Re: [PATCH net] ipv4: fix fnhe usage by non-cached routes

[David Miller <davem@davemloft.net>]

From: Julian Anastasov <ja@ssi.bg>
Date: Wed,  2 May 2018 09:41:19 +0300

> Allow some non-cached routes to use non-expired fnhe:
> 
> 1. ip_del_fnhe: moved above and now called by find_exception.
> The 4.5+ commit deed49df7390 expires fnhe only when caching
> routes. Change that to:
> 
> 1.1. use fnhe for non-cached local output routes, with the help
> from (2)
> 
> 1.2. allow __mkroute_input to detect expired fnhe (outdated
> fnhe_gw, for example) when do_cache is false, eg. when itag!=0
> for unicast destinations.
> 
> 2. __mkroute_output: keep fi to allow local routes with orig_oif != 0
> to use fnhe info even when the new route will not be cached into fnhe.
> After commit 839da4d98960 ("net: ipv4: set orig_oif based on fib
> result for local traffic") it means all local routes will be affected
> because they are not cached. This change is used to solve a PMTU
> problem with IPVS (and probably Netfilter DNAT) setups that redirect
> local clients from target local IP (local route to Virtual IP)
> to new remote IP target, eg. IPVS TUN real server. Loopback has
> 64K MTU and we need to create fnhe on the local route that will
> keep the reduced PMTU for the Virtual IP. Without this change
> fnhe_pmtu is updated from ICMP but never exposed to non-cached
> local routes. This includes routes with flowi4_oif!=0 for 4.6+ and
> with flowi4_oif=any for 4.14+).
> 
> 3. update_or_create_fnhe: make sure fnhe_expires is not 0 for
> new entries
> 
> Fixes: 839da4d98960 ("net: ipv4: set orig_oif based on fib result for local traffic")
> Fixes: d6d5e999e5df ("route: do not cache fib route info on local routes with oif")
> Fixes: deed49df7390 ("route: check and remove route cache when we get route")
> Cc: David Ahern <dsahern@gmail.com>
> Cc: Xin Long <lucien.xin@gmail.com>
> Signed-off-by: Julian Anastasov <ja@ssi.bg>

Applied and queued up for -stable, thanks Julian.