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/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/init.h>
  15 #include <linux/sched/mm.h>
  16 #include <linux/magic.h>
  17 #include <linux/binfmts.h>
  18 #include <linux/slab.h>
  19 #include <linux/ctype.h>
  20 #include <linux/string_helpers.h>
  21 #include <linux/file.h>
  22 #include <linux/pagemap.h>
  23 #include <linux/namei.h>
  24 #include <linux/mount.h>
  25 #include <linux/syscalls.h>
  26 #include <linux/fs.h>
  27 #include <linux/uaccess.h>
  28
  29 #include "internal.h"
  30
  31 #ifdef DEBUG
  32 # define USE_DEBUG 1
  33 #else
  34 # define USE_DEBUG 0
  35 #endif
  36
  37 enum {
  38         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  39 };
  40
  41 static LIST_HEAD(entries);
  42 static int enabled = 1;
  43
  44 enum {Enabled, Magic};
  45 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  46 #define MISC_FMT_OPEN_BINARY (1 << 30)
  47 #define MISC_FMT_CREDENTIALS (1 << 29)
  48 #define MISC_FMT_OPEN_FILE (1 << 28)
  49
  50 typedef struct {
  51         struct list_head list;
  52         unsigned long flags;            /* type, status, etc. */
  53         int offset;                     /* offset of magic */
  54         int size;                       /* size of magic/mask */
  55         char *magic;                    /* magic or filename extension */
  56         char *mask;                     /* mask, NULL for exact match */
  57         char *interpreter;              /* filename of interpreter */
  58         char *name;
  59         struct dentry *dentry;
  60         struct file *interp_file;
  61 } Node;
  62
  63 static DEFINE_RWLOCK(entries_lock);
  64 static struct file_system_type bm_fs_type;
  65 static struct vfsmount *bm_mnt;
  66 static int entry_count;
  67
  68 /*
  69  * Max length of the register string.  Determined by:
  70  *  - 7 delimiters
  71  *  - name:   ~50 bytes
  72  *  - type:   1 byte
  73  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  74  *  - magic:  128 bytes (512 in escaped form)
  75  *  - mask:   128 bytes (512 in escaped form)
  76  *  - interp: ~50 bytes
  77  *  - flags:  5 bytes
  78  * Round that up a bit, and then back off to hold the internal data
  79  * (like struct Node).
  80  */
  81 #define MAX_REGISTER_LENGTH 1920
  82
  83 /*
  84  * Check if we support the binfmt
  85  * if we do, return the node, else NULL
  86  * locking is done in load_misc_binary
  87  */
  88 static Node *check_file(struct linux_binprm *bprm)
  89 {
  90         char *p = strrchr(bprm->interp, '.');
  91         struct list_head *l;
  92
  93         /* Walk all the registered handlers. */
  94         list_for_each(l, &entries) {
  95                 Node *e = list_entry(l, Node, list);
  96                 char *s;
  97                 int j;
  98
  99                 /* Make sure this one is currently enabled. */
 100                 if (!test_bit(Enabled, &e->flags))
 101                         continue;
 102
 103                 /* Do matching based on extension if applicable. */
 104                 if (!test_bit(Magic, &e->flags)) {
 105                         if (p && !strcmp(e->magic, p + 1))
 106                                 return e;
 107                         continue;
 108                 }
 109
 110                 /* Do matching based on magic & mask. */
 111                 s = bprm->buf + e->offset;
 112                 if (e->mask) {
 113                         for (j = 0; j < e->size; j++)
 114                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 115                                         break;
 116                 } else {
 117                         for (j = 0; j < e->size; j++)
 118                                 if ((*s++ ^ e->magic[j]))
 119                                         break;
 120                 }
 121                 if (j == e->size)
 122                         return e;
 123         }
 124         return NULL;
 125 }
 126
 127 /*
 128  * the loader itself
 129  */
 130 static int load_misc_binary(struct linux_binprm *bprm)
 131 {
 132         Node *fmt;
 133         struct file *interp_file = NULL;
 134         char iname[BINPRM_BUF_SIZE];
