1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * CUSE: Character device in Userspace
4 *
5 * Copyright (C) 2008-2009 SUSE Linux Products GmbH
6 * Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
7 *
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.
13 *
14 * A CUSE instance involves the following objects.
15 *
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
20 *
21 * Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with
22 * devices, it's called 'channel' to reduce confusion.
23 *
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
28 * put.
29 *
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
32 * closed.
33 */
34
35#define pr_fmt(fmt) "CUSE: " fmt
36
37#include <linux/fuse.h>
38#include <linux/cdev.h>
39#include <linux/device.h>
40#include <linux/file.h>
41#include <linux/fs.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>
53
54#include "fuse_i.h"
55#include "fuse_dev_i.h"
56
57#define CUSE_CONNTBL_LEN 64
58
59struct cuse_conn {
60 struct list_head list; /* linked on cuse_conntbl */
61 struct fuse_mount fm; /* Dummy mount referencing fc */
62 struct fuse_conn fc; /* fuse connection */
63 struct cdev *cdev; /* associated character device */
64 struct device *dev; /* device representing @cdev */
65
66 /* init parameters, set once during initialization */
67 bool unrestricted_ioctl;
68};
69
70static DEFINE_MUTEX(cuse_lock); /* protects registration */
71static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
72static struct class *cuse_class;
73
74static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
75{
76 return container_of(fc, struct cuse_conn, fc);
77}
78
79static struct list_head *cuse_conntbl_head(dev_t devt)
80{
81 return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
82}
83
84
85/**************************************************************************
86 * CUSE frontend operations
87 *
88 * These are file operations for the character device.
89 *
90 * On open, CUSE opens a file from the FUSE mnt and stores it to
91 * private_data of the open file. All other ops call FUSE ops on the
92 * FUSE file.
93 */
94
95static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
96{
97 struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
98 loff_t pos = 0;
99
100 return fuse_direct_io(io: &io, iter: to, ppos: &pos, FUSE_DIO_CUSE);
101}
102
103static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
104{
105 struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
106 loff_t pos = 0;
107 /*
108 * No locking or generic_write_checks(), the server is
109 * responsible for locking and sanity checks.
110 */
111 return fuse_direct_io(io: &io, iter: from, ppos: &pos,
112 FUSE_DIO_WRITE | FUSE_DIO_CUSE);
113}
114
115static int cuse_open(struct inode *inode, struct file *file)
116{
117 dev_t devt = inode->i_cdev->dev;
118 struct cuse_conn *cc = NULL, *pos;
119 int rc;
120
121 /* look up and get the connection */
122 mutex_lock(&cuse_lock);
123 list_for_each_entry(pos, cuse_conntbl_head(devt), list)
124 if (pos->dev->devt == devt) {
125 fuse_conn_get(fc: &pos->fc);
126 cc = pos;
127 break;
128 }
129 mutex_unlock(lock: &cuse_lock);
130
131 /* dead? */
132 if (!cc)
133 return -ENODEV;
134
135 /*
136 * Generic permission check is already done against the chrdev
137 * file, proceed to open.
