On Mon, Mar 13, 2017 at 01:28:09PM +0100, Sabrina Dubroca wrote:
> Commit 27596472473a ("ipv6: fix ECMP route replacement") introduced a
> loop that removes all siblings of an ECMP route that is being
> replaced. However, this loop doesn't stop when it has replaced
> siblings, and keeps removing other routes with a higher metric.
> We also end up triggering the WARN_ON after the loop, because after
> this nsiblings < 0.
>
> Instead, stop the loop when we have taken care of all routes with the
> same metric as the route being replaced.
>
> Reproducer:
> ===========
> #!/bin/sh
>
> ip netns add ns1
> ip netns add ns2
> ip -net ns1 link set lo up
>
> for x in 0 1 2 ; do
> ip link add veth$x netns ns2 type veth peer name eth$x netns ns1
> ip -net ns1 link set eth$x up
> ip -net ns2 link set veth$x up
> done
>
> ip -net ns1 -6 r a 2000::/64 nexthop via fe80::0 dev eth0 \
> nexthop via fe80::1 dev eth1 nexthop via fe80::2 dev eth2
> ip -net ns1 -6 r a 2000::/64 via fe80::42 dev eth0 metric 256
> ip -net ns1 -6 r a 2000::/64 via fe80::43 dev eth0 metric 2048
>
> echo "before replace, 3 routes"
> ip -net ns1 -6 r | grep -v '^fe80\|^ff00'
> echo
>
> ip -net ns1 -6 r c 2000::/64 nexthop via fe80::4 dev eth0 \
> nexthop via fe80::5 dev eth1 nexthop via fe80::6 dev eth2
>
> echo "after replace, only 2 routes, metric 2048 is gone"
> ip -net ns1 -6 r | grep -v '^fe80\|^ff00'
>
> Fixes: 27596472473a ("ipv6: fix ECMP route replacement")
> Signed-off-by: Sabrina Dubroca <[email protected]>
> ---
> net/ipv6/ip6_fib.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index e4266746e4a2..d4bf2c68a545 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -923,6 +923,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct
> rt6_info *rt,
> ins = &rt->dst.rt6_next;
> iter = *ins;
> while (iter) {
> + if (iter->rt6i_metric > rt->rt6i_metric)
> + break;
> if (rt6_qualify_for_ecmp(iter)) {
> *ins = iter->dst.rt6_next;
> fib6_purge_rt(iter, fn, info->nl_net);
> --
> 2.12.0
>
Good catch, thank you. The metric comparison could be merged into the
cycle condition but this way it doesn't seem any worse.
Reviewed-by: Michal Kubecek <[email protected]>
