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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-hostbased.c,v 1.53 2024/05/17 00:30:23 djm 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 <sys/types.h>

#include <stdlib.h>
#include <pwd.h>
#include <string.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "ssh2.h"
#include "packet.h"
#include "kex.h"
#include "sshbuf.h"
#include "log.h"
#include "misc.h"
#include "servconf.h"
#include "sshkey.h"
#include "hostfile.h"
#include "auth.h"
#include "canohost.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "pathnames.h"
#include "ssherr.h"
#include "match.h"

/* import */
extern ServerOptions options;
extern struct authmethod_cfg methodcfg_hostbased;

static int
userauth_hostbased(struct ssh *ssh, const char *method)
{
	Authctxt *authctxt = ssh->authctxt;
	struct sshbuf *b;
	struct sshkey *key = NULL;
	char *pkalg, *cuser, *chost;
	u_char *pkblob, *sig;
	size_t alen, blen, slen;
	int r, pktype, authenticated = 0;

	/* XXX use sshkey_froms() */
	if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
	    (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
		fatal_fr(r, "parse packet");

	debug_f("cuser %s chost %s pkalg %s slen %zu",
	    cuser, chost, pkalg, slen);
#ifdef DEBUG_PK
	debug("signature:");
	sshbuf_dump_data(sig, slen, stderr);
#endif
	pktype = sshkey_type_from_name(pkalg);
	if (pktype == KEY_UNSPEC) {
		/* this is perfectly legal */
		logit_f("unsupported public key algorithm: %s",
		    pkalg);
		goto done;
	}
	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
		error_fr(r, "key_from_blob");
		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 (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
		logit_f("signature algorithm %s not in "
		    "HostbasedAcceptedAlgorithms", 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;
	}

	if (!authctxt->valid || authctxt->user == NULL) {
		debug2_f("disabled because of invalid user");
		goto done;
	}

	if ((b = sshbuf_new()) == NULL)
		fatal_f("sshbuf_new failed");
	/* reconstruct packet */
	if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
	    (r = sshbuf_put_cstring(b, method)) != 0 ||
	    (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
	    (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
	    (r = sshbuf_put_cstring(b, cuser)) != 0)
		fatal_fr(r, "reconstruct packet");
#ifdef DEBUG_PK
	sshbuf_dump(b, stderr);
#endif

	auth2_record_info(authctxt,
	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);

	/* test for allowed key and correct signature */
	authenticated = 0;
	if (mm_hostbased_key_allowed(ssh, authctxt->pw, cuser,
	    chost, key) &&
	    mm_sshkey_verify(key, sig, slen,
	    sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL) == 0)
		authenticated = 1;

	auth2_record_key(authctxt, authenticated, key);
	sshbuf_free(b);
done:
	debug2_f("authenticated %d", authenticated);
	sshkey_free(key);
	free(pkalg);
	free(pkblob);
	free(cuser);
	free(chost);
	free(sig);
	return authenticated;
}

/* return 1 if given hostkey is allowed */
int
hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
    const char *cuser, char *chost, struct sshkey *key)
{
	const char *resolvedname, *ipaddr, *lookup, *reason;
	HostStatus host_status;
	int len;
	char *fp;

	if (auth_key_is_revoked(key))
		return 0;

	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
	ipaddr = ssh_remote_ipaddr(ssh);

	debug2_f("chost %s resolvedname %s ipaddr %s",
	    chost, resolvedname, ipaddr);

	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
		debug2("stripping trailing dot from chost %s", chost);
		chost[len - 1] = '\0';
	}

	if (options.hostbased_uses_name_from_packet_only) {
		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
			debug2_f("auth_rhosts2 refused user \"%.100s\" "
			    "host \"%.100s\" (from packet)", cuser, chost);
			return 0;
		}
		lookup = chost;
	} else {
		if (strcasecmp(resolvedname, chost) != 0)
			logit("userauth_hostbased mismatch: "
			    "client sends %s, but we resolve %s to %s",
			    chost, ipaddr, resolvedname);
		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
			debug2_f("auth_rhosts2 refused "
			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
			    cuser, resolvedname, ipaddr);
			return 0;
		}
		lookup = resolvedname;
	}
	debug2_f("access allowed by auth_rhosts2");

	if (sshkey_is_cert(key) &&
	    sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
		error("%s", reason);
		auth_debug_add("%s", reason);
		return 0;
	}

	host_status = check_key_in_hostfiles(pw, key, lookup,
	    _PATH_SSH_SYSTEM_HOSTFILE,
	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);

	/* backward compat if no key has been found. */
	if (host_status == HOST_NEW) {
		host_status = check_key_in_hostfiles(pw, key, lookup,
		    _PATH_SSH_SYSTEM_HOSTFILE2,
		    options.ignore_user_known_hosts ? NULL :
		    _PATH_SSH_USER_HOSTFILE2);
	}

	if (host_status == HOST_OK) {
		if (sshkey_is_cert(key)) {
			if ((fp = sshkey_fingerprint(key->cert->signature_key,
			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
				fatal_f("sshkey_fingerprint fail");
			verbose("Accepted certificate ID \"%s\" signed by "
			    "%s CA %s from %s@%s", key->cert->key_id,
			    sshkey_type(key->cert->signature_key), fp,
			    cuser, lookup);
		} else {
			if ((fp = sshkey_fingerprint(key,
			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
				fatal_f("sshkey_fingerprint fail");
			verbose("Accepted %s public key %s from %s@%s",
			    sshkey_type(key), fp, cuser, lookup);
		}
		free(fp);
	}

	return (host_status == HOST_OK);
}

Authmethod method_hostbased = {
	&methodcfg_hostbased,
	userauth_hostbased,
};