#include <linux/if_tun.h>
#include <assert.h>
+#include <array>
#include <atomic>
#include <chrono>
#include <thread>
static std::atomic<uint16_t> local_port(0);
static uint16_t remote_port;
static bool are_server;
+static uint64_t timestamps_magic;
-static void build_tcp_header(unsigned char* buf, uint32_t len, int syn, int synack, in_addr_t src_addr, in_addr_t dest_addr) {
+static int build_tcp_header(unsigned char* buf, uint32_t len, int syn, int synack, in_addr_t src_addr, in_addr_t dest_addr) {
buf[0 ] = local_port >> 8; // src port
buf[1 ] = local_port; // src port
buf[2 ] = remote_port >> 8; // dst port
buf[10] = their_seq >> (8 * 1); // ACK
buf[11] = their_seq >> (8 * 0); // ACK
- bool longpkt = syn || synack;
- buf[12] = (longpkt ? 6 : 5) << 4; // data offset
+ unsigned char hdrlen = syn ? 36 : (synack ? 24 : 20);
+ buf[12] = (hdrlen/4) << 4; // data offset
if (syn)
buf[13] = 1 << 1; // SYN
else if (synack)
buf[18] = 0x00; // URG Pointer
buf[19] = 0x00; // URG Pointer
- if (longpkt) {
+ if (syn || synack) {
buf[20] = 0x01; // NOP
buf[21] = 0x03; // Window Scale
buf[22] = 0x03; // Window Scale Option Length
buf[23] = 0x0e; // 1GB Window Size (0xffff << 0x0e)
}
+ if (syn) {
+ buf[24] = 0x01; // NOP
+ buf[25] = 0x01; // NOP
+ buf[26] = 8; // Timestamp
+ buf[27] = 10; // Timestamp Option Length
+ memcpy(buf + 28, ×tamps_magic, 8);
+ }
- uint16_t checksum = tcp_checksum(buf, len + 20 + (longpkt ? 4 : 0), src_addr, dest_addr);
+ uint16_t checksum = tcp_checksum(buf, len + hdrlen, src_addr, dest_addr);
buf[16] = checksum; // Checksum
buf[17] = checksum >> 8; // Checksum
+
+ return hdrlen;
}
static void build_ip_header(unsigned char* buf, struct pkt_hdr hdr, const in_addr_t& src_addr, const in_addr_t& dest_addr) {
static int fd[TUN_IF_COUNT];
static struct sockaddr_in dest;
static in_addr_t src, tun_src, tun_dest;
-static uint64_t tcp_init_magic;
+static uint32_t starting_ack;
#define PENDING_MESSAGES_BUFF_SIZE (0x800)
#define THREAD_POLL_SLEEP_MICS 250
bool ack = tcp_buf[13] & (1 << 4);
if (are_server && syn && !ack) {
- // We're a server and just got a client
- if (tcp_buf[4 ] != uint8_t(tcp_init_magic >> (7 * 8)) ||
- tcp_buf[5 ] != uint8_t(tcp_init_magic >> (6 * 8)) ||
- tcp_buf[6 ] != uint8_t(tcp_init_magic >> (5 * 8)) ||
- tcp_buf[7 ] != uint8_t(tcp_init_magic >> (4 * 8)) ||
- tcp_buf[8 ] != uint8_t(tcp_init_magic >> (3 * 8)) ||
- tcp_buf[9 ] != uint8_t(tcp_init_magic >> (2 * 8)) ||
- tcp_buf[10] != uint8_t(tcp_init_magic >> (1 * 8)) ||
- tcp_buf[11] != uint8_t(tcp_init_magic >> (0 * 8)))
+ uint32_t expected_ack = htobe32(starting_ack);
+ if (memcmp(tcp_buf + 8, &expected_ack, 4))
continue;
+ if (nread < 36 + header_size) { continue; }
+ // We're a server and just got a client...walk options until we find timestamps
