Avoid crash in Chrome, issue 41487612 by michaelDCurran · Pull Request #16893 · nvaccess/nvda

michaelDCurran · 2024-07-23T01:10:05Z

Link to issue number:

Fixes Chrome issue 41487612
Fixes Chrome crash introduced in NVDA pr #14647

Summary of the issue:

Google has detected crashes in Chrome when users are running NVDA.
Exact steps to reproduce are not known, but it is when an NVDA virtual buffer is destroyed. Could be on Chrome exit, NVDA exit, or closing a Chrome window.
Chrome issue: https://issues.chromium.org/issues/41487612
It shows that a COM object tries to be released from an RPC worker thread by NVDA's in-process code, which causes Chrome to crash.

NVDA pr #14647 introduced code to hold a reference to the document root accessible on the virtual buffer, so that NVDA could check if the document had died. However, it is this COM object that is automatically released when the virtual buffer id destroyed from an RPC worker thread.
The COM object should really however be released when the virtual buffer is terminated in the correct UI thread, before destruction.

Description of user facing changes

No longer cause Google Chrome to crash when closing a document or exiting Chrome.

Description of development approach

VBufBackend_gecko_ia2::renderThread_terminate: correctly release the document root accessible.
VBufBackend_gecko_ia2's destructor: in the very unlikely case where the VBufBackend_gecko_ia2::renderThread_terminate has not been called, detach the document root accessible, leaking it rather than inappropriately releasing it on the wrong thread.

Testing strategy:

With Firefox and Google Chrome with NvDA running, open and close many documents, and exit the browser many times, ensuring that no crash occurs.

Known issues with pull request:

In the very unlikely case that the virtual buffer cannot be terminated in the UI thread correctly (Perhaps that thread has been terminated, or the browser is exiting such that wm_destroy messages are not being sent), the document root accessible will be leaked I.e. never released. This may hold memory or other resources. However, the original behaviour of calling release from the wrong thread was much worse as it could crash the browser entirely.

Code Review Checklist:

Documentation:
- Change log entry
- User Documentation
- Developer / Technical Documentation
- Context sensitive help for GUI changes
Testing:
- Unit tests
- System (end to end) tests
- Manual testing
UX of all users considered:
- Speech
- Braille
- Low Vision
- Different web browsers
- Localization in other languages / culture than English
API is compatible with existing add-ons.
Security precautions taken.

Summary by CodeRabbit

Bug Fixes
- Improved memory management and resource cleanup to prevent potential memory leaks.
- Enhanced stability of the backend by ensuring proper handling of critical resources during termination and destruction phases.

… when terminating the backend in the UI thread, and if this does not occur, leak the COM object rather than crashing the browser.

coderabbitai · 2024-07-23T01:10:12Z

Walkthrough

The changes enhance the GeckoVBufBackend_t class by improving resource management in the renderThread_terminate method and the destructor. The modifications ensure that the rootDocAcc reference is properly released during termination and destruction, addressing potential memory management issues and preventing resource leaks. This results in increased stability and safety within the lifecycle of the backend.

Changes

Files	Change Summary
`nvdaHelper/vbufBackends/gecko_ia2/gecko_ia2.cpp`	Modified `renderThread_terminate` and destructor to ensure proper release of `rootDocAcc`, improving memory management and stability.

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jcsteh · 2024-07-23T01:22:19Z

In the very unlikely case that the virtual buffer cannot be terminated in the UI thread correctly (Perhaps that thread has been terminated, or the browser is exiting such that wm_destroy messages are not being sent), the document root accessible will be leaked I.e. never released.

I think terminating a thread or terminating its message loop without cleaning up COM objects would be a violation of COM rules on the part of the application anyway, so I wouldn't consider this a problem with this PR as such.

jcsteh

Sorry for the oversight.

jcsteh · 2024-07-23T01:26:21Z

nvdaHelper/vbufBackends/gecko_ia2/gecko_ia2.cpp

+	// See https://issues.chromium.org/issues/41487612
+	// In most cases this will be released in renderThread_terminate.
+	// However in the unlikely case terminate can't run,
+	// it will be deleted along with the backend, but in an RPC thread!


