lib/libwrap/shell_cmd.c

   1 /*      $NetBSD: shell_cmd.c,v 1.7 2012/03/22 22:59:43 joerg Exp $      */
   2
   3  /*
   4   * shell_cmd() takes a shell command after %<character> substitutions. The
   5   * command is executed by a /bin/sh child process, with standard input,
   6   * standard output and standard error connected to /dev/null.
   7   *
   8   * Diagnostics are reported through syslog(3).
   9   *
  10   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  11   */
  12
  13 #include <sys/cdefs.h>
  14 #ifndef lint
  15 #if 0
  16 static char sccsid[] = "@(#) shell_cmd.c 1.5 94/12/28 17:42:44";
  17 #else
  18 __RCSID("$NetBSD: shell_cmd.c,v 1.7 2012/03/22 22:59:43 joerg Exp $");
  19 #endif
  20 #endif
  21
  22 /* System libraries. */
  23
  24 #include <sys/types.h>
  25 #include <sys/param.h>
  26 #include <sys/wait.h>
  27 #include <signal.h>
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <unistd.h>
  31 #include <fcntl.h>
  32 #include <syslog.h>
  33 #include <string.h>
  34
  35 /* Local stuff. */
  36
  37 #include "tcpd.h"
  38
  39 /* Forward declarations. */
  40
  41 static void do_child(char *) __dead;
  42
  43 /* shell_cmd - execute shell command */
  44
  45 void
  46 shell_cmd(char *command)
  47 {
  48     int     child_pid;
  49     int     wait_pid;
  50
  51     /*
  52      * Most of the work is done within the child process, to minimize the
  53      * risk of damage to the parent.
  54      */
  55
  56     switch (child_pid = fork()) {
  57     case -1:                                    /* error */
  58         tcpd_warn("cannot fork: %m");
  59         break;
  60     case 00:                                    /* child */
  61         do_child(command);
  62         /* NOTREACHED */
  63     default:                                    /* parent */
  64         while ((wait_pid = wait((int *) 0)) != -1 && wait_pid != child_pid)
  65              /* void */ ;
  66     }
  67 }
  68
  69 /* do_child - exec command with { stdin, stdout, stderr } to /dev/null */
  70
  71 static void
  72 do_child(char *command)
  73 {
  74     int     tmp_fd;
  75
  76     /*
  77      * Systems with POSIX sessions may send a SIGHUP to grandchildren if the
  78      * child exits first. This is sick, sessions were invented for terminals.
  79      */
  80
  81     signal(SIGHUP, SIG_IGN);
  82
  83     /* Set up new stdin, stdout, stderr, and exec the shell command. */
  84
  85     for (tmp_fd = 0; tmp_fd < 3; tmp_fd++)
  86         (void) close(tmp_fd);
  87     if (open("/dev/null", 2) != 0) {
  88         tcpd_warn("open /dev/null: %m");
  89     } else if (dup(0) != 1 || dup(0) != 2) {
  90         tcpd_warn("dup: %m");
  91     } else {
  92         (void) execl("/bin/sh", "sh", "-c", command, (char *) 0);
  93         tcpd_warn("execl /bin/sh: %m");
  94     }
  95
  96     /* Something went wrong. We MUST terminate the child process. */
  97     _exit(0);
  98 }