1 // SPDX-License-Identifier: GPL-2.0-only
3 * CUSE: Character device in Userspace
5 * Copyright (C) 2008-2009 SUSE Linux Products GmbH
6 * Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
8 * CUSE enables character devices to be implemented from userland much
9 * like FUSE allows filesystems. On initialization /dev/cuse is
10 * created. By opening the file and replying to the CUSE_INIT request
11 * userland CUSE server can create a character device. After that the
12 * operation is very similar to FUSE.
14 * A CUSE instance involves the following objects.
16 * cuse_conn : contains fuse_conn and serves as bonding structure
17 * channel : file handle connected to the userland CUSE server
18 * cdev : the implemented character device
19 * dev : generic device for cdev
21 * Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with
22 * devices, it's called 'channel' to reduce confusion.
24 * channel determines when the character device dies. When channel is
25 * closed, everything begins to destruct. The cuse_conn is taken off
26 * the lookup table preventing further access from cdev, cdev and
27 * generic device are removed and the base reference of cuse_conn is
30 * On each open, the matching cuse_conn is looked up and if found an
31 * additional reference is taken which is released when the file is
35 #define pr_fmt(fmt) "CUSE: " fmt
37 #include <linux/fuse.h>
38 #include <linux/cdev.h>
39 #include <linux/device.h>
40 #include <linux/file.h>
42 #include <linux/kdev_t.h>
43 #include <linux/kthread.h>
44 #include <linux/list.h>
45 #include <linux/magic.h>
46 #include <linux/miscdevice.h>
47 #include <linux/mutex.h>
48 #include <linux/slab.h>
49 #include <linux/stat.h>
50 #include <linux/module.h>
51 #include <linux/uio.h>
52 #include <linux/user_namespace.h>
56 #define CUSE_CONNTBL_LEN 64
59 struct list_head list; /* linked on cuse_conntbl */
60 struct fuse_mount fm; /* Dummy mount referencing fc */
61 struct fuse_conn fc; /* fuse connection */
62 struct cdev *cdev; /* associated character device */
63 struct device *dev; /* device representing @cdev */
65 /* init parameters, set once during initialization */
66 bool unrestricted_ioctl;
69 static DEFINE_MUTEX(cuse_lock); /* protects registration */
70 static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
71 static struct class *cuse_class;
73 static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
75 return container_of(fc, struct cuse_conn, fc);
78 static struct list_head *cuse_conntbl_head(dev_t devt)
80 return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
84 /**************************************************************************
85 * CUSE frontend operations
87 * These are file operations for the character device.
89 * On open, CUSE opens a file from the FUSE mnt and stores it to
90 * private_data of the open file. All other ops call FUSE ops on the
94 static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
96 struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
99 return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
102 static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
104 struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
107 * No locking or generic_write_checks(), the server is
108 * responsible for locking and sanity checks.
110 return fuse_direct_io(&io, from, &pos,
111 FUSE_DIO_WRITE | FUSE_DIO_CUSE);
114 static int cuse_open(struct inode *inode, struct file *file)
116 dev_t devt = inode->i_cdev->dev;
117 struct cuse_conn *cc = NULL, *pos;
120 /* look up and get the connection */
121 mutex_lock(&cuse_lock);
122 list_for_each_entry(pos, cuse_conntbl_head(devt), list)
123 if (pos->dev->devt == devt) {
124 fuse_conn_get(&pos->fc);
128 mutex_unlock(&cuse_lock);
135 * Generic permission check is already done against the chrdev
136 * file, proceed to open.
