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/fs_context.h>
  27 #include <linux/syscalls.h>
  28 #include <linux/fs.h>
  29 #include <linux/uaccess.h>
  30
  31 #include "internal.h"
  32
  33 #ifdef DEBUG
  34 # define USE_DEBUG 1
  35 #else
  36 # define USE_DEBUG 0
  37 #endif
  38
  39 enum {
  40         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  41 };
  42
  43 static LIST_HEAD(entries);
  44 static int enabled = 1;
  45
  46 enum {Enabled, Magic};
  47 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
  48 #define MISC_FMT_OPEN_BINARY (1 << 30)
  49 #define MISC_FMT_CREDENTIALS (1 << 29)
  50 #define MISC_FMT_OPEN_FILE (1 << 28)
  51
  52 typedef struct {
  53         struct list_head list;
  54         unsigned long flags;            /* type, status, etc. */
  55         int offset;                     /* offset of magic */
  56         int size;                       /* size of magic/mask */
  57         char *magic;                    /* magic or filename extension */
  58         char *mask;                     /* mask, NULL for exact match */
  59         const char *interpreter;        /* filename of interpreter */
  60         char *name;
  61         struct dentry *dentry;
  62         struct file *interp_file;
  63 } Node;
  64
  65 static DEFINE_RWLOCK(entries_lock);
  66 static struct file_system_type bm_fs_type;
  67 static struct vfsmount *bm_mnt;
  68 static int entry_count;
  69
  70 /*
  71  * Max length of the register string.  Determined by:
  72  *  - 7 delimiters
  73  *  - name:   ~50 bytes
  74  *  - type:   1 byte
  75  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  76  *  - magic:  128 bytes (512 in escaped form)
  77  *  - mask:   128 bytes (512 in escaped form)
  78  *  - interp: ~50 bytes
  79  *  - flags:  5 bytes
  80  * Round that up a bit, and then back off to hold the internal data
  81  * (like struct Node).
  82  */
  83 #define MAX_REGISTER_LENGTH 1920
  84
  85 /*
  86  * Check if we support the binfmt
  87  * if we do, return the node, else NULL
  88  * locking is done in load_misc_binary
  89  */
  90 static Node *check_file(struct linux_binprm *bprm)
  91 {
  92         char *p = strrchr(bprm->interp, '.');
  93         struct list_head *l;
  94
  95         /* Walk all the registered handlers. */
  96         list_for_each(l, &entries) {
  97                 Node *e = list_entry(l, Node, list);
  98                 char *s;
  99                 int j;
 100
 101                 /* Make sure this one is currently enabled. */
 102                 if (!test_bit(Enabled, &e->flags))
 103                         continue;
 104
 105                 /* Do matching based on extension if applicable. */
 106                 if (!test_bit(Magic, &e->flags)) {
 107                         if (p && !strcmp(e->magic, p + 1))
 108                                 return e;
 109                         continue;
 110                 }
 111
 112                 /* Do matching based on magic & mask. */
 113                 s = bprm->buf + e->offset;
 114                 if (e->mask) {
 115                         for (j = 0; j < e->size; j++)
 116                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 117                                         break;
 118                 } else {
 119                         for (j = 0; j < e->size; j++)
 120                                 if ((*s++ ^ e->magic[j]))
 121                                         break;
 122                 }
 123                 if (j == e->size)
 124                         return e;
 125         }
 126         return NULL;
 127 }
 128
 129 /*
 130  * the loader itself
 131  */
 132 static int load_misc_binary(struct linux_binprm *bprm)
 133 {
 134         Node *fmt;
 135         struct file *interp_file = NULL;
 136         int retval;
 137         int fd_binary = -1;
 138
 139         retval = -ENOEXEC;
 140         if (!enabled)
 141                 return retval;
 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                 dget(fmt->dentry);
 148         read_unlock(&entries_lock);
