1/*	$OpenBSD: opentap.c,v 1.1 2016/09/28 12:40:35 bluhm Exp $ */
2
3/*
4 * Copyright (c) 2014 Alexander Bluhm <bluhm@openbsd.org>
5 *
6 * Permission to use, copy, modify, and distribute this software for any
7 * purpose with or without fee is hereby granted, provided that the above
8 * copyright notice and this permission notice appear in all copies.
9 *
10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17 */
18
19#include <ctype.h>
20#include <err.h>
21#include <fcntl.h>
22#include <limits.h>
23#include <stdio.h>
24#include <stdlib.h>
25#include <string.h>
26
27#include <sys/socket.h>
28
29void usage(void);
30
31void
32usage(void)
33{
34	fprintf(stderr, "usage: sudo %s fd# tap#\n", getprogname());
35	fprintf(stderr, "  fd#   number of file descriptor for fd passing\n");
36	fprintf(stderr, "  tap#  number of tap device to open\n");
37	exit(2);
38}
39
40int
41main(int argc, char *argv[])
42{
43	int		 fd, tap;
44	char		 dev[FILENAME_MAX];
45	const char	*errstr;
46	struct msghdr	 msg;
47	struct cmsghdr	*cmsg;
48	union {
49		struct cmsghdr	 hdr;
50		unsigned char	 buf[CMSG_SPACE(sizeof(int))];
51	} cmsgbuf;
52
53	if (argc != 3)
54		usage();
55
56	fd = strtonum(argv[1], 0, INT_MAX, &errstr);
57	if (errstr)
58		errx(2, "file descriptor number %s: %s", errstr, argv[1]);
59	tap = strtonum(argv[2], 0, INT_MAX, &errstr);
60	if (errstr)
61		errx(2, "tap device number %s: %s", errstr, argv[2]);
62	snprintf(dev, FILENAME_MAX, "/dev/tap%d", tap);
63
64	if ((tap = open(dev, O_RDWR)) == -1)
65		err(1, "open %s", dev);
66
67	memset(&msg, 0, sizeof(msg));
68	msg.msg_control = &cmsgbuf.buf;
69	msg.msg_controllen = sizeof(cmsgbuf.buf);
70
71	cmsg = CMSG_FIRSTHDR(&msg);
72	cmsg->cmsg_len = CMSG_LEN(sizeof(int));
73	cmsg->cmsg_level = SOL_SOCKET;
74	cmsg->cmsg_type = SCM_RIGHTS;
75	*(int *)CMSG_DATA(cmsg) = tap;
76
77	if (sendmsg(fd, &msg, 0) == -1)
78		err(1, "sendmsg %d", fd);
79
80	return 0;
81}
82