From 1636c4c60e48ba87f2179701302cb0aae953c179 Mon Sep 17 00:00:00 2001
From: Adam <24621027+WhiteDopeOnPunk@users.noreply.github.com>
Date: Fri, 12 Jan 2024 07:57:39 -0500
Subject: [PATCH] add stuff

---
 .gitignore  |   1 +
 Cargo.lock  | 628 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 Cargo.toml  |  10 +
 run         |   6 +
 src/main.rs |  70 ++++++
 src/tcp.rs  | 322 +++++++++++++++++++++++++++
 6 files changed, 1037 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100755 run
 create mode 100644 src/main.rs
 create mode 100644 src/tcp.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
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diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..1ad60ad
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,628 @@
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
+
+[[package]]
+name = "ws2_32-sys"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d59cefebd0c892fa2dd6de581e937301d8552cb44489cdff035c6187cb63fa5e"
+dependencies = [
+ "winapi 0.2.8",
+ "winapi-build",
+]
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..3a5205d
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "tcp"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+etherparse = "0.13.0"
+tun-tap = "0.1.4"
diff --git a/run b/run
new file mode 100755
index 0000000..baf3f06
--- /dev/null
+++ b/run
@@ -0,0 +1,6 @@
+#!/bin/bash
+cargo b --release &&
+sudo setcap cap_net_admin=eip ./target/release/tcp &&
+./target/release/tcp &&
+sudo ip addr add 192.168.69.1/24 dev tun0 &&
+trap "killall tcp" INT TERM
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..68258f8
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,70 @@
+use std::io;
+mod tcp;
+use std::collections::HashMap;
+use std::collections::hash_map::Entry;
+use std::net::Ipv4Addr;
+
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
+struct Quad {
+    src: (Ipv4Addr, u16),
+    dst: (Ipv4Addr, u16),
+}
+
+fn main() -> io::Result<()> {
+    let mut connections: HashMap<Quad, tcp::State> = Default::default();
+
+    let mut nic = tun_tap::Iface::without_packet_info("tun0", tun_tap::Mode::Tun)?;
+
+    // buffer size 1504 bytes (maximum Ethernet frame size without CRC)
+    let mut buf = [0u8; 1504];
+
+    let stfu_unused = true;
+    while stfu_unused {
+        let nbytes = nic.recv(&mut buf[..])?;
+
+        match etherparse::Ipv4HeaderSlice::from_slice(&buf[..nbytes]) {
+            Ok(iph) => {
+                let src = iph.source_addr();
+                let dst = iph.destination_addr();
+
+                if iph.protocol() != 0x06 {
+                    eprintln!("Not TCP, skipping...");
+                    continue;
+                }
+
+                match etherparse::TcpHeaderSlice::from_slice(&buf[iph.slice().len()..nbytes]) {
+                    Ok(tcph) => {
+                        let datai = iph.slice().len() + tcph.slice().len();
+
+                        match connections.entry(Quad {
+                            src: (src, tcph.source_port()),
+                            dst: (dst, tcph.destination_port()),
+                        }) {
+                            Entry::Occupied(mut c) => {
+                                c.get_mut()
+                                    .on_packet(&mut nic, iph, tcph, &buf[datai..nbytes])?;
+                            }
+                            Entry::Vacant(mut e) => {
+                                if let Some(c) = tcp::Connection::accept(
+                                    &mut nic,
+                                    iph,
+                                    tcph,
+                                    &buf[datai..nbytes],
+                                )? {
+                                    e.insert(c);
+                                }
+                            }
+                        }
+                    }
+                    Err(e) => {
+                        eprintln!("An error occurred while parsing TCP packet: {:?}", e);
+                    }
+                }
+            }
+            Err(e) => {
+                eprintln!("An error occurred while parsing IP packet: {:?}", e);
+            }
+        }
+    }
+    Ok(())
+}
diff --git a/src/tcp.rs b/src/tcp.rs
new file mode 100644
index 0000000..b7fd5eb
