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         return s;
 258 }
 259
 260 static char *check_special_flags(char *sfs, Node *e)
 261 {
 262         char *p = sfs;
 263         int cont = 1;
 264
 265         /* special flags */
 266         while (cont) {
 267                 switch (*p) {
 268                 case 'P':
 269                         pr_debug("register: flag: P (preserve argv0)\n");
 270                         p++;
 271                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 272                         break;
 273                 case 'O':
 274                         pr_debug("register: flag: O (open binary)\n");
 275                         p++;
 276                         e->flags |= MISC_FMT_OPEN_BINARY;
 277                         break;
 278                 case 'C':
 279                         pr_debug("register: flag: C (preserve creds)\n");
 280                         p++;
 281                         /* this flags also implies the
 282                            open-binary flag */
 283                         e->flags |= (MISC_FMT_CREDENTIALS |
 284                                         MISC_FMT_OPEN_BINARY);
 285                         break;
 286                 default:
 287                         cont = 0;
 288                 }
 289         }
 290
 291         return p;
 292 }
 293
 294 /*
 295  * This registers a new binary format, it recognises the syntax
 296  * ':name:type:offset:magic:mask:interpreter:flags'
 297  * where the ':' is the IFS, that can be chosen with the first char
 298  */
 299 static Node *create_entry(const char __user *buffer, size_t count)
 300 {
 301         Node *e;
 302         int memsize, err;
 303         char *buf, *p;
 304         char del;
 305
 306         pr_debug("register: received %zu bytes\n", count);
 307
 308         /* some sanity checks */
 309         err = -EINVAL;
 310         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 311                 goto out;
 312
 313         err = -ENOMEM;
 314         memsize = sizeof(Node) + count + 8;
 315         e = kmalloc(memsize, GFP_KERNEL);
 316         if (!e)
 317                 goto out;
 318
 319         p = buf = (char *)e + sizeof(Node);
 320
 321         memset(e, 0, sizeof(Node));
 322         if (copy_from_user(buf, buffer, count))
 323                 goto efault;
 324
 325         del = *p++;     /* delimeter */
 326
 327         pr_debug("register: delim: %#x {%c}\n", del, del);
 328
 329         /* Pad the buffer with the delim to simplify parsing below. */
 330         memset(buf + count, del, 8);
 331
 332         /* Parse the 'name' field. */
 333         e->name = p;
 334         p = strchr(p, del);
 335         if (!p)
 336                 goto einval;
 337         *p++ = '\0';
 338         if (!e->name[0] ||
 339             !strcmp(e->name, ".") ||
 340             !strcmp(e->name, "..") ||
 341             strchr(e->name, '/'))
 342                 goto einval;
 343
 344         pr_debug("register: name: {%s}\n", e->name);
 345
 346         /* Parse the 'type' field. */
 347         switch (*p++) {
 348         case 'E':
 349                 pr_debug("register: type: E (extension)\n");
 350                 e->flags = 1 << Enabled;
 351                 break;
 352         case 'M':
 353                 pr_debug("register: type: M (magic)\n");
 354                 e->flags = (1 << Enabled) | (1 << Magic);
 355                 break;
 356         default:
 357                 goto einval;
 358         }
 359         if (*p++ != del)
 360                 goto einval;
 361
 362         if (test_bit(Magic, &e->flags)) {
 363                 /* Handle the 'M' (magic) format. */
 364                 char *s;
 365
 366                 /* Parse the 'offset' field. */
 367                 s = strchr(p, del);
 368                 if (!s)
 369                         goto einval;
 370                 *s++ = '\0';
 371                 e->offset = simple_strtoul(p, &p, 10);
 372                 if (*p++)
 373                         goto einval;
 374                 pr_debug("register: offset: %#x\n", e->offset);
 375
 376                 /* Parse the 'magic' field. */
 377                 e->magic = p;
 378                 p = scanarg(p, del);
 379                 if (!p)
 380                         goto einval;
 381                 p[-1] = '\0';
 382                 if (p == e->magic)
 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                 p[-1] = '\0';
 395                 if (p == e->mask) {
 396                         e->mask = NULL;
 397                         pr_debug("register:  mask[raw]: none\n");
 398                 } else if (USE_DEBUG)
 399                         print_hex_dump_bytes(
 400                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 401                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 402
 403                 /*
 404                  * Decode the magic & mask fields.
