On Mon, Dec 11, 2023 at 07:08:14AM -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.
>
> 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()")
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
>
> Changes in v2:
> - Return immediately if no driver, as per Alan.
>
> drivers/usb/core/generic.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
> index dcb897158228..2be1e8901e2f 100644
> --- a/drivers/usb/core/generic.c
> +++ b/drivers/usb/core/generic.c
> @@ -59,7 +59,11 @@ 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 (!udev->dev.driver)
> + return -1;
This is a rather unusual condition. It would be good to put a comment
just before the test, explaining that 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.
Along with the comment, feel free to add:
Reviewed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Alan Stern
> + udriver = to_usb_device_driver(udev->dev.driver);
>
> if (usb_device_is_owned(udev))
> return 0;
> --
> 2.43.0.472.g3155946c3a-goog
>
