USB: Move wusbcore and UWB to staging as it is obsolete

The UWB and wusbcore code is long obsolete, so let us just move the code
out of the real part of the kernel and into the drivers/staging/
location with plans to remove it entirely in a few releases.

Link: https://lore.kernel.org/r/20190806101509.GA11280@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 599 insertions, 0 deletions

diff --git a/drivers/staging/wusbcore/security.c b/drivers/staging/wusbcore/security.c
new file mode 100644
index 000000000000..14ac8c98ac9e
--- /dev/null
+++ b/drivers/staging/wusbcore/security.c
@@ -0,0 +1,599 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Wireless USB Host Controller
+ * Security support: encryption enablement, etc
+ *
+ * Copyright (C) 2006 Intel Corporation
+ * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
+ *
+ * FIXME: docs
+ */
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/usb/ch9.h>
+#include <linux/random.h>
+#include <linux/export.h>
+#include "wusbhc.h"
+#include <asm/unaligned.h>
+
+static void wusbhc_gtk_rekey_work(struct work_struct *work);
+
+int wusbhc_sec_create(struct wusbhc *wusbhc)
+{
+	/*
+	 * WQ is singlethread because we need to serialize rekey operations.
+	 * Use a separate workqueue for security operations instead of the
+	 * wusbd workqueue because security operations may need to communicate
+	 * directly with downstream wireless devices using synchronous URBs.
+	 * If a device is not responding, this could block other host
+	 * controller operations.
+	 */
+	wusbhc->wq_security = create_singlethread_workqueue("wusbd_security");
+	if (wusbhc->wq_security == NULL) {
+		pr_err("WUSB-core: Cannot create wusbd_security workqueue\n");
+		return -ENOMEM;
+	}
+
+	wusbhc->gtk.descr.bLength = sizeof(wusbhc->gtk.descr) +
+		sizeof(wusbhc->gtk.data);
+	wusbhc->gtk.descr.bDescriptorType = USB_DT_KEY;
+	wusbhc->gtk.descr.bReserved = 0;
+	wusbhc->gtk_index = 0;
+
+	INIT_WORK(&wusbhc->gtk_rekey_work, wusbhc_gtk_rekey_work);
+
+	return 0;
+}
+
+
+/* Called when the HC is destroyed */
+void wusbhc_sec_destroy(struct wusbhc *wusbhc)
+{
+	destroy_workqueue(wusbhc->wq_security);
+}
+
+
+/**
+ * wusbhc_next_tkid - generate a new, currently unused, TKID
+ * @wusbhc:   the WUSB host controller
+ * @wusb_dev: the device whose PTK the TKID is for
+ *            (or NULL for a TKID for a GTK)
+ *
+ * The generated TKID consists of two parts: the device's authenticated
+ * address (or 0 or a GTK); and an incrementing number.  This ensures
+ * that TKIDs cannot be shared between devices and by the time the
+ * incrementing number wraps around the older TKIDs will no longer be
+ * in use (a maximum of two keys may be active at any one time).
+ */
+static u32 wusbhc_next_tkid(struct wusbhc *wusbhc, struct wusb_dev *wusb_dev)
+{
+	u32 *tkid;
+	u32 addr;
+
+	if (wusb_dev == NULL) {
+		tkid = &wusbhc->gtk_tkid;
+		addr = 0;
+	} else {
+		tkid = &wusb_port_by_idx(wusbhc, wusb_dev->port_idx)->ptk_tkid;
+		addr = wusb_dev->addr & 0x7f;
+	}
+
+	*tkid = (addr << 8) | ((*tkid + 1) & 0xff);
+
+	return *tkid;
+}
+
+static void wusbhc_generate_gtk(struct wusbhc *wusbhc)
+{
+	const size_t key_size = sizeof(wusbhc->gtk.data);
+	u32 tkid;
+
+	tkid = wusbhc_next_tkid(wusbhc, NULL);
+
+	wusbhc->gtk.descr.tTKID[0] = (tkid >>  0) & 0xff;
+	wusbhc->gtk.descr.tTKID[1] = (tkid >>  8) & 0xff;
+	wusbhc->gtk.descr.tTKID[2] = (tkid >> 16) & 0xff;
+
+	get_random_bytes(wusbhc->gtk.descr.bKeyData, key_size);
+}
+
+/**
+ * wusbhc_sec_start - start the security management process
+ * @wusbhc: the WUSB host controller
+ *
+ * Generate and set an initial GTK on the host controller.
