key));
+		goto done;
+	}
+	key_s = format_key(key);
+	if (sshkey_is_cert(key))
+		ca_s = format_key(key->cert->signature_key);
+
+	if (have_sig) {
+		debug3_f("%s have %s signature for %s%s%s",
+		    method, pkalg, key_s,
+		    ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
+		if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
+		    (r = sshpkt_get_end(ssh)) != 0)
+			fatal_fr(r, "parse signature packet");
+		if ((b = sshbuf_new()) == NULL)
+			fatal_f("sshbuf_new failed");
+		if (ssh->compat & SSH_OLD_SESSIONID) {
+			if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0)
+				fatal_fr(r, "put old session id");
+		} else {
+			if ((r = sshbuf_put_stringb(b,
+			    ssh->kex->session_id)) != 0)
+				fatal_fr(r, "put session id");
+		}
+		if (!authctxt->valid || authctxt->user == NULL) {
+			debug2_f("disabled because of invalid user");
+			goto done;
+		}
+		/* reconstruct packet */
+		xasprintf(&userstyle, "%s%s%s", authctxt->user,
+		    authctxt->style ? ":" : "",
+		    authctxt->style ? authctxt->style : "");
+		if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
+		    (r = sshbuf_put_cstring(b, userstyle)) != 0 ||
+		    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
+		    (r = sshbuf_put_cstring(b, method)) != 0 ||
+		    (r = sshbuf_put_u8(b, have_sig)) != 0 ||
+		    (r = sshbuf_put_cstring(b, pkalg)) != 0 ||
+		    (r = sshbuf_put_string(b, pkblob, blen)) != 0)
+			fatal_fr(r, "reconstruct %s packet", method);
+		if (hostbound &&
+		    (r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0)
+			fatal_fr(r, "reconstruct %s packet", method);
+#ifdef DEBUG_PK
+		sshbuf_dump(b, stderr);
+#endif
+		/* test for correct signature */
+		authenticated = 0;
+		if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
+		    PRIVSEP(sshkey_verify(key, sig, slen,
+		    sshbuf_ptr(b), sshbuf_len(b),
+		    (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
+		    ssh->compat, &sig_details)) == 0) {
+			authenticated = 1;
+		}
+		if (authenticated == 1 && sig_details != NULL) {
+			auth2_record_info(authctxt, "signature count = %u",
+			    sig_details->sk_counter);
+			debug_f("sk_counter = %u, sk_flags = 0x%02x",
+			    sig_details->sk_counter, sig_details->sk_flags);
+			req_presence = (options.pubkey_auth_options &
+			    PUBKEYAUTH_TOUCH_REQUIRED) ||
+			    !authopts->no_require_user_presence;
+			if (req_presence && (sig_details->sk_flags &
+			    SSH_SK_USER_PRESENCE_REQD) == 0) {
+				error("public key %s signature for %s%s from "
+				    "%.128s port %d rejected: user presence "
+				    "(authenticator touch) requirement "
+				    "not met ", key_s,
+				    authctxt->valid ? "" : "invalid user ",
+				    authctxt->user, ssh_remote_ipaddr(ssh),
+				    ssh_remote_port(ssh));
+				authenticated = 0;
+				goto done;
+			}
+			req_verify = (options.pubkey_auth_options &
+			    PUBKEYAUTH_VERIFY_REQUIRED) ||
+			    authopts->require_verify;
+			if (req_verify && (sig_details->sk_flags &
+			    SSH_SK_USER_VERIFICATION_REQD) == 0) {
+				error("public key %s signature for %s%s from "
+				    "%.128s port %d rejected: user "
+				    "verification requirement not met ", key_s,
+				    authctxt->valid ? "" : "invalid user ",
+				    authctxt->user, ssh_remote_ipaddr(ssh),
+				    ssh_remote_port(ssh));
+				authenticated = 0;
+				goto done;
+			}
+		}
+		auth2_record_key(authctxt, authenticated, key);
