[PATCH] wg-quick: use bind mount for DNS when no openresolv

["Jason A. Donenfeld" <Jason@zx2c4.com>]

Posting this to the mailing list for review. Based on the thread
entitled, "Fixing wg-quick's DNS= directive with a hatchet". Comments
are very welcome.

---
 src/tools/wg-quick.bash | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/tools/wg-quick.bash b/src/tools/wg-quick.bash
index def78af..2fc19f1 100755
--- a/src/tools/wg-quick.bash
+++ b/src/tools/wg-quick.bash
@@ -131,11 +131,33 @@ set_mtu() {
 }
 
 set_dns() {
-	[[ ${#DNS[@]} -eq 0 ]] || printf 'nameserver %s\n' "${DNS[@]}" | cmd resolvconf -a "tun.$INTERFACE" -m 0 -x
+	[[ ${#DNS[@]} -gt 0 ]] || return 0
+
+	if [[ $(resolvconf --version 2>/dev/null) == openresolv\ * ]]; then
+		printf 'nameserver %s\n' "${DNS[@]}" | cmd resolvconf -a "$INTERFACE" -m 0 -x
+	else
+		local our_resolv="/etc/resolv.conf.wg-quick.$INTERFACE"
+		[[ -e /etc/resolv.conf ]] || touch /etc/resolv.conf
+		{ echo "# This file was generated by wg-quick(8) for use with"
+		  echo "# the WireGuard interface $INTERFACE. It cannot be"
+		  echo "# removed or altered directly. You may remove this file"
+		  echo "# by running \`wg-quick down $INTERFACE\`, or if that"
+		  echo "# poses problems, run \`unmount /etc/resolv.conf\`."
+		  printf 'nameserver %s\n' "${DNS[@]}"
+		} > "$our_resolv"
+		cmd mount -Br "$our_resolv" /etc/resolv.conf || { unlink "$our_resolv"; false; }
+		unlink "$our_resolv"
+	fi
 }
 
 unset_dns() {
-	[[ ${#DNS[@]} -eq 0 ]] || cmd resolvconf -d "tun.$INTERFACE"
+	[[ ${#DNS[@]} -gt 0 ]] || return 0
+
+	if [[ $(resolvconf --version 2>/dev/null) == openresolv\ * ]]; then
+		cmd resolvconf -d "$INTERFACE"
+	else
+		cmd umount /etc/resolv.conf
+	fi
 }
 
 add_route() {
@@ -254,8 +276,8 @@ cmd_down() {
 	[[ " $(wg show interfaces) " == *" $INTERFACE "* ]] || die "\`$INTERFACE' is not a WireGuard interface"
 	execute_hooks "${PRE_DOWN[@]}"
 	[[ $SAVE_CONFIG -eq 0 ]] || save_config
-	unset_dns
 	del_if
+	unset_dns
 	execute_hooks "${POST_DOWN[@]}"
 }
 
-- 
2.14.2