466 lines
12 KiB
C
466 lines
12 KiB
C
/* $OpenBSD: auth2-pubkey.c,v 1.29 2011/05/23 03:30:07 djm 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 <fcntl.h>
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#include <pwd.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 "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 "misc.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;
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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 (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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buffer_put_cstring(&b, authctxt->user);
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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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/* 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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xfree(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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xfree(pkalg);
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xfree(pkblob);
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return authenticated;
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}
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static int
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match_principals_option(const char *principal_list, struct KeyCert *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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xfree(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 KeyCert *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 from file \"%.100s\"",
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cert->principals[i]);
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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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/* return 1 if user allows given key */
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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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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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FILE *f;
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u_long linenum = 0;
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Key *found;
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char *fp;
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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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f = auth_openkeyfile(file, pw, options.strict_modes);
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if (!f) {
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restore_uid();
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return 0;
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}
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found_key = 0;
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found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
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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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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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xfree(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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xfree(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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xfree(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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debug("matching key found: file %s, line %lu",
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file, linenum);
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fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
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verbose("Found matching %s key: %s",
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key_type(found), fp);
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xfree(fp);
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break;
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}
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}
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restore_uid();
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fclose(f);
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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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if (principals_file != NULL)
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xfree(principals_file);
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if (ca_fp != NULL)
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xfree(ca_fp);
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return ret;
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}
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/* check whether given key is in .ssh/authorized_keys* */
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int
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user_key_allowed(struct passwd *pw, Key *key)
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{
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u_int success, i;
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char *file;
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if (auth_key_is_revoked(key))
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return 0;
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if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
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return 0;
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success = user_cert_trusted_ca(pw, key);
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if (success)
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return success;
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for (i = 0; !success && i < options.num_authkeys_files; i++) {
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file = expand_authorized_keys(
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options.authorized_keys_files[i], pw);
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success = user_key_allowed2(pw, key, file);
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xfree(file);
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}
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return success;
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}
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Authmethod method_pubkey = {
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"publickey",
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userauth_pubkey,
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&options.pubkey_authentication
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};
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