commit 804008933d66a6e7d177fcbc59ed24ef33903313
Author: redxef <federanko.manuel@gmail.com>
Date:   Thu Jun 15 01:05:12 2023 +0200

    Initial commit.

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..af87c9e
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,10 @@
+SCRIPT := gre-on-wg.sh
+SCRIPT_NAME := $(SCRIPT:.sh=)
+PREFIX ?= /usr/local
+
+install: install-bin
+
+install-bin: $(SCRIPT)
+	install -D -m 0755 -o root -g root -T $(SCRIPT) $(PREFIX)/bin/$(SCRIPT_NAME)
+
+.PHONY: install install-bin
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1cc9f0c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,51 @@
+# gre-on-wg
+
+Create a GRETAP mesh network on top of wireguard.
+
+## Usage
+
+`gre-on-wg WG_QUICK_CONFIG_FILE ADDRESS_TRANSLATIONS`
+
+The first argument is the path to a wg-quick config file, while the
+second argument provides address translations for wireguard internal ip
+addresses to the new addresses.
+
+The wireguard configuration must have the `Address` config in the
+`[Interface]` section set to exactly **one** address, similarly every
+`[Peer]` section may only contain **one** AllowedIPs entry with **one**
+addresss.
+
+The translation file should contain lines of the following format:
+`<wireguard private ip> <space> <new bridge network ip>`
+
+### Example
+
+Consider the following wg0.conf file
+
+```
+[Interface]
+Address = 192.168.3.100/24
+
+[Peer]
+AllowedIPs = 192.168.3.101/32
+
+[Peer]
+AllowedIPs = 192.168.3.102/32
+
+[Peer]
+AllowedIPs = 192.168.3.103/32
+```
+
+And the following translation file
+
+```
+192.168.3.100/24 192.168.4.100/24
+192.168.3.101/24 192.168.4.101/24
+192.168.3.102/24 192.168.4.102/24
+192.168.3.103/24 192.168.4.103/24
+```
+
+This would result in the creation of the bridge network `wg0br1` on host
+`192.168.3.100` where the different peers have the addresses
+`192.168.4.10[0123]`. Additionally the point-to-point networks
+`wg0gre[1234]` would be created.
diff --git a/gre-on-wg.sh b/gre-on-wg.sh
new file mode 100755
index 0000000..824458a
--- /dev/null
+++ b/gre-on-wg.sh
@@ -0,0 +1,115 @@
+#!/bin/bash
+
+set -euo pipefail
+
+strstrip() {
+    sed -E -e 's/^\s*//' -e 's/\s*$//'
+}
+
+create_br() {
+    local name
+    name="$1"
+
+    $DEBUG ip link add "$name" type bridge
+}
+
+create_gre() {
+    local name local_ip remote_ip
+    name="$1"
+    local_ip="$(sed 's_/.*$__' <<< "$2")"
+    remote_ip="$(sed 's_/.*$__' <<< "$3")"
+
+    $DEBUG ip link add "$name" type gretap local "$local_ip" remote "$remote_ip"
+    $DEBUG ip link set up "$name"
+}
+
+add_gre_to_br() {
+    local br_name gre_name
+    br_name="$1"
+    gre_name="$2"
+
+    $DEBUG ip link set "$gre_name" master "$br_name"
+}
+
+finish_br() {
+    local name local_ip
+    name="$1"
+    local_ip="$2"
+
+    $DEBUG ip addr add "$local_ip" dev "$name"
+    $DEBUG ip link set up "$name"
+}
+
+read_wg_conf() {
+    local filepath
+    local local_ip remote_ips mode line
+    filepath="$1"
+
+    local_ip=
+    remote_ips=
+    mode=
+    while read -r line; do
+        line="$(strstrip <<< "$line")"
+        if [[ "$line" = '[Interface]' ]]; then
+            mode=interface
+            continue
+        elif [[ "$line" = '[Peer]' ]]; then
+            mode=peer
+            continue
+        fi
+        if [[ "$mode" = 'interface' ]] && [[ "$line"  =~ ^Address\ *=\ * ]]; then
+            local_ip="$(awk -F= '{print $2}' <<< "$line" | strstrip)"
+        elif [[ "$mode" = 'peer' ]] && [[ "$line" =~ ^AllowedIPs\ *=\ * ]]; then
+            remote_ips="$remote_ips $(awk -F= '{print $2}' <<< "$line" | strstrip)"
+        fi
+    done < "$filepath"
+    remote_ips="$(strstrip <<< "$remote_ips")"
+
+    echo "$local_ip"
+    echo "$remote_ips"
+}
+
+create_networks() {
+    local wg_name local_ip local_ip_trans remote_ips
+    local br_name n
+    wg_name="$1"
+    local_ip="$2"
+    local_ip_trans="$3"
+    remote_ips="$4"
+
+    br_name="${wg_name}br1"
+    n=1
+
+    create_br "$br_name"
+    for remote_ip in $remote_ips ; do
+        create_gre "${wg_name}gre$n" "$local_ip" "$remote_ip"
+        add_gre_to_br "$br_name" "${wg_name}gre$n"
+        n=$((n+1))
+    done
+
+    finish_br "$br_name" "$local_ip_trans"
+}
+
+main() {
+    local filepath translation_filepath
+    local r local_ip remote_ips local_ip_trans
+    filepath="$1"
+    if [[ "$filepath" =~ .*/.* ]]; then
+        # path, not a name, leave as is
+        :
+    else
+        filepath="/etc/wireguard/$filepath"
+    fi
+    translation_filepath="$(sort <<< "$2" | uniq)"
+
+    r="$(read_wg_conf "$filepath")"
+    local_ip="$(head -n1 <<< "$r")"
+    remote_ips="$(tail -n1 <<< "$r")"
+    unset r
+
+    local_ip_trans="$(grep -E "$(sed 's_\._\\._g' <<< "$local_ip")" "$translation_filepath" | awk '{print $2}')"
+
+    create_networks "$(basename --suffix='.conf' "$filepath")" "$local_ip" "$local_ip_trans" "$remote_ips"
+}
+
+main "$@"