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 = store_get(sizeof(struct pam_response) * num_msg, FALSE);
  75
  76 for (int i = 0; i < num_msg; i++)
  77   {
  78   uschar *arg;
  79   switch (msg[i]->msg_style)
  80     {
  81     case PAM_PROMPT_ECHO_ON:
  82     case PAM_PROMPT_ECHO_OFF:
  83     arg = string_nextinlist(&pam_args, &sep, big_buffer, big_buffer_size);
  84     if (arg == NULL)
  85       {
  86       arg = US"";
  87       pam_arg_ended = TRUE;
  88       }
  89     reply[i].resp = CS string_copy_perm(arg, FALSE); /* PAM frees resp */
  90     reply[i].resp_retcode = PAM_SUCCESS;
  91     break;
  92
  93     case PAM_TEXT_INFO:    /* Just acknowledge messages */
  94     case PAM_ERROR_MSG:
  95     reply[i].resp_retcode = PAM_SUCCESS;
  96     reply[i].resp = NULL;
  97     break;
  98
  99     default:  /* Must be an error of some sort... */
 100     pam_conv_had_error = TRUE;
 101     return PAM_CONV_ERR;
 102     }
 103   }
 104
 105 *resp = reply;
 106 return PAM_SUCCESS;
 107 }
 108
 109
 110
 111 /*************************************************
 112 *              Perform PAM authentication        *
 113 *************************************************/
 114
 115 /* This function calls the PAM authentication mechanism, passing over one or
 116 more data strings.
 117
 118 Arguments:
 119   s        a colon-separated list of strings
 120   errptr   where to point an error message
 121
 122 Returns:   OK if authentication succeeded
 123            FAIL if authentication failed
 124            ERROR some other error condition
 125 */
 126
 127 int
 128 auth_call_pam(const uschar *s, uschar **errptr)
 129 {
 130 pam_handle_t *pamh = NULL;
 131 struct pam_conv pamc;
 132 int pam_error;
 133 int sep = 0;
 134 uschar *user;
 135
 136 /* Set up the input data structure: the address of the conversation function,
 137 and a pointer to application data, which we don't use because I couldn't get it
 138 to work under Solaris 2.6 - it always arrived in pam_converse() as NULL. */
 139
 140 pamc.conv = pam_converse;
 141 pamc.appdata_ptr = NULL;
 142
 143 /* Initialize the static data - the current input data, the error flag, and the
 144 flag for data end. */
 145
 146 pam_args = s;
 147 pam_conv_had_error = FALSE;
 148 pam_arg_ended = FALSE;
 149
 150 /* The first string in the list is the user. If this is an empty string, we
 151 fail. PAM doesn't support authentication with an empty user (it prompts for it,
 152 causing a potential mis-interpretation). */
 153
 154 user = string_nextinlist(&pam_args, &sep, big_buffer, big_buffer_size);
 155 if (user == NULL || user[0] == 0) return FAIL;
 156
 157 /* Start off PAM interaction */
 158
 159 DEBUG(D_auth)
 160   debug_printf("Running PAM authentication for user \"%s\"\n", user);
 161
 162 pam_error = pam_start ("exim", CS user, &pamc, &pamh);
 163
 164 /* Do the authentication - the pam_authenticate() will call pam_converse() to
 165 get the data it wants. After successful authentication we call pam_acct_mgmt()
 166 to apply any other restrictions (e.g. only some times of day). */
 167
 168 if (pam_error == PAM_SUCCESS)
 169   {
 170   pam_error = pam_authenticate (pamh, PAM_SILENT);
 171   if (pam_error == PAM_SUCCESS && !pam_conv_had_error)
 172     pam_error = pam_acct_mgmt (pamh, PAM_SILENT);
 173   }
 174
 175 /* Finish the PAM interaction - this causes it to clean up store etc. Unclear
 176 what should be passed as the second argument. */
 177
 178 pam_end(pamh, PAM_SUCCESS);
 179
 180 /* Sort out the return code. If not success, set the error message. */
 181
 182 if (pam_error == PAM_SUCCESS)
 183   {
 184   DEBUG(D_auth) debug_printf("PAM success\n");
 185   return OK;
 186   }
 187
 188 *errptr = US pam_strerror(pamh, pam_error);
 189 DEBUG(D_auth) debug_printf("PAM error: %s\n", *errptr);
 190
 191 if (pam_error == PAM_USER_UNKNOWN ||
 192     pam_error == PAM_AUTH_ERR ||
 193     pam_error == PAM_ACCT_EXPIRED)
 194   return FAIL;
 195
 196 return ERROR;
 197 }
 198
 199 #endif  /* SUPPORT_PAM */
 200
 201 /* End of call_pam.c */