+ const unsigned char* opt_buf = tcp_buf + 20;
+ bool found_magic = false;
+ while (!found_magic && opt_buf < buf + nread) {
+ switch (*opt_buf) {
+ case 1: opt_buf += 1; break;
+ case 2: opt_buf += 4; break;
+ case 3: opt_buf += 3; break;
+ // SACK should never appear
+ case 8:
+ if (opt_buf + 10 <= buf + nread) {
+ if (!memcmp(opt_buf + 2, ×tamps_magic, 8)) {
+ found_magic = true;
+ break;
+ }
+ }
+ // Fall through
+ default: opt_buf = buf + nread;
+ }
+ }
+ if (!found_magic) continue;
fprintf(stderr, "Got SYN, sending SYNACK\n");
remote_port = (tcp_buf[0] << 8) | tcp_buf[1];
last_ack_recv = std::chrono::steady_clock::now();
if (are_server && syn && !ack) {
- build_tcp_header(tcp_buf, 0, 0, 1, src, dest.sin_addr.s_addr);
+ int len = build_tcp_header(tcp_buf, 0, 0, 1, src, dest.sin_addr.s_addr);
- ssize_t res = sendto(fdr, tcp_buf, 20 + 4, 0, (struct sockaddr*)&dest, sizeof(dest));
+ ssize_t res = sendto(fdr, tcp_buf, len, 0, (struct sockaddr*)&dest, sizeof(dest));
if (res < 0) {
int err = errno;
fprintf(stderr, "Failed to send SYNACK with err %d (%s)\n", err, strerror(err));
local_port = local_port_tmp;
}
- uint32_t starting_ack = 0, starting_seq = 0;
- memcpy(&starting_ack, &tcp_init_magic, 4);
- memcpy(&starting_seq, ((const unsigned char*)&tcp_init_magic) + 4, 4);
highest_recvd_seq = starting_ack;
+ uint32_t starting_seq;
+ assert(getrandom(&starting_seq, sizeof(starting_seq), 0) == sizeof(starting_seq));
cur_seq = starting_seq;
if (!pause_tun_read_reinit_tcp) { // Not doing a re-init
unsigned char buf[1500];
if (!are_server) {
- build_tcp_header(buf, 0, 1, 0, src, dest.sin_addr.s_addr);
- ssize_t res = sendto(fdr, buf, 20 + 4, 0, (struct sockaddr*)&dest, sizeof(dest));
+ int len = build_tcp_header(buf, 0, 1, 0, src, dest.sin_addr.s_addr);
+ ssize_t res = sendto(fdr, buf, len, 0, (struct sockaddr*)&dest, sizeof(dest));
if (res < 0) {
int err = errno;
fprintf(stderr, "Failed to send initial SYN with err %d (%s)\n", err, strerror(err));
if (!are_server) {
fprintf(stderr, "Got SYNACK, sending ACK and starting tun listen\n");
- build_tcp_header(buf, 0, 0, 0, src, dest.sin_addr.s_addr);
- ssize_t res = sendto(fdr, buf, 20, 0, (struct sockaddr*)&dest, sizeof(dest));
+ int len = build_tcp_header(buf, 0, 0, 0, src, dest.sin_addr.s_addr);
+ ssize_t res = sendto(fdr, buf, len, 0, (struct sockaddr*)&dest, sizeof(dest));
if (res < 0) {
int err = errno;
fprintf(stderr, "Failed to send initial ACK with err %d (%s)\n", err, strerror(err));
remote_port = atoi(argv[4]);
}
- tcp_init_magic = atoll(argv[5]);
+ uint64_t tcp_init_magic = atoll(argv[5]);
+ starting_ack = tcp_init_magic >> 32;
+ timestamps_magic = htobe64(tcp_init_magic);
src = inet_addr(argv[7]);
projects / tunudptotcp / blobdiff