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:

quoted

From: Reilly Grant <redacted>

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 <redacted>
Signed-off-by: Emilio López <emilio.lopez-ZGY8ohtN/8pPYcu2f3hruQ@public.gmane.org>

---

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

quoted

@@ -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.

quoted

@@ -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.

quoted

+				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