[Backport] CVE-2021-21193: Use after free in Blink

Cherry-pick of patch originally reviewed on
https://chromium-review.googlesource.com/c/chromium/src/+/2748756:
Mark additional RootInlineBox dirty when culled inline box is removed

When a |LayoutInline| is removed, |LineBoxList::
DirtyLinesFromChangedChild| tries to mark affected
|RootInlineBox| dirty.

When the |LayoutInline| to be removed is culled, it tries to
find the |RootInlineBox| from its previous siblings, then look
for its previous and next |RootInlineBox|es.

Occasionally, the next next line of the previous sibling is
wrapped at the |LayoutInline|, and that its |LineBreakObj()|
holds the reference to the |LayoutInline|. This patch marks
such |RootInlineBox| dirty.

(cherry picked from commit 2dbdabb28d647c8ee20cbe36e3c957e74aff663b)

Bug: 1186287
Change-Id: I8ca73ebb4f5e4f13e997662fffd803d6a74ef49a
Auto-Submit: Koji Ishii <[email protected]>
Reviewed-by: Ian Kilpatrick <[email protected]>
Commit-Queue: Ian Kilpatrick <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#861724}
Commit-Queue: Jana Grill <[email protected]>
Reviewed-by: Achuith Bhandarkar <[email protected]>
Reviewed-by: Koji Ishii <[email protected]>
Cr-Commit-Position: refs/branch-heads/4240@{#1577}
Cr-Branched-From: f297677702651916bbf65e59c0d4bbd4ce57d1ee-refs/heads/master@{#800218}
Reviewed-by: Jüri Valdmann <[email protected]>

Author: Jana Grill

chromium/third_party/blink/renderer/core/layout/line/line_box_list.cc

@@ -359,14 +359,32 @@ void LineBoxList::DirtyLinesFromChangedChild(LineLayoutItem container,
     // findNextLineBreak. findNextLineBreak, despite the name, actually returns
     // the first LayoutObject after the BR. <rdar://problem/3849947> "Typing
     // after pasting line does not appear until after window resize."
-    if (RootInlineBox* prev_root_box = box->PrevRootBox())
+    if (RootInlineBox* prev_root_box = box->PrevRootBox()) {
       prev_root_box->MarkDirty();
+#if DCHECK_IS_ON()
+      for (; prev_root_box; prev_root_box = prev_root_box->PrevRootBox()) {
+        DCHECK(prev_root_box->IsDirty() ||
+               prev_root_box->LineBreakObj() != child);
+      }
+#endif
+    }
     // If |child| or any of its immediately previous siblings with culled
     // lineboxes is the object after a line-break in |box| or the linebox after
     // it then that means |child| actually sits on the linebox after |box| (or
     // is its line-break object) and so we need to dirty it as well.
-    if (RootInlineBox* next_root_box = box->NextRootBox())
+    if (RootInlineBox* next_root_box = box->NextRootBox()) {
       next_root_box->MarkDirty();
+
+      next_root_box = next_root_box->NextRootBox();
+      if (next_root_box && next_root_box->LineBreakObj() == child)
+        next_root_box->MarkDirty();
+#if DCHECK_IS_ON()
+      for (; next_root_box; next_root_box = next_root_box->NextRootBox()) {
+        DCHECK(next_root_box->IsDirty() ||
+               next_root_box->LineBreakObj() != child);
+      }
+#endif
+    }
   }
 }