Re: [PATCH v2] net: ip6: ndisc: fix incorrect forwarding of proxied ns packets

[Paolo Abeni <pabeni@redhat.com>]

On 8/15/24 17:18, Nils Fuhler wrote:
> When enabling proxy_ndp per interface instead of globally, neighbor
> solicitation packets sent to proxied global unicast addresses are
> forwarded instead of generating a neighbor advertisement. When
> proxy_ndp is enabled globally, these packets generate na responses as
> expected.
> 
> This patch fixes this behaviour. When an ns packet is sent to a
> proxied unicast address, it generates an na response regardless
> whether proxy_ndp is enabled per interface or globally.
> 
> Signed-off-by: Nils Fuhler <nils@nilsfuhler.de>

I have mixed feeling WRT this patch. It looks like a fix, but it's 
changing an established behaviour that is there since a lot of time.

I think it could go via the net-next tree, without fixes
tag to avoid stable backports. As such I guess it deserves a self-test 
script validating the new behavior.

> ---
> v1 -> v2: ensure that idev is not NULL
> 
>   net/ipv6/ip6_output.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index ab504d31f0cd..0356c8189e21 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -551,8 +551,8 @@ 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))) &&
>   	    pneigh_lookup(&nd_tbl, net, &hdr->daddr, skb->dev, 0)) {
>   		int proxied = ip6_forward_proxy_check(skb);
>   		if (proxied > 0) {

Note that there is similar chunk in ndisc_recv_na() that also ignores 
idev->cnf.proxy_ndp, why don't you need to such function, too?

Thanks,

Paolo