138 */
139 rc = fuse_do_open(fm: &cc->fm, nodeid: 0, file, isdir: 0);
140 if (rc)
141 fuse_conn_put(fc: &cc->fc);
142 return rc;
143}
144
145static int cuse_release(struct inode *inode, struct file *file)
146{
147 struct fuse_file *ff = file->private_data;
148 struct fuse_mount *fm = ff->fm;
149
150 fuse_sync_release(NULL, ff, flags: file->f_flags);
151 fuse_conn_put(fc: fm->fc);
152
153 return 0;
154}
155
156static long cuse_file_ioctl(struct file *file, unsigned int cmd,
157 unsigned long arg)
158{
159 struct fuse_file *ff = file->private_data;
160 struct cuse_conn *cc = fc_to_cc(fc: ff->fm->fc);
161 unsigned int flags = 0;
162
163 if (cc->unrestricted_ioctl)
164 flags |= FUSE_IOCTL_UNRESTRICTED;
165
166 return fuse_do_ioctl(file, cmd, arg, flags);
167}
168
169static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
170 unsigned long arg)
171{
172 struct fuse_file *ff = file->private_data;
173 struct cuse_conn *cc = fc_to_cc(fc: ff->fm->fc);
174 unsigned int flags = FUSE_IOCTL_COMPAT;
175
176 if (cc->unrestricted_ioctl)
177 flags |= FUSE_IOCTL_UNRESTRICTED;
178
179 return fuse_do_ioctl(file, cmd, arg, flags);
180}
181
182static const struct file_operations cuse_frontend_fops = {
183 .owner = THIS_MODULE,
184 .read_iter = cuse_read_iter,
185 .write_iter = cuse_write_iter,
186 .open = cuse_open,
187 .release = cuse_release,
188 .unlocked_ioctl = cuse_file_ioctl,
189 .compat_ioctl = cuse_file_compat_ioctl,
190 .poll = fuse_file_poll,
191 .llseek = noop_llseek,
192};
193
194
195/**************************************************************************
196 * CUSE channel initialization and destruction
197 */
198
199struct cuse_devinfo {
200 const char *name;
201};
202
203/**
204 * cuse_parse_one - parse one key=value pair
205 * @pp: i/o parameter for the current position
206 * @end: points to one past the end of the packed string
207 * @keyp: out parameter for key
208 * @valp: out parameter for value
209 *
210 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
211 * at @end - 1. This function parses one pair and set *@keyp to the
212 * start of the key and *@valp to the start of the value. Note that
213 * the original string is modified such that the key string is
214 * terminated with '\0'. *@pp is updated to point to the next string.
215 *
216 * RETURNS:
217 * 1 on successful parse, 0 on EOF, -errno on failure.
218 */
219static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
220{
221 char *p = *pp;
222 char *key, *val;
223
224 while (p < end && *p == '\0')
225 p++;
226 if (p == end)
227 return 0;
228
229 if (end[-1] != '\0') {
230 pr_err("info not properly terminated\n");
231 return -EINVAL;
232 }
233
234 key = val = p;
235 p += strlen(p);
236
237 if (valp) {
238 strsep(&val, "=");
239 if (!val)
240 val = key + strlen(key);
241 key = strstrip(str: key);
242 val = strstrip(str: val);
243 } else
244 key = strstrip(str: key);
245
246 if (!strlen(key)) {
247 pr_err("zero length info key specified\n");
248 return -EINVAL;
249 }
250
251 *pp = p;
252 *keyp = key;
253 if (valp)
254 *valp = val;
255
256 return 1;
257}
258
259/**
260 * cuse_parse_devinfo - parse device info
261 * @p: device info string
262 * @len: length of device info string
263 * @devinfo: out parameter for parsed device info
264 *
265 * Parse @p to extract device info and store it into @devinfo. String
266 * pointed to by @p is modified by parsing and @devinfo points into
267 * them, so @p shouldn't be freed while @devinfo is in use.
268 *
269 * RETURNS:
270 * 0 on success, -errno on failure.
271 */
272static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
273{
274 char *end = p + len;
275 char *key, *val;
276 int rc;
277
278 while (true) {
279 rc = cuse_parse_one(pp: &p, end, keyp: &key, valp: &val);
280 if (rc < 0)
281 return rc;
282 if (!rc)
283 break;
284 if (strcmp(key, "DEVNAME") == 0)
285 devinfo->name = val;
286 else
287 pr_warn("unknown device info \"%s\"\n", key);
288 }
289
290 if (!devinfo->name || !strlen(devinfo->name)) {
291 pr_err("DEVNAME unspecified\n");
292 return -EINVAL;
293 }
294
295 return 0;
296}
297
298static void cuse_gendev_release(struct device *dev)
299{
300 kfree(objp: dev);
301}
302
303struct cuse_init_args {
304 struct fuse_args_pages ap;
305 struct cuse_init_in in;
306 struct cuse_init_out out;
307 struct folio *folio;
308 struct fuse_folio_desc desc;
309};
310
311/**
312 * cuse_process_init_reply - finish initializing CUSE channel
313 *
314 * @fm: The fuse mount information containing the CUSE connection.
