Re: [PATCH net-next v2] ipv6: honor per-interface proxy_ndp in forward and NA paths

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

Le 29/06/2026 à 08:18, Chenguang Zhao a écrit :
> ndisc_recv_ns() has always checked both devconf_all and idev->cnf for
> proxy_ndp, but ip6_forward() and ndisc_recv_na() only looked at the
> global setting. The original commit left XXX comments in these paths
> likely because idev was not available there at the time; ip6_forward()
> now obtains idev from IP6CB(skb)->iif.
> 
> Honor per-interface proxy_ndp in both places to match the NS path and
> allow setups that only enable proxy_ndp on specific interfaces.
> 
> In ip6_forward(), idev is looked up via the ingress interface (iif) while
> pneigh_lookup() uses skb->dev. For ND packets this is correct because
> vrf_ip6_rcv() does not modify skb->dev for neighbour discovery frames,
> so both refer to the ingress interface.
> 
> Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
> ---
> v2:
>  Per Ido's review, the following changes were made in v2:
>  - Target net-next instead of net
>  - Drop Fixes tag
>  - Expand commit message: XXX comment history, idev vs skb->dev for ND packets
>  - Fix subject prefix
> 
> v1:
>  - https://lore.kernel.org/all/20260623085600.396401-1-zhaochenguang@kylinos.cn/
> 
>  net/ipv6/ip6_output.c | 4 ++--
>  net/ipv6/ndisc.c      | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 368e4fa3b43c..c4ca4a813479 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -579,8 +579,8 @@ int ip6_forward(struct sk_buff *skb)
>  		return -ETIMEDOUT;
>  	}
>  
> -	/* XXX: idev->cnf.proxy_ndp? */
> -	if (READ_ONCE(net->ipv6.devconf_all->proxy_ndp) &&
> +	if ((READ_ONCE(net->ipv6.devconf_all->proxy_ndp) ||
> +	     (idev && READ_ONCE(idev->cnf.proxy_ndp))) &&
As stated by Ido, this changes a 20 years old user-visible behavior. It suddenly
may enable proxy NDP on a system.
I was thinking that this kind of change was prohibited.

Regards,
Nicolas