linux-kernel - Re: [PATCH v3] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

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Message-ID: <56B7F5D3.6050009@collabora.co.uk>
Date:	Sun, 7 Feb 2016 22:56:35 -0300
From:	Emilio López <emilio.lopez@...labora.co.uk>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	gregkh@...uxfoundation.org, kborer@...il.com, bjorn@...k.no,
	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 v3] usb: devio: Add ioctl to disallow detaching kernel USB
 drivers.

Hello Alan,

El 04/02/16 a las 13:27, Alan Stern escribió:
> On Thu, 4 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.
>>
>> Signed-off-by: Reilly Grant <reillyg@...omium.org>
>> Signed-off-by: Emilio López <emilio.lopez@...labora.co.uk>
>>
>> ---
>>
>> Changes in v3:
>> - Switch ioctl to use a __u32 given the iface qty is capped at 32
>> - Reword comments as requested by Alan
>> - Allow callers to shrink the allowed interfaces mask
>
>> @@ -624,6 +626,10 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
>>   	if (test_bit(ifnum, &ps->ifclaimed))
>>   		return 0;
>>
>> +	if (ps->privileges_dropped
>> +	 && !test_bit(ifnum, &ps->interface_allowed_mask))
>
> Continuation lines in this file are indented by 2 tab stops, not 1
> space.

Ok, I'll change it.

>> @@ -1198,6 +1202,27 @@ static int proc_connectinfo(struct usb_dev_state *ps, void __user *arg)
>>
>>   static int proc_resetdevice(struct usb_dev_state *ps)
>>   {
>> +	struct usb_host_config *actconfig = ps->dev->actconfig;
>> +	struct usb_interface *interface;
>> +	int i, number;
>> +
>> +	/* Don't allow a device reset if the process has dropped the
>> +	 * privilege to do such things and any of the interfaces are
>> +	 * currently claimed.
>> +	 */
>> +	if (ps->privileges_dropped && actconfig) {
>> +		for (i = 0; i < actconfig->desc.bNumInterfaces; ++i) {
>> +			interface = actconfig->interface[i];
>> +			number = interface->cur_altsetting->desc.bInterfaceNumber;
>> +			if (usb_interface_claimed(interface)) {
>
> The test should be:
>
> 			if (usb_interface_claimed(interface) &&
> 					!test_bit(number, &ps->ifclaimed)) {
>
> We don't want to prevent people from resetting a device merely because
> they have claimed an interface.  Only if someone else has claimed one.

Sounds sensible, now changed as well.

>> +				dev_warn(&ps->dev->dev,
>> +					"usbfs: interface %d claimed by %s while '%s' resets device\n",
>> +					number,	interface->dev.driver->name, current->comm);
>> +				return -EACCES;
>> +			}
>> +		}
>> +	}
>> +
>>   	return usb_reset_device(ps->dev);
>>   }
>
> Also, it wouldn't hurt to change proc_get_capabilities() and
> include/uapi/linux/usbdevicefs.h to add a USBDEVFS_CAP_DROP_PRIVILEGES
> bit.

Good idea, I've added a bit now. I'm writing some docs and polishing a 
program to test this as Greg requested and I'll submit v4 then.

Thanks!
Emilio