[PATCH] usb: gadget: goku_udc: avoid NULL deref of dev->driver in INT_USBRESET log

[Stepan Ionichev <sozdayvek@gmail.com>]

goku_irq() handles a number of bus events under a single ep0 path.
It already guards the gadget driver suspend/resume callbacks against a
NULL ->driver:

	if (dev->gadget.speed != USB_SPEED_UNKNOWN
			&& dev->driver
			&& dev->driver->resume) {
		spin_unlock(&dev->lock);
		dev->driver->resume(&dev->gadget);
		...
	}

but the very next branch unconditionally dereferences dev->driver
when an INT_USBRESET arrives:

	if (stat & INT_USBRESET) {
		ACK(INT_USBRESET);
		INFO(dev, "USB reset done, gadget %s\n",
			dev->driver->driver.name);
	}

If the controller raises INT_USBRESET before any gadget driver has
been bound (or after one has been unbound), dev->driver is NULL and
the printk dereferences NULL.

smatch flags the inconsistency:

  drivers/usb/gadget/udc/goku_udc.c:1618 goku_irq() error:
  we previously assumed 'dev->driver' could be null (see line 1607)

Fall back to a placeholder when the gadget driver is not bound.

No functional change while a gadget driver is bound.

Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
---
 drivers/usb/gadget/udc/goku_udc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/goku_udc.c b/drivers/usb/gadget/udc/goku_udc.c
index db42a5e3e..ac2a984c2 100644
--- a/drivers/usb/gadget/udc/goku_udc.c
+++ b/drivers/usb/gadget/udc/goku_udc.c
@@ -1616,7 +1616,8 @@ static irqreturn_t goku_irq(int irq, void *_dev)
 		if (stat & INT_USBRESET) {		/* hub reset done */
 			ACK(INT_USBRESET);
 			INFO(dev, "USB reset done, gadget %s\n",
-				dev->driver->driver.name);
+				dev->driver ? dev->driver->driver.name :
+					      "<not bound>");
 		}
 		// and INT_ERR on some endpoint's crc/bitstuff/... problem
 	}
-- 
2.43.0