linux-kernel - Re: [PATCH RESEND] fpga: region: Fix possible memory leak in fpga_region_register

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Message-ID: <9842e1cc-3e61-3759-30f0-b4968622e0a7@intel.com>
Date:   Thu, 28 Sep 2023 08:45:11 -0700
From:   Russ Weight <russell.h.weight@...el.com>
To:     Jinjie Ruan <ruanjinjie@...wei.com>, <mdf@...nel.org>,
        <hao.wu@...el.com>, <yilun.xu@...el.com>, <trix@...hat.com>,
        <linux-fpga@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] fpga: region: Fix possible memory leak in
 fpga_region_register_full()

On 9/28/23 02:16, Jinjie Ruan wrote:
> If device_register() fails in fpga_region_register_full(), the region
> allocated by kzalloc() and the id allocated by ida_alloc() also need be
> freed otherwise will cause memory leak.
>
> Fixes: 8886a579744f ("fpga: region: Use standard dev_release for class driver")
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>  drivers/fpga/fpga-region.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/fpga/fpga-region.c b/drivers/fpga/fpga-region.c
> index b364a929425c..9dc6314976ef 100644
> --- a/drivers/fpga/fpga-region.c
> +++ b/drivers/fpga/fpga-region.c
> @@ -228,12 +228,13 @@ fpga_region_register_full(struct device *parent, const struct fpga_region_info *
>  
>  	ret = device_register(&region->dev);

The comments for device_register() say:

 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up the
 * reference initialized in this function instead.

Note that dev is embedded in the region structure, so freeing region
means freeing dev.

The expectation is that after device_register() has been called, even
if it returns an error, put_device() is used to lower the reference
count. When the reference count is zero, the fpga_region_dev_release()
function is called. fpga_region_dev_release() frees calls ida_free()
and frees the region.

Have you observed different behavior? Do you have evidence of a memory
leak?

Thanks,
- Russ

>  	if (ret) {
> -		put_device(&region->dev);
> -		return ERR_PTR(ret);
> +		goto err_put_device;
>  	}
>  
>  	return region;
>  
> +err_put_device:
> +	put_device(&region->dev);
>  err_remove:
>  	ida_free(&fpga_region_ida, id);
>  err_free: