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444 lines
13 KiB
C
444 lines
13 KiB
C
/*
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* Dropbear - a SSH2 server
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*
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* Copyright (c) 2002,2003 Matt Johnston
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* All rights reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE. */
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/*
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* This file incorporates work covered by the following copyright and
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* permission notice:
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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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* This copyright and permission notice applies to the code parsing public keys
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* options string which can also be found in OpenSSH auth2-pubkey.c file
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* (user_key_allowed2). It has been adapted to work with buffers.
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*
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*/
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/* Process a pubkey auth request */
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#include "includes.h"
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#include "session.h"
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#include "dbutil.h"
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#include "buffer.h"
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#include "signkey.h"
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#include "auth.h"
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#include "ssh.h"
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#include "packet.h"
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#include "algo.h"
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#ifdef ENABLE_SVR_PUBKEY_AUTH
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#define MIN_AUTHKEYS_LINE 10 /* "ssh-rsa AB" - short but doesn't matter */
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#define MAX_AUTHKEYS_LINE 4200 /* max length of a line in authkeys */
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static int checkpubkey(unsigned char* algo, unsigned int algolen,
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unsigned char* keyblob, unsigned int keybloblen);
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static int checkpubkeyperms();
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static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
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unsigned char* keyblob, unsigned int keybloblen);
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static int checkfileperm(char * filename);
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/* process a pubkey auth request, sending success or failure message as
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* appropriate */
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void svr_auth_pubkey() {
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unsigned char testkey; /* whether we're just checking if a key is usable */
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unsigned char* algo = NULL; /* pubkey algo */
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unsigned int algolen;
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unsigned char* keyblob = NULL;
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unsigned int keybloblen;
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buffer * signbuf = NULL;
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sign_key * key = NULL;
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char* fp = NULL;
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enum signkey_type type = -1;
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TRACE(("enter pubkeyauth"))
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/* 0 indicates user just wants to check if key can be used, 1 is an
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* actual attempt*/
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testkey = (buf_getbool(ses.payload) == 0);
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algo = buf_getstring(ses.payload, &algolen);
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keybloblen = buf_getint(ses.payload);
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keyblob = buf_getptr(ses.payload, keybloblen);
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/* check if the key is valid */
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if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
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send_msg_userauth_failure(0, 0);
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goto out;
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}
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/* let them know that the key is ok to use */
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if (testkey) {
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send_msg_userauth_pk_ok(algo, algolen, keyblob, keybloblen);
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goto out;
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}
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/* now we can actually verify the signature */
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/* get the key */
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key = new_sign_key();
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type = DROPBEAR_SIGNKEY_ANY;
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if (buf_get_pub_key(ses.payload, key, &type) == DROPBEAR_FAILURE) {
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send_msg_userauth_failure(0, 1);
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goto out;
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}
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/* create the data which has been signed - this a string containing
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* session_id, concatenated with the payload packet up to the signature */
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signbuf = buf_new(ses.payload->pos + 4 + ses.session_id->len);
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buf_putbufstring(signbuf, ses.session_id);
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buf_putbytes(signbuf, ses.payload->data, ses.payload->pos);
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buf_setpos(signbuf, 0);
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/* ... and finally verify the signature */
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fp = sign_key_fingerprint(keyblob, keybloblen);
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if (buf_verify(ses.payload, key, signbuf) == DROPBEAR_SUCCESS) {
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dropbear_log(LOG_NOTICE,
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"Pubkey auth succeeded for '%s' with key %s from %s",
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ses.authstate.pw_name, fp, svr_ses.addrstring);
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send_msg_userauth_success();
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} else {
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dropbear_log(LOG_WARNING,
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"Pubkey auth bad signature for '%s' with key %s from %s",
