netdev - Re: [PATCH net-next 4/7] ipv4: nexthop: Correctly update nexthop group when removing a nexthop

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Date:   Wed, 26 Aug 2020 13:12:28 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 4/7] ipv4: nexthop: Correctly update nexthop
 group when removing a nexthop

On 8/26/20 10:48 AM, Ido Schimmel wrote:
> From: Ido Schimmel <idosch@...dia.com>
> 
> Each nexthop group contains an indication if it has IPv4 nexthops
> ('has_v4'). Its purpose is to prevent IPv6 routes from using groups with
> IPv4 nexthops.
> 
> However, the indication is not updated when a nexthop is removed. This
> results in the kernel wrongly rejecting IPv6 routes from pointing to
> groups that only contain IPv6 nexthops. Example:
> 
> # ip nexthop replace id 1 via 192.0.2.2 dev dummy10
> # ip nexthop replace id 2 via 2001:db8:1::2 dev dummy10
> # ip nexthop replace id 10 group 1/2
> # ip nexthop del id 1
> # ip route replace 2001:db8:10::/64 nhid 10
> Error: IPv6 routes can not use an IPv4 nexthop.
> 
> Solve this by updating the indication according to the new set of
> member nexthops.
> 
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> ---
>  net/ipv4/nexthop.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index 1b736e3e1baa..5199a2815df6 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -797,7 +797,7 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
>  		return;
>  	}
>  
> -	newg->has_v4 = nhg->has_v4;
> +	newg->has_v4 = false;
>  	newg->mpath = nhg->mpath;
>  	newg->fdb_nh = nhg->fdb_nh;
>  	newg->num_nh = nhg->num_nh;
> @@ -806,12 +806,18 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
>  	nhges = nhg->nh_entries;
>  	new_nhges = newg->nh_entries;
>  	for (i = 0, j = 0; i < nhg->num_nh; ++i) {
> +		struct nh_info *nhi;
> +
>  		/* current nexthop getting removed */
>  		if (nhg->nh_entries[i].nh == nh) {
>  			newg->num_nh--;
>  			continue;
>  		}
>  
> +		nhi = rtnl_dereference(nhges[i].nh->nh_info);
> +		if (nhi->family == AF_INET)
> +			newg->has_v4 = true;
> +
>  		list_del(&nhges[i].nh_list);
>  		new_nhges[j].nh_parent = nhges[i].nh_parent;
>  		new_nhges[j].nh = nhges[i].nh;
> 

Reviewed-by: David Ahern <dsahern@...il.com>