fix(host/security): close audit findings S1,#1,#4,#10,#12,#7,#6,S2-S6 (Linux/cross-platform)

Remediations from design/security-review-2026-06-28.md verified on Linux
(cargo check/clippy/test green; Windows-gated paths verify in CI):

- S1 [HIGH]: bump quinn-proto 0.11.14 -> 0.11.15 (RUSTSEC-2026-0185,
  pre-auth out-of-order STREAM reassembly memory exhaustion on the
  always-on default QUIC listener).
- #1 [HIGH]: remove the unauthenticated nvhttp `GET /pin` endpoint; the
  GameStream PIN is delivered ONLY via the bearer-gated mgmt API, so a
  network client can no longer submit its own displayed PIN and self-pair.
- #4 [HIGH->MED]: gate the unauthenticated RTSP/UDP media plane on a paired
  `/launch` and bind it to the launching client's source IP (threaded
  through the HTTPS handler), so an unpaired peer can neither start capture
  on an idle host nor ride a paired client's active launch.
- #12: bound concurrent parked pairing waiters (MAX_PARKED_WAITERS) so a
  pre-auth peer can't pin unbounded 300s handshakes. +regression test.
- #10: throttle the per-packet ENet control GCM-decrypt-failed warn
  (exponential backoff) so a junk flood can't spam the log.
- #7 [MED->LOW]: serialize all process-global env mutation on the
  session-setup path under a new vdisplay::ENV_LOCK (apply_session_env /
  apply_input_env / the launch-cmd set_var / the gamescope env read), so
  concurrent native sessions can't race set_var/getenv (data-race UB ->
  host-wide DoS). Full per-session SessionContext threading remains a
  follow-up for cross-session value confusion.
- #6 [MED]: move the gamescope EIS socket relay from world-writable /tmp to
  $XDG_RUNTIME_DIR (per-user 0700) and reject a symlinked relay file, so a
  local user can't intercept (keylog) or deny the remote session's input.
- S2: a malformed client Opus mic frame now drops that frame instead of
  tearing down the shared host-lifetime virtual mic (cross-session DoS).
- S3: track held buttons/keys in capped HashSets (was unbounded Vec with
  O(n) scans) so a paired client can't grow per-session input state.
- S5: reject fps==0/absurd at the open_video chokepoint (covers Hello,
  ANNOUNCE, Reconfigure) so the encoder time_base/pts math can't div-by-0.
- S6: bound the shared mic mpsc (drop-newest when full).
- S4: cap Epic launcher-cache reads (catcache.bin/.item) so a planted giant
  can't OOM the host during library enumeration.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/encode.rs

@@ -230,6 +230,14 @@ pub fn open_video(
     chroma: ChromaFormat,
 ) -> Result<Box<dyn Encoder>> {
     validate_dimensions(codec, width, height)?;
+    // Refresh/fps must be positive and sane: fps feeds the encoder time_base (`Rational(1, fps)`)
+    // and the pts→ns conversion (`pts * 1e9 / fps`), so 0 builds a 1/0 rational / divides by zero.
+    // The mid-stream Reconfigure path already guards `refresh_hz > 0`; enforcing it at this single
+    // open chokepoint makes EVERY path (initial Hello, GameStream ANNOUNCE, Reconfigure) safe
+    // regardless of which backend opens (security-review 2026-06-28 S5).
+    if fps == 0 || fps > 1000 {
+        anyhow::bail!("invalid refresh/fps {fps}: must be 1..=1000 Hz");
+    }
     // 4:4:4 is HEVC-only. The negotiator should never pass `Yuv444` for another codec (it gates on
     // `codec == H265`), but defend the contract here so a future caller can't silently emit a stream
     // no decoder expects: a non-HEVC 4:4:4 request degrades to 4:2:0 with a warning.

crates/punktfunk-host/src/gamestream/control.rs

@@ -56,6 +56,9 @@ pub fn spawn(state: Arc<AppState>) -> Result<()> {
         .spawn(move || {
             // GCM scheme detected from the first authenticating packet; reused thereafter.
             let mut detected: Option<Scheme> = None;
+            // Consecutive control-decrypt failures for this peer — throttles the warn log so a
+            // junk-packet flood can't spam unbounded lines (security-review 2026-06-28 #10).
+            let mut decrypt_fails: u64 = 0;
             // Decoded keyboard/mouse is forwarded to a dedicated host-lifetime injector thread —
             // NEVER injected inline, so a slow Wayland/libei/SendInput call can't head-block ENet
             // keepalive/retransmit servicing on this thread. The injector owns non-Send compositor
@@ -77,6 +80,7 @@ pub fn spawn(state: Arc<AppState>) -> Result<()> {
                             Event::Disconnect { .. } => {
                                 tracing::info!("control: client disconnected");
                                 detected = None;
+                                decrypt_fails = 0;
                                 peer = None;
                                 // Unplug the session's virtual pads.
                                 pads = GamepadManager::new();
@@ -89,6 +93,7 @@ pub fn spawn(state: Arc<AppState>) -> Result<()> {
                                     channel_id,
                                     packet.data(),
                                     &mut detected,
+                                    &mut decrypt_fails,
                                     &inj_tx,
                                     &mut pads,
                                 );
@@ -163,6 +168,7 @@ fn on_receive(
     _channel_id: u8,
     d: &[u8],
     detected: &mut Option<Scheme>,
+    decrypt_fails: &mut u64,
     inj_tx: &Sender<InputEvent>,
     pads: &mut GamepadManager,
 ) {
@@ -180,10 +186,20 @@ fn on_receive(
                 tracing::info!(?scheme, "control: GCM scheme locked in");
             }
             *detected = Some(scheme);
+            *decrypt_fails = 0;
             pt
         }
         None => {
-            tracing::warn!(len = d.len(), "control: GCM decrypt failed");
+            // Throttle: a junk-packet flood must not spam one warn line per packet. Log the first
+            // failure, then only at exponentially-spaced counts (1, 2, 4, 8, …).
+            *decrypt_fails += 1;
+            if decrypt_fails.is_power_of_two() {
+                tracing::warn!(
+                    len = d.len(),
+                    fails = *decrypt_fails,
+                    "control: GCM decrypt failed"
+                );
+            }
             return;
         }
     };