 405                  * Note: while we might have accepted embedded NUL bytes from
 406                  * above, the unescape helpers here will stop at the first one
 407                  * it encounters.
 408                  */
 409                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 410                 if (e->mask &&
 411                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 412                         goto einval;
 413                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 414                         goto einval;
 415                 pr_debug("register: magic/mask length: %i\n", e->size);
 416                 if (USE_DEBUG) {
 417                         print_hex_dump_bytes(
 418                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 419                                 DUMP_PREFIX_NONE, e->magic, e->size);
 420
 421                         if (e->mask) {
 422                                 int i;
 423                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 424
 425                                 print_hex_dump_bytes(
 426                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 427                                         DUMP_PREFIX_NONE, e->mask, e->size);
 428
 429                                 if (masked) {
 430                                         for (i = 0; i < e->size; ++i)
 431                                                 masked[i] = e->magic[i] & e->mask[i];
 432                                         print_hex_dump_bytes(
 433                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 434                                                 DUMP_PREFIX_NONE, masked, e->size);
 435
 436                                         kfree(masked);
 437                                 }
 438                         }
 439                 }
 440         } else {
 441                 /* Handle the 'E' (extension) format. */
 442
 443                 /* Skip the 'offset' field. */
 444                 p = strchr(p, del);
 445                 if (!p)
 446                         goto einval;
 447                 *p++ = '\0';
 448
 449                 /* Parse the 'magic' field. */
 450                 e->magic = p;
 451                 p = strchr(p, del);
 452                 if (!p)
 453                         goto einval;
 454                 *p++ = '\0';
 455                 if (!e->magic[0] || strchr(e->magic, '/'))
 456                         goto einval;
 457                 pr_debug("register: extension: {%s}\n", e->magic);
 458
 459                 /* Skip the 'mask' field. */
 460                 p = strchr(p, del);
 461                 if (!p)
 462                         goto einval;
 463                 *p++ = '\0';
 464         }
 465
 466         /* Parse the 'interpreter' field. */
 467         e->interpreter = p;
 468         p = strchr(p, del);
 469         if (!p)
 470                 goto einval;
 471         *p++ = '\0';
 472         if (!e->interpreter[0])
 473                 goto einval;
 474         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 475
 476         /* Parse the 'flags' field. */
 477         p = check_special_flags(p, e);
 478         if (*p == '\n')
 479                 p++;
 480         if (p != buf + count)
 481                 goto einval;
 482
 483         return e;
 484
 485 out:
 486         return ERR_PTR(err);
 487
 488 efault:
 489         kfree(e);
 490         return ERR_PTR(-EFAULT);
 491 einval:
 492         kfree(e);
 493         return ERR_PTR(-EINVAL);
 494 }
 495
 496 /*
 497  * Set status of entry/binfmt_misc:
 498  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 499  */
 500 static int parse_command(const char __user *buffer, size_t count)
 501 {
 502         char s[4];
 503
 504         if (count > 3)
 505                 return -EINVAL;
 506         if (copy_from_user(s, buffer, count))
 507                 return -EFAULT;
 508         if (!count)
 509                 return 0;
 510         if (s[count - 1] == '\n')
 511                 count--;
 512         if (count == 1 && s[0] == '0')
 513                 return 1;
 514         if (count == 1 && s[0] == '1')
 515                 return 2;
 516         if (count == 2 && s[0] == '-' && s[1] == '1')
 517                 return 3;
 518         return -EINVAL;
 519 }
 520
 521 /* generic stuff */
 522
 523 static void entry_status(Node *e, char *page)
 524 {
 525         char *dp;
 526         char *status = "disabled";
 527         const char *flags = "flags: ";
 528
 529         if (test_bit(Enabled, &e->flags))
 530                 status = "enabled";
 531
 532         if (!VERBOSE_STATUS) {
 533                 sprintf(page, "%s\n", status);
 534                 return;
 535         }
 536
 537         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 538         dp = page + strlen(page);