+ *
+ * Called when the HC is started.
+ */
+int wusbhc_sec_start(struct wusbhc *wusbhc)
+{
+	const size_t key_size = sizeof(wusbhc->gtk.data);
+	int result;
+
+	wusbhc_generate_gtk(wusbhc);
+
+	result = wusbhc->set_gtk(wusbhc, wusbhc->gtk_tkid,
+				&wusbhc->gtk.descr.bKeyData, key_size);
+	if (result < 0)
+		dev_err(wusbhc->dev, "cannot set GTK for the host: %d\n",
+			result);
+
+	return result;
+}
+
+/**
+ * wusbhc_sec_stop - stop the security management process
+ * @wusbhc: the WUSB host controller
+ *
+ * Wait for any pending GTK rekeys to stop.
+ */
+void wusbhc_sec_stop(struct wusbhc *wusbhc)
+{
+	cancel_work_sync(&wusbhc->gtk_rekey_work);
+}
+
+
+/** @returns encryption type name */
+const char *wusb_et_name(u8 x)
+{
+	switch (x) {
+	case USB_ENC_TYPE_UNSECURE:	return "unsecure";
+	case USB_ENC_TYPE_WIRED:	return "wired";
+	case USB_ENC_TYPE_CCM_1:	return "CCM-1";
+	case USB_ENC_TYPE_RSA_1:	return "RSA-1";
+	default:			return "unknown";
+	}
+}
+EXPORT_SYMBOL_GPL(wusb_et_name);
+
+/*
+ * Set the device encryption method
+ *
+ * We tell the device which encryption method to use; we do this when
+ * setting up the device's security.
+ */
+static int wusb_dev_set_encryption(struct usb_device *usb_dev, int value)
+{
+	int result;
+	struct device *dev = &usb_dev->dev;
+	struct wusb_dev *wusb_dev = usb_dev->wusb_dev;
+
+	if (value) {
+		value = wusb_dev->ccm1_etd.bEncryptionValue;
+	} else {
+		/* FIXME: should be wusb_dev->etd[UNSECURE].bEncryptionValue */
+		value = 0;
+	}
+	/* Set device's */
+	result = usb_control_msg(usb_dev, usb_sndctrlpipe(usb_dev, 0),
+			USB_REQ_SET_ENCRYPTION,
+			USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+			value, 0, NULL, 0, USB_CTRL_SET_TIMEOUT);
+	if (result < 0)
+		dev_err(dev, "Can't set device's WUSB encryption to "
+			"%s (value %d): %d\n",
+			wusb_et_name(wusb_dev->ccm1_etd.bEncryptionType),
+			wusb_dev->ccm1_etd.bEncryptionValue,  result);
+	return result;
+}
+
+/*
+ * Set the GTK to be used by a device.
+ *
+ * The device must be authenticated.