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ses.authstate.pw_name, fp, svr_ses.addrstring);
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send_msg_userauth_failure(0, 1);
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}
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m_free(fp);
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out:
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/* cleanup stuff */
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if (signbuf) {
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buf_free(signbuf);
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}
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if (algo) {
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m_free(algo);
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}
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if (key) {
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sign_key_free(key);
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key = NULL;
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}
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TRACE(("leave pubkeyauth"))
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}
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/* Reply that the key is valid for auth, this is sent when the user sends
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* a straight copy of their pubkey to test, to avoid having to perform
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* expensive signing operations with a worthless key */
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static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
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unsigned char* keyblob, unsigned int keybloblen) {
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TRACE(("enter send_msg_userauth_pk_ok"))
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CHECKCLEARTOWRITE();
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buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_PK_OK);
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buf_putstring(ses.writepayload, algo, algolen);
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buf_putstring(ses.writepayload, keyblob, keybloblen);
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encrypt_packet();
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TRACE(("leave send_msg_userauth_pk_ok"))
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}
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/* Checks whether a specified publickey (and associated algorithm) is an
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* acceptable key for authentication */
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/* Returns DROPBEAR_SUCCESS if key is ok for auth, DROPBEAR_FAILURE otherwise */
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static int checkpubkey(unsigned char* algo, unsigned int algolen,
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unsigned char* keyblob, unsigned int keybloblen) {
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FILE * authfile = NULL;
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char * filename = NULL;
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int ret = DROPBEAR_FAILURE;
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buffer * line = NULL;
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unsigned int len, pos;
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buffer * options_buf = NULL;
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int line_num;
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TRACE(("enter checkpubkey"))
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/* check that we can use the algo */
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if (have_algo(algo, algolen, sshhostkey) == DROPBEAR_FAILURE) {
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dropbear_log(LOG_WARNING,
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"Pubkey auth attempt with unknown algo for '%s' from %s",
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ses.authstate.pw_name, svr_ses.addrstring);
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goto out;
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}
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/* check file permissions, also whether file exists */
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if (checkpubkeyperms() == DROPBEAR_FAILURE) {
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TRACE(("bad authorized_keys permissions, or file doesn't exist"))
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goto out;
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}
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/* we don't need to check pw and pw_dir for validity, since
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* its been done in checkpubkeyperms. */
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len = strlen(ses.authstate.pw_dir);
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/* allocate max required pathname storage,
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* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
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filename = m_malloc(len + 22);
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snprintf(filename, len + 22, "%s/.ssh/authorized_keys",
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ses.authstate.pw_dir);
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/* open the file */
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authfile = fopen(filename, "r");
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if (authfile == NULL) {
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goto out;
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}
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TRACE(("checkpubkey: opened authorized_keys OK"))
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line = buf_new(MAX_AUTHKEYS_LINE);
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line_num = 0;
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/* iterate through the lines */
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do {
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/* new line : potentially new options */
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if (options_buf) {
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buf_free(options_buf);
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options_buf = NULL;
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}
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if (buf_getline(line, authfile) == DROPBEAR_FAILURE) {
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/* EOF reached */
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TRACE(("checkpubkey: authorized_keys EOF reached"))
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break;
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}
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line_num++;
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if (line->len < MIN_AUTHKEYS_LINE) {
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TRACE(("checkpubkey: line too short"))
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continue; /* line is too short for it to be a valid key */
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}
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/* check the key type - will fail if there are options */
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TRACE(("a line!"))