 135         const char *iname_addr = iname;
 136         int retval;
 137         int fd_binary = -1;
 138
 139         retval = -ENOEXEC;
 140         if (!enabled)
 141                 goto ret;
 142
 143         /* to keep locking time low, we copy the interpreter string */
 144         read_lock(&entries_lock);
 145         fmt = check_file(bprm);
 146         if (fmt)
 147                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 148         read_unlock(&entries_lock);
 149         if (!fmt)
 150                 goto ret;
 151
 152         /* Need to be able to load the file after exec */
 153         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 154                 return -ENOENT;
 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
 164                 /* if the binary should be opened on behalf of the
 165                  * interpreter than keep it open and assign descriptor
 166                  * to it
 167                  */
 168                 fd_binary = get_unused_fd_flags(0);
 169                 if (fd_binary < 0) {
 170                         retval = fd_binary;
 171                         goto ret;
 172                 }
 173                 fd_install(fd_binary, bprm->file);
 174
 175                 /* if the binary is not readable than enforce mm->dumpable=0
 176                    regardless of the interpreter's permissions */
 177                 would_dump(bprm, bprm->file);
 178
 179                 allow_write_access(bprm->file);
 180                 bprm->file = NULL;
 181
 182                 /* mark the bprm that fd should be passed to interp */
 183                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 184                 bprm->interp_data = fd_binary;
 185
 186         } else {
 187                 allow_write_access(bprm->file);
 188                 fput(bprm->file);
 189                 bprm->file = NULL;
 190         }
 191         /* make argv[1] be the path to the binary */
 192         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 193         if (retval < 0)
 194                 goto error;
 195         bprm->argc++;
 196
 197         /* add the interp as argv[0] */
 198         retval = copy_strings_kernel(1, &iname_addr, bprm);
 199         if (retval < 0)
 200                 goto error;
 201         bprm->argc++;
 202
 203         /* Update interp in case binfmt_script needs it. */
 204         retval = bprm_change_interp(iname, bprm);
 205         if (retval < 0)
 206                 goto error;
 207
 208         if (fmt->flags & MISC_FMT_OPEN_FILE && fmt->interp_file) {
 209                 interp_file = filp_clone_open(fmt->interp_file);
 210                 if (!IS_ERR(interp_file))
 211                         deny_write_access(interp_file);
 212         } else {
 213                 interp_file = open_exec(iname);
 214         }
 215         retval = PTR_ERR(interp_file);
 216         if (IS_ERR(interp_file))
 217                 goto error;
 218
 219         bprm->file = interp_file;
 220         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 221                 /*
 222                  * No need to call prepare_binprm(), it's already been
 223                  * done.  bprm->buf is stale, update from interp_file.
 224                  */
 225                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 226                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 227         } else
 228                 retval = prepare_binprm(bprm);
 229
 230         if (retval < 0)
 231                 goto error;
 232
 233         retval = search_binary_handler(bprm);
 234         if (retval < 0)
 235                 goto error;
 236
 237 ret:
 238         return retval;
 239 error:
 240         if (fd_binary > 0)
 241                 sys_close(fd_binary);
 242         bprm->interp_flags = 0;
 243         bprm->interp_data = 0;
 244         goto ret;
 245 }
 246
 247 /* Command parsers */
 248
 249 /*
 250  * parses and copies one argument enclosed in del from *sp to *dp,
 251  * recognising the \x special.
 252  * returns pointer to the copied argument or NULL in case of an
 253  * error (and sets err) or null argument length.
