[PATCH v3] usb: core: Fix crash w/ usb_choose_configuration() if no driver

[Douglas Anderson]

It's possible that usb_choose_configuration() can get called when a
USB device has no driver. In this case the recent commit a87b8e3be926
("usb: core: Allow subclassed USB drivers to override
usb_choose_configuration()") can cause a crash since it dereferenced
the driver structure without checking for NULL. Let's add a check.

A USB device with no driver is an anomaly, so make
usb_choose_configuration() return immediately if there is no driver.

This was seen in the real world when usbguard got ahold of a r8152
device at the wrong time. It can also be simulated via this on a
computer with one r8152-based USB Ethernet adapter:
  cd /sys/bus/usb/drivers/r8152-cfgselector
  to_unbind="$(ls -d *-*)"
  real_dir="$(readlink -f "${to_unbind}")"
  echo "${to_unbind}" > unbind
  cd "${real_dir}"
  echo 0 > authorized
  echo 1 > authorized

Fixes: a87b8e3be926 ("usb: core: Allow subclassed USB drivers to override usb_choose_configuration()")
Reviewed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v3:
- Add comment in code, as per Alan.

Changes in v2:
- Return immediately if no driver, as per Alan.

 drivers/usb/core/generic.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
index dcb897158228..b134bff5c3fe 100644
--- a/drivers/usb/core/generic.c
+++ b/drivers/usb/core/generic.c
@@ -59,7 +59,16 @@ int usb_choose_configuration(struct usb_device *udev)
 	int num_configs;
 	int insufficient_power = 0;
 	struct usb_host_config *c, *best;
-	struct usb_device_driver *udriver = to_usb_device_driver(udev->dev.driver);
+	struct usb_device_driver *udriver;
+
+	/*
+	 * If a USB device (not an interface) doesn't have a driver then the
+	 * kernel has no business trying to select or install a configuration
+	 * for it.
+	 */
+	if (!udev->dev.driver)
+		return -1;
+	udriver = to_usb_device_driver(udev->dev.driver);
 
 	if (usb_device_is_owned(udev))
 		return 0;
-- 
2.43.0.472.g3155946c3a-goog