linux-kernel - Re: [PATCH v2] acpi: Fix use-after-free in acpi

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Message-ID: <CAJZ5v0hbLh3EKGmy-wCvE_z_BBnWBmnyN+5onL_n2R6VK3BDdg@mail.gmail.com>
Date:   Thu, 26 Nov 2020 15:22:27 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Youling Tang <tangyouling@...ngson.cn>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] acpi: Fix use-after-free in acpi_ipmi.c

On Thu, Nov 26, 2020 at 2:26 AM Youling Tang <tangyouling@...ngson.cn> wrote:
>
> kfree() has been called inside put_device so anther kfree would cause a
> use-after-free bug.
>
> Signed-off-by: Youling Tang <tangyouling@...ngson.cn>
> ---
>  drivers/acpi/acpi_ipmi.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/acpi/acpi_ipmi.c b/drivers/acpi/acpi_ipmi.c
> index 9d6c0fc..18edf8b 100644
> --- a/drivers/acpi/acpi_ipmi.c
> +++ b/drivers/acpi/acpi_ipmi.c
> @@ -142,7 +142,6 @@ static void ipmi_dev_release(struct acpi_ipmi_device *ipmi_device)
>  {
>         ipmi_destroy_user(ipmi_device->user_interface);
>         put_device(ipmi_device->dev);

Does putting ipmi_device->dev (which is a different object than
ipmi_device itself) really cause ipmi_device to be freed
automatically?  If not, the change below will introduce a memory leak.

> -       kfree(ipmi_device);
>  }
>
>  static void ipmi_dev_release_kref(struct kref *kref)
> --