netdev - Re: [PATCH net v2] net: handle ARPHRD_PPP in dev_is_mac_header

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Date: Thu, 3 Aug 2023 10:46:01 +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 v2] net: handle ARPHRD_PPP in dev_is_mac_header_xmit()

On Wed, Aug 02, 2023 at 02:21:06PM +0200, Nicolas Dichtel wrote:
> This kind of interface doesn't have a mac header.

Well, PPP does have a link layer header.
Do you instead mean that PPP automatically adds it?

> This patch fixes bpf_redirect() to a ppp interface.

Can you give more details? Which kind of packets are you trying to
redirect to PPP interfaces?

To me this looks like a hack to work around the fact that
ppp_start_xmit() automatically adds a PPP header. Maybe that's the
best we can do given the current state of ppp_generic.c, but the
commit message should be clear about what the real problem is and
why the patch takes this approach to fix or work around it.

> 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>
> ---
> 
> v1 -> v2:
>  - I forgot the 'Tested-by' tag in the v1 :/
> 
>  include/linux/if_arp.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/if_arp.h b/include/linux/if_arp.h
> index 1ed52441972f..8efbe29a6f0c 100644
> --- a/include/linux/if_arp.h
> +++ b/include/linux/if_arp.h
> @@ -53,6 +53,7 @@ static inline bool dev_is_mac_header_xmit(const struct net_device *dev)
>  	case ARPHRD_NONE:
>  	case ARPHRD_RAWIP:
>  	case ARPHRD_PIMREG:
> +	case ARPHRD_PPP:
>  		return false;
>  	default:
>  		return true;
> -- 
> 2.39.2
> 
>