From: Jakub Sitnicki <j...@redhat.com> Date: Wed, 8 Jun 2016 15:13:34 +0200
> At present we perform an xfrm_lookup() for each UDPv6 message we > send. The lookup involves querying the flow cache (flow_cache_lookup) > and, in case of a cache miss, creating an XFRM bundle. > > If we miss the flow cache, we can end up creating a new bundle and > deriving the path MTU (xfrm_init_pmtu) from on an already transformed > dst_entry, which we pass from the socket cache (sk->sk_dst_cache) down > to xfrm_lookup(). This can happen only if we're caching the dst_entry > in the socket, that is when we're using a connected UDP socket. > > To put it another way, the path MTU shrinks each time we miss the flow > cache, which later on leads to incorrectly fragmented payload. It can > be observed with ESPv6 in transport mode: ... > To prevent the recreation of an XFRM bundle, avoid an XFRM lookup > altogether whenever we already have a destination entry cached in the > socket. This prevents the path MTU shrinkage and brings us on par with > UDPv4. > > The fix also benefits connected PINGv6 sockets, another user of > ip6_sk_dst_lookup_flow(), who also suffer messages being transformed > twice. > > Joint work with Hannes Frederic Sowa. > > Reported-by: Jan Tluka <jtl...@redhat.com> > Signed-off-by: Jakub Sitnicki <j...@redhat.com> > Acked-by: Hannes Frederic Sowa <han...@stressinduktion.org> Applied and queued up for -stable, thanks.
