2023-12-08 20:32:22

by Douglas Anderson

Subject: [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 <[email protected]>
---

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

2023-12-08 20:48:17

by Alan Stern

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

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 <[email protected]>
> ---

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