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