linux-kernel - Re: [PATCH v3] drivers/mmc: fix reference count leaks in moxart

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Date:   Thu, 30 Sep 2021 13:13:59 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Xin Xiong <xiongx18@...an.edu.cn>
Cc:     linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yuanxzhang@...an.edu.cn, Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH v3] drivers/mmc: fix reference count leaks in moxart_probe

On Tue, 28 Sept 2021 at 04:15, Xin Xiong <xiongx18@...an.edu.cn> wrote:
>
> The issue happens in several error handling paths on two refcounted
> object related to the object "host" (dma_chan_rx, dma_chan_tx). In
> these paths, the function forgets to decrement one or both objects'
> reference count increased earlier by dma_request_chan(), causing
> reference count leaks.
>
> Fix it by balancing the refcounts of both objects in some error
> handling paths.
>
> Signed-off-by: Xin Xiong <xiongx18@...an.edu.cn>
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> ---
>  drivers/mmc/host/moxart-mmc.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/mmc/host/moxart-mmc.c b/drivers/mmc/host/moxart-mmc.c
> index 6c9d38132..f421be7ce 100644
> --- a/drivers/mmc/host/moxart-mmc.c
> +++ b/drivers/mmc/host/moxart-mmc.c
> @@ -621,6 +621,14 @@ static int moxart_probe(struct platform_device *pdev)
>                         ret = -EPROBE_DEFER;
>                         goto out;
>                 }
> +               if (!IS_ERR(host->dma_chan_tx)) {
> +                       dma_release_channel(host->dma_chan_tx);
> +                       host->dma_chan_tx = NULL;
> +               }
> +               if (!IS_ERR(host->dma_chan_rx)) {
> +                       dma_release_channel(host->dma_chan_rx);
> +                       host->dma_chan_rx = NULL;
> +               }
>                 dev_dbg(dev, "PIO mode transfer enabled\n");
>                 host->have_dma = false;
>         } else {
> @@ -675,6 +683,10 @@ static int moxart_probe(struct platform_device *pdev)
>         return 0;
>
>  out:
> +       if (!IS_ERR_OR_NULL(host->dma_chan_tx))
> +               dma_release_channel(host->dma_chan_tx);
> +       if (!IS_ERR_OR_NULL(host->dma_chan_rx))
> +               dma_release_channel(host->dma_chan_rx);
>         if (mmc)
>                 mmc_free_host(mmc);
>         return ret;

This looks much better! However, it seems like we also need to deal
with the NULL case in moxart_remove(), similar to as above.

Kind regards
Uffe