[Bug 1853956] Re: 34 wireguard peers result in invalid peer configuration

[Joshua Sjoding]

On two systems with 33 peers I noticed that this shows up in dmesg after
a reboot:

netlink: 'systemd-network': attribute type 5 has an invalid length.

These lines also show up whenever I run `sudo systemctl restart systemd-
networkd` now. They didn't show up before the reboot.

This suggests that there may be issues I haven't noticed yet even with
fewer than 34 peers. In our production environment not all of our peers
are online all the time, so an issue affecting a few of them could go
unnoticed.

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https://bugs.launchpad.net/bugs/1853956

Title:
  34 wireguard peers result in invalid peer configuration

Status in systemd package in Ubuntu:
  New

Bug description:
  ubuntu server 18.04.3 LTS
  systemd 237-3ubuntu10.31
  wireguard 0.0.20191012-wg1~bionic from PPA.

  We're using systemd-networkd to configure wireguard via
  wireguard.netdev and wireguard.network files in /etc/systemd/network/.
  All endpoints have IPv4 addresses.

  When we include 34, 35, or 36 [WireGuardPeer] entries in the netdev
  file some peers are configured incorrectly. The affected peers seem to
  be related to the total number of peers (counting from 0 here):

  33 peers: No issue
  34 peers: Peer 1 and 2 fail
  35 peers: Peer 2 and 3 fail
  36 peers: Peer 3 and 4 fail
  37 peers: No issue

  In all cases peer 0 is functional. For an affected pair of peers A and
  B, peer A ends up with the allowed IP address range of peer B. Peer B
  ends up with no allowed IP addresses. This can be seen in the output
  of wg. The connections to both peers fail because of incorrect address
  range assignments.

  We first encountered this issue in a production environment when we
  moved from 33 to 34 unique peers on each server. The issue was
  reproduced on 3 different physical servers with similar configuration
  by adding and removing peer 34.

  The [WireGuardPeer] entries do not need to be unique to reproduce the
  issue. In my testing I used 6 distinct peers and then used 28 or more
  identical copies of a 7th peer. The results were the same.

  In January 2019 a bug was reported that was also related to the number of wireguard peers, but the description seems sufficiently different from our case that I felt I should file a distinct bug report. Here's a link to that report in case I'm wrong about that:
  https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1811149

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