crates/punktfunk-host/src/gamestream/mod.rs

@@ -90,6 +90,11 @@ pub struct LaunchSession {
     pub fps: u32,
     /// `/launch?appid=N` — selects the app-catalog entry (session recipe).
     pub appid: u32,
+    /// Source IP of the paired HTTPS client that issued `/launch`. The unauthenticated RTSP/UDP
+    /// media plane binds to this so only the launching peer can start/own the stream — an
+    /// unpaired RTSP peer cannot ride a paired client's launch (security-review 2026-06-28 #4).
+    /// `None` if the address could not be captured (then RTSP falls back to launch-present only).
+    pub peer_ip: Option<std::net::IpAddr>,
 }
 
 /// Shared control-plane state used as the axum app state.

crates/punktfunk-host/src/gamestream/nvhttp.rs

@@ -1,9 +1,14 @@
 //! The nvhttp servers: plain HTTP on 47989 and mutual-TLS on 47984. Serves `/serverinfo`,
-//! the `/pair` flow, `/applist`, and `/launch`/`/resume`/`/cancel`, plus a punktfunk-only
-//! `/pin` endpoint to deliver the Moonlight-displayed PIN. Over HTTPS the client is
+//! the `/pair` flow, `/applist`, and `/launch`/`/resume`/`/cancel`. Over HTTPS the client is
 //! mutual-TLS-authenticated, so `/serverinfo` reports `PairStatus=1` there.
+//!
+//! The pairing PIN is delivered out-of-band ONLY through the bearer-authenticated management
+//! API (`POST /api/v1/pair/pin`): the operator reads the PIN off the Moonlight client and
+//! types it into the host console. There is deliberately NO unauthenticated nvhttp PIN
+//! endpoint — one would let a network client submit its own displayed PIN and drive the whole
+//! ceremony to a pinned cert with no operator consent (security-review 2026-06-28 #1).
 
-use super::tls::PeerCertFingerprint;
+use super::tls::{PeerAddr, PeerCertFingerprint};
 use super::{serverinfo, AppState, LaunchSession, HTTPS_PORT, HTTP_PORT, RTSP_PORT};
 use anyhow::{anyhow, Context, Result};
 use axum::{
@@ -58,7 +63,6 @@ fn router(state: Arc<AppState>, https: bool) -> Router {
     Router::new()
         .route("/serverinfo", get(h_serverinfo))
         .route("/pair", get(h_pair))
-        .route("/pin", get(h_pin))
         .route("/applist", get(h_applist))
         .route("/launch", get(h_launch))
         .route("/resume", get(h_resume))
@@ -82,19 +86,6 @@ async fn h_serverinfo(
     xml(serverinfo::serverinfo_xml(&st.host, https, paired))
 }
 
-async fn h_pin(
-    State(st): State<Arc<AppState>>,
-    Query(q): Query<HashMap<String, String>>,
-) -> impl IntoResponse {
-    match q.get("pin").filter(|p| !p.is_empty()) {
-        Some(pin) => {
-            st.pairing.pin.submit(pin.clone());
-            "PIN accepted\n".to_string()
-        }
-        None => "usage: GET /pin?pin=NNNN\n".to_string(),
-    }
-}
-
 async fn h_applist(
     State(st): State<Arc<AppState>>,
     peer: Option<Extension<PeerCertFingerprint>>,
@@ -110,6 +101,7 @@ async fn h_applist(
 async fn h_launch(
     State(st): State<Arc<AppState>>,
     peer: Option<Extension<PeerCertFingerprint>>,
+    addr: Option<Extension<PeerAddr>>,
     Query(q): Query<HashMap<String, String>>,
 ) -> impl IntoResponse {
     if !peer_is_paired(&peer, &st) {
@@ -117,7 +109,9 @@ async fn h_launch(
         return xml(error_xml());
     }
     match launch(&st, &q) {
-        Ok(session) => {
+        Ok(mut session) => {
+            // Bind the (unauthenticated) RTSP/UDP media plane to this paired client's source IP.
+            session.peer_ip = addr.map(|Extension(PeerAddr(a))| a.ip());
             *st.launch.lock().unwrap() = Some(session);
             tracing::info!(
                 w = session.width,
@@ -193,6 +187,7 @@ fn launch(_st: &AppState, q: &HashMap<String, String>) -> Result<LaunchSession>
         height,
         fps,
         appid,
+        peer_ip: None, // set by `h_launch` from the verified HTTPS peer address
     })
 }
 

crates/punktfunk-host/src/gamestream/pairing.rs

@@ -17,9 +17,14 @@ use std::sync::Mutex;
 use std::time::Duration;
 use tokio::sync::Notify;
 