 149         if (!fmt)
 150                 return retval;
 151
 152         /* Need to be able to load the file after exec */
 153         retval = -ENOENT;
 154         if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 155                 goto ret;
 156
 157         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 158                 retval = remove_arg_zero(bprm);
 159                 if (retval)
 160                         goto ret;
 161         }
 162
 163         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 164
 165                 /* if the binary should be opened on behalf of the
 166                  * interpreter than keep it open and assign descriptor
 167                  * to it
 168                  */
 169                 fd_binary = get_unused_fd_flags(0);
 170                 if (fd_binary < 0) {
 171                         retval = fd_binary;
 172                         goto ret;
 173                 }
 174                 fd_install(fd_binary, bprm->file);
 175
 176                 /* if the binary is not readable than enforce mm->dumpable=0
 177                    regardless of the interpreter's permissions */
 178                 would_dump(bprm, bprm->file);
 179
 180                 allow_write_access(bprm->file);
 181                 bprm->file = NULL;
 182
 183                 /* mark the bprm that fd should be passed to interp */
 184                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 185                 bprm->interp_data = fd_binary;
 186
 187         } else {
 188                 allow_write_access(bprm->file);
 189                 fput(bprm->file);
 190                 bprm->file = NULL;
 191         }
 192         /* make argv[1] be the path to the binary */
 193         retval = copy_strings_kernel(1, &bprm->interp, bprm);
 194         if (retval < 0)
 195                 goto error;
 196         bprm->argc++;
 197
 198         /* add the interp as argv[0] */
 199         retval = copy_strings_kernel(1, &fmt->interpreter, bprm);
 200         if (retval < 0)
 201                 goto error;
 202         bprm->argc++;
 203
 204         /* Update interp in case binfmt_script needs it. */
 205         retval = bprm_change_interp(fmt->interpreter, bprm);
 206         if (retval < 0)
 207                 goto error;
 208
 209         if (fmt->flags & MISC_FMT_OPEN_FILE) {
 210                 interp_file = file_clone_open(fmt->interp_file);
 211                 if (!IS_ERR(interp_file))
 212                         deny_write_access(interp_file);
 213         } else {
 214                 interp_file = open_exec(fmt->interpreter);
 215         }
 216         retval = PTR_ERR(interp_file);
 217         if (IS_ERR(interp_file))
 218                 goto error;
 219
 220         bprm->file = interp_file;
 221         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 222                 loff_t pos = 0;
 223
 224                 /*
 225                  * No need to call prepare_binprm(), it's already been
 226                  * done.  bprm->buf is stale, update from interp_file.
 227                  */
 228                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 229                 retval = kernel_read(bprm->file, bprm->buf, BINPRM_BUF_SIZE,
 230                                 &pos);
 231         } else
 232                 retval = prepare_binprm(bprm);
 233
 234         if (retval < 0)
 235                 goto error;
 236
 237         retval = search_binary_handler(bprm);
 238         if (retval < 0)
 239                 goto error;
 240
 241 ret:
 242         dput(fmt->dentry);
 243         return retval;
 244 error:
 245         if (fd_binary > 0)
 246                 ksys_close(fd_binary);
 247         bprm->interp_flags = 0;
 248         bprm->interp_data = 0;
 249         goto ret;
 250 }
 251
 252 /* Command parsers */
 253
 254 /*
 255  * parses and copies one argument enclosed in del from *sp to *dp,
 256  * recognising the \x special.
 257  * returns pointer to the copied argument or NULL in case of an
 258  * error (and sets err) or null argument length.