 254  */
 255 static char *scanarg(char *s, char del)
 256 {
 257         char c;
 258
 259         while ((c = *s++) != del) {
 260                 if (c == '\\' && *s == 'x') {
 261                         s++;
 262                         if (!isxdigit(*s++))
 263                                 return NULL;
 264                         if (!isxdigit(*s++))
 265                                 return NULL;
 266                 }
 267         }
 268         s[-1] ='\0';
 269         return s;
 270 }
 271
 272 static char *check_special_flags(char *sfs, Node *e)
 273 {
 274         char *p = sfs;
 275         int cont = 1;
 276
 277         /* special flags */
 278         while (cont) {
 279                 switch (*p) {
 280                 case 'P':
 281                         pr_debug("register: flag: P (preserve argv0)\n");
 282                         p++;
 283                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 284                         break;
 285                 case 'O':
 286                         pr_debug("register: flag: O (open binary)\n");
 287                         p++;
 288                         e->flags |= MISC_FMT_OPEN_BINARY;
 289                         break;
 290                 case 'C':
 291                         pr_debug("register: flag: C (preserve creds)\n");
 292                         p++;
 293                         /* this flags also implies the
 294                            open-binary flag */
 295                         e->flags |= (MISC_FMT_CREDENTIALS |
 296                                         MISC_FMT_OPEN_BINARY);
 297                         break;
 298                 case 'F':
 299                         pr_debug("register: flag: F: open interpreter file now\n");
 300                         p++;
 301                         e->flags |= MISC_FMT_OPEN_FILE;
 302                         break;
 303                 default:
 304                         cont = 0;
 305                 }
 306         }
 307
 308         return p;
 309 }
 310
 311 /*
 312  * This registers a new binary format, it recognises the syntax
 313  * ':name:type:offset:magic:mask:interpreter:flags'
 314  * where the ':' is the IFS, that can be chosen with the first char
 315  */
 316 static Node *create_entry(const char __user *buffer, size_t count)
 317 {
 318         Node *e;
 319         int memsize, err;
 320         char *buf, *p;
 321         char del;
 322
 323         pr_debug("register: received %zu bytes\n", count);
 324
 325         /* some sanity checks */
 326         err = -EINVAL;
 327         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 328                 goto out;
 329
 330         err = -ENOMEM;
 331         memsize = sizeof(Node) + count + 8;
 332         e = kmalloc(memsize, GFP_KERNEL);
 333         if (!e)
 334                 goto out;
 335
 336         p = buf = (char *)e + sizeof(Node);
 337
 338         memset(e, 0, sizeof(Node));
 339         if (copy_from_user(buf, buffer, count))
 340                 goto efault;
 341
 342         del = *p++;     /* delimeter */
 343
 344         pr_debug("register: delim: %#x {%c}\n", del, del);
 345
 346         /* Pad the buffer with the delim to simplify parsing below. */
 347         memset(buf + count, del, 8);
 348
 349         /* Parse the 'name' field. */
 350         e->name = p;
 351         p = strchr(p, del);
 352         if (!p)
 353                 goto einval;
 354         *p++ = '\0';
 355         if (!e->name[0] ||
 356             !strcmp(e->name, ".") ||
 357             !strcmp(e->name, "..") ||
 358             strchr(e->name, '/'))
 359                 goto einval;
 360
 361         pr_debug("register: name: {%s}\n", e->name);
 362
 363         /* Parse the 'type' field. */
 364         switch (*p++) {
 365         case 'E':
 366                 pr_debug("register: type: E (extension)\n");
 367                 e->flags = 1 << Enabled;
 368                 break;
 369         case 'M':
 370                 pr_debug("register: type: M (magic)\n");
 371                 e->flags = (1 << Enabled) | (1 << Magic);
 372                 break;
 373         default:
 374                 goto einval;
 375         }
 376         if (*p++ != del)
 377                 goto einval;
 378
 379         if (test_bit(Magic, &e->flags)) {
 380                 /* Handle the 'M' (magic) format. */
 381                 char *s;
 382
 383                 /* Parse the 'offset' field. */
 384                 s = strchr(p, del);
 385                 if (!s)
 386                         goto einval;
 387                 *s++ = '\0';
 388                 e->offset = simple_strtoul(p, &p, 10);
 389                 if (*p++)
 390                         goto einval;
 391                 pr_debug("register: offset: %#x\n", e->offset);
 392
 393                 /* Parse the 'magic' field. */
 394                 e->magic = p;
 395                 p = scanarg(p, del);
 396                 if (!p)
 397                         goto einval;
 398                 if (!e->magic[0])
 399                         goto einval;
 400                 if (USE_DEBUG)
 401                         print_hex_dump_bytes(
 402                                 KBUILD_MODNAME ": register: magic[raw]: ",
 403                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 404
 405                 /* Parse the 'mask' field. */
 406                 e->mask = p;
 407                 p = scanarg(p, del);
 408                 if (!p)
 409                         goto einval;
 410                 if (!e->mask[0]) {
 411                         e->mask = NULL;
 412                         pr_debug("register:  mask[raw]: none\n");
 413                 } else if (USE_DEBUG)
 414                         print_hex_dump_bytes(
 415                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 416                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 417
 418                 /*
 419                  * Decode the magic & mask fields.
 420                  * Note: while we might have accepted embedded NUL bytes from
 421                  * above, the unescape helpers here will stop at the first one
 422                  * it encounters.