+ */
+static int wusb_dev_set_gtk(struct wusbhc *wusbhc, struct wusb_dev *wusb_dev)
+{
+	struct usb_device *usb_dev = wusb_dev->usb_dev;
+	u8 key_index = wusb_key_index(wusbhc->gtk_index,
+		WUSB_KEY_INDEX_TYPE_GTK, WUSB_KEY_INDEX_ORIGINATOR_HOST);
+
+	return usb_control_msg(
+		usb_dev, usb_sndctrlpipe(usb_dev, 0),
+		USB_REQ_SET_DESCRIPTOR,
+		USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+		USB_DT_KEY << 8 | key_index, 0,
+		&wusbhc->gtk.descr, wusbhc->gtk.descr.bLength,
+		USB_CTRL_SET_TIMEOUT);
+}
+
+
+/* FIXME: prototype for adding security */
+int wusb_dev_sec_add(struct wusbhc *wusbhc,
+		     struct usb_device *usb_dev, struct wusb_dev *wusb_dev)
+{
+	int result, bytes, secd_size;
+	struct device *dev = &usb_dev->dev;
+	struct usb_security_descriptor *secd, *new_secd;
+	const struct usb_encryption_descriptor *etd, *ccm1_etd = NULL;
+	const void *itr, *top;
+	char buf[64];
+
+	secd = kmalloc(sizeof(*secd), GFP_KERNEL);
+	if (secd == NULL) {
+		result = -ENOMEM;
+		goto out;
+	}
+
+	result = usb_get_descriptor(usb_dev, USB_DT_SECURITY,
+				    0, secd, sizeof(*secd));
+	if (result < (int)sizeof(*secd)) {
+		dev_err(dev, "Can't read security descriptor or "
+			"not enough data: %d\n", result);
+		goto out;
+	}
+	secd_size = le16_to_cpu(secd->wTotalLength);
+	new_secd = krealloc(secd, secd_size, GFP_KERNEL);
+	if (new_secd == NULL) {
+		dev_err(dev,
+			"Can't allocate space for security descriptors\n");
+		result = -ENOMEM;
+		goto out;
+	}
+	secd = new_secd;
+	result = usb_get_descriptor(usb_dev, USB_DT_SECURITY,
+				    0, secd, secd_size);
+	if (result < secd_size) {
+		dev_err(dev, "Can't read security descriptor or "
+			"not enough data: %d\n", result);
+		goto out;
+	}
+	bytes = 0;
+	itr = &secd[1];
+	top = (void *)secd + result;
+	while (itr < top) {
+		etd = itr;
+		if (top - itr < sizeof(*etd)) {
+			dev_err(dev, "BUG: bad device security descriptor; "
+				"not enough data (%zu vs %zu bytes left)\n",
+				top - itr, sizeof(*etd));
+			break;
+		}
+		if (etd->bLength < sizeof(*etd)) {
+			dev_err(dev, "BUG: bad device encryption descriptor; "
+				"descriptor is too short "
+				"(%u vs %zu needed)\n",
+				etd->bLength, sizeof(*etd));
+			break;
+		}
+		itr += etd->bLength;
+		bytes += snprintf(buf + bytes, sizeof(buf) - bytes,
+				  "%s (0x%02x/%02x) ",
+				  wusb_et_name(etd->bEncryptionType),
+				  etd->bEncryptionValue, etd->bAuthKeyIndex);
+		if (etd->bEncryptionType == USB_ENC_TYPE_CCM_1)
+			ccm1_etd = etd;
+	}
+	/* This code only supports CCM1 as of now. */
+	/* FIXME: user has to choose which sec mode to use?
+	 * In theory we want CCM */
+	if (ccm1_etd == NULL) {
+		dev_err(dev, "WUSB device doesn't support CCM1 encryption, "
+			"can't use!\n");
+		result = -EINVAL;
+		goto out;
+	}
+	wusb_dev->ccm1_etd = *ccm1_etd;
+	dev_dbg(dev, "supported encryption: %s; using %s (0x%02x/%02x)\n",
+		buf, wusb_et_name(ccm1_etd->bEncryptionType),
+		ccm1_etd->bEncryptionValue, ccm1_etd->bAuthKeyIndex);
+	result = 0;
+out:
+	kfree(secd);
+	return result;
+}
+
+void wusb_dev_sec_rm(struct wusb_dev *wusb_dev)
+{
+	/* Nothing so far */
+}
+
+/**
+ * Update the address of an unauthenticated WUSB device
+ *
+ * Once we have successfully authenticated, we take it to addr0 state
+ * and then to a normal address.
+ *
+ * Before the device's address (as known by it) was usb_dev->devnum |
+ * 0x80 (unauthenticated address). With this we update it to usb_dev->devnum.