 259  */
 260 static char *scanarg(char *s, char del)
 261 {
 262         char c;
 263
 264         while ((c = *s++) != del) {
 265                 if (c == '\\' && *s == 'x') {
 266                         s++;
 267                         if (!isxdigit(*s++))
 268                                 return NULL;
 269                         if (!isxdigit(*s++))
 270                                 return NULL;
 271                 }
 272         }
 273         s[-1] ='\0';
 274         return s;
 275 }
 276
 277 static char *check_special_flags(char *sfs, Node *e)
 278 {
 279         char *p = sfs;
 280         int cont = 1;
 281
 282         /* special flags */
 283         while (cont) {
 284                 switch (*p) {
 285                 case 'P':
 286                         pr_debug("register: flag: P (preserve argv0)\n");
 287                         p++;
 288                         e->flags |= MISC_FMT_PRESERVE_ARGV0;
 289                         break;
 290                 case 'O':
 291                         pr_debug("register: flag: O (open binary)\n");
 292                         p++;
 293                         e->flags |= MISC_FMT_OPEN_BINARY;
 294                         break;
 295                 case 'C':
 296                         pr_debug("register: flag: C (preserve creds)\n");
 297                         p++;
 298                         /* this flags also implies the
 299                            open-binary flag */
 300                         e->flags |= (MISC_FMT_CREDENTIALS |
 301                                         MISC_FMT_OPEN_BINARY);
 302                         break;
 303                 case 'F':
 304                         pr_debug("register: flag: F: open interpreter file now\n");
 305                         p++;
 306                         e->flags |= MISC_FMT_OPEN_FILE;
 307                         break;
 308                 default:
 309                         cont = 0;
 310                 }
 311         }
 312
 313         return p;
 314 }
 315
 316 /*
 317  * This registers a new binary format, it recognises the syntax
 318  * ':name:type:offset:magic:mask:interpreter:flags'
 319  * where the ':' is the IFS, that can be chosen with the first char
 320  */
 321 static Node *create_entry(const char __user *buffer, size_t count)
 322 {
 323         Node *e;
 324         int memsize, err;
 325         char *buf, *p;
 326         char del;
 327
 328         pr_debug("register: received %zu bytes\n", count);
 329
 330         /* some sanity checks */
 331         err = -EINVAL;
 332         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 333                 goto out;
 334
 335         err = -ENOMEM;
 336         memsize = sizeof(Node) + count + 8;
 337         e = kmalloc(memsize, GFP_KERNEL);
 338         if (!e)
 339                 goto out;
 340
 341         p = buf = (char *)e + sizeof(Node);
 342
 343         memset(e, 0, sizeof(Node));
 344         if (copy_from_user(buf, buffer, count))
 345                 goto efault;
 346
 347         del = *p++;     /* delimeter */
 348
 349         pr_debug("register: delim: %#x {%c}\n", del, del);
 350
 351         /* Pad the buffer with the delim to simplify parsing below. */
 352         memset(buf + count, del, 8);
 353
 354         /* Parse the 'name' field. */
 355         e->name = p;
 356         p = strchr(p, del);
 357         if (!p)
 358                 goto einval;
 359         *p++ = '\0';
 360         if (!e->name[0] ||
 361             !strcmp(e->name, ".") ||
 362             !strcmp(e->name, "..") ||
 363             strchr(e->name, '/'))
 364                 goto einval;
 365
 366         pr_debug("register: name: {%s}\n", e->name);
 367
 368         /* Parse the 'type' field. */
 369         switch (*p++) {
 370         case 'E':
 371                 pr_debug("register: type: E (extension)\n");
 372                 e->flags = 1 << Enabled;
 373                 break;
 374         case 'M':
 375                 pr_debug("register: type: M (magic)\n");
 376                 e->flags = (1 << Enabled) | (1 << Magic);
 377                 break;
 378         default:
 379                 goto einval;
 380         }
 381         if (*p++ != del)
 382                 goto einval;
 383
 384         if (test_bit(Magic, &e->flags)) {
 385                 /* Handle the 'M' (magic) format. */
 386                 char *s;
 387
 388                 /* Parse the 'offset' field. */
 389                 s = strchr(p, del);
 390                 if (!s)
 391                         goto einval;
 392                 *s = '\0';
 393                 if (p != s) {
 394                         int r = kstrtoint(p, 10, &e->offset);
 395                         if (r != 0 || e->offset < 0)
 396                                 goto einval;
 397                 }
 398                 p = s;
 399                 if (*p++)
 400                         goto einval;
 401                 pr_debug("register: offset: %#x\n", e->offset);
 402
 403                 /* Parse the 'magic' field. */
 404                 e->magic = p;
 405                 p = scanarg(p, del);
 406                 if (!p)
 407                         goto einval;
 408                 if (!e->magic[0])
 409                         goto einval;
 410                 if (USE_DEBUG)
 411                         print_hex_dump_bytes(
 412                                 KBUILD_MODNAME ": register: magic[raw]: ",
 413                                 DUMP_PREFIX_NONE, e->magic, p - e->magic);
 414
 415                 /* Parse the 'mask' field. */
 416                 e->mask = p;
 417                 p = scanarg(p, del);
 418                 if (!p)
 419                         goto einval;
 420                 if (!e->mask[0]) {
 421                         e->mask = NULL;
 422                         pr_debug("register:  mask[raw]: none\n");
 423                 } else if (USE_DEBUG)
 424                         print_hex_dump_bytes(
 425                                 KBUILD_MODNAME ": register:  mask[raw]: ",
 426                                 DUMP_PREFIX_NONE, e->mask, p - e->mask);
 427
 428                 /*
 429                  * Decode the magic & mask fields.
