/*      $NetBSD: shell_cmd.c,v 1.7 2012/03/22 22:59:43 joerg Exp $      */

/*
 * shell_cmd() takes a shell command after %<character> substitutions. The
 * command is executed by a /bin/sh child process, with standard input,
 * standard output and standard error connected to /dev/null.
 *
 * Diagnostics are reported through syslog(3).
 *
 * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
 */

#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#) shell_cmd.c 1.5 94/12/28 17:42:44";
#else
__RCSID("$NetBSD: shell_cmd.c,v 1.7 2012/03/22 22:59:43 joerg Exp $");
#endif
#endif

/* System libraries. */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/wait.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <syslog.h>
#include <string.h>

/* Local stuff. */

#include "tcpd.h"

/* Forward declarations. */

static void do_child(char *) __dead;

/* shell_cmd - execute shell command */

void
shell_cmd(char *command)
{
   int     child_pid;
   int     wait_pid;

   /*
    * Most of the work is done within the child process, to minimize the
    * risk of damage to the parent.
    */

   switch (child_pid = fork()) {
   case -1:                                    /* error */
       tcpd_warn("cannot fork: %m");
       break;
   case 00:                                    /* child */
       do_child(command);
       /* NOTREACHED */
   default:                                    /* parent */
       while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid)
            /* void */ ;
   }
}

/* do_child - exec command with { stdin, stdout, stderr } to /dev/null */

static void
do_child(char *command)
{
   int     tmp_fd;

   /*
    * Systems with POSIX sessions may send a SIGHUP to grandchildren if the
    * child exits first. This is sick, sessions were invented for terminals.
    */

   signal(SIGHUP, SIG_IGN);

   /* Set up new stdin, stdout, stderr, and exec the shell command. */

   for (tmp_fd = 0; tmp_fd < 3; tmp_fd++)
       (void) close(tmp_fd);
   if (open("/dev/null", 2) != 0) {
       tcpd_warn("open /dev/null: %m");
   } else if (dup(0) != 1 || dup(0) != 2) {
       tcpd_warn("dup: %m");
   } else {
       (void) execl("/bin/sh", "sh", "-c", command, (char *) 0);
       tcpd_warn("execl /bin/sh: %m");
   }

   /* Something went wrong. We MUST terminate the child process. */
   _exit(0);
}