Mercurial > dropbear
view svr-authpasswd.c @ 1086:50f8a24953e6
note about constant_time_strcmp and lengths
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 03 Jun 2015 22:15:12 +0800 |
parents | a625f9e135a4 |
children | aaf576b27a10 |
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/* * Dropbear - a SSH2 server * * Copyright (c) 2002,2003 Matt Johnston * All rights reserved. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ /* Validates a user password */ #include "includes.h" #include "session.h" #include "buffer.h" #include "dbutil.h" #include "auth.h" #include "runopts.h" #ifdef ENABLE_SVR_PASSWORD_AUTH /* not constant time when strings are differing lengths. string content isn't leaked, and crypt hashes are predictable length. */ static int constant_time_strcmp(const char* a, const char* b) { size_t la = strlen(a); size_t lb = strlen(b); if (la != lb) { return 1; } return constant_time_memcmp(a, b, la); } /* Process a password auth request, sending success or failure messages as * appropriate */ void svr_auth_password() { char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */ char * testcrypt = NULL; /* crypt generated from the user's password sent */ unsigned char * password; unsigned int passwordlen; unsigned int changepw; passwdcrypt = ses.authstate.pw_passwd; #ifdef DEBUG_HACKCRYPT /* debugging crypt for non-root testing with shadows */ passwdcrypt = DEBUG_HACKCRYPT; #endif /* check if client wants to change password */ changepw = buf_getbool(ses.payload); if (changepw) { /* not implemented by this server */ send_msg_userauth_failure(0, 1); return; } password = buf_getstring(ses.payload, &passwordlen); /* the first bytes of passwdcrypt are the salt */ testcrypt = crypt((char*)password, passwdcrypt); m_burn(password, passwordlen); m_free(password); if (testcrypt == NULL) { /* crypt() with an invalid salt like "!!" */ dropbear_log(LOG_WARNING, "User account '%s' is locked", ses.authstate.pw_name); send_msg_userauth_failure(0, 1); return; } /* check for empty password */ if (passwdcrypt[0] == '\0') { dropbear_log(LOG_WARNING, "User '%s' has blank password, rejected", ses.authstate.pw_name); send_msg_userauth_failure(0, 1); return; } if (constant_time_strcmp(testcrypt, passwdcrypt) == 0) { /* successful authentication */ dropbear_log(LOG_NOTICE, "Password auth succeeded for '%s' from %s", ses.authstate.pw_name, svr_ses.addrstring); send_msg_userauth_success(); } else { dropbear_log(LOG_WARNING, "Bad password attempt for '%s' from %s", ses.authstate.pw_name, svr_ses.addrstring); send_msg_userauth_failure(0, 1); } } #endif