[PATCH v2] 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.

v1:
https://lore.kernel.org/all/20260608081948.3-1-ruoyuw560@gmail.com/

Changes in v2:
- Simplify the allocation-failure cleanup path as suggested by Andrew
  Jeffery: disable the clock in the allocation-failure branch and let
  err_cleanup fall through to err.

diff --git a/drivers/usb/gadget/udc/aspeed_udc.c b/drivers/usb/gadget/udc/aspeed_udc.c
--- a/drivers/usb/gadget/udc/aspeed_udc.c
+++ b/drivers/usb/gadget/udc/aspeed_udc.c
@@ -1434,25 +1434,12 @@ static void ast_udc_init_hw(struct ast_u
 	ast_udc_write(udc, 0, AST_UDC_EP0_CTRL);
 }
 
-static void ast_udc_remove(struct platform_device *pdev)
+static void ast_udc_cleanup(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) {
-		/*
-		 * This is broken as only some cleanup is skipped, *udev is
-		 * freed and the register mapping goes away. Any further usage
-		 * probably crashes. Also the device is unbound, so the skipped
-		 * cleanup is never catched up later.
-		 */
-		dev_alert(&pdev->dev,
-			  "Driver is busy and still going away. Fasten your seat belts!\n");
-		return;
-	}
-
 	spin_lock_irqsave(&udc->lock, flags);
 
 	/* Disable upstream port connection */
@@ -1472,6 +1459,26 @@ static void ast_udc_remove(struct platfo
 	udc->ep0_buf = NULL;
 }
 
+static void ast_udc_remove(struct platform_device *pdev)
+{
+	struct ast_udc_dev *udc = platform_get_drvdata(pdev);
+
+	usb_del_gadget_udc(&udc->gadget);
+	if (udc->driver) {
+		/*
+		 * This is broken as only some cleanup is skipped, *udev is
+		 * freed and the register mapping goes away. Any further usage
+		 * probably crashes. Also the device is unbound, so the skipped
+		 * cleanup is never catched up later.
+		 */
+		dev_alert(&pdev->dev,
+			  "Driver is busy and still going away. Fasten your seat belts!\n");
+		return;
+	}
+
+	ast_udc_cleanup(pdev);
+}
+
 static int ast_udc_probe(struct platform_device *pdev)
 {
 	enum usb_device_speed max_speed;
@@ -1524,6 +1531,12 @@ static int ast_udc_probe(struct platform
 					  AST_UDC_NUM_ENDPOINTS,
 					  &udc->ep0_buf_dma, GFP_KERNEL);
 
+	if (!udc->ep0_buf) {
+		clk_disable_unprepare(udc->clk);
+		rc = -ENOMEM;
+		goto err;
+	}
+
 	udc->gadget.speed = USB_SPEED_UNKNOWN;
 	udc->gadget.max_speed = USB_SPEED_HIGH;
 	udc->creq = udc->reg + AST_UDC_SETUP0;
@@ -1553,20 +1566,20 @@ static int ast_udc_probe(struct platform
 	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 +1587,10 @@ static int ast_udc_probe(struct platform
 
 	return 0;
 
+err_cleanup:
+	ast_udc_cleanup(pdev);
 err:
 	dev_err(&pdev->dev, "Failed to udc probe, rc:0x%x\n", rc);
-	ast_udc_remove(pdev);
 
 	return rc;
 }