Mercurial > dropbear

annotate svr-authpasswd.c @ 1831:0a3d02c66bf6

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Comment on reason for DROPBEAR_MAX_PASSWORD_LEN limit
author Matt Johnston <matt@codeconstruct.com.au>
date Tue, 12 Oct 2021 21:29:25 +0800
parents 228b086794b7
children
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1 /*
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2 * Dropbear - a SSH2 server
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3 *
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4 * Copyright (c) 2002,2003 Matt Johnston
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5 * All rights reserved.
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6 *
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7 * Permission is hereby granted, free of charge, to any person obtaining a copy
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8 * of this software and associated documentation files (the "Software"), to deal
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9 * in the Software without restriction, including without limitation the rights
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10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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11 * copies of the Software, and to permit persons to whom the Software is
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12 * furnished to do so, subject to the following conditions:
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13 *
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14 * The above copyright notice and this permission notice shall be included in
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15 * all copies or substantial portions of the Software.
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16 *
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17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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23 * SOFTWARE. */
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24
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25 /* Validates a user password */
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26
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27 #include "includes.h"
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28 #include "session.h"
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29 #include "buffer.h"
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30 #include "dbutil.h"
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31 #include "auth.h"
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32 #include "runopts.h"
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33
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34 #if DROPBEAR_SVR_PASSWORD_AUTH
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35
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36 /* not constant time when strings are differing lengths.
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37 string content isn't leaked, and crypt hashes are predictable length. */
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38 static int constant_time_strcmp(const char* a, const char* b) {
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39 size_t la = strlen(a);
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40 size_t lb = strlen(b);
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41
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42 if (la != lb) {
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43 return 1;
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44 }
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45
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46 return constant_time_memcmp(a, b, la);
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47 }
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48
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49 /* Process a password auth request, sending success or failure messages as
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50 * appropriate */
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51 void svr_auth_password(int valid_user) {
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52
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53 char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */
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54 char * testcrypt = NULL; /* crypt generated from the user's password sent */
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55 char * password = NULL;
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56 unsigned int passwordlen;
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57 unsigned int changepw;
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58
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59 /* check if client wants to change password */
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60 changepw = buf_getbool(ses.payload);
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61 if (changepw) {
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62 /* not implemented by this server */
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63 send_msg_userauth_failure(0, 1);
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64 return;
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65 }
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66
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67 password = buf_getstring(ses.payload, &passwordlen);
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68 if (valid_user && passwordlen <= DROPBEAR_MAX_PASSWORD_LEN) {
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69 /* the first bytes of passwdcrypt are the salt */
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70 passwdcrypt = ses.authstate.pw_passwd;
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71 testcrypt = crypt(password, passwdcrypt);
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72 }
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73 m_burn(password, passwordlen);
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74 m_free(password);
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76 /* After we have got the payload contents we can exit if the username
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77 is invalid. Invalid users have already been logged. */
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78 if (!valid_user) {
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79 send_msg_userauth_failure(0, 1);
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80 return;
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81 }
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82
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83 if (passwordlen > DROPBEAR_MAX_PASSWORD_LEN) {
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84 dropbear_log(LOG_WARNING,
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85 "Too-long password attempt for '%s' from %s",
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86 ses.authstate.pw_name,
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87 svr_ses.addrstring);
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88 send_msg_userauth_failure(0, 1);
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89 return;
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90 }
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91
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92 if (testcrypt == NULL) {
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93 /* crypt() with an invalid salt like "!!" */
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94 dropbear_log(LOG_WARNING, "User account '%s' is locked",
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95 ses.authstate.pw_name);
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96 send_msg_userauth_failure(0, 1);
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97 return;
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98 }
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99
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100 /* check for empty password */
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101 if (passwdcrypt[0] == '\0') {
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102 dropbear_log(LOG_WARNING, "User '%s' has blank password, rejected",
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103 ses.authstate.pw_name);
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104 send_msg_userauth_failure(0, 1);
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105 return;
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106 }
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107
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108 if (constant_time_strcmp(testcrypt, passwdcrypt) == 0) {
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109 /* successful authentication */
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110 dropbear_log(LOG_NOTICE,
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111 "Password auth succeeded for '%s' from %s",
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112 ses.authstate.pw_name,
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113 svr_ses.addrstring);
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114 send_msg_userauth_success();
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115 } else {
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116 dropbear_log(LOG_WARNING,
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117 "Bad password attempt for '%s' from %s",
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118 ses.authstate.pw_name,
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119 svr_ses.addrstring);
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120 send_msg_userauth_failure(0, 1);
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121 }
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122 }
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123
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124 #endif