patch "usbcore/driver: Fix specific driver selection" added to usb-linus

This is a note to let you know that I've just added the patch titled

usbcore/driver: Fix specific driver selection

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From aea850cd35ae3d266fe6f93fb9edb25e4a555230 Mon Sep 17 00:00:00 2001
From: "M. Vefa Bicakci" <[email protected]>
Date: Tue, 22 Sep 2020 14:07:01 +0300
Subject: usbcore/driver: Fix specific driver selection

This commit resolves a bug in the selection/discovery of more specific USB device drivers for devices that are currently bound to generic USB device drivers.

The bug is in the logic that determines whether a device currently bound to a generic USB device driver should be re-probed by a more specific USB device driver or not. The code in __usb_bus_reprobe_drivers() used to have the following lines:

if (usb_device_match_id(udev, new_udriver->id_table) == NULL &&

      (!new_udriver->match || new_udriver->match(udev) != 0))

return 0;

  ret = device_reprobe(dev);

As the reader will notice, the code checks whether the USB device in consideration matches the identifier table (id_table) of a specific USB device_driver (new_udriver), followed by a similar check, but this time with the USB device driver's match function. However, the match function's return value is not checked correctly. When match() returns zero, it means that the specific USB device driver is *not* applicable to the USB device in question, but the code then goes on to reprobe the device with the new USB device driver under consideration. All this to say, the logic is inverted.

This bug was found by code inspection and instrumentation while investigating the root cause of the issue reported by Andrey Konovalov, where usbip took over syzkaller's virtual USB devices in an undesired manner. The report is linked below.

---
 drivers/usb/core/driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 7e73e989645b..715782995428 100644
@@ -924,7 +924,7 @@ static int __usb_bus_reprobe_drivers(struct device *dev, void *data)
 
 	udev = to_usb_device(dev);
 	if (usb_device_match_id(udev, new_udriver->id_table) == NULL &&
-	    (!new_udriver->match || new_udriver->match(udev) != 0))
+	    (!new_udriver->match || new_udriver->match(udev) == 0))
 		return 0;
 
 	ret = device_reprobe(dev);

2.28.0