fs/binfmt_misc.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * binfmt_misc.c
   4  *
   5  * Copyright (C) 1997 Richard Günther
   6  *
   7  * binfmt_misc detects binaries via a magic or filename extension and invokes
   8  * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
   9  */
  10
  11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/sched/mm.h>
  17 #include <linux/magic.h>
  18 #include <linux/binfmts.h>
  19 #include <linux/slab.h>
  20 #include <linux/ctype.h>
  21 #include <linux/string_helpers.h>
  22 #include <linux/file.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/namei.h>
  25 #include <linux/mount.h>
  26 #include <linux/fs_context.h>
  27 #include <linux/syscalls.h>
  28 #include <linux/fs.h>
  29 #include <linux/uaccess.h>
  30
  31 #include "internal.h"
  32
  33 #ifdef DEBUG
  34 # define USE_DEBUG 1
  35 #else
  36 # define USE_DEBUG 0
  37 #endif
  38
  39 enum {
  40         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  41 };
  42
  43 static LIST_HEAD(entries);
  44 static int enabled = 1;
  45
  46 enum {Enabled, Magic};
  47 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  48 #define MISC_FMT_OPEN_BINARY (1 << 30)
  49 #define MISC_FMT_CREDENTIALS (1 << 29)
  50 #define MISC_FMT_OPEN_FILE (1 << 28)
  51
  52 typedef struct {
  53         struct list_head list;
  54         unsigned long flags;            /* type, status, etc. */
  55         int offset;                     /* offset of magic */
  56         int size;                       /* size of magic/mask */
  57         char *magic;                    /* magic or filename extension */
  58         char *mask;                     /* mask, NULL for exact match */
  59         const char *interpreter;        /* filename of interpreter */
  60         char *name;
  61         struct dentry *dentry;
  62         struct file *interp_file;
  63 } Node;
  64
  65 static DEFINE_RWLOCK(entries_lock);
  66 static struct file_system_type bm_fs_type;
  67 static struct vfsmount *bm_mnt;
  68 static int entry_count;
  69
  70 /*
  71  * Max length of the register string.  Determined by:
  72  *  - 7 delimiters
  73  *  - name:   ~50 bytes
  74  *  - type:   1 byte
  75  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  76  *  - magic:  128 bytes (512 in escaped form)
  77  *  - mask:   128 bytes (512 in escaped form)
  78  *  - interp: ~50 bytes
  79  *  - flags:  5 bytes
  80  * Round that up a bit, and then back off to hold the internal data
  81  * (like struct Node).
  82  */
  83 #define MAX_REGISTER_LENGTH 1920
  84
  85 /*
  86  * Check if we support the binfmt
  87  * if we do, return the node, else NULL
  88  * locking is done in load_misc_binary
  89  */
  90 static Node *check_file(struct linux_binprm *bprm)
  91 {
  92         char *p = strrchr(bprm->interp, '.');
  93         struct list_head *l;
  94
  95         /* Walk all the registered handlers. */
  96         list_for_each(l, &entries) {
  97                 Node *e = list_entry(l, Node, list);
  98                 char *s;
  99                 int j;
 100
 101                 /* Make sure this one is currently enabled. */
 102                 if (!test_bit(Enabled, &e->flags))
 103                         continue;
 104
 105                 /* Do matching based on extension if applicable. */
 106                 if (!test_bit(Magic, &e->flags)) {
 107                         if (p && !strcmp(e->magic, p + 1))
 108                                 return e;
 109                         continue;
 110                 }
 111
 112                 /* Do matching based on magic & mask. */
 113                 s = bprm->buf + e->offset;
 114                 if (e->mask) {
 115                         for (j = 0; j < e->size; j++)
 116                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 117                                         break;
 118                 } else {
 119                         for (j = 0; j < e->size; j++)
 120                                 if ((*s++ ^ e->magic[j]))
 121                                         break;
 122                 }
 123                 if (j == e->size)
 124                         return e;
 125         }
 126         return NULL;
 127 }
 128
 129 /*
 130  * the loader itself
 131  */
 132 static int load_misc_binary(struct linux_binprm *bprm)
 133 {
 134         Node *fmt;
 135         struct file *interp_file = NULL;
 136         int retval;
 137
