feat: add check permission

cmd/cmd.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/binary"
 	"fmt"
+	"gotproxy/common"
 	"log"
 	"net"
 	"os"
@@ -29,6 +30,14 @@ var rootCmd = &cobra.Command{
 			ProxyPort: proxyPort,
 		}
 
+		if ok, err := common.HasPermission(); err != nil {
+			log.Fatal("check capabilities failed: ", err)
+			return
+		} else if !ok {
+			log.Fatal("gotproxy requires CAP_BPF to run. Please run gotproxy with sudo.")
+			return
+		}
+
 		ip, err := ipStrToUnit32()
 		if err != nil {
 			log.Fatal(err)

common/permission.go

@@ -0,0 +1,24 @@
+package common
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+const (
+	// capBpf 0000 0000 0000 0000 0000 0000 1000 0000
+	capBpf = 1 << (unix.CAP_BPF - 32)
+	// capSysAdmin 0000 0000 0010 0000 0000 0000 0000 0000
+	capSysAdmin = 1 << unix.CAP_SYS_ADMIN
+)
+
+// HasPermission reference: https://man7.org/linux/man-pages/man2/capset.2.html
+func HasPermission() (bool, error) {
+	hdr := unix.CapUserHeader{Version: unix.LINUX_CAPABILITY_VERSION_3}
+	var data [2]unix.CapUserData
+	if err := unix.Capget(&hdr, &data[0]); err != nil {
+		return false, err
+	}
+	// Note that the CAP_* values are bit indexes and need to be bit-shifted before ORing into the bit fields.
+	// Note that 64-bit capabilities use datap[0] and datap[1], whereas 32-bit capabilities use only datap[0].
+	return data[1].Permitted&capBpf != 0 || data[0].Permitted&capSysAdmin != 0, nil
+}