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/* SPDX-License-Identifier: GPL-3.0-or-later */
#include "tun.h"
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <linux/sockios.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <unistd.h>
static int parse_cidr(const char* cidr, struct in_addr* addr, struct in_addr* netmask) {
char ip[INET_ADDRSTRLEN];
int prefix = 0;
if (sscanf(cidr, "%[^/]/%d", ip, &prefix) != 2 || prefix < 0 || prefix > 32) {
return -1;
}
*netmask = (struct in_addr) {
.s_addr = htonl(0xFFFFFFFF << (32 - prefix)),
};
if (!inet_aton(ip, addr)) {
return -1;
}
return 0;
}
int tun_alloc(const char* ifname, const char* cidr, int mtu) {
struct in_addr addr, netmask;
if (parse_cidr(cidr, &addr, &netmask) < 0) {
errno = EINVAL;
goto err;
}
struct ifreq ifr = {0};
strncpy(ifr.ifr_name, ifname, IFNAMSIZ);
// Create the tun device
int fd = open("/dev/net/tun", O_RDWR);
if (fd < 0) {
goto err;
}
ifr.ifr_flags = (short) (IFF_TUN | IFF_NO_PI | IFF_TUN_EXCL);
if (ioctl(fd, TUNSETIFF, &ifr) < 0) {
goto err_close_fd;
}
// Configure IP address, netmask and MTU
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
goto err_close_fd;
}
struct sockaddr_in* sin = (struct sockaddr_in*) &ifr.ifr_data;
*sin = (struct sockaddr_in) {
.sin_family = AF_INET,
.sin_addr = addr,
};
if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
goto err_close_sockfd;
}
*sin = (struct sockaddr_in) {
.sin_family = AF_INET,
.sin_addr = netmask,
};
if (ioctl(sockfd, SIOCSIFNETMASK, &ifr) < 0) {
goto err_close_sockfd;
}
ifr.ifr_mtu = mtu;
if (ioctl(sockfd, SIOCSIFMTU, &ifr) < 0) {
goto err_close_sockfd;
}
// Bring interface up
ifr.ifr_flags = 0;
if (ioctl(sockfd, SIOCGIFFLAGS, &ifr) < 0) {
goto err_close_sockfd;
}
ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
if (ioctl(sockfd, SIOCSIFFLAGS, &ifr) < 0) {
goto err_close_sockfd;
}
return fd;
err_close_sockfd:
close(sockfd);
err_close_fd:
close(fd);
err:
return -1;
}
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