 138         retval = -ENOEXEC;
 139         if (!enabled)
 140                 return retval;
 141
 142         /* to keep locking time low, we copy the interpreter string */
 143         read_lock(&entries_lock);
 144         fmt = check_file(bprm);
 145         if (fmt)
 146                 dget(fmt->dentry);
 147         read_unlock(&entries_lock);
 148         if (!fmt)
 149                 return retval;
 150
 151         /* Need to be able to load the file after exec */
 152         retval = -ENOENT;
 153         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 154                 goto ret;
 155
 156         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 157                 retval = remove_arg_zero(bprm);
 158                 if (retval)
 159                         goto ret;
 160         }
 161
 162         if (fmt->flags & MISC_FMT_OPEN_BINARY)
 163                 bprm->have_execfd = 1;
 164
 165         /* make argv[1] be the path to the binary */
 166         retval = copy_string_kernel(bprm->interp, bprm);
 167         if (retval < 0)
 168                 goto ret;
 169         bprm->argc++;
 170
 171         /* add the interp as argv[0] */
 172         retval = copy_string_kernel(fmt->interpreter, bprm);
 173         if (retval < 0)
 174                 goto ret;
 175         bprm->argc++;
 176
 177         /* Update interp in case binfmt_script needs it. */
 178         retval = bprm_change_interp(fmt->interpreter, bprm);
 179         if (retval < 0)
 180                 goto ret;
 181
 182         if (fmt->flags & MISC_FMT_OPEN_FILE) {
 183                 interp_file = file_clone_open(fmt->interp_file);
 184                 if (!IS_ERR(interp_file))
 185                         deny_write_access(interp_file);
 186         } else {
 187                 interp_file = open_exec(fmt->interpreter);
 188         }
 189         retval = PTR_ERR(interp_file);
 190         if (IS_ERR(interp_file))
 191                 goto ret;
 192
 193         bprm->interpreter = interp_file;
 194         if (fmt->flags & MISC_FMT_CREDENTIALS)
 195                 bprm->execfd_creds = 1;
 196
 197         retval = 0;
 198 ret:
 199         dput(fmt->dentry);
 200         return retval;
 201 }
 202
 203 /* Command parsers */
 204
 205 /*
 206  * parses and copies one argument enclosed in del from *sp to *dp,
 207  * recognising the \x special.
 208  * returns pointer to the copied argument or NULL in case of an
 209  * error (and sets err) or null argument length.
 210  */
 211 static char *scanarg(char *s, char del)
 212 {
 213         char c;
 214
 215         while ((c = *s++) != del) {
 216                 if (c == '\\' && *s == 'x') {
 217                         s++;
 218                         if (!isxdigit(*s++))
 219                                 return NULL;
 220                         if (!isxdigit(*s++))
 221                                 return NULL;
 222                 }
 223         }
 224         s[-1] ='\0';
 225         return s;
 226 }
 227
 228 static char *check_special_flags(char *sfs, Node *e)
 229 {
 230         char *p = sfs;
 231         int cont = 1;
 232
 233         /* special flags */
 234         while (cont) {
 235                 switch (*p) {
 236                 case 'P':
 237                         pr_debug("register: flag: P (preserve argv0)\n");
 238                         p++;
 239                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 240                         break;
 241                 case 'O':
 242                         pr_debug("register: flag: O (open binary)\n");
 243                         p++;
 244                         e->flags |= MISC_FMT_OPEN_BINARY;
 245                         break;
 246                 case 'C':
 247                         pr_debug("register: flag: C (preserve creds)\n");
 248                         p++;
 249                         /* this flags also implies the
 250                            open-binary flag */
 251                         e->flags |= (MISC_FMT_CREDENTIALS |
 252                                         MISC_FMT_OPEN_BINARY);
 253                         break;
 254                 case 'F':
 255                         pr_debug("register: flag: F: open interpreter file now\n");
 256                         p++;
 257                         e->flags |= MISC_FMT_OPEN_FILE;
 258                         break;
 259                 default:
 260                         cont = 0;
