linux-kernel - Re: [PATCH] nvmem: core: Fix a potential use after free

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Message-ID: <a5734013-f80b-772a-7fed-b548ff98ec4b@linaro.org>
Date:   Mon, 6 Jan 2020 12:35:17 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Xu Wang <vulab@...as.ac.cn>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvmem: core: Fix a potential use after free


Thanks for the patch.

On 27/12/2019 09:20, Xu Wang wrote:
> Free the nvmem structure only after we are done using it.
> This patch just moves the put_device() down a bit to avoid the
> use after free.

Could you explain the issue bit more here on what exactly could go wrong 
with the exiting order?
may be the stack trace of the use-after-free case? Or steps to reproduce 
the issue?

nvmem device is protected with kref.

--srini

> 
> Signed-off-by: Xu Wang <vulab@...as.ac.cn>
> ---
>   drivers/nvmem/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 9f1ee9c..7051d34 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -535,8 +535,8 @@ static struct nvmem_device *__nvmem_device_get(void *data,
>   
>   static void __nvmem_device_put(struct nvmem_device *nvmem)
>   {
> -	put_device(&nvmem->dev);
>   	module_put(nvmem->owner);
> +	put_device(&nvmem->dev);
>   	kref_put(&nvmem->refcnt, nvmem_device_release);
>   }
>   
>