+ */
+int wusb_dev_update_address(struct wusbhc *wusbhc, struct wusb_dev *wusb_dev)
+{
+	int result = -ENOMEM;
+	struct usb_device *usb_dev = wusb_dev->usb_dev;
+	struct device *dev = &usb_dev->dev;
+	u8 new_address = wusb_dev->addr & 0x7F;
+
+	/* Set address 0 */
+	result = usb_control_msg(usb_dev, usb_sndctrlpipe(usb_dev, 0),
+			USB_REQ_SET_ADDRESS,
+			USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+			 0, 0, NULL, 0, USB_CTRL_SET_TIMEOUT);
+	if (result < 0) {
+		dev_err(dev, "auth failed: can't set address 0: %d\n",
+			result);
+		goto error_addr0;
+	}
+	result = wusb_set_dev_addr(wusbhc, wusb_dev, 0);
+	if (result < 0)
+		goto error_addr0;
+	usb_set_device_state(usb_dev, USB_STATE_DEFAULT);
+	usb_ep0_reinit(usb_dev);
+
+	/* Set new (authenticated) address. */
+	result = usb_control_msg(usb_dev, usb_sndctrlpipe(usb_dev, 0),
+			USB_REQ_SET_ADDRESS,
+			USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+			new_address, 0, NULL, 0,
+			USB_CTRL_SET_TIMEOUT);
+	if (result < 0) {
+		dev_err(dev, "auth failed: can't set address %u: %d\n",
+			new_address, result);
+		goto error_addr;
+	}
+	result = wusb_set_dev_addr(wusbhc, wusb_dev, new_address);
+	if (result < 0)
+		goto error_addr;
+	usb_set_device_state(usb_dev, USB_STATE_ADDRESS);
+	usb_ep0_reinit(usb_dev);
+	usb_dev->authenticated = 1;
+error_addr:
+error_addr0:
+	return result;
+}
+
+/*
+ *
+ *
+ */
+/* FIXME: split and cleanup */
+int wusb_dev_4way_handshake(struct wusbhc *wusbhc, struct wusb_dev *wusb_dev,
+			    struct wusb_ckhdid *ck)
+{
+	int result = -ENOMEM;
+	struct usb_device *usb_dev = wusb_dev->usb_dev;
+	struct device *dev = &usb_dev->dev;
+	u32 tkid;
+	struct usb_handshake *hs;
+	struct aes_ccm_nonce ccm_n;
+	u8 mic[8];
+	struct wusb_keydvt_in keydvt_in;
+	struct wusb_keydvt_out keydvt_out;
+
+	hs = kcalloc(3, sizeof(hs[0]), GFP_KERNEL);
+	if (!hs)
+		goto error_kzalloc;
+
+	/* We need to turn encryption before beginning the 4way
+	 * hshake (WUSB1.0[.3.2.2]) */
+	result = wusb_dev_set_encryption(usb_dev, 1);
+	if (result < 0)
+		goto error_dev_set_encryption;
+
+	tkid = wusbhc_next_tkid(wusbhc, wusb_dev);
+
+	hs[0].bMessageNumber = 1;
+	hs[0].bStatus = 0;
+	put_unaligned_le32(tkid, hs[0].tTKID);
+	hs[0].bReserved = 0;
+	memcpy(hs[0].CDID, &wusb_dev->cdid, sizeof(hs[0].CDID));
+	get_random_bytes(&hs[0].nonce, sizeof(hs[0].nonce));
+	memset(hs[0].MIC, 0, sizeof(hs[0].MIC)); /* Per WUSB1.0[T7-22] */
+
+	result = usb_control_msg(
+		usb_dev, usb_sndctrlpipe(usb_dev, 0),
+		USB_REQ_SET_HANDSHAKE,
+		USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+		1, 0, &hs[0], sizeof(hs[0]), USB_CTRL_SET_TIMEOUT);
+	if (result < 0) {
+		dev_err(dev, "Handshake1: request failed: %d\n", result);
+		goto error_hs1;
+	}
+
+	/* Handshake 2, from the device -- need to verify fields */
+	result = usb_control_msg(
+		usb_dev, usb_rcvctrlpipe(usb_dev, 0),
+		USB_REQ_GET_HANDSHAKE,
+		USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+		2, 0, &hs[1], sizeof(hs[1]), USB_CTRL_GET_TIMEOUT);
+	if (result < 0) {
+		dev_err(dev, "Handshake2: request failed: %d\n", result);
+		goto error_hs2;
+	}
+
+	result = -EINVAL;
+	if (hs[1].bMessageNumber != 2) {
+		dev_err(dev, "Handshake2 failed: bad message number %u\n",
+			hs[1].bMessageNumber);
+		goto error_hs2;
+	}
+	if (hs[1].bStatus != 0) {
+		dev_err(dev, "Handshake2 failed: bad status %u\n",
+			hs[1].bStatus);
