linux-kernel - RE: [PATCH] acpica: Fix double-free in acpi_ns_repair

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Date:   Mon, 6 Feb 2017 01:44:15 +0000
From:   "Zheng, Lv" <lv.zheng@...el.com>
To:     "Moore, Robert" <robert.moore@...el.com>,
        Jo?o Paulo Rechi Vita <jprvita@...il.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Len Brown" <lenb@...nel.org>, Lin Ming <ming.m.lin@...el.com>
CC:     "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Daniel Drake <drake@...lessm.com>,
        "linux@...lessm.com" <linux@...lessm.com>,
        Jo?o Paulo Rechi Vita <jprvita@...lessm.com>,
        "Box, David E" <david.e.box@...el.com>,
        "Schmauss, Erik" <erik.schmauss@...el.com>
Subject: RE: [PATCH] acpica: Fix double-free in acpi_ns_repair_CID()

Hi,

So if a real problem related to package reference counting is triggered, the problem should be fixed elsewhere IMO.
See this bug for reference:
https://bugs.acpica.org/show_bug.cgi?id=1336

Thanks and best regards
Lv

> From: Moore, Robert
> Subject: RE: [PATCH] acpica: Fix double-free in acpi_ns_repair_CID()
> 
> Here's the sequence of events as I see it:
> 
> Repair_HID is a standalone function that removes one reference on the incoming object. For simple _HID
> objects, this in fact deletes the object.
> 
> For _CID, all elements of the package are examined. If a repair was made on a _HID within the _CID
> function, one reference on the original object was removed by Repair_HID. However, since the object is
> part of a package, it has an extra reference to reflect this fact. Thus, in the case in question, the
> elements of the package all have at least two references. Repair_HID removes one reference, thus the
> extra RemoveReference is needed in Repair_CID to bring the reference count down to zero actually
> delete the object (in the typical case where the object had two references).
> 
> Bob
> 
> 
> > From: João Paulo Rechi Vita [mailto:jprvita@...il.com]
> > Subject: [PATCH] acpica: Fix double-free in acpi_ns_repair_CID()
> >
> > When acpi_ns_repair_CID() is called for a _CID which returns a package of
> > strings, it calls acpi_ns_repair_HID() for each of the package elements.
> > acpi_ns_repair_HID() calls acpi_ut_remove_reference() on the original
> > object, but acpi_ns_repair_CID() calls it again on return, leading to a
> > double free.
> >
> > This problem was seen on a Acer TravelMate P449-G2-MG.
> >
> > Thanks to Daniel Drake for helping investigating this problem.
> >
> > Signed-off-by: João Paulo Rechi Vita <jprvita@...lessm.com>
> > ---
> >  drivers/acpi/acpica/nsrepair2.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/drivers/acpi/acpica/nsrepair2.c
> > b/drivers/acpi/acpica/nsrepair2.c index d5336122486b..c429c8eca476 100644
> > --- a/drivers/acpi/acpica/nsrepair2.c
> > +++ b/drivers/acpi/acpica/nsrepair2.c
> > @@ -411,8 +411,6 @@ acpi_ns_repair_CID(struct acpi_evaluate_info *info,
> >
> >  			(*element_ptr)->common.reference_count =
> >  			    original_ref_count;
> > -
> > -			acpi_ut_remove_reference(original_element);
> >  		}
> >
> >  		element_ptr++;
> > --
> > 2.11.0