 430                  * Note: while we might have accepted embedded NUL bytes from
 431                  * above, the unescape helpers here will stop at the first one
 432                  * it encounters.
 433                  */
 434                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 435                 if (e->mask &&
 436                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 437                         goto einval;
 438                 if (e->size > BINPRM_BUF_SIZE ||
 439                     BINPRM_BUF_SIZE - e->size < e->offset)
 440                         goto einval;
 441                 pr_debug("register: magic/mask length: %i\n", e->size);
 442                 if (USE_DEBUG) {
 443                         print_hex_dump_bytes(
 444                                 KBUILD_MODNAME ": register: magic[decoded]: ",
 445                                 DUMP_PREFIX_NONE, e->magic, e->size);
 446
 447                         if (e->mask) {
 448                                 int i;
 449                                 char *masked = kmalloc(e->size, GFP_KERNEL);
 450
 451                                 print_hex_dump_bytes(
 452                                         KBUILD_MODNAME ": register:  mask[decoded]: ",
 453                                         DUMP_PREFIX_NONE, e->mask, e->size);
 454
 455                                 if (masked) {
 456                                         for (i = 0; i < e->size; ++i)
 457                                                 masked[i] = e->magic[i] & e->mask[i];
 458                                         print_hex_dump_bytes(
 459                                                 KBUILD_MODNAME ": register:  magic[masked]: ",
 460                                                 DUMP_PREFIX_NONE, masked, e->size);
 461
 462                                         kfree(masked);
 463                                 }
 464                         }
 465                 }
 466         } else {
 467                 /* Handle the 'E' (extension) format. */
 468
 469                 /* Skip the 'offset' field. */
 470                 p = strchr(p, del);
 471                 if (!p)
 472                         goto einval;
 473                 *p++ = '\0';
 474
 475                 /* Parse the 'magic' field. */
 476                 e->magic = p;
 477                 p = strchr(p, del);
 478                 if (!p)
 479                         goto einval;
 480                 *p++ = '\0';
 481                 if (!e->magic[0] || strchr(e->magic, '/'))
 482                         goto einval;
 483                 pr_debug("register: extension: {%s}\n", e->magic);
 484
 485                 /* Skip the 'mask' field. */
 486                 p = strchr(p, del);
 487                 if (!p)
 488                         goto einval;
 489                 *p++ = '\0';
 490         }
 491
 492         /* Parse the 'interpreter' field. */
 493         e->interpreter = p;
 494         p = strchr(p, del);
 495         if (!p)
 496                 goto einval;
 497         *p++ = '\0';
 498         if (!e->interpreter[0])
 499                 goto einval;
 500         pr_debug("register: interpreter: {%s}\n", e->interpreter);
 501
 502         /* Parse the 'flags' field. */
 503         p = check_special_flags(p, e);
 504         if (*p == '\n')
 505                 p++;
 506         if (p != buf + count)
 507                 goto einval;
 508
 509         return e;
 510
 511 out:
 512         return ERR_PTR(err);
 513
 514 efault:
 515         kfree(e);
 516         return ERR_PTR(-EFAULT);
 517 einval:
 518         kfree(e);
 519         return ERR_PTR(-EINVAL);
 520 }
 521
 522 /*
 523  * Set status of entry/binfmt_misc:
 524  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 525  */
 526 static int parse_command(const char __user *buffer, size_t count)
 527 {
 528         char s[4];
 529
 530         if (count > 3)
 531                 return -EINVAL;
 532         if (copy_from_user(s, buffer, count))
 533                 return -EFAULT;
 534         if (!count)
 535                 return 0;
 536         if (s[count - 1] == '\n')
 537                 count--;
 538         if (count == 1 && s[0] == '0')
 539                 return 1;
 540         if (count == 1 && s[0] == '1')
 541                 return 2;
 542         if (count == 2 && s[0] == '-' && s[1] == '1')
 543                 return 3;
 544         return -EINVAL;
 545 }
 546
 547 /* generic stuff */
 548
 549 static void entry_status(Node *e, char *page)
