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/admin-guide/binfmt-misc.rst 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         const 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         int retval;
 135         int fd_binary = -1;
 136
 137         retval = -ENOEXEC;
 138         if (!enabled)
 139                 return retval;
 140
 141         /* to keep locking time low, we copy the interpreter string */
 142         read_lock(&entries_lock);
 143         fmt = check_file(bprm);
 144         if (fmt)
 145                 dget(fmt->dentry);
 146         read_unlock(&entries_lock);
 147         if (!fmt)
 148                 return retval;
 149
 150         /* Need to be able to load the file after exec */
 151         retval = -ENOENT;
 152         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 153                 goto ret;
 154
 155         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 156                 retval = remove_arg_zero(bprm);
 157                 if (retval)
 158                         goto ret;
 159         }
 160
 161         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 162
 163                 /* if the binary should be opened on behalf of the
 164                  * interpreter than keep it open and assign descriptor
 165                  * to it
 166                  */
 167                 fd_binary = get_unused_fd_flags(0);
 168                 if (fd_binary < 0) {
 169                         retval = fd_binary;
 170                         goto ret;
 171                 }
 172                 fd_install(fd_binary, bprm->file);
 173
 174                 /* if the binary is not readable than enforce mm->dumpable=0
 175                    regardless of the interpreter's permissions */
 176                 would_dump(bprm, bprm->file);
 177
 178                 allow_write_access(bprm->file);
 179                 bprm->file = NULL;
 180
 181                 /* mark the bprm that fd should be passed to interp */
 182                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 183                 bprm->interp_data = fd_binary;
 184
 185         } else {
 186                 allow_write_access(bprm->file);
 187                 fput(bprm->file);
 188                 bprm->file = NULL;
 189         }
 190         /* make argv[1] be the path to the binary */
 191         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 192         if (retval < 0)
 193                 goto error;
 194         bprm->argc++;
 195
 196         /* add the interp as argv[0] */
 197         retval = copy_strings_kernel(1, &fmt->interpreter, bprm);
 198         if (retval < 0)
 199                 goto error;
 200         bprm->argc++;
 201
 202         /* Update interp in case binfmt_script needs it. */
 203         retval = bprm_change_interp(fmt->interpreter, bprm);
 204         if (retval < 0)
 205                 goto error;
 206
 207         if (fmt->flags & MISC_FMT_OPEN_FILE) {
 208                 interp_file = file_clone_open(fmt->interp_file);
 209                 if (!IS_ERR(interp_file))
 210                         deny_write_access(interp_file);
 211         } else {
 212                 interp_file = open_exec(fmt->interpreter);
 213         }
 214         retval = PTR_ERR(interp_file);
 215         if (IS_ERR(interp_file))
 216                 goto error;
 217
 218         bprm->file = interp_file;
 219         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 220                 loff_t pos = 0;
 221
 222                 /*
 223                  * No need to call prepare_binprm(), it's already been
 224                  * done.  bprm->buf is stale, update from interp_file.
 225                  */
 226                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 227                 retval = kernel_read(bprm->file, bprm->buf, BINPRM_BUF_SIZE,
 228                                 &pos);
 229         } else
 230                 retval = prepare_binprm(bprm);
 231
 232         if (retval < 0)
 233                 goto error;
 234
 235         retval = search_binary_handler(bprm);
 236         if (retval < 0)
 237                 goto error;
 238
 239 ret:
 240         dput(fmt->dentry);
 241         return retval;
 242 error:
 243         if (fd_binary > 0)
 244                 ksys_close(fd_binary);
 245         bprm->interp_flags = 0;
 246         bprm->interp_data = 0;
 247         goto ret;
 248 }
 249
 250 /* Command parsers */
 251
 252 /*
 253  * parses and copies one argument enclosed in del from *sp to *dp,
 254  * recognising the \x special.
 255  * returns pointer to the copied argument or NULL in case of an
 256  * error (and sets err) or null argument length.
