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| | // SPDX-FileCopyrightText: 2019 Alyssa Ross <hi@alyssa.is>
// SPDX-License-Identifier: GPL-2.0-only
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <linux/if_tun.h>
/*
* ifr_flags, ifr_name, etc. are macros, so throughout this program
* variable names are suffixed with underscores where not doing so
* would conflict with a macro.
*/
// Adapted 2019-12-14 from Documentation/networking/tuntuntap.txt in Linux.
int tuntap_alloc(char *dev, int open_flags, short ifr_flags_)
{
struct ifreq ifr;
int fd, err;
if ((fd = open("/dev/net/tun", O_RDWR | open_flags)) < 0)
return -1;
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = ifr_flags_;
if (*dev)
strncpy(ifr.ifr_name, dev, IFNAMSIZ);
if ((err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0) {
close(fd);
return err;
}
strcpy(dev, ifr.ifr_name);
return fd;
}
void ex_usage()
{
fputs("mktuntap: usage: mktuntap (-n | -p) [-v] [-B] [-P] [-E] [-i ifr_name] fd prog...\n", stderr);
exit(EX_USAGE);
}
int main(int argc, char **argv)
{
char *ifr_name_in = NULL;
bool name_env = true;
bool tap = false, tun = false;
bool vnet_hdr = false, non_block = false, no_pi = true;
int c;
while ((c = getopt(argc, argv, "+npvBPEi:")) != -1) {
switch (c) {
case 'n':
tun = true;
break;
case 'p':
tap = true;
break;
case 'v':
vnet_hdr = true;
break;
case 'B':
non_block = true;
break;
case 'P':
no_pi = false;
break;
case 'E':
name_env = false;
break;
case 'i':
ifr_name_in = optarg;
break;
default:
ex_usage();
}
}
if (argc - optind < 2 || !(tap ^ tun))
ex_usage();
char *ifr_name_ = calloc(IFNAMSIZ, sizeof(char));
if (ifr_name_in) {
if (strlen(ifr_name_in) > IFNAMSIZ - 1) {
fprintf(stderr, "mktuntap: ifr_name too long (max %i)\n", IFNAMSIZ - 1);
return EX_USAGE;
}
strcpy(ifr_name_, ifr_name_in);
}
errno = 0;
char *target_fd_end;
long int target_fd_l = strtol(argv[optind], &target_fd_end, 10);
if (errno) {
perror("mktuntap");
return EX_USAGE;
}
if (argv[optind][0] == '\0' || target_fd_end[0] != '\0') {
fprintf(stderr, "mktuntap: invalid integer: `%s'\n", argv[optind]);
return EX_USAGE;
}
if (target_fd_l < INT_MIN || target_fd_l > INT_MAX) {
fprintf(stderr, "mktuntap: out of range for file descriptor: `%li'\n", target_fd_l);
return EX_USAGE;
}
int target_fd = (int)target_fd_l;
short open_flags = 0;
if (non_block)
open_flags |= O_NONBLOCK;
short ifr_flags_ = tap ? IFF_TAP : IFF_TUN;
if (no_pi)
ifr_flags_ |= IFF_NO_PI;
if (vnet_hdr)
ifr_flags_ |= IFF_VNET_HDR;
int tuntap_fd = tuntap_alloc(ifr_name_, open_flags, ifr_flags_);
if (tuntap_fd < 0) {
perror("mktuntap: failed to open tuntap device");
return EX_IOERR;
}
if (tuntap_fd != target_fd) {
if (dup2(tuntap_fd, target_fd) == -1) {
perror("mktuntap");
return EX_IOERR;
}
if (close(tuntap_fd) == -1) {
perror("mktuntap");
return EX_IOERR;
}
}
if (name_env) {
if (setenv("TUNTAP_NAME", ifr_name_, 1) == -1) {
perror("mktunap");
return EX_OSERR;
}
}
execvp(argv[optind + 1], &argv[optind + 1]);
perror("failed to exec");
return EX_OSERR;
}
|