+	} else {
+		debug_f("%s test pkalg %s pkblob %s%s%s", method, pkalg, key_s,
+		    ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
+
+		if ((r = sshpkt_get_end(ssh)) != 0)
+			fatal_fr(r, "parse packet");
+
+		if (!authctxt->valid || authctxt->user == NULL) {
+			debug2_f("disabled because of invalid user");
+			goto done;
+		}
+		/* XXX fake reply and always send PK_OK ? */
+		/*
+		 * XXX this allows testing whether a user is allowed
+		 * to login: if you happen to have a valid pubkey this
+		 * message is sent. the message is NEVER sent at all
+		 * if a user is not allowed to login. is this an
+		 * issue? -markus
+		 */
+		if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) {
+			if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
+			    != 0 ||
+			    (r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
+			    (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
+			    (r = sshpkt_send(ssh)) != 0 ||
+			    (r = ssh_packet_write_wait(ssh)) != 0)
+				fatal_fr(r, "send packet");
+			authctxt->postponed = 1;
+		}
+	}
+done:
+	if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
+		debug_f("key options inconsistent with existing");
+		authenticated = 0;
+	}
+	debug2_f("authenticated %d pkalg %s", authenticated, pkalg);
+
+	sshbuf_free(b);
+	sshauthopt_free(authopts);
+	sshkey_free(key);
+	sshkey_free(hostkey);
+	free(userstyle);
+	free(pkalg);
+	free(pkblob);
+	free(key_s);
+	free(ca_s);
+	free(sig);
+	sshkey_sig_details_free(sig_details);
+	return authenticated;
+}
+
+static int
+match_principals_file(struct passwd *pw, char *file,
+    struct sshkey_cert *cert, struct sshauthopt **authoptsp)
+{
+	FILE *f;
+	int success;
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+
+	temporarily_use_uid(pw);
+	debug("trying authorized principals file %s", file);
+	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
+		restore_uid();
+		return 0;
+	}
+	success = auth_process_principals(f, file, cert, authoptsp);
+	fclose(f);
+	restore_uid();
+	return success;
+}
+
+/*
+ * Checks whether principal is allowed in output of command.
+ * returns 1 if the principal is allowed or 0 otherwise.
+ */
+static int
+match_principals_command(struct passwd *user_pw,
+    const struct sshkey *key, struct sshauthopt **authoptsp)
+{
+	struct passwd *runas_pw = NULL;
+	const struct sshkey_cert *cert = key->cert;
+	FILE *f = NULL;
+	int r, ok, found_principal = 0;
+	int i, ac = 0, uid_swapped = 0;
+	pid_t pid;
+	char *tmp, *username = NULL, *command = NULL, **av = NULL;
+	char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
+	char serial_s[32], uidstr[32];
+	void (*osigchld)(int);
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+	if (options.authorized_principals_command == NULL)
+		return 0;
+	if (options.authorized_principals_command_user == NULL) {
+		error("No user for AuthorizedPrincipalsCommand specified, "
+		    "skipping");
+		return 0;
+	}
+
+	/*
+	 * 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);
+
+	/* Prepare and verify the user for the command */
+	username = percent_expand(options.authorized_principals_command_user,
+	    "u", user_pw->pw_name, (char *)NULL);
+	runas_pw = getpwnam(username);
+	if (runas_pw == NULL) {
+		error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
+		    username, strerror(errno));
+		goto out;
+	}
+
+	/* Turn the command into an argument vector */
