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usplash.c

/*  -*- coding: utf-8 -*- */
/*
 * Usplash - Read a password from usplash and output it
 * 
 * Copyright © 2008-2010 Teddy Hogeborn
 * Copyright © 2008-2010 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           /* asprintf(), TEMP_FAILURE_RETRY() */
#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 <error.h>
#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()*/
#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(),
                           getenv() */
#include <dirent.h>           /* opendir(), readdir(), closedir() */
#include <inttypes.h>         /* intmax_t, strtoimax() */
#include <sys/stat.h>         /* struct stat, lstat(), S_ISLNK */
#include <sysexits.h>         /* EX_OSERR, EX_UNAVAILABLE */
#include <argz.h>       /* argz_count(), argz_extract() */

sig_atomic_t interrupted_by_signal = 0;
int signal_received;
const char usplash_name[] = "/sbin/usplash";

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

static bool usplash_write(int *fifo_fd_r,
                    const char *cmd, const char *arg){
  /* 
   * usplash_write(&fd, "TIMEOUT", "15") will write "TIMEOUT 15\0"
   * usplash_write(&fd, "PULSATE", NULL) will write "PULSATE\0"
   * SEE ALSO
   *         usplash_write(8)
   */
  int ret;
  if(*fifo_fd_r == -1){
    ret = open("/dev/.initramfs/usplash_fifo", O_WRONLY);
    if(ret == -1){
      return false;
    }
    *fifo_fd_r = ret;
  }
  
  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) + 1;
  } else {
    do {
      ret = asprintf(&cmd_line_alloc, "%s %s", cmd, arg);
      if(ret == -1){
      int e = errno;
      TEMP_FAILURE_RETRY(close(*fifo_fd_r));
      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(written < cmd_line_len){
    sret = write(*fifo_fd_r, cmd_line + written,
             cmd_line_len - written);
    if(sret == -1){
      int e = errno;
      TEMP_FAILURE_RETRY(close(*fifo_fd_r));
      free(cmd_line_alloc);
      errno = e;
      return false;
    }
    written += (size_t)sret;
  }
  free(cmd_line_alloc);
  
  return true;
}

/* Create prompt string */
char *makeprompt(void){
  int ret = 0;
  char *prompt;
  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 NULL;
  }
  return prompt;
}

pid_t find_usplash(char **cmdline_r, size_t *cmdline_len_r){
  int ret = 0;
  ssize_t sret = 0;
  char *cmdline = NULL;
  size_t cmdline_len = 0;
  DIR *proc_dir = opendir("/proc");
  if(proc_dir == NULL){
    error(0, errno, "opendir");
    return -1;
  }
  errno = 0;
  for(struct dirent *proc_ent = readdir(proc_dir);
      proc_ent != NULL;
      proc_ent = readdir(proc_dir)){
    pid_t pid;
    {
      intmax_t tmpmax;
      char *tmp;
      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 */
      errno = 0;
      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){
      error(0, errno, "asprintf");
      goto fail_find_usplash;
      }
      
      /* 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;
      }
      error(0, errno, "lstat");
      free(exe_link);
      goto fail_find_usplash;
      }
      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);
    }
    /* Compare executable name */
    if((sret != ((ssize_t)sizeof(exe_target)-1))
       or (memcmp(usplash_name, exe_target,
              sizeof(exe_target)-1) != 0)){
      /* Not it */
      continue;
    }
    /* Found usplash */
    /* 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){
        error(0, errno, "asprintf");
        goto fail_find_usplash;
      }
      cl_fd = open(cmdline_filename, O_RDONLY);
      free(cmdline_filename);
      if(cl_fd == -1){
        error(0, errno, "open");
        goto fail_find_usplash;
      }
      }
      size_t cmdline_allocated = 0;
      char *tmp;
      const size_t blocksize = 1024;
      do {
      /* Allocate more space? */
      if(cmdline_len + blocksize > cmdline_allocated){
        tmp = realloc(cmdline, cmdline_allocated + blocksize);
        if(tmp == NULL){
          error(0, errno, "realloc");
          close(cl_fd);
          goto fail_find_usplash;
        }
        cmdline = tmp;
        cmdline_allocated += blocksize;
      }
      /* Read data */
      sret = read(cl_fd, cmdline + cmdline_len,
                cmdline_allocated - cmdline_len);
      if(sret == -1){
        error(0, errno, "read");
        close(cl_fd);
        goto fail_find_usplash;
      }
      cmdline_len += (size_t)sret;
      } while(sret != 0);
      ret = close(cl_fd);
      if(ret == -1){
      error(0, errno, "close");
      goto fail_find_usplash;
      }
    }
    /* Close directory */
    ret = closedir(proc_dir);
    if(ret == -1){
      error(0, errno, "closedir");
      goto fail_find_usplash;
    }
    /* Success */
    *cmdline_r = cmdline;
    *cmdline_len_r = cmdline_len;
    return pid;
  }
  
