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splashy.c

/*  -*- coding: utf-8 -*- */
/*
 * Splashy - Read a password from splashy 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 <stddef.h>           /* NULL */
#include <stdlib.h>           /* getenv() */
#include <stdio.h>            /* asprintf(), perror() */
#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() */
#include <string.h>           /* memcmp() */
#include <errno.h>            /* errno */
#include <sys/wait.h>         /* waitpid(), WIFEXITED(),
                           WEXITSTATUS() */

sig_atomic_t interrupted_by_signal = 0;

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

int main(__attribute__((unused))int argc,
       __attribute__((unused))char **argv){
  int ret = 0;
  
  /* Create prompt string */
  char *prompt = NULL;
  {
    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){
      return EXIT_FAILURE;
    }
  }
  
  /* Find splashy process */
  pid_t splashy_pid = 0;
  {
    const char splashy_name[] = "/sbin/splashy";
    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(splashy_name)];
      ssize_t sret;
      {
      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(splashy_name, exe_target,
                 sizeof(exe_target)-1) == 0)){
      splashy_pid = pid;
      break;
      }
    }
    closedir(proc_dir);
  }
  if(splashy_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;
      }
    }
  }
  
  /* Fork off the splashy command to prompt for password */
  pid_t splashy_command_pid = 0;
  if(not interrupted_by_signal){
    splashy_command_pid = fork();
    if(splashy_command_pid == -1){
      if(not interrupted_by_signal){
      perror("fork");
      }
      return EXIT_FAILURE;
    }
    /* Child */
    if(splashy_command_pid == 0){
      const char splashy_command[] = "/sbin/splashy_update";
      ret = execl(splashy_command, splashy_command, prompt,
              (char *)NULL);
      if(not interrupted_by_signal){
      perror("execl");
      }
      free(prompt);
      _exit(EXIT_FAILURE);
    }
  }
  
  /* Parent */
  free(prompt);
  
  /* Wait for command to complete */
  if(not interrupted_by_signal and splashy_command_pid != 0){
    int status;
    ret = waitpid(splashy_command_pid, &status, 0);
    if(ret == -1){
      if(errno != EINTR){
      perror("waitpid");
      }
      if(errno == ECHILD){
      splashy_command_pid = 0;
      }
    } else {
      /* The child process has exited */
      splashy_command_pid = 0;
      if(not interrupted_by_signal and WIFEXITED(status)
       and WEXITSTATUS(status)==0){
      return EXIT_SUCCESS;
      }
    }
  }
  kill(splashy_pid, SIGTERM);
  if(interrupted_by_signal and splashy_command_pid != 0){
    kill(splashy_command_pid, SIGTERM);
  }
  sleep(2);
  while(kill(splashy_pid, 0) == 0){
    kill(splashy_pid, SIGKILL);
    sleep(1);
  }
  pid_t new_splashy_pid = 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){
      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);
    }
    
    execl("/sbin/splashy", "/sbin/splashy", "boot", (char *)NULL);
    if(not interrupted_by_signal){
      perror("execl");
    }
    _exit(EXIT_FAILURE);
  }
  
  return EXIT_FAILURE;
}

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