// SPDX-License-Identifier: GPL-2.0-only
/*
 * CUSE: Character device in Userspace
 *
 * Copyright (C) 2008-2009  SUSE Linux Products GmbH
 * Copyright (C) 2008-2009  Tejun Heo <tj@kernel.org>
 *
 * CUSE enables character devices to be implemented from userland much
 * like FUSE allows filesystems.  On initialization /dev/cuse is
 * created.  By opening the file and replying to the CUSE_INIT request
 * userland CUSE server can create a character device.  After that the
 * operation is very similar to FUSE.
 *
 * A CUSE instance involves the following objects.
 *
 * cuse_conn    : contains fuse_conn and serves as bonding structure
 * channel      : file handle connected to the userland CUSE server
 * cdev         : the implemented character device
 * dev          : generic device for cdev
 *
 * Note that 'channel' is what 'dev' is in FUSE.  As CUSE deals with
 * devices, it's called 'channel' to reduce confusion.
 *
 * channel determines when the character device dies.  When channel is
 * closed, everything begins to destruct.  The cuse_conn is taken off
 * the lookup table preventing further access from cdev, cdev and
 * generic device are removed and the base reference of cuse_conn is
 * put.
 *
 * On each open, the matching cuse_conn is looked up and if found an
 * additional reference is taken which is released when the file is
 * closed.
 */

#define pr_fmt(fmt) "CUSE: " fmt

#include <linux/fuse.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/module.h>
#include <linux/uio.h>
#include <linux/user_namespace.h>

#include "fuse_i.h"

#define CUSE_CONNTBL_LEN        64

struct cuse_conn {
        struct list_head        list;   /* linked on cuse_conntbl */
        struct fuse_conn        fc;     /* fuse connection */
        struct cdev             *cdev;  /* associated character device */
        struct device           *dev;   /* device representing @cdev */

        /* init parameters, set once during initialization */
        bool                    unrestricted_ioctl;
};

static DEFINE_MUTEX(cuse_lock);         /* protects registration */
static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
static struct class *cuse_class;

static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
{
        return container_of(fc, struct cuse_conn, fc);
}

static struct list_head *cuse_conntbl_head(dev_t devt)
{
        return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
}


/**************************************************************************
 * CUSE frontend operations
 *
 * These are file operations for the character device.
 *
 * On open, CUSE opens a file from the FUSE mnt and stores it to
 * private_data of the open file.  All other ops call FUSE ops on the
 * FUSE file.
 */

static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
        struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
        loff_t pos = 0;

        return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
}

static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
{
        struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
        loff_t pos = 0;
        /*
         * No locking or generic_write_checks(), the server is
         * responsible for locking and sanity checks.
         */
        return fuse_direct_io(&io, from, &pos,
                              FUSE_DIO_WRITE | FUSE_DIO_CUSE);
}

static int cuse_open(struct inode *inode, struct file *file)
{
        dev_t devt = inode->i_cdev->dev;
        struct cuse_conn *cc = NULL, *pos;
        int rc;

        /* look up and get the connection */
        mutex_lock(&cuse_lock);
        list_for_each_entry(pos, cuse_conntbl_head(devt), list)
                if (pos->dev->devt == devt) {
                        fuse_conn_get(&pos->fc);
                        cc = pos;
                        break;
                }
        mutex_unlock(&cuse_lock);

        /* dead? */
        if (!cc)
                return -ENODEV;

        /*
         * Generic permission check is already done against the chrdev
         * file, proceed to open.
         */
        rc = fuse_do_open(&cc->fc, 0, file, 0);
        if (rc)
                fuse_conn_put(&cc->fc);
        return rc;
}

static int cuse_release(struct inode *inode, struct file *file)
{
        struct fuse_file *ff = file->private_data;
        struct fuse_conn *fc = ff->fc;

        fuse_sync_release(NULL, ff, file->f_flags);
        fuse_conn_put(fc);

        return 0;
}

static long cuse_file_ioctl(struct file *file, unsigned int cmd,
                            unsigned long arg)
{
        struct fuse_file *ff = file->private_data;
        struct cuse_conn *cc = fc_to_cc(ff->fc);
        unsigned int flags = 0;

        if (cc->unrestricted_ioctl)
                flags |= FUSE_IOCTL_UNRESTRICTED;

        return fuse_do_ioctl(file, cmd, arg, flags);
}

static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
                                   unsigned long arg)
{
        struct fuse_file *ff = file->private_data;
        struct cuse_conn *cc = fc_to_cc(ff->fc);
        unsigned int flags = FUSE_IOCTL_COMPAT;