 550 {
 551         char *dp = page;
 552         const char *status = "disabled";
 553
 554         if (test_bit(Enabled, &e->flags))
 555                 status = "enabled";
 556
 557         if (!VERBOSE_STATUS) {
 558                 sprintf(page, "%s\n", status);
 559                 return;
 560         }
 561
 562         dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
 563
 564         /* print the special flags */
 565         dp += sprintf(dp, "flags: ");
 566         if (e->flags & MISC_FMT_PRESERVE_ARGV0)
 567                 *dp++ = 'P';
 568         if (e->flags & MISC_FMT_OPEN_BINARY)
 569                 *dp++ = 'O';
 570         if (e->flags & MISC_FMT_CREDENTIALS)
 571                 *dp++ = 'C';
 572         if (e->flags & MISC_FMT_OPEN_FILE)
 573                 *dp++ = 'F';
 574         *dp++ = '\n';
 575
 576         if (!test_bit(Magic, &e->flags)) {
 577                 sprintf(dp, "extension .%s\n", e->magic);
 578         } else {
 579                 dp += sprintf(dp, "offset %i\nmagic ", e->offset);
 580                 dp = bin2hex(dp, e->magic, e->size);
 581                 if (e->mask) {
 582                         dp += sprintf(dp, "\nmask ");
 583                         dp = bin2hex(dp, e->mask, e->size);
 584                 }
 585                 *dp++ = '\n';
 586                 *dp = '\0';
 587         }
 588 }
 589
 590 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 591 {
 592         struct inode *inode = new_inode(sb);
 593
 594         if (inode) {
 595                 inode->i_ino = get_next_ino();
 596                 inode->i_mode = mode;
 597                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 598                         current_time(inode);
 599         }
 600         return inode;
 601 }
 602
 603 static void bm_evict_inode(struct inode *inode)
 604 {
 605         Node *e = inode->i_private;
 606
 607         if (e && e->flags & MISC_FMT_OPEN_FILE)
 608                 filp_close(e->interp_file, NULL);
 609
 610         clear_inode(inode);
 611         kfree(e);
 612 }
 613
 614 static void kill_node(Node *e)
 615 {
 616         struct dentry *dentry;
 617
 618         write_lock(&entries_lock);
 619         list_del_init(&e->list);
 620         write_unlock(&entries_lock);
 621
 622         dentry = e->dentry;
 623         drop_nlink(d_inode(dentry));
 624         d_drop(dentry);
 625         dput(dentry);
 626         simple_release_fs(&bm_mnt, &entry_count);
 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                 if (!list_empty(&e->list))
 672                         kill_node(e);
 673
 674                 inode_unlock(d_inode(root));
 675                 break;
 676         default:
 677                 return res;
 678         }
 679
 680         return count;
 681 }
 682
 683 static const struct file_operations bm_entry_operations = {
 684         .read           = bm_entry_read,
 685         .write          = bm_entry_write,
 686         .llseek         = default_llseek,
 687 };
 688
 689 /* /register */
 690
 691 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 692                                size_t count, loff_t *ppos)
 693 {
 694         Node *e;
 695         struct inode *inode;
 696         struct super_block *sb = file_inode(file)->i_sb;
 697         struct dentry *root = sb->s_root, *dentry;
 698         int err = 0;
 699
 700         e = create_entry(buffer, count);
 701
 702         if (IS_ERR(e))
 703                 return PTR_ERR(e);
 704
 705         inode_lock(d_inode(root));
 706         dentry = lookup_one_len(e->name, root, strlen(e->name));
 707         err = PTR_ERR(dentry);
 708         if (IS_ERR(dentry))
 709                 goto out;
 710
 711         err = -EEXIST;
 712         if (d_really_is_positive(dentry))
 713                 goto out2;
 714
 715         inode = bm_get_inode(sb, S_IFREG | 0644);
 716
 717         err = -ENOMEM;
 718         if (!inode)
 719                 goto out2;
 720
 721         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 722         if (err) {
 723                 iput(inode);
 724                 inode = NULL;
 725                 goto out2;
 726         }
 727
 728         if (e->flags & MISC_FMT_OPEN_FILE) {
 729                 struct file *f;
 730
 731                 f = open_exec(e->interpreter);
 732                 if (IS_ERR(f)) {
 733                         err = PTR_ERR(f);
 734                         pr_notice("register: failed to install interpreter file %s\n", e->interpreter);
