src/src/auths/get_data.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2018 */
   6 /* Copyright (c) The Exim Maintainers 2020 */
   7 /* See the file NOTICE for conditions of use and distribution. */
   8
   9 #include "../exim.h"
  10
  11
  12 /****************************************************************
  13 *       Decode and split the argument of an AUTH command        *
  14 ****************************************************************/
  15
  16 /* If data was supplied on the AUTH command, decode it, and split it up into
  17 multiple items at binary zeros. The strings are put into $auth1, $auth2, etc,
  18 up to a maximum. To retain backwards compatibility, they are also put int $1,
  19 $2, etc. If the data consists of the string "=" it indicates a single, empty
  20 string. */
  21
  22 int
  23 auth_read_input(const uschar * data)
  24 {
  25 if (Ustrcmp(data, "=") == 0)
  26   {
  27   auth_vars[0] = expand_nstring[++expand_nmax] = US"";
  28   expand_nlength[expand_nmax] = 0;
  29   }
  30 else
  31   {
  32   uschar * clear, * end;
  33   int len;
  34
  35   if ((len = b64decode(data, &clear)) < 0) return BAD64;
  36   DEBUG(D_auth) debug_printf("auth input decode:");
  37   for (end = clear + len; clear < end && expand_nmax < EXPAND_MAXN; )
  38     {
  39     DEBUG(D_auth) debug_printf(" '%s'", clear);
  40     if (expand_nmax < AUTH_VARS) auth_vars[expand_nmax] = clear;
  41     expand_nstring[++expand_nmax] = clear;
  42     while (*clear != 0) clear++;
  43     expand_nlength[expand_nmax] = clear++ - expand_nstring[expand_nmax];
  44     }
  45   DEBUG(D_auth) debug_printf("\n");
  46   }
  47 return OK;
  48 }
  49
  50
  51
  52
  53 /*************************************************
  54 *      Issue a challenge and get a response      *
  55 *************************************************/
  56
  57 /* This function is used by authentication drivers to b64-encode and
  58 output a challenge to the SMTP client, and read the response line.
  59
  60 Arguments:
  61    aptr       set to point to the response (which is in big_buffer)
  62    challenge  the challenge data (unencoded, may be binary)
  63    challen    the length of the challenge data, in bytes
  64
  65 Returns:      OK on success
  66               BAD64 if response too large for buffer
  67               CANCELLED if response is "*"
  68 */
  69
  70 int
  71 auth_get_data(uschar ** aptr, const uschar * challenge, int challen)
  72 {
  73 int c;
  74 int p = 0;
  75 smtp_printf("334 %s\r\n", FALSE, b64encode(challenge, challen));
  76 while ((c = receive_getc(GETC_BUFFER_UNLIMITED)) != '\n' && c != EOF)
  77   {
  78   if (p >= big_buffer_size - 1) return BAD64;
  79   big_buffer[p++] = c;
  80   }
  81 if (p > 0 && big_buffer[p-1] == '\r') p--;
  82 big_buffer[p] = 0;
  83 DEBUG(D_receive) debug_printf("SMTP<< %s\n", big_buffer);
  84 if (Ustrcmp(big_buffer, "*") == 0) return CANCELLED;
  85 *aptr = big_buffer;
  86 return OK;
  87 }
  88
  89
  90
  91 int
  92 auth_prompt(const uschar * challenge)
  93 {
  94 int rc, len;
  95 uschar * resp, * clear, * end;
  96
  97 if ((rc = auth_get_data(&resp, challenge, Ustrlen(challenge))) != OK)
  98   return rc;
  99 if ((len = b64decode(resp, &clear)) < 0)
 100   return BAD64;
 101 end = clear + len;
 102
 103 /* This loop must run at least once, in case the length is zero */
 104 do
 105   {
 106   if (expand_nmax < AUTH_VARS) auth_vars[expand_nmax] = clear;
 107   expand_nstring[++expand_nmax] = clear;
 108   while (*clear != 0) clear++;
 109   expand_nlength[expand_nmax] = clear++ - expand_nstring[expand_nmax];
 110   }
 111 while (clear < end && expand_nmax < EXPAND_MAXN);
 112 return OK;
 113 }
 114
 115
 116 /***********************************************
 117 *       Send an AUTH-negotiation item           *
 118 ************************************************/
 119
 120 /* Expand and send one client auth item and read the response.
 121 Include the AUTH command and method if tagged as "first".  Use the given buffer
 122 for receiving the b6-encoded reply; decode it it return it in the string arg.