+		goto error_hs2;
+	}
+	if (memcmp(hs[0].tTKID, hs[1].tTKID, sizeof(hs[0].tTKID))) {
+		dev_err(dev, "Handshake2 failed: TKID mismatch "
+			"(#1 0x%02x%02x%02x vs #2 0x%02x%02x%02x)\n",
+			hs[0].tTKID[0], hs[0].tTKID[1], hs[0].tTKID[2],
+			hs[1].tTKID[0], hs[1].tTKID[1], hs[1].tTKID[2]);
+		goto error_hs2;
+	}
+	if (memcmp(hs[0].CDID, hs[1].CDID, sizeof(hs[0].CDID))) {
+		dev_err(dev, "Handshake2 failed: CDID mismatch\n");
+		goto error_hs2;
+	}
+
+	/* Setup the CCM nonce */
+	memset(&ccm_n.sfn, 0, sizeof(ccm_n.sfn)); /* Per WUSB1.0[6.5.2] */
+	put_unaligned_le32(tkid, ccm_n.tkid);
+	ccm_n.src_addr = wusbhc->uwb_rc->uwb_dev.dev_addr;
+	ccm_n.dest_addr.data[0] = wusb_dev->addr;
+	ccm_n.dest_addr.data[1] = 0;
+
+	/* Derive the KCK and PTK from CK, the CCM, H and D nonces */
+	memcpy(keydvt_in.hnonce, hs[0].nonce, sizeof(keydvt_in.hnonce));
+	memcpy(keydvt_in.dnonce, hs[1].nonce, sizeof(keydvt_in.dnonce));
+	result = wusb_key_derive(&keydvt_out, ck->data, &ccm_n, &keydvt_in);
+	if (result < 0) {
+		dev_err(dev, "Handshake2 failed: cannot derive keys: %d\n",
+			result);
+		goto error_hs2;
+	}
+
+	/* Compute MIC and verify it */
+	result = wusb_oob_mic(mic, keydvt_out.kck, &ccm_n, &hs[1]);
+	if (result < 0) {
+		dev_err(dev, "Handshake2 failed: cannot compute MIC: %d\n",
+			result);
+		goto error_hs2;
+	}
+
+	if (memcmp(hs[1].MIC, mic, sizeof(hs[1].MIC))) {
+		dev_err(dev, "Handshake2 failed: MIC mismatch\n");
+		goto error_hs2;
+	}
+
+	/* Send Handshake3 */
+	hs[2].bMessageNumber = 3;
+	hs[2].bStatus = 0;
+	put_unaligned_le32(tkid, hs[2].tTKID);
+	hs[2].bReserved = 0;
+	memcpy(hs[2].CDID, &wusb_dev->cdid, sizeof(hs[2].CDID));
+	memcpy(hs[2].nonce, hs[0].nonce, sizeof(hs[2].nonce));
+	result = wusb_oob_mic(hs[2].MIC, keydvt_out.kck, &ccm_n, &hs[2]);
+	if (result < 0) {
+		dev_err(dev, "Handshake3 failed: cannot compute MIC: %d\n",
+			result);
+		goto error_hs2;
+	}
+
+	result = usb_control_msg(
+		usb_dev, usb_sndctrlpipe(usb_dev, 0),
+		USB_REQ_SET_HANDSHAKE,
+		USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE,
+		3, 0, &hs[2], sizeof(hs[2]), USB_CTRL_SET_TIMEOUT);
+	if (result < 0) {
+		dev_err(dev, "Handshake3: request failed: %d\n", result);
+		goto error_hs3;
+	}
+
+	result = wusbhc->set_ptk(wusbhc, wusb_dev->port_idx, tkid,
+				 keydvt_out.ptk, sizeof(keydvt_out.ptk));
+	if (result < 0)
+		goto error_wusbhc_set_ptk;
+
+	result = wusb_dev_set_gtk(wusbhc, wusb_dev);
+	if (result < 0) {
+		dev_err(dev, "Set GTK for device: request failed: %d\n",
+			result);
+		goto error_wusbhc_set_gtk;
+	}
+
+	/* Update the device's address from unauth to auth */
+	if (usb_dev->authenticated == 0) {
+		result = wusb_dev_update_address(wusbhc, wusb_dev);
+		if (result < 0)
+			goto error_dev_update_address;
+	}
+	result = 0;
+	dev_info(dev, "device authenticated\n");
+
+error_dev_update_address:
+error_wusbhc_set_gtk:
+error_wusbhc_set_ptk:
+error_hs3:
+error_hs2:
+error_hs1:
+	memset(hs, 0, 3*sizeof(hs[0]));
+	memzero_explicit(&keydvt_out, sizeof(keydvt_out));
+	memzero_explicit(&keydvt_in, sizeof(keydvt_in));
+	memzero_explicit(&ccm_n, sizeof(ccm_n));
+	memzero_explicit(mic, sizeof(mic));
+	if (result < 0)
+		wusb_dev_set_encryption(usb_dev, 0);
+error_dev_set_encryption:
+	kfree(hs);
+error_kzalloc:
+	return result;
+}
+
+/*
+ * Once all connected and authenticated devices have received the new
+ * GTK, switch the host to using it.
