// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * User-space I/O driver support for HID subsystem
 * Copyright (c) 2012 David Herrmann
 */

/*
 */

#include <linux/atomic.h>
#include <linux/compat.h>
#include <linux/cred.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/hid.h>
#include <linux/input.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/uhid.h>
#include <linux/wait.h>

#define UHID_NAME       "uhid"
#define UHID_BUFSIZE    32

struct uhid_device {
        struct mutex devlock;

        /* This flag tracks whether the HID device is usable for commands from
         * userspace. The flag is already set before hid_add_device(), which
         * runs in workqueue context, to allow hid_add_device() to communicate
         * with userspace.
         * However, if hid_add_device() fails, the flag is cleared without
         * holding devlock.
         * We guarantee that if @running changes from true to false while you're
         * holding @devlock, it's still fine to access @hid.
         */
        bool running;

        __u8 *rd_data;
        uint rd_size;

        /* When this is NULL, userspace may use UHID_CREATE/UHID_CREATE2. */
        struct hid_device *hid;
        struct uhid_event input_buf;

        wait_queue_head_t waitq;
        spinlock_t qlock;
        __u8 head;
        __u8 tail;
        struct uhid_event *outq[UHID_BUFSIZE];

        /* blocking GET_REPORT support; state changes protected by qlock */
        struct mutex report_lock;
        wait_queue_head_t report_wait;
        bool report_running;
        u32 report_id;
        u32 report_type;
        struct uhid_event report_buf;
        struct work_struct worker;
};

static struct miscdevice uhid_misc;

static void uhid_device_add_worker(struct work_struct *work)
{
        struct uhid_device *uhid = container_of(work, struct uhid_device, worker);
        int ret;

        ret = hid_add_device(uhid->hid);
        if (ret) {
                hid_err(uhid->hid, "Cannot register HID device: error %d\n", ret);

                /* We used to call hid_destroy_device() here, but that's really
                 * messy to get right because we have to coordinate with
                 * concurrent writes from userspace that might be in the middle
                 * of using uhid->hid.
                 * Just leave uhid->hid as-is for now, and clean it up when
                 * userspace tries to close or reinitialize the uhid instance.
                 *
                 * However, we do have to clear the ->running flag and do a
                 * wakeup to make sure userspace knows that the device is gone.
                 */
                WRITE_ONCE(uhid->running, false);
                wake_up_interruptible(&uhid->report_wait);
        }
}

static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
{
        __u8 newhead;

        newhead = (uhid->head + 1) % UHID_BUFSIZE;

        if (newhead != uhid->tail) {
                uhid->outq[uhid->head] = ev;
                uhid->head = newhead;
                wake_up_interruptible(&uhid->waitq);
        } else {
                hid_warn(uhid->hid, "Output queue is full\n");
                kfree(ev);
        }
}

static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
{
        unsigned long flags;
        struct uhid_event *ev;

        ev = kzalloc_obj(*ev);
        if (!ev)
                return -ENOMEM;

        ev->type = event;

        spin_lock_irqsave(&uhid->qlock, flags);
        uhid_queue(uhid, ev);
        spin_unlock_irqrestore(&uhid->qlock, flags);

        return 0;
}

static int uhid_hid_start(struct hid_device *hid)
{
        struct uhid_device *uhid = hid->driver_data;
        struct uhid_event *ev;
        unsigned long flags;

        ev = kzalloc_obj(*ev);
        if (!ev)
                return -ENOMEM;

        ev->type = UHID_START;

        if (hid->report_enum[HID_FEATURE_REPORT].numbered)
                ev->u.start.dev_flags |= UHID_DEV_NUMBERED_FEATURE_REPORTS;
        if (hid->report_enum[HID_OUTPUT_REPORT].numbered)
                ev->u.start.dev_flags |= UHID_DEV_NUMBERED_OUTPUT_REPORTS;
        if (hid->report_enum[HID_INPUT_REPORT].numbered)
                ev->u.start.dev_flags |= UHID_DEV_NUMBERED_INPUT_REPORTS;