 257  */
 258 static char *scanarg(char *s, char del)
 259 {
 260         char c;
 261
 262         while ((c = *s++) != del) {
 263                 if (c == '\\' && *s == 'x') {
 264                         s++;
 265                         if (!isxdigit(*s++))
 266                                 return NULL;
 267                         if (!isxdigit(*s++))
 268                                 return NULL;
 269                 }
 270         }
 271         s[-1] ='\0';
 272         return s;
 273 }
 274
 275 static char *check_special_flags(char *sfs, Node *e)
 276 {
 277         char *p = sfs;
 278         int cont = 1;
 279
 280         /* special flags */
 281         while (cont) {
 282                 switch (*p) {
 283                 case 'P':
 284                         pr_debug("register: flag: P (preserve argv0)\n");
 285                         p++;
 286                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 287                         break;
 288                 case 'O':
 289                         pr_debug("register: flag: O (open binary)\n");
 290                         p++;
 291                         e->flags |= MISC_FMT_OPEN_BINARY;
 292                         break;
 293                 case 'C':
 294                         pr_debug("register: flag: C (preserve creds)\n");
 295                         p++;
 296                         /* this flags also implies the
 297                            open-binary flag */
 298                         e->flags |= (MISC_FMT_CREDENTIALS |
 299                                         MISC_FMT_OPEN_BINARY);
 300                         break;
 301                 case 'F':
 302                         pr_debug("register: flag: F: open interpreter file now\n");
 303                         p++;
 304                         e->flags |= MISC_FMT_OPEN_FILE;
 305                         break;
 306                 default:
 307                         cont = 0;
 308                 }
 309         }
 310
 311         return p;
 312 }
 313
 314 /*
 315  * This registers a new binary format, it recognises the syntax
 316  * ':name:type:offset:magic:mask:interpreter:flags'
 317  * where the ':' is the IFS, that can be chosen with the first char
 318  */
 319 static Node *create_entry(const char __user *buffer, size_t count)
 320 {
 321         Node *e;
 322         int memsize, err;
 323         char *buf, *p;
 324         char del;
 325
 326         pr_debug("register: received %zu bytes\n", count);
 327
 328         /* some sanity checks */
 329         err = -EINVAL;
 330         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 331                 goto out;
 332
 333         err = -ENOMEM;
 334         memsize = sizeof(Node) + count + 8;
 335         e = kmalloc(memsize, GFP_KERNEL);
 336         if (!e)
 337                 goto out;
 338
 339         p = buf = (char *)e + sizeof(Node);
 340
 341         memset(e, 0, sizeof(Node));
 342         if (copy_from_user(buf, buffer, count))
 343                 goto efault;
 344
 345         del = *p++;     /* delimeter */
 346
 347         pr_debug("register: delim: %#x {%c}\n", del, del);
 348
 349         /* Pad the buffer with the delim to simplify parsing below. */
 350         memset(buf + count, del, 8);
 351
 352         /* Parse the 'name' field. */
 353         e->name = p;
 354         p = strchr(p, del);
 355         if (!p)
 356                 goto einval;
 357         *p++ = '\0';
 358         if (!e->name[0] ||
 359             !strcmp(e->name, ".") ||
 360             !strcmp(e->name, "..") ||
 361             strchr(e->name, '/'))
 362                 goto einval;
 363
 364         pr_debug("register: name: {%s}\n", e->name);
 365
 366         /* Parse the 'type' field. */
 367         switch (*p++) {
 368         case 'E':
 369                 pr_debug("register: type: E (extension)\n");
 370                 e->flags = 1 << Enabled;
 371                 break;
 372         case 'M':
 373                 pr_debug("register: type: M (magic)\n");
 374                 e->flags = (1 << Enabled) | (1 << Magic);
 375                 break;
 376         default:
 377                 goto einval;
 378         }
 379         if (*p++ != del)
 380                 goto einval;
 381
 382         if (test_bit(Magic, &e->flags)) {
 383                 /* Handle the 'M' (magic) format. */
 384                 char *s;
 385
 386                 /* Parse the 'offset' field. */
 387                 s = strchr(p, del);
 388                 if (!s)
 389                         goto einval;
 390                 *s = '\0';
 391                 if (p != s) {
 392                         int r = kstrtoint(p, 10, &e->offset);
 393                         if (r != 0 || e->offset < 0)
 394                                 goto einval;
 395                 }
 396                 p = s;
 397                 if (*p++)
 398                         goto einval;
 399                 pr_debug("register: offset: %#x\n", e->offset);
 400
 401                 /* Parse the 'magic' field. */
 402                 e->magic = p;
 403                 p = scanarg(p, del);
 404                 if (!p)
 405                         goto einval;
 406                 if (!e->magic[0])
 407                         goto einval;
 408                 if (USE_DEBUG)
 409                         print_hex_dump_bytes(
 410                                 KBUILD_MODNAME ": register: magic[raw]: ",
 411                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 412
 413                 /* Parse the 'mask' field. */
 414                 e->mask = p;
 415                 p = scanarg(p, del);
 416                 if (!p)
 417                         goto einval;
 418                 if (!e->mask[0]) {
 419                         e->mask = NULL;
 420                         pr_debug("register:  mask[raw]: none\n");
 421                 } else if (USE_DEBUG)
 422                         print_hex_dump_bytes(
 423                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 424                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 425
 426                 /*
 427                  * Decode the magic & mask fields.
