fs/binfmt_misc.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * binfmt_misc.c
   4  *
   5  * Copyright (C) 1997 Richard Günther
   6  *
   7  * binfmt_misc detects binaries via a magic or filename extension and invokes
   8  * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
   9  */
  10
  11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/sched/mm.h>
  17 #include <linux/magic.h>
  18 #include <linux/binfmts.h>
  19 #include <linux/slab.h>
  20 #include <linux/ctype.h>
  21 #include <linux/string_helpers.h>
  22 #include <linux/file.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/namei.h>
  25 #include <linux/mount.h>
  26 #include <linux/syscalls.h>
  27 #include <linux/fs.h>
  28 #include <linux/uaccess.h>
  29
  30 #include "internal.h"
  31
  32 #ifdef DEBUG
  33 # define USE_DEBUG 1
  34 #else
  35 # define USE_DEBUG 0
  36 #endif
  37
  38 enum {
  39         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  40 };
  41
  42 static LIST_HEAD(entries);
  43 static int enabled = 1;
  44
  45 enum {Enabled, Magic};
  46 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  47 #define MISC_FMT_OPEN_BINARY (1 << 30)
  48 #define MISC_FMT_CREDENTIALS (1 << 29)
  49 #define MISC_FMT_OPEN_FILE (1 << 28)
  50
  51 typedef struct {
  52         struct list_head list;
  53         unsigned long flags;            /* type, status, etc. */
  54         int offset;                     /* offset of magic */
  55         int size;                       /* size of magic/mask */
  56         char *magic;                    /* magic or filename extension */
  57         char *mask;                     /* mask, NULL for exact match */
  58         const char *interpreter;        /* filename of interpreter */
  59         char *name;
  60         struct dentry *dentry;
  61         struct file *interp_file;
  62 } Node;
  63
  64 static DEFINE_RWLOCK(entries_lock);
  65 static struct file_system_type bm_fs_type;
  66 static struct vfsmount *bm_mnt;
  67 static int entry_count;
  68
  69 /*
  70  * Max length of the register string.  Determined by:
  71  *  - 7 delimiters
  72  *  - name:   ~50 bytes
  73  *  - type:   1 byte
  74  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  75  *  - magic:  128 bytes (512 in escaped form)
  76  *  - mask:   128 bytes (512 in escaped form)
  77  *  - interp: ~50 bytes
  78  *  - flags:  5 bytes
  79  * Round that up a bit, and then back off to hold the internal data
  80  * (like struct Node).
  81  */
  82 #define MAX_REGISTER_LENGTH 1920
  83
  84 /*
  85  * Check if we support the binfmt
  86  * if we do, return the node, else NULL
  87  * locking is done in load_misc_binary
  88  */
  89 static Node *check_file(struct linux_binprm *bprm)
  90 {
  91         char *p = strrchr(bprm->interp, '.');
  92         struct list_head *l;
  93
  94         /* Walk all the registered handlers. */
  95         list_for_each(l, &entries) {
  96                 Node *e = list_entry(l, Node, list);
  97                 char *s;
  98                 int j;
  99
 100                 /* Make sure this one is currently enabled. */
 101                 if (!test_bit(Enabled, &e->flags))
 102                         continue;
 103
 104                 /* Do matching based on extension if applicable. */
 105                 if (!test_bit(Magic, &e->flags)) {
 106                         if (p && !strcmp(e->magic, p + 1))
 107                                 return e;
 108                         continue;
 109                 }
 110
 111                 /* Do matching based on magic & mask. */
 112                 s = bprm->buf + e->offset;
 113                 if (e->mask) {
 114                         for (j = 0; j < e->size; j++)
 115                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 116                                         break;
 117                 } else {
 118                         for (j = 0; j < e->size; j++)
 119                                 if ((*s++ ^ e->magic[j]))
 120                                         break;
 121                 }
 122                 if (j == e->size)
 123                         return e;
 124         }
 125         return NULL;
 126 }
 127
 128 /*
 129  * the loader itself
 130  */
 131 static int load_misc_binary(struct linux_binprm *bprm)
 132 {
 133         Node *fmt;
 134         struct file *interp_file = NULL;
 135         int retval;
 136         int fd_binary = -1;
 137
 138         retval = -ENOEXEC;
 139         if (!enabled)
 140                 return retval;
 141
 142         /* to keep locking time low, we copy the interpreter string */
 143         read_lock(&entries_lock);
 144         fmt = check_file(bprm);
 145         if (fmt)
 146                 dget(fmt->dentry);
 147         read_unlock(&entries_lock);
 148         if (!fmt)
 149                 return retval;
 150
 151         /* Need to be able to load the file after exec */
 152         retval = -ENOENT;
 153         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 154                 goto ret;
 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, &fmt->interpreter, 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(fmt->interpreter, bprm);
 205         if (retval < 0)
 206                 goto error;
 207
 208         if (fmt->flags & MISC_FMT_OPEN_FILE) {
 209                 interp_file = file_clone_open(fmt->interp_file);
 210                 if (!IS_ERR(interp_file))
 211                         deny_write_access(interp_file);
 212         } else {
 213                 interp_file = open_exec(fmt->interpreter);
 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                 loff_t pos = 0;
 222
 223                 /*
 224                  * No need to call prepare_binprm(), it's already been
 225                  * done.  bprm->buf is stale, update from interp_file.