--- /dev/null
+++ b/src/tcp.rs
@@ -0,0 +1,322 @@
+use std::io;
+use std::io::prelude::*;
+
+pub enum State {
+    Closed,
+    Listen,
+    SynRcvd,
+    Estab,
+}
+
+pub struct Connection {
+    state: State,
+    send: SendSequenceSpace,
+    recv: RecvSequenceSpace,
+    ip: etherparse::Ipv4Header,
+    tcp: etherparse::TcpHeader,
+}
+
+struct SendSequenceSpace {
+    una: u32,
+    nxt: u32,
+    wnd: u16,
+    up: bool,
+    wl1: usize,
+    wl2: usize,
+    iss: u32,
+}
+
+struct RecvSequenceSpace {
+    nxt: u32,
+    wnd: u16,
+    up: bool,
+    irs: u32,
+}
+
+impl Default for State {
+    fn default() -> Self {
+        State::Listen
+    }
+}
+
+impl Connection {
+    fn write(&mut self, nic: &mut tun_tap::Iface, seq: u32, mut limit: usize) -> io::Result<usize> {
+        // 1500 bytes ethernet max transmission unit (MTU)
+        let mut buf = [0u8; 1500];
+
+        self.tcp.sequence_number = seq;
+        self.tcp.acknowledgment_number = self.recv.nxt;
+        println!(
+            "write(ack: {}, seq: {}, limit: {}) syn {:?} fin {:?}",
+            self.recv.nxt - self.recv.irs,
+            seq,
+            limit,
+            self.tcp.syn,
+            self.tcp.fin,
+        );
+
+        let mut offset = seq.wrapping_sub(self.send.una) as usize;
+
+        if let Some(closed_at) = self.closed_at {
+            if seq == closed_at.wrapping_add(1) {
+                offset = 0;
+                limit = 0;
+            }
+        }
+
+        println!(
+            "using offset {} base {} in {:?}",
+            offset,
+            self.send.una,
+            self.unacked.as_slices()
+        );
+
+        let (mut h, mut t) = self.unacked.as_slices();
+        if h.len() > offset {
+            h = &h[offset..];
+        } else {
+            let skipped = h.len();
+            h = &[];
+            t = &t[(offset - skipped)..];
+        }
+
+        let max_data = std::cmp::min(limit, h.len() + t.len());
+        let size = std::cmp::min(
+            buf.len(),
+            self.tcp.header_len() as usize + self.ip.header_len() as usize + max_data,
+        );
+
+        self.ip
+            .set_payload_len(size - self.ip.header_len() as usize);
+
+        let buf_len = buf.len();
+        let mut unwritten = &mut buf[..];
+
+        self.ip.write(&mut unwritten);
+
+        let ip_header_ends_at = buf_len - unwritten.len();
+
+        unwritten = &mut unwritten[self.tcp.header_len() as usize..];
+        let tcp_header_ends_at = buf_len - unwritten.len();
+
+        let payload_bytes = {
+            let mut written = 0;
+            let mut limit = max_data;
+
+            let p1l = std::cmp::min(limit, h.len());
+            written += unwritten.write(&h[..p1l])?;
+            limit -= written;
+
+            let p2l = std::cmp::min(limit, t.len());
+            written += unwritten.write(&t[..p2l])?;
+            written
+        };
+
+        let payload_ends_at = buf_len - unwritten.len();
+
+        self.tcp.checksum = self
+            .tcp
+            .calc_checksum_ipv4(&self.ip, &buf[tcp_header_ends_at..payload_ends_at])
+            .expect("failed to compute checksum");
+
+        let mut unwritten = &mut buf[ip_header_ends_at..];
+        self.tcp.write(&mut unwritten);
+
+        let write_len = nic.send(&buf[..payload_ends_at])?;
+
+        Ok(payload_bytes)
+    }
+}
+pub fn accept<'a>(
+    nic: &mut tun_tap::Iface,
+    iph: etherparse::Ipv4HeaderSlice<'a>,
+    tcph: etherparse::TcpHeaderSlice<'a>,
+    data: &'a [u8],
+) -> io::Result<Option<Self>> {
+    let mut buf = [0u8; 1500];
+    if !tcph.syn() {
+        return Ok(None);
+    }
+    let iss = 0;
+    let wnd = 10;
+    let mut c = Connection {
+        state: State::SynRcvd,
+        send: SendSequenceSpace {
+            iss,
+            una: iss,
+            nxt: 1,
+            wnd: wnd,
+            up: false,
+            wl1: 0,
+            wl2: 0,
+        },
+        recv: RecvSequenceSpace {
+            irs: tcph.sequence_number(),
+            nxt: tcph.sequence_number() + 1,
+            wnd: tcph.window_size(),
+            up: false,
+        },
+
+        // TODO: Consider keeping track of sender info for future use.
+
+        // Prepare a SYN-ACK packet in response to the SYN packet.
