Re: [PATCH net v2] net: handle ARPHRD_PPP in dev_is_mac_header_xmit()

[Guillaume Nault <gnault@redhat.com>]

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@vger.kernel.org
> Fixes: 27b29f63058d ("bpf: add bpf_redirect() helper")
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> Tested-by: Siwar Zitouni <siwar.zitouni@6wind.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
> 
>