upstream) and a number of security fixes which we had already backported. MFC after: 1 week
688 lines
18 KiB
C
688 lines
18 KiB
C
/* $OpenBSD: auth2-pubkey.c,v 1.41 2014/07/15 15:54:14 millert Exp $ */
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/*
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* Copyright (c) 2000 Markus Friedl. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "includes.h"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/wait.h>
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#include <errno.h>
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#include <fcntl.h>
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#ifdef HAVE_PATHS_H
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# include <paths.h>
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#endif
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#include <pwd.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdarg.h>
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#include <string.h>
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#include <time.h>
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#include <unistd.h>
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#include "xmalloc.h"
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#include "ssh.h"
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#include "ssh2.h"
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#include "packet.h"
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#include "buffer.h"
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#include "log.h"
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#include "misc.h"
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#include "servconf.h"
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#include "compat.h"
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#include "key.h"
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#include "hostfile.h"
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#include "auth.h"
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#include "pathnames.h"
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#include "uidswap.h"
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#include "auth-options.h"
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#include "canohost.h"
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#ifdef GSSAPI
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#include "ssh-gss.h"
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#endif
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#include "monitor_wrap.h"
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#include "authfile.h"
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#include "match.h"
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/* import */
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extern ServerOptions options;
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extern u_char *session_id2;
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extern u_int session_id2_len;
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static int
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userauth_pubkey(Authctxt *authctxt)
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{
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Buffer b;
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Key *key = NULL;
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char *pkalg, *userstyle;
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u_char *pkblob, *sig;
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u_int alen, blen, slen;
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int have_sig, pktype;
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int authenticated = 0;
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if (!authctxt->valid) {
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debug2("userauth_pubkey: disabled because of invalid user");
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return 0;
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}
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have_sig = packet_get_char();
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if (datafellows & SSH_BUG_PKAUTH) {
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debug2("userauth_pubkey: SSH_BUG_PKAUTH");
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/* no explicit pkalg given */
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pkblob = packet_get_string(&blen);
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buffer_init(&b);
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buffer_append(&b, pkblob, blen);
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/* so we have to extract the pkalg from the pkblob */
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pkalg = buffer_get_string(&b, &alen);
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buffer_free(&b);
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} else {
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pkalg = packet_get_string(&alen);
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pkblob = packet_get_string(&blen);
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}
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pktype = key_type_from_name(pkalg);
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if (pktype == KEY_UNSPEC) {
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/* this is perfectly legal */
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logit("userauth_pubkey: unsupported public key algorithm: %s",
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pkalg);
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goto done;
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}
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key = key_from_blob(pkblob, blen);
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if (key == NULL) {
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error("userauth_pubkey: cannot decode key: %s", pkalg);
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goto done;
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}
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if (key->type != pktype) {
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error("userauth_pubkey: type mismatch for decoded key "
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"(received %d, expected %d)", key->type, pktype);
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goto done;
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}
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if (key_type_plain(key->type) == KEY_RSA &&
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(datafellows & SSH_BUG_RSASIGMD5) != 0) {
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logit("Refusing RSA key because client uses unsafe "
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"signature scheme");
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goto done;
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}
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if (have_sig) {
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sig = packet_get_string(&slen);
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packet_check_eom();
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buffer_init(&b);
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if (datafellows & SSH_OLD_SESSIONID) {
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buffer_append(&b, session_id2, session_id2_len);
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} else {
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buffer_put_string(&b, session_id2, session_id2_len);
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}
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/* reconstruct packet */
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buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
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xasprintf(&userstyle, "%s%s%s", authctxt->user,
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authctxt->style ? ":" : "",
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authctxt->style ? authctxt->style : "");
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buffer_put_cstring(&b, userstyle);
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free(userstyle);
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buffer_put_cstring(&b,
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datafellows & SSH_BUG_PKSERVICE ?