        spin_lock_irqsave(&uhid->qlock, flags);
        uhid_queue(uhid, ev);
        spin_unlock_irqrestore(&uhid->qlock, flags);

        return 0;
}

static void uhid_hid_stop(struct hid_device *hid)
{
        struct uhid_device *uhid = hid->driver_data;

        hid->claimed = 0;
        uhid_queue_event(uhid, UHID_STOP);
}

static int uhid_hid_open(struct hid_device *hid)
{
        struct uhid_device *uhid = hid->driver_data;

        return uhid_queue_event(uhid, UHID_OPEN);
}

static void uhid_hid_close(struct hid_device *hid)
{
        struct uhid_device *uhid = hid->driver_data;

        uhid_queue_event(uhid, UHID_CLOSE);
}

static int uhid_hid_parse(struct hid_device *hid)
{
        struct uhid_device *uhid = hid->driver_data;

        return hid_parse_report(hid, uhid->rd_data, uhid->rd_size);
}

/* must be called with report_lock held */
static int __uhid_report_queue_and_wait(struct uhid_device *uhid,
                                        struct uhid_event *ev,
                                        __u32 *report_id)
{
        unsigned long flags;
        int ret;

        spin_lock_irqsave(&uhid->qlock, flags);
        *report_id = ++uhid->report_id;
        uhid->report_type = ev->type + 1;
        uhid->report_running = true;
        uhid_queue(uhid, ev);
        spin_unlock_irqrestore(&uhid->qlock, flags);

        ret = wait_event_interruptible_timeout(uhid->report_wait,
                                !uhid->report_running || !READ_ONCE(uhid->running),
                                5 * HZ);
        if (!ret || !READ_ONCE(uhid->running) || uhid->report_running)
                ret = -EIO;
        else if (ret < 0)
                ret = -ERESTARTSYS;
        else
                ret = 0;

        uhid->report_running = false;

        return ret;
}

static void uhid_report_wake_up(struct uhid_device *uhid, u32 id,
                                const struct uhid_event *ev)
{
        unsigned long flags;

        spin_lock_irqsave(&uhid->qlock, flags);

        /* id for old report; drop it silently */
        if (uhid->report_type != ev->type || uhid->report_id != id)
                goto unlock;
        if (!uhid->report_running)
                goto unlock;

        memcpy(&uhid->report_buf, ev, sizeof(*ev));
        uhid->report_running = false;
        wake_up_interruptible(&uhid->report_wait);

unlock:
        spin_unlock_irqrestore(&uhid->qlock, flags);
}

static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
                               u8 *buf, size_t count, u8 rtype)
{
        struct uhid_device *uhid = hid->driver_data;
        struct uhid_get_report_reply_req *req;
        struct uhid_event *ev;
        int ret;

        if (!READ_ONCE(uhid->running))
                return -EIO;

        ev = kzalloc_obj(*ev);
        if (!ev)
                return -ENOMEM;

        ev->type = UHID_GET_REPORT;
        ev->u.get_report.rnum = rnum;
        ev->u.get_report.rtype = rtype;

        ret = mutex_lock_interruptible(&uhid->report_lock);
        if (ret) {
                kfree(ev);
                return ret;
        }

        /* this _always_ takes ownership of @ev */
        ret = __uhid_report_queue_and_wait(uhid, ev, &ev->u.get_report.id);
        if (ret)
                goto unlock;

        req = &uhid->report_buf.u.get_report_reply;
        if (req->err) {
                ret = -EIO;
        } else {
                ret = min3(count, (size_t)req->size, (size_t)UHID_DATA_MAX);
                memcpy(buf, req->data, ret);
        }

unlock:
        mutex_unlock(&uhid->report_lock);
        return ret;
}

static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
                               const u8 *buf, size_t count, u8 rtype)
{
        struct uhid_device *uhid = hid->driver_data;
        struct uhid_event *ev;
        int ret;

        if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
                return -EIO;

        ev = kzalloc_obj(*ev);
        if (!ev)
                return -ENOMEM;

        ev->type = UHID_SET_REPORT;
        ev->u.set_report.rnum = rnum;
        ev->u.set_report.rtype = rtype;
        ev->u.set_report.size = count;
        memcpy(ev->u.set_report.data, buf, count);

        ret = mutex_lock_interruptible(&uhid->report_lock);
        if (ret) {
                kfree(ev);
                return ret;
        }

