Bug in helper contrib/examples/reresolve-dns/reresolve-dns.sh

Bug in helper contrib/examples/reresolve-dns/reresolve-dns.sh

[Conrad Meyer]

Hi,

reresolve-dns.sh seems to have a bug where interfaces with more than a
single peer configured do not match the output of "latest-handshakes"
correctly.  Chiefly, the ^ and $ regex anchors in the script match on
the full, multiline output of 'wg foo latest-handshakes' in bash,
rather than matching on individual lines (which is clearly the
intent).

This is observed on both bash 4.4.23 and 5.0.11.

The easiest fix to this problem is simply to remove the anchors.
There should be no issue with false positive matching, nor correctly
parsing the last handshake time.  With this minor change,
reresolve-dns.sh actually functions on my host with two peers
configured.

I did not spot any obvious way to change bash's regex line-matching
behavior.  If that exists, it may be preferable.

Thank you,
Conrad
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Re: Bug in helper contrib/examples/reresolve-dns/reresolve-dns.sh

[Jason A. Donenfeld]

Thanks for the suggestion!

https://git.zx2c4.com/WireGuard/commit/?id=d05b6606886018853da20ca3ee8bda16524b53b9
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Re: Bug in helper contrib/examples/reresolve-dns/reresolve-dns.sh

[Conrad Meyer]

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Thanks for fixing it so quickly!

Would it be possible to use env as the interpreter for systems which don't
place bash directly in /bin?  I think that's my only other significant
local modification to the script on my BSD systems.  I.e.,

-#!/bin/bash
+#!/usr/bin/env bash

Best regards,
Conrad

P.S., If it is helpful, I also have some example SystemD unit files for
connecting this script up in that universe, which I'm pretty sure I stole
from ArchWiki (https://wiki.archlinux.org/index.php/WireGuard) but I don't
remember at this point.  It might be nice to other users to shove some
version of them in the examples/reresolve-dns directory as an example for
folks on systemd.

$ cat wg-reresolve-dns.timer
[Unit]
Description=Periodically reresolve DNS of Wireguard endpoints that have
stopped responding

[Timer]
OnCalendar=*:*:0/30

[Install]
WantedBy=timers.target

# The hardcoded wgnet0 below could probably be transformed into
an @.service, like wg-quick@.service.  Also, dnsmasq.service is just a
quirk of my personal DNS configuration; others might depend on different or
non-local resolvers.

$ cat wg-reresolve-dns.service
[Unit]
Description=Reresolve DNS of all WireGuard endpoints that have missed a
handshake
Wants=network-online.target dnsmasq.service wg-quick@wgnet0.service
After=network-online.target dnsmasq.service wg-quick@wgnet0.service

[Service]
Type=oneshot
ExecStart=/bin/sh -c 'for i in /etc/wireguard/*.conf; do
/usr/share/doc/wireguard/examples/reresolve-dns/reresolve-dns.sh "$i"; done'

# Finally, here's an example of systemd units that use the more general
@.timer and @.service (but lack the unit dependencies):
https://gist.github.com/ephemient/45ffc8c143d3c4f3d1a940f4293e4b84


On Wed, Nov 27, 2019 at 04:31 Jason A. Donenfeld <Jason@zx2c4.com> wrote:

> Thanks for the suggestion!
>
>
> https://git.zx2c4.com/WireGuard/commit/?id=d05b6606886018853da20ca3ee8bda16524b53b9
>

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