315 * @args: The arguments passed to the init reply.
316 * @error: The error code signifying if any error occurred during the process.
317 *
318 * This function creates the character device and sets up all the
319 * required data structures for it. Please read the comment at the
320 * top of this file for high level overview.
321 */
322static void cuse_process_init_reply(struct fuse_mount *fm,
323 struct fuse_args *args, int error)
324{
325 struct fuse_conn *fc = fm->fc;
326 struct cuse_init_args *ia = container_of(args, typeof(*ia), ap.args);
327 struct fuse_args_pages *ap = &ia->ap;
328 struct cuse_conn *cc = fc_to_cc(fc), *pos;
329 struct cuse_init_out *arg = &ia->out;
330 struct folio *folio = ap->folios[0];
331 struct cuse_devinfo devinfo = { };
332 struct device *dev;
333 struct cdev *cdev;
334 dev_t devt;
335 int rc, i;
336
337 if (error || arg->major != FUSE_KERNEL_VERSION || arg->minor < 11)
338 goto err;
339
340 fc->minor = arg->minor;
341 fc->max_read = max_t(unsigned, arg->max_read, 4096);
342 fc->max_write = max_t(unsigned, arg->max_write, 4096);
343
344 /* parse init reply */
345 cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
346
347 rc = cuse_parse_devinfo(p: folio_address(folio), len: ap->args.out_args[1].size,
348 devinfo: &devinfo);
349 if (rc)
350 goto err;
351
352 /* determine and reserve devt */
353 devt = MKDEV(arg->dev_major, arg->dev_minor);
354 if (!MAJOR(devt))
355 rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
356 else
357 rc = register_chrdev_region(devt, 1, devinfo.name);
358 if (rc) {
359 pr_err("failed to register chrdev region\n");
360 goto err;
361 }
362
363 /* devt determined, create device */
364 rc = -ENOMEM;
365 dev = kzalloc(sizeof(*dev), GFP_KERNEL);
366 if (!dev)
367 goto err_region;
368
369 device_initialize(dev);
370 dev_set_uevent_suppress(dev, val: 1);
371 dev->class = cuse_class;
372 dev->devt = devt;
373 dev->release = cuse_gendev_release;
374 dev_set_drvdata(dev, data: cc);
375 dev_set_name(dev, name: "%s", devinfo.name);
376
377 mutex_lock(&cuse_lock);
378
379 /* make sure the device-name is unique */
380 for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
381 list_for_each_entry(pos, &cuse_conntbl[i], list)
382 if (!strcmp(dev_name(dev: pos->dev), dev_name(dev)))
383 goto err_unlock;
384 }
385
386 rc = device_add(dev);
387 if (rc)
388 goto err_unlock;
389
390 /* register cdev */
391 rc = -ENOMEM;
392 cdev = cdev_alloc();
393 if (!cdev)
394 goto err_unlock;
395
396 cdev->owner = THIS_MODULE;
397 cdev->ops = &cuse_frontend_fops;
398
399 rc = cdev_add(cdev, devt, 1);
400 if (rc)
401 goto err_cdev;
402
403 cc->dev = dev;
404 cc->cdev = cdev;
405
406 /* make the device available */
407 list_add(new: &cc->list, head: cuse_conntbl_head(devt));
408 mutex_unlock(lock: &cuse_lock);
409
410 /* announce device availability */
411 dev_set_uevent_suppress(dev, val: 0);
412 kobject_uevent(kobj: &dev->kobj, action: KOBJ_ADD);
413out:
414 kfree(objp: ia);
415 folio_put(folio);
416 return;
417
418err_cdev:
419 cdev_del(cdev);
420err_unlock:
421 mutex_unlock(lock: &cuse_lock);
422 put_device(dev);
423err_region:
424 unregister_chrdev_region(devt, 1);
425err:
426 fuse_abort_conn(fc);
427 goto out;
