fs/binfmt_misc.c

   1 /*
   2  * binfmt_misc.c
   3  *
   4  * Copyright (C) 1997 Richard Günther
   5  *
   6  * binfmt_misc detects binaries via a magic or filename extension and invokes
   7  * a specified wrapper. See Documentation/binfmt_misc.txt for more details.
   8  */
   9
  10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/magic.h>
  16 #include <linux/binfmts.h>
  17 #include <linux/slab.h>
  18 #include <linux/ctype.h>
  19 #include <linux/string_helpers.h>
  20 #include <linux/file.h>
  21 #include <linux/pagemap.h>
  22 #include <linux/namei.h>
  23 #include <linux/mount.h>
  24 #include <linux/syscalls.h>
  25 #include <linux/fs.h>
  26 #include <linux/uaccess.h>
  27
  28 #ifdef DEBUG
  29 # define USE_DEBUG 1
  30 #else
  31 # define USE_DEBUG 0
  32 #endif
  33
  34 enum {
  35         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  36 };
  37
  38 static LIST_HEAD(entries);
  39 static int enabled = 1;
  40
  41 enum {Enabled, Magic};
  42 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  43 #define MISC_FMT_OPEN_BINARY (1 << 30)
  44 #define MISC_FMT_CREDENTIALS (1 << 29)
  45
  46 typedef struct {
  47         struct list_head list;
  48         unsigned long flags;            /* type, status, etc. */
  49         int offset;                     /* offset of magic */
  50         int size;                       /* size of magic/mask */
  51         char *magic;                    /* magic or filename extension */
  52         char *mask;                     /* mask, NULL for exact match */
  53         char *interpreter;              /* filename of interpreter */
  54         char *name;
  55         struct dentry *dentry;
  56 } Node;
  57
  58 static DEFINE_RWLOCK(entries_lock);
  59 static struct file_system_type bm_fs_type;
  60 static struct vfsmount *bm_mnt;
  61 static int entry_count;
  62
  63 /*
  64  * Max length of the register string.  Determined by:
  65  *  - 7 delimiters
  66  *  - name:   ~50 bytes
  67  *  - type:   1 byte
  68  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  69  *  - magic:  128 bytes (512 in escaped form)
  70  *  - mask:   128 bytes (512 in escaped form)
  71  *  - interp: ~50 bytes
  72  *  - flags:  5 bytes
  73  * Round that up a bit, and then back off to hold the internal data
  74  * (like struct Node).
  75  */
  76 #define MAX_REGISTER_LENGTH 1920
  77
  78 /*
  79  * Check if we support the binfmt
  80  * if we do, return the node, else NULL
  81  * locking is done in load_misc_binary
  82  */
  83 static Node *check_file(struct linux_binprm *bprm)
  84 {
  85         char *p = strrchr(bprm->interp, '.');
  86         struct list_head *l;
  87
  88         /* Walk all the registered handlers. */
  89         list_for_each(l, &entries) {
  90                 Node *e = list_entry(l, Node, list);
  91                 char *s;
  92                 int j;
  93
  94                 /* Make sure this one is currently enabled. */
  95                 if (!test_bit(Enabled, &e->flags))
  96                         continue;
  97
  98                 /* Do matching based on extension if applicable. */
  99                 if (!test_bit(Magic, &e->flags)) {
 100                         if (p && !strcmp(e->magic, p + 1))
 101                                 return e;
 102                         continue;
 103                 }
 104
 105                 /* Do matching based on magic & mask. */
 106                 s = bprm->buf + e->offset;
 107                 if (e->mask) {
 108                         for (j = 0; j < e->size; j++)
 109                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 110                                         break;
 111                 } else {
 112                         for (j = 0; j < e->size; j++)
 113                                 if ((*s++ ^ e->magic[j]))
 114                                         break;
 115                 }
 116                 if (j == e->size)
 117                         return e;
 118         }
 119         return NULL;
 120 }
 121
 122 /*
 123  * the loader itself
 124  */
 125 static int load_misc_binary(struct linux_binprm *bprm)
 126 {
 127         Node *fmt;
