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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/287867">287867</a></dd>
<dt>Author</dt> <dd>zalan@apple.com</dd>
<dt>Date</dt> <dd>2022-01-10 19:21:20 -0800 (Mon, 10 Jan 2022)</dd>
</dl>

<h3>Log Message</h3>
<pre>null ptr deref in WebCore::LayoutIntegration::LineLayout::collectOverflow()
https://bugs.webkit.org/show_bug.cgi?id=234654
<rdar://problem/86571571>

Reviewed by Antti Koivisto.

Source/WebCore:

needsLayout() check in invalidateLineLayoutPath is insufficient for modern line layout.

m_lineLayout = std::monostate() does not only destroy the line layout object but it also nukes all the IFC geometries.
It is equivalent to having all the child boxes dirty, since in order to re-generate the geometry information,
we have to layout _all_ the boxes (note that nuking the legacy line layout object does not destroy the inline tree).
The bug here is that needsLayout() returns true for cases (e.g. posChildNeedsLayout) when
while the geometry is all gone, we are going to take a special layout codepath which expects pre-computed geometries.

Test: fast/block/line-layout/line-layout-collect-overflow-crash.html

* rendering/RenderBlockFlow.cpp:
(WebCore::RenderBlockFlow::invalidateLineLayoutPath):

LayoutTests:

* fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt: Added.
* fast/block/line-layout/line-layout-collect-overflow-crash.html: Added.</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCorerenderingRenderBlockFlowcpp">trunk/Source/WebCore/rendering/RenderBlockFlow.cpp</a></li>
</ul>

<h3>Added Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsfastblocklinelayoutlinelayoutcollectoverflowcrashexpectedtxt">trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt</a></li>
<li><a href="#trunkLayoutTestsfastblocklinelayoutlinelayoutcollectoverflowcrashhtml">trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash.html</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (287866 => 287867)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog      2022-01-11 02:17:09 UTC (rev 287866)
+++ trunk/LayoutTests/ChangeLog 2022-01-11 03:21:20 UTC (rev 287867)
</span><span class="lines">@@ -1,3 +1,14 @@
</span><ins>+2022-01-10  Alan Bujtas  <zalan@apple.com>
+
+        null ptr deref in WebCore::LayoutIntegration::LineLayout::collectOverflow()
+        https://bugs.webkit.org/show_bug.cgi?id=234654
+        <rdar://problem/86571571>
+
+        Reviewed by Antti Koivisto.
+
+        * fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt: Added.
+        * fast/block/line-layout/line-layout-collect-overflow-crash.html: Added.
+
</ins><span class="cx"> 2022-01-10  Wenson Hsieh  <wenson_hsieh@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Followup to r287863 - adjust line wrapping behavior in image overlays
</span></span></pre></div>
<a id="trunkLayoutTestsfastblocklinelayoutlinelayoutcollectoverflowcrashexpectedtxt"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt (0 => 287867)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt                         (rev 0)
+++ trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash-expected.txt    2022-01-11 03:21:20 UTC (rev 287867)
</span><span class="lines">@@ -0,0 +1,4 @@
</span><ins>+CONSOLE MESSAGE: This test passes if it does not crash.
+
+a
+
</ins></span></pre></div>
<a id="trunkLayoutTestsfastblocklinelayoutlinelayoutcollectoverflowcrashhtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash.html (0 => 287867)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash.html                         (rev 0)
+++ trunk/LayoutTests/fast/block/line-layout/line-layout-collect-overflow-crash.html    2022-01-11 03:21:20 UTC (rev 287867)
</span><span class="lines">@@ -0,0 +1,25 @@
</span><ins>+<!DOCTYPE html>
+<style>
+  :nth-last-child(odd) {
+    position: absolute;
+  }
+  div {
+    rotate: 0 0 0 0deg;
+  }
+</style>
+<script>
+  onload = () => {
+    let div0 = document.createElement('div');
+    document.body.append(document.createElement('table'));
+    document.body.append(div0);
+    div0.append(document.createElement('img'));
+    document.execCommand('SelectAll');
+    div0.append('a');
+    document.body.append(document.createElement('div'));
+    document.designMode = 'on';
+    document.execCommand('FormatBlock', false, 'div');
+    if (window.testRunner)
+      testRunner.dumpAsText();
+    console.log("This test passes if it does not crash.");
+  };
+</script>
</ins></span></pre></div>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (287866 => 287867)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2022-01-11 02:17:09 UTC (rev 287866)
+++ trunk/Source/WebCore/ChangeLog      2022-01-11 03:21:20 UTC (rev 287867)
</span><span class="lines">@@ -1,3 +1,24 @@
</span><ins>+2022-01-10  Alan Bujtas  <zalan@apple.com>
+
+        null ptr deref in WebCore::LayoutIntegration::LineLayout::collectOverflow()
+        https://bugs.webkit.org/show_bug.cgi?id=234654
+        <rdar://problem/86571571>
+
+        Reviewed by Antti Koivisto.
+
+        needsLayout() check in invalidateLineLayoutPath is insufficient for modern line layout.
+
+        m_lineLayout = std::monostate() does not only destroy the line layout object but it also nukes all the IFC geometries.
+        It is equivalent to having all the child boxes dirty, since in order to re-generate the geometry information,
+        we have to layout _all_ the boxes (note that nuking the legacy line layout object does not destroy the inline tree).
+        The bug here is that needsLayout() returns true for cases (e.g. posChildNeedsLayout) when
+        while the geometry is all gone, we are going to take a special layout codepath which expects pre-computed geometries.
+
+        Test: fast/block/line-layout/line-layout-collect-overflow-crash.html
+
+        * rendering/RenderBlockFlow.cpp:
+        (WebCore::RenderBlockFlow::invalidateLineLayoutPath):
+
</ins><span class="cx"> 2022-01-10  Wenson Hsieh  <wenson_hsieh@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Followup to r287863 - adjust line wrapping behavior in image overlays
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingRenderBlockFlowcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderBlockFlow.cpp (287866 => 287867)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/RenderBlockFlow.cpp       2022-01-11 02:17:09 UTC (rev 287866)
+++ trunk/Source/WebCore/rendering/RenderBlockFlow.cpp  2022-01-11 03:21:20 UTC (rev 287867)
</span><span class="lines">@@ -3562,7 +3562,7 @@
</span><span class="cx"> #endif
</span><span class="cx">         m_lineLayout = std::monostate();
</span><span class="cx">         setLineLayoutPath(path);
</span><del>-        if (needsLayout())
</del><ins>+        if (selfNeedsLayout() || normalChildNeedsLayout())
</ins><span class="cx">             return;
</span><span class="cx">         // FIXME: We should just kick off a subtree layout here (if needed at all) see webkit.org/b/172947.
</span><span class="cx">         setNeedsLayout();
</span></span></pre>
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