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"ssh-userauth" :
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authctxt->service);
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if (datafellows & SSH_BUG_PKAUTH) {
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buffer_put_char(&b, have_sig);
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} else {
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buffer_put_cstring(&b, "publickey");
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buffer_put_char(&b, have_sig);
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buffer_put_cstring(&b, pkalg);
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}
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buffer_put_string(&b, pkblob, blen);
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#ifdef DEBUG_PK
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buffer_dump(&b);
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#endif
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pubkey_auth_info(authctxt, key, NULL);
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/* test for correct signature */
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authenticated = 0;
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if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
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PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
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buffer_len(&b))) == 1)
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authenticated = 1;
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buffer_free(&b);
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free(sig);
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} else {
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debug("test whether pkalg/pkblob are acceptable");
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packet_check_eom();
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/* XXX fake reply and always send PK_OK ? */
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/*
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* XXX this allows testing whether a user is allowed
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* to login: if you happen to have a valid pubkey this
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* message is sent. the message is NEVER sent at all
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* if a user is not allowed to login. is this an
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* issue? -markus
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*/
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if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
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packet_start(SSH2_MSG_USERAUTH_PK_OK);
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packet_put_string(pkalg, alen);
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packet_put_string(pkblob, blen);
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packet_send();
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packet_write_wait();
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authctxt->postponed = 1;
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}
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}
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if (authenticated != 1)
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auth_clear_options();
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done:
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debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
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if (key != NULL)
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key_free(key);
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free(pkalg);
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free(pkblob);
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return authenticated;
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}
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void
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pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...)
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{
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char *fp, *extra;
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va_list ap;
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int i;
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extra = NULL;
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if (fmt != NULL) {
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va_start(ap, fmt);
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i = vasprintf(&extra, fmt, ap);
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va_end(ap);
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if (i < 0 || extra == NULL)
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fatal("%s: vasprintf failed", __func__);
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}
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if (key_is_cert(key)) {
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fp = key_fingerprint(key->cert->signature_key,
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SSH_FP_MD5, SSH_FP_HEX);
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auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
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key_type(key), key->cert->key_id,
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(unsigned long long)key->cert->serial,
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key_type(key->cert->signature_key), fp,
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extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
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free(fp);
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} else {
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fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
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auth_info(authctxt, "%s %s%s%s", key_type(key), fp,
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extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
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free(fp);
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}
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free(extra);
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}
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static int
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match_principals_option(const char *principal_list, struct sshkey_cert *cert)
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{
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char *result;
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u_int i;
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/* XXX percent_expand() sequences for authorized_principals? */
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for (i = 0; i < cert->nprincipals; i++) {
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if ((result = match_list(cert->principals[i],
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principal_list, NULL)) != NULL) {
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debug3("matched principal from key options \"%.100s\"",
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result);
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free(result);
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return 1;
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}
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}
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return 0;
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}
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static int
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match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
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{
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FILE *f;
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char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
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u_long linenum = 0;
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u_int i;
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temporarily_use_uid(pw);
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debug("trying authorized principals file %s", file);
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if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
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restore_uid();
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return 0;
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}
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while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
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/* Skip leading whitespace. */
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for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
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;
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/* Skip blank and comment lines. */
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if ((ep = strchr(cp, '#')) != NULL)
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*ep = '\0';
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if (!*cp || *cp == '\n')
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continue;
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/* Trim trailing whitespace. */
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ep = cp + strlen(cp) - 1;
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while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
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*ep-- = '\0';
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/*
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* If the line has internal whitespace then assume it has
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* key options.