 128         struct file *interp_file = NULL;
 129         char iname[BINPRM_BUF_SIZE];
 130         const char *iname_addr = iname;
 131         int retval;
 132         int fd_binary = -1;
 133
 134         retval = -ENOEXEC;
 135         if (!enabled)
 136                 goto ret;
 137
 138         /* to keep locking time low, we copy the interpreter string */
 139         read_lock(&entries_lock);
 140         fmt = check_file(bprm);
 141         if (fmt)
 142                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 143         read_unlock(&entries_lock);
 144         if (!fmt)
 145                 goto ret;
 146
 147         /* Need to be able to load the file after exec */
 148         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 149                 return -ENOENT;
 150
 151         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 152                 retval = remove_arg_zero(bprm);
 153                 if (retval)
 154                         goto ret;
 155         }
 156
 157         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 158
 159                 /* if the binary should be opened on behalf of the
 160                  * interpreter than keep it open and assign descriptor
 161                  * to it
 162                  */
 163                 fd_binary = get_unused_fd_flags(0);
 164                 if (fd_binary < 0) {
 165                         retval = fd_binary;
 166                         goto ret;
 167                 }
 168                 fd_install(fd_binary, bprm->file);
 169
 170                 /* if the binary is not readable than enforce mm->dumpable=0
 171                    regardless of the interpreter's permissions */
 172                 would_dump(bprm, bprm->file);
 173
 174                 allow_write_access(bprm->file);
 175                 bprm->file = NULL;
 176
 177                 /* mark the bprm that fd should be passed to interp */
 178                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 179                 bprm->interp_data = fd_binary;
 180
 181         } else {
 182                 allow_write_access(bprm->file);
 183                 fput(bprm->file);
 184                 bprm->file = NULL;
 185         }
 186         /* make argv[1] be the path to the binary */
 187         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 188         if (retval < 0)
 189                 goto error;
 190         bprm->argc++;
 191
 192         /* add the interp as argv[0] */
 193         retval = copy_strings_kernel(1, &iname_addr, bprm);
 194         if (retval < 0)
 195                 goto error;
 196         bprm->argc++;
 197
 198         /* Update interp in case binfmt_script needs it. */
 199         retval = bprm_change_interp(iname, bprm);
 200         if (retval < 0)
 201                 goto error;
 202
 203         interp_file = open_exec(iname);
 204         retval = PTR_ERR(interp_file);
 205         if (IS_ERR(interp_file))
 206                 goto error;
 207
 208         bprm->file = interp_file;
 209         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 210                 /*
 211                  * No need to call prepare_binprm(), it's already been
 212                  * done.  bprm->buf is stale, update from interp_file.
 213                  */
 214                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 215                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 216         } else
 217                 retval = prepare_binprm(bprm);
 218
 219         if (retval < 0)
 220                 goto error;
 221
 222         retval = search_binary_handler(bprm);
 223         if (retval < 0)
 224                 goto error;
 225
 226 ret:
 227         return retval;
 228 error:
 229         if (fd_binary > 0)
 230                 sys_close(fd_binary);
 231         bprm->interp_flags = 0;
 232         bprm->interp_data = 0;
 233         goto ret;
 234 }
 235
 236 /* Command parsers */
 237
 238 /*
 239  * parses and copies one argument enclosed in del from *sp to *dp,
 240  * recognising the \x special.
 241  * returns pointer to the copied argument or NULL in case of an
 242  * error (and sets err) or null argument length.