 261                 }
 262         }
 263
 264         return p;
 265 }
 266
 267 /*
 268  * This registers a new binary format, it recognises the syntax
 269  * ':name:type:offset:magic:mask:interpreter:flags'
 270  * where the ':' is the IFS, that can be chosen with the first char
 271  */
 272 static Node *create_entry(const char __user *buffer, size_t count)
 273 {
 274         Node *e;
 275         int memsize, err;
 276         char *buf, *p;
 277         char del;
 278
 279         pr_debug("register: received %zu bytes\n", count);
 280
 281         /* some sanity checks */
 282         err = -EINVAL;
 283         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 284                 goto out;
 285
 286         err = -ENOMEM;
 287         memsize = sizeof(Node) + count + 8;
 288         e = kmalloc(memsize, GFP_KERNEL);
 289         if (!e)
 290                 goto out;
 291
 292         p = buf = (char *)e + sizeof(Node);
 293
 294         memset(e, 0, sizeof(Node));
 295         if (copy_from_user(buf, buffer, count))
 296                 goto efault;
 297
 298         del = *p++;     /* delimeter */
 299
 300         pr_debug("register: delim: %#x {%c}\n", del, del);
 301
 302         /* Pad the buffer with the delim to simplify parsing below. */
 303         memset(buf + count, del, 8);
 304
 305         /* Parse the 'name' field. */
 306         e->name = p;
 307         p = strchr(p, del);
 308         if (!p)
 309                 goto einval;
 310         *p++ = '\0';
 311         if (!e->name[0] ||
 312             !strcmp(e->name, ".") ||
 313             !strcmp(e->name, "..") ||
 314             strchr(e->name, '/'))
 315                 goto einval;
 316
 317         pr_debug("register: name: {%s}\n", e->name);
 318
 319         /* Parse the 'type' field. */
 320         switch (*p++) {
 321         case 'E':
 322                 pr_debug("register: type: E (extension)\n");
 323                 e->flags = 1 << Enabled;
 324                 break;
 325         case 'M':
 326                 pr_debug("register: type: M (magic)\n");
 327                 e->flags = (1 << Enabled) | (1 << Magic);
 328                 break;
 329         default:
 330                 goto einval;
 331         }
 332         if (*p++ != del)
 333                 goto einval;
 334
 335         if (test_bit(Magic, &e->flags)) {
 336                 /* Handle the 'M' (magic) format. */
 337                 char *s;
 338
 339                 /* Parse the 'offset' field. */
 340                 s = strchr(p, del);
 341                 if (!s)
 342                         goto einval;
 343                 *s = '\0';
 344                 if (p != s) {
 345                         int r = kstrtoint(p, 10, &e->offset);
 346                         if (r != 0 || e->offset < 0)
 347                                 goto einval;
 348                 }
 349                 p = s;
 350                 if (*p++)
 351                         goto einval;
 352                 pr_debug("register: offset: %#x\n", e->offset);
 353
 354                 /* Parse the 'magic' field. */
 355                 e->magic = p;
 356                 p = scanarg(p, del);
 357                 if (!p)
 358                         goto einval;
 359                 if (!e->magic[0])
 360                         goto einval;
 361                 if (USE_DEBUG)
 362                         print_hex_dump_bytes(
 363                                 KBUILD_MODNAME ": register: magic[raw]: ",
 364                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 365
 366                 /* Parse the 'mask' field. */
 367                 e->mask = p;
 368                 p = scanarg(p, del);
 369                 if (!p)
 370                         goto einval;
 371                 if (!e->mask[0]) {
 372                         e->mask = NULL;
 373                         pr_debug("register:  mask[raw]: none\n");
 374                 } else if (USE_DEBUG)
 375                         print_hex_dump_bytes(
 376                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 377                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 378
 379                 /*
 380                  * Decode the magic & mask fields.
 381                  * Note: while we might have accepted embedded NUL bytes from
 382                  * above, the unescape helpers here will stop at the first one
 383                  * it encounters.
