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password-prompt.c

/*  -*- coding: utf-8; mode: c; mode: orgtbl -*- */
/*
 * Password-prompt - Read a password from the terminal and print it
 * 
 * Copyright © 2008,2009 Teddy Hogeborn
 * Copyright © 2008,2009 Björn Påhlsson
 * 
 * This program is free software: you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see
 * <http://www.gnu.org/licenses/>.
 * 
 * Contact the authors at <mandos@fukt.bsnet.se>.
 */

#define _GNU_SOURCE           /* getline() */

#include <termios.h>          /* struct termios, tcsetattr(),
                           TCSAFLUSH, tcgetattr(), ECHO */
#include <unistd.h>           /* struct termios, tcsetattr(),
                           STDIN_FILENO, TCSAFLUSH,
                           tcgetattr(), ECHO */
#include <signal.h>           /* sig_atomic_t, raise(), struct
                           sigaction, sigemptyset(),
                           sigaction(), sigaddset(), SIGINT,
                           SIGQUIT, SIGHUP, SIGTERM,
                           raise() */
#include <stddef.h>           /* NULL, size_t, ssize_t */
#include <sys/types.h>        /* ssize_t */
#include <stdlib.h>           /* EXIT_SUCCESS, EXIT_FAILURE,
                           getopt_long, getenv() */
#include <stdio.h>            /* fprintf(), stderr, getline(),
                           stdin, feof(), perror(), fputc(),
                           stdout, getopt_long */
#include <errno.h>            /* errno, EINVAL */
#include <iso646.h>           /* or, not */
#include <stdbool.h>          /* bool, false, true */
#include <string.h>           /* strlen, rindex, strncmp, strcmp */
#include <argp.h>       /* struct argp_option, struct
                           argp_state, struct argp,
                           argp_parse(), error_t,
                           ARGP_KEY_ARG, ARGP_KEY_END,
                           ARGP_ERR_UNKNOWN */

volatile sig_atomic_t quit_now = 0;
int signal_received;
bool debug = false;
const char *argp_program_version = "password-prompt " VERSION;
const char *argp_program_bug_address = "<mandos@fukt.bsnet.se>";

static void termination_handler(int signum){
  if(quit_now){
    return;
  }
  quit_now = 1;
  signal_received = signum;
}

int main(int argc, char **argv){
  ssize_t ret;
  size_t n;
  struct termios t_new, t_old;
  char *buffer = NULL;
  char *prefix = NULL;
  int status = EXIT_SUCCESS;
  struct sigaction old_action,
    new_action = { .sa_handler = termination_handler,
               .sa_flags = 0 };
  {
    struct argp_option options[] = {
      { .name = "prefix", .key = 'p',
      .arg = "PREFIX", .flags = 0,
      .doc = "Prefix shown before the prompt", .group = 2 },
      { .name = "debug", .key = 128,
      .doc = "Debug mode", .group = 3 },
      { .name = NULL }
    };
    
    error_t parse_opt (int key, char *arg, struct argp_state *state){
      switch (key){
      case 'p':
      prefix = arg;
      break;
      case 128:
      debug = true;
      break;
      case ARGP_KEY_ARG:
      argp_usage(state);
      break;
      case ARGP_KEY_END:
      break;
      default:
      return ARGP_ERR_UNKNOWN;
      }
      return 0;
    }
    
    struct argp argp = { .options = options, .parser = parse_opt,
                   .args_doc = "",
                   .doc = "Mandos password-prompt -- Read and"
                   " output a password" };
    ret = argp_parse(&argp, argc, argv, 0, 0, NULL);
    if(ret == ARGP_ERR_UNKNOWN){
      fprintf(stderr, "Unknown error while parsing arguments\n");
      return EXIT_FAILURE;
    }
  }
  
  if(debug){
    fprintf(stderr, "Starting %s\n", argv[0]);
  }
  if(debug){
    fprintf(stderr, "Storing current terminal attributes\n");
  }
  
  if(tcgetattr(STDIN_FILENO, &t_old) != 0){
    perror("tcgetattr");
    return EXIT_FAILURE;
  }
  
