fs/fuse/cuse.c

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

DEFINITIONS