 539
 540         /* print the special flags */
 541         sprintf(dp, "%s", flags);
 542         dp += strlen(flags);
 543         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 544                 *dp++ = 'P';
 545         if (e->flags & MISC_FMT_OPEN_BINARY)
 546                 *dp++ = 'O';
 547         if (e->flags & MISC_FMT_CREDENTIALS)
 548                 *dp++ = 'C';
 549         *dp++ = '\n';
 550
 551         if (!test_bit(Magic, &e->flags)) {
 552                 sprintf(dp, "extension .%s\n", e->magic);
 553         } else {
 554                 int i;
 555
 556                 sprintf(dp, "offset %i\nmagic ", e->offset);
 557                 dp = page + strlen(page);
 558                 for (i = 0; i < e->size; i++) {
 559                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 560                         dp += 2;
 561                 }
 562                 if (e->mask) {
 563                         sprintf(dp, "\nmask ");
 564                         dp += 6;
 565                         for (i = 0; i < e->size; i++) {
 566                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 567                                 dp += 2;
 568                         }
 569                 }
 570                 *dp++ = '\n';
 571                 *dp = '\0';
 572         }
 573 }
 574
 575 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 576 {
 577         struct inode *inode = new_inode(sb);
 578
 579         if (inode) {
 580                 inode->i_ino = get_next_ino();
 581                 inode->i_mode = mode;
 582                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 583                         current_fs_time(inode->i_sb);
 584         }
 585         return inode;
 586 }
 587
 588 static void bm_evict_inode(struct inode *inode)
 589 {
 590         clear_inode(inode);
 591         kfree(inode->i_private);
 592 }
 593
 594 static void kill_node(Node *e)
 595 {
 596         struct dentry *dentry;
 597
 598         write_lock(&entries_lock);
 599         dentry = e->dentry;
 600         if (dentry) {
 601                 list_del_init(&e->list);
 602                 e->dentry = NULL;
 603         }
 604         write_unlock(&entries_lock);
 605
 606         if (dentry) {
 607                 drop_nlink(dentry->d_inode);
 608                 d_drop(dentry);
 609                 dput(dentry);
 610                 simple_release_fs(&bm_mnt, &entry_count);
 611         }
 612 }
 613
 614 /* /<entry> */
 615
 616 static ssize_t
 617 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 618 {
 619         Node *e = file_inode(file)->i_private;
 620         ssize_t res;
 621         char *page;
 622
 623         page = (char *) __get_free_page(GFP_KERNEL);
 624         if (!page)
 625                 return -ENOMEM;
 626
 627         entry_status(e, page);
 628
 629         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 630
 631         free_page((unsigned long) page);
 632         return res;
 633 }
 634
 635 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 636                                 size_t count, loff_t *ppos)
 637 {
 638         struct dentry *root;
 639         Node *e = file_inode(file)->i_private;
 640         int res = parse_command(buffer, count);
 641
 642         switch (res) {
 643         case 1:
 644                 /* Disable this handler. */
 645                 clear_bit(Enabled, &e->flags);
 646                 break;
 647         case 2:
 648                 /* Enable this handler. */
 649                 set_bit(Enabled, &e->flags);
 650                 break;
 651         case 3:
 652                 /* Delete this handler. */
 653                 root = dget(file->f_path.dentry->d_sb->s_root);
 654                 mutex_lock(&root->d_inode->i_mutex);
 655
 656                 kill_node(e);
 657
 658                 mutex_unlock(&root->d_inode->i_mutex);
 659                 dput(root);
 660                 break;
 661         default:
 662                 return res;
 663         }
 664
 665         return count;
 666 }
 667
 668 static const struct file_operations bm_entry_operations = {
 669         .read           = bm_entry_read,
 670         .write          = bm_entry_write,
 671         .llseek         = default_llseek,
 672 };
 673
 674 /* /register */
 675
 676 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 677                                size_t count, loff_t *ppos)
 678 {
 679         Node *e;
 680         struct inode *inode;
 681         struct dentry *root, *dentry;
 682         struct super_block *sb = file->f_path.dentry->d_sb;
 683         int err = 0;
 684
 685         e = create_entry(buffer, count);
 686
 687         if (IS_ERR(e))
 688                 return PTR_ERR(e);
 689
 690         root = dget(sb->s_root);
