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encoding/base32: reduce the overflow risk when computing encode/decode length

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This commit is contained in:
chanxuehong 2023-07-24 15:29:47 +08:00
parent 7141d1e6d8
commit 652c8c6712
2 changed files with 82 additions and 47 deletions
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5
src/encoding/base32/base32.go
View File

@ -271,7 +271,7 @@ 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 + 4) / 5
return n/5*8 + (n%5*8+4)/5
}
return (n + 4) / 5 * 8
}
@ -545,8 +545,7 @@ func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
// corresponding to n bytes of base32-encoded data.
func (enc *Encoding) DecodedLen(n int) int {
if enc.padChar == NoPadding {
return n * 5 / 8
return n/8*5 + n%8*5/8
}
return n / 8 * 5
}

124
src/encoding/base32/base32_test.go
View File

@ -8,6 +8,8 @@ import (
"bytes"
"errors"
"io"
"math"
"strconv"
"strings"
"testing"
)
@ -679,52 +681,86 @@ func TestBufferedDecodingPadding(t *testing.T) {
}
}
func TestEncodedDecodedLen(t *testing.T) {
func TestEncodedLen(t *testing.T) {
var rawStdEncoding = StdEncoding.WithPadding(NoPadding)
type test struct {
in int
wantEnc int
wantDec int
enc *Encoding
n int
want int64
}
data := bytes.Repeat([]byte("x"), 100)
for _, test := range []struct {
name string
enc *Encoding
cases []test
}{
{"StdEncoding", StdEncoding, []test{
{0, 0, 0},
{1, 8, 5},
{5, 8, 5},
{6, 16, 10},
{10, 16, 10},
}},
{"NoPadding", StdEncoding.WithPadding(NoPadding), []test{
{0, 0, 0},
{1, 2, 1},
{2, 4, 2},
{5, 8, 5},
{6, 10, 6},
{7, 12, 7},
{10, 16, 10},
{11, 18, 11},
}},
} {
t.Run(test.name, func(t *testing.T) {
for _, tc := range test.cases {
encLen := test.enc.EncodedLen(tc.in)
decLen := test.enc.DecodedLen(encLen)
enc := test.enc.EncodeToString(data[:tc.in])
if len(enc) != encLen {
t.Fatalf("EncodedLen(%d) = %d but encoded to %q (%d)", tc.in, encLen, enc, len(enc))
}
if encLen != tc.wantEnc {
t.Fatalf("EncodedLen(%d) = %d; want %d", tc.in, encLen, tc.wantEnc)
}
if decLen != tc.wantDec {
t.Fatalf("DecodedLen(%d) = %d; want %d", encLen, decLen, tc.wantDec)
}
}
})
tests := []test{
{StdEncoding, 0, 0},
{StdEncoding, 1, 8},
{StdEncoding, 2, 8},
{StdEncoding, 3, 8},
{StdEncoding, 4, 8},
{StdEncoding, 5, 8},
{StdEncoding, 6, 16},
{StdEncoding, 10, 16},
{StdEncoding, 11, 24},
{rawStdEncoding, 0, 0},
{rawStdEncoding, 1, 2},
{rawStdEncoding, 2, 4},
{rawStdEncoding, 3, 5},
{rawStdEncoding, 4, 7},
{rawStdEncoding, 5, 8},
{rawStdEncoding, 6, 10},
{rawStdEncoding, 7, 12},
{rawStdEncoding, 10, 16},
{rawStdEncoding, 11, 18},
}
// check overflow
switch strconv.IntSize {
case 32:
tests = append(tests, test{rawStdEncoding, (math.MaxInt-4)/8 + 1, 429496730})
tests = append(tests, test{rawStdEncoding, math.MaxInt/8*5 + 4, math.MaxInt})
case 64:
tests = append(tests, test{rawStdEncoding, (math.MaxInt-4)/8 + 1, 1844674407370955162})
tests = append(tests, test{rawStdEncoding, math.MaxInt/8*5 + 4, 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) {
var rawStdEncoding = StdEncoding.WithPadding(NoPadding)
type test struct {
enc *Encoding
n int
want int64
}
tests := []test{
{StdEncoding, 0, 0},
{StdEncoding, 8, 5},
{StdEncoding, 16, 10},
{StdEncoding, 24, 15},
{rawStdEncoding, 0, 0},
{rawStdEncoding, 2, 1},
{rawStdEncoding, 4, 2},
{rawStdEncoding, 5, 3},
{rawStdEncoding, 7, 4},
{rawStdEncoding, 8, 5},
{rawStdEncoding, 10, 6},
{rawStdEncoding, 12, 7},
{rawStdEncoding, 16, 10},
{rawStdEncoding, 18, 11},
}
// check overflow
switch strconv.IntSize {
case 32:
tests = append(tests, test{rawStdEncoding, math.MaxInt/5 + 1, 268435456})
tests = append(tests, test{rawStdEncoding, math.MaxInt, 1342177279})
case 64:
tests = append(tests, test{rawStdEncoding, math.MaxInt/5 + 1, 1152921504606846976})
tests = append(tests, test{rawStdEncoding, math.MaxInt, 5764607523034234879})
}
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)
}
}
}