hw/usb/u2f-passthru.c - qemu - Git at Google

 /*
  * U2F USB Passthru device.
  *
  * Copyright (c) 2020 César Belley <cesar.belley@lse.epita.fr>
  * Written by César Belley <cesar.belley@lse.epita.fr>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "qemu/osdep.h"
 #include "qemu/module.h"
 #include "qemu/main-loop.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "hw/qdev-properties.h"
 #include "hw/usb.h"
 #include "migration/vmstate.h"

 #include "u2f.h"

 #ifdef CONFIG_LIBUDEV
 #include <libudev.h>
 #endif
 #include <linux/hidraw.h>
 #include <sys/ioctl.h>

 #define NONCE_SIZE 8
 #define BROADCAST_CID 0xFFFFFFFF
 #define TRANSACTION_TIMEOUT 120000

 struct transaction {
     uint32_t cid;
     uint16_t resp_bcnt;
     uint16_t resp_size;

     /* Nonce for broadcast isolation */
     uint8_t nonce[NONCE_SIZE];
 };

 typedef struct U2FPassthruState U2FPassthruState;

 #define CURRENT_TRANSACTIONS_NUM 4

 struct U2FPassthruState {
     U2FKeyState base;

     /* Host device */
     char *hidraw;
     int hidraw_fd;

     /* Current Transactions */
     struct transaction current_transactions[CURRENT_TRANSACTIONS_NUM];
     uint8_t current_transactions_start;
     uint8_t current_transactions_end;
     uint8_t current_transactions_num;

     /* Transaction time checking */
     int64_t last_transaction_time;
     QEMUTimer timer;
 };

 #define TYPE_U2F_PASSTHRU "u2f-passthru"
 #define PASSTHRU_U2F_KEY(obj) \
     OBJECT_CHECK(U2FPassthruState, (obj), TYPE_U2F_PASSTHRU)

 /* Init packet sizes */
 #define PACKET_INIT_HEADER_SIZE 7
 #define PACKET_INIT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_INIT_HEADER_SIZE)

 /* Cont packet sizes */
 #define PACKET_CONT_HEADER_SIZE 5
 #define PACKET_CONT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_CONT_HEADER_SIZE)

 struct packet_init {
     uint32_t cid;
     uint8_t cmd;
     uint8_t bcnth;
     uint8_t bcntl;
     uint8_t data[PACKET_INIT_DATA_SIZE];
 } QEMU_PACKED;

 static inline uint32_t packet_get_cid(const void *packet)
 {
     return *((uint32_t *)packet);
 }

 static inline bool packet_is_init(const void *packet)
 {
     return ((uint8_t *)packet)[4] & (1 << 7);
 }

 static inline uint16_t packet_init_get_bcnt(
         const struct packet_init *packet_init)
 {
     uint16_t bcnt = 0;
     bcnt |= packet_init->bcnth << 8;
     bcnt |= packet_init->bcntl;

     return bcnt;
 }

 static void u2f_passthru_reset(U2FPassthruState *key)
 {
     timer_del(&key->timer);
     qemu_set_fd_handler(key->hidraw_fd, NULL, NULL, key);
     key->last_transaction_time = 0;
     key->current_transactions_start = 0;
     key->current_transactions_end = 0;
     key->current_transactions_num = 0;
 }

 static void u2f_timeout_check(void *opaque)
 {
     U2FPassthruState *key = opaque;
     int64_t time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);

     if (time > key->last_transaction_time + TRANSACTION_TIMEOUT) {
         u2f_passthru_reset(key);
     } else {
         timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
     }
 }

 static int u2f_transaction_get_index(U2FPassthruState *key, uint32_t cid)
 {
     for (int i = 0; i < key->current_transactions_num; ++i) {
         int index = (key->current_transactions_start + i)
             % CURRENT_TRANSACTIONS_NUM;
         if (cid == key->current_transactions[index].cid) {
             return index;
         }
     }
     return -1;
 }

