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 > -----Original Message----- > From: João Paulo Rechi Vita [mailto:jprv...@gmail.com] > Sent: Friday, February 03, 2017 12:57 PM > To: Moore, Robert; Zheng, Lv; Wysocki, Rafael J; Len Brown; Lin Ming > Cc: linux-a...@vger.kernel.org; de...@acpica.org; linux- > ker...@vger.kernel.org; Daniel Drake; li...@endlessm.com; João Paulo Rechi > Vita > 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 <jprv...@endlessm.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