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if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
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int is_comment = 0;
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char *options_start = NULL;
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int options_len = 0;
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int escape, quoted;
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/* skip over any comments or leading whitespace */
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while (line->pos < line->len) {
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const char c = buf_getbyte(line);
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if (c == ' ' || c == '\t') {
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continue;
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} else if (c == '#') {
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is_comment = 1;
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break;
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}
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buf_incrpos(line, -1);
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break;
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}
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if (is_comment) {
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/* next line */
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continue;
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}
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/* remember start of options */
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options_start = buf_getptr(line, 1);
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quoted = 0;
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escape = 0;
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options_len = 0;
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/* figure out where the options are */
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while (line->pos < line->len) {
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const char c = buf_getbyte(line);
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if (!quoted && (c == ' ' || c == '\t')) {
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break;
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}
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escape = (!escape && c == '\\');
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if (!escape && c == '"') {
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quoted = !quoted;
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}
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options_len++;
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}
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options_buf = buf_new(options_len);
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buf_putbytes(options_buf, options_start, options_len);
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/* compare the algorithm. +3 so we have enough bytes to read a space and some base64 characters too. */
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if (line->pos + algolen+3 > line->len) {
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continue;
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}
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if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
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continue;
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}
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}
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buf_incrpos(line, algolen);
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/* check for space (' ') character */
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if (buf_getbyte(line) != ' ') {
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TRACE(("checkpubkey: space character expected, isn't there"))
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continue;
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}
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/* truncate the line at the space after the base64 data */
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pos = line->pos;
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for (len = 0; line->pos < line->len; len++) {
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if (buf_getbyte(line) == ' ') break;
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}
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buf_setpos(line, pos);
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buf_setlen(line, line->pos + len);
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TRACE(("checkpubkey: line pos = %d len = %d", line->pos, line->len))
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ret = cmp_base64_key(keyblob, keybloblen, algo, algolen, line, NULL);
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if (ret == DROPBEAR_SUCCESS && options_buf) {
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ret = svr_add_pubkey_options(options_buf, line_num, filename);
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}
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if (ret == DROPBEAR_SUCCESS) {
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break;
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}
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/* We continue to the next line otherwise */
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} while (1);
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out:
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if (authfile) {
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fclose(authfile);
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}
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if (line) {
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buf_free(line);
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}
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m_free(filename);
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if (options_buf) {
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buf_free(options_buf);
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}
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TRACE(("leave checkpubkey: ret=%d", ret))
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return ret;
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}
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/* Returns DROPBEAR_SUCCESS if file permissions for pubkeys are ok,
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* DROPBEAR_FAILURE otherwise.
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* Checks that the user's homedir, ~/.ssh, and
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* ~/.ssh/authorized_keys are all owned by either root or the user, and are
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* g-w, o-w */
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static int checkpubkeyperms() {
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char* filename = NULL;
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int ret = DROPBEAR_FAILURE;
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unsigned int len;
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TRACE(("enter checkpubkeyperms"))
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if (ses.authstate.pw_dir == NULL) {
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goto out;
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}
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if ((len = strlen(ses.authstate.pw_dir)) == 0) {
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goto out;
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}
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/* allocate max required pathname storage,
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* = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
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filename = m_malloc(len + 22);
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strncpy(filename, ses.authstate.pw_dir, len+1);
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/* check ~ */
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if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
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goto out;
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}
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/* check ~/.ssh */
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strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */
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if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
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goto out;
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}
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/* now check ~/.ssh/authorized_keys */
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strncat(filename, "/authorized_keys", 16);
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if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
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goto out;
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}
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/* file looks ok, return success */
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ret = DROPBEAR_SUCCESS;
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out:
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m_free(filename);
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TRACE(("leave checkpubkeyperms"))
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return ret;
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}
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/* Checks that a file is owned by the user or root, and isn't writable by
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* group or other */
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/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
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static int checkfileperm(char * filename) {
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struct stat filestat;
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int badperm = 0;
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TRACE(("enter checkfileperm(%s)", filename))
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if (stat(filename, &filestat) != 0) {
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TRACE(("leave checkfileperm: stat() != 0"))
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return DROPBEAR_FAILURE;
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}
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/* check ownership - user or root only*/
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if (filestat.st_uid != ses.authstate.pw_uid
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&& filestat.st_uid != 0) {
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badperm = 1;
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TRACE(("wrong ownership"))
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}
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/* check permissions - don't want group or others +w */
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if (filestat.st_mode & (S_IWGRP | S_IWOTH)) {
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badperm = 1;
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TRACE(("wrong perms"))
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}
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if (badperm) {
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if (!ses.authstate.perm_warn) {
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ses.authstate.perm_warn = 1;
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dropbear_log(LOG_INFO, "%s must be owned by user or root, and not writable by others", filename);
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}
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TRACE(("leave checkfileperm: failure perms/owner"))
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return DROPBEAR_FAILURE;
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}
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TRACE(("leave checkfileperm: success"))
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return DROPBEAR_SUCCESS;
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}
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#endif
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