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

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.

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()")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/usb/core/generic.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
index dcb897158228..365482347333 100644
--- a/drivers/usb/core/generic.c
+++ b/drivers/usb/core/generic.c

@@ -59,15 +59,19 @@ 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 (usb_device_is_owned(udev))
 		return 0;
 
-	if (udriver->choose_configuration) {
-		i = udriver->choose_configuration(udev);
-		if (i >= 0)
-			return i;
+	if (udev->dev.driver) {
+		udriver = to_usb_device_driver(udev->dev.driver);
+
+		if (udriver->choose_configuration) {
+			i = udriver->choose_configuration(udev);
+			if (i >= 0)
+				return i;
+		}
 	}
 
 	best = NULL;

-- 
2.43.0.472.g3155946c3a-goog

On Fri, Dec 08, 2023 at 12:31:24PM -0800, Douglas Anderson wrote:

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.

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()")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

I'm not sure this is the best solution.  A USB device with no driver is 
an anomaly; in all likelihood we shouldn't be calling 
usb_choose_configuration() for such a device in the first place.

So I think a better solution would be to put this check in 
usb_authorize_device() before it does the autoresume, or else to make 
usb_choose_configuration() return immediately, right at the start, if 
there is no driver.

Alan Stern