[SRU][Artful][Bionic][PATCH 0/1] ip_gre: remove the incorrect mtu limit for ipgre tap

Joseph Salisbury joseph.salisbury at canonical.com
Fri Jan 19 15:54:18 UTC 2018

BugLink: http://bugs.launchpad.net/bugs/1743746

== SRU Justification ==
The following mainline commit introduced a regression in v4.10-rc1:
61e84623ace3 ("net: centralize net_device min/max MTU checking")

In Artful and Bionic, it is not possible to configure GRE tunnel devices 
with a MTU larger than 1500; this impacts on Open vSwitch (which creates 
tunnel devices for GRE overlay networking) and the ip tools.

The kernel will error with:
  "gre_sys: Invalid MTU 65000 requested, hw max 1500"

The side effect of this is that if overlay networks are configured with 
high MTUs, the gre devices fragment the packets and networking is generally 
This regression is now fixed by mainline commit cfddd4c33c25, which was 
added in v4.15-rc5.

== Fix ==
commit cfddd4c33c254954927942599d299b3865743146
Author: Xin Long <lucien.xin at gmail.com>
Date:   Mon Dec 18 14:24:35 2017 +0800

    ip_gre: remove the incorrect mtu limit for ipgre tap

== Regression Potential ==
Low.  This patch fixes a current regression.  It was cc'd to upstream stable
so had additional upstream review.

== Test Case ==
A test kernel was built with this patch and tested by the original bug reporter.
The bug reporter states the test kernel resolved the bug.

Xin Long (1):
  ip_gre: remove the incorrect mtu limit for ipgre tap

 net/ipv4/ip_gre.c | 1 +
 1 file changed, 1 insertion(+)


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