usplash.c

/*  -*- coding: utf-8 -*- */
/*
 * Usplash - Read a password from usplash and output 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 <https://www.fukt.bsnet.se/~belorn/> and
 * <https://www.fukt.bsnet.se/~teddy/>.
 */

#define _GNU_SOURCE           /* asprintf() */
#include <signal.h>           /* sig_atomic_t, struct sigaction,
                           sigemptyset(), sigaddset(), SIGINT,
                           SIGHUP, SIGTERM, sigaction(),
                           SIG_IGN, kill(), SIGKILL */
#include <stdbool.h>          /* bool, false, true */
#include <fcntl.h>            /* open(), O_WRONLY, O_RDONLY */
#include <iso646.h>           /* and, or, not*/
#include <errno.h>            /* errno, EINTR */
#include <sys/types.h>        /* size_t, ssize_t, pid_t, DIR, struct
                           dirent */
#include <stddef.h>           /* NULL */
#include <string.h>           /* strlen(), memcmp() */
#include <stdio.h>            /* asprintf(), perror() */
#include <unistd.h>           /* close(), write(), readlink(),
                           read(), STDOUT_FILENO, sleep(),
                           fork(), setuid(), geteuid(),
                           setsid(), chdir(), dup2(),
                           STDERR_FILENO, execv() */
#include <stdlib.h>           /* free(), EXIT_FAILURE, realloc(),
                           EXIT_SUCCESS, malloc(), _exit() */
#include <stdlib.h>           /* getenv() */
#include <dirent.h>           /* opendir(), readdir(), closedir() */
#include <inttypes.h>         /* intmax_t, strtoimax() */
#include <sys/stat.h>         /* struct stat, lstat(), S_ISLNK */

sig_atomic_t interrupted_by_signal = 0;

static void termination_handler(__attribute__((unused))int signum){
  interrupted_by_signal = 1;
}

static bool usplash_write(const char *cmd, const char *arg){
  /* 
   * usplash_write("TIMEOUT", "15") will write "TIMEOUT 15\0"
   * usplash_write("PULSATE", NULL) will write "PULSATE\0"
   * SEE ALSO
   *         usplash_write(8)
   */
  int ret;
  int fifo_fd;
  do{
    fifo_fd = open("/dev/.initramfs/usplash_fifo", O_WRONLY);
    if(fifo_fd == -1 and (errno != EINTR or interrupted_by_signal)){
      return false;
    }
  }while(fifo_fd == -1);
  
  const char *cmd_line;
  size_t cmd_line_len;
  char *cmd_line_alloc = NULL;
  if(arg == NULL){
    cmd_line = cmd;
    cmd_line_len = strlen(cmd);
  }else{
    do{
      ret = asprintf(&cmd_line_alloc, "%s %s", cmd, arg);
      if(ret == -1 and (errno != EINTR or interrupted_by_signal)){
      int e = errno;
      close(fifo_fd);
      errno = e;
      return false;
      }
    }while(ret == -1);
    cmd_line = cmd_line_alloc;
    cmd_line_len = (size_t)ret + 1;
  }
  
  size_t written = 0;
  ssize_t sret = 0;
  while(not interrupted_by_signal and written < cmd_line_len){
    sret = write(fifo_fd, cmd_line + written,
             cmd_line_len - written);
    if(sret == -1){
      if(errno != EINTR or interrupted_by_signal){
      int e = errno;
      close(fifo_fd);
      free(cmd_line_alloc);
      errno = e;
      return false;
      } else {
      continue;
      }
    }
    written += (size_t)sret;
  }
  free(cmd_line_alloc);
  do{
    ret = close(fifo_fd);
    if(ret == -1 and (errno != EINTR or interrupted_by_signal)){
      return false;
    }
  }while(ret == -1);
  if(interrupted_by_signal){
    return false;
  }
  return true;
}

int main(__attribute__((unused))int argc,
       __attribute__((unused))char **argv){
  int ret = 0;
  ssize_t sret;
  bool an_error_occured = false;
  
  /* Create prompt string */
  char *prompt = NULL;
  {
    const char *const cryptsource = getenv("cryptsource");
    const char *const crypttarget = getenv("crypttarget");
    const char prompt_start[] = "Enter passphrase to unlock the disk";
    
    if(cryptsource == NULL){
      if(crypttarget == NULL){
      ret = asprintf(&prompt, "%s: ", prompt_start);
      } else {
      ret = asprintf(&prompt, "%s (%s): ", prompt_start,
                   crypttarget);
      }
    } else {
      if(crypttarget == NULL){
      ret = asprintf(&prompt, "%s %s: ", prompt_start, cryptsource);
      } else {
      ret = asprintf(&prompt, "%s %s (%s): ", prompt_start,
                   cryptsource, crypttarget);
      }
    }
    if(ret == -1){
      return EXIT_FAILURE;
    }
  }
  
