[Bug 1811149] Re: 23 wireguard peers hang systemd-networkd

[Leonid Evdokimov]

I've written a small script to reproduce the issue and I got following
results using VMs from Linode:

- broken with systemd=237-3ubuntu10.9  on Ubuntu 18.04, 4.15.0-43-generic #46-Ubuntu.
- broken with systemd=237-3ubuntu10.11 on Ubuntu 18.04, 4.15.0-43-generic #46-Ubuntu.
- broken with systemd=239-7ubuntu10.6  on Ubuntu 18.10, 4.18.0-13-generic #14-Ubuntu.

The way I used to reproduce the issue was to 1) start Linode VM, 2) run
`./systemd-wg 23`.

For some reason, 23 is the magic number of peers: 22 peers, 24 peers and
1500 peers work okay, but 23 peers trigger the bug.

Given the fact that 239 is also affected, I'm submitting it upstream.

** Attachment added: "bash script to reproduce the issue"
   https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1811149/+attachment/5228725/+files/systemd-wg

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https://bugs.launchpad.net/bugs/1811149

Title:
  23 wireguard peers hang systemd-networkd

Status in systemd package in Ubuntu:
  New

Bug description:
  I'm running Ubuntu 18.04.1 LTS with systemd=237-3ubuntu10.9.
  Linux kernel version is 4.15.0-32-generic #35-Ubuntu SMP.
  wireguard=0.0.20181218-wg1~bionic from PPA.

  I have a Wireguard-based VPN server that has several peers. As soon as
  number of peers is 22 or lower, everything works okay. As soon as I
  add the 23rd peer, restart of `systemd-networkd` service fails with
  timeout while systemd-networkd hogs CPU.

  Moreover, if I reboot the box while wireguard configuration is
  "broken", systemd-networkd fails to apply network settings on boot and
  the box is no longer accessible over the network.

  Configuration is structured in a following way (keys are fake):

  ==> wg0.netdev
  [NetDev]
  Name=wg0
  Kind=wireguard
  Description=Wireguard VPN server
  [WireGuard]
  ListenPort=4500
  PrivateKey=kNl7tkhCM1Crj8RhUIn8xvwcg+UoOkw26kQjQEtZk1k=
  [WireGuardPeer]
  PublicKey=AfM1AN4IIUe5AVypFg2pcNrQmqOtZQIJLgusbkDYXkI=
  AllowedIPs=fd6f:b446:a2ca:0400:cb6f:b446:a2ca:bd0b/128
  AllowedIPs=fd6f:b446:a2ca:cb6f:b446:a2ca::/96
  # and 22 more [WireGuardPeer] like that

  ==> wg0.network
  Name=wg0
  [Network]
  Address=fd6f:b446:a2ca:0400::1/64
  [Route]
  Destination=fd6f:b446:a2ca:cb6f:b446:a2ca::/96
  # and 22 more [Route] sections like that

  syslog logs are attached both for "good" and "bad" cases, sample of
  strace logs is also attached for "bad" case.

  I'm filling the issue here as the aforementioned systemd version is
  already out of scope of upstream bug tracker per
  https://github.com/systemd/systemd/blob/master/docs/CONTRIBUTING.md
  #filing-issues

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