 static struct transaction *u2f_transaction_get(U2FPassthruState *key,
                                                uint32_t cid)
 {
     int index = u2f_transaction_get_index(key, cid);
     if (index < 0) {
         return NULL;
     }
     return &key->current_transactions[index];
 }

 static struct transaction *u2f_transaction_get_from_nonce(U2FPassthruState *key,
                                 const uint8_t nonce[NONCE_SIZE])
 {
     for (int i = 0; i < key->current_transactions_num; ++i) {
         int index = (key->current_transactions_start + i)
             % CURRENT_TRANSACTIONS_NUM;
         if (key->current_transactions[index].cid == BROADCAST_CID
             && memcmp(nonce, key->current_transactions[index].nonce,
                       NONCE_SIZE) == 0) {
             return &key->current_transactions[index];
         }
     }
     return NULL;
 }

 static void u2f_transaction_close(U2FPassthruState *key, uint32_t cid)
 {
     int index, next_index;
     index = u2f_transaction_get_index(key, cid);
     if (index < 0) {
         return;
     }
     next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;

     /* Rearrange to ensure the oldest is at the start position */
     while (next_index != key->current_transactions_end) {
         memcpy(&key->current_transactions[index],
                &key->current_transactions[next_index],
                sizeof(struct transaction));

         index = next_index;
         next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;
     }

     key->current_transactions_end = index;
     --key->current_transactions_num;

     if (key->current_transactions_num == 0) {
         u2f_passthru_reset(key);
     }
 }

 static void u2f_transaction_add(U2FPassthruState *key, uint32_t cid,
                                 const uint8_t nonce[NONCE_SIZE])
 {
     uint8_t index;
     struct transaction *transaction;

     if (key->current_transactions_num >= CURRENT_TRANSACTIONS_NUM) {
         /* Close the oldest transaction */
         index = key->current_transactions_start;
         transaction = &key->current_transactions[index];
         u2f_transaction_close(key, transaction->cid);
     }

     /* Index */
     index = key->current_transactions_end;
     key->current_transactions_end = (index + 1) % CURRENT_TRANSACTIONS_NUM;
     ++key->current_transactions_num;

     /* Transaction */
     transaction = &key->current_transactions[index];
     transaction->cid = cid;
     transaction->resp_bcnt = 0;
     transaction->resp_size = 0;

     /* Nonce */
     if (nonce != NULL) {
         memcpy(transaction->nonce, nonce, NONCE_SIZE);
     }
 }

 static void u2f_passthru_read(void *opaque);

 static void u2f_transaction_start(U2FPassthruState *key,
                                   const struct packet_init *packet_init)
 {
     int64_t time;

     /* Transaction */
     if (packet_init->cid == BROADCAST_CID) {
         u2f_transaction_add(key, packet_init->cid, packet_init->data);
     } else {
         u2f_transaction_add(key, packet_init->cid, NULL);
     }

     /* Time */
     time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
     if (key->last_transaction_time == 0) {
         qemu_set_fd_handler(key->hidraw_fd, u2f_passthru_read, NULL, key);
         timer_init_ms(&key->timer, QEMU_CLOCK_VIRTUAL, u2f_timeout_check, key);
         timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
     }
     key->last_transaction_time = time;
 }

 static void u2f_passthru_recv_from_host(U2FPassthruState *key,
                                     const uint8_t packet[U2FHID_PACKET_SIZE])
 {
     struct transaction *transaction;
     uint32_t cid;

     /* Retrieve transaction */
     cid = packet_get_cid(packet);
     if (cid == BROADCAST_CID) {
         struct packet_init *packet_init;
         if (!packet_is_init(packet)) {
             return;
         }
         packet_init = (struct packet_init *)packet;
         transaction = u2f_transaction_get_from_nonce(key, packet_init->data);
     } else {
         transaction = u2f_transaction_get(key, cid);
     }

