wg-quick: verify wireguard interface in more clever way

This helps with old Debian which has ancient iproute2, as well as paving
the path toward this script supporting userspace implementations.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/src/wg-quick.bash b/src/wg-quick.bash
index c70c0789ff47bc9967b6fc6406d6540c39ac25de..5295c8bfff65ca0a886d40e60dfc1bc4bbfa8889 100755 (executable)
--- a/src/wg-quick.bash
+++ b/src/wg-quick.bash
@@ -249,7 +249,7 @@ cmd_up() {
 }
 
 cmd_down() {
-       [[ -n $(ip link show dev "$INTERFACE" type wireguard 2>/dev/null) ]] || die "\`$INTERFACE' is not a WireGuard interface"
+       [[ " $(wg show interfaces) " == *" $INTERFACE "* ]] || die "\`$INTERFACE' is not a WireGuard interface"
        execute_hook "$PRE_DOWN"
        [[ $SAVE_CONFIG -eq 0 ]] || save_config
        unset_dns