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buffer: backport --zero-fill-buffers cli option · nodejs/node@fb03e57 · GitHub

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jasnell
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Myles Borins
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buffer: backport --zero-fill-buffers cli option
This backports the --zero-fill-buffers command line flag introduced in master. When used, all Buffer and SlowBuffer instances will zero fill by default. This does *not* backport any of the other Buffer API or behavior changes. PR-URL: #5745 Reviewed-By: Trevor Norris <trev.norris@gmail.com>
1 parent 55f8689 commit fb03e57

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‎doc/api/buffer.markdown‎

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@@ -145,6 +145,23 @@ for (var b of buf)
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Additionally, the [`buf.values()`][], [`buf.keys()`][], and
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[`buf.entries()`][] methods can be used to create iterators.
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## The `--zero-fill-buffers` command line option
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Node.js can be started using the `--zero-fill-buffers` command line option to
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force all newly allocated `Buffer` and `SlowBuffer` instances created using
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either `new Buffer(size)` and `new SlowBuffer(size)` to be *automatically
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zero-filled* upon creation. Use of this flag *changes the default behavior* of
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these methods and *can have a significant impact* on performance. Use of the
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`--zero-fill-buffers` option is recommended only when absolutely necessary to
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enforce that newly allocated `Buffer` instances cannot contain potentially
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sensitive data.
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```
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$ node --zero-fill-buffers
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> Buffer(5);
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<Buffer 00 00 00 00 00>
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```
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## Class: Buffer
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The Buffer class is a global type for dealing with binary data directly.

‎doc/node.1‎

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@@ -95,6 +95,10 @@ Process v8 profiler output generated using the v8 option \fB\-\-prof\fR
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.BR \-\-v8\-options
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Print v8 command line options.
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.TP
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.BR \-\-zero\-fill\-buffers
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Automatically zero-fills all newly allocated Buffer and SlowBuffer instances.
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.TP
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.BR \-\-tls\-cipher\-list =\fIlist\fR
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Specify an alternative default TLS cipher list. (Requires Node.js to be built with crypto support. (Default))

‎src/node.cc‎

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@@ -947,7 +947,9 @@ Local<Value> WinapiErrnoException(Isolate* isolate,
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void* ArrayBufferAllocator::Allocate(size_t size) {
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if (env_ == nullptr || !env_->array_buffer_allocator_info()->no_zero_fill())
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if (env_ == nullptr ||
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!env_->array_buffer_allocator_info()->no_zero_fill() ||
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zero_fill_all_buffers)
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return calloc(size, 1);
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env_->array_buffer_allocator_info()->reset_fill_flag();
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return malloc(size);
@@ -3283,6 +3285,8 @@ static void PrintHelp() {
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"snapshots\n"
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" --prof-process process v8 profiler output generated\n"
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" using --prof\n"
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" --zero-fill-buffers automatically zero-fill all newly allocated\n"
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" Buffer and SlowBuffer instances\n"
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" --v8-options print v8 command line options\n"
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#if HAVE_OPENSSL
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" --tls-cipher-list=val use an alternative default TLS cipher list\n"
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} else if (strcmp(arg, "--prof-process") == 0) {
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prof_process = true;
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short_circuit = true;
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} else if (strcmp(arg, "--zero-fill-buffers") == 0) {
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zero_fill_all_buffers = true;
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} else if (strcmp(arg, "--v8-options") == 0) {
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new_v8_argv[new_v8_argc] = "--help";
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new_v8_argc += 1;

‎src/node_buffer.cc‎

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@@ -48,7 +48,14 @@
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CHECK_NOT_OOB(end <= end_max); \
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size_t length = end - start;
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#define BUFFER_MALLOC(length) \
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zero_fill_all_buffers ? calloc(length, 1) : malloc(length)
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namespace node {
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// if true, all Buffer and SlowBuffer instances will automatically zero-fill
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bool zero_fill_all_buffers = false;
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namespace Buffer {
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using v8::ArrayBuffer;
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// nullptr for zero-sized allocation requests. Normalize by always using
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// a nullptr.
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if (length > 0) {
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data = static_cast<char*>(malloc(length));
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data = static_cast<char*>(BUFFER_MALLOC(length));
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if (data == nullptr)
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return Local<Object>();
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void* data;
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if (length > 0) {
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data = malloc(length);
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data = BUFFER_MALLOC(length);
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if (data == nullptr)
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return Local<Object>();
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} else {

‎src/node_buffer.h‎

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#include "v8.h"
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namespace node {
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extern bool zero_fill_all_buffers;
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namespace Buffer {
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static const unsigned int kMaxLength =

‎test/parallel/test-buffer-zero-fill-cli.js‎

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'use strict';
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// Flags: --zero-fill-buffers
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// when using --zero-fill-buffers, every Buffer and SlowBuffer
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// instance must be zero filled upon creation
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require('../common');
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const SlowBuffer = require('buffer').SlowBuffer;
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const assert = require('assert');
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function isZeroFilled(buf) {
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for (let n = 0; n < buf.length; n++)
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if (buf[n] > 0) return false;
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return true;
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}
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// This can be somewhat unreliable because the
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// allocated memory might just already happen to
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// contain all zeroes. The test is run multiple
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// times to improve the reliability.
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for (let i = 0; i < 50; i++) {
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const bufs = [
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SlowBuffer(20),
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Buffer(20),
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new SlowBuffer(20)
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];
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for (const buf of bufs) {
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assert(isZeroFilled(buf));
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}
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}

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