Skip to content

Black hole detection fixes #2400

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Oct 11, 2025
Merged

Black hole detection fixes #2400

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
9cb1035
Fix some comparisons in the black hole detector
zdave-parity Sep 29, 2025
3e4cbb0
Relax MTU discovery state assertion
zdave-parity Sep 29, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
25 changes: 17 additions & 8 deletions quinn-proto/src/connection/mtud.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,14 @@ impl MtuDiscovery {
self.current_mtu = self.current_mtu.min(peer_max_udp_payload_size);

if let Some(state) = self.state.as_mut() {
// MTUD is only active after the connection has been fully established, so it is
// guaranteed we will receive the peer's transport parameters before we start probing
debug_assert!(matches!(state.phase, Phase::Initial));
// It is possible for black hole detection to trigger before the connection has been
// fully established, if the initial MTU is greater the minimum MTU. We should never
// send probes before the connection has been fully established and we have received
// the peer's transport parameters though.
debug_assert!(
!matches!(state.phase, Phase::Searching(_)),
"Transport parameters received after MTU probing started"
);
state.peer_max_udp_payload_size = peer_max_udp_payload_size;
}
}
Expand Down Expand Up @@ -450,9 +455,9 @@ impl BlackHoleDetector {
};
// If a loss burst contains a packet smaller than the minimum MTU or a more recently
// transmitted packet, it is not suspicious.
if burst.smallest_packet_size < self.min_mtu
if burst.smallest_packet_size <= self.min_mtu
|| (burst.latest_non_probe < self.largest_post_loss_packet
&& burst.smallest_packet_size < self.acked_mtu)
&& burst.smallest_packet_size <= self.acked_mtu)
{
return;
}
Expand Down Expand Up @@ -733,10 +738,14 @@ mod tests {

#[cfg(debug_assertions)]
#[test]
#[should_panic]
fn mtu_discovery_with_peer_max_udp_payload_size_after_search_panics() {
#[should_panic(expected = "Transport parameters received after MTU probing started")]
fn mtu_discovery_with_peer_max_udp_payload_size_during_search_panics() {
let mut mtud = default_mtud();
drive_to_completion(&mut mtud, Instant::now(), 1500);
assert!(mtud.poll_transmit(Instant::now(), 0).is_some());
assert!(matches!(
mtud.state.as_ref().unwrap().phase,
Phase::Searching(_)
));
mtud.on_peer_max_udp_payload_size_received(1300);
}

Expand Down