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/* $OpenBSD: opentap.c,v 1.1 2016/09/28 12:40:35 bluhm Exp $ */
/*
* Copyright (c) 2014 Alexander Bluhm <bluhm@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <ctype.h>
#include <err.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
void usage(void);
void
usage(void)
{
fprintf(stderr, "usage: sudo %s fd# tap#\n", getprogname());
fprintf(stderr, " fd# number of file descriptor for fd passing\n");
fprintf(stderr, " tap# number of tap device to open\n");
exit(2);
}
int
main(int argc, char *argv[])
{
int fd, tap;
char dev[FILENAME_MAX];
const char *errstr;
struct msghdr msg;
struct cmsghdr *cmsg;
union {
struct cmsghdr hdr;
unsigned char buf[CMSG_SPACE(sizeof(int))];
} cmsgbuf;
if (argc != 3)
usage();
fd = strtonum(argv[1], 0, INT_MAX, &errstr);
if (errstr)
errx(2, "file descriptor number %s: %s", errstr, argv[1]);
tap = strtonum(argv[2], 0, INT_MAX, &errstr);
if (errstr)
errx(2, "tap device number %s: %s", errstr, argv[2]);
snprintf(dev, FILENAME_MAX, "/dev/tap%d", tap);
if ((tap = open(dev, O_RDWR)) == -1)
err(1, "open %s", dev);
memset(&msg, 0, sizeof(msg));
msg.msg_control = &cmsgbuf.buf;
msg.msg_controllen = sizeof(cmsgbuf.buf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
*(int *)CMSG_DATA(cmsg) = tap;
if (sendmsg(fd, &msg, 0) == -1)
err(1, "sendmsg %d", fd);
return 0;
}
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