From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Mark Asselstine <mark.asselstine@windriver.com>
Cc: ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
Erik Kaneda <erik.kaneda@intel.com>,
Robert Moore <robert.moore@intel.com>
Subject: Re: [PATCH] ACPICA: avoid double free when object already has a zero reference count
Date: Thu, 29 Oct 2020 15:05:46 +0100 [thread overview]
Message-ID: <CAJZ5v0hr4xFA9bGJM+0e4i-QpESPnwy5ZT4KPwfJgby5Sz3UBw@mail.gmail.com> (raw)
In-Reply-To: <20201028200523.111028-1-mark.asselstine@windriver.com>
+Erik and Bob
On Thu, Oct 29, 2020 at 3:05 AM Mark Asselstine
<mark.asselstine@windriver.com> wrote:
>
> The first trip into acpi_ut_update_ref_count() for an object where
> 'object->common.reference_count' is 1 and we are performing a
> REF_DECREMENT will result in 'new_count' being 0 and thus the object
> is deleted via acpi_ut_delete_internal_obj().
>
> If for some reason we make a subsequent trip into
> acpi_ut_update_ref_count() with the same object,
> object->common.reference_count' will be 0 and performing a
> REF_DECREMENT will produce a warning msg "Reference Count is already
> zero, cannot decrement", 'new_count' will again be 0 and the already
> deleted object will be attempted to be deleted again via
> acpi_ut_delete_internal_obj().
>
> Since the object deletion doesn't NULL the object the calls to
> acpi_ut_delete_internal_obj(), acpi_ut_delete_object_desc(),
> acpi_os_release_object(), kmem_cache_free() will operate on the object
> as if it hasn't been deleted. In many cases this can result in no
> issues, but if you are using the slab and a new object has been
> created with the same address this can be the cause slab corruption.
>
> Adding a check if we are decrementing to 0 for the first time and only
> calling acpi_ut_delete_internal_obj() in this case will prevent
> another attempt at deleting the object.
>
> Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
> ---
> drivers/acpi/acpica/utdelete.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpica/utdelete.c b/drivers/acpi/acpica/utdelete.c
> index 4c0d4e434196..c6b860fd9eb5 100644
> --- a/drivers/acpi/acpica/utdelete.c
> +++ b/drivers/acpi/acpica/utdelete.c
> @@ -421,9 +421,9 @@ acpi_ut_update_ref_count(union acpi_operand_object *object, u32 action)
> ACPI_GET_FUNCTION_NAME, object,
> object->common.type, new_count));
>
> - /* Actually delete the object on a reference count of zero */
> + /* If we haven't already, actually delete the object on a reference count of zero */
>
> - if (new_count == 0) {
> + if (new_count == 0 && original_count != 0) {
> acpi_ut_delete_internal_obj(object);
> }
> message = "Decrement";
> --
> 2.17.1
>
next prev parent reply other threads:[~2020-10-29 14:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 20:05 [PATCH] ACPICA: avoid double free when object already has a zero reference count Mark Asselstine
2020-10-29 14:05 ` Rafael J. Wysocki [this message]
2020-11-02 18:11 ` Kaneda, Erik
2020-11-02 18:51 ` Mark Asselstine
2020-11-03 18:28 ` Kaneda, Erik
2020-11-03 18:52 ` Mark Asselstine
2020-11-19 22:30 ` Mark Asselstine
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