Bug 76812 – Crash in previousLinePosition when moving into a root inline box without leaves

• Component: HTML Editing
• Status: RESOLVED FIXED

[Berend-Jan Wever]

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

Uploader: [e-mail]

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@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

[Ryosuke Niwa]

Created attachment 124603 [details]
fixes the crash

[Enrica Casucci]

Comment on attachment 124603 [details]
fixes the crash

Looks good to me.

[Ryosuke Niwa]

Thanks for review! Landing it now.

[Ryosuke Niwa]

Comment on attachment 124603 [details]
fixes the crash

Clearing flags on attachment: 124603

Committed r106298: <http://trac.webkit.org/changeset/106298>

[Ryosuke Niwa]

All reviewed patches have been landed.  Closing bug.