+	if (argv_split(options.authorized_principals_command,
+	    &ac, &av, 0) != 0) {
+		error("AuthorizedPrincipalsCommand \"%s\" contains "
+		    "invalid quotes", options.authorized_principals_command);
+		goto out;
+	}
+	if (ac == 0) {
+		error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
+		    options.authorized_principals_command);
+		goto out;
+	}
+	if ((ca_fp = sshkey_fingerprint(cert->signature_key,
+	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
+		error_f("sshkey_fingerprint failed");
+		goto out;
+	}
+	if ((key_fp = sshkey_fingerprint(key,
+	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
+		error_f("sshkey_fingerprint failed");
+		goto out;
+	}
+	if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
+		error_fr(r, "sshkey_to_base64 failed");
+		goto out;
+	}
+	if ((r = sshkey_to_base64(key, &keytext)) != 0) {
+		error_fr(r, "sshkey_to_base64 failed");
+		goto out;
+	}
+	snprintf(serial_s, sizeof(serial_s), "%llu",
+	    (unsigned long long)cert->serial);
+	snprintf(uidstr, sizeof(uidstr), "%llu",
+	    (unsigned long long)user_pw->pw_uid);
+	for (i = 1; i < ac; i++) {
+		tmp = percent_expand(av[i],
+		    "U", uidstr,
+		    "u", user_pw->pw_name,
+		    "h", user_pw->pw_dir,
+		    "t", sshkey_ssh_name(key),
+		    "T", sshkey_ssh_name(cert->signature_key),
+		    "f", key_fp,
+		    "F", ca_fp,
+		    "k", keytext,
+		    "K", catext,
+		    "i", cert->key_id,
+		    "s", serial_s,
+		    (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("AuthorizedPrincipalsCommand", command,
+	    ac, av, &f,
+	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
+	    runas_pw, temporarily_use_uid, restore_uid)) == 0)
+		goto out;
+
+	uid_swapped = 1;
+	temporarily_use_uid(runas_pw);
+
+	ok = auth_process_principals(f, "(command)", cert, authoptsp);
+
+	fclose(f);
+	f = NULL;
+
+	if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
+		goto out;
+
+	/* Read completed successfully */
+	found_principal = ok;
+ out:
+	if (f != NULL)
+		fclose(f);
+	ssh_signal(SIGCHLD, osigchld);
+	for (i = 0; i < ac; i++)
+		free(av[i]);
+	free(av);
+	if (uid_swapped)
+		restore_uid();
+	free(command);
+	free(username);
+	free(ca_fp);
+	free(key_fp);
+	free(catext);
+	free(keytext);
+	return found_principal;
+}
+
+/* Authenticate a certificate key against TrustedUserCAKeys */
+static int
+user_cert_trusted_ca(struct passwd *pw, struct sshkey *key,
+    const char *remote_ip, const char *remote_host,
+    struct sshauthopt **authoptsp)
+{
+	char *ca_fp, *principals_file = NULL;
+	const char *reason;
+	struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
+	struct sshauthopt *final_opts = NULL;
+	int r, ret = 0, found_principal = 0, use_authorized_principals;
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+
+	if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
+		return 0;
+
+	if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
+	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
+		return 0;
+
+	if ((r = sshkey_in_file(key->cert->signature_key,
+	    options.trusted_user_ca_keys, 1, 0)) != 0) {
+		debug2_fr(r, "CA %s %s is not listed in %s",
+		    sshkey_type(key->cert->signature_key), ca_fp,
+		    options.trusted_user_ca_keys);
+		goto out;
+	}
+	/*
+	 * If AuthorizedPrincipals is in use, then compare the certificate
+	 * principals against the names in that file rather than matching
+	 * against the username.
