638026 - "ASSERTION: should have a JS object by this point" with setUserData, GC

Status: RESOLVED FIXED

(Core :: XPConnect, defect)

Description

[Jesse Ruderman]

Attachment: testcase (requires extension for GC)

1. Install 'DOM Fuzz Lite' from
    https://www.squarefree.com/extensions/domFuzzLite.xpi
2. Load the testcase.

###!!! ASSERTION: should have a JS object by this point: 'win->GetOuterWindowInternal()->IsCreatingInnerWindow()', file dom/base/nsDOMClassInfo.cpp, line 5022

###!!! ASSERTION: Non-global object has the wrong flags: '!(jsclazz->flags & JSCLASS_IS_GLOBAL)', file js/src/xpconnect/src/xpcwrappednative.cpp, line 1153

Security-sensitive because I'm scared of anything that involves GC. Or inner and outer windows.

Comment 1

[Jesse Ruderman]

Attachment: stack traces

Comment 2

[Andreas Gal :gal]

This doesn't look exploitable. Why blocking?

Comment 3

[Andreas Gal :gal]

b- please renom if we see any indication that this is indeed exploitable

Comment 4

[Johnny Stenback (:jst)]

Given that we don't know of this being exploitable or anything, marking this sg:nse, and keeping it closed for now. Blake, can you have a look?

Comment 5

[Blake Kaplan (:mrbkap) (inactive)]

Attachment: Proposed fix

So, the problem here is that the variant holds a reference to the outer window proxy and a reference to the current inner window's C++ object. After the iframe navigates, we brain transplant the outer window, and the old inner window's JS object has no more references to it, so we collect it. Later, we attempt to wrap the inner window into JS and recreate its JS object (and hit the assertion). This patch fixes this by making us hold a reference to the non-brain-transplanted inner object, meaning we won't recreate the JS object. This means we'll hold the old inner window alive longer, but I'm OK with that.

Comment 6

[Blake Kaplan (:mrbkap) (inactive)]

http://hg.mozilla.org/tracemonkey/rev/41ea0740c97d

Comment 7

[Daniel Veditz [:dveditz]]

Blake: we don't have brain transplants on the 1.9.x branches, but we do have inner and outer windows and we have seen the assertions in comment 0 (bug 637226). Do we need a variant of this fix on branches? Maybe not if it's truly unexploitable.

Comment 8

[Blake Kaplan (:mrbkap) (inactive)]

No. On older branches, the variant ends up holding a strong reference to the outer window, not the inner and the jsval that it holds is also for the outer, so it won't be garbage collected. Because the value and the nsISupports match there is no bug.

Comment 9

[Blake Kaplan (:mrbkap) (inactive)]

http://hg.mozilla.org/mozilla-central/rev/41ea0740c97d