     /* Ignore no started transaction */
     if (transaction == NULL) {
         return;
     }

     if (packet_is_init(packet)) {
         struct packet_init *packet_init = (struct packet_init *)packet;
         transaction->resp_bcnt = packet_init_get_bcnt(packet_init);
         transaction->resp_size = PACKET_INIT_DATA_SIZE;

         if (packet_init->cid == BROADCAST_CID) {
             /* Nonce checking for legitimate response */
             if (memcmp(transaction->nonce, packet_init->data, NONCE_SIZE)
                 != 0) {
                 return;
             }
         }
     } else {
         transaction->resp_size += PACKET_CONT_DATA_SIZE;
     }

     /* Transaction end check */
     if (transaction->resp_size >= transaction->resp_bcnt) {
         u2f_transaction_close(key, cid);
     }
     u2f_send_to_guest(&key->base, packet);
 }

 static void u2f_passthru_read(void *opaque)
 {
     U2FPassthruState *key = opaque;
     U2FKeyState *base = &key->base;
     uint8_t packet[2 * U2FHID_PACKET_SIZE];
     int ret;

     /* Full size base queue check */
     if (base->pending_in_num >= U2FHID_PENDING_IN_NUM) {
         return;
     }

     ret = read(key->hidraw_fd, packet, sizeof(packet));
     if (ret < 0) {
         /* Detach */
         if (base->dev.attached) {
             usb_device_detach(&base->dev);
             u2f_passthru_reset(key);
         }
         return;
     }
     if (ret != U2FHID_PACKET_SIZE) {
         return;
     }
     u2f_passthru_recv_from_host(key, packet);
 }

 static void u2f_passthru_recv_from_guest(U2FKeyState *base,
                                     const uint8_t packet[U2FHID_PACKET_SIZE])
 {
     U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
     uint8_t host_packet[U2FHID_PACKET_SIZE + 1];
     ssize_t written;

     if (packet_is_init(packet)) {
         u2f_transaction_start(key, (struct packet_init *)packet);
     }

     host_packet[0] = 0;
     memcpy(host_packet + 1, packet, U2FHID_PACKET_SIZE);

     written = write(key->hidraw_fd, host_packet, sizeof(host_packet));
     if (written != sizeof(host_packet)) {
         error_report("%s: Bad written size (req 0x%zu, val 0x%zd)",
                      TYPE_U2F_PASSTHRU, sizeof(host_packet), written);
     }
 }

 static bool u2f_passthru_is_u2f_device(int fd)
 {
     int ret, rdesc_size;
     struct hidraw_report_descriptor rdesc;
     const uint8_t u2f_hid_report_desc_header[] = {
         0x06, 0xd0, 0xf1, /* Usage Page (FIDO) */
         0x09, 0x01,       /* Usage (FIDO) */
     };

     /* Get report descriptor size */
     ret = ioctl(fd, HIDIOCGRDESCSIZE, &rdesc_size);
     if (ret < 0 || rdesc_size < sizeof(u2f_hid_report_desc_header)) {
         return false;
     }

     /* Get report descriptor */
     memset(&rdesc, 0x0, sizeof(rdesc));
     rdesc.size = rdesc_size;
     ret = ioctl(fd, HIDIOCGRDESC, &rdesc);
     if (ret < 0) {
         return false;
     }

     /* Header bytes cover specific U2F rdesc values */
     return memcmp(u2f_hid_report_desc_header, rdesc.value,
                   sizeof(u2f_hid_report_desc_header)) == 0;
 }

 #ifdef CONFIG_LIBUDEV
 static int u2f_passthru_open_from_device(struct udev_device *device)
 {
     const char *devnode = udev_device_get_devnode(device);

     int fd = qemu_open_old(devnode, O_RDWR);
     if (fd < 0) {
         return -1;
     } else if (!u2f_passthru_is_u2f_device(fd)) {
         qemu_close(fd);
         return -1;
     }
     return fd;
 }

 static int u2f_passthru_open_from_enumerate(struct udev *udev,
                                             struct udev_enumerate *enumerate)
 {
     struct udev_list_entry *devices, *entry;
     int ret, fd;

     ret = udev_enumerate_scan_devices(enumerate);
     if (ret < 0) {
         return -1;
     }

     devices = udev_enumerate_get_list_entry(enumerate);
     udev_list_entry_foreach(entry, devices) {
         struct udev_device *device;
         const char *syspath = udev_list_entry_get_name(entry);