 243  */
 244 static char *scanarg(char *s, char del)
 245 {
 246         char c;
 247
 248         while ((c = *s++) != del) {
 249                 if (c == '\\' && *s == 'x') {
 250                         s++;
 251                         if (!isxdigit(*s++))
 252                                 return NULL;
 253                         if (!isxdigit(*s++))
 254                                 return NULL;
 255                 }
 256         }
 257         s[-1] ='\0';
 258         return s;
 259 }
 260
 261 static char *check_special_flags(char *sfs, Node *e)
 262 {
 263         char *p = sfs;
 264         int cont = 1;
 265
 266         /* special flags */
 267         while (cont) {
 268                 switch (*p) {
 269                 case 'P':
 270                         pr_debug("register: flag: P (preserve argv0)\n");
 271                         p++;
 272                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 273                         break;
 274                 case 'O':
 275                         pr_debug("register: flag: O (open binary)\n");
 276                         p++;
 277                         e->flags |= MISC_FMT_OPEN_BINARY;
 278                         break;
 279                 case 'C':
 280                         pr_debug("register: flag: C (preserve creds)\n");
 281                         p++;
 282                         /* this flags also implies the
 283                            open-binary flag */
 284                         e->flags |= (MISC_FMT_CREDENTIALS |
 285                                         MISC_FMT_OPEN_BINARY);
 286                         break;
 287                 default:
 288                         cont = 0;
 289                 }
 290         }
 291
 292         return p;
 293 }
 294
 295 /*
 296  * This registers a new binary format, it recognises the syntax
 297  * ':name:type:offset:magic:mask:interpreter:flags'
 298  * where the ':' is the IFS, that can be chosen with the first char
 299  */
 300 static Node *create_entry(const char __user *buffer, size_t count)
 301 {
 302         Node *e;
 303         int memsize, err;
 304         char *buf, *p;
 305         char del;
 306
 307         pr_debug("register: received %zu bytes\n", count);
 308
 309         /* some sanity checks */
 310         err = -EINVAL;
 311         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 312                 goto out;
 313
 314         err = -ENOMEM;
 315         memsize = sizeof(Node) + count + 8;
 316         e = kmalloc(memsize, GFP_KERNEL);
 317         if (!e)
 318                 goto out;
 319
 320         p = buf = (char *)e + sizeof(Node);
 321
 322         memset(e, 0, sizeof(Node));
 323         if (copy_from_user(buf, buffer, count))
 324                 goto efault;
 325
 326         del = *p++;     /* delimeter */
 327
 328         pr_debug("register: delim: %#x {%c}\n", del, del);
 329
 330         /* Pad the buffer with the delim to simplify parsing below. */
 331         memset(buf + count, del, 8);
 332
 333         /* Parse the 'name' field. */
 334         e->name = p;
 335         p = strchr(p, del);
 336         if (!p)
 337                 goto einval;
 338         *p++ = '\0';
 339         if (!e->name[0] ||
 340             !strcmp(e->name, ".") ||
 341             !strcmp(e->name, "..") ||
 342             strchr(e->name, '/'))
 343                 goto einval;
 344
 345         pr_debug("register: name: {%s}\n", e->name);
 346
 347         /* Parse the 'type' field. */
 348         switch (*p++) {
 349         case 'E':
 350                 pr_debug("register: type: E (extension)\n");
 351                 e->flags = 1 << Enabled;
 352                 break;
 353         case 'M':
 354                 pr_debug("register: type: M (magic)\n");
 355                 e->flags = (1 << Enabled) | (1 << Magic);
 356                 break;
 357         default:
 358                 goto einval;
 359         }
 360         if (*p++ != del)
 361                 goto einval;
 362
 363         if (test_bit(Magic, &e->flags)) {
 364                 /* Handle the 'M' (magic) format. */
 365                 char *s;
 366
 367                 /* Parse the 'offset' field. */
 368                 s = strchr(p, del);
 369                 if (!s)
 370                         goto einval;
 371                 *s++ = '\0';
 372                 e->offset = simple_strtoul(p, &p, 10);
 373                 if (*p++)
 374                         goto einval;
 375                 pr_debug("register: offset: %#x\n", e->offset);
 376
 377                 /* Parse the 'magic' field. */
 378                 e->magic = p;
 379                 p = scanarg(p, del);
 380                 if (!p)
 381                         goto einval;
 382                 if (!e->magic[0])
 383                         goto einval;
 384                 if (USE_DEBUG)
 385                         print_hex_dump_bytes(
 386                                 KBUILD_MODNAME ": register: magic[raw]: ",
 387                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 388
 389                 /* Parse the 'mask' field. */
 390                 e->mask = p;
 391                 p = scanarg(p, del);
 392                 if (!p)
 393                         goto einval;
 394                 if (!e->mask[0]) {
 395                         e->mask = NULL;
 396                         pr_debug("register:  mask[raw]: none\n");
 397                 } else if (USE_DEBUG)
 398                         print_hex_dump_bytes(
 399                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 400                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 401
 402                 /*
 403                  * Decode the magic & mask fields.
 404                  * Note: while we might have accepted embedded NUL bytes from
 405                  * above, the unescape helpers here will stop at the first one
 406                  * it encounters.
