netdev - Re: [PATCH net v3] net: handle ARPHRD_PPP in dev_is_mac_header

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Message-ID: <ZOYc/Uhb0RSUvi47@debian>
Date: Wed, 23 Aug 2023 16:51:41 +0200
From: Guillaume Nault <gnault@...hat.com>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
	bpf@...r.kernel.org, stable@...r.kernel.org,
	Siwar Zitouni <siwar.zitouni@...nd.com>
Subject: Re: [PATCH net v3] net: handle ARPHRD_PPP in dev_is_mac_header_xmit()

On Wed, Aug 23, 2023 at 03:41:02PM +0200, Nicolas Dichtel wrote:
> The goal is to support a bpf_redirect() from an ethernet device (ingress)
> to a ppp device (egress).
> The l2 header is added automatically by the ppp driver, thus the ethernet
> header should be removed.

Reviewed-by: Guillaume Nault <gnault@...hat.com>

> CC: stable@...r.kernel.org
> Fixes: 27b29f63058d ("bpf: add bpf_redirect() helper")
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> Tested-by: Siwar Zitouni <siwar.zitouni@...nd.com>
> ---
> 
> v2 -> v3:
>  - add a comment in the code
>  - rework the commit log
> 
> v1 -> v2:
>  - I forgot the 'Tested-by' tag in the v1 :/
> 
>  include/linux/if_arp.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/if_arp.h b/include/linux/if_arp.h
> index 1ed52441972f..10a1e81434cb 100644
> --- a/include/linux/if_arp.h
> +++ b/include/linux/if_arp.h
> @@ -53,6 +53,10 @@ static inline bool dev_is_mac_header_xmit(const struct net_device *dev)
>  	case ARPHRD_NONE:
>  	case ARPHRD_RAWIP:
>  	case ARPHRD_PIMREG:
> +	/* PPP adds its l2 header automatically in ppp_start_xmit().
> +	 * This makes it look like an l3 device to __bpf_redirect() and tcf_mirred_init().
> +	 */
> +	case ARPHRD_PPP:
>  		return false;
>  	default:
>  		return true;
> -- 
> 2.39.2
>