contrib/tcp_wrappers/shell_cmd.c

   1  /*
   2   * shell_cmd() takes a shell command after %<character> substitutions. The
   3   * command is executed by a /bin/sh child process, with standard input,
   4   * standard output and standard error connected to /dev/null.
   5   *
   6   * Diagnostics are reported through syslog(3).
   7   *
   8   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
   9   */
  10
  11 /* System libraries. */
  12
  13 #include <sys/types.h>
  14 #include <sys/param.h>
  15 #include <sys/wait.h>
  16 #include <signal.h>
  17 #include <stdio.h>
  18 #include <unistd.h>
  19 #include <syslog.h>
  20 #include <string.h>
  21 #include <fcntl.h>
  22
  23 extern void exit();
  24
  25 /* Local stuff. */
  26
  27 #include "tcpd.h"
  28
  29 /* Forward declarations. */
  30
  31 static void do_child();
  32
  33 /* shell_cmd - execute shell command */
  34
  35 void    shell_cmd(command)
  36 char   *command;
  37 {
  38     int     child_pid;
  39     int     wait_pid;
  40
  41     /*
  42      * Most of the work is done within the child process, to minimize the
  43      * risk of damage to the parent.
  44      */
  45
  46     switch (child_pid = fork()) {
  47     case -1:                                    /* error */
  48         tcpd_warn("cannot fork: %m");
  49         break;
  50     case 00:                                    /* child */
  51         do_child(command);
  52         /* NOTREACHED */
  53     default:                                    /* parent */
  54         while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid)
  55              /* void */ ;
  56     }
  57 }
  58
  59 /* do_child - exec command with { stdin, stdout, stderr } to /dev/null */
  60
  61 static void do_child(command)
  62 char   *command;
  63 {
  64     char   *error;
  65     int     tmp_fd;
  66
  67     /*
  68      * Systems with POSIX sessions may send a SIGHUP to grandchildren if the
  69      * child exits first. This is sick, sessions were invented for terminals.
  70      */
  71
  72     signal(SIGHUP, SIG_IGN);
  73
  74     /* Set up new stdin, stdout, stderr, and exec the shell command. */
  75
  76     for (tmp_fd = 0; tmp_fd < 3; tmp_fd++)
  77         (void) close(tmp_fd);
  78     if (open("/dev/null", 2) != 0) {
  79         error = "open /dev/null: %m";
  80     } else if (dup(0) != 1 || dup(0) != 2) {
  81         error = "dup: %m";
  82     } else {
  83         (void) execl("/bin/sh", "sh", "-c", command, (char *) 0);
  84         error = "execl /bin/sh: %m";
  85     }
  86
  87     /* Something went wrong. We MUST terminate the child process. */
  88
  89     tcpd_warn("%s", error);
  90     _exit(0);
  91 }