Re: [PATCH] usb: gadget: aspeed_udc: check endpoint DMA allocation

[Andrew Jeffery <andrew@codeconstruct.com.au>]

On Mon, 2026-06-08 at 16:19 +0800, Ruoyu Wang wrote:
> ast_udc_probe() allocates a coherent DMA buffer used as the backing store
> for endpoint buffers. ast_udc_init_ep() derives per-endpoint buffer
> pointers from udc->ep0_buf, so a failed allocation is dereferenced during
> probe.
> 
> Check the allocation before endpoint setup. The existing probe error path
> called ast_udc_remove(), which unregisters the gadget unconditionally and
> is not safe before usb_add_gadget_udc() succeeds. Add a local cleanup
> helper for probe failures so pre-registration failures only unwind the
> resources that were actually initialized.
> 
> This was found by a local static analysis checker for unchecked allocator
> returns while scanning Linux 6.16. The change was checked by applying it
> to current mainline and by running checkpatch. I do not have access to
> Aspeed UDC hardware, so no runtime testing was performed.
> 
> Fixes: 055276c13205 ("usb: gadget: add Aspeed ast2600 udc driver")
> Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
> ---
> Note: a 2022 patch attempted to add only a NULL check for this
> allocation:
> https://lore.kernel.org/all/20221213025120.23149-1-jiasheng@iscas.ac.cn/
> 
> This version also fixes the probe unwind path so the clock is disabled
> on allocation failure and usb_del_gadget_udc() is not called before the
> gadget has been registered.
> 
> diff --git a/drivers/usb/gadget/udc/aspeed_udc.c b/drivers/usb/gadget/udc/aspeed_udc.c
> index 7fc6696b7..809a7d5b7 100644
> --- a/drivers/usb/gadget/udc/aspeed_udc.c
> +++ b/drivers/usb/gadget/udc/aspeed_udc.c
> @@ -1434,11 +1434,34 @@ static void ast_udc_init_hw(struct ast_udc_dev *udc)
>  	ast_udc_write(udc, 0, AST_UDC_EP0_CTRL);
>  }
>  
> +static void ast_udc_cleanup(struct platform_device *pdev)
> +{
> +	struct ast_udc_dev *udc = platform_get_drvdata(pdev);
> +	unsigned long flags;
> +	u32 ctrl;
> +
> +	spin_lock_irqsave(&udc->lock, flags);
> +
> +	/* Disable upstream port connection */
> +	ctrl = ast_udc_read(udc, AST_UDC_FUNC_CTRL) & ~USB_UPSTREAM_EN;
> +	ast_udc_write(udc, ctrl, AST_UDC_FUNC_CTRL);
> +
> +	clk_disable_unprepare(udc->clk);
> +
> +	spin_unlock_irqrestore(&udc->lock, flags);
> +
> +	if (udc->ep0_buf)
> +		dma_free_coherent(&pdev->dev,
> +				  AST_UDC_EP_DMA_SIZE * AST_UDC_NUM_ENDPOINTS,
> +				  udc->ep0_buf,
> +				  udc->ep0_buf_dma);
> +
> +	udc->ep0_buf = NULL;
> +}
> +
>  static void ast_udc_remove(struct platform_device *pdev)
>  {
>  	struct ast_udc_dev *udc = platform_get_drvdata(pdev);
> -	unsigned long flags;
> -	u32 ctrl;
>  
>  	usb_del_gadget_udc(&udc->gadget);
>  	if (udc->driver) {
> @@ -1453,23 +1476,7 @@ static void ast_udc_remove(struct platform_device *pdev)
>  		return;
>  	}
>  
> -	spin_lock_irqsave(&udc->lock, flags);
> -
> -	/* Disable upstream port connection */
> -	ctrl = ast_udc_read(udc, AST_UDC_FUNC_CTRL) & ~USB_UPSTREAM_EN;
> -	ast_udc_write(udc, ctrl, AST_UDC_FUNC_CTRL);
> -
> -	clk_disable_unprepare(udc->clk);
> -
> -	spin_unlock_irqrestore(&udc->lock, flags);
> -
> -	if (udc->ep0_buf)
> -		dma_free_coherent(&pdev->dev,
> -				  AST_UDC_EP_DMA_SIZE * AST_UDC_NUM_ENDPOINTS,
> -				  udc->ep0_buf,
> -				  udc->ep0_buf_dma);
> -
> -	udc->ep0_buf = NULL;
> +	ast_udc_cleanup(pdev);
>  }
>  
>  static int ast_udc_probe(struct platform_device *pdev)
> @@ -1523,6 +1530,10 @@ static int ast_udc_probe(struct platform_device *pdev)
>  					  AST_UDC_EP_DMA_SIZE *
>  					  AST_UDC_NUM_ENDPOINTS,
>  					  &udc->ep0_buf_dma, GFP_KERNEL);
> +	if (!udc->ep0_buf) {
> +		rc = -ENOMEM;
> +		goto err_disable_clk;
> +	}
>  
>  	udc->gadget.speed = USB_SPEED_UNKNOWN;
>  	udc->gadget.max_speed = USB_SPEED_HIGH;
> @@ -1553,20 +1564,20 @@ static int ast_udc_probe(struct platform_device *pdev)
>  	udc->irq = platform_get_irq(pdev, 0);
>  	if (udc->irq < 0) {
>  		rc = udc->irq;
> -		goto err;
> +		goto err_cleanup;
>  	}
>  
>  	rc = devm_request_irq(&pdev->dev, udc->irq, ast_udc_isr, 0,
>  			      KBUILD_MODNAME, udc);
>  	if (rc) {
>  		dev_err(&pdev->dev, "Failed to request interrupt\n");
> -		goto err;
> +		goto err_cleanup;
>  	}
>  
>  	rc = usb_add_gadget_udc(&pdev->dev, &udc->gadget);
>  	if (rc) {
>  		dev_err(&pdev->dev, "Failed to add gadget udc\n");
> -		goto err;
> +		goto err_cleanup;
>  	}
>  
>  	dev_info(&pdev->dev, "Initialized udc in USB%s mode\n",
> @@ -1574,9 +1585,14 @@ static int ast_udc_probe(struct platform_device *pdev)
>  
>  	return 0;
>  
> +err_disable_clk:
> +	clk_disable_unprepare(udc->clk);
> +	goto err;
> +err_cleanup:
> +	ast_udc_cleanup(pdev);
> +	goto err;
>  err:

That last goto is unnecessary.

However, I find it unsettling that in a patch fixing resource handling
we add a mildly convoluted cleanup path, with portions jumping over
each other in this way.

The err_disable_clk label is only used once, and itself jumps down to
the err label. This is the case because beyond its goto we free udc-
>ep0_buf in ast_udc_cleanup(). I think it would make more sense to move
the call to clk_disable_unprepare() into the conditional body of the
allocation failure test, then change its goto label to 'err'. That way
the above hunk becomes:

   +err_cleanup:
   +    ast_udc_cleanup(pdev);
    err:
        ...

Which seems a bit more natural.

Andrew

>  	dev_err(&pdev->dev, "Failed to udc probe, rc:0x%x\n", rc);
> -	ast_udc_remove(pdev);
>  
>  	return rc;
>  }