+ */
+static void wusbhc_gtk_rekey_work(struct work_struct *work)
+{
+	struct wusbhc *wusbhc = container_of(work,
+					struct wusbhc, gtk_rekey_work);
+	size_t key_size = sizeof(wusbhc->gtk.data);
+	int port_idx;
+	struct wusb_dev *wusb_dev, *wusb_dev_next;
+	LIST_HEAD(rekey_list);
+
+	mutex_lock(&wusbhc->mutex);
+	/* generate the new key */
+	wusbhc_generate_gtk(wusbhc);
+	/* roll the gtk index. */
+	wusbhc->gtk_index = (wusbhc->gtk_index + 1) % (WUSB_KEY_INDEX_MAX + 1);
+	/*
+	 * Save all connected devices on a list while holding wusbhc->mutex and
+	 * take a reference to each one.  Then submit the set key request to
+	 * them after releasing the lock in order to avoid a deadlock.
+	 */
+	for (port_idx = 0; port_idx < wusbhc->ports_max; port_idx++) {
+		wusb_dev = wusbhc->port[port_idx].wusb_dev;
+		if (!wusb_dev || !wusb_dev->usb_dev
+			|| !wusb_dev->usb_dev->authenticated)
+			continue;
+
+		wusb_dev_get(wusb_dev);
+		list_add_tail(&wusb_dev->rekey_node, &rekey_list);
+	}
+	mutex_unlock(&wusbhc->mutex);
+
+	/* Submit the rekey requests without holding wusbhc->mutex. */
+	list_for_each_entry_safe(wusb_dev, wusb_dev_next, &rekey_list,
+		rekey_node) {
+		list_del_init(&wusb_dev->rekey_node);
+		dev_dbg(&wusb_dev->usb_dev->dev,
+			"%s: rekey device at port %d\n",
+			__func__, wusb_dev->port_idx);
+
+		if (wusb_dev_set_gtk(wusbhc, wusb_dev) < 0) {
+			dev_err(&wusb_dev->usb_dev->dev,
+				"%s: rekey device at port %d failed\n",
+				__func__, wusb_dev->port_idx);
+		}
+		wusb_dev_put(wusb_dev);
+	}
+
+	/* Switch the host controller to use the new GTK. */
+	mutex_lock(&wusbhc->mutex);
+	wusbhc->set_gtk(wusbhc, wusbhc->gtk_tkid,
+		&wusbhc->gtk.descr.bKeyData, key_size);
+	mutex_unlock(&wusbhc->mutex);
+}
+
+/**
+ * wusbhc_gtk_rekey - generate and distribute a new GTK
+ * @wusbhc: the WUSB host controller
+ *
+ * Generate a new GTK and distribute it to all connected and
+ * authenticated devices.  When all devices have the new GTK, the host
+ * starts using it.
+ *
+ * This must be called after every device disconnect (see [WUSB]
+ * section 6.2.11.2).
+ */
+void wusbhc_gtk_rekey(struct wusbhc *wusbhc)
+{
+	/*
+	 * We need to submit a URB to the downstream WUSB devices in order to
+	 * change the group key.  This can't be done while holding the
+	 * wusbhc->mutex since that is also taken in the urb_enqueue routine
+	 * and will cause a deadlock.  Instead, queue a work item to do
+	 * it when the lock is not held
+	 */
+	queue_work(wusbhc->wq_security, &wusbhc->gtk_rekey_work);
+}