-/// Out-of-band PIN delivery. Moonlight generates + displays a PIN; the user submits it
-/// (via the management API's `POST /api/v1/pair/pin` or nvhttp's `GET /pin?pin=NNNN`).
-/// `getservercert` parks until a PIN arrives.
+/// Out-of-band PIN delivery. Moonlight generates + displays a PIN; the operator submits it
+/// via the bearer-authenticated management API (`POST /api/v1/pair/pin`) only — there is no
+/// unauthenticated nvhttp delivery path (a network client must never be able to submit its
+/// own PIN; security-review 2026-06-28 #1). `getservercert` parks until a PIN arrives.
+/// Max pairing handshakes parked in [`PinGate::take`] at once (each holds a slot for up to
+/// 300s), bounding a pre-auth waiter flood. Real pairing is one operator-driven client at a time.
+const MAX_PARKED_WAITERS: usize = 4;
+
 pub struct PinGate {
     pin: Mutex<Option<String>>,
     notify: Notify,
@@ -48,7 +53,20 @@ impl PinGate {
     }
 
     async fn take(&self, timeout: Duration) -> Option<String> {
-        self.waiters.fetch_add(1, Ordering::SeqCst);
+        // Bound the number of pairing handshakes parked at once: each `getservercert` is
+        // pre-auth and parks for up to 300s, so without a cap an unpaired LAN peer could pin
+        // unbounded tasks + keep `awaiting_pin` asserted (security-review 2026-06-28 #12).
+        // Reserve a slot atomically; refuse (treated as "no PIN") once the cap is reached.
+        if self
+            .waiters
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |n| {
+                (n < MAX_PARKED_WAITERS).then_some(n + 1)
+            })
+            .is_err()
+        {
+            tracing::warn!("pairing: too many handshakes awaiting a PIN — refusing");
+            return None;
+        }
         // Decrement on every exit path (PIN delivered, timeout, or future cancellation).
         struct WaiterGuard<'a>(&'a AtomicUsize);
         impl Drop for WaiterGuard<'_> {
@@ -117,7 +135,8 @@ impl Pairing {
 
         tracing::info!(
             uniqueid,
-            "pairing phase 1 (getservercert) — awaiting PIN: submit `GET /pin?pin=NNNN`"
+            "pairing phase 1 (getservercert) — awaiting PIN: deliver it via the management \
+             API `POST /api/v1/pair/pin` (operator reads the PIN off the Moonlight client)"
         );
         let pin = self
             .pin
@@ -304,4 +323,28 @@ mod tests {
         assert_eq!(pairing.pin.take(Duration::from_millis(10)).await, None);
         assert!(!pairing.pin.awaiting_pin());
     }
+
+    /// A pre-auth peer flood can park at most `MAX_PARKED_WAITERS` pairing handshakes; the next
+    /// `take` is refused immediately (returns `None` without parking), bounding the 300s-waiter DoS
+    /// (security-review 2026-06-28 #12).
+    #[tokio::test]
+    async fn pin_gate_caps_parked_waiters() {
+        let pairing = Arc::new(Pairing::new());
+        let mut handles = Vec::new();
+        for _ in 0..MAX_PARKED_WAITERS {
+            let p = pairing.clone();
+            handles.push(tokio::spawn(async move {
+                p.pin.take(Duration::from_secs(5)).await
+            }));
+        }
+        // Wait until all the slots are taken.
+        while pairing.pin.waiters.load(Ordering::SeqCst) < MAX_PARKED_WAITERS {
+            tokio::time::sleep(Duration::from_millis(2)).await;
+        }
+        // One more is refused right away (no parking), even with a long timeout.
+        assert_eq!(pairing.pin.take(Duration::from_secs(5)).await, None);
+        for h in handles {
+            h.abort();
+        }
+    }
 }

crates/punktfunk-host/src/gamestream/rtsp.rs

@@ -14,7 +14,7 @@ use crate::encode::Codec;
 use anyhow::{Context, Result};
 use std::collections::HashMap;
 use std::io::{Read, Write};
-use std::net::{TcpListener, TcpStream};
+use std::net::{SocketAddr, TcpListener, TcpStream};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
@@ -102,13 +102,12 @@ fn handle_conn(mut stream: TcpStream, state: Arc<AppState>) -> Result<()> {
             "RTSP {} | {}", req.head.replace("\r\n", " | "),
             if req.body.is_empty() { String::new() } else { format!("body: {}", req.body.replace("\r\n", " | ")) }
         );
-        let resp = handle_request(&req, &state);
+        let resp = handle_request(&req, &state, peer);
         stream.write_all(resp.as_bytes()).context("RTSP write")?;
         stream.flush().ok();
         // Close (FIN after the flushed response) so the client detects end-of-response.
         let _ = stream.shutdown(std::net::Shutdown::Both);
     }
-    let _ = peer;
     Ok(())
 }
 
@@ -171,7 +170,7 @@ fn parse_request(head: &str, body: String) -> Request {
     }
 }
 
