linux-kernel - Re: [PATCH] platform/chrome: fix double-free in chromeos_laptop

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Message-ID: <YwG56T86sYkH/eCw@google.com>
Date:   Sat, 20 Aug 2022 21:51:53 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Rustam Subkhankulov <subkhankulov@...ras.ru>
Cc:     Tzung-Bi Shih <tzungbi@...nel.org>,
        Benson Leung <bleung@...omium.org>,
        chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] platform/chrome: fix double-free in
 chromeos_laptop_prepare()

On Sat, Aug 20, 2022 at 08:05:13PM +0300, Rustam Subkhankulov wrote:
> On Mon, 2022-08-15 at 05:00 +0000, Tzung-Bi Shih wrote:
> > Alternatively, I would prefer to fix the double-free by setting
> > `i2c_peripherals` to NULL after [1].
> 
> Since 'cros_laptop->num_i2c_peripherals' is assigned with nonzero value
> (otherwise the code on 'err_out' is not executed), setting 
> 'i2c_peripherals' to NULL after [1] will cause dereferencing of 
> NULL pointer in chromeos_laptop_destroy() at [2]. 
> 
> [1]:
> https://elixir.bootlin.com/linux/v5.19/source/drivers/platform/chrome/chromeos_laptop.c#L787
> [2]:
> https://elixir.bootlin.com/linux/v5.19/source/drivers/platform/chrome/chromeos_laptop.c#L860
> 
> > After a quick glance, I found an invalid memory access at [2] if
> > `i2c_peripherals` is NULL (see [3]). 
> 
> After applying the patch, there will be no invalid memory access at [2]
> if 'i2c_peripherals' is NULL, because in this situation 
> 'cros_laptop->num_i2c_peripherals' is zero and there is no single 
> iteration of the loop.

Yes, we should either reset both cros_laptop->i2c_peripherals and
cros_laptop->num_i2c_peripherals on error, or avoid setting them until
we are sure that we are not getting an error. I think prefer the latter.

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

Thanks.

-- 
Dmitry