Re: [PATCH net 2/2] ipv6: Fix nlmsg_flags when splitting a multipath route

[Michal Kubecek <mkubecek@suse.cz>]

On Wed, Feb 12, 2020 at 10:41:07AM +0900, Benjamin Poirier wrote:
> When splitting an RTA_MULTIPATH request into multiple routes and adding the
> second and later components, we must not simply remove NLM_F_REPLACE but
> instead replace it by NLM_F_CREATE. Otherwise, it may look like the netlink
> message was malformed.
> 
> For example,
> 	ip route add 2001:db8::1/128 dev dummy0
> 	ip route change 2001:db8::1/128 nexthop via fe80::30:1 dev dummy0 \
> 		nexthop via fe80::30:2 dev dummy0
> results in the following warnings:
> [ 1035.057019] IPv6: RTM_NEWROUTE with no NLM_F_CREATE or NLM_F_REPLACE
> [ 1035.057517] IPv6: NLM_F_CREATE should be set when creating new route
> 
> This patch makes the nlmsg sequence look equivalent for __ip6_ins_rt() to
> what it would get if the multipath route had been added in multiple netlink
> operations:
> 	ip route add 2001:db8::1/128 dev dummy0
> 	ip route change 2001:db8::1/128 nexthop via fe80::30:1 dev dummy0
> 	ip route append 2001:db8::1/128 nexthop via fe80::30:2 dev dummy0
> 
> Fixes: 27596472473a ("ipv6: fix ECMP route replacement")
> Signed-off-by: Benjamin Poirier <bpoirier@cumulusnetworks.com>

Reviewed-by: Michal Kubecek <mkubecek@suse.cz>

> ---
>  net/ipv6/route.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4fbdc60b4e07..2931224b674e 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -5198,6 +5198,7 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
>  		 */
>  		cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
>  						     NLM_F_REPLACE);
> +		cfg->fc_nlinfo.nlh->nlmsg_flags |= NLM_F_CREATE;
>  		nhn++;
>  	}
>  
> -- 
> 2.25.0
>