Subject: Re: [PATCH v2] net/sched: sch_cake: fix NAT destination port not being updated in cake_update_flowkeys

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Mon, 13 Apr 2026 16:40:31 +0200

Dudu Lu <[email-masked]> writes:

> 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 <[email-masked]>

Thank you for the fix!

Acked-by: Toke Høiland-Jørgensen <[email-masked]>