[PATCH] usb: gadget: goku_udc: avoid double-free in error path

[Guangshuo Li <lgs201920130244@gmail.com>]

goku_probe() allocates struct goku_udc and passes &dev->gadget to
usb_add_gadget_udc_release() with gadget_release() as the release
callback. usb_add_gadget_udc_release() initializes the gadget device with
that release callback before calling usb_add_gadget().

If usb_add_gadget() fails, usb_add_gadget_udc_release() calls
usb_put_gadget(), which invokes gadget_release() and frees dev. The
current error path then falls through to kfree(dev), freeing the same
object again.

Set dev to NULL before jumping to the common error path so the explicit
kfree(dev) is skipped after ownership has already been dropped by the
gadget core.

This issue was found by a static analysis tool I am developing.

Fixes: 2a334cfaf393 ("usb: gadget: goku_udc: fix memory leak in goku_probe()")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
 drivers/usb/gadget/udc/goku_udc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/udc/goku_udc.c b/drivers/usb/gadget/udc/goku_udc.c
index db42a5e3e805..46a7e0f6541e 100644
--- a/drivers/usb/gadget/udc/goku_udc.c
+++ b/drivers/usb/gadget/udc/goku_udc.c
@@ -1819,15 +1819,20 @@ static int goku_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 
 	retval = usb_add_gadget_udc_release(&pdev->dev, &dev->gadget,
 			gadget_release);
-	if (retval)
+	if (retval) {
+		/*
+		 * usb_add_gadget_udc_release() calls the gadget release
+		 * function on failure, and gadget_release() frees dev.
+		 */
+		dev = NULL;
 		goto err;
+	}
 
 	return 0;
 
 err:
 	if (dev)
 		goku_remove (pdev);
-	/* gadget_release is not registered yet, kfree explicitly */
 	kfree(dev);
 	return retval;
 }
-- 
2.43.0