Conntrack entries are created for UDP flows even if there's nowhere to
route these packets (ie. no listening socket and no NAT rules to
apply). Moreover, iptables NAT rules are evaluated by netfilter only
when creating a new conntrack entry.
When Docker adds NAT rules, netfilter will ignore them for any packet
matching a pre-existing conntrack entry. In such case, when
dockerd runs with userland proxy enabled, packets got routed to it and
the main symptom will be bad source IP address (as shown by #44688).
If the publishing container is run through Docker Swarm or in
"standalone" Docker but with no userland proxy, affected packets will
be dropped (eg. routed to nowhere).
As such, Docker needs to flush all conntrack entries for published UDP
ports to make sure NAT rules are correctly applied to all packets.
- Fixes#44688
- Fixes#8795
- Fixes#16720
- Fixes#7540
- Fixesmoby/libnetwork#2423
- and probably more.
As a precautionary measure, those conntrack entries are also flushed
when revoking external connectivity to avoid those entries to be reused
when a new sandbox is created (although the kernel should already
prevent such case).
Signed-off-by: Albin Kerouanton <albinker@gmail.com>
(cherry picked from commit b37d34307d)
Signed-off-by: Cory Snider <csnider@mirantis.com>
Flush all the endpoint flows when the external
connectivity is removed.
This will prevent issues where if there is a flow
in conntrack this will have precedence and will
let the packet skip the POSTROUTING chain.
Signed-off-by: Flavio Crisciani <flavio.crisciani@docker.com>
