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encoding/binary: limit bytes read by Uvarint to <= 10

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Limits the number of bytes that can be consumed by Uvarint
to MaxVarintLen64 (10) to avoid wasted computations.
With this change, if Uvarint reads more than MaxVarintLen64
bytes, it'll return the erroring byte count of n=-(MaxVarintLen64+1)
which is -11, as per the function signature.

Updated some tests to reflect the new change in expectations of n
when the number of bytes to be read exceeds the limits..

Fixes #41185

Change-Id: Ie346457b1ddb0214b60c72e81128e24d604d083d
Reviewed-on: https://go-review.googlesource.com/c/go/+/299531
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
This commit is contained in:
Emmanuel T Odeke 2021-03-06 23:14:21 -08:00 committed by Emmanuel Odeke
parent 125eca0f72
commit aafad20b61
2 changed files with 66 additions and 4 deletions
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7
src/encoding/binary/varint.go
View File

@ -61,8 +61,13 @@ func Uvarint(buf []byte) (uint64, int) {
var x uint64
var s uint
for i, b := range buf {
if i == MaxVarintLen64 {
// Catch byte reads past MaxVarintLen64.
// See issue https://golang.org/issues/41185
return 0, -(i + 1) // overflow
}
if b < 0x80 {
if i >= MaxVarintLen64 || i == MaxVarintLen64-1 && b > 1 {
if i == MaxVarintLen64-1 && b > 1 {
return 0, -(i + 1) // overflow
}
return x | uint64(b)<<s, i + 1

63
src/encoding/binary/varint_test.go
View File

@ -7,6 +7,7 @@ package binary
import (
"bytes"
"io"
"math"
"testing"
)
@ -121,10 +122,66 @@ func TestBufferTooSmall(t *testing.T) {
}
}
// Ensure that we catch overflows of bytes going past MaxVarintLen64.
// See issue https://golang.org/issues/41185
func TestBufferTooBigWithOverflow(t *testing.T) {
tests := []struct {
in []byte
name string
wantN int
wantValue uint64
}{
{
name: "invalid: 1000 bytes",
in: func() []byte {
b := make([]byte, 1000)
for i := range b {
b[i] = 0xff
}
b[999] = 0
return b
}(),
wantN: -11,
wantValue: 0,
},
{
name: "valid: math.MaxUint64-40",
in: []byte{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x01},
wantValue: math.MaxUint64 - 40,
wantN: 10,
},
{
name: "invalid: with more than MaxVarintLen64 bytes",
in: []byte{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x01},
wantN: -11,
wantValue: 0,
},
{
name: "invalid: 10th byte",
in: []byte{0xd7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f},
wantN: -10,
wantValue: 0,
},
}
for _, tt := range tests {
tt := tt
t.Run(tt.name, func(t *testing.T) {
value, n := Uvarint(tt.in)
if g, w := n, tt.wantN; g != w {
t.Errorf("bytes returned=%d, want=%d", g, w)
}
if g, w := value, tt.wantValue; g != w {
t.Errorf("value=%d, want=%d", g, w)
}
})
}
}
func testOverflow(t *testing.T, buf []byte, x0 uint64, n0 int, err0 error) {
x, n := Uvarint(buf)
if x != 0 || n != n0 {
t.Errorf("Uvarint(%v): got x = %d, n = %d; want 0, %d", buf, x, n, n0)
t.Errorf("Uvarint(% X): got x = %d, n = %d; want 0, %d", buf, x, n, n0)
}
r := bytes.NewReader(buf)
@ -140,8 +197,8 @@ func testOverflow(t *testing.T, buf []byte, x0 uint64, n0 int, err0 error) {
func TestOverflow(t *testing.T) {
testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x2}, 0, -10, overflow)
testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x1, 0, 0}, 0, -13, overflow)
testOverflow(t, []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}, 1<<64-1, 0, overflow) // 11 bytes, should overflow
testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x1, 0, 0}, 0, -11, overflow)
testOverflow(t, []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}, 1<<64-1, -11, overflow) // 11 bytes, should overflow
}
func TestNonCanonicalZero(t *testing.T) {