         if (syspath == NULL) {
             continue;
         }

         device = udev_device_new_from_syspath(udev, syspath);
         if (device == NULL) {
             continue;
         }

         fd = u2f_passthru_open_from_device(device);
         udev_device_unref(device);
         if (fd >= 0) {
             return fd;
         }
     }
     return -1;
 }

 static int u2f_passthru_open_from_scan(void)
 {
     struct udev *udev;
     struct udev_enumerate *enumerate;
     int ret, fd = -1;

     udev = udev_new();
     if (udev == NULL) {
         return -1;
     }

     enumerate = udev_enumerate_new(udev);
     if (enumerate == NULL) {
         udev_unref(udev);
         return -1;
     }

     ret = udev_enumerate_add_match_subsystem(enumerate, "hidraw");
     if (ret >= 0) {
         fd = u2f_passthru_open_from_enumerate(udev, enumerate);
     }

     udev_enumerate_unref(enumerate);
     udev_unref(udev);

     return fd;
 }
 #endif

 static void u2f_passthru_unrealize(U2FKeyState *base)
 {
     U2FPassthruState *key = PASSTHRU_U2F_KEY(base);

     u2f_passthru_reset(key);
     qemu_close(key->hidraw_fd);
 }

 static void u2f_passthru_realize(U2FKeyState *base, Error **errp)
 {
     U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
     int fd;

     if (key->hidraw == NULL) {
 #ifdef CONFIG_LIBUDEV
         fd = u2f_passthru_open_from_scan();
         if (fd < 0) {
             error_setg(errp, "%s: Failed to find a U2F USB device",
                        TYPE_U2F_PASSTHRU);
             return;
         }
 #else
         error_setg(errp, "%s: Missing hidraw", TYPE_U2F_PASSTHRU);
         return;
 #endif
     } else {
         fd = qemu_open(key->hidraw, O_RDWR, errp);
         if (fd < 0) {
             return;
         }

         if (!u2f_passthru_is_u2f_device(fd)) {
             qemu_close(fd);
             error_setg(errp, "%s: Passed hidraw does not represent "
                        "a U2F HID device", TYPE_U2F_PASSTHRU);
             return;
         }
     }
     key->hidraw_fd = fd;
     u2f_passthru_reset(key);
 }

 static int u2f_passthru_post_load(void *opaque, int version_id)
 {
     U2FPassthruState *key = opaque;
     u2f_passthru_reset(key);
     return 0;
 }

 static const VMStateDescription u2f_passthru_vmstate = {
     .name = "u2f-key-passthru",
     .version_id = 1,
     .minimum_version_id = 1,
     .post_load = u2f_passthru_post_load,
     .fields = (const VMStateField[]) {
         VMSTATE_U2F_KEY(base, U2FPassthruState),
         VMSTATE_END_OF_LIST()
     }
 };

 static Property u2f_passthru_properties[] = {
     DEFINE_PROP_STRING("hidraw", U2FPassthruState, hidraw),
     DEFINE_PROP_END_OF_LIST(),
 };

 static void u2f_passthru_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     U2FKeyClass *kc = U2F_KEY_CLASS(klass);

     kc->realize = u2f_passthru_realize;
     kc->unrealize = u2f_passthru_unrealize;
     kc->recv_from_guest = u2f_passthru_recv_from_guest;
     dc->desc = "QEMU U2F passthrough key";
     dc->vmsd = &u2f_passthru_vmstate;
     device_class_set_props(dc, u2f_passthru_properties);
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
 }

 static const TypeInfo u2f_key_passthru_info = {
     .name = TYPE_U2F_PASSTHRU,
     .parent = TYPE_U2F_KEY,
     .instance_size = sizeof(U2FPassthruState),
     .class_init = u2f_passthru_class_init
 };

 static void u2f_key_passthru_register_types(void)
 {
     type_register_static(&u2f_key_passthru_info);
 }

 type_init(u2f_key_passthru_register_types)
	/*
	* U2F USB Passthru device.
	*
	* Copyright (c) 2020 César Belley <cesar.belley@lse.epita.fr>
	* Written by César Belley <cesar.belley@lse.epita.fr>
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "qemu/osdep.h"
	#include "qemu/module.h"
	#include "qemu/main-loop.h"
	#include "qemu/error-report.h"
	#include "qapi/error.h"
	#include "hw/qdev-properties.h"
	#include "hw/usb.h"
	#include "migration/vmstate.h"

