linux-kernel - Re: [PATCH] dmaengine: imx-sdma: fix use-after-free on probe error path

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Date:   Fri, 5 Jul 2019 12:58:47 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Robin Gong <yibin.gong@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: imx-sdma: fix use-after-free on probe error
 path

On 24-06-19, 10:07, Sven Van Asbroeck wrote:
> If probe() fails anywhere beyond the point where
> sdma_get_firmware() is called, then a kernel oops may occur.
> 
> Problematic sequence of events:
> 1. probe() calls sdma_get_firmware(), which schedules the
>    firmware callback to run when firmware becomes available,
>    using the sdma instance structure as the context
> 2. probe() encounters an error, which deallocates the
>    sdma instance structure
> 3. firmware becomes available, firmware callback is
>    called with deallocated sdma instance structure
> 4. use after free - kernel oops !
> 
> Solution: only attempt to load firmware when we're certain
> that probe() will succeed. This guarantees that the firmware
> callback's context will remain valid.
> 
> Note that the remove() path is unaffected by this issue: the
> firmware loader will increment the driver module's use count,
> ensuring that the module cannot be unloaded while the
> firmware callback is pending or running.
> 
> To: Robin Gong <yibin.gong@....com>
> Cc: Vinod Koul <vkoul@...nel.org>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: Pengutronix Kernel Team <kernel@...gutronix.de>
> Cc: Fabio Estevam <festevam@...il.com>
> Cc: NXP Linux Team <linux-imx@....com>
> Cc: dmaengine@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Sven Van Asbroeck <TheSven73@...il.com>
> ---
>  drivers/dma/imx-sdma.c | 48 ++++++++++++++++++++++++------------------
>  1 file changed, 27 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 99d9f431ae2c..3f0f41d16e1c 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -2096,27 +2096,6 @@ static int sdma_probe(struct platform_device *pdev)
>  	if (pdata && pdata->script_addrs)
>  		sdma_add_scripts(sdma, pdata->script_addrs);
>  
> -	if (pdata) {
> -		ret = sdma_get_firmware(sdma, pdata->fw_name);
> -		if (ret)
> -			dev_warn(&pdev->dev, "failed to get firmware from platform data\n");
> -	} else {
> -		/*
> -		 * Because that device tree does not encode ROM script address,
> -		 * the RAM script in firmware is mandatory for device tree
> -		 * probe, otherwise it fails.
> -		 */
> -		ret = of_property_read_string(np, "fsl,sdma-ram-script-name",
> -					      &fw_name);
> -		if (ret)
> -			dev_warn(&pdev->dev, "failed to get firmware name\n");
> -		else {
> -			ret = sdma_get_firmware(sdma, fw_name);
> -			if (ret)
> -				dev_warn(&pdev->dev, "failed to get firmware from device tree\n");
> -		}
> -	}
> -
>  	sdma->dma_device.dev = &pdev->dev;
>  
>  	sdma->dma_device.device_alloc_chan_resources = sdma_alloc_chan_resources;
> @@ -2161,6 +2140,33 @@ static int sdma_probe(struct platform_device *pdev)
>  		of_node_put(spba_bus);
>  	}
>  
> +	/*
> +	 * Kick off firmware loading as the very last step:
> +	 * attempt to load firmware only if we're not on the error path, because
> +	 * the firmware callback requires a fully functional and allocated sdma
> +	 * instance.
> +	 */
> +	if (pdata) {
> +		ret = sdma_get_firmware(sdma, pdata->fw_name);
> +		if (ret)
> +			dev_warn(&pdev->dev, "failed to get firmware from platform data\n");
> +	} else {
> +		/*
> +		 * Because that device tree does not encode ROM script address,
> +		 * the RAM script in firmware is mandatory for device tree
> +		 * probe, otherwise it fails.
> +		 */
> +		ret = of_property_read_string(np, "fsl,sdma-ram-script-name",
> +					      &fw_name);
> +		if (ret)
> +			dev_warn(&pdev->dev, "failed to get firmware name\n");

if should have braces!

> +		else {
> +			ret = sdma_get_firmware(sdma, fw_name);
> +			if (ret)
> +				dev_warn(&pdev->dev, "failed to get firmware from device tree\n");
> +		}
> +	}
> +
>  	return 0;
>  
>  err_register:
> -- 
> 2.17.1

Applied after fixing braces!


-- 
~Vinod