 226                  */
 227                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 228                 retval = kernel_read(bprm->file, bprm->buf, BINPRM_BUF_SIZE,
 229                                 &pos);
 230         } else
 231                 retval = prepare_binprm(bprm);
 232
 233         if (retval < 0)
 234                 goto error;
 235
 236         retval = search_binary_handler(bprm);
 237         if (retval < 0)
 238                 goto error;
 239
 240 ret:
 241         dput(fmt->dentry);
 242         return retval;
 243 error:
 244         if (fd_binary > 0)
 245                 ksys_close(fd_binary);
 246         bprm->interp_flags = 0;
 247         bprm->interp_data = 0;
 248         goto ret;
 249 }
 250
 251 /* Command parsers */
 252
 253 /*
 254  * parses and copies one argument enclosed in del from *sp to *dp,
 255  * recognising the \x special.
 256  * returns pointer to the copied argument or NULL in case of an
 257  * error (and sets err) or null argument length.
 258  */
 259 static char *scanarg(char *s, char del)
 260 {
 261         char c;
 262
 263         while ((c = *s++) != del) {
 264                 if (c == '\\' && *s == 'x') {
 265                         s++;
 266                         if (!isxdigit(*s++))
 267                                 return NULL;
 268                         if (!isxdigit(*s++))
 269                                 return NULL;
 270                 }
 271         }
 272         s[-1] ='\0';
 273         return s;
 274 }
 275
 276 static char *check_special_flags(char *sfs, Node *e)
 277 {
 278         char *p = sfs;
 279         int cont = 1;
 280
 281         /* special flags */
 282         while (cont) {
 283                 switch (*p) {
 284                 case 'P':
 285                         pr_debug("register: flag: P (preserve argv0)\n");
 286                         p++;
 287                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 288                         break;
 289                 case 'O':
 290                         pr_debug("register: flag: O (open binary)\n");
 291                         p++;
 292                         e->flags |= MISC_FMT_OPEN_BINARY;
 293                         break;
 294                 case 'C':
 295                         pr_debug("register: flag: C (preserve creds)\n");
 296                         p++;
 297                         /* this flags also implies the
 298                            open-binary flag */
 299                         e->flags |= (MISC_FMT_CREDENTIALS |
 300                                         MISC_FMT_OPEN_BINARY);
 301                         break;
 302                 case 'F':
 303                         pr_debug("register: flag: F: open interpreter file now\n");
 304                         p++;
 305                         e->flags |= MISC_FMT_OPEN_FILE;
 306                         break;
 307                 default:
 308                         cont = 0;
 309                 }
 310         }
 311
 312         return p;
 313 }
 314
 315 /*
 316  * This registers a new binary format, it recognises the syntax
 317  * ':name:type:offset:magic:mask:interpreter:flags'
 318  * where the ':' is the IFS, that can be chosen with the first char
 319  */
 320 static Node *create_entry(const char __user *buffer, size_t count)
 321 {
 322         Node *e;
 323         int memsize, err;
 324         char *buf, *p;
 325         char del;
 326
 327         pr_debug("register: received %zu bytes\n", count);
 328
 329         /* some sanity checks */
 330         err = -EINVAL;
 331         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 332                 goto out;
 333
 334         err = -ENOMEM;
 335         memsize = sizeof(Node) + count + 8;
 336         e = kmalloc(memsize, GFP_KERNEL);
 337         if (!e)
 338                 goto out;
 339
 340         p = buf = (char *)e + sizeof(Node);
 341
 342         memset(e, 0, sizeof(Node));
 343         if (copy_from_user(buf, buffer, count))
 344                 goto efault;
 345
 346         del = *p++;     /* delimeter */
 347
 348         pr_debug("register: delim: %#x {%c}\n", del, del);
 349
 350         /* Pad the buffer with the delim to simplify parsing below. */
 351         memset(buf + count, del, 8);
 352
 353         /* Parse the 'name' field. */
 354         e->name = p;
 355         p = strchr(p, del);
 356         if (!p)
 357                 goto einval;
 358         *p++ = '\0';
 359         if (!e->name[0] ||
 360             !strcmp(e->name, ".") ||
 361             !strcmp(e->name, "..") ||
 362             strchr(e->name, '/'))
 363                 goto einval;
 364
 365         pr_debug("register: name: {%s}\n", e->name);
 366
 367         /* Parse the 'type' field. */
 368         switch (*p++) {
 369         case 'E':
 370                 pr_debug("register: type: E (extension)\n");
 371                 e->flags = 1 << Enabled;
 372                 break;
 373         case 'M':
 374                 pr_debug("register: type: M (magic)\n");
 375                 e->flags = (1 << Enabled) | (1 << Magic);
 376                 break;
 377         default:
 378                 goto einval;
