input.c

   1 /* input.c -- password getting module for vlock
   2  *
   3  * This program is copyright (C) 1994 Michael K. Johnson, and is free
   4  * software which is freely distributable under the terms of the
   5  * GNU General Public License version 2, included as the file COPYING in this
   6  * distribution.  It is NOT public domain software, and any
   7  * redistribution not permitted by the GNU General Public License is
   8  * expressly forbidden without prior written permission from
   9  * the author.
  10  *
  11  */
  12
  13   /* Marek hacked the code a bit:
  14       - use /dev/tty instead of /dev/console (permissions on the latter
  15         shouldn't allow all users to open it)
  16       - get encrypted password once at startup, drop privileges as soon
  17         as possible (we have to be setuid root for shadow passwords)
  18         * This may not be a good idea, because it makes vlock a way for
  19           the user to get at root's encrypted password (if user can
  20           ptrace process after setuid(getuid()); -- check this)
  21         * (probably) can't give up id with PAM anyway, at least with
  22           shadow
  23       - error message instead of core dump if getpwuid() returns NULL
  24       - added check if encrypted password is valid (>=13 characters)
  25       - terminal modes should be properly restored (don't leave echo off)
  26         if getpass() fails.
  27   */
  28
  29 #include <errno.h>
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <signal.h>
  34 #include <sys/types.h>
  35 #include <pwd.h>
  36
  37 #include <security/pam_appl.h>
  38 #include <security/pam_misc.h>
  39
  40 static struct pam_conv PAM_conversation = {
  41     &misc_conv,
  42     NULL
  43 };
  44
  45 #include "vlock.h"
  46
  47
  48 static char prompt[100];  /* password prompt ("user's password: ") */
  49 static char username[40]; /* current user's name */
  50
  51
  52 static int
  53 correct_password(void)
  54 {
  55   pam_handle_t *pamh;
  56   int pam_error;
  57
  58   /* Now use PAM to do authentication.
  59    */
  60   #define PAM_BAIL if (pam_error != PAM_SUCCESS) { \
  61      pam_end(pamh, 0); \
  62      /* fix signals that may have been disordered by pam */ \
  63      set_signal_mask(0); \
  64      return 0; \
  65      }
  66   pam_error = pam_start("vlock", username, &PAM_conversation, &pamh);
  67   PAM_BAIL;
  68   printf("%s's ", username); fflush(stdout);
  69   pam_error = pam_set_item(pamh, PAM_USER_PROMPT, strdup(prompt));
  70   PAM_BAIL;
  71   pam_error = pam_authenticate(pamh, 0);
  72   /* fix signals that may have been disordered by pam */
  73   set_signal_mask(0);
  74 #ifdef NO_ROOT_PASS
  75   PAM_BAIL;
  76 #else
  77   if (pam_error != PAM_SUCCESS) {
  78     /* Try as root; bail if no success there either */
  79     printf("root's "); fflush(stdout);
  80     pam_error = pam_set_item(pamh, PAM_USER_PROMPT, strdup(prompt));
  81     PAM_BAIL;
  82     pam_error = pam_set_item(pamh, PAM_USER, "root");
  83     PAM_BAIL;
  84     pam_error = pam_authenticate(pamh, 0);
  85     /* fix signals that may have been disordered by pam */
  86     set_signal_mask(0);
  87     PAM_BAIL;
  88   }
  89 #endif /* !NO_ROOT_PASS */
  90   pam_end(pamh, PAM_SUCCESS);
  91   /* If this point is reached, the user has been authenticated. */
  92   return 1;
  93 }
  94
  95
  96
  97
  98 void
  99 get_password(void)
 100 {
 101   set_terminal(0);
 102   do {
 103     if (o_lock_all) {
 104       /* To do: allow logging the user out safely without shutting down
 105          the whole machine...  */
 106       printf("The entire console display is now completely locked.\n"
 107        "You will not be able to switch to another virtual console.\n");
 108
 109     } else {
 110       printf("This TTY is now locked.\n");
 111       if (is_vt)
 112         printf("Use Alt-function keys to switch to other virtual consoles.\n");
 113     }
 114     printf("Please enter the password to unlock.\n");
 115     fflush(stdout);
 116
 117     /* correct_password() sets the terminal status as necessary */
 118     if (correct_password()) {
 119       restore_signals();
 120       restore_terminal();
 121       return;
 122     }
 123
 124     /* correct_password() may have failed to return success because the   */
 125     /* terminal is closed.  In this case, it would not be appropriate to  */
 126     /* try again...                                                       */
 127     if (isatty(STDIN_FILENO) == 0) {
 128         perror("isatty");
 129         restore_terminal();
 130         exit(1);
 131     }
 132
 133
 134     /* Need to slow down people who are trying to break in by brute force */
 135     /* Note that it is technically possible to break this, but I can't    */
 136     /* make it happen, even knowing the code and knowing how to try.      */
 137     /* If you manage to kill vlock from the terminal while in this code,  */
 138     /* please tell me how you did it.                                     */
 139     printf(" *** That password is incorrect; please try again. *** \n");
 140     printf("\n");
 141
 142   } while (1);
 143 }
 144
 145   /* Get the user's and root passwords once at startup and store them
 146      for use later.  This has several advantages:
 147       - to support shadow passwords, we have to be installed setuid
 148         root, but we can completely drop privileges very early
 149       - we avoid problems with unlocking when using NIS, after the
 150         NIS server goes down
 151       - before locking, we can check if any real password has a chance
 152         to match the encrypted password (should be >=13 chars)
 153       - this is the same way xlockmore does it.
 154      Warning: this code runs as root - be careful if you modify it.
 155
 156      With PAM, applications never see encrypted passwords, so we can't
 157      get the encrypted password ahead of time.  We just have to hope
 158      things work later on, just like we do with PAMified xlockmore.
 159    */
 160
 161 static struct passwd *
 162 my_getpwuid(uid_t uid)
 163 {
 164   struct passwd *pw;
 165
 166   pw = getpwuid(uid);
 167   if (!pw) {
 168     fprintf(stderr, "vlock: getpwuid(%d) failed: %s\n", uid, strerror(errno));
 169     exit(1);
 170   }
 171   return pw;
 172 }
 173
 174 void
 175 init_passwords(void)
 176 {
 177   struct passwd *pw;
 178
 179   /* Get the password entry for this user (never returns NULL).  */
 180   pw = my_getpwuid(getuid());
 181
 182   /* Save the results where they will not get overwritten.  */
 183   strncpy(username, pw->pw_name, sizeof(username) - 1);
 184   username[sizeof(username) - 1] = '\0';
 185 }