+	 */
+	if ((principals_file = authorized_principals_file(pw)) != NULL) {
+		if (match_principals_file(pw, principals_file,
+		    key->cert, &principals_opts))
+			found_principal = 1;
+	}
+	/* Try querying command if specified */
+	if (!found_principal && match_principals_command(pw, key,
+	    &principals_opts))
+		found_principal = 1;
+	/* If principals file or command is specified, then require a match */
+	use_authorized_principals = principals_file != NULL ||
+	    options.authorized_principals_command != NULL;
+	if (!found_principal && use_authorized_principals) {
+		reason = "Certificate does not contain an authorized principal";
+		goto fail_reason;
+	}
+	if (use_authorized_principals && principals_opts == NULL)
+		fatal_f("internal error: missing principals_opts");
+	if (sshkey_cert_check_authority_now(key, 0, 1, 0,
+	    use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
+		goto fail_reason;
+
+	/* Check authority from options in key and from principals file/cmd */
+	if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
+		reason = "Invalid certificate options";
+		goto fail_reason;
+	}
+	if (auth_authorise_keyopts(pw, cert_opts, 0,
+	    remote_ip, remote_host, "cert") != 0) {
+		reason = "Refused by certificate options";
+		goto fail_reason;
+	}
+	if (principals_opts == NULL) {
+		final_opts = cert_opts;
+		cert_opts = NULL;
+	} else {
+		if (auth_authorise_keyopts(pw, principals_opts, 0,
+		    remote_ip, remote_host, "principals") != 0) {
+			reason = "Refused by certificate principals options";
+			goto fail_reason;
+		}
+		if ((final_opts = sshauthopt_merge(principals_opts,
+		    cert_opts, &reason)) == NULL) {
+ fail_reason:
+			error("%s", reason);
+			auth_debug_add("%s", reason);
+			goto out;
+		}
+	}
+
+	/* Success */
+	verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
+	    "%s CA %s via %s", key->cert->key_id,
+	    (unsigned long long)key->cert->serial,
+	    sshkey_type(key->cert->signature_key), ca_fp,
+	    options.trusted_user_ca_keys);
+	if (authoptsp != NULL) {
+		*authoptsp = final_opts;
+		final_opts = NULL;
+	}
+	ret = 1;
+ out:
+	sshauthopt_free(principals_opts);
+	sshauthopt_free(cert_opts);
+	sshauthopt_free(final_opts);
+	free(principals_file);
+	free(ca_fp);
+	return ret;
+}
+
+/*
+ * Checks whether key is allowed in file.
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
+static int
+user_key_allowed2(struct passwd *pw, struct sshkey *key,
+    char *file, const char *remote_ip, const char *remote_host,
+    struct sshauthopt **authoptsp)
+{
+	FILE *f;
+	int found_key = 0;
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+
+	/* Temporarily use the user's uid. */
+	temporarily_use_uid(pw);
+
+	debug("trying public key file %s", file);
+	if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
+		found_key = auth_check_authkeys_file(pw, f, file,
+		    key, remote_ip, remote_host, authoptsp);
+		fclose(f);
+	}
+
+	restore_uid();
+	return found_key;
+}
+
+/*
+ * Checks whether key is allowed in output of command.
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
+static int
+user_key_command_allowed2(struct passwd *user_pw, struct sshkey *key,
+    const char *remote_ip, const char *remote_host,
+    struct sshauthopt **authoptsp)
+{
+	struct passwd *runas_pw = NULL;
+	FILE *f = NULL;
+	int r, ok, found_key = 0;
+	int i, uid_swapped = 0, ac = 0;
+	pid_t pid;
+	char *username = NULL, *key_fp = NULL, *keytext = NULL;
+	char uidstr[32], *tmp, *command = NULL, **av = NULL;
+	void (*osigchld)(int);
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+	if (options.authorized_keys_command == NULL)
+		return 0;
+	if (options.authorized_keys_command_user == NULL) {
+		error("No user for AuthorizedKeysCommand specified, skipping");
+		return 0;
+	}
+
+	/*
+	 * 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);
+
+	/* Prepare and verify the user for the command */
+	username = percent_expand(options.authorized_keys_command_user,
+	    "u", user_pw->pw_name, (char *)NULL);
+	runas_pw = getpwnam(username);
+	if (runas_pw == NULL) {
+		error("AuthorizedKeysCommandUser \"%s\" not found: %s",
+		    username, strerror(errno));
+		goto out;
+	}
+
+	/* Prepare AuthorizedKeysCommand */
+	if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
+	    SSH_FP_DEFAULT)) == NULL) {
+		error_f("sshkey_fingerprint failed");
+		goto out;
+	}
+	if ((r = sshkey_to_base64(key, &keytext)) != 0) {
+		error_fr(r, "sshkey_to_base64 failed");
+		goto out;
+	}
+
+	/* Turn the command into an argument vector */
+	if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) {
+		error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
+		    options.authorized_keys_command);
+		goto out;
+	}
+	if (ac == 0) {
+		error("AuthorizedKeysCommand \"%s\" yielded no arguments",
+		    options.authorized_keys_command);
+		goto out;
+	}
+	snprintf(uidstr, sizeof(uidstr), "%llu",
+	    (unsigned long long)user_pw->pw_uid);
+	for (i = 1; i < ac; i++) {
+		tmp = percent_expand(av[i],
+		    "U", uidstr,
+		    "u", user_pw->pw_name,
+		    "h", user_pw->pw_dir,
+		    "t", sshkey_ssh_name(key),
+		    "f", key_fp,
+		    "k", 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 AuthorizedKeysCommand was run without arguments
+	 * then fall back to the old behaviour of passing the
+	 * target username as a single argument.
