[PATCH net] net l2tp: drop flow hash on forward

[PATCH net] net l2tp: drop flow hash on forward

[David Bauer]

Drop the flow-hash of the skb when forwarding to the L2TP netdev.

This avoids the L2TP qdisc from using the flow-hash from the outer
packet, which is identical for every flow within the tunnel.

This does not affect every platform but is specific for the ethernet
driver. It depends on the platform including L4 information in the
flow-hash.

One such example is the Mediatek Filogic MT798x family of networking
processors.

Fixes: d9e31d17ceba ("l2tp: Add L2TP ethernet pseudowire support")
Acked-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David Bauer <mail@david-bauer.net>
---
 net/l2tp/l2tp_eth.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 39e487ccc468..8ba00ad433c2 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -127,6 +127,9 @@ static void l2tp_eth_dev_recv(struct l2tp_session *session, struct sk_buff *skb,
 	/* checksums verified by L2TP */
 	skb->ip_summed = CHECKSUM_NONE;
 
+	/* drop outer flow-hash */
+	skb_clear_hash(skb);
+
 	skb_dst_drop(skb);
 	nf_reset_ct(skb);
 
-- 
2.43.0

Re: [PATCH net] net l2tp: drop flow hash on forward

[Simon Horman]

+ Randy Dunlap

On Wed, Apr 24, 2024 at 07:11:10PM +0200, David Bauer wrote:
> Drop the flow-hash of the skb when forwarding to the L2TP netdev.
> 
> This avoids the L2TP qdisc from using the flow-hash from the outer
> packet, which is identical for every flow within the tunnel.
> 
> This does not affect every platform but is specific for the ethernet
> driver. It depends on the platform including L4 information in the
> flow-hash.
> 
> One such example is the Mediatek Filogic MT798x family of networking
> processors.
> 
> Fixes: d9e31d17ceba ("l2tp: Add L2TP ethernet pseudowire support")
> Acked-by: James Chapman <jchapman@katalix.com>
> Signed-off-by: David Bauer <mail@david-bauer.net>

Reviewed-by: Simon Horman <horms@kernel.org>

> ---
>  net/l2tp/l2tp_eth.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
> index 39e487ccc468..8ba00ad433c2 100644
> --- a/net/l2tp/l2tp_eth.c
> +++ b/net/l2tp/l2tp_eth.c
> @@ -127,6 +127,9 @@ static void l2tp_eth_dev_recv(struct l2tp_session *session, struct sk_buff *skb,
>  	/* checksums verified by L2TP */
>  	skb->ip_summed = CHECKSUM_NONE;
>  
> +	/* drop outer flow-hash */
> +	skb_clear_hash(skb);
> +
>  	skb_dst_drop(skb);
>  	nf_reset_ct(skb);
>  
> -- 
> 2.43.0
> 
> 

Re: [PATCH net] net l2tp: drop flow hash on forward

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 24 Apr 2024 19:11:10 +0200 you wrote:
> Drop the flow-hash of the skb when forwarding to the L2TP netdev.
> 
> This avoids the L2TP qdisc from using the flow-hash from the outer
> packet, which is identical for every flow within the tunnel.
> 
> This does not affect every platform but is specific for the ethernet
> driver. It depends on the platform including L4 information in the
> flow-hash.
> 
> [...]

Here is the summary with links:
  - [net] net l2tp: drop flow hash on forward
    https://git.kernel.org/netdev/net/c/42f853b42899

You are awesome, thank you!
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