138 rc = fuse_do_open(&cc->fm, 0, file, 0);
140 fuse_conn_put(&cc->fc);
144 static int cuse_release(struct inode *inode, struct file *file)
146 struct fuse_file *ff = file->private_data;
147 struct fuse_mount *fm = ff->fm;
149 fuse_sync_release(NULL, ff, file->f_flags);
150 fuse_conn_put(fm->fc);
155 static long cuse_file_ioctl(struct file *file, unsigned int cmd,
158 struct fuse_file *ff = file->private_data;
159 struct cuse_conn *cc = fc_to_cc(ff->fm->fc);
160 unsigned int flags = 0;
162 if (cc->unrestricted_ioctl)
163 flags |= FUSE_IOCTL_UNRESTRICTED;
165 return fuse_do_ioctl(file, cmd, arg, flags);
168 static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
171 struct fuse_file *ff = file->private_data;
172 struct cuse_conn *cc = fc_to_cc(ff->fm->fc);
173 unsigned int flags = FUSE_IOCTL_COMPAT;
175 if (cc->unrestricted_ioctl)
176 flags |= FUSE_IOCTL_UNRESTRICTED;
178 return fuse_do_ioctl(file, cmd, arg, flags);
181 static const struct file_operations cuse_frontend_fops = {
182 .owner = THIS_MODULE,
183 .read_iter = cuse_read_iter,
184 .write_iter = cuse_write_iter,
186 .release = cuse_release,
187 .unlocked_ioctl = cuse_file_ioctl,
188 .compat_ioctl = cuse_file_compat_ioctl,
189 .poll = fuse_file_poll,
190 .llseek = noop_llseek,
194 /**************************************************************************
195 * CUSE channel initialization and destruction
198 struct cuse_devinfo {
203 * cuse_parse_one - parse one key=value pair
204 * @pp: i/o parameter for the current position
205 * @end: points to one past the end of the packed string
206 * @keyp: out parameter for key
207 * @valp: out parameter for value
209 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
210 * at @end - 1. This function parses one pair and set *@keyp to the
211 * start of the key and *@valp to the start of the value. Note that
212 * the original string is modified such that the key string is
213 * terminated with '\0'. *@pp is updated to point to the next string.
216 * 1 on successful parse, 0 on EOF, -errno on failure.
218 static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
223 while (p < end && *p == '\0')
228 if (end[-1] != '\0') {
229 pr_err("info not properly terminated\n");
239 val = key + strlen(key);
246 pr_err("zero length info key specified\n");
259 * cuse_parse_dev_info - parse device info
260 * @p: device info string
261 * @len: length of device info string
262 * @devinfo: out parameter for parsed device info
264 * Parse @p to extract device info and store it into @devinfo. String
265 * pointed to by @p is modified by parsing and @devinfo points into
266 * them, so @p shouldn't be freed while @devinfo is in use.
269 * 0 on success, -errno on failure.
271 static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
278 rc = cuse_parse_one(&p, end, &key, &val);
283 if (strcmp(key, "DEVNAME") == 0)
286 pr_warn("unknown device info \"%s\"\n", key);
289 if (!devinfo->name || !strlen(devinfo->name)) {
290 pr_err("DEVNAME unspecified\n");
297 static void cuse_gendev_release(struct device *dev)
302 struct cuse_init_args {
303 struct fuse_args_pages ap;
304 struct cuse_init_in in;
305 struct cuse_init_out out;
307 struct fuse_page_desc desc;
311 * cuse_process_init_reply - finish initializing CUSE channel
313 * This function creates the character device and sets up all the
314 * required data structures for it. Please read the comment at the
315 * top of this file for high level overview.
