/* $OpenBSD: auth2-hostbased.c,v 1.59 2026/09/16 00:31:27 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 "includes.h"

#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 *keyblob = NULL, *b = NULL;

  struct sshkey *key = NULL;

  char *pkalg, *cuser, *chost;

  u_char *sig;

  size_t alen, slen;

  int r, pktype, authenticated = 0;

  if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||

      (r = sshpkt_getb_froms(ssh, &keyblob)) != 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 (match_pattern_list(pkalg,

      options.hostbased_accepted_algos, 0) != 1) {

    logit_f("signature algorithm %s not in "

        "HostbasedAcceptedAlgorithms", pkalg);

    goto done;

  }

  if ((b = sshbuf_fromb(keyblob)) == NULL)

    fatal_f("sshbuf_fromb failed");

  switch ((r = sshkey_fromb_allowlist(b, &key,

      options.hostbased_accepted_algos, options.ca_sign_algorithms))) {

  case 0:

    /* ok */

    break;

  case SSH_ERR_KEY_ALG_UNSUPPORTED:

    /* This shouldn't happen unless the client is being weird */

    logit_f("key algorithm differs from signature algorithm %s and "

        "is not in HostbasedAcceptedAlgorithms", pkalg);

    goto done;

  case SSH_ERR_SIGN_ALG_UNSUPPORTED:

    logit_fr(r, "certificate signature algorithm not in "

        "CASignatureAlgorithms");

    goto done;

  default:

    error_fr(r, "parse key");

    goto done;

  }

  sshbuf_free(b);

  b = NULL;

  if (key->type != pktype || (sshkey_type_plain(pktype) == KEY_ECDSA &&

      sshkey_ecdsa_nid_from_name(pkalg) != key->ecdsa_nid)) {

    error_f("key type mismatch for decoded key "

        "(received %s, expected %s)", sshkey_ssh_name(key), pkalg);

    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_stringb(b, keyblob)) != 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);

done:

  debug2_f("authenticated %d", authenticated);

  sshkey_free(key);

  sshbuf_free(b);

  sshbuf_free(keyblob);

  free(pkalg);

  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_host(key, lookup,

       options.ca_sign_algorithms, &reason) != 0) {

    if ((fp = sshkey_fingerprint(key->cert->signature_key,

        options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)

      fatal_f("sshkey_fingerprint fail");

    error("Refusing certificate ID \"%s\" serial=%llu signed by "

        "%s CA %s: %s", key->cert->key_id,

        (unsigned long long)key->cert->serial,

        sshkey_type(key->cert->signature_key), fp, reason);

    auth_debug_add("Refused Certificate ID \"%s\" serial=%llu: %s",

        key->cert->key_id, (unsigned long long)key->cert->serial,

        reason);

    free(fp);

    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,

};