[Webkit-unassigned] [Bug 76812] New: NULL ptr in WebCore::RootInlineBox::closestLeafChildForLogicalLeftPosition

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=76812

           Summary: NULL ptr in
                    WebCore::RootInlineBox::closestLeafChildForLogicalLeft
                    Position
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Windows Vista
            Status: NEW
          Severity: Normal
          Priority: P1
         Component: HTML Editing
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: skylined at chromium.org
                CC: rniwa at webkit.org


Chromium: http://code.google.com/p/chromium/issues/detail?id=111026
Detailed report: https://cluster-fuzz.appspot.com/testcase?key=15314965

Uploader: skylined at chromium.org

Crash Type: UNKNOWN
Crash Address: 0x000000000035
Crash State:
  - crash stack -
  WebCore::RootInlineBox::closestLeafChildForLogicalLeftPosition
  WebCore::nextLinePosition
  WebCore::nextParagraphPosition

Regressed: https://cluster-fuzz.appspot.com/revisions?range=108839:108881

There are two variations, the first one crashes in nextLinePosition, the second one calls RootInlineBox::closestLeafChildForLogicalLeftPosition from nextLinePosition and crashes in the later. The repro from is almost the same; one turns "design-mode" off before modifying the selection, the other does not. Given the similarity in stack and repro, I assume the root cause is the same, so I'm not filing a separate bug for the variation.
<script>
window.onload=function(){
  document.designMode="on";
  document.write("\x3Clabel style=\"-webkit-mask-attachment: locarit; -webkit-margin-start: inherit;\" class=\"class_2\" ondurationchange/\x3E");
  document.execCommand("selectall", false);
  document.execCommand("inserthorizontalrule", false);
  document.execCommand("selectall");
  document.execCommand("ForwardDelete", false);
  document.designMode="off"; // Remove to get a different crash
  window.getSelection().modify("move","forward","paragraph");
}
</script>

Stack:
id:             chrome.dll!WebCore::RootInlineBox::closestLeafChildForLogicalLeftPosition ReadAV at NULL (2e192a450f79a729ce10a9a093aa98c7)
description:    Attempt to read from unallocated NULL pointer+0x21 in chrome.dll!WebCore::RootInlineBox::closestLeafChildForLogicalLeftPosition
application:    Chromium 18.0.1011.0
stack:          chrome.dll!WebCore::RootInlineBox::closestLeafChildForLogicalLeftPosition
                chrome.dll!WebCore::nextLinePosition
                chrome.dll!WebCore::nextParagraphPosition
                chrome.dll!WebCore::FrameSelection::modifyMovingForward
                chrome.dll!WebCore::FrameSelection::modify
                chrome.dll!WebCore::DOMSelection::modify
                chrome.dll!WebCore::DOMSelectionInternal::modifyCallback

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