317 static void cuse_process_init_reply(struct fuse_mount *fm,
318 struct fuse_args *args, int error)
320 struct fuse_conn *fc = fm->fc;
321 struct cuse_init_args *ia = container_of(args, typeof(*ia), ap.args);
322 struct fuse_args_pages *ap = &ia->ap;
323 struct cuse_conn *cc = fc_to_cc(fc), *pos;
324 struct cuse_init_out *arg = &ia->out;
325 struct page *page = ap->pages[0];
326 struct cuse_devinfo devinfo = { };
332 if (error || arg->major != FUSE_KERNEL_VERSION || arg->minor < 11)
335 fc->minor = arg->minor;
336 fc->max_read = max_t(unsigned, arg->max_read, 4096);
337 fc->max_write = max_t(unsigned, arg->max_write, 4096);
339 /* parse init reply */
340 cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
342 rc = cuse_parse_devinfo(page_address(page), ap->args.out_args[1].size,
347 /* determine and reserve devt */
348 devt = MKDEV(arg->dev_major, arg->dev_minor);
350 rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
352 rc = register_chrdev_region(devt, 1, devinfo.name);
354 pr_err("failed to register chrdev region\n");
358 /* devt determined, create device */
360 dev = kzalloc(sizeof(*dev), GFP_KERNEL);
364 device_initialize(dev);
365 dev_set_uevent_suppress(dev, 1);
366 dev->class = cuse_class;
368 dev->release = cuse_gendev_release;
369 dev_set_drvdata(dev, cc);
370 dev_set_name(dev, "%s", devinfo.name);
372 mutex_lock(&cuse_lock);
374 /* make sure the device-name is unique */
375 for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
376 list_for_each_entry(pos, &cuse_conntbl[i], list)
377 if (!strcmp(dev_name(pos->dev), dev_name(dev)))
381 rc = device_add(dev);
391 cdev->owner = THIS_MODULE;
392 cdev->ops = &cuse_frontend_fops;
394 rc = cdev_add(cdev, devt, 1);
401 /* make the device available */
402 list_add(&cc->list, cuse_conntbl_head(devt));
403 mutex_unlock(&cuse_lock);
405 /* announce device availability */
406 dev_set_uevent_suppress(dev, 0);
407 kobject_uevent(&dev->kobj, KOBJ_ADD);
416 mutex_unlock(&cuse_lock);
419 unregister_chrdev_region(devt, 1);
425 static int cuse_send_init(struct cuse_conn *cc)
429 struct fuse_mount *fm = &cc->fm;
430 struct cuse_init_args *ia;
431 struct fuse_args_pages *ap;
433 BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
436 page = alloc_page(GFP_KERNEL | __GFP_ZERO);
440 ia = kzalloc(sizeof(*ia), GFP_KERNEL);
445 ia->in.major = FUSE_KERNEL_VERSION;
446 ia->in.minor = FUSE_KERNEL_MINOR_VERSION;
447 ia->in.flags |= CUSE_UNRESTRICTED_IOCTL;
448 ap->args.opcode = CUSE_INIT;
449 ap->args.in_numargs = 1;
450 ap->args.in_args[0].size = sizeof(ia->in);
451 ap->args.in_args[0].value = &ia->in;
452 ap->args.out_numargs = 2;
453 ap->args.out_args[0].size = sizeof(ia->out);
454 ap->args.out_args[0].value = &ia->out;
455 ap->args.out_args[1].size = CUSE_INIT_INFO_MAX;
456 ap->args.out_argvar = true;
457 ap->args.out_pages = true;
459 ap->pages = &ia->page;
460 ap->descs = &ia->desc;
462 ia->desc.length = ap->args.out_args[1].size;
463 ap->args.end = cuse_process_init_reply;
465 rc = fuse_simple_background(fm, &ap->args, GFP_KERNEL);
475 static void cuse_fc_release(struct fuse_conn *fc)
477 struct cuse_conn *cc = fc_to_cc(fc);
478 kfree_rcu(cc, fc.rcu);
482 * cuse_channel_open - open method for /dev/cuse
483 * @inode: inode for /dev/cuse
484 * @file: file struct being opened
486 * Userland CUSE server can create a CUSE device by opening /dev/cuse
487 * and replying to the initialization request kernel sends. This
488 * function is responsible for handling CUSE device initialization.
489 * Because the fd opened by this function is used during
490 * initialization, this function only creates cuse_conn and sends
491 * init. The rest is delegated to a kthread.
494 * 0 on success, -errno on failure.