-fn handle_request(req: &Request, state: &AppState) -> String {
+fn handle_request(req: &Request, state: &AppState, peer: Option<SocketAddr>) -> String {
     match req.method.as_str() {
         "OPTIONS" => response(
             &req.cseq,
@@ -216,16 +215,30 @@ fn handle_request(req: &Request, state: &AppState) -> String {
             response(&req.cseq, &[], None)
         }
         "PLAY" => {
+            // The RTSP/UDP media plane is UNAUTHENTICATED. A stream may start only for the paired
+            // client that completed the pairing-gated `/launch` (which set `state.launch`), and —
+            // when the launching IP is known — only from that same source IP. So an unpaired RTSP
+            // peer can neither start a stream on an idle host nor ride a paired client's active
+            // launch (security-review 2026-06-28 #4). `nvhttp` gates `/launch` on a pinned cert.
+            let launch = *state.launch.lock().unwrap();
+            let Some(ls) = launch else {
+                tracing::warn!(?peer, "RTSP PLAY — refused: no paired `/launch` session");
+                return response_status("401 Unauthorized", &req.cseq, &[], None);
+            };
+            if let (Some(want), Some(got)) = (ls.peer_ip, peer.map(|p| p.ip())) {
+                if want != got {
+                    tracing::warn!(
+                        %want, %got,
+                        "RTSP PLAY — refused: peer IP does not match the launching client"
+                    );
+                    return response_status("401 Unauthorized", &req.cseq, &[], None);
+                }
+            }
             let cfg = *state.stream.lock().unwrap();
             match cfg {
                 Some(cfg) if !state.streaming.swap(true, Ordering::SeqCst) => {
                     // Resolve the launched catalog entry (session recipe) for the stream.
-                    let app = state
-                        .launch
-                        .lock()
-                        .unwrap()
-                        .map(|l| l.appid)
-                        .and_then(super::apps::by_id);
+                    let app = super::apps::by_id(ls.appid);
                     tracing::info!(app = ?app.as_ref().map(|a| &a.title), "RTSP PLAY — starting video stream");
                     stream::start(
                         cfg,
@@ -243,8 +256,6 @@ fn handle_request(req: &Request, state: &AppState) -> String {
             // Audio runs independently (Opus on UDP 48000, stereo or 5.1/7.1 multistream per
             // the ANNOUNCE); it needs the launch key for the AES-CBC payload encryption the
             // client expects.
-            let launch = *state.launch.lock().unwrap();
-            if let Some(ls) = launch {
             if !state.audio_streaming.swap(true, Ordering::SeqCst) {
                 tracing::info!("RTSP PLAY — starting audio stream");
                 audio::start(
@@ -255,7 +266,6 @@ fn handle_request(req: &Request, state: &AppState) -> String {
                     state.audio_cap.clone(),
                 );
             }
-            }
             response(&req.cseq, &[("Session", "DEADBEEFCAFE;timeout = 90")], None)
         }
         "TEARDOWN" => {

crates/punktfunk-host/src/gamestream/tls.rs

@@ -24,6 +24,12 @@ use std::sync::Arc;
 #[derive(Clone)]
 pub(crate) struct PeerCertFingerprint(pub Option<String>);
 
+/// The TCP source address of an HTTPS request, injected per-connection by [`serve_https`]. Used by
+/// `/launch` to record which paired client owns the session so the unauthenticated RTSP/UDP media
+/// plane can bind to that peer's IP (security-review 2026-06-28 #4).
+#[derive(Clone, Copy)]
+pub(crate) struct PeerAddr(pub SocketAddr);
+
 /// HTTPS server that surfaces the verified client cert to handlers. `axum_server` can't expose the
 /// peer cert, so this runs the rustls handshake itself (tokio-rustls), reads the peer certificate,
 /// and serves the axum `Router` over hyper with the peer's fingerprint attached to every request as
@@ -39,7 +45,7 @@ pub(crate) async fn serve_https(
         .await
         .with_context(|| format!("bind HTTPS {bind}"))?;
     loop {
-        let (tcp, _peer) = match listener.accept().await {
+        let (tcp, peer) = match listener.accept().await {
             Ok(v) => v,
             Err(e) => {
                 tracing::warn!(error = %e, "HTTPS accept failed");
@@ -63,14 +69,16 @@ pub(crate) async fn serve_https(
                 .peer_certificates()
                 .and_then(|c| c.first())
                 .map(|c| hex::encode(punktfunk_core::quic::endpoint::cert_fingerprint(c.as_ref())));
-            let peer = PeerCertFingerprint(fp);
+            let fp = PeerCertFingerprint(fp);
+            let addr = PeerAddr(peer);
             let svc =
                 hyper::service::service_fn(move |req: hyper::Request<hyper::body::Incoming>| {
                     let app = app.clone();
-                    let peer = peer.clone();
+                    let fp = fp.clone();
                     async move {
                         let mut req = req.map(axum::body::Body::new);
-                        req.extensions_mut().insert(peer);
+                        req.extensions_mut().insert(fp);
+                        req.extensions_mut().insert(addr);
                         app.oneshot(req).await // Router error is Infallible
                     }
                 });

crates/punktfunk-host/src/inject.rs

@@ -76,9 +76,7 @@ pub fn open(backend: Backend) -> Result<Box<dyn InputInjector>> {
             #[cfg(target_os = "linux")]
             {
                 Ok(Box::new(libei::LibeiInjector::open_with(
-                    libei::EiSource::SocketPathFile(
-                        crate::vdisplay::gamescope_ei_socket_file().into(),
-                    ),
+                    libei::EiSource::SocketPathFile(crate::vdisplay::gamescope_ei_socket_file()),
                 )?))
             }
             #[cfg(not(target_os = "linux"))]

crates/punktfunk-host/src/inject/linux/libei.rs

@@ -305,6 +305,19 @@ async fn connect_socket_file(file: &std::path::Path) -> Result<UnixStream> {
     let deadline = std::time::Instant::now() + Duration::from_secs(15);
     let mut logged = String::new();
     loop {
+        // Defense-in-depth: never follow a symlinked relay file. It lives under `$XDG_RUNTIME_DIR`
+        // (per-user 0700) so a cross-user plant is already blocked, but refuse a symlink outright
+        // rather than read through one to an attacker-chosen target (a rogue EIS server would
+        // keylog/deny the session's input; security-review 2026-06-28 #6).
+        if std::fs::symlink_metadata(file)
+            .map(|m| m.file_type().is_symlink())
+            .unwrap_or(false)
+        {
+            return Err(anyhow!(
+                "EIS relay file {} is a symlink — refusing to follow it",
+                file.display()
+            ));
+        }
         if let Ok(s) = std::fs::read_to_string(file) {
             let name = s.trim();
             if !name.is_empty() {

crates/punktfunk-host/src/library.rs

@@ -577,10 +577,11 @@ impl LibraryProvider for EpicProvider {
             if p.extension().and_then(|e| e.to_str()) != Some("item") {
                 continue;
             }
-            let Ok(text) = std::fs::read_to_string(&p) else {
+            // `.item` manifests are small JSON; cap the read so a planted giant can't OOM the host.
+            let Some(bytes) = read_capped(&p, 1024 * 1024) else {
                 continue;
             };
-            let Ok(v) = serde_json::from_str::<serde_json::Value>(&text) else {
+            let Ok(v) = serde_json::from_slice::<serde_json::Value>(&bytes) else {
                 continue;
             };
             if let Some(g) = epic_entry(&v, &art) {
@@ -650,6 +651,23 @@ fn epic_entry(
     })
 }
 