 423                  */
 424                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 425                 if (e->mask &&
 426                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 427                         goto einval;
 428                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 429                         goto einval;
 430                 pr_debug("register: magic/mask length: %i\n", e->size);
 431                 if (USE_DEBUG) {
 432                         print_hex_dump_bytes(
 433                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 434                                 DUMP_PREFIX_NONE, e->magic, e->size);
 435
 436                         if (e->mask) {
 437                                 int i;
 438                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 439
 440                                 print_hex_dump_bytes(
 441                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 442                                         DUMP_PREFIX_NONE, e->mask, e->size);
 443
 444                                 if (masked) {
 445                                         for (i = 0; i < e->size; ++i)
 446                                                 masked[i] = e->magic[i] & e->mask[i];
 447                                         print_hex_dump_bytes(
 448                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 449                                                 DUMP_PREFIX_NONE, masked, e->size);
 450
 451                                         kfree(masked);
 452                                 }
 453                         }
 454                 }
 455         } else {
 456                 /* Handle the 'E' (extension) format. */
 457
 458                 /* Skip the 'offset' field. */
 459                 p = strchr(p, del);
 460                 if (!p)
 461                         goto einval;
 462                 *p++ = '\0';
 463
 464                 /* Parse the 'magic' field. */
 465                 e->magic = p;
 466                 p = strchr(p, del);
 467                 if (!p)
 468                         goto einval;
 469                 *p++ = '\0';
 470                 if (!e->magic[0] || strchr(e->magic, '/'))
 471                         goto einval;
 472                 pr_debug("register: extension: {%s}\n", e->magic);
 473
 474                 /* Skip the 'mask' field. */
 475                 p = strchr(p, del);
 476                 if (!p)
 477                         goto einval;
 478                 *p++ = '\0';
 479         }
 480
 481         /* Parse the 'interpreter' field. */
 482         e->interpreter = p;
 483         p = strchr(p, del);
 484         if (!p)
 485                 goto einval;
 486         *p++ = '\0';
 487         if (!e->interpreter[0])
 488                 goto einval;
 489         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 490
 491         /* Parse the 'flags' field. */
 492         p = check_special_flags(p, e);
 493         if (*p == '\n')
 494                 p++;
 495         if (p != buf + count)
 496                 goto einval;
 497
 498         return e;
 499
 500 out:
 501         return ERR_PTR(err);
 502
 503 efault:
 504         kfree(e);
 505         return ERR_PTR(-EFAULT);
 506 einval:
 507         kfree(e);
 508         return ERR_PTR(-EINVAL);
 509 }
 510
 511 /*
 512  * Set status of entry/binfmt_misc:
 513  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 514  */
 515 static int parse_command(const char __user *buffer, size_t count)
 516 {
 517         char s[4];
 518
 519         if (count > 3)
 520                 return -EINVAL;
 521         if (copy_from_user(s, buffer, count))
 522                 return -EFAULT;
 523         if (!count)
 524                 return 0;
 525         if (s[count - 1] == '\n')
 526                 count--;
 527         if (count == 1 && s[0] == '0')
 528                 return 1;
 529         if (count == 1 && s[0] == '1')
 530                 return 2;
 531         if (count == 2 && s[0] == '-' && s[1] == '1')
 532                 return 3;
 533         return -EINVAL;
 534 }
 535
 536 /* generic stuff */
 537
 538 static void entry_status(Node *e, char *page)
 539 {
 540         char *dp = page;
 541         const char *status = "disabled";
 542
 543         if (test_bit(Enabled, &e->flags))
 544                 status = "enabled";
 545
 546         if (!VERBOSE_STATUS) {
 547                 sprintf(page, "%s\n", status);
 548                 return;
 549         }
 550
 551         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 552
 553         /* print the special flags */
 554         dp += sprintf(dp, "flags: ");
 555         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 556                 *dp++ = 'P';
 557         if (e->flags & MISC_FMT_OPEN_BINARY)