        if (cc->unrestricted_ioctl)
                flags |= FUSE_IOCTL_UNRESTRICTED;

        return fuse_do_ioctl(file, cmd, arg, flags);
}

static const struct file_operations cuse_frontend_fops = {
        .owner                  = THIS_MODULE,
        .read_iter              = cuse_read_iter,
        .write_iter             = cuse_write_iter,
        .open                   = cuse_open,
        .release                = cuse_release,
        .unlocked_ioctl         = cuse_file_ioctl,
        .compat_ioctl           = cuse_file_compat_ioctl,
        .poll                   = fuse_file_poll,
        .llseek         = noop_llseek,
};


/**************************************************************************
 * CUSE channel initialization and destruction
 */

struct cuse_devinfo {
        const char              *name;
};

/**
 * cuse_parse_one - parse one key=value pair
 * @pp: i/o parameter for the current position
 * @end: points to one past the end of the packed string
 * @keyp: out parameter for key
 * @valp: out parameter for value
 *
 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
 * at @end - 1.  This function parses one pair and set *@keyp to the
 * start of the key and *@valp to the start of the value.  Note that
 * the original string is modified such that the key string is
 * terminated with '\0'.  *@pp is updated to point to the next string.
 *
 * RETURNS:
 * 1 on successful parse, 0 on EOF, -errno on failure.
 */
static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
{
        char *p = *pp;
        char *key, *val;

        while (p < end && *p == '\0')
                p++;
        if (p == end)
                return 0;

        if (end[-1] != '\0') {
                pr_err("info not properly terminated\n");
                return -EINVAL;
        }

        key = val = p;
        p += strlen(p);

        if (valp) {
                strsep(&val, "=");
                if (!val)
                        val = key + strlen(key);
                key = strstrip(key);
                val = strstrip(val);
        } else
                key = strstrip(key);

        if (!strlen(key)) {
                pr_err("zero length info key specified\n");
                return -EINVAL;
        }

        *pp = p;
        *keyp = key;
        if (valp)
                *valp = val;

        return 1;
}

/**
 * cuse_parse_dev_info - parse device info
 * @p: device info string
 * @len: length of device info string
 * @devinfo: out parameter for parsed device info
 *
 * Parse @p to extract device info and store it into @devinfo.  String
 * pointed to by @p is modified by parsing and @devinfo points into
 * them, so @p shouldn't be freed while @devinfo is in use.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
{
        char *end = p + len;
        char *key, *val;
        int rc;

        while (true) {
                rc = cuse_parse_one(&p, end, &key, &val);
                if (rc < 0)
                        return rc;
                if (!rc)
                        break;
                if (strcmp(key, "DEVNAME") == 0)
                        devinfo->name = val;
                else
                        pr_warn("unknown device info \"%s\"\n", key);
        }

        if (!devinfo->name || !strlen(devinfo->name)) {
                pr_err("DEVNAME unspecified\n");
                return -EINVAL;
        }

        return 0;
}

static void cuse_gendev_release(struct device *dev)
{
        kfree(dev);
}

struct cuse_init_args {
        struct fuse_args_pages ap;
        struct cuse_init_in in;
        struct cuse_init_out out;
        struct page *page;
        struct fuse_page_desc desc;
};

/**
 * cuse_process_init_reply - finish initializing CUSE channel
 *
 * This function creates the character device and sets up all the
 * required data structures for it.  Please read the comment at the
 * top of this file for high level overview.
 */
static void cuse_process_init_reply(struct fuse_conn *fc,
                                    struct fuse_args *args, int error)
{
        struct cuse_init_args *ia = container_of(args, typeof(*ia), ap.args);
        struct fuse_args_pages *ap = &ia->ap;
        struct cuse_conn *cc = fc_to_cc(fc), *pos;
        struct cuse_init_out *arg = &ia->out;
        struct page *page = ap->pages[0];
        struct cuse_devinfo devinfo = { };
        struct device *dev;
        struct cdev *cdev;
        dev_t devt;
        int rc, i;

        if (error || arg->major != FUSE_KERNEL_VERSION || arg->minor < 11)
                goto err;

        fc->minor = arg->minor;
        fc->max_read = max_t(unsigned, arg->max_read, 4096);
        fc->max_write = max_t(unsigned, arg->max_write, 4096);

