From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fredrik=20S=C3=B6derqvist?= <fs@opera.com>
Date: Fri, 9 Jul 2021 08:44:55 +0000
Subject: Set SVGImage::page_ after document install
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We can end up having the associated ImageResource call
SVGImage::ResetAnimation() before the Document has been associated with
the SVGImage's LocalFrame, but after the link to the initial Document
was severed, if a GC is triggered within that window and ends up
collecting the last observer of the ImageResource.

By assigning |SVGImage::page_| after the installing the document, we
close this hole since SVGImage::RootElement() (called by
SVGImage::ResetAnimation()) will now observe a null Page and return null
without attempting to dereference the document.

Bug: 1216190
Change-Id: I26e08848e5b9bd52e3377841eee35e4acc03d320
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3010140
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#899922}

diff --git a/third_party/blink/renderer/core/svg/graphics/svg_image.cc b/third_party/blink/renderer/core/svg/graphics/svg_image.cc
index 2ce8a78b3537c72206e2d3e6d55f9cc1fc5d3208..0dec91614edb0caa6f8e473f027c3be7b8bf1e4e 100644
--- a/third_party/blink/renderer/core/svg/graphics/svg_image.cc
+++ b/third_party/blink/renderer/core/svg/graphics/svg_image.cc
@@ -830,12 +830,15 @@ Image::SizeAvailability SVGImage::DataChanged(bool all_data_received) {
   // SVG Images are transparent.
   frame->View()->SetBaseBackgroundColor(Color::kTransparent);
 
-  page_ = page;
-
   TRACE_EVENT0("blink", "SVGImage::dataChanged::load");
 
   frame->ForceSynchronousDocumentInstall("image/svg+xml", Data());
 
+  // Set up our Page reference after installing our document. This avoids
+  // tripping on a non-existing (null) Document if a GC is triggered during the
+  // set up and ends up collecting the last owner/observer of this image.
+  page_ = page;
+
   // Intrinsic sizing relies on computed style (e.g. font-size and
   // writing-mode).
   frame->GetDocument()->UpdateStyleAndLayoutTree();
