From: Dudu Lu <phx0fer@gmail.com>
Date: Mon, 13 Apr 2026 11:00:41 +0000 (+0800)
Subject: net/sched: sch_cake: fix NAT destination port not being updated in cake_update_flowkeys
X-Git-Tag: v7.1-rc1~36^2~72
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f9e40664706927d7ae22a448a3383e23c38a4c0b;p=thirdparty%2Fkernel%2Flinux.git

net/sched: sch_cake: fix NAT destination port not being updated in cake_update_flowkeys

cake_update_flowkeys() is supposed to update the flow dissector keys
with the NAT-translated addresses and ports from conntrack, so that
CAKE's per-flow fairness correctly identifies post-NAT flows as
belonging to the same connection.

For the source port, this works correctly:
    keys->ports.src = port;

But for the destination port, the assignment is reversed:
    port = keys->ports.dst;

This means the NAT destination port is never updated in the flow keys.
As a result, when multiple connections are NATed to the same destination,
CAKE treats them as separate flows because the original (pre-NAT)
destination ports differ. This breaks CAKE's NAT-aware flow isolation
when using the "nat" mode.

The bug was introduced in commit b0c19ed6088a ("sch_cake: Take advantage
of skb->hash where appropriate") which refactored the original direct
assignment into a compare-and-conditionally-update pattern, but wrote
the destination port update backwards.

Fix by reversing the assignment direction to match the source port
pattern.

Fixes: b0c19ed6088a ("sch_cake: Take advantage of skb->hash where appropriate")
Signed-off-by: Dudu Lu <phx0fer@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260413110041.44704-1-phx0fer@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index ffea9fbd522d..02e1fa4577ae 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -619,7 +619,7 @@ static bool cake_update_flowkeys(struct flow_keys *keys,
 		}
 		port = rev ? tuple.src.u.all : tuple.dst.u.all;
 		if (port != keys->ports.dst) {
-			port = keys->ports.dst;
+			keys->ports.dst = port;
 			upd = true;
 		}
 	}