496 static int cuse_channel_open(struct inode *inode, struct file *file)
498 struct fuse_dev *fud;
499 struct cuse_conn *cc;
502 /* set up cuse_conn */
503 cc = kzalloc(sizeof(*cc), GFP_KERNEL);
508 * Limit the cuse channel to requests that can
509 * be represented in file->f_cred->user_ns.
511 fuse_conn_init(&cc->fc, &cc->fm, file->f_cred->user_ns,
512 &fuse_dev_fiq_ops, NULL);
514 cc->fc.release = cuse_fc_release;
515 fud = fuse_dev_alloc_install(&cc->fc);
516 fuse_conn_put(&cc->fc);
520 INIT_LIST_HEAD(&cc->list);
522 cc->fc.initialized = 1;
523 rc = cuse_send_init(cc);
528 file->private_data = fud;
534 * cuse_channel_release - release method for /dev/cuse
535 * @inode: inode for /dev/cuse
536 * @file: file struct being closed
538 * Disconnect the channel, deregister CUSE device and initiate
539 * destruction by putting the default reference.
542 * 0 on success, -errno on failure.
544 static int cuse_channel_release(struct inode *inode, struct file *file)
546 struct fuse_dev *fud = file->private_data;
547 struct cuse_conn *cc = fc_to_cc(fud->fc);
550 /* remove from the conntbl, no more access from this point on */
551 mutex_lock(&cuse_lock);
552 list_del_init(&cc->list);
553 mutex_unlock(&cuse_lock);
557 device_unregister(cc->dev);
559 unregister_chrdev_region(cc->cdev->dev, 1);
563 rc = fuse_dev_release(inode, file); /* puts the base reference */
568 static struct file_operations cuse_channel_fops; /* initialized during init */
571 /**************************************************************************
572 * Misc stuff and module initializatiion
574 * CUSE exports the same set of attributes to sysfs as fusectl.
577 static ssize_t cuse_class_waiting_show(struct device *dev,
578 struct device_attribute *attr, char *buf)
580 struct cuse_conn *cc = dev_get_drvdata(dev);
582 return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
584 static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);
586 static ssize_t cuse_class_abort_store(struct device *dev,
587 struct device_attribute *attr,
588 const char *buf, size_t count)
590 struct cuse_conn *cc = dev_get_drvdata(dev);
592 fuse_abort_conn(&cc->fc);
595 static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
597 static struct attribute *cuse_class_dev_attrs[] = {
598 &dev_attr_waiting.attr,
599 &dev_attr_abort.attr,
602 ATTRIBUTE_GROUPS(cuse_class_dev);
604 static struct miscdevice cuse_miscdev = {
607 .fops = &cuse_channel_fops,
610 MODULE_ALIAS_MISCDEV(CUSE_MINOR);
611 MODULE_ALIAS("devname:cuse");
613 static int __init cuse_init(void)
618 for (i = 0; i < CUSE_CONNTBL_LEN; i++)
619 INIT_LIST_HEAD(&cuse_conntbl[i]);
621 /* inherit and extend fuse_dev_operations */
622 cuse_channel_fops = fuse_dev_operations;
623 cuse_channel_fops.owner = THIS_MODULE;
624 cuse_channel_fops.open = cuse_channel_open;
625 cuse_channel_fops.release = cuse_channel_release;
626 /* CUSE is not prepared for FUSE_DEV_IOC_CLONE */
627 cuse_channel_fops.unlocked_ioctl = NULL;
629 cuse_class = class_create(THIS_MODULE, "cuse");
630 if (IS_ERR(cuse_class))
631 return PTR_ERR(cuse_class);
633 cuse_class->dev_groups = cuse_class_dev_groups;
635 rc = misc_register(&cuse_miscdev);
637 class_destroy(cuse_class);
644 static void __exit cuse_exit(void)
646 misc_deregister(&cuse_miscdev);
647 class_destroy(cuse_class);
650 module_init(cuse_init);
651 module_exit(cuse_exit);
653 MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
654 MODULE_DESCRIPTION("Character device in Userspace");
655 MODULE_LICENSE("GPL");