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splashy.c

/*  -*- coding: utf-8 -*- */
/*
 * Splashy - Read a password from splashy and output it
 * 
 * Copyright © 2008-2011 Teddy Hogeborn
 * Copyright © 2008-2011 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@recompile.se>.
 */

#define _GNU_SOURCE           /* TEMP_FAILURE_RETRY(), asprintf() */
#include <signal.h>           /* sig_atomic_t, struct sigaction,
                           sigemptyset(), sigaddset(), SIGINT,
                           SIGHUP, SIGTERM, sigaction,
                           SIG_IGN, kill(), SIGKILL */
#include <stddef.h>           /* NULL */
#include <stdlib.h>           /* getenv() */
#include <stdio.h>            /* asprintf(), vasprintf(), vprintf(),
                           fprintf() */
#include <stdlib.h>           /* EXIT_FAILURE, free(),
                           EXIT_SUCCESS */
#include <sys/types.h>        /* pid_t, DIR, struct dirent,
                           ssize_t */
#include <dirent.h>           /* opendir(), readdir(), closedir() */
#include <inttypes.h>         /* intmax_t, strtoimax() */
#include <sys/stat.h>         /* struct stat, lstat(), S_ISLNK */
#include <iso646.h>           /* not, or, and */
#include <unistd.h>           /* readlink(), fork(), execl(),
                           sleep(), dup2() STDERR_FILENO,
                           STDOUT_FILENO, _exit(),
                           pause() */
#include <string.h>           /* memcmp(), strerror() */
#include <errno.h>            /* errno, EACCES, ENOTDIR, ELOOP,
                           ENOENT, ENAMETOOLONG, EMFILE,
                           ENFILE, ENOMEM, ENOEXEC, EINVAL,
                           E2BIG, EFAULT, EIO, ETXTBSY,
                           EISDIR, ELIBBAD, EPERM, EINTR,
                           ECHILD */
#include <error.h>            /* error() */
#include <sys/wait.h>         /* waitpid(), WIFEXITED(),
                           WEXITSTATUS() */
#include <sysexits.h>         /* EX_OSERR, EX_OSFILE,
                           EX_UNAVAILABLE */
#include <stdarg.h>           /* va_list, va_start(), ... */

sig_atomic_t interrupted_by_signal = 0;
int signal_received;

/* Function to use when printing errors */
void error_plus(int status, int errnum, const char *formatstring,
            ...){
  va_list ap;
  char *text;
  int ret;
  
  va_start(ap, formatstring);
  ret = vasprintf(&text, formatstring, ap);
  if (ret == -1){
    fprintf(stderr, "Mandos plugin %s: ",
          program_invocation_short_name);
    vfprintf(stderr, formatstring, ap);
    fprintf(stderr, ": ");
    fprintf(stderr, "%s\n", strerror(errnum));
    error(status, errno, "vasprintf while printing error");
    return;
  }
  fprintf(stderr, "Mandos plugin ");
  error(status, errnum, "%s", text);
  free(text);
}


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

int main(__attribute__((unused))int argc,
       __attribute__((unused))char **argv){
  int ret = 0;
  char *prompt = NULL;
  DIR *proc_dir = NULL;
  pid_t splashy_pid = 0;
  pid_t splashy_command_pid = 0;
  int exitstatus = EXIT_FAILURE;
  
  /* Create prompt string */
  {
    const char *const cryptsource = getenv("cryptsource");
    const char *const crypttarget = getenv("crypttarget");
    const char *const prompt_start = "getpass "
      "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){
      prompt = NULL;
      exitstatus = EX_OSERR;
      goto failure;
    }
  }
  
