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#include "common.h"
#include <unistd.h>
#include <errno.h>
#include <net/if.h>
#include <linux/if_tun.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <poll.h>
static int tun_fd, utun_fd;
static struct sockaddr_in utun_peer;
static void setup_tundev(const char *in_ifname)
{
#define DEVNETTUN "/dev/net/tun"
int fd = open(DEVNETTUN, O_RDWR);
if (fd < 0)
fatal("setup_tundev: open("DEVNETTUN"): %s", strerror(errno));
struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
strncpy(ifr.ifr_name, in_ifname, IFNAMSIZ - 1);
if (ioctl(fd, TUNSETIFF, &ifr) < 0)
fatal("setup_tundev: ioctl(TUNSETIFF): %s", strerror(errno));
debug("setup_tundev: created tuntap interface: %s", in_ifname);
struct ifreq ifr2;
memset(&ifr2, 0, sizeof(ifr2));
ifr2.ifr_flags = IFF_UP|IFF_RUNNING;
ifr2.ifr_mtu = 1438;
strncpy(ifr2.ifr_name, in_ifname, IFNAMSIZ - 1);
int tmpfd = socket(AF_INET, SOCK_DGRAM, 0);
if (tmpfd < 0)
fatal("setup_tundev: socket(): %s", strerror(errno));
if (ioctl(tmpfd, SIOCSIFFLAGS, &ifr2) < 0)
fatal("setup_tundev: ioctl(SIOCSIFFLAGS): %s", strerror(errno));
if (ioctl(tmpfd, SIOCSIFMTU, &ifr2) < 0)
fatal("setup_tundev: ioctl(SIOCSIFMTU): %s", strerror(errno));
close(tmpfd);
tun_fd = fd;
}
static void setup_utun(struct in_addr local_addr, uint16_t local_port,
struct in_addr remote_addr, uint16_t remote_port)
{
int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (fd < 0)
fatal("setup_utun: socket(): %s", strerror(errno));
struct sockaddr_in local;
local.sin_family = AF_INET;
local.sin_port = htons(local_port);
local.sin_addr = local_addr;
if (bind(fd, (struct sockaddr *)&local, sizeof(local)) < 0)
fatal("setup_utun: bind(port=%d): %s", (int)local_port,
strerror(errno));
debug("setup_utun: created utun socket: %s:%d",
inet_ntoa(local_addr), (int)local_port);
struct sockaddr_in remote;
remote.sin_family = AF_INET;
remote.sin_port = htons(remote_port);
remote.sin_addr = remote_addr;
utun_peer = remote;
utun_fd = fd;
}
static void read_tundev(void)
{
const ssize_t gre_header_len = 4;
uint8_t buf[2048];
// GRE header comes first, inside the UDP packet
buf[0] = 0;
buf[1] = 0;
*(uint16_t *)&buf[2] = htons(0x6558);
// Ethernet frame follows
ssize_t nread = read(tun_fd, buf + gre_header_len,
sizeof(buf) - gre_header_len);
if (nread < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK)
return;
fatal("tundev: read(): %s", strerror(errno));
}
ssize_t nsent = sendto(utun_fd, buf, nread + gre_header_len, 0,
(struct sockaddr *)&utun_peer,
sizeof(utun_peer));
if (nsent != nread + gre_header_len)
fatal("tundev: sendto(utun): %s", strerror(errno));
if (TUN_DEBUG > 0)
fprintf(stderr, ">");
}
static void read_utun(void)
{
const ssize_t gre_header_len = 4;
uint8_t buf[2048];
struct sockaddr_in remote;
socklen_t remote_len = sizeof(remote);
ssize_t nread = recvfrom(utun_fd, buf, sizeof(buf), 0,
(struct sockaddr *)&remote,
&remote_len);
if (nread < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK)
return;
fatal("utun: read(): %s", strerror(errno));
}
if (memcmp(&utun_peer, &remote, sizeof(remote))) {
debug("utun: packet from unexpected peer; expected=%s:%d, "
"actual=%s:%d", inet_ntoa(utun_peer.sin_addr),
(int)utun_peer.sin_port, inet_ntoa(remote.sin_addr),
(int)remote.sin_port);
return;
}
if (nread < gre_header_len || buf[0] != 0 || buf[1] != 0 ||
ntohs(*(uint16_t *)&buf[2]) != 0x6558) {
debug("utun: packet in unexpected format");
return;
}
ssize_t nwritten = write(tun_fd, buf + gre_header_len,
nread - gre_header_len);
if (nwritten != nread - gre_header_len)
fatal("utun: write(tundev) failed: %s", strerror(errno));
if (TUN_DEBUG > 0)
fprintf(stderr, "<");
}
int main(int argc, char **argv)
{
if (argc != 6)
fatal("usage: ulfougretap <dev> <local addr> <local port> " \
"<peer addr> <peer port>\n");
setup_tundev(argv[1]);
setup_utun(parse_ipv4(argv[2]), parse_u16(argv[3]),
parse_ipv4(argv[4]), parse_u16(argv[5]));
struct pollfd pollfds[2] = {
{ .fd = tun_fd, .events = POLLIN, },
{ .fd = utun_fd, .events = POLLIN, },
};
while (1) {
if (poll(pollfds, numberof(pollfds), -1) < 0)
fatal("poll(): %s", strerror(errno));
if (pollfds[0].revents)
read_tundev();
if (pollfds[1].revents)
read_utun();
}
}
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