 379         }
 380         if (*p++ != del)
 381                 goto einval;
 382
 383         if (test_bit(Magic, &e->flags)) {
 384                 /* Handle the 'M' (magic) format. */
 385                 char *s;
 386
 387                 /* Parse the 'offset' field. */
 388                 s = strchr(p, del);
 389                 if (!s)
 390                         goto einval;
 391                 *s = '\0';
 392                 if (p != s) {
 393                         int r = kstrtoint(p, 10, &e->offset);
 394                         if (r != 0 || e->offset < 0)
 395                                 goto einval;
 396                 }
 397                 p = s;
 398                 if (*p++)
 399                         goto einval;
 400                 pr_debug("register: offset: %#x\n", e->offset);
 401
 402                 /* Parse the 'magic' field. */
 403                 e->magic = p;
 404                 p = scanarg(p, del);
 405                 if (!p)
 406                         goto einval;
 407                 if (!e->magic[0])
 408                         goto einval;
 409                 if (USE_DEBUG)
 410                         print_hex_dump_bytes(
 411                                 KBUILD_MODNAME ": register: magic[raw]: ",
 412                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 413
 414                 /* Parse the 'mask' field. */
 415                 e->mask = p;
 416                 p = scanarg(p, del);
 417                 if (!p)
 418                         goto einval;
 419                 if (!e->mask[0]) {
 420                         e->mask = NULL;
 421                         pr_debug("register:  mask[raw]: none\n");
 422                 } else if (USE_DEBUG)
 423                         print_hex_dump_bytes(
 424                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 425                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 426
 427                 /*
 428                  * Decode the magic & mask fields.
 429                  * Note: while we might have accepted embedded NUL bytes from
 430                  * above, the unescape helpers here will stop at the first one
 431                  * it encounters.
 432                  */
 433                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 434                 if (e->mask &&
 435                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 436                         goto einval;
 437                 if (e->size > BINPRM_BUF_SIZE ||
 438                     BINPRM_BUF_SIZE - e->size < e->offset)
 439                         goto einval;
 440                 pr_debug("register: magic/mask length: %i\n", e->size);
 441                 if (USE_DEBUG) {
 442                         print_hex_dump_bytes(
 443                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 444                                 DUMP_PREFIX_NONE, e->magic, e->size);
 445
 446                         if (e->mask) {
 447                                 int i;
 448                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 449
 450                                 print_hex_dump_bytes(
 451                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 452                                         DUMP_PREFIX_NONE, e->mask, e->size);
 453
 454                                 if (masked) {
 455                                         for (i = 0; i < e->size; ++i)
 456                                                 masked[i] = e->magic[i] & e->mask[i];
 457                                         print_hex_dump_bytes(
 458                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 459                                                 DUMP_PREFIX_NONE, masked, e->size);
 460
 461                                         kfree(masked);
 462                                 }
 463                         }
 464                 }
 465         } else {
 466                 /* Handle the 'E' (extension) format. */
 467
 468                 /* Skip the 'offset' field. */
 469                 p = strchr(p, del);
 470                 if (!p)
 471                         goto einval;
 472                 *p++ = '\0';
 473
 474                 /* Parse the 'magic' field. */
 475                 e->magic = p;
 476                 p = strchr(p, del);
 477                 if (!p)
 478                         goto einval;
 479                 *p++ = '\0';
 480                 if (!e->magic[0] || strchr(e->magic, '/'))
 481                         goto einval;
 482                 pr_debug("register: extension: {%s}\n", e->magic);
 483
 484                 /* Skip the 'mask' field. */
 485                 p = strchr(p, del);
 486                 if (!p)
 487                         goto einval;
 488                 *p++ = '\0';
 489         }
 490
 491         /* Parse the 'interpreter' field. */
 492         e->interpreter = p;
 493         p = strchr(p, del);
 494         if (!p)
 495                 goto einval;
 496         *p++ = '\0';
 497         if (!e->interpreter[0])
 498                 goto einval;
 499         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 500
 501         /* Parse the 'flags' field. */
