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Bug 1955167

Summary:	OVN does not check length of OpenFlow FLOW_MOD messages
Product:	Red Hat Enterprise Linux Fast Datapath	Reporter:	Mark Michelson <mmichels>
Component:	ovn23.09	Assignee:	Ales Musil <amusil>
Status:	CLOSED ERRATA	QA Contact:	Ehsan Elahi <eelahi>
Severity:	unspecified	Docs Contact:
Priority:	high
Version:	FDP 21.D	CC:	amusil, ctrautma, i.maximets, jiji, jishi
Target Milestone:	---
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	ovn23.09-23.09.0-beta.36.el9fdp	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2024-01-24 11:17:39 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1953613

Description Mark Michelson 2021-04-29 15:01:47 UTC

Because of issue https://bugzilla.redhat.com/show_bug.cgi?id=1955161 generating extra conjunction actions, we saw an instance where OVN generated a flow that was larger than the maximum size of an openflow message. The result was this:

1) ovn-controller generates huge OF message and sends to ovs-vswitchd. The OF message has a truncated length field 'len'.
2) ovs-vswitchd attempts to parse the OF message. It pulls 'len' bytes from the OF message and reports back to ovn-controller that it has a bad length.
3) ovn-controller closes the UNIX socket connection to ovs-vswitchd.
4) ovs-vswitchd attempts to read the rest of the OF message from the socket. Since it is reading malformed OF, it repeatedly generates "bad version" messages until the entire OF message has been read from the socket.
5) ovn-controller then re-establishes a connection with ovs-vswitchd.
6) Repeat from step (1)

There likely is some clever way that we can ensure that ovn-controller can break a large flow into smaller sub-flows. However, it's unlikely that we would ever need to legitimately generate such a large flow. In this case in particular, the large flow is generated due to a bug. Instead, we should just check the size of the OpenFlow message ovn-controller is generating and just not send it if it's too large.

Comment 1 Casey Callendrello 2021-05-05 20:50:13 UTC

Additionally, for the purposes of alerting, it would be good to have a db table that tracks the number of un-programmable flows. It should be incremented whenever a "bad" flow is encountered, and decremented when that flow is deleted.

That way we can write reliable alerts.

Comment 3 Ilya Maximets 2023-02-20 14:26:59 UTC

>  However, it's unlikely that we would ever need to legitimately generate such a large flow.

Unfortunately, there is a legitimate use case for Load Balancers with 'hairpin_snat_ip' option set described in BZ 2171423.

Comment 4 Ales Musil 2023-08-29 09:14:39 UTC

Patch posted for review: https://patchwork.ozlabs.org/project/ovn/patch/20230829084753.209210-1-amusil@redhat.com/

Comment 5 OVN Bot 2023-09-15 04:06:41 UTC

ovn23.06 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239063
ovn23.03 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239064
ovn22.12 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239066
ovn22.09 fast-datapath-rhel-8 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239069
ovn22.09 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239070
ovn22.06 fast-datapath-rhel-8 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239073
ovn22.06 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239074
ovn22.03 fast-datapath-rhel-8 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239077
ovn22.03 fast-datapath-rhel-9 clone created at https://bugzilla.redhat.com/show_bug.cgi?id=2239078

Comment 9 errata-xmlrpc 2024-01-24 11:17:39 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (ovn23.09 bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2024:0392