Bug 248437 – Canvas' security should not take into account Single Origin for SVG images

• Component: Canvas
• Status: NEW

[Jean-Yves Avenard [:jya]]

This is similar to bug 242889, but requires a more extensive solution.

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.

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."

And various methods will reject their promise according to this origin-clean flag.
Such as getImageData: https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-getimagedata
2. If the CanvasRenderingContext2D's origin-clean flag is set to false, then throw a "SecurityError" DOMException.

`CanvasRenderingContext::wouldTaintOrigin` is the method used to determine if a particular object can be used with a canvas.
Image:
https://searchfox.org/wubkat/rev/3c7828ddd50109debe235dded88a94e66d33e879/Source/WebCore/html/canvas/CanvasRenderingContext.cpp#132-133
```
   if (!image->hasSingleSecurityOrigin())
        return true;
```

The requirement that the SVG be of a single security origin is incorrect. It was introduced in https://trac.webkit.org/changeset/195614/webkit which made foreignObject regardless of their cross-origin data to taint the image.

[Jean-Yves Avenard [:jya]]

rdar://102738351