	#include "u2f.h"

	#ifdef CONFIG_LIBUDEV
	#include <libudev.h>
	#endif
	#include <linux/hidraw.h>
	#include <sys/ioctl.h>

	#define NONCE_SIZE 8
	#define BROADCAST_CID 0xFFFFFFFF
	#define TRANSACTION_TIMEOUT 120000

	struct transaction {
	uint32_t cid;
	uint16_t resp_bcnt;
	uint16_t resp_size;

	/* Nonce for broadcast isolation */
	uint8_t nonce[NONCE_SIZE];
	};

	typedef struct U2FPassthruState U2FPassthruState;

	#define CURRENT_TRANSACTIONS_NUM 4

	struct U2FPassthruState {
	U2FKeyState base;

	/* Host device */
	char *hidraw;
	int hidraw_fd;

	/* Current Transactions */
	struct transaction current_transactions[CURRENT_TRANSACTIONS_NUM];
	uint8_t current_transactions_start;
	uint8_t current_transactions_end;
	uint8_t current_transactions_num;

	/* Transaction time checking */
	int64_t last_transaction_time;
	QEMUTimer timer;
	};

	#define TYPE_U2F_PASSTHRU "u2f-passthru"
	#define PASSTHRU_U2F_KEY(obj) \
	OBJECT_CHECK(U2FPassthruState, (obj), TYPE_U2F_PASSTHRU)

	/* Init packet sizes */
	#define PACKET_INIT_HEADER_SIZE 7
	#define PACKET_INIT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_INIT_HEADER_SIZE)

	/* Cont packet sizes */
	#define PACKET_CONT_HEADER_SIZE 5
	#define PACKET_CONT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_CONT_HEADER_SIZE)

	struct packet_init {
	uint32_t cid;
	uint8_t cmd;
	uint8_t bcnth;
	uint8_t bcntl;
	uint8_t data[PACKET_INIT_DATA_SIZE];
	} QEMU_PACKED;

	static inline uint32_t packet_get_cid(const void *packet)
	{
	return ((uint32_t )packet);
	}

	static inline bool packet_is_init(const void *packet)
	{
	return ((uint8_t *)packet)[4] & (1 << 7);
	}

	static inline uint16_t packet_init_get_bcnt(
	const struct packet_init *packet_init)
	{
	uint16_t bcnt = 0;
	bcnt \|= packet_init->bcnth << 8;
	bcnt \|= packet_init->bcntl;

	return bcnt;
	}

	static void u2f_passthru_reset(U2FPassthruState *key)
	{
	timer_del(&key->timer);
	qemu_set_fd_handler(key->hidraw_fd, NULL, NULL, key);
	key->last_transaction_time = 0;
	key->current_transactions_start = 0;
	key->current_transactions_end = 0;
	key->current_transactions_num = 0;
	}

	static void u2f_timeout_check(void *opaque)
	{
	U2FPassthruState *key = opaque;
	int64_t time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);

	if (time > key->last_transaction_time + TRANSACTION_TIMEOUT) {
	u2f_passthru_reset(key);
	} else {
	timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
	}
	}

	static int u2f_transaction_get_index(U2FPassthruState *key, uint32_t cid)
	{
	for (int i = 0; i < key->current_transactions_num; ++i) {
	int index = (key->current_transactions_start + i)
	% CURRENT_TRANSACTIONS_NUM;
	if (cid == key->current_transactions[index].cid) {
	return index;
	}
	}
	return -1;
	}

	static struct transaction u2f_transaction_get(U2FPassthruState key,
	uint32_t cid)
	{
	int index = u2f_transaction_get_index(key, cid);
	if (index < 0) {
	return NULL;
	}
	return &key->current_transactions[index];
	}

