On 17/09/2020 18.01, Alan Stern wrote:
On Thu, Sep 17, 2020 at 05:41:50PM +0300, M. Vefa Bicakci wrote:
This commit resolves a minor 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 related to the way a candidate USB device driver is
compared against the generic USB device driver. The code in
is_dev_usb_generic_driver() assumes that the device driver in question
is a USB device driver by calling to_usb_device_driver(dev->driver)
to downcast; however I have observed that this assumption is not always
true, through code instrumentation.
Given that USB device drivers are bound to struct device instances with
of the type &usb_device_type, this commit checks the return value of
is_usb_device() before the call to is_dev_usb_generic_driver(), and
therefore ensures that incorrect type downcasts do not occur. The use
of is_usb_device() was suggested by Bastien Nocera.
This bug was found while investigating Andrey Konovalov's report
indicating USB/IP subsystem's misbehaviour with the generic USB device
driver matching code.
Fixes: d5643d2249 ("USB: Fix device driver race")
Link: https://lore.kernel.org/linux-usb/CAAeHK+zOrHnxjRFs=OE8T=O9208B9HP_oo8RZpyVOZ9AJ54pAA@xxxxxxxxxxxxxx/
Cc: <stable@xxxxxxxxxxxxxxx> # 5.8
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Bastien Nocera <hadess@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: M. Vefa Bicakci <m.v.b@xxxxxxxxxx>
---
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 950044a6e77f..ba7acd6e7cc4 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -919,7 +919,7 @@ static int __usb_bus_reprobe_drivers(struct device *dev, void *data)
struct usb_device *udev;
int ret;
- if (!is_dev_usb_generic_driver(dev))
+ if (!is_usb_device(dev) || !is_dev_usb_generic_driver(dev))
return 0;
udev = to_usb_device(dev);
--
2.26.2
Why not simplify the whole thing by testing the underlying driver
pointer?
/* Don't reprobe if current driver isn't usb_generic_driver */
if (dev->driver != &usb_generic_driver.drvwrap.driver)
return 0;
Then is_dev_usb_generic_driver can be removed entirely.
Alan, sorry for the delay, and thanks for the review! I had not thought
of this. I will apply the changes you have suggested with the next version
of the patch series.
Thanks again,
Vefa