 384                  */
 385                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 386                 if (e->mask &&
 387                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 388                         goto einval;
 389                 if (e->size > BINPRM_BUF_SIZE ||
 390                     BINPRM_BUF_SIZE - e->size < e->offset)
 391                         goto einval;
 392                 pr_debug("register: magic/mask length: %i\n", e->size);
 393                 if (USE_DEBUG) {
 394                         print_hex_dump_bytes(
 395                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 396                                 DUMP_PREFIX_NONE, e->magic, e->size);
 397
 398                         if (e->mask) {
 399                                 int i;
 400                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 401
 402                                 print_hex_dump_bytes(
 403                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 404                                         DUMP_PREFIX_NONE, e->mask, e->size);
 405
 406                                 if (masked) {
 407                                         for (i = 0; i < e->size; ++i)
 408                                                 masked[i] = e->magic[i] & e->mask[i];
 409                                         print_hex_dump_bytes(
 410                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 411                                                 DUMP_PREFIX_NONE, masked, e->size);
 412
 413                                         kfree(masked);
 414                                 }
 415                         }
 416                 }
 417         } else {
 418                 /* Handle the 'E' (extension) format. */
 419
 420                 /* Skip the 'offset' field. */
 421                 p = strchr(p, del);
 422                 if (!p)
 423                         goto einval;
 424                 *p++ = '\0';
 425
 426                 /* Parse the 'magic' field. */
 427                 e->magic = p;
 428                 p = strchr(p, del);
 429                 if (!p)
 430                         goto einval;
 431                 *p++ = '\0';
 432                 if (!e->magic[0] || strchr(e->magic, '/'))
 433                         goto einval;
 434                 pr_debug("register: extension: {%s}\n", e->magic);
 435
 436                 /* Skip the 'mask' field. */
 437                 p = strchr(p, del);
 438                 if (!p)
 439                         goto einval;
 440                 *p++ = '\0';
 441         }
 442
 443         /* Parse the 'interpreter' field. */
 444         e->interpreter = p;
 445         p = strchr(p, del);
 446         if (!p)
 447                 goto einval;
 448         *p++ = '\0';
 449         if (!e->interpreter[0])
 450                 goto einval;
 451         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 452
 453         /* Parse the 'flags' field. */
 454         p = check_special_flags(p, e);
 455         if (*p == '\n')
 456                 p++;
 457         if (p != buf + count)
 458                 goto einval;
 459
 460         return e;
 461
 462 out:
 463         return ERR_PTR(err);
 464
 465 efault:
 466         kfree(e);
 467         return ERR_PTR(-EFAULT);
 468 einval:
 469         kfree(e);
 470         return ERR_PTR(-EINVAL);
 471 }
 472
 473 /*
 474  * Set status of entry/binfmt_misc:
 475  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 476  */
 477 static int parse_command(const char __user *buffer, size_t count)
 478 {
 479         char s[4];
 480
 481         if (count > 3)
 482                 return -EINVAL;
 483         if (copy_from_user(s, buffer, count))
 484                 return -EFAULT;
 485         if (!count)
 486                 return 0;
 487         if (s[count - 1] == '\n')
 488                 count--;
 489         if (count == 1 && s[0] == '0')
 490                 return 1;
 491         if (count == 1 && s[0] == '1')
 492                 return 2;
 493         if (count == 2 && s[0] == '-' && s[1] == '1')
 494                 return 3;
 495         return -EINVAL;
 496 }
 497
 498 /* generic stuff */
 499
 500 static void entry_status(Node *e, char *page)
 501 {
 502         char *dp = page;
 503         const char *status = "disabled";
 504
 505         if (test_bit(Enabled, &e->flags))
 506                 status = "enabled";
 507
 508         if (!VERBOSE_STATUS) {
 509                 sprintf(page, "%s\n", status);
 510                 return;
 511         }
 512
 513         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 514
 515         /* print the special flags */
 516         dp += sprintf(dp, "flags: ");
 517         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 518                 *dp++ = 'P';
