Re: [PATCH net] net/ipv6: Only update MTU metric if it set

[David Miller <davem@davemloft.net>]

From: dsahern@kernel.org
Date: Thu, 30 Aug 2018 14:15:43 -0700

> From: David Ahern <dsahern@gmail.com>
> 
> Jan reported a regression after an update to 4.18.5. In this case ipv6
> default route is setup by systemd-networkd based on data from an RA. The
> RA contains an MTU of 1492 which is used when the route is first inserted
> but then systemd-networkd pushes down updates to the default route
> without the mtu set.
> 
> Prior to the change to fib6_info, metrics such as MTU were held in the
> dst_entry and rt6i_pmtu in rt6_info contained an update to the mtu if
> any. ip6_mtu would look at rt6i_pmtu first and use it if set. If not,
> the value from the metrics is used if it is set and finally falling
> back to the idev value.
> 
> After the fib6_info change metrics are contained in the fib6_info struct
> and there is no equivalent to rt6i_pmtu. To maintain consistency with
> the old behavior the new code should only reset the MTU in the metrics
> if the route update has it set.
> 
> Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info")
> Reported-by: Jan Janssen <medhefgo@web.de>
> Signed-off-by: David Ahern <dsahern@gmail.com>

Applied and queued up for -stable, thanks David.