  /* Find splashy process */
  {
    const char splashy_name[] = "/sbin/splashy";
    proc_dir = opendir("/proc");
    if(proc_dir == NULL){
      int e = errno;
      error_plus(0, errno, "opendir");
      switch(e){
      case EACCES:
      case ENOTDIR:
      case ELOOP:
      case ENOENT:
      default:
      exitstatus = EX_OSFILE;
      break;
      case ENAMETOOLONG:
      case EMFILE:
      case ENFILE:
      case ENOMEM:
      exitstatus = EX_OSERR;
      break;
      }
      goto 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(splashy_name)];
      ssize_t sret;
      {
      char *exe_link;
      ret = asprintf(&exe_link, "/proc/%s/exe", proc_ent->d_name);
      if(ret == -1){
        error_plus(0, errno, "asprintf");
        exitstatus = EX_OSERR;
        goto 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;
        }
        int e = errno;
        error_plus(0, errno, "lstat");
        free(exe_link);
        switch(e){
        case EACCES:
        case ENOTDIR:
        case ELOOP:
        default:
          exitstatus = EX_OSFILE;
          break;
        case ENAMETOOLONG:
          exitstatus = EX_OSERR;
          break;
        }
        goto 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(splashy_name, exe_target,
                 sizeof(exe_target)-1) == 0)){
      splashy_pid = pid;
      break;
      }
    }
    closedir(proc_dir);
    proc_dir = NULL;
  }
  if(splashy_pid == 0){
    exitstatus = 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_plus(0, errno, "sigaddset");
      exitstatus = EX_OSERR;
      goto failure;
    }
    ret = sigaddset(&new_action.sa_mask, SIGHUP);
    if(ret == -1){
      error_plus(0, errno, "sigaddset");
      exitstatus = EX_OSERR;
      goto failure;
    }
    ret = sigaddset(&new_action.sa_mask, SIGTERM);
    if(ret == -1){
      error_plus(0, errno, "sigaddset");
      exitstatus = EX_OSERR;
      goto failure;
    }
    ret = sigaction(SIGINT, NULL, &old_action);
    if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGINT, &new_action, NULL);
      if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
      }
    }
    ret = sigaction(SIGHUP, NULL, &old_action);
    if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGHUP, &new_action, NULL);
      if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
      }
    }
    ret = sigaction(SIGTERM, NULL, &old_action);
    if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
    }
    if(old_action.sa_handler != SIG_IGN){
      ret = sigaction(SIGTERM, &new_action, NULL);
      if(ret == -1){
      error_plus(0, errno, "sigaction");
      exitstatus = EX_OSERR;
      goto failure;
      }
    }
  }
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  /* Fork off the splashy command to prompt for password */
  splashy_command_pid = fork();
  if(splashy_command_pid != 0 and interrupted_by_signal){
    goto failure;
  }
  if(splashy_command_pid == -1){
    error_plus(0, errno, "fork");
    exitstatus = EX_OSERR;
    goto failure;
  }
  /* Child */
  if(splashy_command_pid == 0){
    if(not interrupted_by_signal){
      const char splashy_command[] = "/sbin/splashy_update";
      execl(splashy_command, splashy_command, prompt, (char *)NULL);
      int e = errno;
      error_plus(0, errno, "execl");
      switch(e){
      case EACCES:
      case ENOENT:
      case ENOEXEC:
      case EINVAL:
      _exit(EX_UNAVAILABLE);
      case ENAMETOOLONG:
      case E2BIG:
      case ENOMEM:
      case EFAULT:
      case EIO:
      case EMFILE:
      case ENFILE:
      case ETXTBSY:
      default:
      _exit(EX_OSERR);
      case ENOTDIR:
      case ELOOP:
      case EISDIR:
#ifdef ELIBBAD
      case ELIBBAD:           /* Linux only */
#endif
      case EPERM:
      _exit(EX_OSFILE);
      }
    }
    free(prompt);
    _exit(EXIT_FAILURE);
  }
  
  /* Parent */
  free(prompt);
  prompt = NULL;
  
  if(interrupted_by_signal){
    goto failure;
  }
  
  /* Wait for command to complete */
  {
    int status;
    do {
      ret = waitpid(splashy_command_pid, &status, 0);
    } while(ret == -1 and errno == EINTR
          and not interrupted_by_signal);
    if(interrupted_by_signal){
      goto failure;
    }
    if(ret == -1){
      error_plus(0, errno, "waitpid");
      if(errno == ECHILD){
      splashy_command_pid = 0;
      }
    } else {
      /* The child process has exited */
      splashy_command_pid = 0;
      if(WIFEXITED(status) and WEXITSTATUS(status) == 0){
      return EXIT_SUCCESS;
      }
    }
  }
  
 failure:
  
  free(prompt);
  
  if(proc_dir != NULL){
    TEMP_FAILURE_RETRY(closedir(proc_dir));
  }
  
  if(splashy_command_pid != 0){
    TEMP_FAILURE_RETRY(kill(splashy_command_pid, SIGTERM));
    
    TEMP_FAILURE_RETRY(kill(splashy_pid, SIGTERM));
    sleep(2);
    while(TEMP_FAILURE_RETRY(kill(splashy_pid, 0)) == 0){
      TEMP_FAILURE_RETRY(kill(splashy_pid, SIGKILL));
      sleep(1);
    }
    pid_t new_splashy_pid = (pid_t)TEMP_FAILURE_RETRY(fork());
    if(new_splashy_pid == 0){
      /* Child; will become new splashy 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_plus(0, errno, "setuid");
      }
      
      setsid();
      ret = chdir("/");
      if(ret == -1){
      error_plus(0, errno, "chdir");
      }
/*       if(fork() != 0){ */
/*    _exit(EXIT_SUCCESS); */
/*       } */
      ret = dup2(STDERR_FILENO, STDOUT_FILENO); /* replace stdout */
      if(ret == -1){
      error_plus(0, errno, "dup2");
      _exit(EX_OSERR);
      }
      
      execl("/sbin/splashy", "/sbin/splashy", "boot", (char *)NULL);
      {
      int e = errno;
      error_plus(0, errno, "execl");
      switch(e){
      case EACCES:
      case ENOENT:
      case ENOEXEC:
      default:
        _exit(EX_UNAVAILABLE);
      case ENAMETOOLONG:
      case E2BIG:
      case ENOMEM:
        _exit(EX_OSERR);
      case ENOTDIR:
      case ELOOP:
        _exit(EX_OSFILE);
      }
      }
    }
  }
  
  if(interrupted_by_signal){
    struct sigaction signal_action;
    sigemptyset(&signal_action.sa_mask);
    signal_action.sa_handler = SIG_DFL;
    ret = (int)TEMP_FAILURE_RETRY(sigaction(signal_received,
                                  &signal_action, NULL));
    if(ret == -1){
      error_plus(0, errno, "sigaction");
    }
    do {
      ret = raise(signal_received);
    } while(ret != 0 and errno == EINTR);
    if(ret != 0){
      error_plus(0, errno, "raise");
      abort();
    }
    TEMP_FAILURE_RETRY(pause());
  }
  
  return exitstatus;
}

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