Lua: Sandbox by default (whitelisted functions); Disable inline scripts for now; Add more checks for security reasons (#7136)

https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6158632073
https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6170831601
https://github.com/XTLS/Xray-core/pull/7136#issuecomment-6184362904

common/lua/privileged.go

@@ -0,0 +1,117 @@
+package lua
+
+import (
+	"bytes"
+	"crypto/ed25519"
+	"crypto/sha256"
+	"encoding/base64"
+	"sync"
+
+	"github.com/xtls/xray-core/common/errors"
+)
+
+var privilegedKey struct {
+	sync.Once
+	publicKey ed25519.PublicKey
+}
+
+// SetPrivilegedPublicKey configures the trusted Ed25519 public key once at
+// startup, before compiling scripts. An empty value disables authorization.
+// Nonempty values must be unpadded Base64URL encodings of exactly 32 bytes.
+func SetPrivilegedPublicKey(value string) error {
+	var publicKey ed25519.PublicKey
+	if value != "" {
+		decoded, err := decodePrivilegedValue(value, ed25519.PublicKeySize)
+		if err != nil {
+			return errors.New("invalid Lua privileged public key").Base(err)
+		}
+		publicKey = ed25519.PublicKey(decoded)
+	}
+	privilegedKey.Do(func() {
+		privilegedKey.publicKey = publicKey
+	})
+	return nil
+}
+
+func decodePrivilegedValue(value string, size int) ([]byte, error) {
+	encoding := base64.RawURLEncoding.Strict()
+	if len(value) != encoding.EncodedLen(size) {
+		return nil, errors.New("expected an unpadded Base64URL encoding of ", size, " bytes")
+	}
+	decoded, err := encoding.DecodeString(value)
+	if err != nil || len(decoded) != size || encoding.EncodeToString(decoded) != value {
+		return nil, errors.New("expected an unpadded Base64URL encoding of ", size, " bytes")
+	}
+	return decoded, nil
+}
+
+func verifyPrivilegedSignature(code []byte) (bool, error) {
+	_, end, value, found := privilegedSignatureLine(code)
+	if !found {
+		return false, nil
+	}
+
+	publicKey := privilegedKey.publicKey
+	if len(publicKey) == 0 {
+		return false, errors.New("Lua privileged signature requires --lua-privileged-pubkey")
+	}
+	signature, err := decodePrivilegedValue(string(bytes.TrimSpace(value)), ed25519.SignatureSize)
+	if err != nil {
+		return false, errors.New("invalid Lua privileged signature").Base(err)
+	}
+	digest := sha256.Sum256(bytes.TrimSpace(code[end:]))
+	if !ed25519.Verify(publicKey, digest[:], signature) {
+		return false, errors.New("Lua privileged signature verification failed")
+	}
+	return true, nil
+}
+
+// SignPrivilegedScript signs the script body, then prepends or replaces the signature line.
+func SignPrivilegedScript(code []byte, seed string) ([]byte, error) {
+	decoded, err := decodePrivilegedValue(seed, ed25519.SeedSize)
+	if err != nil {
+		return nil, errors.New("invalid Ed25519 private key seed").Base(err)
+	}
+
+	start, end, _, found := privilegedSignatureLine(code)
+	body := code
+	if found {
+		body = code[end:]
+	}
+
+	digest := sha256.Sum256(bytes.TrimSpace(body))
+	signature := ed25519.Sign(ed25519.NewKeyFromSeed(decoded), digest[:])
+	header := []byte("-- @xray:privileged-signature=" + base64.RawURLEncoding.EncodeToString(signature))
+
+	if !found {
+		if newline := bytes.IndexByte(code, '\n'); newline > 0 && code[newline-1] == '\r' {
+			header = append(header, '\r')
+		}
+		header = append(header, '\n')
+		return append(header, code...), nil
+	}
+	signed := make([]byte, 0, start+len(header)+len(code)-end)
+	signed = append(signed, code[:start]...)
+	signed = append(signed, header...)
+	return append(signed, code[end:]...), nil
+}
+
+func privilegedSignatureLine(code []byte) (start, end int, value []byte, found bool) {
+	for rest := code; len(rest) != 0; {
+		start = len(code) - len(rest)
+		var line []byte
+		line, rest, _ = bytes.Cut(rest, []byte{'\n'})
+		line = bytes.TrimSuffix(line, []byte{'\r'})
+		if len(bytes.TrimSpace(line)) == 0 {
+			continue
+		}
+		end = start + len(line)
+		line, found := bytes.CutPrefix(bytes.TrimLeft(line, " \t"), []byte("--"))
+		if !found {
+			return 0, 0, nil, false
+		}
+		value, found = bytes.CutPrefix(bytes.TrimLeft(line, " \t"), []byte("@xray:privileged-signature="))
+		return start, end, value, found
+	}
+	return 0, 0, nil, false
+}