linux-kernel - Re: [PATCH] dmaengine: plx_dma: Fix potential double free in plx_dma

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Date:   Tue, 20 Dec 2022 09:35:38 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Miaoqian Lin <linmq006@...il.com>, Vinod Koul <vkoul@...nel.org>,
        Dan Carpenter <error27@...il.com>, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: plx_dma: Fix potential double free in
 plx_dma_create



On 2022-12-19 23:17, Miaoqian Lin wrote:
> When all references are dropped, callback function plx_dma_release()
> for put_device() will call kfree(plxdev) to release memory.
> Fix the error path to fix the possible double free.
>
> Fixes: 07503e6aefe4 ("dmaengine: plx_dma: add a missing put_device() on error path")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
> Please correct me if I make mistakes, thanks for your review.
> ---
>  drivers/dma/plx_dma.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/plx_dma.c b/drivers/dma/plx_dma.c
> index 12725fa1655f..bce724ff4e16 100644
> --- a/drivers/dma/plx_dma.c
> +++ b/drivers/dma/plx_dma.c
> @@ -546,8 +546,9 @@ static int plx_dma_create(struct pci_dev *pdev)
>  	return 0;
>  
>  put_device:
> -	put_device(&pdev->dev);
>  	free_irq(pci_irq_vector(pdev, 0),  plxdev);
> +	put_device(&pdev->dev);
> +	return rc;
>  free_plx:
>  	kfree(plxdev);
>  


Sorry, after reviewing, I don't think this patch is correct.

plx_dma_release() is called from dma_async_device_unregister() which
won't be called if dma_async_device_register() fails. It does not get
freed when the pci device is put. So I don't think this is a possible
double free.

Logan