        /* this _always_ takes ownership of @ev */
        ret = __uhid_report_queue_and_wait(uhid, ev, &ev->u.set_report.id);
        if (ret)
                goto unlock;

        if (uhid->report_buf.u.set_report_reply.err)
                ret = -EIO;
        else
                ret = count;

unlock:
        mutex_unlock(&uhid->report_lock);
        return ret;
}

static int uhid_hid_raw_request(struct hid_device *hid, unsigned char reportnum,
                                __u8 *buf, size_t len, unsigned char rtype,
                                int reqtype)
{
        u8 u_rtype;

        switch (rtype) {
        case HID_FEATURE_REPORT:
                u_rtype = UHID_FEATURE_REPORT;
                break;
        case HID_OUTPUT_REPORT:
                u_rtype = UHID_OUTPUT_REPORT;
                break;
        case HID_INPUT_REPORT:
                u_rtype = UHID_INPUT_REPORT;
                break;
        default:
                return -EINVAL;
        }

        switch (reqtype) {
        case HID_REQ_GET_REPORT:
                return uhid_hid_get_report(hid, reportnum, buf, len, u_rtype);
        case HID_REQ_SET_REPORT:
                return uhid_hid_set_report(hid, reportnum, buf, len, u_rtype);
        default:
                return -EIO;
        }
}

static int uhid_hid_output_raw(struct hid_device *hid, __u8 *buf, size_t count,
                               unsigned char report_type)
{
        struct uhid_device *uhid = hid->driver_data;
        __u8 rtype;
        unsigned long flags;
        struct uhid_event *ev;

        switch (report_type) {
        case HID_FEATURE_REPORT:
                rtype = UHID_FEATURE_REPORT;
                break;
        case HID_OUTPUT_REPORT:
                rtype = UHID_OUTPUT_REPORT;
                break;
        default:
                return -EINVAL;
        }

        if (count < 1 || count > UHID_DATA_MAX)
                return -EINVAL;

        ev = kzalloc_obj(*ev);
        if (!ev)
                return -ENOMEM;

        ev->type = UHID_OUTPUT;
        ev->u.output.size = count;
        ev->u.output.rtype = rtype;
        memcpy(ev->u.output.data, buf, count);

        spin_lock_irqsave(&uhid->qlock, flags);
        uhid_queue(uhid, ev);
        spin_unlock_irqrestore(&uhid->qlock, flags);

        return count;
}

static int uhid_hid_output_report(struct hid_device *hid, __u8 *buf,
                                  size_t count)
{
        return uhid_hid_output_raw(hid, buf, count, HID_OUTPUT_REPORT);
}

static const struct hid_ll_driver uhid_hid_driver = {
        .start = uhid_hid_start,
        .stop = uhid_hid_stop,
        .open = uhid_hid_open,
        .close = uhid_hid_close,
        .parse = uhid_hid_parse,
        .raw_request = uhid_hid_raw_request,
        .output_report = uhid_hid_output_report,
        .max_buffer_size = UHID_DATA_MAX,
};

#ifdef CONFIG_COMPAT

/* Apparently we haven't stepped on these rakes enough times yet. */
struct uhid_create_req_compat {
        __u8 name[128];
        __u8 phys[64];
        __u8 uniq[64];

        compat_uptr_t rd_data;
        __u16 rd_size;

        __u16 bus;
        __u32 vendor;
        __u32 product;
        __u32 version;
        __u32 country;
} __attribute__((__packed__));

static int uhid_event_from_user(const char __user *buffer, size_t len,
                                struct uhid_event *event)
{
        if (in_compat_syscall()) {
                u32 type;

                if (get_user(type, buffer))
                        return -EFAULT;

                if (type == UHID_CREATE) {
                        /*
                         * This is our messed up request with compat pointer.
                         * It is largish (more than 256 bytes) so we better
                         * allocate it from the heap.
                         */
                        struct uhid_create_req_compat *compat;

