wireguard-tools: add wireguard_watchdog script

This watchdog script tries to re-resolve hostnames for inactive WireGuard peers.
Use it for peers with a frequently changing dynamic IP.
persistent_keepalive must be set, recommended value is 25 seconds.
Run this script from cron every minute:
echo '* * * * * /usr/bin/wireguard_watchdog' >> /etc/crontabs/root

Signed-off-by: Aleksandr V. Piskunov <aleksandr.v.piskunov@gmail.com>
[bump the package release]
Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

package/network/services/wireguard/Makefile

@@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/kernel.mk
 PKG_NAME:=wireguard
 
 PKG_VERSION:=0.0.20180718
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=WireGuard-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://git.zx2c4.com/WireGuard/snapshot/
@@ -84,12 +84,13 @@ define Package/wireguard-tools/description
   $(call Package/wireguard/Default/description)
 
   This package provides the userspace control program for WireGuard,
-  `wg(8)`, and a netifd protocol helper.
+  `wg(8)`, a netifd protocol helper, and a re-resolve watchdog script.
 endef
 
 define Package/wireguard-tools/install
 	$(INSTALL_DIR) $(1)/usr/bin/
 	$(INSTALL_BIN) $(PKG_BUILD_DIR)/src/tools/wg $(1)/usr/bin/
+	$(INSTALL_BIN) ./files/wireguard_watchdog $(1)/usr/bin/
 	$(INSTALL_DIR) $(1)/lib/netifd/proto/
 	$(INSTALL_BIN) ./files/wireguard.sh $(1)/lib/netifd/proto/
 endef

package/network/services/wireguard/files/wireguard_watchdog

@@ -0,0 +1,60 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2018 Aleksandr V. Piskunov <aleksandr.v.piskunov@gmail.com>.
+# Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+#
+# This watchdog script tries to re-resolve hostnames for inactive WireGuard peers.
+# Use it for peers with a frequently changing dynamic IP.
+# persistent_keepalive must be set, recommended value is 25 seconds.
+#
+# Run this script from cron every minute:
+# echo '* * * * * /usr/bin/wireguard_watchdog' >> /etc/crontabs/root
+
+
+. /lib/functions.sh
+
+check_peer_activity() {
+  local cfg=$1
+  local iface=$2
+  local public_key
+  local endpoint_host
+  local endpoint_port
+  local persistent_keepalive
+  local last_handshake
+  local idle_seconds
+
+  config_get public_key "${cfg}" "public_key"
+  config_get endpoint_host "${cfg}" "endpoint_host"
+  config_get endpoint_port "${cfg}" "endpoint_port"
+  persistent_keepalive=`wg show ${iface} persistent-keepalive | grep ${public_key} | awk '{print $2}'`
+
+  # only process peers with endpoints and keepalive set
+  [ -z ${endpoint_host} ] && return 0;
+  [ -z ${persistent_keepalive} -o ${persistent_keepalive} = "off" ] && return 0;
+
+  # skip IP addresses
+  # check taken from packages/net/ddns-scripts/files/dynamic_dns_functions.sh
+  local IPV4_REGEX="[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}"
+  local IPV6_REGEX="\(\([0-9A-Fa-f]\{1,4\}:\)\{1,\}\)\(\([0-9A-Fa-f]\{1,4\}\)\{0,1\}\)\(\(:[0-9A-Fa-f]\{1,4\}\)\{1,\}\)"
+  local IPV4=$(echo ${endpoint_host} | grep -m 1 -o "$IPV4_REGEX$")    # do not detect ip in 0.0.0.0.example.com
+  local IPV6=$(echo ${endpoint_host} | grep -m 1 -o "$IPV6_REGEX")
+  [ -n "${IPV4}" -o -n "${IPV6}" ] && return 0;
+
+  # re-resolve endpoint hostname if not responding for too long
+  last_handshake=`wg show ${iface} latest-handshakes | grep ${public_key} | awk '{print $2}'`
+  [ -z ${last_handshake} ] && return 0;
+  idle_seconds=$((`date +%s`-${last_handshake}))
+  [ ${idle_seconds} -lt 150 ] && return 0;
+  logger -t "wireguard_monitor" "${iface} endpoint ${endpoint_host}:${endpoint_port} is not responding for ${idle_seconds} seconds, trying to re-resolve hostname"
+  wg set ${iface} peer ${public_key} endpoint "${endpoint_host}:${endpoint_port}"
+}
+
+# query ubus for all active wireguard interfaces
+wg_ifaces=`ubus -S call network.interface dump | jsonfilter -e '@.interface[@.up=true]' | jsonfilter -a -e '@[@.proto="wireguard"].interface' | tr "\n" " "`
+
+# check every peer in every active wireguard interface
+config_load network
+for iface in $wg_ifaces; do
+  config_foreach check_peer_activity "wireguard_${iface}" "${iface}"
+done