From fec14b2c7cdbe12b9cb34019eb97e9fb1c368f0e Mon Sep 17 00:00:00 2001
From: Nils Andreas Svee <me@lochnair.net>
Date: Wed, 13 May 2026 00:37:37 +0700
Subject: [PATCH] feat(session): restrict DSCP negotiation to allow only
 disabling (reset to 0)

---
 crates/irtt-client/src/session.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/crates/irtt-client/src/session.rs b/crates/irtt-client/src/session.rs
index 9adbfaf..11647a8 100644
--- a/crates/irtt-client/src/session.rs
+++ b/crates/irtt-client/src/session.rs
@@ -273,7 +273,12 @@ pub(crate) fn negotiate_params(
             },
         )?;
     }
-    if returned.dscp != requested.dscp {
+    if returned.dscp != requested.dscp && returned.dscp != 0 {
+        return Err(ClientError::NegotiationRejected {
+            reason: "server returned unsupported DSCP change".to_owned(),
+        });
+    }
+    if returned.dscp == 0 && requested.dscp != 0 {
         record_restriction(
             policy,
             &mut restrictions,