        /* parse init reply */
        cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;

        rc = cuse_parse_devinfo(page_address(page), ap->args.out_args[1].size,
                                &devinfo);
        if (rc)
                goto err;

        /* determine and reserve devt */
        devt = MKDEV(arg->dev_major, arg->dev_minor);
        if (!MAJOR(devt))
                rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
        else
                rc = register_chrdev_region(devt, 1, devinfo.name);
        if (rc) {
                pr_err("failed to register chrdev region\n");
                goto err;
        }

        /* devt determined, create device */
        rc = -ENOMEM;
        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (!dev)
                goto err_region;

        device_initialize(dev);
        dev_set_uevent_suppress(dev, 1);
        dev->class = cuse_class;
        dev->devt = devt;
        dev->release = cuse_gendev_release;
        dev_set_drvdata(dev, cc);
        dev_set_name(dev, "%s", devinfo.name);

        mutex_lock(&cuse_lock);

        /* make sure the device-name is unique */
        for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
                list_for_each_entry(pos, &cuse_conntbl[i], list)
                        if (!strcmp(dev_name(pos->dev), dev_name(dev)))
                                goto err_unlock;
        }

        rc = device_add(dev);
        if (rc)
                goto err_unlock;

        /* register cdev */
        rc = -ENOMEM;
        cdev = cdev_alloc();
        if (!cdev)
                goto err_unlock;

        cdev->owner = THIS_MODULE;
        cdev->ops = &cuse_frontend_fops;

        rc = cdev_add(cdev, devt, 1);
        if (rc)
                goto err_cdev;

        cc->dev = dev;
        cc->cdev = cdev;

        /* make the device available */
        list_add(&cc->list, cuse_conntbl_head(devt));
        mutex_unlock(&cuse_lock);

        /* announce device availability */
        dev_set_uevent_suppress(dev, 0);
        kobject_uevent(&dev->kobj, KOBJ_ADD);
out:
        kfree(ia);
        __free_page(page);
        return;

err_cdev:
        cdev_del(cdev);
err_unlock:
        mutex_unlock(&cuse_lock);
        put_device(dev);
err_region:
        unregister_chrdev_region(devt, 1);
err:
        fuse_abort_conn(fc);
        goto out;
}

static int cuse_send_init(struct cuse_conn *cc)
{
        int rc;
        struct page *page;
        struct fuse_conn *fc = &cc->fc;
        struct cuse_init_args *ia;
        struct fuse_args_pages *ap;

        BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);

        rc = -ENOMEM;
        page = alloc_page(GFP_KERNEL | __GFP_ZERO);
        if (!page)
                goto err;

        ia = kzalloc(sizeof(*ia), GFP_KERNEL);
        if (!ia)
                goto err_free_page;

        ap = &ia->ap;
        ia->in.major = FUSE_KERNEL_VERSION;
        ia->in.minor = FUSE_KERNEL_MINOR_VERSION;
        ia->in.flags |= CUSE_UNRESTRICTED_IOCTL;
        ap->args.opcode = CUSE_INIT;
        ap->args.in_numargs = 1;
        ap->args.in_args[0].size = sizeof(ia->in);
        ap->args.in_args[0].value = &ia->in;
        ap->args.out_numargs = 2;
        ap->args.out_args[0].size = sizeof(ia->out);
        ap->args.out_args[0].value = &ia->out;
        ap->args.out_args[1].size = CUSE_INIT_INFO_MAX;
        ap->args.out_argvar = true;
        ap->args.out_pages = true;
        ap->num_pages = 1;
        ap->pages = &ia->page;
        ap->descs = &ia->desc;
        ia->page = page;
        ia->desc.length = ap->args.out_args[1].size;
        ap->args.end = cuse_process_init_reply;

        rc = fuse_simple_background(fc, &ap->args, GFP_KERNEL);
        if (rc) {
                kfree(ia);
err_free_page:
                __free_page(page);
        }
err:
        return rc;
}

static void cuse_fc_release(struct fuse_conn *fc)
{
        struct cuse_conn *cc = fc_to_cc(fc);
        kfree_rcu(cc, fc.rcu);
}

/**
 * cuse_channel_open - open method for /dev/cuse
 * @inode: inode for /dev/cuse
 * @file: file struct being opened
 *
 * Userland CUSE server can create a CUSE device by opening /dev/cuse
 * and replying to the initialization request kernel sends.  This
 * function is responsible for handling CUSE device initialization.
 * Because the fd opened by this function is used during
 * initialization, this function only creates cuse_conn and sends
 * init.  The rest is delegated to a kthread.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int cuse_channel_open(struct inode *inode, struct file *file)
{
        struct fuse_dev *fud;
        struct cuse_conn *cc;
        int rc;