428}
429
430static int cuse_send_init(struct cuse_conn *cc)
431{
432 int rc;
433 struct folio *folio;
434 struct fuse_mount *fm = &cc->fm;
435 struct cuse_init_args *ia;
436 struct fuse_args_pages *ap;
437
438 BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
439
440 rc = -ENOMEM;
441
442 folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, 0);
443 if (!folio)
444 goto err;
445
446 ia = kzalloc(sizeof(*ia), GFP_KERNEL);
447 if (!ia)
448 goto err_free_folio;
449
450 ap = &ia->ap;
451 ia->in.major = FUSE_KERNEL_VERSION;
452 ia->in.minor = FUSE_KERNEL_MINOR_VERSION;
453 ia->in.flags |= CUSE_UNRESTRICTED_IOCTL;
454 ap->args.opcode = CUSE_INIT;
455 ap->args.in_numargs = 1;
456 ap->args.in_args[0].size = sizeof(ia->in);
457 ap->args.in_args[0].value = &ia->in;
458 ap->args.out_numargs = 2;
459 ap->args.out_args[0].size = sizeof(ia->out);
460 ap->args.out_args[0].value = &ia->out;
461 ap->args.out_args[1].size = CUSE_INIT_INFO_MAX;
462 ap->args.out_argvar = true;
463 ap->args.out_pages = true;
464 ap->num_folios = 1;
465 ap->folios = &ia->folio;
466 ap->descs = &ia->desc;
467 ia->folio = folio;
468 ia->desc.length = ap->args.out_args[1].size;
469 ap->args.end = cuse_process_init_reply;
470
471 rc = fuse_simple_background(fm, args: &ap->args, GFP_KERNEL);
472 if (rc) {
473 kfree(objp: ia);
474err_free_folio:
475 folio_put(folio);
476 }
477err:
478 return rc;
479}
480
481static void cuse_fc_release(struct fuse_conn *fc)
482{
483 kfree(objp: fc_to_cc(fc));
484}
485
486/**
487 * cuse_channel_open - open method for /dev/cuse
488 * @inode: inode for /dev/cuse
489 * @file: file struct being opened
490 *
491 * Userland CUSE server can create a CUSE device by opening /dev/cuse
492 * and replying to the initialization request kernel sends. This
493 * function is responsible for handling CUSE device initialization.
494 * Because the fd opened by this function is used during
495 * initialization, this function only creates cuse_conn and sends
496 * init. The rest is delegated to a kthread.
497 *
498 * RETURNS:
499 * 0 on success, -errno on failure.
500 */
501static int cuse_channel_open(struct inode *inode, struct file *file)
502{
503 struct fuse_dev *fud;
504 struct cuse_conn *cc;
505 int rc;
506
507 /* set up cuse_conn */
508 cc = kzalloc(sizeof(*cc), GFP_KERNEL);
509 if (!cc)
510 return -ENOMEM;
511
512 /*
513 * Limit the cuse channel to requests that can
514 * be represented in file->f_cred->user_ns.
515 */
516 fuse_conn_init(fc: &cc->fc, fm: &cc->fm, user_ns: file->f_cred->user_ns,
517 fiq_ops: &fuse_dev_fiq_ops, NULL);
518
519 cc->fc.release = cuse_fc_release;
520 fud = fuse_dev_alloc_install(fc: &cc->fc);
521 fuse_conn_put(fc: &cc->fc);
522 if (!fud)
523 return -ENOMEM;
524
525 INIT_LIST_HEAD(list: &cc->list);
526
527 cc->fc.initialized = 1;
528 rc = cuse_send_init(cc);
529 if (rc) {
530 fuse_dev_free(fud);
531 return rc;
532 }
533 file->private_data = fud;
534
535 return 0;
536}
537
538/**
539 * cuse_channel_release - release method for /dev/cuse
540 * @inode: inode for /dev/cuse
541 * @file: file struct being closed
542 *
543 * Disconnect the channel, deregister CUSE device and initiate
544 * destruction by putting the default reference.
