Fix potential overflow in promptenc arithmetic

wavesrv/pkg/promptenc/promptenc.go

@@ -12,6 +12,7 @@ import (
 	"io"
 	"reflect"
 
+	"github.com/wavetermdev/waveterm/wavesrv/pkg/utilfn"
 	ccp "golang.org/x/crypto/chacha20poly1305"
 )
 
@@ -65,9 +66,13 @@ func MakeEncryptorB64(key64 string) (*Encryptor, error) {
 }
 
 func (enc *Encryptor) EncryptData(plainText []byte, odata string) ([]byte, error) {
-	outputBuf := make([]byte, enc.AEAD.NonceSize()+enc.AEAD.Overhead()+len(plainText))
+	bufSize, err := utilfn.AddIntSlice(enc.AEAD.NonceSize(), enc.AEAD.Overhead(), len(plainText))
+	if err != nil {
+		return nil, err
+	}
+	outputBuf := make([]byte, bufSize)
 	nonce := outputBuf[0:enc.AEAD.NonceSize()]
-	_, err := io.ReadFull(rand.Reader, nonce)
+	_, err = io.ReadFull(rand.Reader, nonce)
 	if err != nil {
 		return nil, err
 	}

wavesrv/pkg/utilfn/utilfn.go

@@ -6,6 +6,8 @@ package utilfn
 import (
 	"crypto/sha1"
 	"encoding/base64"
+	"errors"
+	"math"
 	"regexp"
 	"strings"
 	"unicode/utf8"
@@ -209,3 +211,32 @@ func ChunkSlice[T any](s []T, chunkSize int) [][]T {
 	}
 	return rtn
 }
+
+var ErrOverflow = errors.New("integer overflow")
+
+// Add two int values, returning an error if the result overflows.
+func AddInt(left, right int) (int, error) {
+	if right > 0 {
+		if left > math.MaxInt-right {
+			return 0, ErrOverflow
+		}
+	} else {
+		if left < math.MaxInt-right {
+			return 0, ErrOverflow
+		}
+	}
+	return left + right, nil
+}
+
+// Add a slice of ints, returning an error if the result overflows.
+func AddIntSlice(vals ...int) (int, error) {
+	var rtn int
+	for _, v := range vals {
+		var err error
+		rtn, err = AddInt(rtn, v)
+		if err != nil {
+			return 0, err
+		}
+	}
+	return rtn, nil
+}

wavesrv/pkg/utilfn/utilfn_test.go

@@ -5,6 +5,7 @@ package utilfn
 
 import (
 	"fmt"
+	"math"
 	"testing"
 )
 
@@ -49,3 +50,56 @@ func TestDiff(t *testing.T) {
 	testDiff(t, Str1, Str3)
 	testDiff(t, Str3, Str1)
 }
+
+const unexpectedError = "unexpected error"
+const expectedError = "expected error"
+const wrongRetVal = "wrong return value"
+
+func testAddInt(t *testing.T, a int, b int, shouldError bool, expected int) {
+	retVal, err := AddInt(a, b)
+	if err != nil {
+		if !shouldError {
+			t.Errorf(unexpectedError)
+		}
+		return
+	}
+	if shouldError {
+		t.Errorf(expectedError)
+		return
+	}
+	if retVal != expected {
+		t.Errorf(wrongRetVal)
+	}
+}
+
+func TestAddInt(t *testing.T) {
+	testAddInt(t, 1, 2, false, 3)
+	testAddInt(t, 1, math.MaxInt, true, 0)
+}
+
+func testAddIntSlice(t *testing.T, shouldError bool, expected int, vals ...int) {
+	retVal, err := AddIntSlice(vals...)
+	if err != nil {
+		if !shouldError {
+			t.Errorf(unexpectedError)
+		}
+		return
+	}
+	if shouldError {
+		t.Errorf(expectedError)
+		return
+	}
+	if retVal != expected {
+		t.Errorf(wrongRetVal)
+	}
+}
+
+func TestAddIntSlice(t *testing.T) {
+	testAddIntSlice(t, false, 0)
+	testAddIntSlice(t, false, 1, 1)
+	testAddIntSlice(t, false, 3, 1, 2)
+	testAddIntSlice(t, false, 6, 1, 2, 3)
+	testAddIntSlice(t, true, 0, 1, math.MaxInt)
+	testAddIntSlice(t, true, 0, 1, 2, math.MaxInt)
+	testAddIntSlice(t, true, 0, math.MaxInt, 2, 1)
+}