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      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 }
     99