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-rw-r--r--auth2-hostbased.c266
1 files changed, 266 insertions, 0 deletions
diff --git a/auth2-hostbased.c b/auth2-hostbased.c
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+++ b/auth2-hostbased.c
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+/* $OpenBSD: auth2-hostbased.c,v 1.50 2022/09/17 10:34:29 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 "compat.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;
+
+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 (sshkey_type_plain(key->type) == KEY_RSA &&
+ (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
+ error("Refusing RSA key because peer uses unsafe "
+ "signature format");
+ 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 (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser,
+ chost, key)) &&
+ PRIVSEP(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 = {
+ "hostbased",
+ NULL,
+ userauth_hostbased,
+ &options.hostbased_authentication
+};
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-30 01:27:26 +0000