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*/
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line_opts = NULL;
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if ((ep = strrchr(cp, ' ')) != NULL ||
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(ep = strrchr(cp, '\t')) != NULL) {
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for (; *ep == ' ' || *ep == '\t'; ep++)
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;
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line_opts = cp;
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cp = ep;
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}
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for (i = 0; i < cert->nprincipals; i++) {
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if (strcmp(cp, cert->principals[i]) == 0) {
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debug3("matched principal \"%.100s\" "
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"from file \"%s\" on line %lu",
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cert->principals[i], file, linenum);
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if (auth_parse_options(pw, line_opts,
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file, linenum) != 1)
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continue;
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fclose(f);
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restore_uid();
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return 1;
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}
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}
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}
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fclose(f);
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restore_uid();
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return 0;
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}
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/*
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* Checks whether key is allowed in authorized_keys-format file,
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* returns 1 if the key is allowed or 0 otherwise.
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*/
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static int
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check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
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{
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char line[SSH_MAX_PUBKEY_BYTES];
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const char *reason;
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int found_key = 0;
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u_long linenum = 0;
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Key *found;
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char *fp;
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found_key = 0;
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found = NULL;
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while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
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char *cp, *key_options = NULL;
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if (found != NULL)
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key_free(found);
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found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
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auth_clear_options();
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/* Skip leading whitespace, empty and comment lines. */
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for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
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;
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if (!*cp || *cp == '\n' || *cp == '#')
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continue;
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if (key_read(found, &cp) != 1) {
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/* no key? check if there are options for this key */
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int quoted = 0;
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debug2("user_key_allowed: check options: '%s'", cp);
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key_options = cp;
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for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
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if (*cp == '\\' && cp[1] == '"')
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cp++; /* Skip both */
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else if (*cp == '"')
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quoted = !quoted;
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}
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/* Skip remaining whitespace. */
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for (; *cp == ' ' || *cp == '\t'; cp++)
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;
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if (key_read(found, &cp) != 1) {
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debug2("user_key_allowed: advance: '%s'", cp);
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/* still no key? advance to next line*/
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continue;
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}
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}
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if (key_is_cert(key)) {
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if (!key_equal(found, key->cert->signature_key))
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continue;
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if (auth_parse_options(pw, key_options, file,
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linenum) != 1)
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continue;
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if (!key_is_cert_authority)
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continue;
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fp = key_fingerprint(found, SSH_FP_MD5,
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SSH_FP_HEX);
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debug("matching CA found: file %s, line %lu, %s %s",
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file, linenum, key_type(found), fp);
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/*
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* If the user has specified a list of principals as
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* a key option, then prefer that list to matching
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* their username in the certificate principals list.
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*/
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if (authorized_principals != NULL &&
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!match_principals_option(authorized_principals,
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key->cert)) {
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reason = "Certificate does not contain an "
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"authorized principal";
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fail_reason:
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free(fp);
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error("%s", reason);
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auth_debug_add("%s", reason);
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continue;
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}
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if (key_cert_check_authority(key, 0, 0,
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authorized_principals == NULL ? pw->pw_name : NULL,
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&reason) != 0)
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goto fail_reason;
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if (auth_cert_options(key, pw) != 0) {
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free(fp);
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continue;
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}
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verbose("Accepted certificate ID \"%s\" "
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"signed by %s CA %s via %s", key->cert->key_id,
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key_type(found), fp, file);
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free(fp);
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found_key = 1;
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break;
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} else if (key_equal(found, key)) {
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if (auth_parse_options(pw, key_options, file,
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linenum) != 1)
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continue;
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if (key_is_cert_authority)
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continue;
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found_key = 1;
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fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
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debug("matching key found: file %s, line %lu %s %s",
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file, linenum, key_type(found), fp);
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free(fp);
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break;
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}
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}
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if (found != NULL)
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key_free(found);
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if (!found_key)
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debug2("key not found");
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return found_key;
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}
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/* Authenticate a certificate key against TrustedUserCAKeys */
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static int
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user_cert_trusted_ca(struct passwd *pw, Key *key)
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{
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char *ca_fp, *principals_file = NULL;
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const char *reason;
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int ret = 0;
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if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
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return 0;
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ca_fp = key_fingerprint(key->cert->signature_key,
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SSH_FP_MD5, SSH_FP_HEX);
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if (key_in_file(key->cert->signature_key,
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options.trusted_user_ca_keys, 1) != 1) {
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debug2("%s: CA %s %s is not listed in %s", __func__,
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key_type(key->cert->signature_key), ca_fp,
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options.trusted_user_ca_keys);
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goto out;
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}
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/*
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* If AuthorizedPrincipals is in use, then compare the certificate
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* principals against the names in that file rather than matching
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* against the username.
