Return to auth2-pubkey.c CVS log

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Start the process of splitting sshd into separate binaries. This step
splits sshd into a listener and a session binary. More splits are
planned.

After this changes, the listener binary will validate the configuration,
load the hostkeys, listen on port 22 and manage MaxStartups only. All
session handling will be performed by a new sshd-session binary that the
listener fork+execs.

This reduces the listener process to the minimum necessary and sets us
up for future work on the sshd-session binary.

feedback/ok markus@ deraadt@

NB. if you're updating via source, please restart sshd after installing,
otherwise you run the risk of locking yourself out.

/* $OpenBSD: auth2-pubkey.c,v 1.120 2024/05/17 00:30:23 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 <sys/types.h>

#include <stdlib.h>
#include <errno.h>
#include <paths.h>
#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;
extern struct authmethod_cfg methodcfg_pubkey;

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 (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 (mm_user_key_allowed(ssh, pw, key, 1, &authopts) &&
		    mm_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 (mm_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,
    const char *conn_id, const char *rdomain, 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],
		    "C", conn_id,
		    "D", rdomain,
		    "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,
    const char *conn_id, const char *rdomain, 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,
	    conn_id, rdomain, &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,
    const char *conn_id, const char *rdomain, 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],
		    "C", conn_id,
		    "D", rdomain,
		    "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, *conn_id;
	struct sshauthopt *opts = NULL;
	const char *rdomain, *remote_ip, *remote_host;

	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;

	if ((rdomain = ssh_packet_rdomain_in(ssh)) == NULL)
		rdomain = "";
	remote_ip = ssh_remote_ipaddr(ssh);
	remote_host = auth_get_canonical_hostname(ssh, options.use_dns);
	xasprintf(&conn_id, "%s %d %s %d",
	    ssh_local_ipaddr(ssh), ssh_local_port(ssh),
	    remote_ip, ssh_remote_port(ssh));

	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,
	    conn_id, rdomain, &opts)) != 0)
		goto out;
	sshauthopt_free(opts);
	opts = NULL;

	if ((success = user_key_command_allowed2(pw, key, remote_ip,
	    remote_host, conn_id, rdomain, &opts)) != 0)
		goto out;
	sshauthopt_free(opts);
	opts = NULL;

 out:
	free(conn_id);
	if (success && authoptsp != NULL) {
		*authoptsp = opts;
		opts = NULL;
	}
	sshauthopt_free(opts);
	return success;
}

Authmethod method_pubkey = {
	&methodcfg_pubkey,
	userauth_pubkey,
};