From 81879fe34648d1aba618df5a065591538d1492c2 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Sat, 14 Apr 2018 02:34:28 +0200
Subject: [PATCH] wg-quick: account for specified fwmark in auto routing mode

If we're doing automatic routing with default routes, but the config has
also specified an explicit fwmark, then use that explicit fwmark, even
if it's conflicting, since the administrator has explicitly opted into
using it. Also, when shutting down the interface, we only now remove the
fancy rules if we're in automatic routing mode with default routes.

Suggested-by: Luis Ressel <aranea@aixah.de>
Reported-by: Saeid Akbari <saeidscorp@yahoo.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 src/wg-quick.bash | 42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

diff --git a/src/wg-quick.bash b/src/wg-quick.bash
index 2a0abe0..f8c1ce7 100755
--- a/src/wg-quick.bash
+++ b/src/wg-quick.bash
@@ -87,20 +87,17 @@ add_if() {
 }
 
 del_if() {
-	local fwmark
+	local table
 	[[ $HAVE_SET_DNS -eq 0 ]] || unset_dns
-	fwmark="$(wg show "$INTERFACE" fwmark)"
-	DEFAULT_TABLE=0
-	[[ $fwmark != off ]] && DEFAULT_TABLE=$(( fwmark ))
-	if [[ $DEFAULT_TABLE -ne 0 ]]; then
-		while [[ $(ip -4 rule show) == *"lookup $DEFAULT_TABLE"* ]]; do
-			cmd ip -4 rule delete table $DEFAULT_TABLE
+	if [[ -z $TABLE || $TABLE == auto ]] && get_fwmark table && [[ $(wg show "$INTERFACE" allowed-ips) =~ /0(\ |$'\n'|$) ]]; then
+		while [[ $(ip -4 rule show) == *"lookup $table"* ]]; do
+			cmd ip -4 rule delete table $table
 		done
 		while [[ $(ip -4 rule show) == *"from all lookup main suppress_prefixlength 0"* ]]; do
 			cmd ip -4 rule delete table main suppress_prefixlength 0
 		done
-		while [[ $(ip -6 rule show) == *"lookup $DEFAULT_TABLE"* ]]; do
-			cmd ip -6 rule delete table $DEFAULT_TABLE
+		while [[ $(ip -6 rule show) == *"lookup $table"* ]]; do
+			cmd ip -6 rule delete table $table
 		done
 		while [[ $(ip -6 rule show) == *"from all lookup main suppress_prefixlength 0"* ]]; do
 			cmd ip -6 rule delete table main suppress_prefixlength 0
@@ -169,21 +166,28 @@ add_route() {
 	fi
 }
 
-DEFAULT_TABLE=
+get_fwmark() {
+	local fwmark
+	fwmark="$(wg show "$INTERFACE" fwmark)" || return 1
+	[[ -n $fwmark && $fwmark != off ]] || return 1
+	printf -v "$1" "%d" "$fwmark"
+	return 0
+}
+
 add_default() {
-	if [[ -z $DEFAULT_TABLE ]]; then
-		DEFAULT_TABLE=51820
-		while [[ -n $(ip -4 route show table $DEFAULT_TABLE) || -n $(ip -6 route show table $DEFAULT_TABLE) ]]; do
-			((DEFAULT_TABLE++))
+	local table proto key value
+	if ! get_fwmark table; then
+		table=51820
+		while [[ -n $(ip -4 route show table $table) || -n $(ip -6 route show table $table) ]]; do
+			((table++))
 		done
+		cmd wg set "$INTERFACE" fwmark $table
 	fi
-	local proto=-4
+	proto=-4
 	[[ $1 == *:* ]] && proto=-6
-	cmd wg set "$INTERFACE" fwmark $DEFAULT_TABLE
-	cmd ip $proto route add "$1" dev "$INTERFACE" table $DEFAULT_TABLE
-	cmd ip $proto rule add not fwmark $DEFAULT_TABLE table $DEFAULT_TABLE
+	cmd ip $proto route add "$1" dev "$INTERFACE" table $table
+	cmd ip $proto rule add not fwmark $table table $table
 	cmd ip $proto rule add table main suppress_prefixlength 0
-	local key value
 	while read -r key _ value; do
 		[[ $value -eq 1 ]] && sysctl -q "$key=2"
 	done < <(sysctl -a -r '^net\.ipv4.conf\.[^ .=]+\.rp_filter$')