+	 */
+	if (ac == 1) {
+		av = xreallocarray(av, ac + 2, sizeof(*av));
+		av[1] = xstrdup(user_pw->pw_name);
+		av[2] = NULL;
+		/* Fix up command too, since it is used in log messages */
+		free(command);
+		xasprintf(&command, "%s %s", av[0], av[1]);
+	}
+
+	if ((pid = subprocess("AuthorizedKeysCommand", command,
+	    ac, av, &f,
+	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
+	    runas_pw, temporarily_use_uid, restore_uid)) == 0)
+		goto out;
+
+	uid_swapped = 1;
+	temporarily_use_uid(runas_pw);
+
+	ok = auth_check_authkeys_file(user_pw, f,
+	    options.authorized_keys_command, key, remote_ip,
+	    remote_host, authoptsp);
+
+	fclose(f);
+	f = NULL;
+
+	if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
+		goto out;
+
+	/* Read completed successfully */
+	found_key = ok;
+ out:
+	if (f != NULL)
+		fclose(f);
+	ssh_signal(SIGCHLD, osigchld);
+	for (i = 0; i < ac; i++)
+		free(av[i]);
+	free(av);
+	if (uid_swapped)
+		restore_uid();
+	free(command);
+	free(username);
+	free(key_fp);
+	free(keytext);
+	return found_key;
+}
+
+/*
+ * Check whether key authenticates and authorises the user.
+ */
+int
+user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
+    int auth_attempt, struct sshauthopt **authoptsp)
+{
+	u_int success = 0, i;
+	char *file;
+	struct sshauthopt *opts = NULL;
+	const char *remote_ip = ssh_remote_ipaddr(ssh);
+	const char *remote_host = auth_get_canonical_hostname(ssh,
+	    options.use_dns);
+
+	if (authoptsp != NULL)
+		*authoptsp = NULL;
+
+	if (auth_key_is_revoked(key))
+		return 0;
+	if (sshkey_is_cert(key) &&
+	    auth_key_is_revoked(key->cert->signature_key))
+		return 0;
+
+	for (i = 0; !success && i < options.num_authkeys_files; i++) {
+		if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
+			continue;
+		file = expand_authorized_keys(
+		    options.authorized_keys_files[i], pw);
+		success = user_key_allowed2(pw, key, file,
+		    remote_ip, remote_host, &opts);
+		free(file);
+		if (!success) {
+			sshauthopt_free(opts);
+			opts = NULL;
+		}
+	}
+	if (success)
+		goto out;
+
+	if ((success = user_cert_trusted_ca(pw, key, remote_ip, remote_host,
+	    &opts)) != 0)
+		goto out;
+	sshauthopt_free(opts);
+	opts = NULL;
+
+	if ((success = user_key_command_allowed2(pw, key, remote_ip,
+	    remote_host, &opts)) != 0)
+		goto out;
+	sshauthopt_free(opts);
+	opts = NULL;
+
+ out:
+	if (success && authoptsp != NULL) {
+		*authoptsp = opts;
+		opts = NULL;
+	}
+	sshauthopt_free(opts);
+	return success;
+}
+
+Authmethod method_pubkey = {
+	"publickey",
+	"publickey-hostbound-v00@openssh.com",
+	userauth_pubkey,
+	&options.pubkey_authentication
+};