linux-kernel - Re: [PATCH] peci: fix potential memory leak in devm_adev

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Message-ID: <d4bfcbfa4fbbb1acdd8110287744a39d6525306d.camel@intel.com>
Date:   Tue, 5 Jul 2022 10:18:51 +0000
From:   "Winiarska, Iwona" <iwona.winiarska@...el.com>
To:     "niejianglei2021@....com" <niejianglei2021@....com>
CC:     "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] peci: fix potential memory leak in devm_adev_add()

On Mon, 2022-07-04 at 20:59 +0800, Jianglei Nie wrote:
> devm_adev_add() allocates a memory chunk for "adev" and "adev->name"
> with adev_alloc(). When auxiliary_device_add() fails, the function calls
> auxiliary_device_uninit(), which doesn't release the allocated "adev"
> and "adev->name", thus leading to a memory leak bug.
> 
> We should call adev_release() instead of auxiliary_device_uninit() to
> release the "adev" and "adev->name".
> 
> Signed-off-by: Jianglei Nie <niejianglei2021@....com>
> ---
>  drivers/peci/cpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/peci/cpu.c b/drivers/peci/cpu.c
> index 68eb61c65d34..de865997ccde 100644
> --- a/drivers/peci/cpu.c
> +++ b/drivers/peci/cpu.c
> @@ -248,7 +248,7 @@ static int devm_adev_add(struct device *dev, int idx)
>  
>         ret = auxiliary_device_add(adev);
>         if (ret) {
> -               auxiliary_device_uninit(adev);
> +               adev_release(&adev->dev);
>                 return ret;
>         }
>  

When we call auxiliary_device_uninit() the .release callback (adev_release())
will be triggered, so there's no memory leak here.

But thank you for pointing to this - it made me realize that we have a bug in
adev_release(), because we call auxiliary_device_uninit() there, which will
cause a use-after-free with refcount underflow in this case.

I'd appreciate if you could review it:
https://lore.kernel.org/lkml/20220705101501.298395-1-iwona.winiarska@intel.com/

Thanks
-Iwona