 735                         simple_release_fs(&bm_mnt, &entry_count);
 736                         iput(inode);
 737                         inode = NULL;
 738                         goto out2;
 739                 }
 740                 e->interp_file = f;
 741         }
 742
 743         e->dentry = dget(dentry);
 744         inode->i_private = e;
 745         inode->i_fop = &bm_entry_operations;
 746
 747         d_instantiate(dentry, inode);
 748         write_lock(&entries_lock);
 749         list_add(&e->list, &entries);
 750         write_unlock(&entries_lock);
 751
 752         err = 0;
 753 out2:
 754         dput(dentry);
 755 out:
 756         inode_unlock(d_inode(root));
 757
 758         if (err) {
 759                 kfree(e);
 760                 return err;
 761         }
 762         return count;
 763 }
 764
 765 static const struct file_operations bm_register_operations = {
 766         .write          = bm_register_write,
 767         .llseek         = noop_llseek,
 768 };
 769
 770 /* /status */
 771
 772 static ssize_t
 773 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 774 {
 775         char *s = enabled ? "enabled\n" : "disabled\n";
 776
 777         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 778 }
 779
 780 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 781                 size_t count, loff_t *ppos)
 782 {
 783         int res = parse_command(buffer, count);
 784         struct dentry *root;
 785
 786         switch (res) {
 787         case 1:
 788                 /* Disable all handlers. */
 789                 enabled = 0;
 790                 break;
 791         case 2:
 792                 /* Enable all handlers. */
 793                 enabled = 1;
 794                 break;
 795         case 3:
 796                 /* Delete all handlers. */
 797                 root = file_inode(file)->i_sb->s_root;
 798                 inode_lock(d_inode(root));
 799
 800                 while (!list_empty(&entries))
 801                         kill_node(list_first_entry(&entries, Node, list));
 802
 803                 inode_unlock(d_inode(root));
 804                 break;
 805         default:
 806                 return res;
 807         }
 808
 809         return count;
 810 }
 811
 812 static const struct file_operations bm_status_operations = {
 813         .read           = bm_status_read,
 814         .write          = bm_status_write,
 815         .llseek         = default_llseek,
 816 };
 817
 818 /* Superblock handling */
 819
 820 static const struct super_operations s_ops = {
 821         .statfs         = simple_statfs,
 822         .evict_inode    = bm_evict_inode,
 823 };
 824
 825 static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 826 {
 827         int err;
 828         static const struct tree_descr bm_files[] = {
 829                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 830                 [3] = {"register", &bm_register_operations, S_IWUSR},
 831                 /* last one */ {""}
 832         };
 833
 834         err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 835         if (!err)
 836                 sb->s_op = &s_ops;
 837         return err;
 838 }
 839
 840 static int bm_get_tree(struct fs_context *fc)
 841 {
 842         return get_tree_single(fc, bm_fill_super);
 843 }
 844
 845 static const struct fs_context_operations bm_context_ops = {
 846         .get_tree       = bm_get_tree,
 847 };
 848
 849 static int bm_init_fs_context(struct fs_context *fc)
 850 {
 851         fc->ops = &bm_context_ops;
 852         return 0;
 853 }
 854
 855 static struct linux_binfmt misc_format = {
 856         .module = THIS_MODULE,
 857         .load_binary = load_misc_binary,
 858 };
 859
 860 static struct file_system_type bm_fs_type = {
 861         .owner          = THIS_MODULE,
 862         .name           = "binfmt_misc",
 863         .init_fs_context = bm_init_fs_context,
 864         .kill_sb        = kill_litter_super,
 865 };
 866 MODULE_ALIAS_FS("binfmt_misc");
 867
 868 static int __init init_misc_binfmt(void)
 869 {
 870         int err = register_filesystem(&bm_fs_type);
 871         if (!err)
 872                 insert_binfmt(&misc_format);
 873         return err;
 874 }
 875
 876 static void __exit exit_misc_binfmt(void)
 877 {
 878         unregister_binfmt(&misc_format);
 879         unregister_filesystem(&bm_fs_type);
 880 }
 881
 882 core_initcall(init_misc_binfmt);
 883 module_exit(exit_misc_binfmt);
 884 MODULE_LICENSE("GPL");