This might be misconstrued to mean that even with the code below, it will be deleted from the wrong thread. Perhaps this could say "if we don't do anything here, it will be deleted along with..."

nvdaHelper/vbufBackends/gecko_ia2/gecko_ia2.cpp

seanbudd · 2024-07-28T23:49:02Z

user_docs/en/changes.md

 * Playing NVDA sounds no longer fails on a mono audio device. (#16770, @jcsteh)
 * NVDA will report addresses when arrowing through To/CC/BCC fields in outlook.com / Modern Outlook. (#16856)
 * NVDA now handles add-on installation failures more gracefully. (#16704)
+* No longer cause Google Chrome to crash when closing a document or exiting Chrome. (#16893)


can you move this to the "web browser fixes" sub-list at the start of bug fixes

CyrilleB79 · 2024-07-31T07:22:52Z

user_docs/en/changes.md

  * NVDA will correctly announce radio and checkbox menu items when first entering sub-menus in Google Chrome and Mozilla Firefox. (#14550)
  * NVDA's browse mode find functionality is now more accurate when the page contains emojis. (#16317, @LeonarddeR)
  * In Mozilla Firefox, NVDA now correctly reports the current character, word and line when the cursor is at the insertion point at the end of a line. (#3156, @jcsteh)
+  * No longer cause Google Chrome to crash when closing a document or exiting Chrome. (#16893)


@michaelDCurran or @seanbudd, I am reviewing the translation of this item.

Translating this sentence sounds a bit strange because grammatically, the subject is missing in this sentence.

Said otherwise, I wonder, what (or who) no longer causes Chrome to crash? Is it NVDA?

Or maybe I haven't understood the sentence correctly...

jcsteh · 2024-07-31T07:25:51Z

This should be: NVDA no longer causes Google Chrome to crash when closing a document or exiting Chrome.

Gecko_ia2 vbufBackend: ensure we release the document root accessible…

aad11f1

… when terminating the backend in the UI thread, and if this does not occur, leak the COM object rather than crashing the browser.

michaelDCurran requested a review from a team as a code owner July 23, 2024 01:10

michaelDCurran requested review from gerald-hartig and removed request for a team July 23, 2024 01:10

michaelDCurran requested a review from jcsteh July 23, 2024 01:11

michaelDCurran added this to the 2024.3 milestone Jul 23, 2024

jcsteh previously approved these changes Jul 23, 2024

View reviewed changes

Gecko vbufBackend: add assertion

1709917

michaelDCurran dismissed jcsteh’s stale review via 1709917 July 23, 2024 01:31

michaelDCurran added 2 commits July 23, 2024 12:58

Clarify comment

9a41e9f

Update what's new

0a151bc

seanbudd previously approved these changes Jul 28, 2024

View reviewed changes

seanbudd dismissed their stale review via bd7b688 July 28, 2024 23:49

seanbudd and others added 2 commits July 29, 2024 09:49

lint fixes

bd7b688

Update what's new

13caf00

seanbudd approved these changes Jul 29, 2024

View reviewed changes

seanbudd merged commit c78f338 into beta Jul 29, 2024

seanbudd deleted the chromeIssue41487612 branch July 29, 2024 00:54

CyrilleB79 reviewed Jul 31, 2024

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Avoid crash in Chrome, issue 41487612#16893

Avoid crash in Chrome, issue 41487612#16893
seanbudd merged 6 commits intobetafrom
chromeIssue41487612

michaelDCurran commented Jul 23, 2024 •

edited by seanbudd

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Link to issue number:

Summary of the issue:

Description of user facing changes

Description of development approach

Testing strategy:

Known issues with pull request:

Code Review Checklist:

Summary by CodeRabbit

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michaelDCurran commented Jul 23, 2024 •

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