Subject: Re: [PATCH net-next] pppoe: optional deactivation of PADT packet handling

From: Dan Williams <[email-masked]>
Date: Tue, 15 Dec 2015 10:50:05 -0600

On Tue, 2015-12-15 at 17:06 +0100, Guillaume Nault wrote:
> Kernel space shouldn't handle PADT packets since PADT belongs to
> PPPoE's control plane.
> With "handle_padt" module option, user space can now decide to avoid
> kernel interpretation of PADT packets and be responsible for session
> disconnection.

In general, module options like this kinda suck.  How about a new PPPoE
ioctl so the option can be toggled for a given socket/session instead? 
 Then at least you're not locked into a specific PPPoE implementation
for all sessions on the machine.

Dan

> Signed-off-by: Guillaume Nault <[email-masked]>
> ---
> The two open-source PPPoE programs I know of are accel-ppp and pppd
> (with the rp-pppoe plugin). Accel-ppp already handles PADT, while
> pppd + rp-pppoe doesn't (seems like it doesn't even listen to its
> PPPoE Discovery socket once session is established).
> 
> 
>  drivers/net/ppp/pppoe.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
> index b8da2ea..1846c3a 100644
> --- a/drivers/net/ppp/pppoe.c
> +++ b/drivers/net/ppp/pppoe.c
> @@ -109,6 +109,18 @@ struct pppoe_net {
>  	rwlock_t hash_lock;
>  };
>  
> +/* PADT packets belong to PPPoE's discovery stage (i.e. control
> plane)
> + * and should be handled by user space. Unfortunately, some programs
> + * don't listen out for PADT packets and rely on pppoe module for
> + * closing session after reception of PADT.
> + *
> + * This option can be deactivated when PPPoE discovery is handled by
> + * a PADT aware program.
> + */
> +static bool handle_padt __read_mostly = true;
> +module_param(handle_padt, bool, 0444);
> +MODULE_PARM_DESC(handle_padt, "Let kernel interpret incoming PADT");
> +
>  /*
>   * PPPoE could be in the following stages:
>   * 1) Discovery stage (to obtain remote MAC and Session ID)
> @@ -1173,7 +1185,8 @@ static int __init pppoe_init(void)
>  		goto out_unregister_pppoe_proto;
>  
>  	dev_add_pack(&pppoes_ptype);
> -	dev_add_pack(&pppoed_ptype);
> +	if (handle_padt)
> +		dev_add_pack(&pppoed_ptype);
>  	register_netdevice_notifier(&pppoe_notifier);
>  
>  	return 0;
> @@ -1189,7 +1202,8 @@ out:
>  static void __exit pppoe_exit(void)
>  {
>  	unregister_netdevice_notifier(&pppoe_notifier);
> -	dev_remove_pack(&pppoed_ptype);
> +	if (handle_padt)
> +		dev_remove_pack(&pppoed_ptype);
>  	dev_remove_pack(&pppoes_ptype);
>  	unregister_pppox_proto(PX_PROTO_OE);
>  	proto_unregister(&pppoe_sk_proto);