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.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                 if (p != s) {
 389                         int r = kstrtoint(p, 10, &e->offset);
 390                         if (r != 0 || e->offset < 0)
 391                                 goto einval;
 392                 }
 393                 p = s;
 394                 if (*p++)
 395                         goto einval;
 396                 pr_debug("register: offset: %#x\n", e->offset);
 397
 398                 /* Parse the 'magic' field. */
 399                 e->magic = p;
 400                 p = scanarg(p, del);
 401                 if (!p)
 402                         goto einval;
 403                 if (!e->magic[0])
 404                         goto einval;
 405                 if (USE_DEBUG)
 406                         print_hex_dump_bytes(
 407                                 KBUILD_MODNAME ": register: magic[raw]: ",
 408                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 409
 410                 /* Parse the 'mask' field. */
 411                 e->mask = p;
 412                 p = scanarg(p, del);
 413                 if (!p)
 414                         goto einval;
 415                 if (!e->mask[0]) {
 416                         e->mask = NULL;
 417                         pr_debug("register:  mask[raw]: none\n");
 418                 } else if (USE_DEBUG)
 419                         print_hex_dump_bytes(
 420                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 421                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 422
 423                 /*
 424                  * Decode the magic & mask fields.
 425                  * Note: while we might have accepted embedded NUL bytes from
 426                  * above, the unescape helpers here will stop at the first one
 427                  * it encounters.
 428                  */
 429                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 430                 if (e->mask &&
 431                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 432                         goto einval;
 433                 if (e->size > BINPRM_BUF_SIZE ||
 434                     BINPRM_BUF_SIZE - e->size < e->offset)
 435                         goto einval;
 436                 pr_debug("register: magic/mask length: %i\n", e->size);
 437                 if (USE_DEBUG) {
 438                         print_hex_dump_bytes(
 439                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 440                                 DUMP_PREFIX_NONE, e->magic, e->size);
 441
 442                         if (e->mask) {
 443                                 int i;
 444                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 445
 446                                 print_hex_dump_bytes(
 447                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 448                                         DUMP_PREFIX_NONE, e->mask, e->size);
 449
 450                                 if (masked) {
 451                                         for (i = 0; i < e->size; ++i)
 452                                                 masked[i] = e->magic[i] & e->mask[i];
 453                                         print_hex_dump_bytes(
 454                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 455                                                 DUMP_PREFIX_NONE, masked, e->size);
 456
 457                                         kfree(masked);
 458                                 }
 459                         }
 460                 }
 461         } else {
 462                 /* Handle the 'E' (extension) format. */
 463
 464                 /* Skip the 'offset' field. */
 465                 p = strchr(p, del);
 466                 if (!p)
 467                         goto einval;
 468                 *p++ = '\0';
 469
 470                 /* Parse the 'magic' field. */
 471                 e->magic = p;
 472                 p = strchr(p, del);
 473                 if (!p)
 474                         goto einval;
 475                 *p++ = '\0';
 476                 if (!e->magic[0] || strchr(e->magic, '/'))
 477                         goto einval;
 478                 pr_debug("register: extension: {%s}\n", e->magic);
 479
 480                 /* Skip the 'mask' field. */
 481                 p = strchr(p, del);
 482                 if (!p)
 483                         goto einval;
 484                 *p++ = '\0';
 485         }
 486
 487         /* Parse the 'interpreter' field. */
 488         e->interpreter = p;
 489         p = strchr(p, del);
 490         if (!p)
 491                 goto einval;
 492         *p++ = '\0';
 493         if (!e->interpreter[0])
 494                 goto einval;
 495         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 496
 497         /* Parse the 'flags' field. */
 498         p = check_special_flags(p, e);
 499         if (*p == '\n')
 500                 p++;
 501         if (p != buf + count)
 502                 goto einval;
 503
 504         return e;
 505
 506 out:
 507         return ERR_PTR(err);
 508
 509 efault:
 510         kfree(e);
 511         return ERR_PTR(-EFAULT);
 512 einval:
 513         kfree(e);
 514         return ERR_PTR(-EINVAL);
 515 }
 516
 517 /*
 518  * Set status of entry/binfmt_misc:
 519  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 520  */
 521 static int parse_command(const char __user *buffer, size_t count)