	static struct transaction u2f_transaction_get_from_nonce(U2FPassthruState key,
	const uint8_t nonce[NONCE_SIZE])
	{
	for (int i = 0; i < key->current_transactions_num; ++i) {
	int index = (key->current_transactions_start + i)
	% CURRENT_TRANSACTIONS_NUM;
	if (key->current_transactions[index].cid == BROADCAST_CID
	&& memcmp(nonce, key->current_transactions[index].nonce,
	NONCE_SIZE) == 0) {
	return &key->current_transactions[index];
	}
	}
	return NULL;
	}

	static void u2f_transaction_close(U2FPassthruState *key, uint32_t cid)
	{
	int index, next_index;
	index = u2f_transaction_get_index(key, cid);
	if (index < 0) {
	return;
	}
	next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;

	/* Rearrange to ensure the oldest is at the start position */
	while (next_index != key->current_transactions_end) {
	memcpy(&key->current_transactions[index],
	&key->current_transactions[next_index],
	sizeof(struct transaction));

	index = next_index;
	next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;
	}

	key->current_transactions_end = index;
	--key->current_transactions_num;

	if (key->current_transactions_num == 0) {
	u2f_passthru_reset(key);
	}
	}

	static void u2f_transaction_add(U2FPassthruState *key, uint32_t cid,
	const uint8_t nonce[NONCE_SIZE])
	{
	uint8_t index;
	struct transaction *transaction;

	if (key->current_transactions_num >= CURRENT_TRANSACTIONS_NUM) {
	/* Close the oldest transaction */
	index = key->current_transactions_start;
	transaction = &key->current_transactions[index];
	u2f_transaction_close(key, transaction->cid);
	}

	/* Index */
	index = key->current_transactions_end;
	key->current_transactions_end = (index + 1) % CURRENT_TRANSACTIONS_NUM;
	++key->current_transactions_num;

	/* Transaction */
	transaction = &key->current_transactions[index];
	transaction->cid = cid;
	transaction->resp_bcnt = 0;
	transaction->resp_size = 0;

	/* Nonce */
	if (nonce != NULL) {
	memcpy(transaction->nonce, nonce, NONCE_SIZE);
	}
	}

	static void u2f_passthru_read(void *opaque);

	static void u2f_transaction_start(U2FPassthruState *key,
	const struct packet_init *packet_init)
	{
	int64_t time;

	/* Transaction */
	if (packet_init->cid == BROADCAST_CID) {
	u2f_transaction_add(key, packet_init->cid, packet_init->data);
	} else {
	u2f_transaction_add(key, packet_init->cid, NULL);
	}

	/* Time */
	time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
	if (key->last_transaction_time == 0) {
	qemu_set_fd_handler(key->hidraw_fd, u2f_passthru_read, NULL, key);
	timer_init_ms(&key->timer, QEMU_CLOCK_VIRTUAL, u2f_timeout_check, key);
	timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
	}
	key->last_transaction_time = time;
	}

	static void u2f_passthru_recv_from_host(U2FPassthruState *key,
	const uint8_t packet[U2FHID_PACKET_SIZE])
	{
	struct transaction *transaction;
	uint32_t cid;

	/* Retrieve transaction */
	cid = packet_get_cid(packet);
	if (cid == BROADCAST_CID) {
	struct packet_init *packet_init;
	if (!packet_is_init(packet)) {
	return;
	}
	packet_init = (struct packet_init *)packet;
	transaction = u2f_transaction_get_from_nonce(key, packet_init->data);
	} else {
	transaction = u2f_transaction_get(key, cid);
	}

	/* Ignore no started transaction */
	if (transaction == NULL) {
	return;
	}

	if (packet_is_init(packet)) {
	struct packet_init packet_init = (struct packet_init )packet;
	transaction->resp_bcnt = packet_init_get_bcnt(packet_init);
	transaction->resp_size = PACKET_INIT_DATA_SIZE;

	if (packet_init->cid == BROADCAST_CID) {
	/* Nonce checking for legitimate response */
	if (memcmp(transaction->nonce, packet_init->data, NONCE_SIZE)
	!= 0) {
	return;
	}
	}
	} else {
	transaction->resp_size += PACKET_CONT_DATA_SIZE;
	}

