1608440 - Firefox UI freeze when Web Worker loads large script

Status: RESOLVED FIXED

(Core :: DOM: Workers, defect, P2)

Description

[Claas Augner [:claas]]

This behavior could be abused by malicious sites to freeze Firefox indefinitely (by loading the large script in a loop).

Steps to reproduce the behavior:

1. See repository: https://github.com/caugner/vue-ffmpeg-worker-firefox-freeze
2. git clone https://github.com/caugner/vue-ffmpeg-worker-firefox-freeze
3. cd vue-ffmpeg-worker-firefox-freeze
4. yarn install
5. yarn serve
6. Open http://localhost:8080 in Firefox.
7. Notice how the UI freezes (the website itself does not always freeze).

See also: https://github.com/ffmpegjs/ffmpeg.js/issues/19

Note that Chrome does not behave this way.

PS: The relevant JS code is in App.vue and Worker.js at commit ae36e0a: https://github.com/caugner/vue-ffmpeg-worker-firefox-freeze/commit/ae36e0a86aedc49a0065cf64d3325c5047699029#diff-ea994a51b0d9884f4fc046eca11a5c99

Comment 1

[Claas Augner [:claas]]

Here's a direct link to reproduce the Firefox UI freeze: https://caugner.github.io/vue-ffmpeg-worker-firefox-freeze/

Comment 2

[Claas Augner [:claas]]

Firefox Profiler: https://perfht.ml/2Xy4kMq

Note the 6.8s event processing delay at the top. That's the freeze.

Comment 3

[Claas Augner [:claas]]

I cannot reproduce the freeze in Firefox 78.0a1 (2020-05-05) (64-Bit).

Comment 4

[Claas Augner [:claas]]

I cannot reproduce the freeze in Firefox 76.0 either, so I assume that the issue has been fixed.