4.13: unable to increase MTU configuration for GRE devices

[James Page]

[Impact]
GRE overlay networks can't carry traffic with MTU > 1500

[Test Case]
sudo add-apt-repository cloud-archive:pike
sudo apt update
sudo apt install openvswitch-switch
sudo ovs-vsctl add-br br-tun
sudo ovs-vsctl add-port br-tun gre0 -- set interface gre0 type=gre options:remote_ip=10.100.1.1

gre_sys device will be configured with MTU 1472.

sudo ip link set gre_sys mtu 65000

will fail with EINVAL.

[Regression Potential]

[Bug Report]

Under Linux 4.13 its 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 slow/broken.

This is resolved as part of the upcoming 4.15 kernel under:

  https://github.com/torvalds/linux/commit/cfddd4c33c254954927942599d299b3865743146

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1743746

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Joseph Salisbury (jsalisbury)]

I built a test kernel with commit cfddd4c. The test kernel can be downloaded from:
http://kernel.ubuntu.com/~jsalisbury/lp1743746

Can you test this kernel and see if it resolves this bug?

Note, to test this kernel, you need to install both the linux-image and linux-image-extra .deb packages.

Thanks in advance!

[James Page (james-page)]

Hi Joseph

I reconfirmed the bug on the current artful kernel, upgraded to your test kernel and I can confirm that the test kernel resolves the issue:

7: gre_sys@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc pfifo_fast master ovs-system state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 3a:14:f5:6d:cd:93 brd ff:ff:ff:ff:ff:ff

I was able to set the MTU of the gre_sys device to 65000.

[Joseph Salisbury (jsalisbury)]

Thanks for testing, James. I'll submit an SRU request for this commit to be included in the Ubuntu kernel.

[Joseph Salisbury (jsalisbury)]

Submitted Artful and Bionic SRU requests:
https://lists.ubuntu.com/archives/kernel-team/2018-January/089420.html

[James Page (james-page)]

Thanks!

[James Page (james-page)]

Appreciate the kernel team has been pretty busy the last few months; is there an ETA on when this fix might make it into the 4.13 kernels? I know we've pushed the HWE kernel version forward for xenial - so any OpenStack deployments using HWE with GRE tunnels will hit this problem.

[Kleber Sacilotto de Souza (kleber-souza)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-artful' to 'verification-done-artful'. If the problem still exists, change the tag 'verification-needed-artful' to 'verification-failed-artful'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[James Page (james-page)]

LGTM to artful-proposed:

15: gre_sys@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc pfifo_fast master ovs-system state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 92:92:4d:84:14:1d brd ff:ff:ff:ff:ff:ff

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 17.10
Release: 17.10
Codename: artful

$ uname -a
Linux juju-9b0cd0-artful-proposed-19 4.13.0-35-generic #39-Ubuntu SMP Mon Feb 12 11:06:39 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

[Timo Aaltonen (tjaalton)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-xenial' to 'verification-done-xenial'. If the problem still exists, change the tag 'verification-needed-xenial' to 'verification-failed-xenial'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Timo Aaltonen (tjaalton)]

disregard that last comment, it was caused by a buggy script

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 4.13.0-36.40

---------------
linux (4.13.0-36.40) artful; urgency=medium

  * linux: 4.13.0-36.40 -proposed tracker (LP: #1750010)

  * Rebuild without "CVE-2017-5754 ARM64 KPTI fixes" patch set

linux (4.13.0-35.39) artful; urgency=medium

  * linux: 4.13.0-35.39 -proposed tracker (LP: #1748743)

  * CVE-2017-5715 (Spectre v2 Intel)
    - Revert "UBUNTU: SAUCE: turn off IBPB when full retpoline is present"
    - SAUCE: turn off IBRS when full retpoline is present
    - [Packaging] retpoline files must be sorted
    - [Packaging] pull in retpoline files

linux (4.13.0-34.37) artful; urgency=medium

  * linux: 4.13.0-34.37 -proposed tracker (LP: #1748475)

  * libata: apply MAX_SEC_1024 to all LITEON EP1 series devices (LP: #1743053)
    - libata: apply MAX_SEC_1024 to all LITEON EP1 series devices

  * KVM patches for s390x to provide facility bits 81 (ppa15) and 82 (bpb)
    (LP: #1747090)
    - KVM: s390: wire up bpb feature

  * artful 4.13 i386 kernels crash after memory hotplug remove (LP: #1747069)
    - Revert "mm, memory_hotplug: do not associate hotadded memory to zones until
      online"

  * CVE-2017-5715 (Spectre v2 Intel)
    - x86/feature: Enable the x86 feature to control Speculation
    - x86/feature: Report presence of IBPB and IBRS control
    - x86/enter: MACROS to set/clear IBRS and set IBPB
    - x86/enter: Use IBRS on syscall and interrupts
    - x86/idle: Disable IBRS entering idle and enable it on wakeup
    - x86/idle: Disable IBRS when offlining cpu and re-enable on wakeup
    - x86/mm: Set IBPB upon context switch
    - x86/mm: Only set IBPB when the new thread cannot ptrace current thread
    - x86/entry: Stuff RSB for entry to kernel for non-SMEP platform
    - x86/kvm: add MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD to kvm
    - x86/kvm: Set IBPB when switching VM
    - x86/kvm: Toggle IBRS on VM entry and exit
    - x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature
    - x86/spec_ctrl: Add lock to serialize changes to ibrs and ibpb control
    - x86/cpu/AMD: Add speculative control support for AMD
    - x86/microcode: Extend post microcode reload to support IBPB feature
    - KVM: SVM: Do not intercept new speculative control MSRs
    - x86/svm: Set IBRS value on VM entry and exit
    - x86/svm: Set IBPB when running a different VCPU
    - KVM: x86: Add speculative control CPUID support for guests
    - SAUCE: turn off IBPB when full retpoline is present

  * Artful 4.13 fixes for tun (LP: #1748846)
    - tun: call dev_get_valid_name() before register_netdevice()
    - tun: allow positive return values on dev_get_valid_name() call
    - tun/tap: sanitize TUNSETSNDBUF input

  * boot failure on AMD Raven + WestonXT (LP: #1742759)
    - SAUCE: drm/amdgpu: add atpx quirk handling (v2)

linux (4.13.0-33.36) artful; urgency=low

  * linux: 4.13.0-33.36 -proposed tracker (LP: #1746903)

  [ Stefan Bader ]
  * starting VMs causing retpoline4 to reboot (LP: #1747507) // CVE-2017-5715
    (Spectre v2 retpoline)
    - x86/retpoline: Fill RSB on context switch for affected CPUs
    - x86/retpoline: Add LFENCE to the retpoline/RSB filling RSB macros
    - x86/retpol...