 522 {
 523         char s[4];
 524
 525         if (count > 3)
 526                 return -EINVAL;
 527         if (copy_from_user(s, buffer, count))
 528                 return -EFAULT;
 529         if (!count)
 530                 return 0;
 531         if (s[count - 1] == '\n')
 532                 count--;
 533         if (count == 1 && s[0] == '0')
 534                 return 1;
 535         if (count == 1 && s[0] == '1')
 536                 return 2;
 537         if (count == 2 && s[0] == '-' && s[1] == '1')
 538                 return 3;
 539         return -EINVAL;
 540 }
 541
 542 /* generic stuff */
 543
 544 static void entry_status(Node *e, char *page)
 545 {
 546         char *dp = page;
 547         const char *status = "disabled";
 548
 549         if (test_bit(Enabled, &e->flags))
 550                 status = "enabled";
 551
 552         if (!VERBOSE_STATUS) {
 553                 sprintf(page, "%s\n", status);
 554                 return;
 555         }
 556
 557         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 558
 559         /* print the special flags */
 560         dp += sprintf(dp, "flags: ");
 561         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 562                 *dp++ = 'P';
 563         if (e->flags & MISC_FMT_OPEN_BINARY)
 564                 *dp++ = 'O';
 565         if (e->flags & MISC_FMT_CREDENTIALS)
 566                 *dp++ = 'C';
 567         if (e->flags & MISC_FMT_OPEN_FILE)
 568                 *dp++ = 'F';
 569         *dp++ = '\n';
 570
 571         if (!test_bit(Magic, &e->flags)) {
 572                 sprintf(dp, "extension .%s\n", e->magic);
 573         } else {
 574                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 575                 dp = bin2hex(dp, e->magic, e->size);
 576                 if (e->mask) {
 577                         dp += sprintf(dp, "\nmask ");
 578                         dp = bin2hex(dp, e->mask, e->size);
 579                 }
 580                 *dp++ = '\n';
 581                 *dp = '\0';
 582         }
 583 }
 584
 585 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 586 {
 587         struct inode *inode = new_inode(sb);
 588
 589         if (inode) {
 590                 inode->i_ino = get_next_ino();
 591                 inode->i_mode = mode;
 592                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 593                         current_time(inode);
 594         }
 595         return inode;
 596 }
 597
 598 static void bm_evict_inode(struct inode *inode)
 599 {
 600         clear_inode(inode);
 601         kfree(inode->i_private);
 602 }
 603
 604 static void kill_node(Node *e)
 605 {
 606         struct dentry *dentry;
 607
 608         write_lock(&entries_lock);
 609         dentry = e->dentry;
 610         if (dentry) {
 611                 list_del_init(&e->list);
 612                 e->dentry = NULL;
 613         }
 614         write_unlock(&entries_lock);
 615
 616         if ((e->flags & MISC_FMT_OPEN_FILE) && e->interp_file) {
 617                 filp_close(e->interp_file, NULL);
 618                 e->interp_file = NULL;
 619         }
 620
 621         if (dentry) {
 622                 drop_nlink(d_inode(dentry));
 623                 d_drop(dentry);
 624                 dput(dentry);
 625                 simple_release_fs(&bm_mnt, &entry_count);
 626         }
 627 }
 628
 629 /* /<entry> */
 630
 631 static ssize_t
 632 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 633 {
 634         Node *e = file_inode(file)->i_private;
 635         ssize_t res;
 636         char *page;
 637
 638         page = (char *) __get_free_page(GFP_KERNEL);
 639         if (!page)
 640                 return -ENOMEM;
 641
 642         entry_status(e, page);
 643
 644         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 645
 646         free_page((unsigned long) page);
 647         return res;
 648 }
 649
 650 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 651                                 size_t count, loff_t *ppos)
 652 {
 653         struct dentry *root;
 654         Node *e = file_inode(file)->i_private;
 655         int res = parse_command(buffer, count);
 656
 657         switch (res) {
 658         case 1:
 659                 /* Disable this handler. */
 660                 clear_bit(Enabled, &e->flags);
 661                 break;
 662         case 2:
 663                 /* Enable this handler. */
 664                 set_bit(Enabled, &e->flags);
 665                 break;
 666         case 3:
 667                 /* Delete this handler. */
 668                 root = file_inode(file)->i_sb->s_root;
 669                 inode_lock(d_inode(root));
 670
 671                 kill_node(e);
 672
 673                 inode_unlock(d_inode(root));
 674                 break;
 675         default:
 676                 return res;
 677         }
 678
 679         return count;
 680 }
 681
 682 static const struct file_operations bm_entry_operations = {
 683         .read           = bm_entry_read,
 684         .write          = bm_entry_write,
 685         .llseek         = default_llseek,
 686 };
 687
 688 /* /register */
 689
 690 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 691                                size_t count, loff_t *ppos)
 692 {
 693         Node *e;
 694         struct inode *inode;
 695         struct super_block *sb = file_inode(file)->i_sb;
 696         struct dentry *root = sb->s_root, *dentry;