 519         if (e->flags & MISC_FMT_OPEN_BINARY)
 520                 *dp++ = 'O';
 521         if (e->flags & MISC_FMT_CREDENTIALS)
 522                 *dp++ = 'C';
 523         if (e->flags & MISC_FMT_OPEN_FILE)
 524                 *dp++ = 'F';
 525         *dp++ = '\n';
 526
 527         if (!test_bit(Magic, &e->flags)) {
 528                 sprintf(dp, "extension .%s\n", e->magic);
 529         } else {
 530                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 531                 dp = bin2hex(dp, e->magic, e->size);
 532                 if (e->mask) {
 533                         dp += sprintf(dp, "\nmask ");
 534                         dp = bin2hex(dp, e->mask, e->size);
 535                 }
 536                 *dp++ = '\n';
 537                 *dp = '\0';
 538         }
 539 }
 540
 541 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 542 {
 543         struct inode *inode = new_inode(sb);
 544
 545         if (inode) {
 546                 inode->i_ino = get_next_ino();
 547                 inode->i_mode = mode;
 548                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 549                         current_time(inode);
 550         }
 551         return inode;
 552 }
 553
 554 static void bm_evict_inode(struct inode *inode)
 555 {
 556         Node *e = inode->i_private;
 557
 558         if (e && e->flags & MISC_FMT_OPEN_FILE)
 559                 filp_close(e->interp_file, NULL);
 560
 561         clear_inode(inode);
 562         kfree(e);
 563 }
 564
 565 static void kill_node(Node *e)
 566 {
 567         struct dentry *dentry;
 568
 569         write_lock(&entries_lock);
 570         list_del_init(&e->list);
 571         write_unlock(&entries_lock);
 572
 573         dentry = e->dentry;
 574         drop_nlink(d_inode(dentry));
 575         d_drop(dentry);
 576         dput(dentry);
 577         simple_release_fs(&bm_mnt, &entry_count);
 578 }
 579
 580 /* /<entry> */
 581
 582 static ssize_t
 583 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 584 {
 585         Node *e = file_inode(file)->i_private;
 586         ssize_t res;
 587         char *page;
 588
 589         page = (char *) __get_free_page(GFP_KERNEL);
 590         if (!page)
 591                 return -ENOMEM;
 592
 593         entry_status(e, page);
 594
 595         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 596
 597         free_page((unsigned long) page);
 598         return res;
 599 }
 600
 601 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 602                                 size_t count, loff_t *ppos)
 603 {
 604         struct dentry *root;
 605         Node *e = file_inode(file)->i_private;
 606         int res = parse_command(buffer, count);
 607
 608         switch (res) {
 609         case 1:
 610                 /* Disable this handler. */
 611                 clear_bit(Enabled, &e->flags);
 612                 break;
 613         case 2:
 614                 /* Enable this handler. */
 615                 set_bit(Enabled, &e->flags);
 616                 break;
 617         case 3:
 618                 /* Delete this handler. */
 619                 root = file_inode(file)->i_sb->s_root;
 620                 inode_lock(d_inode(root));
 621
 622                 if (!list_empty(&e->list))
 623                         kill_node(e);
 624
 625                 inode_unlock(d_inode(root));
 626                 break;
 627         default:
 628                 return res;
 629         }
 630
 631         return count;
 632 }
 633
 634 static const struct file_operations bm_entry_operations = {
 635         .read           = bm_entry_read,
 636         .write          = bm_entry_write,
 637         .llseek         = default_llseek,
 638 };
 639
 640 /* /register */
 641
 642 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 643                                size_t count, loff_t *ppos)
 644 {
 645         Node *e;
 646         struct inode *inode;
 647         struct super_block *sb = file_inode(file)->i_sb;
 648         struct dentry *root = sb->s_root, *dentry;
 649         int err = 0;
 650         struct file *f = NULL;
 651
 652         e = create_entry(buffer, count);
 653
 654         if (IS_ERR(e))
 655                 return PTR_ERR(e);
 656
 657         if (e->flags & MISC_FMT_OPEN_FILE) {
 658                 f = open_exec(e->interpreter);
 659                 if (IS_ERR(f)) {
 660                         pr_notice("register: failed to install interpreter file %s\n",
 661                                  e->interpreter);
 662                         kfree(e);
 663                         return PTR_ERR(f);
 664                 }
 665                 e->interp_file = f;
 666         }
 667
 668         inode_lock(d_inode(root));
 669         dentry = lookup_one_len(e->name, root, strlen(e->name));
 670         err = PTR_ERR(dentry);