 428                  * Note: while we might have accepted embedded NUL bytes from
 429                  * above, the unescape helpers here will stop at the first one
 430                  * it encounters.
 431                  */
 432                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 433                 if (e->mask &&
 434                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 435                         goto einval;
 436                 if (e->size > BINPRM_BUF_SIZE ||
 437                     BINPRM_BUF_SIZE - e->size < e->offset)
 438                         goto einval;
 439                 pr_debug("register: magic/mask length: %i\n", e->size);
 440                 if (USE_DEBUG) {
 441                         print_hex_dump_bytes(
 442                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 443                                 DUMP_PREFIX_NONE, e->magic, e->size);
 444
 445                         if (e->mask) {
 446                                 int i;
 447                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 448
 449                                 print_hex_dump_bytes(
 450                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 451                                         DUMP_PREFIX_NONE, e->mask, e->size);
 452
 453                                 if (masked) {
 454                                         for (i = 0; i < e->size; ++i)
 455                                                 masked[i] = e->magic[i] & e->mask[i];
 456                                         print_hex_dump_bytes(
 457                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 458                                                 DUMP_PREFIX_NONE, masked, e->size);
 459
 460                                         kfree(masked);
 461                                 }
 462                         }
 463                 }
 464         } else {
 465                 /* Handle the 'E' (extension) format. */
 466
 467                 /* Skip the 'offset' field. */
 468                 p = strchr(p, del);
 469                 if (!p)
 470                         goto einval;
 471                 *p++ = '\0';
 472
 473                 /* Parse the 'magic' field. */
 474                 e->magic = p;
 475                 p = strchr(p, del);
 476                 if (!p)
 477                         goto einval;
 478                 *p++ = '\0';
 479                 if (!e->magic[0] || strchr(e->magic, '/'))
 480                         goto einval;
 481                 pr_debug("register: extension: {%s}\n", e->magic);
 482
 483                 /* Skip the 'mask' field. */
 484                 p = strchr(p, del);
 485                 if (!p)
 486                         goto einval;
 487                 *p++ = '\0';
 488         }
 489
 490         /* Parse the 'interpreter' field. */
 491         e->interpreter = p;
 492         p = strchr(p, del);
 493         if (!p)
 494                 goto einval;
 495         *p++ = '\0';
 496         if (!e->interpreter[0])
 497                 goto einval;
 498         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 499
 500         /* Parse the 'flags' field. */
 501         p = check_special_flags(p, e);
 502         if (*p == '\n')
 503                 p++;
 504         if (p != buf + count)
 505                 goto einval;
 506
 507         return e;
 508
 509 out:
 510         return ERR_PTR(err);
 511
 512 efault:
 513         kfree(e);
 514         return ERR_PTR(-EFAULT);
 515 einval:
 516         kfree(e);
 517         return ERR_PTR(-EINVAL);
 518 }
 519
 520 /*
 521  * Set status of entry/binfmt_misc:
 522  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 523  */
 524 static int parse_command(const char __user *buffer, size_t count)
 525 {
 526         char s[4];
 527
 528         if (count > 3)
 529                 return -EINVAL;
 530         if (copy_from_user(s, buffer, count))
 531                 return -EFAULT;
 532         if (!count)
 533                 return 0;
 534         if (s[count - 1] == '\n')
 535                 count--;
 536         if (count == 1 && s[0] == '0')
 537                 return 1;
 538         if (count == 1 && s[0] == '1')
 539                 return 2;
 540         if (count == 2 && s[0] == '-' && s[1] == '1')
 541                 return 3;
 542         return -EINVAL;
 543 }
 544
 545 /* generic stuff */
 546
 547 static void entry_status(Node *e, char *page)
 548 {
 549         char *dp = page;
 550         const char *status = "disabled";
 551
 552         if (test_bit(Enabled, &e->flags))
 553                 status = "enabled";
 554
 555         if (!VERBOSE_STATUS) {
 556                 sprintf(page, "%s\n", status);
 557                 return;
 558         }
 559
 560         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 561
