[tbb-bugs] #19193 [Applications/Tor Browser]: AudioContext, HTMLMediaElement, and MediaStream provide currentTime to content scripts

[Tor Bug Tracker & Wiki]

#19193: AudioContext, HTMLMediaElement, and MediaStream provide currentTime to
content scripts
--------------------------------------+------------------------------
 Reporter:  arthuredelstein           |          Owner:  tbb-team
     Type:  defect                    |         Status:  needs_review
 Priority:  Medium                    |      Milestone:
Component:  Applications/Tor Browser  |        Version:
 Severity:  Normal                    |     Resolution:
 Keywords:  TorBrowserTeam201605R     |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
--------------------------------------+------------------------------
Changes (by arthuredelstein):

 * status:  new => needs_review
 * keywords:  TorBrowserTeam201605 => TorBrowserTeam201605R


Old description:

> The worst offender is probably AudioContext, where you can get
> the current time thus:
>
> {{{
> var audioContext = new AudioContext();
> audioContext.currentTime;
> }}}
>
> Similarly, HTMLVideoElement.currentTime, HTMLAudioElement.currentTime,
> and CanvasCaptureMediaStream.currentTime can be used as a time source
> with resolution better than 10 ms.

New description:

 The worst offender is probably AudioContext, where you can get
 the current time thus:

 {{{
 var audioContext = new AudioContext();
 audioContext.currentTime;
 }}}

 Similarly, HTMLVideoElement.currentTime, HTMLAudioElement.currentTime, and
 CanvasCaptureMediaStream.currentTime can each be used as a time source
 with resolution better than 10 ms.

--

Comment:

 Here is a branch with two patches.

 https://github.com/arthuredelstein/tor-browser/commits/19193

 b91f47cce42a2e048f970a18710f9c15672a6cfc is a fixup for our #1517 patch
 that rounds the values returned by the `currentTime` attributes mentioned
 above.

 936cadcc8dd2b0e6784be69cabe44880e36839b0 provides regression tests for all
 time sources we are rounding in the old and new patches.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19193#comment:1>
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