Hi,
On Mon, Dec 11, 2023 at 7:27 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> 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>
Thanks for the quick reply. I've added your comment almost verbatim to
the code and sent out a quick v3 with your tag:
https://lore.kernel.org/r/20231211073237.v3.1.If27eb3bf7812f91ab83810f232292f032f4203e0@changeid
