Re: [PATCH 6/7] pasta: Disable neighbour solicitations on device up to prevent DAD

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 15, 2024 at 12:54:28AM +0200, Stefano Brivio wrote:
> As soon as we the kernel notifier for IPv6 address configuration
> (addrconf_notify()) sees that we bring the target interface up
> (NETDEV_UP), it will schedule duplicate address detection, so, by
> itself, setting the nodad flag later is useless, because that won't
> stop a detection that's already in progress.

Ah, I did wonder about that on the earlier patch.

> However, if we disable neighbour solicitations with IFF_NOARP (which
> is a misnomer for IPv6 interfaces, but there's no possibility of
> mixing things up), the notifier will not trigger DAD, because it can't
> be done, of course, without neighbour solicitations.
> 
> Set IFF_NOARP as we bring up the device, and drop it after we had a
> chance to set the nodad attribute on the link.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  pasta.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/pasta.c b/pasta.c
> index cebf54f..babbfd5 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -303,10 +303,15 @@ void pasta_ns_conf(struct ctx *c)
>  		    strerror(-rc));
>  
>  	if (c->pasta_conf_ns) {
> +		unsigned int flags = IFF_UP;
> +
>  		if (c->mtu != -1)
>  			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
>  
> -		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, IFF_UP, IFF_UP);
> +		if (c->ifi6) /* Avoid duplicate address detection on link up */
> +			flags |= IFF_NOARP;
> +
> +		nl_link_set_flags(nl_sock_ns, c->pasta_ifi, flags, flags);
>  
>  		if (c->ifi4) {
>  			if (c->ip4.no_copy_addrs) {
> @@ -353,6 +358,10 @@ void pasta_ns_conf(struct ctx *c)
>  				    strerror(-rc));
>  			}
>  
> +			/* We dodged DAD: re-enable neighbour solicitations */
> +			nl_link_set_flags(nl_sock_ns, c->pasta_ifi,
> +					  0, IFF_NOARP);
> +
>  			if (c->ip6.no_copy_addrs) {
>  				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
>  						 AF_INET6, &c->ip6.addr, 64);

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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