  sigemptyset(&new_action.sa_mask);
  ret = sigaddset(&new_action.sa_mask, SIGINT);
  if(ret == -1){
    perror("sigaddset");
    return EXIT_FAILURE;
  }
  ret = sigaddset(&new_action.sa_mask, SIGHUP);
  if(ret == -1){
    perror("sigaddset");
    return EXIT_FAILURE;
  }
  ret = sigaddset(&new_action.sa_mask, SIGTERM);
  if(ret == -1){
    perror("sigaddset");
    return EXIT_FAILURE;
  }
  /* Need to check if the handler is SIG_IGN before handling:
     | [[info:libc:Initial Signal Actions]] |
     | [[info:libc:Basic Signal Handling]]  |
  */
  ret = sigaction(SIGINT, NULL, &old_action);
  if(ret == -1){
    perror("sigaction");
    return EXIT_FAILURE;
  }
  if(old_action.sa_handler != SIG_IGN){
    ret = sigaction(SIGINT, &new_action, NULL);
    if(ret == -1){
      perror("sigaction");
      return EXIT_FAILURE;
    }
  }
  ret = sigaction(SIGHUP, NULL, &old_action);
  if(ret == -1){
    perror("sigaction");
    return EXIT_FAILURE;
  }
  if(old_action.sa_handler != SIG_IGN){
    ret = sigaction(SIGHUP, &new_action, NULL);
    if(ret == -1){
      perror("sigaction");
      return EXIT_FAILURE;
    }
  }
  ret = sigaction(SIGTERM, NULL, &old_action);
  if(ret == -1){
    perror("sigaction");
    return EXIT_FAILURE;
  }
  if(old_action.sa_handler != SIG_IGN){
    ret = sigaction(SIGTERM, &new_action, NULL);
    if(ret == -1){
      perror("sigaction");
      return EXIT_FAILURE;
    }
  }
  
  
  if(debug){
    fprintf(stderr, "Removing echo flag from terminal attributes\n");
  }
  
  t_new = t_old;
  t_new.c_lflag &= ~ECHO;
  if(tcsetattr(STDIN_FILENO, TCSAFLUSH, &t_new) != 0){
    perror("tcsetattr-echo");
    return EXIT_FAILURE;
  }

  if(debug){
    fprintf(stderr, "Waiting for input from stdin \n");
  }
  while(true){
    if(quit_now){
      if(debug){
      fprintf(stderr, "Interrupted by signal, exiting.\n");
      }
      status = EXIT_FAILURE;
      break;
    }

    if(prefix){
      fprintf(stderr, "%s ", prefix);
    }
    {
      const char *cryptsource = getenv("cryptsource");
      const char *crypttarget = getenv("crypttarget");
      const char *const prompt
      = "Enter passphrase to unlock the disk";
      if(cryptsource == NULL){
      if(crypttarget == NULL){
        fprintf(stderr, "%s: ", prompt);
      } else {
        fprintf(stderr, "%s (%s): ", prompt, crypttarget);
      }
      } else {
      if(crypttarget == NULL){
        fprintf(stderr, "%s %s: ", prompt, cryptsource);
      } else {
        fprintf(stderr, "%s %s (%s): ", prompt, cryptsource,
              crypttarget);
      }
      }
    }
    ret = getline(&buffer, &n, stdin);
    if(ret > 0){
      status = EXIT_SUCCESS;
      /* Make n = data size instead of allocated buffer size */
      n = (size_t)ret;
      /* Strip final newline */
      if(n>0 and buffer[n-1] == '\n'){
      buffer[n-1] = '\0';     /* not strictly necessary */
      n--;
      }
      size_t written = 0;
      while(written < n){
      ret = write(STDOUT_FILENO, buffer + written, n - written);
      if(ret < 0){
        perror("write");
        status = EXIT_FAILURE;
        break;
      }
      written += (size_t)ret;
      }
      break;
    }
    if(ret < 0){
      if(errno != EINTR and not feof(stdin)){
      perror("getline");
      status = EXIT_FAILURE;
      break;
      }
    }
    /* if(ret == 0), then the only sensible thing to do is to retry to
       read from stdin */
    fputc('\n', stderr);
    if(debug and not quit_now){
      /* If quit_now is nonzero, we were interrupted by a signal, and
       will print that later, so no need to show this too. */
      fprintf(stderr, "getline() returned 0, retrying.\n");
    }
  }
  
  free(buffer);
  
  if(debug){
    fprintf(stderr, "Restoring terminal attributes\n");
  }
  if(tcsetattr(STDIN_FILENO, TCSAFLUSH, &t_old) != 0){
    perror("tcsetattr+echo");
  }
  
  if(quit_now){
    sigemptyset(&old_action.sa_mask);
    old_action.sa_handler = SIG_DFL;
    ret = sigaction(signal_received, &old_action, NULL);
    if(ret == -1){
      perror("sigaction");
    }
    raise(signal_received);
  }
  
  if(debug){
    fprintf(stderr, "%s is exiting with status %d\n", argv[0],
          status);
  }
  if(status == EXIT_SUCCESS){
    fputc('\n', stderr);
  }
  
  return status;
}

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