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

[Simon Horman <horms@kernel.org>]

On Wed, Aug 14, 2024 at 02:31:06PM +0200, 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>
> ---
>  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..13eaacc5a747 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) ||
> +	     READ_ONCE(idev->cnf.proxy_ndp)) &&

Hi Nils,

Earlier in this function it is assumed that idev may be NULL,
I think you need to take that into account here too.

Flagged by Smatch.

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https://docs.kernel.org/process/maintainer-netdev.html

>  	    pneigh_lookup(&nd_tbl, net, &hdr->daddr, skb->dev, 0)) {
>  		int proxied = ip6_forward_proxy_check(skb);
>  		if (proxied > 0) {
> -- 
> 2.39.2
> 
>