encoding/binary: read at most MaxVarintLen64 bytes in ReadUvarint
This CL ensures that ReadUvarint consumes only a limited
amount of input (instead of an unbounded amount).
On some inputs, ReadUvarint could read an arbitrary number
of bytes before deciding to return an overflow error.
After this CL, ReadUvarint returns that same overflow
error sooner, after reading at most MaxVarintLen64 bytes.
Fix authored by Robert Griesemer and Filippo Valsorda.
Thanks to Diederik Loerakker, Jonny Rhea, Raúl Kripalani,
and Preston Van Loon for reporting this.
Fixes #40618
Fixes CVE-2020-16845
Change-Id: Ie0cb15972f14c38b7cf7af84c45c4ce54909bb8f
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/812099
Reviewed-by: Filippo Valsorda <valsorda@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/247120
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
diff --git a/src/encoding/binary/varint.go b/src/encoding/binary/varint.go
index bcb8ac9..38af610 100644
--- a/src/encoding/binary/varint.go
+++ b/src/encoding/binary/varint.go
@@ -106,13 +106,13 @@
func ReadUvarint(r io.ByteReader) (uint64, error) {
var x uint64
var s uint
- for i := 0; ; i++ {
+ for i := 0; i < MaxVarintLen64; i++ {
b, err := r.ReadByte()
if err != nil {
return x, err
}
if b < 0x80 {
- if i > 9 || i == 9 && b > 1 {
+ if i == 9 && b > 1 {
return x, overflow
}
return x | uint64(b)<<s, nil
@@ -120,6 +120,7 @@
x |= uint64(b&0x7f) << s
s += 7
}
+ return x, overflow
}
// ReadVarint reads an encoded signed integer from r and returns it as an int64.
diff --git a/src/encoding/binary/varint_test.go b/src/encoding/binary/varint_test.go
index ca411ec..6ef4c99 100644
--- a/src/encoding/binary/varint_test.go
+++ b/src/encoding/binary/varint_test.go
@@ -121,21 +121,27 @@
}
}
-func testOverflow(t *testing.T, buf []byte, n0 int, err0 error) {
+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)
}
- x, err := ReadUvarint(bytes.NewReader(buf))
- if x != 0 || err != err0 {
- t.Errorf("ReadUvarint(%v): got x = %d, err = %s; want 0, %s", buf, x, err, err0)
+ r := bytes.NewReader(buf)
+ len := r.Len()
+ x, err := ReadUvarint(r)
+ if x != x0 || err != err0 {
+ t.Errorf("ReadUvarint(%v): got x = %d, err = %s; want %d, %s", buf, x, err, x0, err0)
+ }
+ if read := len - r.Len(); read > MaxVarintLen64 {
+ t.Errorf("ReadUvarint(%v): read more than MaxVarintLen64 bytes, got %d", buf, read)
}
}
func TestOverflow(t *testing.T) {
- testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x2}, -10, overflow)
- testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x1, 0, 0}, -13, overflow)
+ 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
}
func TestNonCanonicalZero(t *testing.T) {