 691         mutex_lock(&root->d_inode->i_mutex);
 692         dentry = lookup_one_len(e->name, root, strlen(e->name));
 693         err = PTR_ERR(dentry);
 694         if (IS_ERR(dentry))
 695                 goto out;
 696
 697         err = -EEXIST;
 698         if (dentry->d_inode)
 699                 goto out2;
 700
 701         inode = bm_get_inode(sb, S_IFREG | 0644);
 702
 703         err = -ENOMEM;
 704         if (!inode)
 705                 goto out2;
 706
 707         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 708         if (err) {
 709                 iput(inode);
 710                 inode = NULL;
 711                 goto out2;
 712         }
 713
 714         e->dentry = dget(dentry);
 715         inode->i_private = e;
 716         inode->i_fop = &bm_entry_operations;
 717
 718         d_instantiate(dentry, inode);
 719         write_lock(&entries_lock);
 720         list_add(&e->list, &entries);
 721         write_unlock(&entries_lock);
 722
 723         err = 0;
 724 out2:
 725         dput(dentry);
 726 out:
 727         mutex_unlock(&root->d_inode->i_mutex);
 728         dput(root);
 729
 730         if (err) {
 731                 kfree(e);
 732                 return -EINVAL;
 733         }
 734         return count;
 735 }
 736
 737 static const struct file_operations bm_register_operations = {
 738         .write          = bm_register_write,
 739         .llseek         = noop_llseek,
 740 };
 741
 742 /* /status */
 743
 744 static ssize_t
 745 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 746 {
 747         char *s = enabled ? "enabled\n" : "disabled\n";
 748
 749         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 750 }
 751
 752 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 753                 size_t count, loff_t *ppos)
 754 {
 755         int res = parse_command(buffer, count);
 756         struct dentry *root;
 757
 758         switch (res) {
 759         case 1:
 760                 /* Disable all handlers. */
 761                 enabled = 0;
 762                 break;
 763         case 2:
 764                 /* Enable all handlers. */
 765                 enabled = 1;
 766                 break;
 767         case 3:
 768                 /* Delete all handlers. */
 769                 root = dget(file->f_path.dentry->d_sb->s_root);
 770                 mutex_lock(&root->d_inode->i_mutex);
 771
 772                 while (!list_empty(&entries))
 773                         kill_node(list_entry(entries.next, Node, list));
 774
 775                 mutex_unlock(&root->d_inode->i_mutex);
 776                 dput(root);
 777                 break;
 778         default:
 779                 return res;
 780         }
 781
 782         return count;
 783 }
 784
 785 static const struct file_operations bm_status_operations = {
 786         .read           = bm_status_read,
 787         .write          = bm_status_write,
 788         .llseek         = default_llseek,
 789 };
 790
 791 /* Superblock handling */
 792
 793 static const struct super_operations s_ops = {
 794         .statfs         = simple_statfs,
 795         .evict_inode    = bm_evict_inode,
 796 };
 797
 798 static int bm_fill_super(struct super_block *sb, void *data, int silent)
 799 {
 800         int err;
 801         static struct tree_descr bm_files[] = {
 802                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 803                 [3] = {"register", &bm_register_operations, S_IWUSR},
 804                 /* last one */ {""}
 805         };
 806
 807         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 808         if (!err)
 809                 sb->s_op = &s_ops;
 810         return err;
 811 }
 812
 813 static struct dentry *bm_mount(struct file_system_type *fs_type,
 814         int flags, const char *dev_name, void *data)
 815 {
 816         return mount_single(fs_type, flags, data, bm_fill_super);
 817 }
 818
 819 static struct linux_binfmt misc_format = {
 820         .module = THIS_MODULE,
 821         .load_binary = load_misc_binary,
 822 };
 823
 824 static struct file_system_type bm_fs_type = {
 825         .owner          = THIS_MODULE,
 826         .name           = "binfmt_misc",
 827         .mount          = bm_mount,
 828         .kill_sb        = kill_litter_super,
 829 };
 830 MODULE_ALIAS_FS("binfmt_misc");
 831
 832 static int __init init_misc_binfmt(void)
 833 {
 834         int err = register_filesystem(&bm_fs_type);
 835         if (!err)
 836                 insert_binfmt(&misc_format);
 837         return err;
 838 }
 839
 840 static void __exit exit_misc_binfmt(void)
 841 {
 842         unregister_binfmt(&misc_format);
 843         unregister_filesystem(&bm_fs_type);
 844 }
 845
 846 core_initcall(init_misc_binfmt);
 847 module_exit(exit_misc_binfmt);
 848 MODULE_LICENSE("GPL");