 562         /* print the special flags */
 563         dp += sprintf(dp, "flags: ");
 564         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 565                 *dp++ = 'P';
 566         if (e->flags & MISC_FMT_OPEN_BINARY)
 567                 *dp++ = 'O';
 568         if (e->flags & MISC_FMT_CREDENTIALS)
 569                 *dp++ = 'C';
 570         if (e->flags & MISC_FMT_OPEN_FILE)
 571                 *dp++ = 'F';
 572         *dp++ = '\n';
 573
 574         if (!test_bit(Magic, &e->flags)) {
 575                 sprintf(dp, "extension .%s\n", e->magic);
 576         } else {
 577                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 578                 dp = bin2hex(dp, e->magic, e->size);
 579                 if (e->mask) {
 580                         dp += sprintf(dp, "\nmask ");
 581                         dp = bin2hex(dp, e->mask, e->size);
 582                 }
 583                 *dp++ = '\n';
 584                 *dp = '\0';
 585         }
 586 }
 587
 588 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 589 {
 590         struct inode *inode = new_inode(sb);
 591
 592         if (inode) {
 593                 inode->i_ino = get_next_ino();
 594                 inode->i_mode = mode;
 595                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 596                         current_time(inode);
 597         }
 598         return inode;
 599 }
 600
 601 static void bm_evict_inode(struct inode *inode)
 602 {
 603         Node *e = inode->i_private;
 604
 605         if (e && e->flags & MISC_FMT_OPEN_FILE)
 606                 filp_close(e->interp_file, NULL);
 607
 608         clear_inode(inode);
 609         kfree(e);
 610 }
 611
 612 static void kill_node(Node *e)
 613 {
 614         struct dentry *dentry;
 615
 616         write_lock(&entries_lock);
 617         list_del_init(&e->list);
 618         write_unlock(&entries_lock);
 619
 620         dentry = e->dentry;
 621         drop_nlink(d_inode(dentry));
 622         d_drop(dentry);
 623         dput(dentry);
 624         simple_release_fs(&bm_mnt, &entry_count);
 625 }
 626
 627 /* /<entry> */
 628
 629 static ssize_t
 630 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 631 {
 632         Node *e = file_inode(file)->i_private;
 633         ssize_t res;
 634         char *page;
 635
 636         page = (char *) __get_free_page(GFP_KERNEL);
 637         if (!page)
 638                 return -ENOMEM;
 639
 640         entry_status(e, page);
 641
 642         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 643
 644         free_page((unsigned long) page);
 645         return res;
 646 }
 647
 648 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 649                                 size_t count, loff_t *ppos)
 650 {
 651         struct dentry *root;
 652         Node *e = file_inode(file)->i_private;
 653         int res = parse_command(buffer, count);
 654
 655         switch (res) {
 656         case 1:
 657                 /* Disable this handler. */
 658                 clear_bit(Enabled, &e->flags);
 659                 break;
 660         case 2:
 661                 /* Enable this handler. */
 662                 set_bit(Enabled, &e->flags);
 663                 break;
 664         case 3:
 665                 /* Delete this handler. */
 666                 root = file_inode(file)->i_sb->s_root;
 667                 inode_lock(d_inode(root));
 668
 669                 if (!list_empty(&e->list))
 670                         kill_node(e);
 671
 672                 inode_unlock(d_inode(root));
 673                 break;
 674         default:
 675                 return res;
 676         }
 677
 678         return count;
 679 }
 680
 681 static const struct file_operations bm_entry_operations = {
 682         .read           = bm_entry_read,
 683         .write          = bm_entry_write,
 684         .llseek         = default_llseek,
 685 };
 686
 687 /* /register */
 688
 689 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 690                                size_t count, loff_t *ppos)
 691 {
 692         Node *e;
 693         struct inode *inode;
 694         struct super_block *sb = file_inode(file)->i_sb;
 695         struct dentry *root = sb->s_root, *dentry;
 696         int err = 0;
 697
 698         e = create_entry(buffer, count);
 699
 700         if (IS_ERR(e))
 701                 return PTR_ERR(e);
 702
 703         inode_lock(d_inode(root));
 704         dentry = lookup_one_len(e->name, root, strlen(e->name));
 705         err = PTR_ERR(dentry);
 706         if (IS_ERR(dentry))
 707                 goto out;
 708
 709         err = -EEXIST;
 710         if (d_really_is_positive(dentry))
 711                 goto out2;
 712
 713         inode = bm_get_inode(sb, S_IFREG | 0644);
 714
 715         err = -ENOMEM;
 716         if (!inode)
 717                 goto out2;
 718