+        tcp: etherparse::TcpHeader::new(tcph.destination_port(), tcph.source_port(), iss, wnd),
+        ip: etherparse::Ipv4Header::new(
+            syn_ack.header_len(),
+            64,
+            etherparse::IpNumber::Tcp as u8,
+            [
+                iph.destination()[0],
+                iph.destination()[1],
+                iph.destination()[2],
+                iph.destination()[3],
+            ],
+            [
+                iph.source()[0],
+                iph.source()[1],
+                iph.source()[2],
+                iph.source()[3],
+            ],
+        ),
+    };
+
+    c.tcp.acknowledgment_number = c.recv.nxt;
+    c.tcp.syn = true;
+    c.tcp.ack = true;
+
+    c.ip.set_payload_len(c.tcp.header_len() as usize + 0);
+
+    // Calculate and set the checksum for the SYN-ACK packet.
+    c.tcp.checksum = c
+        .tcp
+        .calc_checksum_ipv4(&c.ip, &[])
+        .expect("Failed to compute checksum");
+
+    // Write out the TCP and IP headers to a buffer to be sent.
+    let unwritten = {
+        let mut unwritten = &mut buf[..];
+        ip.write(&mut unwritten);
+        syn_ack.write(&mut unwritten);
+        unwritten.len()
+    };
+
+    // Send the SYN-ACK packet.
+    nic.send(&buf[..unwritten])?;
+    Ok(Some(c))
+}
+
+// TODO: Implement a function to handle incoming packets for an established connection.
+
+// Function to handle incoming packets once a connection is established.
+pub fn on_packet<'a>(
+    &mut self,
+    nic: &mut tun_tap::Iface,
+    iph: etherparse::Ipv4HeaderSlice<'a>,
+    tcph: etherparse::TcpHeaderSlice<'a>,
+    data: &'a [u8],
+) -> io::Result<()> {
+    let seqn = tcph.sequence_number();
+    let mut slen = data.len() as u32;
+    if tcph.fin() {
+        slen += 1;
+    };
+    if tcph.syn() {
+        slen += 1;
+    };
+    let wend = self.recv.nxt.wrapping_add(self.recv.wnd as u32);
+
+    let okay = if slen == 0 {
+        if self.recv.wnd == 0 {
+            seqn == self.recv.nxt
+        } else {
+            is_between_wrapped(self.recv.nxt.wrapping_sub(1), seqn, wend)
+        }
+    } else {
+        if self.recv.wnd == 0 {
+            false
+        } else {
+            is_between_wrapped(self.recv.nxt.wrapping_sub(1), seqn, wend) ||
+            is_between_wrapped(self.recv.nxt.wrapping_sub(1), seqn.wrapping_add(slen - 1), wend)
+        }
+    };
+
+    if !okay {
+        self.write(nic, self.send.nxt, 0)?;
+        return Ok(());
+    }
+
+    self.recv.nxt = seqn.wrapping_add(slen);
+
+    if !tcph.ack() {
+        return Ok(());
+    }
+
+    let ackn = tcph.acknowledgment_number();
+
+    if let State::SynRcvd = self.state {
+        if is_between_wrapped(self.send.una.wrapping_sub(1), ackn, self.send.nxt.wrapping_add(1)) {
+            self.state = State::Estab;
+        } else {
+        }
+    }
+
+    if let State::Estab | State::FinWait1 | State::FinWait2 = self.state {
+        if !is_between_wrapped(self.send.una, ackn, self.send.nxt.wrapping_add(1)) {
+            return Ok(());
+        }
+
+        self.send.una = ackn;
+
+        assert!(data.is_empty());
+
+        if let State::Estab = self.state {
+            self.tcp.fin = true;
+            self.write(nic, self.send.nxt, 0)?;
+            self.state = State::FinWait1;
+        }
+    }
+
+    if let State::FinWait1 = self.state {
+        if self.send.una == self.send.iss + 2 {
+            self.state = State::FinWait2;
+        }
+    }
+
+    if tcph.fin() {
+        match self.state {
+            State::FinWait2 => {
+                self.write(nic, self.send.nxt, 0)?;
+                self.state = State::TimeWait;
+            }
+            _ => { }
+        }
+    }
+
+    Ok(())
+}
+
+fn wrapping_it(lhs: u32, rhs: u32) -> bool {
+    lhs.wrapping_sub(rhs) > (1 << 31)
+}
+
+fn is_between_wrapped(start: u32, x: u32, end: u32) -> bool {
+    wrapping_it(start, x) && wrapping_it(e, end)
+}
+
+impl State {
+    pub fn on_packet<'a>(
+        &mut self,
+        iph: etherparse::Ipv4HeaderSlice<'a>,
+        tcph: etherparse::TcpHeaderSlice<'a>,
+        data: &'a [u8],
+    ) {
+        eprintln!(
+            "{}:{} -> {}:{} {}b of TCP",
+            iph.source_addr(),
+            tcph.source_port(),
+            iph.destination_addr(),
+            tcph.destination_port(),
+            data.len(),
+        );
+    }
+}