chore(pkg/wireguard): replace createLinkUsingUserspaceImpl bash script with native code

There is no reason to use bash, or even to call out to the shell for
most of what was happening. Replacing it allows for better error
handling, clarity and reliability.

Fixes: #79

Author: uhthomas

go.mod

@@ -470,7 +470,7 @@ require (
 	golang.org/x/net v0.24.0 // indirect
 	golang.org/x/oauth2 v0.10.0 // indirect
 	golang.org/x/sync v0.7.0 // indirect
-	golang.org/x/sys v0.19.0 // indirect
+	golang.org/x/sys v0.20.0 // indirect
 	golang.org/x/term v0.19.0 // indirect
 	golang.org/x/text v0.14.0 // indirect
 	golang.org/x/time v0.3.0 // indirect

go.sum

@@ -1330,6 +1330,8 @@ golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
 golang.org/x/sys v0.18.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
 golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
+golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/term v0.1.0/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=

pkg/wireguard/wireguard.go

@@ -2,14 +2,16 @@ package wireguard
 
 import (
 	"fmt"
-	"github.com/go-logr/logr"
 	"net"
+	"os"
 	"os/exec"
 	"syscall"
 
+	"github.com/go-logr/logr"
 	"github.com/jodevsa/wireguard-operator/pkg/agent"
 	"github.com/jodevsa/wireguard-operator/pkg/api/v1alpha1"
 	"github.com/vishvananda/netlink"
+	"golang.org/x/sys/unix"
 	"golang.zx2c4.com/wireguard/wgctrl"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
 )
@@ -71,17 +73,18 @@ func syncAddress(_ agent.State, iface string) error {
 }
 
 func createLinkUsingUserspaceImpl(iface string, wgUserspaceImplementationFallback string) error {
-
-	bashCommand := fmt.Sprintf("mkdir -p /dev/net && if [ ! -c /dev/net/tun ]; then\n    mknod /dev/net/tun c 10 200\nfi && %s %s", wgUserspaceImplementationFallback, iface)
-	cmd := exec.Command("bash", "-c", bashCommand)
-
-	err := cmd.Run()
-	if err != nil {
-		return err
+	if err := os.MkdirAll("/dev/net", 0o600); err != nil {
+		return fmt.Errorf("mkdir all: %w", err)
 	}
 
-	return nil
-
+	if _, err := os.Stat("/dev/net/tun"); os.IsNotExist(err) {
+		if err := unix.Mknod("/dev/net/tun", unix.S_IFIFO|0o600, int(unix.Mkdev(10, 100))); err != nil {
+			return fmt.Errorf("mknod: %w", err)
+		}
+	} else if err != nil {
+		return fmt.Errorf("stat: %w", err)
+	}
+	return exec.Command(wgUserspaceImplementationFallback, iface).Run()
 }
 
 func createLinkUsingKernalModule(iface string) error {