[webkit-changes] [WebKit/WebKit] 2c5193: Canvas' security should not take into account Sing...

[Jean-Yves Avenard]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 2c5193d0471c2417232a02a7aff688e4744f5839
      https://github.com/WebKit/WebKit/commit/2c5193d0471c2417232a02a7aff688e4744f5839
  Author: Jean-Yves Avenard <jya at apple.com>
  Date:   2022-11-30 (Wed, 30 Nov 2022)

  Changed paths:
    M Source/WebCore/html/canvas/CanvasRenderingContext.cpp
    M Source/WebCore/loader/cache/CachedResource.cpp
    M Source/WebCore/loader/cache/CachedResource.h

  Log Message:
  -----------
  Canvas' security should not take into account Single Origin (for videos and images)
https://bugs.webkit.org/show_bug.cgi?id=242889
rdar://97245327

Reviewed by Youenn Fablet.

Per canvas' spec:
https://html.spec.whatwg.org/multipage/canvas.html#the-image-argument-is-not-origin-clean

an object image is not origin-clean if:
HTMLOrSVGImageElement
    image's current request's image data is CORS-cross-origin.
HTMLVideoElement
    image's media data is CORS-cross-origin.
HTMLCanvasElement
ImageBitmap
    image's bitmap's origin-clean flag is false.

And as per the security's policy:
https://html.spec.whatwg.org/multipage/canvas.html#security-with-canvas-elements

"To mitigate this, bitmaps used with canvas elements and ImageBitmap objects are defined to have a flag indicating whether they are origin-clean. All bitmaps start with their origin-clean set to true. The flag is set to false when cross-origin images are used."

The implementation prevented drawing into a canvas a video that was served across multiple mirrors as is commonly found in the media world.

* Source/WebCore/html/canvas/CanvasRenderingContext.cpp:
(WebCore::CanvasRenderingContext::wouldTaintOrigin):
* Source/WebCore/loader/cache/CachedResource.cpp:
(WebCore::CachedResource::isCORSCrossOrigin const):
* Source/WebCore/loader/cache/CachedResource.h:

Canonical link: https://commits.webkit.org/257207@main