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

[Ruoyu Wang <ruoyuw560@gmail.com>]

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

-- 
2.51.0