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encoding/base64: reduce the overflow risk when computing encode/decode length

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This commit is contained in:
chanxuehong 2023-07-18 14:18:50 +08:00
parent 5fe3f0a265
commit c19527a26b
2 changed files with 36 additions and 12 deletions
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4
src/encoding/base64/base64.go
View File

@ -278,7 +278,7 @@ func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
// of an input buffer of length n.
func (enc *Encoding) EncodedLen(n int) int {
if enc.padChar == NoPadding {
return (n*8 + 5) / 6 // minimum # chars at 6 bits per char
return n/3*4 + (n%3*8+5)/6 // minimum # chars at 6 bits per char
}
return (n + 2) / 3 * 4 // minimum # 4-char quanta, 3 bytes each
}
@ -623,7 +623,7 @@ func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
func (enc *Encoding) DecodedLen(n int) int {
if enc.padChar == NoPadding {
// Unpadded data may end with partial block of 2-3 characters.
return n * 6 / 8
return n/4*3 + n%4*6/8
}
// Padded base64 should always be a multiple of 4 characters in length.
return n / 4 * 3

44
src/encoding/base64/base64_test.go
View File

@ -9,8 +9,10 @@ import (
"errors"
"fmt"
"io"
"math"
"reflect"
"runtime/debug"
"strconv"
"strings"
"testing"
"time"
@ -262,11 +264,12 @@ func TestDecodeBounds(t *testing.T) {
}
func TestEncodedLen(t *testing.T) {
for _, tt := range []struct {
type test struct {
enc *Encoding
n int
want int
}{
want int64
}
tests := []test{
{RawStdEncoding, 0, 0},
{RawStdEncoding, 1, 2},
{RawStdEncoding, 2, 3},
@ -278,19 +281,30 @@ func TestEncodedLen(t *testing.T) {
{StdEncoding, 3, 4},
{StdEncoding, 4, 8},
{StdEncoding, 7, 12},
} {
if got := tt.enc.EncodedLen(tt.n); got != tt.want {
}
// check overflow
switch strconv.IntSize {
case 32:
tests = append(tests, test{RawStdEncoding, (math.MaxInt-5)/8 + 1, 357913942})
tests = append(tests, test{RawStdEncoding, math.MaxInt/4*3 + 2, math.MaxInt})
case 64:
tests = append(tests, test{RawStdEncoding, (math.MaxInt-5)/8 + 1, 1537228672809129302})
tests = append(tests, test{RawStdEncoding, math.MaxInt/4*3 + 2, math.MaxInt})
}
for _, tt := range tests {
if got := tt.enc.EncodedLen(tt.n); int64(got) != tt.want {
t.Errorf("EncodedLen(%d): got %d, want %d", tt.n, got, tt.want)
}
}
}
func TestDecodedLen(t *testing.T) {
for _, tt := range []struct {
type test struct {
enc *Encoding
n int
want int
}{
want int64
}
tests := []test{
{RawStdEncoding, 0, 0},
{RawStdEncoding, 2, 1},
{RawStdEncoding, 3, 2},
@ -299,8 +313,18 @@ func TestDecodedLen(t *testing.T) {
{StdEncoding, 0, 0},
{StdEncoding, 4, 3},
{StdEncoding, 8, 6},
} {
if got := tt.enc.DecodedLen(tt.n); got != tt.want {
}
// check overflow
switch strconv.IntSize {
case 32:
tests = append(tests, test{RawStdEncoding, math.MaxInt/6 + 1, 268435456})
tests = append(tests, test{RawStdEncoding, math.MaxInt, 1610612735})
case 64:
tests = append(tests, test{RawStdEncoding, math.MaxInt/6 + 1, 1152921504606846976})
tests = append(tests, test{RawStdEncoding, math.MaxInt, 6917529027641081855})
}
for _, tt := range tests {
if got := tt.enc.DecodedLen(tt.n); int64(got) != tt.want {
t.Errorf("DecodedLen(%d): got %d, want %d", tt.n, got, tt.want)
}
}