298499 - potential race on idFunc and idFuncClosure in plevent.c

Status: RESOLVED INVALID

(Core :: XPCOM, defect)

Description

[Jeffrey J. Cook]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511 Firefox/1.0.4
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8b2) Gecko/20050616 Firefox/1.0+

In xpcom/threads/plevent.c, there is a potential race condition that could cause
badness on variables idFunc and idFuncClosure.  This occurs between functions
PL_PostEvent and PL_RegisterEventIDFunc.  PL_RegisterEventIDFunc could update
the idFunc function pointer but not have updated the idFuncClosure data when
PL_PostEvent performs the function invocation idFunc(idFuncClosure), since only
the non-NULLness of idFunc is tested before executing the function pointer.


From plevent.c:PL_PostEvent:

#if defined(XP_UNIX) && !defined(XP_MACOSX)
    if (self->idFunc && event)
        event->id = self->idFunc(self->idFuncClosure);
#endif


From plevent.c:PL_RegisterEventIDFunc

PL_RegisterEventIDFunc(PLEventQueue *aSelf, PLGetEventIDFunc aFunc,
                       void *aClosure)
{
    aSelf->idFunc = aFunc;
    aSelf->idFuncClosure = aClosure;
}


Solution that has a safe race:

PL_RegisterEventIDFunc(PLEventQueue *aSelf, PLGetEventIDFunc aFunc,
                        void *aClosure)
{
    aSelf->idFunc = 0; /* guard update so that incorrect closure is not applied */
    aSelf->idFuncClosure = aClosure; /* this must precede assigning idFunc */
    aSelf->idFunc = aFunc;
}


Reproducible: Always

Comment 1

[Jeffrey J. Cook]

I should add that I do not know if these two functions can execute in parallel
as I don't fully understand this module.  This bug was reported to me with Intel
Thread Checker and upon non-trivial inspection, I could not classify this as a
false positive.

Comment 2

[Gervase Markham [:gerv]]

This is an automated message, with ID "auto-resolve01".

This bug has had no comments for a long time. Statistically, we have found that
bug reports that have not been confirmed by a second user after three months are
highly unlikely to be the source of a fix to the code.

While your input is very important to us, our resources are limited and so we
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Comment 3

[Gervase Markham [:gerv]]

This bug has been automatically resolved after a period of inactivity (see above
comment). If anyone thinks this is incorrect, they should feel free to reopen it.

Comment 4

[Steve England [:stevee]]

Reopening for examination by someone who can yay/nay this.

Comment 5

[Darin Fisher]

The code in question no longer exists.  See bug 326273.