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