                        compat = kzalloc_obj(*compat);
                        if (!compat)
                                return -ENOMEM;

                        buffer += sizeof(type);
                        len -= sizeof(type);
                        if (copy_from_user(compat, buffer,
                                           min(len, sizeof(*compat)))) {
                                kfree(compat);
                                return -EFAULT;
                        }

                        /* Shuffle the data over to proper structure */
                        event->type = type;

                        memcpy(event->u.create.name, compat->name,
                                sizeof(compat->name));
                        memcpy(event->u.create.phys, compat->phys,
                                sizeof(compat->phys));
                        memcpy(event->u.create.uniq, compat->uniq,
                                sizeof(compat->uniq));

                        event->u.create.rd_data = compat_ptr(compat->rd_data);
                        event->u.create.rd_size = compat->rd_size;

                        event->u.create.bus = compat->bus;
                        event->u.create.vendor = compat->vendor;
                        event->u.create.product = compat->product;
                        event->u.create.version = compat->version;
                        event->u.create.country = compat->country;

                        kfree(compat);
                        return 0;
                }
                /* All others can be copied directly */
        }

        if (copy_from_user(event, buffer, min(len, sizeof(*event))))
                return -EFAULT;

        return 0;
}
#else
static int uhid_event_from_user(const char __user *buffer, size_t len,
                                struct uhid_event *event)
{
        if (copy_from_user(event, buffer, min(len, sizeof(*event))))
                return -EFAULT;

        return 0;
}
#endif

static int uhid_dev_create2(struct uhid_device *uhid,
                            const struct uhid_event *ev)
{
        struct hid_device *hid;
        size_t rd_size;
        void *rd_data;
        int ret;

        if (uhid->hid)
                return -EALREADY;

        rd_size = ev->u.create2.rd_size;
        if (rd_size <= 0 || rd_size > HID_MAX_DESCRIPTOR_SIZE)
                return -EINVAL;

        rd_data = kmemdup(ev->u.create2.rd_data, rd_size, GFP_KERNEL);
        if (!rd_data)
                return -ENOMEM;

        uhid->rd_size = rd_size;
        uhid->rd_data = rd_data;

        hid = hid_allocate_device();
        if (IS_ERR(hid)) {
                ret = PTR_ERR(hid);
                goto err_free;
        }

        BUILD_BUG_ON(sizeof(hid->name) != sizeof(ev->u.create2.name));
        strscpy(hid->name, ev->u.create2.name, sizeof(hid->name));
        BUILD_BUG_ON(sizeof(hid->phys) != sizeof(ev->u.create2.phys));
        strscpy(hid->phys, ev->u.create2.phys, sizeof(hid->phys));
        BUILD_BUG_ON(sizeof(hid->uniq) != sizeof(ev->u.create2.uniq));
        strscpy(hid->uniq, ev->u.create2.uniq, sizeof(hid->uniq));

        hid->ll_driver = &uhid_hid_driver;
        hid->bus = ev->u.create2.bus;
        hid->vendor = ev->u.create2.vendor;
        hid->product = ev->u.create2.product;
        hid->version = ev->u.create2.version;
        hid->country = ev->u.create2.country;
        hid->driver_data = uhid;
        hid->dev.parent = uhid_misc.this_device;

        uhid->hid = hid;
        uhid->running = true;

