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Date:   Sat, 18 Apr 2020 22:16:32 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Julian Squires <julian@cipht.net>,
        Hans de Goede <hdegoede@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        syzbot <syzbot+7bf5a7b0f0a1f9446f4c@syzkaller.appspotmail.com>
cc:     linux-input@vger.kernel.org, <andreyknvl@google.com>,
        <gregkh@linuxfoundation.org>, <ingrassia@epigenesys.com>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        <syzkaller-bugs@googlegroups.com>
Subject: Re: KASAN: use-after-free Read in usbhid_close (3)
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linux-input people:

syzbot has found a bug related to USB/HID/input, and I have narrowed it
down to the wacom driver.  As far as I can tell, the problem is caused
the fact that drivers/hid/wacom_sys.c calls input_register_device()
in several places, but it never calls input_unregister_device().

I know very little about the input subsystem, but this certainly seems 
like a bug.

When the device is unplugged, the disconnect pathway doesn't call
hid_hw_close().  That routine doesn't get called until the user closes
the device file (which can be long after the device is gone and
hid_hw_stop() has run).  Then usbhid_close() gets a use-after-free
error when it tries to access data structures that were deallocated by
usbhid_stop().  No doubt there are other problems too, but this is
the one that syzbot found.

Can any of you help fix this?  Thanks.

Alan Stern