  /* Find usplash process */
  pid_t usplash_pid = 0;
  char *cmdline = NULL;
  size_t cmdline_len = 0;
  const char usplash_name[] = "/sbin/usplash";
  {
    DIR *proc_dir = opendir("/proc");
    if(proc_dir == NULL){
      free(prompt);
      perror("opendir");
      return EXIT_FAILURE;
    }
    for(struct dirent *proc_ent = readdir(proc_dir);
      proc_ent != NULL;
      proc_ent = readdir(proc_dir)){
      pid_t pid;
      {
      intmax_t tmpmax;
      char *tmp;
      errno = 0;
      tmpmax = strtoimax(proc_ent->d_name, &tmp, 10);
      if(errno != 0 or tmp == proc_ent->d_name or *tmp != '\0'
         or tmpmax != (pid_t)tmpmax){
        /* Not a process */
        continue;
      }
      pid = (pid_t)tmpmax;
      }
      /* Find the executable name by doing readlink() on the
       /proc/<pid>/exe link */
      char exe_target[sizeof(usplash_name)];
      {
      /* create file name string */
      char *exe_link;
      ret = asprintf(&exe_link, "/proc/%s/exe", proc_ent->d_name);
      if(ret == -1){
        perror("asprintf");
        free(prompt);
        closedir(proc_dir);
        return EXIT_FAILURE;
      }
      
      /* Check that it refers to a symlink owned by root:root */
      struct stat exe_stat;
      ret = lstat(exe_link, &exe_stat);
      if(ret == -1){
        if(errno == ENOENT){
          free(exe_link);
          continue;
        }
        perror("lstat");
        free(exe_link);
        free(prompt);
        closedir(proc_dir);
        return EXIT_FAILURE;
      }
      if(not S_ISLNK(exe_stat.st_mode)
         or exe_stat.st_uid != 0
         or exe_stat.st_gid != 0){
        free(exe_link);
        continue;
      }
      
      sret = readlink(exe_link, exe_target, sizeof(exe_target));
      free(exe_link);
      }
      if((sret == ((ssize_t)sizeof(exe_target)-1))
       and (memcmp(usplash_name, exe_target,
                 sizeof(exe_target)-1) == 0)){
      usplash_pid = pid;
      /* Read and save the command line of usplash in "cmdline" */
      {
        /* Open /proc/<pid>/cmdline  */
        int cl_fd;
        {
          char *cmdline_filename;
          ret = asprintf(&cmdline_filename, "/proc/%s/cmdline",
                     proc_ent->d_name);
          if(ret == -1){
            perror("asprintf");
            free(prompt);
            closedir(proc_dir);
            return EXIT_FAILURE;
          }
          cl_fd = open(cmdline_filename, O_RDONLY);
          if(cl_fd == -1){
            perror("open");
            free(cmdline_filename);
            free(prompt);
            closedir(proc_dir);
            return EXIT_FAILURE;
          }
          free(cmdline_filename);
        }
        size_t cmdline_allocated = 0;
        char *tmp;
        const size_t blocksize = 1024;
        do{
          if(cmdline_len + blocksize > cmdline_allocated){
            tmp = realloc(cmdline, cmdline_allocated + blocksize);
            if(tmp == NULL){
            perror("realloc");
            free(cmdline);
            free(prompt);
            closedir(proc_dir);
            return EXIT_FAILURE;
            }
            cmdline = tmp;
            cmdline_allocated += blocksize;
          }
          sret = read(cl_fd, cmdline + cmdline_len,
                  cmdline_allocated - cmdline_len);
          if(sret == -1){
            perror("read");
            free(cmdline);
            free(prompt);
            closedir(proc_dir);
            return EXIT_FAILURE;
          }
          cmdline_len += (size_t)sret;
        } while(sret != 0);
        close(cl_fd);
      }
      break;
      }
    }
    closedir(proc_dir);
  }
  if(usplash_pid == 0){
    free(prompt);
    return EXIT_FAILURE;
  }
  
  /* Set up the signal handler */
  {
    struct sigaction old_action,
      new_action = { .sa_handler = termination_handler,
                 .sa_flags = 0 };
    sigemptyset(&new_action.sa_mask);
    sigaddset(&new_action.sa_mask, SIGINT);
    sigaddset(&new_action.sa_mask, SIGHUP);
    sigaddset(&new_action.sa_mask, SIGTERM);
    ret = sigaction(SIGINT, NULL, &old_action);
    if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGINT, &new_action, NULL);
      if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
      }
    }
    ret = sigaction(SIGHUP, NULL, &old_action);
    if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGHUP, &new_action, NULL);
      if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
      }
    }
    ret = sigaction(SIGTERM, NULL, &old_action);
    if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGTERM, &new_action, NULL);
      if(ret == -1){
      perror("sigaction");
      free(prompt);
      return EXIT_FAILURE;
      }
    }
  }
  