 fail_find_usplash:
  
  free(cmdline);
  if(proc_dir != NULL){
    int e = errno;
    closedir(proc_dir);
    errno = e;
  }
  return 0;
}

int main(__attribute__((unused))int argc,
       __attribute__((unused))char **argv){
  int ret = 0;
  ssize_t sret;
  int fifo_fd = -1;
  int outfifo_fd = -1;
  char *buf = NULL;
  size_t buf_len = 0;
  pid_t usplash_pid = -1;
  bool usplash_accessed = false;
  int status = EXIT_FAILURE;  /* Default failure exit status */
  
  char *prompt = makeprompt();
  if(prompt == NULL){
    status = EX_OSERR;
    goto failure;
  }
  
  /* Find usplash process */
  char *cmdline = NULL;
  size_t cmdline_len = 0;
  usplash_pid = find_usplash(&cmdline, &cmdline_len);
  if(usplash_pid == 0){
    status = EX_UNAVAILABLE;
    goto failure;
  }
  
  /* Set up the signal handler */
  {
    struct sigaction old_action,
      new_action = { .sa_handler = termination_handler,
                 .sa_flags = 0 };
    sigemptyset(&new_action.sa_mask);
    ret = sigaddset(&new_action.sa_mask, SIGINT);
    if(ret == -1){
      error(0, errno, "sigaddset");
      status = EX_OSERR;
      goto failure;
    }
    ret = sigaddset(&new_action.sa_mask, SIGHUP);
    if(ret == -1){
      error(0, errno, "sigaddset");
      status = EX_OSERR;
      goto failure;
    }
    ret = sigaddset(&new_action.sa_mask, SIGTERM);
    if(ret == -1){
      error(0, errno, "sigaddset");
      status = EX_OSERR;
      goto failure;
    }
    ret = sigaction(SIGINT, NULL, &old_action);
    if(ret == -1){
      if(errno != EINTR){
      error(0, errno, "sigaction");
      status = EX_OSERR;
      }
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGINT, &new_action, NULL);
      if(ret == -1){
      if(errno != EINTR){
        error(0, errno, "sigaction");
        status = EX_OSERR;
      }
      goto failure;
      }
    }
    ret = sigaction(SIGHUP, NULL, &old_action);
    if(ret == -1){
      if(errno != EINTR){
      error(0, errno, "sigaction");
      status = EX_OSERR;
      }
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGHUP, &new_action, NULL);
      if(ret == -1){
      if(errno != EINTR){
        error(0, errno, "sigaction");
        status = EX_OSERR;
      }
      goto failure;
      }
    }
    ret = sigaction(SIGTERM, NULL, &old_action);
    if(ret == -1){
      if(errno != EINTR){
      error(0, errno, "sigaction");
      status = EX_OSERR;
      }
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGTERM, &new_action, NULL);
      if(ret == -1){
      if(errno != EINTR){
        error(0, errno, "sigaction");
        status = EX_OSERR;
      }
      goto failure;
      }
    }
  }
  
  usplash_accessed = true;
  /* Write command to FIFO */
  if(not usplash_write(&fifo_fd, "TIMEOUT", "0")){
    if(errno != EINTR){
      error(0, errno, "usplash_write");
      status = EX_OSERR;
    }
    goto failure;
  }
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  if(not usplash_write(&fifo_fd, "INPUTQUIET", prompt)){
    if(errno != EINTR){
      error(0, errno, "usplash_write");
      status = EX_OSERR;
    }
    goto failure;
  }
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  free(prompt);
  prompt = NULL;
  