 407                  */
 408                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 409                 if (e->mask &&
 410                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 411                         goto einval;
 412                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 413                         goto einval;
 414                 pr_debug("register: magic/mask length: %i\n", e->size);
 415                 if (USE_DEBUG) {
 416                         print_hex_dump_bytes(
 417                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 418                                 DUMP_PREFIX_NONE, e->magic, e->size);
 419
 420                         if (e->mask) {
 421                                 int i;
 422                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 423
 424                                 print_hex_dump_bytes(
 425                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 426                                         DUMP_PREFIX_NONE, e->mask, e->size);
 427
 428                                 if (masked) {
 429                                         for (i = 0; i < e->size; ++i)
 430                                                 masked[i] = e->magic[i] & e->mask[i];
 431                                         print_hex_dump_bytes(
 432                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 433                                                 DUMP_PREFIX_NONE, masked, e->size);
 434
 435                                         kfree(masked);
 436                                 }
 437                         }
 438                 }
 439         } else {
 440                 /* Handle the 'E' (extension) format. */
 441
 442                 /* Skip the 'offset' field. */
 443                 p = strchr(p, del);
 444                 if (!p)
 445                         goto einval;
 446                 *p++ = '\0';
 447
 448                 /* Parse the 'magic' field. */
 449                 e->magic = p;
 450                 p = strchr(p, del);
 451                 if (!p)
 452                         goto einval;
 453                 *p++ = '\0';
 454                 if (!e->magic[0] || strchr(e->magic, '/'))
 455                         goto einval;
 456                 pr_debug("register: extension: {%s}\n", e->magic);
 457
 458                 /* Skip the 'mask' field. */
 459                 p = strchr(p, del);
 460                 if (!p)
 461                         goto einval;
 462                 *p++ = '\0';
 463         }
 464
 465         /* Parse the 'interpreter' field. */
 466         e->interpreter = p;
 467         p = strchr(p, del);
 468         if (!p)
 469                 goto einval;
 470         *p++ = '\0';
 471         if (!e->interpreter[0])
 472                 goto einval;
 473         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 474
 475         /* Parse the 'flags' field. */
 476         p = check_special_flags(p, e);
 477         if (*p == '\n')
 478                 p++;
 479         if (p != buf + count)
 480                 goto einval;
 481
 482         return e;
 483
 484 out:
 485         return ERR_PTR(err);
 486
 487 efault:
 488         kfree(e);
 489         return ERR_PTR(-EFAULT);
 490 einval:
 491         kfree(e);
 492         return ERR_PTR(-EINVAL);
 493 }
 494
 495 /*
 496  * Set status of entry/binfmt_misc:
 497  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 498  */
 499 static int parse_command(const char __user *buffer, size_t count)
 500 {
 501         char s[4];
 502
 503         if (count > 3)
 504                 return -EINVAL;
 505         if (copy_from_user(s, buffer, count))
 506                 return -EFAULT;
 507         if (!count)
 508                 return 0;
 509         if (s[count - 1] == '\n')
 510                 count--;
 511         if (count == 1 && s[0] == '0')
 512                 return 1;
 513         if (count == 1 && s[0] == '1')
 514                 return 2;
 515         if (count == 2 && s[0] == '-' && s[1] == '1')
 516                 return 3;
 517         return -EINVAL;
 518 }
 519
 520 /* generic stuff */
 521
 522 static void entry_status(Node *e, char *page)
 523 {
 524         char *dp;
 525         char *status = "disabled";
 526         const char *flags = "flags: ";
 527
 528         if (test_bit(Enabled, &e->flags))
 529                 status = "enabled";
 530
 531         if (!VERBOSE_STATUS) {
 532                 sprintf(page, "%s\n", status);
 533                 return;
 534         }
 535
 536         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 537         dp = page + strlen(page);
 538
 539         /* print the special flags */
 540         sprintf(dp, "%s", flags);