+/// Read a launcher cache/manifest with a hard size cap, so a local unprivileged user can't plant a
+/// multi-GB file under the launcher's (Users-writable) data dir that OOMs the privileged host when
+/// it's loaded — then base64/JSON-decoded into further copies — during library enumeration
+/// (security-review 2026-06-28 S4). Returns `None` if missing, empty, or over `max`. Mirrors the
+/// Linux lutris-art reader's 1 MiB cap.
+#[cfg(windows)]
+fn read_capped(path: &Path, max: u64) -> Option<Vec<u8>> {
+    let meta = std::fs::metadata(path).ok()?;
+    if meta.len() == 0 || meta.len() > max {
+        if meta.len() > max {
+            tracing::warn!(path = %path.display(), len = meta.len(), max, "launcher cache exceeds size cap — skipping");
+        }
+        return None;
+    }
+    std::fs::read(path).ok()
+}
+
 /// Best-effort parse of `catcache.bin` (base64-encoded JSON array of catalog items) into
 /// catalogItemId → [`Artwork`] from each item's `keyImages`. Empty map on any read/decode failure
 /// (the format is community-reverse-engineered + can lag a fresh install → titles just show no art).
@@ -657,7 +675,8 @@ fn epic_entry(
 fn epic_art_index(catcache: &Path) -> std::collections::HashMap<String, Artwork> {
     use base64::Engine as _;
     let mut map = std::collections::HashMap::new();
-    let Ok(raw) = std::fs::read(catcache) else {
+    // 32 MiB cap: comfortably fits a real catalog cache, blocks a planted giant (S4).
+    let Some(raw) = read_capped(catcache, 32 * 1024 * 1024) else {
         return map;
     };
     let Ok(decoded) = base64::engine::general_purpose::STANDARD.decode(raw) else {

crates/punktfunk-host/src/mgmt.rs

@@ -1680,6 +1680,7 @@ mod tests {
             height: 1440,
             fps: 120,
             appid: 1,
+            peer_ip: None,
         });
         state.streaming.store(true, Ordering::SeqCst);
 
@@ -1805,6 +1806,7 @@ mod tests {
             height: 1080,
             fps: 60,
             appid: 1,
+            peer_ip: None,
         });
 
         let del = axum::http::Request::delete("/api/v1/session")

crates/punktfunk-host/src/punktfunk1.rs

@@ -497,7 +497,7 @@ async fn serve_session(
     opts: &Punktfunk1Options,
     audio_cap: &AudioCapSlot,
     inj_tx: std::sync::mpsc::Sender<InputEvent>,
-    mic_tx: std::sync::mpsc::Sender<Vec<u8>>,
+    mic_tx: std::sync::mpsc::SyncSender<Vec<u8>>,
     host_fp: &[u8; 32],
     np: &NativePairing,
     last_pairing: &std::sync::Mutex<Option<std::time::Instant>>,
@@ -597,9 +597,11 @@ async fn serve_session(
         // we look it up in OUR library so a client can't inject a command). The bare-spawn gamescope
         // backend picks this up via the `PUNKTFUNK_GAMESCOPE_APP` env fallback in `spawn` (on a shared
         // desktop / attach-to-existing session it's a harmless no-op). This is the process-global env
-        // path — safe under today's ONE-session-at-a-time model; when concurrent native sessions land
-        // (`what's left` §3), resolve the command into the per-session VirtualDisplay via
-        // `set_launch_command` (as the GameStream path now does) so sessions can't stomp each other.
+        // path; the write is serialized via `vdisplay::with_env_lock` so concurrent native-session
+        // handshakes can't race the `set_var` (security-review 2026-06-28 #7). The remaining
+        // cross-session *value* confusion (B's launch id stomping A's pending gamescope spawn) wants
+        // the command resolved into the per-session VirtualDisplay via `set_launch_command` (as the
+        // GameStream path does) — a follow-up; the data-race UB is closed here.
         if let Some(id) = hello.launch.as_deref() {
             // Linux: resolve the id to a gamescope-nested command and stash it in the env the
             // gamescope backend reads. Windows has no gamescope to nest into — the data plane launches
@@ -609,7 +611,9 @@ async fn serve_session(
             match crate::library::launch_command(id) {
                 Some(cmd) => {
                     tracing::info!(launch_id = id, command = %cmd, "launching library title");
-                    std::env::set_var("PUNKTFUNK_GAMESCOPE_APP", &cmd);
+                    crate::vdisplay::with_env_lock(|| {
+                        std::env::set_var("PUNKTFUNK_GAMESCOPE_APP", &cmd)
+                    });
                 }
                 None => tracing::warn!(
                     launch_id = id,
@@ -907,8 +911,9 @@ async fn serve_session(
         while let Ok(d) = input_conn.read_datagram().await {
             if let Some((_seq, _pts, opus)) = punktfunk_core::quic::decode_mic_datagram(&d) {
                 mic_count += 1;
-                // Host-lifetime mic service; a send error just means the host is shutting down.
-                let _ = mic_tx.send(opus.to_vec());
+                // Host-lifetime mic service (bounded queue): `try_send` drops the frame when the
+                // service is full or gone, never blocking this datagram loop (security-review S6).
+                let _ = mic_tx.try_send(opus.to_vec());
             } else if let Some(rich) = punktfunk_core::quic::RichInput::decode(&d) {
                 rich_count += 1;
                 if rich_tx.send(rich).is_err() {
@@ -1185,6 +1190,8 @@ const INJECTOR_REOPEN_BACKOFF: std::time::Duration = std::time::Duration::from_s
 