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*/
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if ((principals_file = authorized_principals_file(pw)) != NULL) {
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if (!match_principals_file(principals_file, pw, key->cert)) {
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reason = "Certificate does not contain an "
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"authorized principal";
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fail_reason:
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error("%s", reason);
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auth_debug_add("%s", reason);
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goto out;
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}
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}
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if (key_cert_check_authority(key, 0, 1,
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principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
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goto fail_reason;
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if (auth_cert_options(key, pw) != 0)
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goto out;
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verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
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key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
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options.trusted_user_ca_keys);
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ret = 1;
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out:
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free(principals_file);
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free(ca_fp);
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return ret;
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}
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/*
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* Checks whether key is allowed in file.
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* returns 1 if the key is allowed or 0 otherwise.
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*/
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static int
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user_key_allowed2(struct passwd *pw, Key *key, char *file)
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{
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FILE *f;
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int found_key = 0;
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/* Temporarily use the user's uid. */
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temporarily_use_uid(pw);
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debug("trying public key file %s", file);
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if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
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found_key = check_authkeys_file(f, file, key, pw);
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fclose(f);
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}
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restore_uid();
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return found_key;
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}
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/*
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* Checks whether key is allowed in output of command.
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* returns 1 if the key is allowed or 0 otherwise.
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*/
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static int
|
|
user_key_command_allowed2(struct passwd *user_pw, Key *key)
|
|
{
|
|
FILE *f;
|
|
int ok, found_key = 0;
|
|
struct passwd *pw;
|
|
struct stat st;
|
|
int status, devnull, p[2], i;
|
|
pid_t pid;
|
|
char *username, errmsg[512];
|
|
|
|
if (options.authorized_keys_command == NULL ||
|
|
options.authorized_keys_command[0] != '/')
|
|
return 0;
|
|
|
|
if (options.authorized_keys_command_user == NULL) {
|
|
error("No user for AuthorizedKeysCommand specified, skipping");
|
|
return 0;
|
|
}
|
|
|
|
username = percent_expand(options.authorized_keys_command_user,
|
|
"u", user_pw->pw_name, (char *)NULL);
|
|
pw = getpwnam(username);
|
|
if (pw == NULL) {
|
|
error("AuthorizedKeysCommandUser \"%s\" not found: %s",
|
|
username, strerror(errno));
|
|
free(username);
|
|
return 0;
|
|
}
|
|
free(username);
|
|
|
|
temporarily_use_uid(pw);
|
|
|
|
if (stat(options.authorized_keys_command, &st) < 0) {
|
|
error("Could not stat AuthorizedKeysCommand \"%s\": %s",
|
|
options.authorized_keys_command, strerror(errno));
|
|
goto out;
|
|
}
|
|
if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
|
|
errmsg, sizeof(errmsg)) != 0) {
|
|
error("Unsafe AuthorizedKeysCommand: %s", errmsg);
|
|
goto out;
|
|
}
|
|
|
|
if (pipe(p) != 0) {
|
|
error("%s: pipe: %s", __func__, strerror(errno));
|
|
goto out;
|
|
}
|
|
|
|
debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
|
|
options.authorized_keys_command, user_pw->pw_name, pw->pw_name);
|
|
|
|
/*
|
|
* Don't want to call this in the child, where it can fatal() and
|
|
* run cleanup_exit() code.