 719         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 720         if (err) {
 721                 iput(inode);
 722                 inode = NULL;
 723                 goto out2;
 724         }
 725
 726         if (e->flags & MISC_FMT_OPEN_FILE) {
 727                 struct file *f;
 728
 729                 f = open_exec(e->interpreter);
 730                 if (IS_ERR(f)) {
 731                         err = PTR_ERR(f);
 732                         pr_notice("register: failed to install interpreter file %s\n", e->interpreter);
 733                         simple_release_fs(&bm_mnt, &entry_count);
 734                         iput(inode);
 735                         inode = NULL;
 736                         goto out2;
 737                 }
 738                 e->interp_file = f;
 739         }
 740
 741         e->dentry = dget(dentry);
 742         inode->i_private = e;
 743         inode->i_fop = &bm_entry_operations;
 744
 745         d_instantiate(dentry, inode);
 746         write_lock(&entries_lock);
 747         list_add(&e->list, &entries);
 748         write_unlock(&entries_lock);
 749
 750         err = 0;
 751 out2:
 752         dput(dentry);
 753 out:
 754         inode_unlock(d_inode(root));
 755
 756         if (err) {
 757                 kfree(e);
 758                 return err;
 759         }
 760         return count;
 761 }
 762
 763 static const struct file_operations bm_register_operations = {
 764         .write          = bm_register_write,
 765         .llseek         = noop_llseek,
 766 };
 767
 768 /* /status */
 769
 770 static ssize_t
 771 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 772 {
 773         char *s = enabled ? "enabled\n" : "disabled\n";
 774
 775         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 776 }
 777
 778 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 779                 size_t count, loff_t *ppos)
 780 {
 781         int res = parse_command(buffer, count);
 782         struct dentry *root;
 783
 784         switch (res) {
 785         case 1:
 786                 /* Disable all handlers. */
 787                 enabled = 0;
 788                 break;
 789         case 2:
 790                 /* Enable all handlers. */
 791                 enabled = 1;
 792                 break;
 793         case 3:
 794                 /* Delete all handlers. */
 795                 root = file_inode(file)->i_sb->s_root;
 796                 inode_lock(d_inode(root));
 797
 798                 while (!list_empty(&entries))
 799                         kill_node(list_first_entry(&entries, Node, list));
 800
 801                 inode_unlock(d_inode(root));
 802                 break;
 803         default:
 804                 return res;
 805         }
 806
 807         return count;
 808 }
 809
 810 static const struct file_operations bm_status_operations = {
 811         .read           = bm_status_read,
 812         .write          = bm_status_write,
 813         .llseek         = default_llseek,
 814 };
 815
 816 /* Superblock handling */
 817
 818 static const struct super_operations s_ops = {
 819         .statfs         = simple_statfs,
 820         .evict_inode    = bm_evict_inode,
 821 };
 822
 823 static int bm_fill_super(struct super_block *sb, void *data, int silent)
 824 {
 825         int err;
 826         static const struct tree_descr bm_files[] = {
 827                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 828                 [3] = {"register", &bm_register_operations, S_IWUSR},
 829                 /* last one */ {""}
 830         };
 831
 832         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 833         if (!err)
 834                 sb->s_op = &s_ops;
 835         return err;
 836 }
 837
 838 static struct dentry *bm_mount(struct file_system_type *fs_type,
 839         int flags, const char *dev_name, void *data)
 840 {
 841         return mount_single(fs_type, flags, data, bm_fill_super);
 842 }
 843
 844 static struct linux_binfmt misc_format = {
 845         .module = THIS_MODULE,
 846         .load_binary = load_misc_binary,
 847 };
 848
 849 static struct file_system_type bm_fs_type = {
 850         .owner          = THIS_MODULE,
 851         .name           = "binfmt_misc",
 852         .mount          = bm_mount,
 853         .kill_sb        = kill_litter_super,
 854 };
 855 MODULE_ALIAS_FS("binfmt_misc");
 856
 857 static int __init init_misc_binfmt(void)
 858 {
 859         int err = register_filesystem(&bm_fs_type);
 860         if (!err)
 861                 insert_binfmt(&misc_format);
 862         return err;
 863 }
 864
 865 static void __exit exit_misc_binfmt(void)
 866 {
 867         unregister_binfmt(&misc_format);
 868         unregister_filesystem(&bm_fs_type);
 869 }
 870
 871 core_initcall(init_misc_binfmt);
 872 module_exit(exit_misc_binfmt);
 873 MODULE_LICENSE("GPL");