 /// Mic is 48 kHz stereo — matches the Opus stereo decoder and the host→client audio layout.
 const MIC_CHANNELS: u32 = 2;
+/// Bound for the shared mic frame queue (drop-newest when full). See [`MicService::start`].
+const MIC_QUEUE_CAP: usize = 64;
 
 /// Host-lifetime virtual microphone, shared across punktfunk/1 sessions (mirror of
 /// [`InjectorService`]). One thread owns the PipeWire `Audio/Source` + an Opus decoder; sessions
@@ -1192,12 +1199,16 @@ const MIC_CHANNELS: u32 = 2;
 /// feeds the source. Opened lazily on the first frame, the source node persists across sessions
 /// (no per-session registration churn), and reopens after a backoff if the source/decoder fails.
 struct MicService {
-    tx: std::sync::mpsc::Sender<Vec<u8>>,
+    tx: std::sync::mpsc::SyncSender<Vec<u8>>,
 }
 
 impl MicService {
     fn start() -> MicService {
-        let (tx, rx) = std::sync::mpsc::channel::<Vec<u8>>();
+        // Bounded so the host-lifetime mic queue (shared across all concurrent sessions) can't grow
+        // without limit under a near-line-rate flood; the producer drops the newest frame when full
+        // (audio is lossy by design) rather than buffering unboundedly (security-review 2026-06-28
+        // S6). 64 × 5–10 ms frames ≈ 0.3–0.6 s of slack, far more than the decode loop ever lags.
+        let (tx, rx) = std::sync::mpsc::sync_channel::<Vec<u8>>(MIC_QUEUE_CAP);
         if let Err(e) = std::thread::Builder::new()
             .name("punktfunk1-mic".into())
             .spawn(move || mic_service_thread(rx))
@@ -1209,7 +1220,7 @@ impl MicService {
 
     /// A sender a session forwards the client's Opus mic frames to. Cloned per session; dropping a
     /// clone does NOT stop the service (it holds the original sender for the host life).
-    fn sender(&self) -> std::sync::mpsc::Sender<Vec<u8>> {
+    fn sender(&self) -> std::sync::mpsc::SyncSender<Vec<u8>> {
         self.tx.clone()
     }
 }
@@ -1224,14 +1235,17 @@ fn mic_service_thread(rx: std::sync::mpsc::Receiver<Vec<u8>>) {
 
 /// The host-lifetime mic worker: lazily open the virtual mic + decoder, then Opus-decode each
 /// forwarded frame and push the PCM into the source. Reopen (after [`INJECTOR_REOPEN_BACKOFF`])
-/// on open failure or a decode error. Exits when every session sender and the service's own
-/// sender drop (host shutdown), tearing the virtual mic down. Linux = PipeWire `Audio/Source`;
-/// Windows = a virtual audio device's render endpoint (see `audio::wasapi_mic`).
+/// only on a backend OPEN failure; a per-frame Opus DECODE error is just a dropped frame (it must
+/// not tear down this mic, which is shared across every concurrent session — otherwise one paired
+/// client's junk frames would deny everyone's mic; security-review 2026-06-28 S2). Exits when every
+/// session sender and the service's own sender drop (host shutdown), tearing the virtual mic down.
+/// Linux = PipeWire `Audio/Source`; Windows = a virtual audio device's render endpoint.
 #[cfg(any(target_os = "linux", target_os = "windows"))]
 fn mic_service_thread(rx: std::sync::mpsc::Receiver<Vec<u8>>) {
     let mut mic: Option<Box<dyn crate::audio::VirtualMic>> = None;
     let mut decoder: Option<opus::Decoder> = None;
     let mut last_failed: Option<std::time::Instant> = None;
+    let mut decode_fails: u64 = 0;
     let mut pcm = vec![0f32; 5760 * MIC_CHANNELS as usize]; // up to 120 ms scratch
     for opus_frame in rx {
         if opus_frame.is_empty() {
@@ -1267,12 +1281,16 @@ fn mic_service_thread(rx: std::sync::mpsc::Receiver<Vec<u8>>) {
             Ok(samples_per_ch) => {
                 let total = (samples_per_ch * MIC_CHANNELS as usize).min(pcm.len());
                 m.push(&pcm[..total]);
+                decode_fails = 0;
             }
             Err(e) => {
-                tracing::warn!(error = %e, "mic opus decode failed — reopening");
-                mic = None;
-                decoder = None;
-                last_failed = Some(std::time::Instant::now());
+                // Malformed/garbage frame: drop it and keep the (shared) mic + decoder open. The
+                // next valid frame decodes normally; only a backend OPEN failure reopens. Throttle
+                // the log (1, 2, 4, … fails) so a junk flood can't spam.
+                decode_fails += 1;
+                if decode_fails.is_power_of_two() {
+                    tracing::warn!(error = %e, fails = decode_fails, "mic opus decode failed — dropping frame");
+                }
             }
         }
     }
@@ -1454,8 +1472,14 @@ fn input_thread(
     // left-button-down then turns every later click into a drag: windows move, but clicking buttons
     // and text inputs does nothing). We synthesize the matching up-events when this session ends —
     // see the release loop after the `break`.
-    let mut held_buttons: Vec<u32> = Vec::new();
-    let mut held_keys: Vec<u32> = Vec::new();
+    // Sets (not Vecs) so the presence test is O(1), not O(n) per event, and bounded by `MAX_HELD`
+    // so a client flooding distinct never-released codes can't grow the tracking state or spike the
+    // input thread (security-review 2026-06-28 S3). A real keyboard+mouse holds far fewer at once;
+    // codes past the cap simply aren't tracked for end-of-session release (worst case: one unreleased
+    // key on a pathological disconnect, which the injector's own state still bounds).
+    const MAX_HELD: usize = 256;
+    let mut held_buttons: std::collections::HashSet<u32> = std::collections::HashSet::new();
+    let mut held_keys: std::collections::HashSet<u32> = std::collections::HashSet::new();
     loop {
         match rx.recv_timeout(std::time::Duration::from_millis(4)) {
             Ok(ev) => match ev.kind {
@@ -1473,14 +1497,18 @@ fn input_thread(
                 _ => {
                     // Track press/release so a mid-press disconnect can be undone below.
                     match ev.kind {
-                        InputKind::MouseButtonDown if !held_buttons.contains(&ev.code) => {
-                            held_buttons.push(ev.code)
+                        InputKind::MouseButtonDown if held_buttons.len() < MAX_HELD => {
+                            held_buttons.insert(ev.code);
                         }
-                        InputKind::MouseButtonUp => held_buttons.retain(|&c| c != ev.code),
-                        InputKind::KeyDown if !held_keys.contains(&ev.code) => {
-                            held_keys.push(ev.code)
+                        InputKind::MouseButtonUp => {
+                            held_buttons.remove(&ev.code);
+                        }
+                        InputKind::KeyDown if held_keys.len() < MAX_HELD => {
+                            held_keys.insert(ev.code);
+                        }
+                        InputKind::KeyUp => {
+                            held_keys.remove(&ev.code);
                         }
-                        InputKind::KeyUp => held_keys.retain(|&c| c != ev.code),
                         _ => {}
                     }
                     // Pointer/keyboard → the host-lifetime injector service (one persistent