 123
 124 Return:
 125   OK          success
 126   FAIL_SEND   error after writing a command; errno is set
 127   FAIL        failed after reading a response;
 128               either errno is set (for timeouts, I/O failures) or
 129               the buffer contains the SMTP response line
 130   CANCELLED   the client cancelled authentication (often "fail" in expansion)
 131               the buffer may contain a message; if not, *buffer = 0
 132   ERROR       local problem (typically expansion error); message in buffer
 133   DEFER       more items expected
 134 */
 135
 136 int
 137 auth_client_item(void * sx, auth_instance * ablock, const uschar ** inout,
 138   unsigned flags, int timeout, uschar * buffer, int buffsize)
 139 {
 140 int len, clear_len;
 141 uschar * ss, * clear;
 142
 143 ss = US expand_cstring(*inout);
 144 if (ss == *inout) ss = string_copy(ss);
 145
 146 /* Forced expansion failure is not an error; authentication is abandoned. On
 147 all but the first string, we have to abandon the authentication attempt by
 148 sending a line containing "*". Save the failed expansion string, because it
 149 is in big_buffer, and that gets used by the sending function. */
 150
 151 if (!ss)
 152   {
 153   if (!(flags & AUTH_ITEM_FIRST))
 154     {
 155     if (smtp_write_command(sx, SCMD_FLUSH, "*\r\n") >= 0)
 156       (void) smtp_read_response(sx, US buffer, buffsize, '2', timeout);
 157     }
 158   if (f.expand_string_forcedfail)
 159     {
 160     *buffer = 0;       /* No message */
 161     return CANCELLED;
 162     }
 163   string_format(buffer, buffsize, "expansion of \"%s\" failed in %s "
 164     "authenticator: %s", *inout, ablock->name, expand_string_message);
 165   return ERROR;
 166   }
 167
 168 len = Ustrlen(ss);
 169
 170 /* The character ^ is used as an escape for a binary zero character, which is
 171 needed for the PLAIN mechanism. It must be doubled if really needed. */
 172
 173 for (int i = 0; i < len; i++)
 174   if (ss[i] == '^')
 175     if (ss[i+1] != '^')
 176       ss[i] = 0;
 177     else
 178       if (--len > ++i) memmove(ss + i, ss + i + 1, len - i);
 179
 180 /* The first string is attached to the AUTH command; others are sent
 181 unembellished. */
 182
 183 if (flags & AUTH_ITEM_FIRST)
 184   {
 185   if (smtp_write_command(sx, SCMD_FLUSH, "AUTH %s%s%s\r\n",
 186        ablock->public_name, len == 0 ? "" : " ", b64encode(CUS ss, len)) < 0)
 187     return FAIL_SEND;
 188   }
 189 else
 190   if (smtp_write_command(sx, SCMD_FLUSH, "%s\r\n", b64encode(CUS ss, len)) < 0)
 191     return FAIL_SEND;
 192
 193 /* If we receive a success response from the server, authentication
 194 has succeeded. There may be more data to send, but is there any point
 195 in provoking an error here? */
 196
 197 if (smtp_read_response(sx, buffer, buffsize, '2', timeout))
 198   {
 199   *inout = NULL;
 200   return OK;
 201   }
 202
 203 /* Not a success response. If errno != 0 there is some kind of transmission
 204 error. Otherwise, check the response code in the buffer. If it starts with
 205 '3', more data is expected. */
 206
 207 if (errno != 0 || buffer[0] != '3') return FAIL;
 208
 209 /* If there is no more data to send, we have to cancel the authentication
 210 exchange and return ERROR. */
 211
 212 if (flags & AUTH_ITEM_LAST)
 213   {
 214   if (smtp_write_command(sx, SCMD_FLUSH, "*\r\n") >= 0)
 215     (void)smtp_read_response(sx, US buffer, buffsize, '2', timeout);
 216   string_format(buffer, buffsize, "Too few items in client_send in %s "
 217     "authenticator", ablock->name);
 218   return ERROR;
 219   }
 220
 221 /* Now that we know we'll continue, we put the received data into $auth<n>,
 222 if possible. First, decode it: buffer+4 skips over the SMTP status code. */
 223
 224 clear_len = b64decode(buffer+4, &clear);
 225
 226 /* If decoding failed, the default is to terminate the authentication, and
 227 return FAIL, with the SMTP response still in the buffer. However, if client_
 228 ignore_invalid_base64 is set, we ignore the error, and put an empty string
 229 into $auth<n>. */
 230
 231 if (clear_len < 0)
 232   {
 233   uschar *save_bad = string_copy(buffer);
 234   if (!(flags & AUTH_ITEM_IGN64))
 235     {
 236     if (smtp_write_command(sx, SCMD_FLUSH, "*\r\n") >= 0)
 237       (void)smtp_read_response(sx, US buffer, buffsize, '2', timeout);
 238     string_format(buffer, buffsize, "Invalid base64 string in server "
 239       "response \"%s\"", save_bad);
 240     return CANCELLED;
 241     }
 242   DEBUG(D_auth) debug_printf("bad b64 decode for '%s';"
 243        " ignoring due to client_ignore_invalid_base64\n", save_bad);
 244   clear = string_copy(US"");
 245   clear_len = 0;
 246   }
 247
 248 *inout = clear;
 249 return DEFER;
 250 }
 251
 252
 253 /* End of get_data.c */