hid-u2fzero.c

// SPDX-License-Identifier: GPL-2.0
/*
 * U2F Zero LED and RNG driver
 *
 * Copyright 2018 Andrej Shadura <andrew@shadura.me>
 * Loosely based on drivers/hid/hid-led.c
 *              and drivers/usb/misc/chaoskey.c
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, version 2.
 */

#include <linux/hid.h>
#include <linux/hidraw.h>
#include <linux/hw_random.h>
#include <linux/leds.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/usb.h>

#include "usbhid/usbhid.h"
#include "hid-ids.h"

#define DRIVER_SHORT		"u2fzero"

#define HID_REPORT_SIZE		64

/* We only use broadcast (CID-less) messages */
#define CID_BROADCAST		0xffffffff

struct u2f_hid_msg {
	u32 cid;
	union {
		struct {
			u8 cmd;
			u8 bcnth;
			u8 bcntl;
			u8 data[HID_REPORT_SIZE - 7];
		} init;
		struct {
			u8 seq;
			u8 data[HID_REPORT_SIZE - 5];
		} cont;
	};
} __packed;

struct u2f_hid_report {
	u8 report_type;
	struct u2f_hid_msg msg;
} __packed;

#define U2F_HID_MSG_LEN(f)	(size_t)(((f).init.bcnth << 8) + (f).init.bcntl)

/* Custom extensions to the U2FHID protocol */
#define U2F_CUSTOM_GET_RNG	0x21
#define U2F_CUSTOM_WINK		0x24

struct u2fzero_device {
	struct hid_device	*hdev;
	struct urb		*urb;	    /* URB for the RNG data */
	struct led_classdev	ldev;	    /* Embedded struct for led */
	struct hwrng		hwrng;	    /* Embedded struct for hwrng */
	char			*led_name;
	char			*rng_name;
	u8			*buf_out;
	u8			*buf_in;
	struct mutex		lock;
	bool			present;
};

static int u2fzero_send(struct u2fzero_device *dev, struct u2f_hid_report *req)
{
	int ret;

	mutex_lock(&dev->lock);

	memcpy(dev->buf_out, req, sizeof(struct u2f_hid_report));

	ret = hid_hw_output_report(dev->hdev, dev->buf_out,
				   sizeof(struct u2f_hid_msg));

	mutex_unlock(&dev->lock);

	if (ret < 0)
		return ret;

	return ret == sizeof(struct u2f_hid_msg) ? 0 : -EMSGSIZE;
}

struct u2fzero_transfer_context {
	struct completion done;
	int status;
};

static void u2fzero_read_callback(struct urb *urb)
{
	struct u2fzero_transfer_context *ctx = urb->context;

	ctx->status = urb->status;
	complete(&ctx->done);
}

static int u2fzero_recv(struct u2fzero_device *dev,
			struct u2f_hid_report *req,
			struct u2f_hid_msg *resp)
{
	int ret;
	struct hid_device *hdev = dev->hdev;
	struct u2fzero_transfer_context ctx;

	mutex_lock(&dev->lock);

	memcpy(dev->buf_out, req, sizeof(struct u2f_hid_report));

	dev->urb->context = &ctx;
	init_completion(&ctx.done);

	ret = usb_submit_urb(dev->urb, GFP_NOIO);
	if (unlikely(ret)) {
		hid_err(hdev, "usb_submit_urb failed: %d", ret);
		goto err;
	}

	ret = hid_hw_output_report(dev->hdev, dev->buf_out,
				   sizeof(struct u2f_hid_msg));

	if (ret < 0) {
		hid_err(hdev, "hid_hw_output_report failed: %d", ret);
		goto err;
	}

	ret = (wait_for_completion_timeout(
		&ctx.done, msecs_to_jiffies(USB_CTRL_SET_TIMEOUT)));
	if (ret == 0) {
		usb_kill_urb(dev->urb);
		hid_err(hdev, "urb submission timed out");
	} else {
		ret = dev->urb->actual_length;
		memcpy(resp, dev->buf_in, ret);
	}

err:
	mutex_unlock(&dev->lock);

	return ret;
}

static int u2fzero_blink(struct led_classdev *ldev)
{
	struct u2fzero_device *dev = container_of(ldev,
		struct u2fzero_device, ldev);
	struct u2f_hid_report req = {
		.report_type = 0,
		.msg.cid = CID_BROADCAST,
		.msg.init = {
			.cmd = U2F_CUSTOM_WINK,
			.bcnth = 0,
			.bcntl = 0,
			.data  = {0},
		}
	};
	return u2fzero_send(dev, &req);
}

static int u2fzero_brightness_set(struct led_classdev *ldev,
				  enum led_brightness brightness)
{
	ldev->brightness = LED_OFF;
	if (brightness)
		return u2fzero_blink(ldev);
	else
		return 0;
}

static int u2fzero_rng_read(struct hwrng *rng, void *data,
			    size_t max, bool wait)
{
	struct u2fzero_device *dev = container_of(rng,
		struct u2fzero_device, hwrng);
	struct u2f_hid_report req = {
		.report_type = 0,
		.msg.cid = CID_BROADCAST,
		.msg.init = {
			.cmd = U2F_CUSTOM_GET_RNG,
			.bcnth = 0,
			.bcntl = 0,
			.data  = {0},
		}
	};
	struct u2f_hid_msg resp;
	int ret;
	size_t actual_length;
	/* valid packets must have a correct header */
	int min_length = offsetof(struct u2f_hid_msg, init.data);

	if (!dev->present) {
		hid_dbg(dev->hdev, "device not present");
		return 0;
	}

	ret = u2fzero_recv(dev, &req, &resp);

