On 2/28/21 7:26 AM, Ido Schimmel wrote:
> From: Ido Schimmel <ido...@nvidia.com>
>
> As far as user space is concerned, blackhole nexthops do not have a
> nexthop device and therefore should not be affected by the
> administrative or carrier state of any netdev.
>
> However, when the loopback netdev goes down all the blackhole nexthops
> are flushed. This happens because internally the kernel associates
> blackhole nexthops with the loopback netdev.
That was not intended, so definitely a bug.
>
> This behavior is both confusing to those not familiar with kernel
> internals and also diverges from the legacy API where blackhole IPv4
> routes are not flushed when the loopback netdev goes down:
>
> # ip route add blackhole 198.51.100.0/24
> # ip link set dev lo down
> # ip route show 198.51.100.0/24
> blackhole 198.51.100.0/24
>
> Blackhole IPv6 routes are flushed, but at least user space knows that
> they are associated with the loopback netdev:
>
> # ip -6 route show 2001:db8:1::/64
> blackhole 2001:db8:1::/64 dev lo metric 1024 pref medium
>
> Fix this by only flushing blackhole nexthops when the loopback netdev is
> unregistered.
>
> Fixes: ab84be7e54fc ("net: Initial nexthop code")
> Signed-off-by: Ido Schimmel <ido...@nvidia.com>
> Reported-by: Donald Sharp <sha...@nvidia.com>
> ---
> net/ipv4/nexthop.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index f1c6cbdb9e43..743777bce179 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -1399,7 +1399,7 @@ static int insert_nexthop(struct net *net, struct
> nexthop *new_nh,
>
> /* rtnl */
> /* remove all nexthops tied to a device being deleted */
> -static void nexthop_flush_dev(struct net_device *dev)
> +static void nexthop_flush_dev(struct net_device *dev, unsigned long event)
> {
> unsigned int hash = nh_dev_hashfn(dev->ifindex);
> struct net *net = dev_net(dev);
> @@ -1411,6 +1411,10 @@ static void nexthop_flush_dev(struct net_device *dev)
> if (nhi->fib_nhc.nhc_dev != dev)
> continue;
>
> + if (nhi->reject_nh &&
> + (event == NETDEV_DOWN || event == NETDEV_CHANGE))
> + continue;
> +
> remove_nexthop(net, nhi->nh_parent, NULL);
> }
> }
> @@ -2189,11 +2193,11 @@ static int nh_netdev_event(struct notifier_block
> *this,
> switch (event) {
> case NETDEV_DOWN:
> case NETDEV_UNREGISTER:
> - nexthop_flush_dev(dev);
> + nexthop_flush_dev(dev, event);
> break;
> case NETDEV_CHANGE:
> if (!(dev_get_flags(dev) & (IFF_RUNNING | IFF_LOWER_UP)))
> - nexthop_flush_dev(dev);
> + nexthop_flush_dev(dev, event);
> break;
> case NETDEV_CHANGEMTU:
> info_ext = ptr;
>
LGTM. I suggest submitting without the RFC.
Reviewed-by: David Ahern <dsah...@gmail.com>
