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.

Fixes: d5643d2249 ("USB: Fix device driver race") Link: https://lore.kernel.org/linux-usb/CAAeHK+zOrHnxjRFs=OE8T=O9208B9HP_oo8RZpyVO... Cc: stable@vger.kernel.org # 5.8 Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Alan Stern stern@rowland.harvard.edu Cc: Bastien Nocera hadess@hadess.net Cc: Shuah Khan shuah@kernel.org Cc: Valentina Manea valentina.manea.m@gmail.com Cc: syzkaller@googlegroups.com Signed-off-by: M. Vefa Bicakci m.v.b@runbox.com

--- v3: No functional changes; only commit message changes. v2: Following Bastien Nocera's suggestion, this is a new patch, split from the patch published at: https://lore.kernel.org/linux-usb/20200917095959.174378-1-m.v.b@runbox.com/ --- drivers/usb/core/driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c index c976ea9f9582..950044a6e77f 100644 --- a/drivers/usb/core/driver.c +++ b/drivers/usb/core/driver.c @@ -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);