[ovs-build] Passed: ovsrobot/ovn#1079 (series_207523 - 22ad2d4)

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Tue Oct 13 09:18:39 UTC 2020


Build Update for ovsrobot/ovn
-------------------------------------

Build: #1079
Status: Passed

Duration: 19 mins and 22 secs
Commit: 22ad2d4 (series_207523)
Author: Dumitru Ceara
Message: ofctrl.c: Add a predictable resolution for conflicting flow actions.

Until now, in case the ACL configuration generates openflows that have
the same match but different actions, ovn-controller was using the
following approach:
1. If the flow being added contains conjunctive actions, merge its
   actions with the already existing flow.
2. Otherwise, if the flow is being added incrementally
   (update_installed_flows_by_track), don't install the new flow but
   instead keep the old one.
3. Otherwise, (update_installed_flows_by_compare), don't install the
   new flow but instead keep the old one.

Even though one can argue that having an ACL with a match that includes
the match of another ACL is a misconfiguration, it can happen that the
users provision OVN like this.  Depending on the order of reading and
installing the logical flows, the above operations can yield
unpredictable results, e.g., allow specific traffic but then after
ovn-controller is restarted (or a recompute happens) that specific
traffic starts being dropped.

A simple example of ACL configuration is:
ovn-nbctl acl-add ls to-lport 3 '(ip4.src==10.0.0.1 ||
ip4.src==10.0.0.2) && (ip4.dst == 10.0.0.3 || ip4.dst == 10.0.0.4)' allow
ovn-nbctl acl-add ls to-lport 3 'ip4.src==10.0.0.1' allow
ovn-nbctl acl-add ls to-lport 2 'arp' allow
ovn-nbctl acl-add ls to-lport 1 'ip4' drop

This is a pattern used by most CMSs:
- define a default deny policy.
- punch holes in the default deny policy based on user specific
  configurations.

Without this commit the behavior for traffic from 10.0.0.1 to 10.0.0.5
is unpredictable.  Depending on the order of operations traffic might be
dropped or allowed.

It's also quite hard to force the CMS to ensure that such match overlaps
never occur.

To address this issue we now ensure that when selecting the active flow
from all desired flows refering the same installed flow we give
precedence to "allow" over "drop" over "conjunction" flows.

Essentially, less restrictive flows are always preferred over more
restrictive flows whenever a match conflict happens.

CC: Daniel Alvarez <dalvarez at redhat.com>
Reported-at: https://bugzilla.redhat.com/1871931
Signed-off-by: Dumitru Ceara <dceara at redhat.com>
Signed-off-by: 0-day Robot <robot at bytheb.org>

View the changeset: https://github.com/ovsrobot/ovn/compare/e49ce9a33f38^...22ad2d44ec5c

View the full build log and details: https://travis-ci.com/github/ovsrobot/ovn/builds/189667737?utm_medium=notification&utm_source=email


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