	/* ignore errors or packets without data */
	if (ret < min_length)
		return 0;

	/* only take the minimum amount of data it is safe to take */
	actual_length = min3((size_t)ret - min_length,
		U2F_HID_MSG_LEN(resp), max);

	memcpy(data, resp.init.data, actual_length);

	return actual_length;
}

static int u2fzero_init_led(struct u2fzero_device *dev,
			    unsigned int minor)
{
	dev->led_name = devm_kasprintf(&dev->hdev->dev, GFP_KERNEL,
		"%s%u", DRIVER_SHORT, minor);
	if (dev->led_name == NULL)
		return -ENOMEM;

	dev->ldev.name = dev->led_name;
	dev->ldev.max_brightness = LED_ON;
	dev->ldev.flags = LED_HW_PLUGGABLE;
	dev->ldev.brightness_set_blocking = u2fzero_brightness_set;

	return devm_led_classdev_register(&dev->hdev->dev, &dev->ldev);
}

static int u2fzero_init_hwrng(struct u2fzero_device *dev,
			      unsigned int minor)
{
	dev->rng_name = devm_kasprintf(&dev->hdev->dev, GFP_KERNEL,
		"%s-rng%u", DRIVER_SHORT, minor);
	if (dev->rng_name == NULL)
		return -ENOMEM;

	dev->hwrng.name = dev->rng_name;
	dev->hwrng.read = u2fzero_rng_read;
	dev->hwrng.quality = 1;

	return devm_hwrng_register(&dev->hdev->dev, &dev->hwrng);
}

static int u2fzero_fill_in_urb(struct u2fzero_device *dev)
{
	struct hid_device *hdev = dev->hdev;
	struct usb_device *udev;
	struct usbhid_device *usbhid = hdev->driver_data;
	unsigned int pipe_in;
	struct usb_host_endpoint *ep;

	if (dev->hdev->bus != BUS_USB)
		return -EINVAL;

	udev = hid_to_usb_dev(hdev);

	if (!usbhid->urbout || !usbhid->urbin)
		return -ENODEV;

	ep = usb_pipe_endpoint(udev, usbhid->urbin->pipe);
	if (!ep)
		return -ENODEV;

	dev->urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->urb)
		return -ENOMEM;

	pipe_in = (usbhid->urbin->pipe & ~(3 << 30)) | (PIPE_INTERRUPT << 30);

	usb_fill_int_urb(dev->urb,
		udev,
		pipe_in,
		dev->buf_in,
		HID_REPORT_SIZE,
		u2fzero_read_callback,
		NULL,
		ep->desc.bInterval);

	return 0;
}

static int u2fzero_probe(struct hid_device *hdev,
			 const struct hid_device_id *id)
{
	struct u2fzero_device *dev;
	unsigned int minor;
	int ret;

	if (!hid_is_usb(hdev))
		return -EINVAL;

	dev = devm_kzalloc(&hdev->dev, sizeof(*dev), GFP_KERNEL);
	if (dev == NULL)
		return -ENOMEM;

	dev->buf_out = devm_kmalloc(&hdev->dev,
		sizeof(struct u2f_hid_report), GFP_KERNEL);
	if (dev->buf_out == NULL)
		return -ENOMEM;

	dev->buf_in = devm_kmalloc(&hdev->dev,
		sizeof(struct u2f_hid_msg), GFP_KERNEL);
	if (dev->buf_in == NULL)
		return -ENOMEM;

	ret = hid_parse(hdev);
	if (ret)
		return ret;

	dev->hdev = hdev;
	hid_set_drvdata(hdev, dev);
	mutex_init(&dev->lock);

	ret = hid_hw_start(hdev, HID_CONNECT_HIDRAW);
	if (ret)
		return ret;

	u2fzero_fill_in_urb(dev);

	dev->present = true;

	minor = ((struct hidraw *) hdev->hidraw)->minor;

	ret = u2fzero_init_led(dev, minor);
	if (ret) {
		hid_hw_stop(hdev);
		return ret;
	}

	hid_info(hdev, "U2F Zero LED initialised\n");

	ret = u2fzero_init_hwrng(dev, minor);
	if (ret) {
		hid_hw_stop(hdev);
		return ret;
	}

	hid_info(hdev, "U2F Zero RNG initialised\n");

	return 0;
}

static void u2fzero_remove(struct hid_device *hdev)
{
	struct u2fzero_device *dev = hid_get_drvdata(hdev);

	mutex_lock(&dev->lock);
	dev->present = false;
	mutex_unlock(&dev->lock);

	hid_hw_stop(hdev);
	usb_poison_urb(dev->urb);
	usb_free_urb(dev->urb);
}

static const struct hid_device_id u2fzero_table[] = {
	{ HID_USB_DEVICE(USB_VENDOR_ID_CYGNAL,
	  USB_DEVICE_ID_U2F_ZERO) },
	{ }
};
MODULE_DEVICE_TABLE(hid, u2fzero_table);

static struct hid_driver u2fzero_driver = {
	.name = "hid-" DRIVER_SHORT,
	.probe = u2fzero_probe,
	.remove = u2fzero_remove,
	.id_table = u2fzero_table,
};

module_hid_driver(u2fzero_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Andrej Shadura <andrew@shadura.me>");
MODULE_DESCRIPTION("U2F Zero LED and RNG driver");