 502         p = check_special_flags(p, e);
 503         if (*p == '\n')
 504                 p++;
 505         if (p != buf + count)
 506                 goto einval;
 507
 508         return e;
 509
 510 out:
 511         return ERR_PTR(err);
 512
 513 efault:
 514         kfree(e);
 515         return ERR_PTR(-EFAULT);
 516 einval:
 517         kfree(e);
 518         return ERR_PTR(-EINVAL);
 519 }
 520
 521 /*
 522  * Set status of entry/binfmt_misc:
 523  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 524  */
 525 static int parse_command(const char __user *buffer, size_t count)
 526 {
 527         char s[4];
 528
 529         if (count > 3)
 530                 return -EINVAL;
 531         if (copy_from_user(s, buffer, count))
 532                 return -EFAULT;
 533         if (!count)
 534                 return 0;
 535         if (s[count - 1] == '\n')
 536                 count--;
 537         if (count == 1 && s[0] == '0')
 538                 return 1;
 539         if (count == 1 && s[0] == '1')
 540                 return 2;
 541         if (count == 2 && s[0] == '-' && s[1] == '1')
 542                 return 3;
 543         return -EINVAL;
 544 }
 545
 546 /* generic stuff */
 547
 548 static void entry_status(Node *e, char *page)
 549 {
 550         char *dp = page;
 551         const char *status = "disabled";
 552
 553         if (test_bit(Enabled, &e->flags))
 554                 status = "enabled";
 555
 556         if (!VERBOSE_STATUS) {
 557                 sprintf(page, "%s\n", status);
 558                 return;
 559         }
 560
 561         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 562
 563         /* print the special flags */
 564         dp += sprintf(dp, "flags: ");
 565         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 566                 *dp++ = 'P';
 567         if (e->flags & MISC_FMT_OPEN_BINARY)
 568                 *dp++ = 'O';
 569         if (e->flags & MISC_FMT_CREDENTIALS)
 570                 *dp++ = 'C';
 571         if (e->flags & MISC_FMT_OPEN_FILE)
 572                 *dp++ = 'F';
 573         *dp++ = '\n';
 574
 575         if (!test_bit(Magic, &e->flags)) {
 576                 sprintf(dp, "extension .%s\n", e->magic);
 577         } else {
 578                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 579                 dp = bin2hex(dp, e->magic, e->size);
 580                 if (e->mask) {
 581                         dp += sprintf(dp, "\nmask ");
 582                         dp = bin2hex(dp, e->mask, e->size);
 583                 }
 584                 *dp++ = '\n';
 585                 *dp = '\0';
 586         }
 587 }
 588
 589 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 590 {
 591         struct inode *inode = new_inode(sb);
 592
 593         if (inode) {
 594                 inode->i_ino = get_next_ino();
 595                 inode->i_mode = mode;
 596                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 597                         current_time(inode);
 598         }
 599         return inode;
 600 }
 601
 602 static void bm_evict_inode(struct inode *inode)
 603 {
 604         Node *e = inode->i_private;
 605
 606         if (e && e->flags & MISC_FMT_OPEN_FILE)
 607                 filp_close(e->interp_file, NULL);
 608
 609         clear_inode(inode);
 610         kfree(e);
 611 }
 612
 613 static void kill_node(Node *e)
 614 {
 615         struct dentry *dentry;
 616
 617         write_lock(&entries_lock);
 618         list_del_init(&e->list);
 619         write_unlock(&entries_lock);
 620
 621         dentry = e->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 /* /<entry> */
 629
 630 static ssize_t
 631 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 632 {
 633         Node *e = file_inode(file)->i_private;
 634         ssize_t res;
 635         char *page;
 636
 637         page = (char *) __get_free_page(GFP_KERNEL);
 638         if (!page)
 639                 return -ENOMEM;
 640
 641         entry_status(e, page);
 642
 643         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 644
 645         free_page((unsigned long) page);
 646         return res;
 647 }
 648
 649 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 650                                 size_t count, loff_t *ppos)
 651 {
 652         struct dentry *root;
 653         Node *e = file_inode(file)->i_private;
 654         int res = parse_command(buffer, count);
 655
 656         switch (res) {
 657         case 1:
 658                 /* Disable this handler. */
 659                 clear_bit(Enabled, &e->flags);
 660                 break;
 661         case 2:
 662                 /* Enable this handler. */
 663                 set_bit(Enabled, &e->flags);
 664                 break;
 665         case 3:
 666                 /* Delete this handler. */
 667                 root = file_inode(file)->i_sb->s_root;
 668                 inode_lock(d_inode(root));
 669
 670                 if (!list_empty(&e->list))
 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_first_entry(&entries, 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 const 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");