linux-kernel - Re: [PATCH v4] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

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Date:	Thu, 18 Feb 2016 13:44:46 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Emilio López <emilio.lopez@...labora.co.uk>
cc:	gregkh@...uxfoundation.org, <kborer@...il.com>,
	<reillyg@...omium.org>, <keescook@...omium.org>,
	<linux-api@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jorgelo@...omium.org>,
	<dan.carpenter@...cle.com>
Subject: Re: [PATCH v4] usb: devio: Add ioctl to disallow detaching kernel
 USB drivers.

On Sun, 14 Feb 2016, Emilio López wrote:

> From: Reilly Grant <reillyg@...omium.org>
> 
> The new USBDEVFS_DROP_PRIVILEGES ioctl allows a process to voluntarily
> relinquish the ability to issue other ioctls that may interfere with
> other processes and drivers that have claimed an interface on the
> device.
> 
> This commit also includes a simple utility to be able to test the
> ioctl, located at Documentation/usb/usbdevfs-drop-permissions.c
> 
> Example (with qemu-kvm's input device):
> 
>     $ lsusb
>     ...
>     Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
> 
>     $ usb-devices
>     ...
>     C:  #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
>     I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=00 Prot=02 Driver=usbhid
> 
>     $ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
>     OK: privileges dropped!
>     Available options:
>     [0] Exit now
>     [1] Reset device. Should fail if device is in use
>     [2] Claim 4 interfaces. Should succeed where not in use
>     [3] Narrow interface permission mask
>     Which option shall I run?: 1
>     ERROR: USBDEVFS_RESET failed! (1 - Operation not permitted)
>     Which test shall I run next?: 2
>     ERROR claiming if 0 (1 - Operation not permitted)
>     ERROR claiming if 1 (1 - Operation not permitted)
>     ERROR claiming if 2 (1 - Operation not permitted)
>     ERROR claiming if 3 (1 - Operation not permitted)
>     Which test shall I run next?: 0
> 
> After unbinding usbhid:
> 
>     $ usb-devices
>     ...
>     I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=00 Prot=02 Driver=(none)
> 
>     $ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
>     ...
>     Which option shall I run?: 2
>     OK: claimed if 0
>     ERROR claiming if 1 (1 - Operation not permitted)
>     ERROR claiming if 2 (1 - Operation not permitted)
>     ERROR claiming if 3 (1 - Operation not permitted)
>     Which test shall I run next?: 1
>     OK: USBDEVFS_RESET succeeded
>     Which test shall I run next?: 0
> 
> After unbinding usbhid and restricting the mask:
> 
>     $ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
>     ...
>     Which option shall I run?: 3
>     Insert new mask: 0
>     OK: privileges dropped!
>     Which test shall I run next?: 2
>     ERROR claiming if 0 (1 - Operation not permitted)
>     ERROR claiming if 1 (1 - Operation not permitted)
>     ERROR claiming if 2 (1 - Operation not permitted)
>     ERROR claiming if 3 (1 - Operation not permitted)
> 
> Signed-off-by: Reilly Grant <reillyg@...omium.org>
> Signed-off-by: Emilio López <emilio.lopez@...labora.co.uk>

Acked-by: Alan Stern <stern@...land.harvard.edu>