        /* Adding of a HID device is done through a worker, to allow HID drivers
         * which use feature requests during .probe to work, without they would
         * be blocked on devlock, which is held by uhid_char_write.
         */
        schedule_work(&uhid->worker);

        return 0;

err_free:
        kfree(uhid->rd_data);
        uhid->rd_data = NULL;
        uhid->rd_size = 0;
        return ret;
}

static int uhid_dev_create(struct uhid_device *uhid,
                           struct uhid_event *ev)
{
        struct uhid_create_req orig;

        orig = ev->u.create;

        if (orig.rd_size <= 0 || orig.rd_size > HID_MAX_DESCRIPTOR_SIZE)
                return -EINVAL;
        if (copy_from_user(&ev->u.create2.rd_data, orig.rd_data, orig.rd_size))
                return -EFAULT;

        memcpy(ev->u.create2.name, orig.name, sizeof(orig.name));
        memcpy(ev->u.create2.phys, orig.phys, sizeof(orig.phys));
        memcpy(ev->u.create2.uniq, orig.uniq, sizeof(orig.uniq));
        ev->u.create2.rd_size = orig.rd_size;
        ev->u.create2.bus = orig.bus;
        ev->u.create2.vendor = orig.vendor;
        ev->u.create2.product = orig.product;
        ev->u.create2.version = orig.version;
        ev->u.create2.country = orig.country;

        return uhid_dev_create2(uhid, ev);
}

static int uhid_dev_destroy(struct uhid_device *uhid)
{
        if (!uhid->hid)
                return -EINVAL;

        WRITE_ONCE(uhid->running, false);
        wake_up_interruptible(&uhid->report_wait);

        cancel_work_sync(&uhid->worker);

        hid_destroy_device(uhid->hid);
        uhid->hid = NULL;
        kfree(uhid->rd_data);

        return 0;
}

static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
{
        if (!READ_ONCE(uhid->running))
                return -EINVAL;

        hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input.data,
                         min_t(size_t, ev->u.input.size, UHID_DATA_MAX), 0);

        return 0;
}

static int uhid_dev_input2(struct uhid_device *uhid, struct uhid_event *ev)
{
        if (!READ_ONCE(uhid->running))
                return -EINVAL;

        hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input2.data,
                         min_t(size_t, ev->u.input2.size, UHID_DATA_MAX), 0);

        return 0;
}

static int uhid_dev_get_report_reply(struct uhid_device *uhid,
                                     struct uhid_event *ev)
{
        if (!READ_ONCE(uhid->running))
                return -EINVAL;

        uhid_report_wake_up(uhid, ev->u.get_report_reply.id, ev);
        return 0;
}

static int uhid_dev_set_report_reply(struct uhid_device *uhid,
                                     struct uhid_event *ev)
{
        if (!READ_ONCE(uhid->running))
                return -EINVAL;

        uhid_report_wake_up(uhid, ev->u.set_report_reply.id, ev);
        return 0;
}

static int uhid_char_open(struct inode *inode, struct file *file)
{
        struct uhid_device *uhid;

        uhid = kzalloc_obj(*uhid);
        if (!uhid)
                return -ENOMEM;

        mutex_init(&uhid->devlock);
        mutex_init(&uhid->report_lock);
        spin_lock_init(&uhid->qlock);
        init_waitqueue_head(&uhid->waitq);
        init_waitqueue_head(&uhid->report_wait);
        uhid->running = false;
        INIT_WORK(&uhid->worker, uhid_device_add_worker);

        file->private_data = uhid;
        stream_open(inode, file);

        return 0;
}

static int uhid_char_release(struct inode *inode, struct file *file)
{
        struct uhid_device *uhid = file->private_data;
        unsigned int i;

        uhid_dev_destroy(uhid);

        for (i = 0; i < UHID_BUFSIZE; ++i)
                kfree(uhid->outq[i]);

        kfree(uhid);

        return 0;
}

static ssize_t uhid_char_read(struct file *file, char __user *buffer,
                                size_t count, loff_t *ppos)
{
        struct uhid_device *uhid = file->private_data;
        int ret;
        unsigned long flags;
        size_t len;

