package/network/services/dropbear/patches/020-Wait-to-fail-invalid-usernames.patch

   1 From 52adbb34c32d3e2e1bcdb941e20a6f81138b8248 Mon Sep 17 00:00:00 2001
   2 From: Matt Johnston <matt@ucc.asn.au>
   3 Date: Thu, 23 Aug 2018 23:43:12 +0800
   4 Subject: [PATCH 2/2] Wait to fail invalid usernames
   5
   6 ---
   7  auth.h           |  6 +++---
   8  svr-auth.c       | 19 +++++--------------
   9  svr-authpam.c    | 26 ++++++++++++++++++++++----
  10  svr-authpasswd.c | 27 ++++++++++++++-------------
  11  svr-authpubkey.c | 11 ++++++++++-
  12  5 files changed, 54 insertions(+), 35 deletions(-)
  13
  14 --- a/auth.h
  15 +++ b/auth.h
  16 @@ -37,9 +37,9 @@ void recv_msg_userauth_request(void);
  17  void send_msg_userauth_failure(int partial, int incrfail);
  18  void send_msg_userauth_success(void);
  19  void send_msg_userauth_banner(buffer *msg);
  20 -void svr_auth_password(void);
  21 -void svr_auth_pubkey(void);
  22 -void svr_auth_pam(void);
  23 +void svr_auth_password(int valid_user);
  24 +void svr_auth_pubkey(int valid_user);
  25 +void svr_auth_pam(int valid_user);
  26
  27  #ifdef ENABLE_SVR_PUBKEY_OPTIONS
  28  int svr_pubkey_allows_agentfwd(void);
  29 --- a/svr-auth.c
  30 +++ b/svr-auth.c
  31 @@ -176,10 +176,8 @@ void recv_msg_userauth_request() {
  32                 if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
  33                                 strncmp(methodname, AUTH_METHOD_PASSWORD,
  34                                         AUTH_METHOD_PASSWORD_LEN) == 0) {
  35 -                       if (valid_user) {
  36 -                               svr_auth_password();
  37 -                               goto out;
  38 -                       }
  39 +                       svr_auth_password(valid_user);
  40 +                       goto out;
  41                 }
  42         }
  43  #endif
  44 @@ -191,10 +189,8 @@ void recv_msg_userauth_request() {
  45                 if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
  46                                 strncmp(methodname, AUTH_METHOD_PASSWORD,
  47                                         AUTH_METHOD_PASSWORD_LEN) == 0) {
  48 -                       if (valid_user) {
  49 -                               svr_auth_pam();
  50 -                               goto out;
  51 -                       }
  52 +                       svr_auth_pam(valid_user);
  53 +                       goto out;
  54                 }
  55         }
  56  #endif
  57 @@ -204,12 +200,7 @@ void recv_msg_userauth_request() {
  58         if (methodlen == AUTH_METHOD_PUBKEY_LEN &&
  59                         strncmp(methodname, AUTH_METHOD_PUBKEY,
  60                                 AUTH_METHOD_PUBKEY_LEN) == 0) {
  61 -               if (valid_user) {
  62 -                       svr_auth_pubkey();
  63 -               } else {
  64 -                       /* pubkey has no failure delay */
  65 -                       send_msg_userauth_failure(0, 0);
  66 -               }
  67 +               svr_auth_pubkey(valid_user);
  68                 goto out;
  69         }
  70  #endif
  71 --- a/svr-authpam.c
  72 +++ b/svr-authpam.c
  73 @@ -178,13 +178,14 @@ pamConvFunc(int num_msg,
  74   * Keyboard interactive would be a lot nicer, but since PAM is synchronous, it
  75   * gets very messy trying to send the interactive challenges, and read the
  76   * interactive responses, over the network. */
  77 -void svr_auth_pam() {
  78 +void svr_auth_pam(int valid_user) {
  79
  80         struct UserDataS userData = {NULL, NULL};
  81         struct pam_conv pamConv = {
  82                 pamConvFunc,
  83                 &userData /* submitted to pamvConvFunc as appdata_ptr */
  84         };
  85 +       const char* printable_user = NULL;
  86
  87         pam_handle_t* pamHandlep = NULL;
  88
  89 @@ -204,12 +205,23 @@ void svr_auth_pam() {
  90
  91         password = buf_getstring(ses.payload, &passwordlen);
  92
  93 +       /* We run the PAM conversation regardless of whether the username is valid
  94 +       in case the conversation function has an inherent delay.
  95 +       Use ses.authstate.username rather than ses.authstate.pw_name.