	/* Transaction end check */
	if (transaction->resp_size >= transaction->resp_bcnt) {
	u2f_transaction_close(key, cid);
	}
	u2f_send_to_guest(&key->base, packet);
	}

	static void u2f_passthru_read(void *opaque)
	{
	U2FPassthruState *key = opaque;
	U2FKeyState *base = &key->base;
	uint8_t packet[2 * U2FHID_PACKET_SIZE];
	int ret;

	/* Full size base queue check */
	if (base->pending_in_num >= U2FHID_PENDING_IN_NUM) {
	return;
	}

	ret = read(key->hidraw_fd, packet, sizeof(packet));
	if (ret < 0) {
	/* Detach */
	if (base->dev.attached) {
	usb_device_detach(&base->dev);
	u2f_passthru_reset(key);
	}
	return;
	}
	if (ret != U2FHID_PACKET_SIZE) {
	return;
	}
	u2f_passthru_recv_from_host(key, packet);
	}

	static void u2f_passthru_recv_from_guest(U2FKeyState *base,
	const uint8_t packet[U2FHID_PACKET_SIZE])
	{
	U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
	uint8_t host_packet[U2FHID_PACKET_SIZE + 1];
	ssize_t written;

	if (packet_is_init(packet)) {
	u2f_transaction_start(key, (struct packet_init *)packet);
	}

	host_packet[0] = 0;
	memcpy(host_packet + 1, packet, U2FHID_PACKET_SIZE);

	written = write(key->hidraw_fd, host_packet, sizeof(host_packet));
	if (written != sizeof(host_packet)) {
	error_report("%s: Bad written size (req 0x%zu, val 0x%zd)",
	TYPE_U2F_PASSTHRU, sizeof(host_packet), written);
	}
	}

	static bool u2f_passthru_is_u2f_device(int fd)
	{
	int ret, rdesc_size;
	struct hidraw_report_descriptor rdesc;
	const uint8_t u2f_hid_report_desc_header[] = {
	0x06, 0xd0, 0xf1, /* Usage Page (FIDO) */
	0x09, 0x01, /* Usage (FIDO) */
	};

	/* Get report descriptor size */
	ret = ioctl(fd, HIDIOCGRDESCSIZE, &rdesc_size);
	if (ret < 0 \|\| rdesc_size < sizeof(u2f_hid_report_desc_header)) {
	return false;
	}

	/* Get report descriptor */
	memset(&rdesc, 0x0, sizeof(rdesc));
	rdesc.size = rdesc_size;
	ret = ioctl(fd, HIDIOCGRDESC, &rdesc);
	if (ret < 0) {
	return false;
	}

	/* Header bytes cover specific U2F rdesc values */
	return memcmp(u2f_hid_report_desc_header, rdesc.value,
	sizeof(u2f_hid_report_desc_header)) == 0;
	}

	#ifdef CONFIG_LIBUDEV
	static int u2f_passthru_open_from_device(struct udev_device *device)
	{
	const char *devnode = udev_device_get_devnode(device);

	int fd = qemu_open_old(devnode, O_RDWR);
	if (fd < 0) {
	return -1;
	} else if (!u2f_passthru_is_u2f_device(fd)) {
	qemu_close(fd);
	return -1;
	}
	return fd;
	}

	static int u2f_passthru_open_from_enumerate(struct udev *udev,
	struct udev_enumerate *enumerate)
	{
	struct udev_list_entry devices, entry;
	int ret, fd;

	ret = udev_enumerate_scan_devices(enumerate);
	if (ret < 0) {
	return -1;
	}

	devices = udev_enumerate_get_list_entry(enumerate);
	udev_list_entry_foreach(entry, devices) {
	struct udev_device *device;
	const char *syspath = udev_list_entry_get_name(entry);

