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
12static 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
24extern void exit();
25
26/* Local stuff. */
27
28#include "tcpd.h"
29
30/* Forward declarations. */
31
32static void do_child();
33
34/* shell_cmd - execute shell command */
35
36void    shell_cmd(command)
37char   *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
62static void do_child(command)
63char   *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}
93