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

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Message-ID: <CAPDyKFr8nkVCQB63rZ6ZcHeTrmQno7aYv2Pa3PmZwzW9Ei3HDQ@mail.gmail.com>
Date:   Thu, 23 Sep 2021 20:12:38 +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] drivers/mmc: fix reference count leaks in moxart_probe

On Thu, 16 Sept 2021 at 20:19, 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 the reference count of
> one or both objects' reference count increased earlier by
> dma_request_chan(), causing reference count leaks.
>
> Fix it by decreasing reference counts of both objects in each path
> separately.
>
> 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 | 38 ++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/mmc/host/moxart-mmc.c b/drivers/mmc/host/moxart-mmc.c
> index 6c9d38132..b5aa1010c 100644
> --- a/drivers/mmc/host/moxart-mmc.c
> +++ b/drivers/mmc/host/moxart-mmc.c
> @@ -606,7 +606,28 @@ static int moxart_probe(struct platform_device *pdev)
>         host->sysclk = clk_get_rate(clk);
>         host->fifo_width = readl(host->base + REG_FEATURE) << 2;
>         host->dma_chan_tx = dma_request_chan(dev, "tx");
> +       if (IS_ERR(host->dma_chan_tx)) {
> +               if (PTR_ERR(host->dma_chan_tx) == -EPROBE_DEFER) {
> +                       ret = -EPROBE_DEFER;
> +            goto out;
> +        }
> +    }
> +
>         host->dma_chan_rx = dma_request_chan(dev, "rx");
> +       if (IS_ERR(host->dma_chan_rx)) {
> +               if (!IS_ERR(host->dma_chan_tx))
> +                       dma_release_channel(host->dma_chan_tx);
> +               if (PTR_ERR(host->dma_chan_rx) == -EPROBE_DEFER) {
> +                       ret = -EPROBE_DEFER;
> +                       goto out;
> +        }
> +        dev_dbg(dev, "PIO mode transfer enabled\n");
> +        host->have_dma = false;
> +    } else if (IS_ERR(host->dma_chan_tx)) {
> +               dma_release_channel(host->chan_rx);
> +               dev_dbg(dev, "PIO mode transfer enabled\n");
> +               host->have_dma = false;
> +    }
>
>         spin_lock_init(&host->lock);
>
> @@ -615,15 +636,7 @@ static int moxart_probe(struct platform_device *pdev)
>         mmc->f_min = DIV_ROUND_CLOSEST(host->sysclk, CLK_DIV_MASK * 2);
>         mmc->ocr_avail = 0xffff00;      /* Support 2.0v - 3.6v power. */
>
> -       if (IS_ERR(host->dma_chan_tx) || IS_ERR(host->dma_chan_rx)) {
> -               if (PTR_ERR(host->dma_chan_tx) == -EPROBE_DEFER ||
> -                   PTR_ERR(host->dma_chan_rx) == -EPROBE_DEFER) {
> -                       ret = -EPROBE_DEFER;
> -                       goto out;
> -               }
> -               dev_dbg(dev, "PIO mode transfer enabled\n");
> -               host->have_dma = false;
> -       } else {
> +    if (!IS_ERR(host->dma_chan_tx) && !IS_ERR(host->dma_chan_rx)) {
>                 dev_dbg(dev, "DMA channels found (%p,%p)\n",
>                          host->dma_chan_tx, host->dma_chan_rx);
>                 host->have_dma = true;
> @@ -664,8 +677,13 @@ static int moxart_probe(struct platform_device *pdev)
>         }
>
>         ret = devm_request_irq(dev, irq, moxart_irq, 0, "moxart-mmc", host);
> -       if (ret)
> +       if (ret) {
> +               if (host->have_dma) {
> +                       dma_release_channel(host->dma_chan_tx);
> +                       dma_release_channel(host->dma_chan_rx);
> +               }
>                 goto out;
> +       }

You are right, that we should call dma_release_channel in some error
paths. Although, the above looks rather messy to me. May I suggest
that we add the error handling below the "out" label instead. Along
the lines of this:

if (!IS_ERR(host->dma_chan_tx))
     dma_release_channel(host->dma_chan_tx);
if (!IS_ERR(host->dma_chan_rx))
     dma_release_channel(host->dma_chan_rx);

>
>         dev_set_drvdata(dev, mmc);
>         mmc_add_host(mmc);
> --
> 2.25.1
>

Kind regards
Uffe