  /* Write command to FIFO */
  if(not interrupted_by_signal){
    if(not usplash_write("TIMEOUT", "0")
       and (errno != EINTR)){
      perror("usplash_write");
      an_error_occured = true;
    }
  }
  if(not interrupted_by_signal and not an_error_occured){
    if(not usplash_write("INPUTQUIET", prompt)
       and (errno != EINTR)){
      perror("usplash_write");
      an_error_occured = true;
    }
  }
  free(prompt);
  
  /* This is not really a loop; while() is used to be able to "break"
     out of it; those breaks are marked "Big" */
  while(not interrupted_by_signal and not an_error_occured){
    char *buf = NULL;
    size_t buf_len = 0;
    
    /* Open FIFO */
    int fifo_fd;
    do{
      fifo_fd = open("/dev/.initramfs/usplash_outfifo", O_RDONLY);
      if(fifo_fd == -1){
      if(errno != EINTR){
        perror("open");
        an_error_occured = true;
        break;
      }
      if(interrupted_by_signal){
        break;
      }
      }
    }while(fifo_fd == -1);
    if(interrupted_by_signal or an_error_occured){
      break;                  /* Big */
    }
    
    /* Read from FIFO */
    size_t buf_allocated = 0;
    const size_t blocksize = 1024;
    do{
      if(buf_len + blocksize > buf_allocated){
      char *tmp = realloc(buf, buf_allocated + blocksize);
      if(tmp == NULL){
        perror("realloc");
        an_error_occured = true;
        break;
      }
      buf = tmp;
      buf_allocated += blocksize;
      }
      do{
      sret = read(fifo_fd, buf + buf_len, buf_allocated - buf_len);
      if(sret == -1){
        if(errno != EINTR){
          perror("read");
          an_error_occured = true;
          break;
        }
        if(interrupted_by_signal){
          break;
        }
      }
      }while(sret == -1);
      if(interrupted_by_signal or an_error_occured){
      break;
      }
      
      buf_len += (size_t)sret;
    }while(sret != 0);
    close(fifo_fd);
    if(interrupted_by_signal or an_error_occured){
      break;                  /* Big */
    }
    
    if(not usplash_write("TIMEOUT", "15")
       and (errno != EINTR)){
      perror("usplash_write");
      an_error_occured = true;
    }
    if(interrupted_by_signal or an_error_occured){
      break;                  /* Big */
    }
    
    /* Print password to stdout */
    size_t written = 0;
    while(written < buf_len){
      do{
      sret = write(STDOUT_FILENO, buf + written, buf_len - written);
      if(sret == -1){
        if(errno != EINTR){
          perror("write");
          an_error_occured = true;
          break;
        }
        if(interrupted_by_signal){
          break;
        }
      }
      }while(sret == -1);
      if(interrupted_by_signal or an_error_occured){
      break;
      }
      written += (size_t)sret;
    }
    free(buf);
    if(not interrupted_by_signal and not an_error_occured){
      free(cmdline);
      return EXIT_SUCCESS;
    }
    break;              /* Big */
  }                     /* end of non-loop while() */
  
  /* If we got here, an error or interrupt must have happened */
  
  /* Create argc and argv for new usplash*/
  int cmdline_argc = 0;
  char **cmdline_argv = malloc(sizeof(char *));
  {
    size_t position = 0;
    while(position < cmdline_len){
      char **tmp = realloc(cmdline_argv,
                     (sizeof(char *)
                      * (size_t)(cmdline_argc + 2)));
      if(tmp == NULL){
      perror("realloc");
      free(cmdline_argv);
      return EXIT_FAILURE;
      }
      cmdline_argv = tmp;
      cmdline_argv[cmdline_argc] = cmdline + position;
      cmdline_argc++;
      position += strlen(cmdline + position) + 1;
    }
    cmdline_argv[cmdline_argc] = NULL;
  }
  /* Kill old usplash */
  kill(usplash_pid, SIGTERM);
  sleep(2);
  while(kill(usplash_pid, 0) == 0){
    kill(usplash_pid, SIGKILL);
    sleep(1);
  }
  pid_t new_usplash_pid = fork();
  if(new_usplash_pid == 0){
    /* Child; will become new usplash process */
    
    /* Make the effective user ID (root) the only user ID instead of
       the real user ID (_mandos) */
    ret = setuid(geteuid());
    if(ret == -1){
      perror("setuid");
    }
    
    setsid();
    ret = chdir("/");
/*     if(fork() != 0){ */
/*       _exit(EXIT_SUCCESS); */
/*     } */
    ret = dup2(STDERR_FILENO, STDOUT_FILENO); /* replace our stdout */
    if(ret == -1){
      perror("dup2");
      _exit(EXIT_FAILURE);
    }
    
    execv(usplash_name, cmdline_argv);
    if(not interrupted_by_signal){
      perror("execv");
    }
    free(cmdline);
    free(cmdline_argv);
    _exit(EXIT_FAILURE);
  }
  free(cmdline);
  free(cmdline_argv);
  sleep(2);
  if(not usplash_write("PULSATE", NULL)
     and (errno != EINTR)){
    perror("usplash_write");
  }
  
  return EXIT_FAILURE;
}