Messages in this thread | | | From | "Zhang, Qiang1" <> | Subject | RE: [syzbot] KASAN: use-after-free Read in dev_uevent | Date | Thu, 24 Feb 2022 01:44:11 +0000 |
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On Wed, Feb 23, 2022 at 05:00:12PM +0100, gregkh@linuxfoundation.org wrote: > On Wed, Feb 23, 2022 at 09:38:20AM -0500, stern@rowland.harvard.edu wrote: > > Which bus locks are you referring to? I'm not aware of any locks > > that synchronize dev_uevent() with anything (in particular, with > > driver unbinding). > > The locks in the driver core that handle the binding and unbinding of > drivers to devices. > > > And as far as I know, usb_gadget_remove_driver() doesn't play any > > odd tricks with pointers. > > Ah, I never noticed that this is doing a "fake" bus and does the > bind/unbind itself outside of the driver core. It should just be a > normal bus type and have the core do the work for it, but oh well. > > And there is a lock that should serialize all of this already, so it's > odd that this is able to be triggered at all.
>>I guess at a minimum the UDC core should hold the device lock when it registers, unregisters, binds, or unbinds UDC and gadget devices. >>Would that be enough to fix the problem? I really don't understand how sysfs file access gets synchronized with device removal.
Agree with you, in usb_gadget_remove_driver() function, the udc->dev.driver and udc->gadget->dev.driver be set to null without any protection, so when the udevd accessed the dev->driver, this address may be invalid at this time. maybe the operation of dev->driver can be protected by device_lock().
Thanks, Zqiang
> Unless the device is being removed at the same time it was manually > unbound from the driver? If so, then this really should be fixed up > to use the driver core logic instead... >> >>Device removal does of course trigger unbinding, but they always take place in the same thread so it isn't an issue. >> >>Probably part of the reason people don't want to use the driver core here is so that they can specify which UDC a gadget driver should bind to. The driver core would always bind each new gadget to the first registered gadget driver. >> >>When Dave Brownell originally wrote the gadget subsystem, I believe he didn't bother to integrate it with the driver core because it was a "bus" with only a single device and a single driver. The ability to have multiple UDCs in the system was added later. >> >>Alan Stern
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