linux-kernel - Re: [PATCH v2 2/7] nvmem: fix another memory leak in error path

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Date:   Tue, 18 Feb 2020 09:56:13 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Khouloud Touil <ktouil@...libre.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 2/7] nvmem: fix another memory leak in error path



On 18/02/2020 09:42, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> The nvmem struct is only freed on the first error check after its
> allocation and leaked after that. Fix it with a new label.
> 
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>   drivers/nvmem/core.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index b0be03d5f240..c9b3f4047154 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -343,10 +343,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   		return ERR_PTR(-ENOMEM);
>   
>   	rval  = ida_simple_get(&nvmem_ida, 0, 0, GFP_KERNEL);
> -	if (rval < 0) {
> -		kfree(nvmem);
> -		return ERR_PTR(rval);
> -	}
> +	if (rval < 0)
> +		goto err_free_nvmem;
>   	if (config->wp_gpio)
>   		nvmem->wp_gpio = config->wp_gpio;
>   	else
> @@ -432,6 +430,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   	put_device(&nvmem->dev);
>   err_ida_remove:
>   	ida_simple_remove(&nvmem_ida, nvmem->id);
> +err_free_nvmem:
> +	kfree(nvmem);

This is not correct fix to start with, if the device has already been 
intialized before jumping here then nvmem would be freed as part of 
nvmem_release().

So the bug was actually introduced by adding err_ida_remove label.

You can free nvmem at that point but not at any point after that as 
device core would be holding a reference to it.

--srini



>   
>   	return ERR_PTR(rval);
>   }
>