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fix(LCEL-04): bind relay to 127.0.0.1 + cap read_line at 8 KiB

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two changes:

1. run_relay_proxy bound TcpListener to 0.0.0.0:61000. any LAN host
   could connect to this port and their bytes were piped to the
   upstream relay - no authentication of the local peer. changed to
   127.0.0.1:61000 since the game process connects on loopback.

2. read_line read byte-by-byte into a Vec<u8> with no size cap. a
   malicious peer (relay or LAN) sending an unbounded line without
   \n could OOM the launcher. capped at 8 KiB (relay control lines
   are tiny - HOST/JOIN tokens + small id).
This commit is contained in:
M1noa 2026-07-16 17:34:50 -05:00
parent 8da6a217bc
commit f4f438f688
1 changed files with 12 additions and 1 deletions
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13
src-tauri/src/networking/relay.rs
View file

@ -6,6 +6,10 @@ use tokio::time::sleep;
use tokio_util::sync::CancellationToken;
use crate::state::ProxyGuard;
const PROXY_ADDR: &str = "proxy.mclegacyedition.xyz:2052"; //neo: yeah bro im hardcoding it
// security: cap read_line at 8 KiB. relay control lines are tiny (HOST/JOIN
// tokens + small id). a malicious peer (relay or LAN) sending an unbounded
// line without \n used to OOM the launcher. (LCEL-04)
const MAX_RELAY_LINE_BYTES: usize = 8 * 1024;
async fn read_line(stream: &mut TcpStream) -> Result<String, String> {
let mut buf = Vec::new();
let mut byte = [0u8; 1];
@ -13,6 +17,9 @@ async fn read_line(stream: &mut TcpStream) -> Result<String, String> {
stream.read_exact(&mut byte).await.map_err(|e| e.to_string())?;
if byte[0] == b'\n' { break; }
if byte[0] != b'\r' { buf.push(byte[0]); }
if buf.len() > MAX_RELAY_LINE_BYTES {
return Err(format!("relay line exceeded {} bytes", MAX_RELAY_LINE_BYTES));
}
}
String::from_utf8(buf).map_err(|e| e.to_string())
}
@ -111,7 +118,11 @@ async fn run_relay_proxy(
.map_err(|e| format!("Proxy connect failed: {}", e))?;
write_line(&mut stream, &format!("JOIN {} 0 {}", auth_token, target_session)).await?;
let listener = TcpListener::bind("0.0.0.0:61000")
// security: bind to loopback only. the game process connects on
// 127.0.0.1:61000; binding 0.0.0.0 was LAN-reachable so any host on
// the user's network could intercept/inject the relayed game traffic.
// (LCEL-04)
let listener = TcpListener::bind("127.0.0.1:61000")
.await
.map_err(|e| format!("Bind failed: {}", e))?;
let local_port = listener.local_addr().map_err(|e| e.to_string())?.port();