 558                 *dp++ = 'O';
 559         if (e->flags & MISC_FMT_CREDENTIALS)
 560                 *dp++ = 'C';
 561         if (e->flags & MISC_FMT_OPEN_FILE)
 562                 *dp++ = 'F';
 563         *dp++ = '\n';
 564
 565         if (!test_bit(Magic, &e->flags)) {
 566                 sprintf(dp, "extension .%s\n", e->magic);
 567         } else {
 568                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 569                 dp = bin2hex(dp, e->magic, e->size);
 570                 if (e->mask) {
 571                         dp += sprintf(dp, "\nmask ");
 572                         dp = bin2hex(dp, e->mask, e->size);
 573                 }
 574                 *dp++ = '\n';
 575                 *dp = '\0';
 576         }
 577 }
 578
 579 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 580 {
 581         struct inode *inode = new_inode(sb);
 582
 583         if (inode) {
 584                 inode->i_ino = get_next_ino();
 585                 inode->i_mode = mode;
 586                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 587                         current_time(inode);
 588         }
 589         return inode;
 590 }
 591
 592 static void bm_evict_inode(struct inode *inode)
 593 {
 594         clear_inode(inode);
 595         kfree(inode->i_private);
 596 }
 597
 598 static void kill_node(Node *e)
 599 {
 600         struct dentry *dentry;
 601
 602         write_lock(&entries_lock);
 603         dentry = e->dentry;
 604         if (dentry) {
 605                 list_del_init(&e->list);
 606                 e->dentry = NULL;
 607         }
 608         write_unlock(&entries_lock);
 609
 610         if ((e->flags & MISC_FMT_OPEN_FILE) && e->interp_file) {
 611                 filp_close(e->interp_file, NULL);
 612                 e->interp_file = NULL;
 613         }
 614
 615         if (dentry) {
 616                 drop_nlink(d_inode(dentry));
 617                 d_drop(dentry);
 618                 dput(dentry);
 619                 simple_release_fs(&bm_mnt, &entry_count);
 620         }
 621 }
 622
 623 /* /<entry> */
 624
 625 static ssize_t
 626 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 627 {
 628         Node *e = file_inode(file)->i_private;
 629         ssize_t res;
 630         char *page;
 631
 632         page = (char *) __get_free_page(GFP_KERNEL);
 633         if (!page)
 634                 return -ENOMEM;
 635
 636         entry_status(e, page);
 637
 638         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 639
 640         free_page((unsigned long) page);
 641         return res;
 642 }
 643
 644 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 645                                 size_t count, loff_t *ppos)
 646 {
 647         struct dentry *root;
 648         Node *e = file_inode(file)->i_private;
 649         int res = parse_command(buffer, count);
 650
 651         switch (res) {
 652         case 1:
 653                 /* Disable this handler. */
 654                 clear_bit(Enabled, &e->flags);
 655                 break;
 656         case 2:
 657                 /* Enable this handler. */
 658                 set_bit(Enabled, &e->flags);
 659                 break;
 660         case 3:
 661                 /* Delete this handler. */
 662                 root = file_inode(file)->i_sb->s_root;
 663                 inode_lock(d_inode(root));
 664
 665                 kill_node(e);
 666
 667                 inode_unlock(d_inode(root));
 668                 break;
 669         default:
 670                 return res;
 671         }
 672
 673         return count;
 674 }
 675
 676 static const struct file_operations bm_entry_operations = {
 677         .read           = bm_entry_read,
 678         .write          = bm_entry_write,
 679         .llseek         = default_llseek,
 680 };
 681
 682 /* /register */
 683
 684 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 685                                size_t count, loff_t *ppos)
 686 {
 687         Node *e;
 688         struct inode *inode;
 689         struct super_block *sb = file_inode(file)->i_sb;
 690         struct dentry *root = sb->s_root, *dentry;
 691         int err = 0;
 692
 693         e = create_entry(buffer, count);
 694
 695         if (IS_ERR(e))
 696                 return PTR_ERR(e);
 697
 698         inode_lock(d_inode(root));
 699         dentry = lookup_one_len(e->name, root, strlen(e->name));
 700         err = PTR_ERR(dentry);
 701         if (IS_ERR(dentry))
 702                 goto out;
 703
 704         err = -EEXIST;
 705         if (d_really_is_positive(dentry))
 706                 goto out2;
 707
 708         inode = bm_get_inode(sb, S_IFREG | 0644);
 709
 710         err = -ENOMEM;
 711         if (!inode)
 712                 goto out2;
 713