 671         if (IS_ERR(dentry))
 672                 goto out;
 673
 674         err = -EEXIST;
 675         if (d_really_is_positive(dentry))
 676                 goto out2;
 677
 678         inode = bm_get_inode(sb, S_IFREG | 0644);
 679
 680         err = -ENOMEM;
 681         if (!inode)
 682                 goto out2;
 683
 684         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 685         if (err) {
 686                 iput(inode);
 687                 inode = NULL;
 688                 goto out2;
 689         }
 690
 691         e->dentry = dget(dentry);
 692         inode->i_private = e;
 693         inode->i_fop = &bm_entry_operations;
 694
 695         d_instantiate(dentry, inode);
 696         write_lock(&entries_lock);
 697         list_add(&e->list, &entries);
 698         write_unlock(&entries_lock);
 699
 700         err = 0;
 701 out2:
 702         dput(dentry);
 703 out:
 704         inode_unlock(d_inode(root));
 705
 706         if (err) {
 707                 if (f)
 708                         filp_close(f, NULL);
 709                 kfree(e);
 710                 return err;
 711         }
 712         return count;
 713 }
 714
 715 static const struct file_operations bm_register_operations = {
 716         .write          = bm_register_write,
 717         .llseek         = noop_llseek,
 718 };
 719
 720 /* /status */
 721
 722 static ssize_t
 723 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 724 {
 725         char *s = enabled ? "enabled\n" : "disabled\n";
 726
 727         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 728 }
 729
 730 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 731                 size_t count, loff_t *ppos)
 732 {
 733         int res = parse_command(buffer, count);
 734         struct dentry *root;
 735
 736         switch (res) {
 737         case 1:
 738                 /* Disable all handlers. */
 739                 enabled = 0;
 740                 break;
 741         case 2:
 742                 /* Enable all handlers. */
 743                 enabled = 1;
 744                 break;
 745         case 3:
 746                 /* Delete all handlers. */
 747                 root = file_inode(file)->i_sb->s_root;
 748                 inode_lock(d_inode(root));
 749
 750                 while (!list_empty(&entries))
 751                         kill_node(list_first_entry(&entries, Node, list));
 752
 753                 inode_unlock(d_inode(root));
 754                 break;
 755         default:
 756                 return res;
 757         }
 758
 759         return count;
 760 }
 761
 762 static const struct file_operations bm_status_operations = {
 763         .read           = bm_status_read,
 764         .write          = bm_status_write,
 765         .llseek         = default_llseek,
 766 };
 767
 768 /* Superblock handling */
 769
 770 static const struct super_operations s_ops = {
 771         .statfs         = simple_statfs,
 772         .evict_inode    = bm_evict_inode,
 773 };
 774
 775 static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 776 {
 777         int err;
 778         static const struct tree_descr bm_files[] = {
 779                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 780                 [3] = {"register", &bm_register_operations, S_IWUSR},
 781                 /* last one */ {""}
 782         };
 783
 784         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 785         if (!err)
 786                 sb->s_op = &s_ops;
 787         return err;
 788 }
 789
 790 static int bm_get_tree(struct fs_context *fc)
 791 {
 792         return get_tree_single(fc, bm_fill_super);
 793 }
 794
 795 static const struct fs_context_operations bm_context_ops = {
 796         .get_tree       = bm_get_tree,
 797 };
 798
 799 static int bm_init_fs_context(struct fs_context *fc)
 800 {
 801         fc->ops = &bm_context_ops;
 802         return 0;
 803 }
 804
 805 static struct linux_binfmt misc_format = {
 806         .module = THIS_MODULE,
 807         .load_binary = load_misc_binary,
 808 };
 809
 810 static struct file_system_type bm_fs_type = {
 811         .owner          = THIS_MODULE,
 812         .name           = "binfmt_misc",
 813         .init_fs_context = bm_init_fs_context,
 814         .kill_sb        = kill_litter_super,
 815 };
 816 MODULE_ALIAS_FS("binfmt_misc");
 817
 818 static int __init init_misc_binfmt(void)
 819 {
 820         int err = register_filesystem(&bm_fs_type);
 821         if (!err)
 822                 insert_binfmt(&misc_format);
 823         return err;
 824 }
 825
 826 static void __exit exit_misc_binfmt(void)
 827 {
 828         unregister_binfmt(&misc_format);
 829         unregister_filesystem(&bm_fs_type);
 830 }
 831
 832 core_initcall(init_misc_binfmt);
 833 module_exit(exit_misc_binfmt);
 834 MODULE_LICENSE("GPL");