From b994fb927303276b600286415cc503d6272b1471 Mon Sep 17 00:00:00 2001
From: Nils Andreas Svee <me@lochnair.net>
Date: Fri, 8 May 2026 10:06:00 +0700
Subject: [PATCH] fix(client): reject runtime-invalid negotiated dscp

---
 .../irtt-client/src/client/tests/negotiation.rs  | 16 ++++++++++++++++
 crates/irtt-client/src/session.rs                | 13 ++++++++++++-
 crates/irtt-proto/src/params.rs                  |  2 +-
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/crates/irtt-client/src/client/tests/negotiation.rs b/crates/irtt-client/src/client/tests/negotiation.rs
index 3870bc7..337e76f 100644
--- a/crates/irtt-client/src/client/tests/negotiation.rs
+++ b/crates/irtt-client/src/client/tests/negotiation.rs
@@ -52,3 +52,19 @@ fn strict_negotiation_rejects_negative_returned_length() {
         Err(ClientError::NegotiationRejected { reason }) if reason == "length must be non-negative"
     ));
 }
+
+#[test]
+fn loose_negotiation_rejects_runtime_invalid_returned_dscp() {
+    let config = ClientConfig::default();
+    let requested = params_from_config(&config).unwrap();
+
+    for dscp in [-1, 64] {
+        let mut returned = requested.clone();
+        returned.dscp = dscp;
+        assert!(matches!(
+            validate_negotiated_params(&requested, &returned, NegotiationPolicy::Loose),
+            Err(ClientError::NegotiationRejected { reason })
+                if reason == "dscp must be in range 0..=63"
+        ));
+    }
+}
diff --git a/crates/irtt-client/src/session.rs b/crates/irtt-client/src/session.rs
index 88d91ec..b52b4ad 100644
--- a/crates/irtt-client/src/session.rs
+++ b/crates/irtt-client/src/session.rs
@@ -3,7 +3,7 @@ use std::time::Instant;
 use irtt_proto::{Params, PROTOCOL_VERSION};
 
 use crate::{
-    config::NegotiationPolicy,
+    config::{NegotiationPolicy, MAX_DSCP_CODEPOINT},
     error::ClientError,
     probe::{CompletedSet, PendingMap, TimedOutMap},
 };
@@ -63,6 +63,7 @@ pub(crate) fn validate_negotiated_params(
             reason: "interval must be positive".to_owned(),
         });
     }
+    validate_dscp_restriction(returned.dscp)?;
 
     if policy == NegotiationPolicy::Strict && returned != requested {
         return Err(ClientError::NegotiationRejected {
@@ -94,6 +95,16 @@ fn validate_duration_restriction(requested: i64, returned: i64) -> Result<(), Cl
     Ok(())
 }
 
+fn validate_dscp_restriction(returned: i64) -> Result<(), ClientError> {
+    if !(0..=i64::from(MAX_DSCP_CODEPOINT)).contains(&returned) {
+        return Err(ClientError::NegotiationRejected {
+            reason: format!("dscp must be in range 0..={MAX_DSCP_CODEPOINT}"),
+        });
+    }
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/crates/irtt-proto/src/params.rs b/crates/irtt-proto/src/params.rs
index 06d1f8a..2b58805 100644
--- a/crates/irtt-proto/src/params.rs
+++ b/crates/irtt-proto/src/params.rs
@@ -272,7 +272,7 @@ mod tests {
 
     #[test]
     fn params_round_trip_dscp_codepoints_without_shifting() {
-        for dscp in [0, 46, 63] {
+        for dscp in [0, 46, 63, 64, 184, -1] {
             let params = Params {
                 protocol_version: 1,
                 dscp,