 714         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 715         if (err) {
 716                 iput(inode);
 717                 inode = NULL;
 718                 goto out2;
 719         }
 720
 721         if (e->flags & MISC_FMT_OPEN_FILE) {
 722                 struct file *f;
 723
 724                 f = open_exec(e->interpreter);
 725                 if (IS_ERR(f)) {
 726                         err = PTR_ERR(f);
 727                         pr_notice("register: failed to install interpreter file %s\n", e->interpreter);
 728                         simple_release_fs(&bm_mnt, &entry_count);
 729                         iput(inode);
 730                         inode = NULL;
 731                         goto out2;
 732                 }
 733                 e->interp_file = f;
 734         }
 735
 736         e->dentry = dget(dentry);
 737         inode->i_private = e;
 738         inode->i_fop = &bm_entry_operations;
 739
 740         d_instantiate(dentry, inode);
 741         write_lock(&entries_lock);
 742         list_add(&e->list, &entries);
 743         write_unlock(&entries_lock);
 744
 745         err = 0;
 746 out2:
 747         dput(dentry);
 748 out:
 749         inode_unlock(d_inode(root));
 750
 751         if (err) {
 752                 kfree(e);
 753                 return err;
 754         }
 755         return count;
 756 }
 757
 758 static const struct file_operations bm_register_operations = {
 759         .write          = bm_register_write,
 760         .llseek         = noop_llseek,
 761 };
 762
 763 /* /status */
 764
 765 static ssize_t
 766 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 767 {
 768         char *s = enabled ? "enabled\n" : "disabled\n";
 769
 770         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 771 }
 772
 773 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 774                 size_t count, loff_t *ppos)
 775 {
 776         int res = parse_command(buffer, count);
 777         struct dentry *root;
 778
 779         switch (res) {
 780         case 1:
 781                 /* Disable all handlers. */
 782                 enabled = 0;
 783                 break;
 784         case 2:
 785                 /* Enable all handlers. */
 786                 enabled = 1;
 787                 break;
 788         case 3:
 789                 /* Delete all handlers. */
 790                 root = file_inode(file)->i_sb->s_root;
 791                 inode_lock(d_inode(root));
 792
 793                 while (!list_empty(&entries))
 794                         kill_node(list_entry(entries.next, Node, list));
 795
 796                 inode_unlock(d_inode(root));
 797                 break;
 798         default:
 799                 return res;
 800         }
 801
 802         return count;
 803 }
 804
 805 static const struct file_operations bm_status_operations = {
 806         .read           = bm_status_read,
 807         .write          = bm_status_write,
 808         .llseek         = default_llseek,
 809 };
 810
 811 /* Superblock handling */
 812
 813 static const struct super_operations s_ops = {
 814         .statfs         = simple_statfs,
 815         .evict_inode    = bm_evict_inode,
 816 };
 817
 818 static int bm_fill_super(struct super_block *sb, void *data, int silent)
 819 {
 820         int err;
 821         static const struct tree_descr bm_files[] = {
 822                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 823                 [3] = {"register", &bm_register_operations, S_IWUSR},
 824                 /* last one */ {""}
 825         };
 826
 827         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 828         if (!err)
 829                 sb->s_op = &s_ops;
 830         return err;
 831 }
 832
 833 static struct dentry *bm_mount(struct file_system_type *fs_type,
 834         int flags, const char *dev_name, void *data)
 835 {
 836         return mount_single(fs_type, flags, data, bm_fill_super);
 837 }
 838
 839 static struct linux_binfmt misc_format = {
 840         .module = THIS_MODULE,
 841         .load_binary = load_misc_binary,
 842 };
 843
 844 static struct file_system_type bm_fs_type = {
 845         .owner          = THIS_MODULE,
 846         .name           = "binfmt_misc",
 847         .mount          = bm_mount,
 848         .kill_sb        = kill_litter_super,
 849 };
 850 MODULE_ALIAS_FS("binfmt_misc");
 851
 852 static int __init init_misc_binfmt(void)
 853 {
 854         int err = register_filesystem(&bm_fs_type);
 855         if (!err)
 856                 insert_binfmt(&misc_format);
 857         return err;
 858 }
 859
 860 static void __exit exit_misc_binfmt(void)
 861 {
 862         unregister_binfmt(&misc_format);
 863         unregister_filesystem(&bm_fs_type);
 864 }
 865
 866 core_initcall(init_misc_binfmt);
 867 module_exit(exit_misc_binfmt);
 868 MODULE_LICENSE("GPL");