linux-kernel - Re: [PATCH v2 2/3] ACPI: battery: Fix possible crash when unregistering a battery hook

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Message-ID: <CAJZ5v0j4S66jp9QvTetj=KtOTqh-ae4gub_6b5DB5zkasB=yVA@mail.gmail.com>
Date: Tue, 1 Oct 2024 20:57:26 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Armin Wolf <W_Armin@....de>
Cc: mjg59@...f.ucam.org, pali@...nel.org, dilinger@...ued.net, 
	rafael@...nel.org, lenb@...nel.org, hdegoede@...hat.com, 
	ilpo.jarvinen@...ux.intel.com, platform-driver-x86@...r.kernel.org, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] ACPI: battery: Fix possible crash when
 unregistering a battery hook

On Sun, Sep 22, 2024 at 8:40 AM Armin Wolf <W_Armin@....de> wrote:
>
> When a battery hook returns an error when adding a new battery, then
> the battery hook is automatically unregistered.
> However the battery hook provider cannot know that, so it will later
> call battery_hook_unregister() on the already unregistered battery
> hook, resulting in a crash.
>
> Fix this by using a boolean flag to mark already unregistered battery
> hooks as "dead" so that they can be ignored by
> battery_hook_unregister().
>
> Fixes: fa93854f7a7e ("battery: Add the battery hooking API")
> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>  drivers/acpi/battery.c | 11 ++++++++++-
>  include/acpi/battery.h |  1 +
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> index 10e9136897a7..b31a6183a082 100644
> --- a/drivers/acpi/battery.c
> +++ b/drivers/acpi/battery.c
> @@ -719,6 +719,7 @@ static void battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
>                         power_supply_changed(battery->bat);
>         }
>         list_del(&hook->list);
> +       hook->dead = true;

It looks like you could do

list_del_init((&hook->list);

here and then do a list_emtpy() check below.

>
>         pr_info("extension unregistered: %s\n", hook->name);
>  }
> @@ -726,7 +727,14 @@ static void battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
>  void battery_hook_unregister(struct acpi_battery_hook *hook)
>  {
>         mutex_lock(&hook_mutex);
> -       battery_hook_unregister_unlocked(hook);
> +       /*
> +        * Ignore already unregistered battery hooks. This might happen
> +        * if a battery hook was previously unloaded due to an error when
> +        * adding a new battery.
> +        */
> +       if (!hook->dead)

if (!list_empty(&hook->list))

> +               battery_hook_unregister_unlocked(hook);
> +
>         mutex_unlock(&hook_mutex);

and the new struct field would not be necessary if I'm not mistaken.

>  }
>  EXPORT_SYMBOL_GPL(battery_hook_unregister);
> @@ -737,6 +745,7 @@ void battery_hook_register(struct acpi_battery_hook *hook)
>
>         mutex_lock(&hook_mutex);
>         INIT_LIST_HEAD(&hook->list);

Also the above statement is redundant, so maybe drop it while you're at it?

> +       hook->dead = false;
>         list_add(&hook->list, &battery_hook_list);
>         /*
>          * Now that the driver is registered, we need
> diff --git a/include/acpi/battery.h b/include/acpi/battery.h
> index c93f16dfb944..5cfe132bb7f5 100644
> --- a/include/acpi/battery.h
> +++ b/include/acpi/battery.h
> @@ -16,6 +16,7 @@ struct acpi_battery_hook {
>         int (*add_battery)(struct power_supply *battery, struct acpi_battery_hook *hook);
>         int (*remove_battery)(struct power_supply *battery, struct acpi_battery_hook *hook);
>         struct list_head list;
> +       bool dead;
>  };
>
>  void battery_hook_register(struct acpi_battery_hook *hook);
> --