From dee9adc0f73d361d00a4d9230bb3517f2448b3b0 Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@golang.org>
Date: Fri, 24 Jun 2022 17:00:24 -0700
Subject: [PATCH] encoding/gob: use saferio to read large buffer

Avoid allocating large amounts of memory for corrupt input.

No test case because the problem can only happen for invalid data.
Let the fuzzer find cases like this.

Fixes #53369

Change-Id: I67c5e75bf181ad84988d6d6da12507df0e6df8e8
Reviewed-on: https://go-review.googlesource.com/c/go/+/413979
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Joedian Reid <joedian@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
---
 src/encoding/gob/decode.go  | 17 ++++++-----------
 src/encoding/gob/decoder.go |  6 ++++--
 src/go/build/deps_test.go   |  8 ++++----
 3 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/src/encoding/gob/decode.go b/src/encoding/gob/decode.go
index 7bca13c957..470e357b10 100644
--- a/src/encoding/gob/decode.go
+++ b/src/encoding/gob/decode.go
@@ -57,17 +57,6 @@ func (d *decBuffer) Drop(n int) {
 	d.offset += n
 }
 
-// Size grows the buffer to exactly n bytes, so d.Bytes() will
-// return a slice of length n. Existing data is first discarded.
-func (d *decBuffer) Size(n int) {
-	d.Reset()
-	if cap(d.data) < n {
-		d.data = make([]byte, n)
-	} else {
-		d.data = d.data[0:n]
-	}
-}
-
 func (d *decBuffer) ReadByte() (byte, error) {
 	if d.offset >= len(d.data) {
 		return 0, io.EOF
@@ -85,6 +74,12 @@ func (d *decBuffer) Bytes() []byte {
 	return d.data[d.offset:]
 }
 
+// SetBytes sets the buffer to the bytes, discarding any existing data.
+func (d *decBuffer) SetBytes(data []byte) {
+	d.data = data
+	d.offset = 0
+}
+
 func (d *decBuffer) Reset() {
 	d.data = d.data[0:0]
 	d.offset = 0
diff --git a/src/encoding/gob/decoder.go b/src/encoding/gob/decoder.go
index 9c4257eb3b..5b77adc7e8 100644
--- a/src/encoding/gob/decoder.go
+++ b/src/encoding/gob/decoder.go
@@ -7,6 +7,7 @@ package gob
 import (
 	"bufio"
 	"errors"
+	"internal/saferio"
 	"io"
 	"reflect"
 	"sync"
@@ -98,8 +99,9 @@ func (dec *Decoder) readMessage(nbytes int) {
 		panic("non-empty decoder buffer")
 	}
 	// Read the data
-	dec.buf.Size(nbytes)
-	_, dec.err = io.ReadFull(dec.r, dec.buf.Bytes())
+	var buf []byte
+	buf, dec.err = saferio.ReadData(dec.r, uint64(nbytes))
+	dec.buf.SetBytes(buf)
 	if dec.err == io.EOF {
 		dec.err = io.ErrUnexpectedEOF
 	}
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 07bac04dcb..19b886875c 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -187,6 +187,9 @@ var depsRules = `
 	  text/scanner,
 	  text/tabwriter;
 
+	io, reflect
+	< internal/saferio;
+
 	# encodings
 	# core ones do not use fmt.
 	io, strconv
@@ -200,7 +203,7 @@ var depsRules = `
 
 	fmt !< encoding/base32, encoding/base64;
 
-	FMT, encoding/base32, encoding/base64
+	FMT, encoding/base32, encoding/base64, internal/saferio
 	< encoding/ascii85, encoding/csv, encoding/gob, encoding/hex,
 	  encoding/json, encoding/pem, encoding/xml, mime;
 
@@ -239,9 +242,6 @@ var depsRules = `
 	encoding/binary, regexp
 	< index/suffixarray;
 
-	io, reflect
-	< internal/saferio;
-
 	# executable parsing
 	FMT, encoding/binary, compress/zlib, internal/saferio
 	< runtime/debug
-- 
2.50.0