crates/punktfunk-host/src/vdisplay.rs

@@ -358,13 +358,30 @@ fn find_wayland_socket(runtime: &str, uid: u32) -> Option<String> {
     cands.into_iter().next().map(|(_, n)| n)
 }
 
+/// Serializes ALL process-global env mutation on the per-session setup path. `std::env::set_var`
+/// concurrent with another thread's `set_var` (glibc `environ` realloc) is a data race = UB. With
+/// the default concurrent native sessions each running `resolve_compositor` in its own
+/// `spawn_blocking`, the per-session env retargeting would otherwise race and could crash the host
+/// (security-review 2026-06-28 #7). Every env write on the setup path takes this lock; steady-state
+/// streaming reads cached config, not env. This removes the memory-unsafety; it is NOT a full fix
+/// for cross-session env *value* confusion (that needs per-session `SessionContext` threading, as the
+/// GameStream/Windows path already does via `set_launch_command`).
+pub static ENV_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());
+
+/// Run `f` with [`ENV_LOCK`] held. Use around any `set_var`/`remove_var` on the session-setup path.
+pub fn with_env_lock<R>(f: impl FnOnce() -> R) -> R {
+    let _g = ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
+    f()
+}
+
 /// Write a detected session's [`SessionEnv`] into the process env so every backend (video capture
 /// and input alike) that reads `WAYLAND_DISPLAY` / `XDG_RUNTIME_DIR` / `DBUS_SESSION_BUS_ADDRESS` /
-/// `XDG_CURRENT_DESKTOP` at open time targets the live session. The host serves one session at a
-/// time, so a process-global write is sound; the next connect re-detects and re-applies. Same
-/// `set_var` discipline already used for `PUNKTFUNK_GAMESCOPE_APP` on the launch path.
+/// `XDG_CURRENT_DESKTOP` at open time targets the live session. Serialized via [`ENV_LOCK`] so
+/// concurrent session handshakes can't race the `set_var`s; the next connect re-detects and
+/// re-applies. Same `set_var` discipline used for `PUNKTFUNK_GAMESCOPE_APP` on the launch path.
 #[cfg(target_os = "linux")]
 pub fn apply_session_env(active: &ActiveSession) {
+    let _env_guard = ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
     let e = &active.env;
     std::env::set_var("XDG_RUNTIME_DIR", &e.xdg_runtime_dir);
     std::env::set_var("DBUS_SESSION_BUS_ADDRESS", &e.dbus_session_bus_address);
@@ -455,6 +472,7 @@ pub fn settle_desktop_portal(_chosen: Compositor) {}
 /// `PUNKTFUNK_GAMESCOPE_MANAGED` forces managed over either.
 #[cfg(target_os = "linux")]
 pub fn apply_input_env(chosen: Compositor) {
+    let _env_guard = ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner());
     let backend = match chosen {
         Compositor::Gamescope => "gamescope",
         // KWin: org_kde_kwin_fake_input — direct injection, no RemoteDesktop portal / approval
@@ -587,10 +605,10 @@ pub fn probe(compositor: Compositor) -> Result<()> {
 }
 
 /// Path of the file where the gamescope backend relays the nested session's `LIBEI_SOCKET`
-/// (gamescope's EIS server) for the input injector.
+/// (gamescope's EIS server) for the input injector. Under `$XDG_RUNTIME_DIR` (per-user 0700).
 #[cfg(target_os = "linux")]
-pub fn gamescope_ei_socket_file() -> &'static str {
-    gamescope::EI_SOCKET_FILE
+pub fn gamescope_ei_socket_file() -> std::path::PathBuf {
+    gamescope::ei_socket_file()
 }
 