545 *
546 * RETURNS:
547 * 0 on success, -errno on failure.
548 */
549static int cuse_channel_release(struct inode *inode, struct file *file)
550{
551 struct fuse_dev *fud = __fuse_get_dev(file);
552 struct cuse_conn *cc = fc_to_cc(fc: fud->fc);
553
554 /* remove from the conntbl, no more access from this point on */
555 mutex_lock(&cuse_lock);
556 list_del_init(entry: &cc->list);
557 mutex_unlock(lock: &cuse_lock);
558
559 /* remove device */
560 if (cc->dev)
561 device_unregister(dev: cc->dev);
562 if (cc->cdev) {
563 unregister_chrdev_region(cc->cdev->dev, 1);
564 cdev_del(cc->cdev);
565 }
566
567 return fuse_dev_release(inode, file);
568}
569
570static struct file_operations cuse_channel_fops; /* initialized during init */
571
572
573/**************************************************************************
574 * Misc stuff and module initializatiion
575 *
576 * CUSE exports the same set of attributes to sysfs as fusectl.
577 */
578
579static ssize_t cuse_class_waiting_show(struct device *dev,
580 struct device_attribute *attr, char *buf)
581{
582 struct cuse_conn *cc = dev_get_drvdata(dev);
583
584 return sprintf(buf, fmt: "%d\n", atomic_read(v: &cc->fc.num_waiting));
585}
586static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);
587
588static ssize_t cuse_class_abort_store(struct device *dev,
589 struct device_attribute *attr,
590 const char *buf, size_t count)
591{
592 struct cuse_conn *cc = dev_get_drvdata(dev);
593
594 fuse_abort_conn(fc: &cc->fc);
595 return count;
596}
597static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
598
599static struct attribute *cuse_class_dev_attrs[] = {
600 &dev_attr_waiting.attr,
601 &dev_attr_abort.attr,
602 NULL,
603};
604ATTRIBUTE_GROUPS(cuse_class_dev);
605
606static struct miscdevice cuse_miscdev = {
607 .minor = CUSE_MINOR,
608 .name = "cuse",
609 .fops = &cuse_channel_fops,
610};
611
612MODULE_ALIAS_MISCDEV(CUSE_MINOR);
613MODULE_ALIAS("devname:cuse");
614
615static int __init cuse_init(void)
616{
617 int i, rc;
618
619 /* init conntbl */
620 for (i = 0; i < CUSE_CONNTBL_LEN; i++)
621 INIT_LIST_HEAD(list: &cuse_conntbl[i]);
622
623 /* inherit and extend fuse_dev_operations */
624 cuse_channel_fops = fuse_dev_operations;
625 cuse_channel_fops.owner = THIS_MODULE;
626 cuse_channel_fops.open = cuse_channel_open;
627 cuse_channel_fops.release = cuse_channel_release;
628 /* CUSE is not prepared for FUSE_DEV_IOC_CLONE */
629 cuse_channel_fops.unlocked_ioctl = NULL;
630
631 cuse_class = class_create(name: "cuse");
632 if (IS_ERR(ptr: cuse_class))
633 return PTR_ERR(ptr: cuse_class);
634
635 cuse_class->dev_groups = cuse_class_dev_groups;
636
637 rc = misc_register(misc: &cuse_miscdev);
638 if (rc) {
639 class_destroy(cls: cuse_class);
640 return rc;
641 }
642
643 return 0;
644}
645
646static void __exit cuse_exit(void)
647{
648 misc_deregister(misc: &cuse_miscdev);
649 class_destroy(cls: cuse_class);
650}
651
652module_init(cuse_init);
653module_exit(cuse_exit);
654
655MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
656MODULE_DESCRIPTION("Character device in Userspace");
657MODULE_LICENSE("GPL");
658

source code of linux/fs/fuse/cuse.c