  /* Read reply from usplash */
  /* Open FIFO */
  outfifo_fd = open("/dev/.initramfs/usplash_outfifo", O_RDONLY);
  if(outfifo_fd == -1){
    if(errno != EINTR){
      error(0, errno, "open");
      status = EX_OSERR;
    }
    goto failure;
  }
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  /* Read from FIFO */
  size_t buf_allocated = 0;
  const size_t blocksize = 1024;
  do {
    /* Allocate more space */
    if(buf_len + blocksize > buf_allocated){
      char *tmp = realloc(buf, buf_allocated + blocksize);
      if(tmp == NULL){
      if(errno != EINTR){
        error(0, errno, "realloc");
        status = EX_OSERR;
      }
      goto failure;
      }
      buf = tmp;
      buf_allocated += blocksize;
    }
    sret = read(outfifo_fd, buf + buf_len,
            buf_allocated - buf_len);
    if(sret == -1){
      if(errno != EINTR){
      error(0, errno, "read");
      status = EX_OSERR;
      }
      TEMP_FAILURE_RETRY(close(outfifo_fd));
      goto failure;
    }
    if(interrupted_by_signal){
      break;
    }
    
    buf_len += (size_t)sret;
  } while(sret != 0);
  ret = close(outfifo_fd);
  if(ret == -1){
    if(errno != EINTR){
      error(0, errno, "close");
      status = EX_OSERR;
    }
    goto failure;
  }
  outfifo_fd = -1;
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  if(not usplash_write(&fifo_fd, "TIMEOUT", "15")){
    if(errno != EINTR){
      error(0, errno, "usplash_write");
      status = EX_OSERR;
    }
    goto failure;
  }
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  ret = close(fifo_fd);
  if(ret == -1){
    if(errno != EINTR){
      error(0, errno, "close");
      status = EX_OSERR;
    }
    goto failure;
  }
  fifo_fd = -1;
  
  /* 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){
        error(0, errno, "write");
        status = EX_OSERR;
      }
      goto failure;
      }
    } while(sret == -1);
    
    if(interrupted_by_signal){
      goto failure;
    }
    written += (size_t)sret;
  }
  free(buf);
  buf = NULL;
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  free(cmdline);
  return EXIT_SUCCESS;
  
 failure:
  
  free(buf);
  
  free(prompt);
  
  /* If usplash was never accessed, we can stop now */
  if(not usplash_accessed){
    return status;
  }
  
  /* Close FIFO */
  if(fifo_fd != -1){
    ret = (int)TEMP_FAILURE_RETRY(close(fifo_fd));
    if(ret == -1 and errno != EINTR){
      error(0, errno, "close");
    }
    fifo_fd = -1;
  }
  
  /* Close output FIFO */
  if(outfifo_fd != -1){
    ret = (int)TEMP_FAILURE_RETRY(close(outfifo_fd));
    if(ret == -1){
      error(0, errno, "close");
    }
  }
  
  /* Create argv for new usplash*/
  char **cmdline_argv = malloc((argz_count(cmdline, cmdline_len) + 1)
                         * sizeof(char *)); /* Count args */
  if(cmdline_argv == NULL){
    error(0, errno, "malloc");
    return status;
  }
  argz_extract(cmdline, cmdline_len, cmdline_argv); /* Create argv */
  
  /* 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){
      error(0, errno, "setuid");
    }
    
    setsid();
    ret = chdir("/");
    if(ret == -1){
      error(0, errno, "chdir");
      _exit(EX_OSERR);
    }
/*     if(fork() != 0){ */
/*       _exit(EXIT_SUCCESS); */
/*     } */
    ret = dup2(STDERR_FILENO, STDOUT_FILENO); /* replace our stdout */
    if(ret == -1){
      error(0, errno, "dup2");
      _exit(EX_OSERR);
    }
    
    execv(usplash_name, cmdline_argv);
    if(not interrupted_by_signal){
      error(0, errno, "execv");
    }
    free(cmdline);
    free(cmdline_argv);
    _exit(EX_OSERR);
  }
  free(cmdline);
  free(cmdline_argv);
  sleep(2);
  if(not usplash_write(&fifo_fd, "PULSATE", NULL)){
    if(errno != EINTR){
      error(0, errno, "usplash_write");
    }
  }
  
  /* Close FIFO (again) */
  if(fifo_fd != -1){
    ret = (int)TEMP_FAILURE_RETRY(close(fifo_fd));
    if(ret == -1 and errno != EINTR){
      error(0, errno, "close");
    }
    fifo_fd = -1;
  }
  
  if(interrupted_by_signal){
    struct sigaction signal_action = { .sa_handler = SIG_DFL };
    sigemptyset(&signal_action.sa_mask);
    ret = (int)TEMP_FAILURE_RETRY(sigaction(signal_received,
                                  &signal_action, NULL));
    if(ret == -1){
      error(0, errno, "sigaction");
    }
    do {
      ret = raise(signal_received);
    } while(ret != 0 and errno == EINTR);
    if(ret != 0){
      error(0, errno, "raise");
      abort();
    }
    TEMP_FAILURE_RETRY(pause());
  }
  
  return status;
}

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