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    SubjectRe: [PATCH v3] usb: devio: Add ioctl to disallow detaching kernel USB drivers.
    On Thu, 4 Feb 2016, Emilio López wrote:

    > From: Reilly Grant <reillyg@chromium.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@chromium.org>
    > Signed-off-by: Emilio López <emilio.lopez@collabora.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.

    > @@ -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.

    > + 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.

    Alan Stern

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