fix(netlink): try loading Wireguard module if not found (#1741)

internal/netlink/wireguard.go

@@ -5,10 +5,42 @@ package netlink
 import (
 	"fmt"
 
+	"github.com/qdm12/gluetun/internal/mod"
 	"github.com/vishvananda/netlink"
 )
 
 func (n *NetLink) IsWireguardSupported() (ok bool, err error) {
+	// Check for Wireguard family without loading the wireguard module.
+	// Some kernels have the wireguard module built-in, and don't have a
+	// modules directory, such as WSL2 kernels.
+	ok, err = hasWireguardFamily()
+	if err != nil {
+		return false, fmt.Errorf("checking for wireguard family: %w", err)
+	}
+	if ok {
+		return true, nil
+	}
+
+	// Try loading the wireguard module, since some systems do not load
+	// it after a boot. If this fails, wireguard is assumed to not be supported.
+	n.debugLogger.Debugf("wireguard family not found, trying to load wireguard kernel module")
+	err = mod.Probe("wireguard")
+	if err != nil {
+		n.debugLogger.Debugf("failed loading wireguard kernel module: %s", err)
+		return false, nil
+	}
+	n.debugLogger.Debugf("wireguard kernel module loaded successfully")
+
+	// Re-check if the Wireguard family is now available, after loading
+	// the wireguard kernel module.
+	ok, err = hasWireguardFamily()
+	if err != nil {
+		return false, fmt.Errorf("checking for wireguard family: %w", err)
+	}
+	return ok, nil
+}
+
+func hasWireguardFamily() (ok bool, err error) {
 	families, err := netlink.GenlFamilyList()
 	if err != nil {
 		return false, fmt.Errorf("listing gen 1 families: %w", err)