 541         dp += strlen(flags);
 542         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 543                 *dp++ = 'P';
 544         if (e->flags & MISC_FMT_OPEN_BINARY)
 545                 *dp++ = 'O';
 546         if (e->flags & MISC_FMT_CREDENTIALS)
 547                 *dp++ = 'C';
 548         *dp++ = '\n';
 549
 550         if (!test_bit(Magic, &e->flags)) {
 551                 sprintf(dp, "extension .%s\n", e->magic);
 552         } else {
 553                 int i;
 554
 555                 sprintf(dp, "offset %i\nmagic ", e->offset);
 556                 dp = page + strlen(page);
 557                 for (i = 0; i < e->size; i++) {
 558                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 559                         dp += 2;
 560                 }
 561                 if (e->mask) {
 562                         sprintf(dp, "\nmask ");
 563                         dp += 6;
 564                         for (i = 0; i < e->size; i++) {
 565                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 566                                 dp += 2;
 567                         }
 568                 }
 569                 *dp++ = '\n';
 570                 *dp = '\0';
 571         }
 572 }
 573
 574 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 575 {
 576         struct inode *inode = new_inode(sb);
 577
 578         if (inode) {
 579                 inode->i_ino = get_next_ino();
 580                 inode->i_mode = mode;
 581                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 582                         current_fs_time(inode->i_sb);
 583         }
 584         return inode;
 585 }
 586
 587 static void bm_evict_inode(struct inode *inode)
 588 {
 589         clear_inode(inode);
 590         kfree(inode->i_private);
 591 }
 592
 593 static void kill_node(Node *e)
 594 {
 595         struct dentry *dentry;
 596
 597         write_lock(&entries_lock);
 598         dentry = e->dentry;
 599         if (dentry) {
 600                 list_del_init(&e->list);
 601                 e->dentry = NULL;
 602         }
 603         write_unlock(&entries_lock);
 604
 605         if (dentry) {
 606                 drop_nlink(d_inode(dentry));
 607                 d_drop(dentry);
 608                 dput(dentry);
 609                 simple_release_fs(&bm_mnt, &entry_count);
 610         }
 611 }
 612
 613 /* /<entry> */
 614
 615 static ssize_t
 616 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 617 {
 618         Node *e = file_inode(file)->i_private;
 619         ssize_t res;
 620         char *page;
 621
 622         page = (char *) __get_free_page(GFP_KERNEL);
 623         if (!page)
 624                 return -ENOMEM;
 625
 626         entry_status(e, page);
 627
 628         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 629
 630         free_page((unsigned long) page);
 631         return res;
 632 }
 633
 634 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 635                                 size_t count, loff_t *ppos)
 636 {
 637         struct dentry *root;
 638         Node *e = file_inode(file)->i_private;
 639         int res = parse_command(buffer, count);
 640
 641         switch (res) {
 642         case 1:
 643                 /* Disable this handler. */
 644                 clear_bit(Enabled, &e->flags);
 645                 break;
 646         case 2:
 647                 /* Enable this handler. */
 648                 set_bit(Enabled, &e->flags);
 649                 break;
 650         case 3:
 651                 /* Delete this handler. */
 652                 root = dget(file->f_path.dentry->d_sb->s_root);
 653                 mutex_lock(&d_inode(root)->i_mutex);
 654
 655                 kill_node(e);
 656
 657                 mutex_unlock(&d_inode(root)->i_mutex);
 658                 dput(root);
 659                 break;
 660         default:
 661                 return res;
 662         }
 663
 664         return count;
 665 }
 666
 667 static const struct file_operations bm_entry_operations = {
 668         .read           = bm_entry_read,
 669         .write          = bm_entry_write,
 670         .llseek         = default_llseek,
 671 };
 672
 673 /* /register */
 674
 675 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 676                                size_t count, loff_t *ppos)
 677 {
 678         Node *e;
 679         struct inode *inode;
 680         struct dentry *root, *dentry;
 681         struct super_block *sb = file->f_path.dentry->d_sb;
 682         int err = 0;
 683
 684         e = create_entry(buffer, count);
 685
 686         if (IS_ERR(e))
 687                 return PTR_ERR(e);
 688
 689         root = dget(sb->s_root);
 690         mutex_lock(&d_inode(root)->i_mutex);