 /// Call when a client session ends: if the host-managed gamescope path took over a box's autologin

crates/punktfunk-host/src/vdisplay/linux/gamescope.rs

@@ -670,11 +670,11 @@ pub fn start_restore_worker() -> std::sync::Arc<()> {
 }
 
 /// Point the libei injector at the running gamescope's EIS socket (it reads the relay file
-/// [`EI_SOCKET_FILE`]). Best-effort — video still works without it (input just won't reach the
+/// [`ei_socket_file`]). Best-effort — video still works without it (input just won't reach the
 /// session). Shared by the attach and host-managed-session paths.
 fn point_injector_at_eis() {
     match find_gamescope_eis_socket() {
-        Some(sock) => match std::fs::write(EI_SOCKET_FILE, &sock) {
+        Some(sock) => match std::fs::write(ei_socket_file(), &sock) {
             Ok(()) => {
                 tracing::info!(socket = %sock, "gamescope: pointed injector at the session's EIS socket")
             }
@@ -770,18 +770,31 @@ fn stop_session(unit_name: &str) {
     let _ = Command::new("systemctl")
         .args(["--user", "stop", unit_name])
         .status();
-    let _ = std::fs::remove_file(EI_SOCKET_FILE);
+    let _ = std::fs::remove_file(ei_socket_file());
 }
 
-/// File where the wrapper below writes gamescope's `LIBEI_SOCKET` (its EIS server socket),
-/// read by the libei injector to drive input into the nested app. See [`crate::inject`].
-pub const EI_SOCKET_FILE: &str = "/tmp/punktfunk-gamescope-ei";
+/// File where the wrapper below writes gamescope's `LIBEI_SOCKET` (its EIS server socket), read by
+/// the libei injector to drive input into the nested app. See [`crate::inject`].
+///
+/// Placed under `$XDG_RUNTIME_DIR` (a per-user, 0700 directory) — NOT a world-writable `/tmp` —
+/// so a second unprivileged local user can neither read the relayed socket path nor pre-plant the
+/// file to redirect the host's injector to a rogue EIS server (which would let them keylog or deny
+/// the remote session's keyboard/mouse input; security-review 2026-06-28 #6). Falls back to `/tmp`
+/// only if `XDG_RUNTIME_DIR` is unset (gamescope itself requires it, so this is rare); the reader
+/// ([`crate::inject`]) additionally rejects a symlinked relay file as defense-in-depth.
+pub fn ei_socket_file() -> std::path::PathBuf {
+    let runtime = crate::vdisplay::with_env_lock(|| std::env::var_os("XDG_RUNTIME_DIR"));
+    match runtime {
+        Some(rt) if !rt.is_empty() => std::path::PathBuf::from(rt).join("punktfunk-gamescope-ei"),
+        _ => std::path::PathBuf::from("/tmp/punktfunk-gamescope-ei"),
+    }
+}
 
 /// Spawn `gamescope --backend headless -W w -H h -r hz -- <app>`. The app comes from
 /// `PUNKTFUNK_GAMESCOPE_APP` (default a no-op that just keeps gamescope alive — set it to a real
 /// game/GL app for actual content, e.g. `steam -gamepadui` for the SteamOS-like session).
 /// stdout/stderr go to `/tmp/punktfunk-gamescope.log`. The app is launched through a tiny shell
-/// wrapper that relays gamescope's `LIBEI_SOCKET` (set for its children) to [`EI_SOCKET_FILE`]
+/// wrapper that relays gamescope's `LIBEI_SOCKET` (set for its children) to [`ei_socket_file`]
 /// so the input injector can connect to gamescope's EIS server from outside.
 fn spawn(w: u32, h: u32, hz: u32, cmd: Option<&str>) -> Result<Child> {
     // A non-empty per-session command (set via `set_launch_command`) wins; else the
@@ -791,10 +804,13 @@ fn spawn(w: u32, h: u32, hz: u32, cmd: Option<&str>) -> Result<Child> {
     let app = cmd
         .map(str::to_string)
         .filter(|s| !s.trim().is_empty())
-        .or_else(|| std::env::var("PUNKTFUNK_GAMESCOPE_APP").ok())
+        // Read the env fallback under the shared env lock so it can't race a concurrent session's
+        // `set_var` of the same key (security-review 2026-06-28 #7).
+        .or_else(|| crate::vdisplay::with_env_lock(|| std::env::var("PUNKTFUNK_GAMESCOPE_APP").ok()))
         .filter(|s| !s.trim().is_empty())
         .unwrap_or_else(|| "sleep infinity".to_string());
-    let _ = std::fs::remove_file(EI_SOCKET_FILE); // stale socket path from a previous session
+    let relay = ei_socket_file();
+    let _ = std::fs::remove_file(&relay); // stale socket path from a previous session
     let mut cmd = Command::new("gamescope");
     cmd.args(["--backend", "headless"])
         .args(["-W", &w.to_string()])
@@ -804,7 +820,10 @@ fn spawn(w: u32, h: u32, hz: u32, cmd: Option<&str>) -> Result<Child> {
         .args([
             "sh",
             "-c",
-            &format!("printf %s \"$LIBEI_SOCKET\" > {EI_SOCKET_FILE}; exec \"$@\""),
+            &format!(
+                "printf %s \"$LIBEI_SOCKET\" > '{}'; exec \"$@\"",
+                relay.display()
+            ),
             "sh",
         ])
         .args(app.split_whitespace())
@@ -997,7 +1016,7 @@ impl Drop for GamescopeProc {
         let _ = self.0.wait();
         // Clear the relayed EIS socket name so the host-lifetime injector can't reconnect to this
         // now-dead session's socket between sessions (the stale path is the "Connection refused").
-        let _ = std::fs::remove_file(EI_SOCKET_FILE);
+        let _ = std::fs::remove_file(ei_socket_file());
     }
 }