        /* set up cuse_conn */
        cc = kzalloc(sizeof(*cc), GFP_KERNEL);
        if (!cc)
                return -ENOMEM;

        /*
         * Limit the cuse channel to requests that can
         * be represented in file->f_cred->user_ns.
         */
        fuse_conn_init(&cc->fc, file->f_cred->user_ns, &fuse_dev_fiq_ops, NULL);

        fud = fuse_dev_alloc_install(&cc->fc);
        if (!fud) {
                kfree(cc);
                return -ENOMEM;
        }

        INIT_LIST_HEAD(&cc->list);
        cc->fc.release = cuse_fc_release;

        cc->fc.initialized = 1;
        rc = cuse_send_init(cc);
        if (rc) {
                fuse_dev_free(fud);
                fuse_conn_put(&cc->fc);
                return rc;
        }
        file->private_data = fud;

        return 0;
}

/**
 * cuse_channel_release - release method for /dev/cuse
 * @inode: inode for /dev/cuse
 * @file: file struct being closed
 *
 * Disconnect the channel, deregister CUSE device and initiate
 * destruction by putting the default reference.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int cuse_channel_release(struct inode *inode, struct file *file)
{
        struct fuse_dev *fud = file->private_data;
        struct cuse_conn *cc = fc_to_cc(fud->fc);
        int rc;

        /* remove from the conntbl, no more access from this point on */
        mutex_lock(&cuse_lock);
        list_del_init(&cc->list);
        mutex_unlock(&cuse_lock);

        /* remove device */
        if (cc->dev)
                device_unregister(cc->dev);
        if (cc->cdev) {
                unregister_chrdev_region(cc->cdev->dev, 1);
                cdev_del(cc->cdev);
        }
        /* Base reference is now owned by "fud" */
        fuse_conn_put(&cc->fc);

        rc = fuse_dev_release(inode, file);     /* puts the base reference */

        return rc;
}

static struct file_operations cuse_channel_fops; /* initialized during init */


/**************************************************************************
 * Misc stuff and module initializatiion
 *
 * CUSE exports the same set of attributes to sysfs as fusectl.
 */

static ssize_t cuse_class_waiting_show(struct device *dev,
                                       struct device_attribute *attr, char *buf)
{
        struct cuse_conn *cc = dev_get_drvdata(dev);

        return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
}
static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);

static ssize_t cuse_class_abort_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf, size_t count)
{
        struct cuse_conn *cc = dev_get_drvdata(dev);

        fuse_abort_conn(&cc->fc);
        return count;
}
static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);

static struct attribute *cuse_class_dev_attrs[] = {
        &dev_attr_waiting.attr,
        &dev_attr_abort.attr,
        NULL,
};
ATTRIBUTE_GROUPS(cuse_class_dev);

static struct miscdevice cuse_miscdev = {
        .minor          = CUSE_MINOR,
        .name           = "cuse",
        .fops           = &cuse_channel_fops,
};

MODULE_ALIAS_MISCDEV(CUSE_MINOR);
MODULE_ALIAS("devname:cuse");

static int __init cuse_init(void)
{
        int i, rc;

        /* init conntbl */
        for (i = 0; i < CUSE_CONNTBL_LEN; i++)
                INIT_LIST_HEAD(&cuse_conntbl[i]);

        /* inherit and extend fuse_dev_operations */
        cuse_channel_fops               = fuse_dev_operations;
        cuse_channel_fops.owner         = THIS_MODULE;
        cuse_channel_fops.open          = cuse_channel_open;
        cuse_channel_fops.release       = cuse_channel_release;

        cuse_class = class_create(THIS_MODULE, "cuse");
        if (IS_ERR(cuse_class))
                return PTR_ERR(cuse_class);

        cuse_class->dev_groups = cuse_class_dev_groups;

        rc = misc_register(&cuse_miscdev);
        if (rc) {
                class_destroy(cuse_class);
                return rc;
        }

        return 0;
}

static void __exit cuse_exit(void)
{
        misc_deregister(&cuse_miscdev);
        class_destroy(cuse_class);
}

module_init(cuse_init);
module_exit(cuse_exit);

MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
MODULE_DESCRIPTION("Character device in Userspace");
MODULE_LICENSE("GPL");