netdev - Re: [PATCH v2 net] net/ipv6: Do not allow device only routes via the multipath API

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Message-ID: <5d9122fa-8f9a-b11a-3496-06976c96a08b@gmail.com>
Date:   Mon, 16 Jul 2018 09:09:44 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     dsahern@...nel.org, netdev@...r.kernel.org
Cc:     David Ahern <dsahern@...il.com>
Subject: Re: [PATCH v2 net] net/ipv6: Do not allow device only routes via the
 multipath API



On 07/15/2018 09:35 AM, dsahern@...nel.org wrote:
> From: David Ahern <dsahern@...il.com>
> 
> Eric reported that reverting the patch that fixed and simplified IPv6
> multipath routes means reverting back to invalid userspace notifications.
> eg.,
> $ ip -6 route add 2001:db8:1::/64 nexthop dev eth0 nexthop dev eth1
> 
> only generates a single notification:
> 2001:db8:1::/64 dev eth0 metric 1024 pref medium
> 
> While working on a fix for this problem I found another case that is just
> broken completely - a multipath route with a gateway followed by device
> followed by gateway:
>     $ ip -6 ro add 2001:db8:103::/64
>           nexthop via 2001:db8:1::64
>           nexthop dev dummy2
>           nexthop via 2001:db8:3::64
> 
> In this case the device only route is dropped completely - no notification
> to userpsace but no addition to the FIB either:
> 
> $ ip -6 ro ls
> 2001:db8:1::/64 dev dummy1 proto kernel metric 256 pref medium
> 2001:db8:2::/64 dev dummy2 proto kernel metric 256 pref medium
> 2001:db8:3::/64 dev dummy3 proto kernel metric 256 pref medium
> 2001:db8:103::/64 metric 1024
> 	nexthop via 2001:db8:1::64 dev dummy1 weight 1
> 	nexthop via 2001:db8:3::64 dev dummy3 weight 1 pref medium
> fe80::/64 dev dummy1 proto kernel metric 256 pref medium
> fe80::/64 dev dummy2 proto kernel metric 256 pref medium
> fe80::/64 dev dummy3 proto kernel metric 256 pref medium
> 
> Really, IPv6 multipath is just FUBAR'ed beyond repair when it comes to
> device only routes, so do not allow it all.
> 
> This change will break any scripts relying on the mpath api for insert,
> but I don't see any other way to handle the permutations. Besides, since
> the routes are added to the FIB as standalone (non-multipath) routes the
> kernel is not doing what the user requested, so it might as well tell the
> user that.

Yes, I guess we have no real choice for the moment.

Thanks David

Reviewed-by: Eric Dumazet <edumazet@...gle.com>