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