 697         int err = 0;
 698
 699         e = create_entry(buffer, count);
 700
 701         if (IS_ERR(e))
 702                 return PTR_ERR(e);
 703
 704         inode_lock(d_inode(root));
 705         dentry = lookup_one_len(e->name, root, strlen(e->name));
 706         err = PTR_ERR(dentry);
 707         if (IS_ERR(dentry))
 708                 goto out;
 709
 710         err = -EEXIST;
 711         if (d_really_is_positive(dentry))
 712                 goto out2;
 713
 714         inode = bm_get_inode(sb, S_IFREG | 0644);
 715
 716         err = -ENOMEM;
 717         if (!inode)
 718                 goto out2;
 719
 720         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 721         if (err) {
 722                 iput(inode);
 723                 inode = NULL;
 724                 goto out2;
 725         }
 726
 727         if (e->flags & MISC_FMT_OPEN_FILE) {
 728                 struct file *f;
 729
 730                 f = open_exec(e->interpreter);
 731                 if (IS_ERR(f)) {
 732                         err = PTR_ERR(f);
 733                         pr_notice("register: failed to install interpreter file %s\n", e->interpreter);
 734                         simple_release_fs(&bm_mnt, &entry_count);
 735                         iput(inode);
 736                         inode = NULL;
 737                         goto out2;
 738                 }
 739                 e->interp_file = f;
 740         }
 741
 742         e->dentry = dget(dentry);
 743         inode->i_private = e;
 744         inode->i_fop = &bm_entry_operations;
 745
 746         d_instantiate(dentry, inode);
 747         write_lock(&entries_lock);
 748         list_add(&e->list, &entries);
 749         write_unlock(&entries_lock);
 750
 751         err = 0;
 752 out2:
 753         dput(dentry);
 754 out:
 755         inode_unlock(d_inode(root));
 756
 757         if (err) {
 758                 kfree(e);
 759                 return err;
 760         }
 761         return count;
 762 }
 763
 764 static const struct file_operations bm_register_operations = {
 765         .write          = bm_register_write,
 766         .llseek         = noop_llseek,
 767 };
 768
 769 /* /status */
 770
 771 static ssize_t
 772 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 773 {
 774         char *s = enabled ? "enabled\n" : "disabled\n";
 775
 776         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 777 }
 778
 779 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 780                 size_t count, loff_t *ppos)
 781 {
 782         int res = parse_command(buffer, count);
 783         struct dentry *root;
 784
 785         switch (res) {
 786         case 1:
 787                 /* Disable all handlers. */
 788                 enabled = 0;
 789                 break;
 790         case 2:
 791                 /* Enable all handlers. */
 792                 enabled = 1;
 793                 break;
 794         case 3:
 795                 /* Delete all handlers. */
 796                 root = file_inode(file)->i_sb->s_root;
 797                 inode_lock(d_inode(root));
 798
 799                 while (!list_empty(&entries))
 800                         kill_node(list_entry(entries.next, Node, list));
 801
 802                 inode_unlock(d_inode(root));
 803                 break;
 804         default:
 805                 return res;
 806         }
 807
 808         return count;
 809 }
 810
 811 static const struct file_operations bm_status_operations = {
 812         .read           = bm_status_read,
 813         .write          = bm_status_write,
 814         .llseek         = default_llseek,
 815 };
 816
 817 /* Superblock handling */
 818
 819 static const struct super_operations s_ops = {
 820         .statfs         = simple_statfs,
 821         .evict_inode    = bm_evict_inode,
 822 };
 823
 824 static int bm_fill_super(struct super_block *sb, void *data, int silent)
 825 {
 826         int err;
 827         static struct tree_descr bm_files[] = {
 828                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 829                 [3] = {"register", &bm_register_operations, S_IWUSR},
 830                 /* last one */ {""}
 831         };
 832
 833         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 834         if (!err)
 835                 sb->s_op = &s_ops;
 836         return err;
 837 }
 838
 839 static struct dentry *bm_mount(struct file_system_type *fs_type,
 840         int flags, const char *dev_name, void *data)
 841 {
 842         return mount_single(fs_type, flags, data, bm_fill_super);
 843 }
 844
 845 static struct linux_binfmt misc_format = {
 846         .module = THIS_MODULE,
 847         .load_binary = load_misc_binary,
 848 };
 849
 850 static struct file_system_type bm_fs_type = {
 851         .owner          = THIS_MODULE,
 852         .name           = "binfmt_misc",
 853         .mount          = bm_mount,
 854         .kill_sb        = kill_litter_super,
 855 };
 856 MODULE_ALIAS_FS("binfmt_misc");
 857
 858 static int __init init_misc_binfmt(void)
 859 {
 860         int err = register_filesystem(&bm_fs_type);
 861         if (!err)
 862                 insert_binfmt(&misc_format);
 863         return err;
 864 }
 865
 866 static void __exit exit_misc_binfmt(void)
 867 {
 868         unregister_binfmt(&misc_format);
 869         unregister_filesystem(&bm_fs_type);
 870 }
 871
 872 core_initcall(init_misc_binfmt);
 873 module_exit(exit_misc_binfmt);
 874 MODULE_LICENSE("GPL");