|
|
*/
|
|
restore_uid();
|
|
|
|
switch ((pid = fork())) {
|
|
case -1: /* error */
|
|
error("%s: fork: %s", __func__, strerror(errno));
|
|
close(p[0]);
|
|
close(p[1]);
|
|
return 0;
|
|
case 0: /* child */
|
|
for (i = 0; i < NSIG; i++)
|
|
signal(i, SIG_DFL);
|
|
|
|
if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
|
|
error("%s: open %s: %s", __func__, _PATH_DEVNULL,
|
|
strerror(errno));
|
|
_exit(1);
|
|
}
|
|
/* Keep stderr around a while longer to catch errors */
|
|
if (dup2(devnull, STDIN_FILENO) == -1 ||
|
|
dup2(p[1], STDOUT_FILENO) == -1) {
|
|
error("%s: dup2: %s", __func__, strerror(errno));
|
|
_exit(1);
|
|
}
|
|
closefrom(STDERR_FILENO + 1);
|
|
|
|
/* Don't use permanently_set_uid() here to avoid fatal() */
|
|
if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
|
|
error("setresgid %u: %s", (u_int)pw->pw_gid,
|
|
strerror(errno));
|
|
_exit(1);
|
|
}
|
|
if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
|
|
error("setresuid %u: %s", (u_int)pw->pw_uid,
|
|
strerror(errno));
|
|
_exit(1);
|
|
}
|
|
/* stdin is pointed to /dev/null at this point */
|
|
if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
|
|
error("%s: dup2: %s", __func__, strerror(errno));
|
|
_exit(1);
|
|
}
|
|
|
|
execl(options.authorized_keys_command,
|
|
options.authorized_keys_command, user_pw->pw_name, NULL);
|
|
|
|
error("AuthorizedKeysCommand %s exec failed: %s",
|
|
options.authorized_keys_command, strerror(errno));
|
|
_exit(127);
|
|
default: /* parent */
|
|
break;
|
|
}
|
|
|
|
temporarily_use_uid(pw);
|
|
|
|
close(p[1]);
|
|
if ((f = fdopen(p[0], "r")) == NULL) {
|
|
error("%s: fdopen: %s", __func__, strerror(errno));
|
|
close(p[0]);
|
|
/* Don't leave zombie child */
|
|
kill(pid, SIGTERM);
|
|
while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
|
|
;
|
|
goto out;
|
|
}
|
|
ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
|
|
fclose(f);
|
|
|
|
while (waitpid(pid, &status, 0) == -1) {
|
|
if (errno != EINTR) {
|
|
error("%s: waitpid: %s", __func__, strerror(errno));
|
|
goto out;
|
|
}
|
|
}
|
|
if (WIFSIGNALED(status)) {
|
|
error("AuthorizedKeysCommand %s exited on signal %d",
|
|
options.authorized_keys_command, WTERMSIG(status));
|
|
goto out;
|
|
} else if (WEXITSTATUS(status) != 0) {
|
|
error("AuthorizedKeysCommand %s returned status %d",
|
|
options.authorized_keys_command, WEXITSTATUS(status));
|
|
goto out;
|
|
}
|
|
found_key = ok;
|
|
out:
|
|
restore_uid();
|
|
return found_key;
|
|
}
|
|
|
|
/*
|
|
* Check whether key authenticates and authorises the user.
|
|
*/
|
|
int
|
|
user_key_allowed(struct passwd *pw, Key *key)
|
|
{
|
|
u_int success, i;
|
|
char *file;
|
|
|
|
if (auth_key_is_revoked(key))
|
|
return 0;
|
|
if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
|
|
return 0;
|
|
|
|
success = user_cert_trusted_ca(pw, key);
|
|
if (success)
|
|
return success;
|
|
|
|
success = user_key_command_allowed2(pw, key);
|
|
if (success > 0)
|
|
return success;
|
|
|
|
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);
|
|
free(file);
|
|
}
|
|
|
|
return success;
|
|
}
|
|
|
|
Authmethod method_pubkey = {
|
|
"publickey",
|
|
userauth_pubkey,
|
|
&options.pubkey_authentication
|
|
};
|