  96 +       After PAM succeeds we then check the valid_user flag too */
  97 +
  98         /* used to pass data to the PAM conversation function - don't bother with
  99          * strdup() etc since these are touched only by our own conversation
 100          * function (above) which takes care of it */
 101 -       userData.user = ses.authstate.pw_name;
 102 +       userData.user = ses.authstate.username;
 103         userData.passwd = password;
 104
 105 +       if (ses.authstate.pw_name) {
 106 +               printable_user = ses.authstate.pw_name;
 107 +       } else {
 108 +               printable_user = "<invalid username>";
 109 +       }
 110 +
 111         /* Init pam */
 112         if ((rc = pam_start("sshd", NULL, &pamConv, &pamHandlep)) != PAM_SUCCESS) {
 113                 dropbear_log(LOG_WARNING, "pam_start() failed, rc=%d, %s",
 114 @@ -236,7 +248,7 @@ void svr_auth_pam() {
 115                                 rc, pam_strerror(pamHandlep, rc));
 116                 dropbear_log(LOG_WARNING,
 117                                 "Bad PAM password attempt for '%s' from %s",
 118 -                               ses.authstate.pw_name,
 119 +                               printable_user,
 120                                 svr_ses.addrstring);
 121                 send_msg_userauth_failure(0, 1);
 122                 goto cleanup;
 123 @@ -247,12 +259,18 @@ void svr_auth_pam() {
 124                                 rc, pam_strerror(pamHandlep, rc));
 125                 dropbear_log(LOG_WARNING,
 126                                 "Bad PAM password attempt for '%s' from %s",
 127 -                               ses.authstate.pw_name,
 128 +                               printable_user,
 129                                 svr_ses.addrstring);
 130                 send_msg_userauth_failure(0, 1);
 131                 goto cleanup;
 132         }
 133
 134 +       if (!valid_user) {
 135 +               /* PAM auth succeeded but the username isn't allowed in for another reason
 136 +               (checkusername() failed) */
 137 +               send_msg_userauth_failure(0, 1);
 138 +       }
 139 +
 140         /* successful authentication */
 141         dropbear_log(LOG_NOTICE, "PAM password auth succeeded for '%s' from %s",
 142                         ses.authstate.pw_name,
 143 --- a/svr-authpasswd.c
 144 +++ b/svr-authpasswd.c
 145 @@ -48,22 +48,14 @@ static int constant_time_strcmp(const ch
 146
 147  /* Process a password auth request, sending success or failure messages as
 148   * appropriate */
 149 -void svr_auth_password() {
 150 +void svr_auth_password(int valid_user) {
 151
 152         char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */
 153         char * testcrypt = NULL; /* crypt generated from the user's password sent */
 154 -       char * password;
 155 +       char * password = NULL;
 156         unsigned int passwordlen;
 157 -
 158         unsigned int changepw;
 159
 160 -       passwdcrypt = ses.authstate.pw_passwd;
 161 -
 162 -#ifdef DEBUG_HACKCRYPT
 163 -       /* debugging crypt for non-root testing with shadows */
 164 -       passwdcrypt = DEBUG_HACKCRYPT;
 165 -#endif
 166 -
 167         /* check if client wants to change password */
 168         changepw = buf_getbool(ses.payload);
 169         if (changepw) {
 170 @@ -73,12 +65,21 @@ void svr_auth_password() {
 171         }
 172
 173         password = buf_getstring(ses.payload, &passwordlen);
 174 -
 175 -       /* the first bytes of passwdcrypt are the salt */
 176 -       testcrypt = crypt(password, passwdcrypt);
 177 +       if (valid_user) {
 178 +               /* the first bytes of passwdcrypt are the salt */
 179 +               passwdcrypt = ses.authstate.pw_passwd;
 180 +               testcrypt = crypt(password, passwdcrypt);
 181 +       }
 182         m_burn(password, passwordlen);
 183         m_free(password);
 184
 185 +       /* After we have got the payload contents we can exit if the username
 186 +       is invalid. Invalid users have already been logged. */
 187 +       if (!valid_user) {
 188 +               send_msg_userauth_failure(0, 1);
 189 +               return;
 190 +       }
 191 +
 192         if (testcrypt == NULL) {
 193                 /* crypt() with an invalid salt like "!!" */
 194                 dropbear_log(LOG_WARNING, "User account '%s' is locked",
 195 --- a/svr-authpubkey.c
 196 +++ b/svr-authpubkey.c
 197 @@ -79,7 +79,7 @@ static int checkfileperm(char * filename
 198
 199  /* process a pubkey auth request, sending success or failure message as
 200   * appropriate */
 201 -void svr_auth_pubkey() {
 202 +void svr_auth_pubkey(int valid_user) {
 203
 204         unsigned char testkey; /* whether we're just checking if a key is usable */
 205         char* algo = NULL; /* pubkey algo */
 206 @@ -102,6 +102,15 @@ void svr_auth_pubkey() {
 207         keybloblen = buf_getint(ses.payload);
 208         keyblob = buf_getptr(ses.payload, keybloblen);
 209
 210 +       if (!valid_user) {
 211 +               /* Return failure once we have read the contents of the packet
 212 +               required to validate a public key.
 213 +               Avoids blind user enumeration though it isn't possible to prevent
 214 +               testing for user existence if the public key is known */
 215 +               send_msg_userauth_failure(0, 0);
 216 +               goto out;
 217 +       }
 218 +
 219         /* check if the key is valid */
 220         if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
 221                 send_msg_userauth_failure(0, 0);