        /* they need at least the "type" member of uhid_event */
        if (count < sizeof(__u32))
                return -EINVAL;

try_again:
        if (file->f_flags & O_NONBLOCK) {
                if (uhid->head == uhid->tail)
                        return -EAGAIN;
        } else {
                ret = wait_event_interruptible(uhid->waitq,
                                                uhid->head != uhid->tail);
                if (ret)
                        return ret;
        }

        ret = mutex_lock_interruptible(&uhid->devlock);
        if (ret)
                return ret;

        if (uhid->head == uhid->tail) {
                mutex_unlock(&uhid->devlock);
                goto try_again;
        } else {
                len = min(count, sizeof(**uhid->outq));
                if (copy_to_user(buffer, uhid->outq[uhid->tail], len)) {
                        ret = -EFAULT;
                } else {
                        kfree(uhid->outq[uhid->tail]);
                        uhid->outq[uhid->tail] = NULL;

                        spin_lock_irqsave(&uhid->qlock, flags);
                        uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;
                        spin_unlock_irqrestore(&uhid->qlock, flags);
                }
        }

        mutex_unlock(&uhid->devlock);
        return ret ? ret : len;
}

static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
                                size_t count, loff_t *ppos)
{
        struct uhid_device *uhid = file->private_data;
        int ret;
        size_t len;

        /* we need at least the "type" member of uhid_event */
        if (count < sizeof(__u32))
                return -EINVAL;

        ret = mutex_lock_interruptible(&uhid->devlock);
        if (ret)
                return ret;

        memset(&uhid->input_buf, 0, sizeof(uhid->input_buf));
        len = min(count, sizeof(uhid->input_buf));

        ret = uhid_event_from_user(buffer, len, &uhid->input_buf);
        if (ret)
                goto unlock;

        switch (uhid->input_buf.type) {
        case UHID_CREATE:
                /*
                 * 'struct uhid_create_req' contains a __user pointer which is
                 * copied from, so it's unsafe to allow this with elevated
                 * privileges (e.g. from a setuid binary) or via kernel_write().
                 */
                if (file->f_cred != current_cred()) {
                        pr_err_once("UHID_CREATE from different security context by process %d (%s), this is not allowed.\n",
                                    task_tgid_vnr(current), current->comm);
                        ret = -EACCES;
                        goto unlock;
                }
                ret = uhid_dev_create(uhid, &uhid->input_buf);
                break;
        case UHID_CREATE2:
                ret = uhid_dev_create2(uhid, &uhid->input_buf);
                break;
        case UHID_DESTROY:
                ret = uhid_dev_destroy(uhid);
                break;
        case UHID_INPUT:
                ret = uhid_dev_input(uhid, &uhid->input_buf);
                break;
        case UHID_INPUT2:
                ret = uhid_dev_input2(uhid, &uhid->input_buf);
                break;
        case UHID_GET_REPORT_REPLY:
                ret = uhid_dev_get_report_reply(uhid, &uhid->input_buf);
                break;
        case UHID_SET_REPORT_REPLY:
                ret = uhid_dev_set_report_reply(uhid, &uhid->input_buf);
                break;
        default:
                ret = -EOPNOTSUPP;
        }

unlock:
        mutex_unlock(&uhid->devlock);

        /* return "count" not "len" to not confuse the caller */
        return ret ? ret : count;
}

static __poll_t uhid_char_poll(struct file *file, poll_table *wait)
{
        struct uhid_device *uhid = file->private_data;
        __poll_t mask = EPOLLOUT | EPOLLWRNORM; /* uhid is always writable */

        poll_wait(file, &uhid->waitq, wait);

        if (uhid->head != uhid->tail)
                mask |= EPOLLIN | EPOLLRDNORM;

        return mask;
}

static const struct file_operations uhid_fops = {
        .owner          = THIS_MODULE,
        .open           = uhid_char_open,
        .release        = uhid_char_release,
        .read           = uhid_char_read,
        .write          = uhid_char_write,
        .poll           = uhid_char_poll,
};

static struct miscdevice uhid_misc = {
        .fops           = &uhid_fops,
        .minor          = UHID_MINOR,
        .name           = UHID_NAME,
};
module_misc_device(uhid_misc);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("David Herrmann <dh.herrmann@gmail.com>");
MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");
MODULE_ALIAS_MISCDEV(UHID_MINOR);
MODULE_ALIAS("devname:" UHID_NAME);