275 lines
7.3 KiB
C
275 lines
7.3 KiB
C
/* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto 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 <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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/* 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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/* 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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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->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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/* 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_equal(found, key) &&
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auth_parse_options(pw, key_options, file, linenum) == 1) {
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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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/* 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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int success;
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char *file;
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file = authorized_keys_file(pw);
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success = user_key_allowed2(pw, key, file);
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xfree(file);
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if (success)
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return success;
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/* try suffix "2" for backward compat, too */
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file = authorized_keys_file2(pw);
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success = user_key_allowed2(pw, key, file);
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xfree(file);
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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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