src/src/auths/call_pam.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2018 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 #include "../exim.h"
   9
  10 /* This module contains functions that call the PAM authentication mechanism
  11 defined by Sun for Solaris and also available for Linux and other OS.
  12
  13 We can't just compile this code and allow the library mechanism to omit the
  14 functions if they are not wanted, because we need to have the PAM headers
  15 available for compiling. Therefore, compile these functions only if SUPPORT_PAM
  16 is defined. However, some compilers don't like compiling empty modules, so keep
  17 them happy with a dummy when skipping the rest. Make it reference itself to
  18 stop picky compilers complaining that it is unused, and put in a dummy argument
  19 to stop even pickier compilers complaining about infinite loops.
  20 Then use a mutually-recursive pair as gcc is just getting stupid. */
  21
  22 #ifndef SUPPORT_PAM
  23 static void dummy(int x);
  24 static void dummy2(int x) { dummy(x-1); }
  25 static void dummy(int x) { dummy2(x-1); }
  26 #else  /* SUPPORT_PAM */
  27
  28 #ifdef PAM_H_IN_PAM
  29 #include <pam/pam_appl.h>
  30 #else
  31 #include <security/pam_appl.h>
  32 #endif
  33
  34 /* According to the specification, it should be possible to have an application
  35 data pointer passed to the conversation function. However, I was unable to get
  36 this to work on Solaris 2.6, so static variables are used instead. */
  37
  38 static int pam_conv_had_error;
  39 static const uschar *pam_args;
  40 static BOOL pam_arg_ended;
  41
  42
  43
  44 /*************************************************
  45 *           PAM conversation function            *
  46 *************************************************/
  47
  48 /* This function is passed to the PAM authentication function, and it calls it
  49 back when it wants data from the client. The string list is in pam_args. When
  50 we reach the end, we pass back an empty string once. If this function is called
  51 again, it will give an error response. This is protection against something
  52 crazy happening.
  53
  54 Arguments:
  55   num_msg        number of messages associated with the call
  56   msg            points to an array of length num_msg of pam_message structures
  57   resp           set to point to the response block, which has to be got by
  58                    this function
  59   appdata_ptr    the application data pointer - not used because in Solaris
  60                    2.6 it always arrived in pam_converse() as NULL
  61
  62 Returns:         a PAM return code
  63 */
  64
  65 static int
  66 pam_converse (int num_msg, PAM_CONVERSE_ARG2_TYPE **msg,
  67   struct pam_response **resp, void *appdata_ptr)
  68 {
  69 int sep = 0;
  70 struct pam_response *reply;
  71
  72 if (pam_arg_ended) return PAM_CONV_ERR;
  73
  74 reply = malloc(sizeof(struct pam_response) * num_msg);
  75
  76 if (reply == NULL) return PAM_CONV_ERR;
  77
  78 for (int i = 0; i < num_msg; i++)
  79   {
  80   uschar *arg;
  81   switch (msg[i]->msg_style)
  82     {
  83     case PAM_PROMPT_ECHO_ON:
  84     case PAM_PROMPT_ECHO_OFF:
  85     arg = string_nextinlist(&pam_args, &sep, big_buffer, big_buffer_size);
  86     if (arg == NULL)
  87       {
  88       arg = US"";
  89       pam_arg_ended = TRUE;
  90       }
  91     reply[i].resp = CS string_copy_malloc(arg); /* PAM frees resp */
  92     reply[i].resp_retcode = PAM_SUCCESS;
  93     break;
  94
  95     case PAM_TEXT_INFO:    /* Just acknowledge messages */
  96     case PAM_ERROR_MSG:
  97     reply[i].resp_retcode = PAM_SUCCESS;
  98     reply[i].resp = NULL;
  99     break;
 100
 101     default:  /* Must be an error of some sort... */
 102     free (reply);
 103     pam_conv_had_error = TRUE;
 104     return PAM_CONV_ERR;
 105     }
 106   }
 107
 108 *resp = reply;
 109 return PAM_SUCCESS;
 110 }
 111
 112
 113
 114 /*************************************************
 115 *              Perform PAM authentication        *
 116 *************************************************/
 117
 118 /* This function calls the PAM authentication mechanism, passing over one or
 119 more data strings.
 120
 121 Arguments:
 122   s        a colon-separated list of strings
 123   errptr   where to point an error message
 124
 125 Returns:   OK if authentication succeeded
 126            FAIL if authentication failed
 127            ERROR some other error condition
 128 */
 129
 130 int
 131 auth_call_pam(const uschar *s, uschar **errptr)
 132 {
 133 pam_handle_t *pamh = NULL;
 134 struct pam_conv pamc;
 135 int pam_error;
 136 int sep = 0;
 137 uschar *user;
 138
 139 /* Set up the input data structure: the address of the conversation function,
 140 and a pointer to application data, which we don't use because I couldn't get it
 141 to work under Solaris 2.6 - it always arrived in pam_converse() as NULL. */
 142
 143 pamc.conv = pam_converse;
 144 pamc.appdata_ptr = NULL;
 145
 146 /* Initialize the static data - the current input data, the error flag, and the
 147 flag for data end. */
 148
 149 pam_args = s;
 150 pam_conv_had_error = FALSE;
 151 pam_arg_ended = FALSE;
 152
 153 /* The first string in the list is the user. If this is an empty string, we
 154 fail. PAM doesn't support authentication with an empty user (it prompts for it,
 155 causing a potential mis-interpretation). */
 156
 157 user = string_nextinlist(&pam_args, &sep, big_buffer, big_buffer_size);
 158 if (user == NULL || user[0] == 0) return FAIL;
 159
 160 /* Start off PAM interaction */
 161
 162 DEBUG(D_auth)
 163   debug_printf("Running PAM authentication for user \"%s\"\n", user);
 164
 165 pam_error = pam_start ("exim", CS user, &pamc, &pamh);
 166
 167 /* Do the authentication - the pam_authenticate() will call pam_converse() to
 168 get the data it wants. After successful authentication we call pam_acct_mgmt()
 169 to apply any other restrictions (e.g. only some times of day). */
 170
 171 if (pam_error == PAM_SUCCESS)
 172   {
 173   pam_error = pam_authenticate (pamh, PAM_SILENT);
 174   if (pam_error == PAM_SUCCESS && !pam_conv_had_error)
 175     pam_error = pam_acct_mgmt (pamh, PAM_SILENT);
 176   }
 177
 178 /* Finish the PAM interaction - this causes it to clean up store etc. Unclear
 179 what should be passed as the second argument. */
 180
 181 pam_end(pamh, PAM_SUCCESS);
 182
 183 /* Sort out the return code. If not success, set the error message. */
 184
 185 if (pam_error == PAM_SUCCESS)
 186   {
 187   DEBUG(D_auth) debug_printf("PAM success\n");
 188   return OK;
 189   }
 190
 191 *errptr = US pam_strerror(pamh, pam_error);
 192 DEBUG(D_auth) debug_printf("PAM error: %s\n", *errptr);
 193
 194 if (pam_error == PAM_USER_UNKNOWN ||
 195     pam_error == PAM_AUTH_ERR ||
 196     pam_error == PAM_ACCT_EXPIRED)
 197   return FAIL;
 198
 199 return ERROR;
 200 }
 201
 202 #endif  /* SUPPORT_PAM */
 203
 204 /* End of call_pam.c */