	if (syspath == NULL) {
	continue;
	}

	device = udev_device_new_from_syspath(udev, syspath);
	if (device == NULL) {
	continue;
	}

	fd = u2f_passthru_open_from_device(device);
	udev_device_unref(device);
	if (fd >= 0) {
	return fd;
	}
	}
	return -1;
	}

	static int u2f_passthru_open_from_scan(void)
	{
	struct udev *udev;
	struct udev_enumerate *enumerate;
	int ret, fd = -1;

	udev = udev_new();
	if (udev == NULL) {
	return -1;
	}

	enumerate = udev_enumerate_new(udev);
	if (enumerate == NULL) {
	udev_unref(udev);
	return -1;
	}

	ret = udev_enumerate_add_match_subsystem(enumerate, "hidraw");
	if (ret >= 0) {
	fd = u2f_passthru_open_from_enumerate(udev, enumerate);
	}

	udev_enumerate_unref(enumerate);
	udev_unref(udev);

	return fd;
	}
	#endif

	static void u2f_passthru_unrealize(U2FKeyState *base)
	{
	U2FPassthruState *key = PASSTHRU_U2F_KEY(base);

	u2f_passthru_reset(key);
	qemu_close(key->hidraw_fd);
	}

	static void u2f_passthru_realize(U2FKeyState base, Error *errp)
	{
	U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
	int fd;

	if (key->hidraw == NULL) {
	#ifdef CONFIG_LIBUDEV
	fd = u2f_passthru_open_from_scan();
	if (fd < 0) {
	error_setg(errp, "%s: Failed to find a U2F USB device",
	TYPE_U2F_PASSTHRU);
	return;
	}
	#else
	error_setg(errp, "%s: Missing hidraw", TYPE_U2F_PASSTHRU);
	return;
	#endif
	} else {
	fd = qemu_open(key->hidraw, O_RDWR, errp);
	if (fd < 0) {
	return;
	}

	if (!u2f_passthru_is_u2f_device(fd)) {
	qemu_close(fd);
	error_setg(errp, "%s: Passed hidraw does not represent "
	"a U2F HID device", TYPE_U2F_PASSTHRU);
	return;
	}
	}
	key->hidraw_fd = fd;
	u2f_passthru_reset(key);
	}

	static int u2f_passthru_post_load(void *opaque, int version_id)
	{
	U2FPassthruState *key = opaque;
	u2f_passthru_reset(key);
	return 0;
	}

	static const VMStateDescription u2f_passthru_vmstate = {
	.name = "u2f-key-passthru",
	.version_id = 1,
	.minimum_version_id = 1,
	.post_load = u2f_passthru_post_load,
	.fields = (const VMStateField[]) {
	VMSTATE_U2F_KEY(base, U2FPassthruState),
	VMSTATE_END_OF_LIST()
	}
	};

	static Property u2f_passthru_properties[] = {
	DEFINE_PROP_STRING("hidraw", U2FPassthruState, hidraw),
	DEFINE_PROP_END_OF_LIST(),
	};

	static void u2f_passthru_class_init(ObjectClass klass, void data)
	{
	DeviceClass *dc = DEVICE_CLASS(klass);
	U2FKeyClass *kc = U2F_KEY_CLASS(klass);

	kc->realize = u2f_passthru_realize;
	kc->unrealize = u2f_passthru_unrealize;
	kc->recv_from_guest = u2f_passthru_recv_from_guest;
	dc->desc = "QEMU U2F passthrough key";
	dc->vmsd = &u2f_passthru_vmstate;
	device_class_set_props(dc, u2f_passthru_properties);
	set_bit(DEVICE_CATEGORY_MISC, dc->categories);
	}

	static const TypeInfo u2f_key_passthru_info = {
	.name = TYPE_U2F_PASSTHRU,
	.parent = TYPE_U2F_KEY,
	.instance_size = sizeof(U2FPassthruState),
	.class_init = u2f_passthru_class_init
	};

	static void u2f_key_passthru_register_types(void)
	{
	type_register_static(&u2f_key_passthru_info);
	}

	type_init(u2f_key_passthru_register_types)