 691         dentry = lookup_one_len(e->name, root, strlen(e->name));
 692         err = PTR_ERR(dentry);
 693         if (IS_ERR(dentry))
 694                 goto out;
 695
 696         err = -EEXIST;
 697         if (d_really_is_positive(dentry))
 698                 goto out2;
 699
 700         inode = bm_get_inode(sb, S_IFREG | 0644);
 701
 702         err = -ENOMEM;
 703         if (!inode)
 704                 goto out2;
 705
 706         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 707         if (err) {
 708                 iput(inode);
 709                 inode = NULL;
 710                 goto out2;
 711         }
 712
 713         e->dentry = dget(dentry);
 714         inode->i_private = e;
 715         inode->i_fop = &bm_entry_operations;
 716
 717         d_instantiate(dentry, inode);
 718         write_lock(&entries_lock);
 719         list_add(&e->list, &entries);
 720         write_unlock(&entries_lock);
 721
 722         err = 0;
 723 out2:
 724         dput(dentry);
 725 out:
 726         mutex_unlock(&d_inode(root)->i_mutex);
 727         dput(root);
 728
 729         if (err) {
 730                 kfree(e);
 731                 return -EINVAL;
 732         }
 733         return count;
 734 }
 735
 736 static const struct file_operations bm_register_operations = {
 737         .write          = bm_register_write,
 738         .llseek         = noop_llseek,
 739 };
 740
 741 /* /status */
 742
 743 static ssize_t
 744 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 745 {
 746         char *s = enabled ? "enabled\n" : "disabled\n";
 747
 748         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 749 }
 750
 751 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 752                 size_t count, loff_t *ppos)
 753 {
 754         int res = parse_command(buffer, count);
 755         struct dentry *root;
 756
 757         switch (res) {
 758         case 1:
 759                 /* Disable all handlers. */
 760                 enabled = 0;
 761                 break;
 762         case 2:
 763                 /* Enable all handlers. */
 764                 enabled = 1;
 765                 break;
 766         case 3:
 767                 /* Delete all handlers. */
 768                 root = dget(file->f_path.dentry->d_sb->s_root);
 769                 mutex_lock(&d_inode(root)->i_mutex);
 770
 771                 while (!list_empty(&entries))
 772                         kill_node(list_entry(entries.next, Node, list));
 773
 774                 mutex_unlock(&d_inode(root)->i_mutex);
 775                 dput(root);
 776                 break;
 777         default:
 778                 return res;
 779         }
 780
 781         return count;
 782 }
 783
 784 static const struct file_operations bm_status_operations = {
 785         .read           = bm_status_read,
 786         .write          = bm_status_write,
 787         .llseek         = default_llseek,
 788 };
 789
 790 /* Superblock handling */
 791
 792 static const struct super_operations s_ops = {
 793         .statfs         = simple_statfs,
 794         .evict_inode    = bm_evict_inode,
 795 };
 796
 797 static int bm_fill_super(struct super_block *sb, void *data, int silent)
 798 {
 799         int err;
 800         static struct tree_descr bm_files[] = {
 801                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 802                 [3] = {"register", &bm_register_operations, S_IWUSR},
 803                 /* last one */ {""}
 804         };
 805
 806         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 807         if (!err)
 808                 sb->s_op = &s_ops;
 809         return err;
 810 }
 811
 812 static struct dentry *bm_mount(struct file_system_type *fs_type,
 813         int flags, const char *dev_name, void *data)
 814 {
 815         return mount_single(fs_type, flags, data, bm_fill_super);
 816 }
 817
 818 static struct linux_binfmt misc_format = {
 819         .module = THIS_MODULE,
 820         .load_binary = load_misc_binary,
 821 };
 822
 823 static struct file_system_type bm_fs_type = {
 824         .owner          = THIS_MODULE,
 825         .name           = "binfmt_misc",
 826         .mount          = bm_mount,
 827         .kill_sb        = kill_litter_super,
 828 };
 829 MODULE_ALIAS_FS("binfmt_misc");
 830
 831 static int __init init_misc_binfmt(void)
 832 {
 833         int err = register_filesystem(&bm_fs_type);
 834         if (!err)
 835                 insert_binfmt(&misc_format);
 836         return err;
 837 }
 838
 839 static void __exit exit_misc_binfmt(void)
 840 {
 841         unregister_binfmt(&misc_format);
 842         unregister_filesystem(&bm_fs_type);
 843 }
 844
 845 core_initcall(init_misc_binfmt);
 846 module_exit(exit_misc_binfmt);
 847 MODULE_LICENSE("GPL");