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. This should obsolete binfmt_java, binfmt_em86 and
   8  *  binfmt_mz.
   9  *
  10  *  1997-04-25 first version
  11  *  [...]
  12  *  1997-05-19 cleanup
  13  *  1997-06-26 hpa: pass the real filename rather than argv[0]
  14  *  1997-06-30 minor cleanup
  15  *  1997-08-09 removed extension stripping, locking cleanup
  16  *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
  17  */
  18
  19 #include <linux/module.h>
  20 #include <linux/init.h>
  21 #include <linux/sched.h>
  22 #include <linux/magic.h>
  23 #include <linux/binfmts.h>
  24 #include <linux/slab.h>
  25 #include <linux/ctype.h>
  26 #include <linux/string_helpers.h>
  27 #include <linux/file.h>
  28 #include <linux/pagemap.h>
  29 #include <linux/namei.h>
  30 #include <linux/mount.h>
  31 #include <linux/syscalls.h>
  32 #include <linux/fs.h>
  33
  34 #include <asm/uaccess.h>
  35
  36 enum {
  37         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  38 };
  39
  40 static LIST_HEAD(entries);
  41 static int enabled = 1;
  42
  43 enum {Enabled, Magic};
  44 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
  45 #define MISC_FMT_OPEN_BINARY (1<<30)
  46 #define MISC_FMT_CREDENTIALS (1<<29)
  47
  48 typedef struct {
  49         struct list_head list;
  50         unsigned long flags;            /* type, status, etc. */
  51         int offset;                     /* offset of magic */
  52         int size;                       /* size of magic/mask */
  53         char *magic;                    /* magic or filename extension */
  54         char *mask;                     /* mask, NULL for exact match */
  55         char *interpreter;              /* filename of interpreter */
  56         char *name;
  57         struct dentry *dentry;
  58 } Node;
  59
  60 static DEFINE_RWLOCK(entries_lock);
  61 static struct file_system_type bm_fs_type;
  62 static struct vfsmount *bm_mnt;
  63 static int entry_count;
  64
  65 /*
  66  * Max length of the register string.  Determined by:
  67  *  - 7 delimiters
  68  *  - name:   ~50 bytes
  69  *  - type:   1 byte
  70  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
  71  *  - magic:  128 bytes (512 in escaped form)
  72  *  - mask:   128 bytes (512 in escaped form)
  73  *  - interp: ~50 bytes
  74  *  - flags:  5 bytes
  75  * Round that up a bit, and then back off to hold the internal data
  76  * (like struct Node).
  77  */
  78 #define MAX_REGISTER_LENGTH 1920
  79
  80 /*
  81  * Check if we support the binfmt
  82  * if we do, return the node, else NULL
  83  * locking is done in load_misc_binary
  84  */
  85 static Node *check_file(struct linux_binprm *bprm)
  86 {
  87         char *p = strrchr(bprm->interp, '.');
  88         struct list_head *l;
  89
  90         list_for_each(l, &entries) {
  91                 Node *e = list_entry(l, Node, list);
  92                 char *s;
  93                 int j;
  94
  95                 if (!test_bit(Enabled, &e->flags))
  96                         continue;
  97
  98                 if (!test_bit(Magic, &e->flags)) {
  99                         if (p && !strcmp(e->magic, p + 1))
 100                                 return e;
 101                         continue;
 102                 }
 103
 104                 s = bprm->buf + e->offset;
 105                 if (e->mask) {
 106                         for (j = 0; j < e->size; j++)
 107                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 108                                         break;
 109                 } else {
 110                         for (j = 0; j < e->size; j++)
 111                                 if ((*s++ ^ e->magic[j]))
 112                                         break;
 113                 }
 114                 if (j == e->size)
 115                         return e;
 116         }
 117         return NULL;
 118 }
 119
 120 /*
 121  * the loader itself
 122  */
 123 static int load_misc_binary(struct linux_binprm *bprm)
 124 {
 125         Node *fmt;
 126         struct file * interp_file = NULL;
 127         char iname[BINPRM_BUF_SIZE];
 128         const char *iname_addr = iname;
 129         int retval;
 130         int fd_binary = -1;
 131
 132         retval = -ENOEXEC;
 133         if (!enabled)
 134                 goto _ret;
 135
 136         /* to keep locking time low, we copy the interpreter string */
 137         read_lock(&entries_lock);
 138         fmt = check_file(bprm);
 139         if (fmt)
 140                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 141         read_unlock(&entries_lock);
 142         if (!fmt)
 143                 goto _ret;
 144
 145         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 146                 retval = remove_arg_zero(bprm);
 147                 if (retval)
 148                         goto _ret;
 149         }
 150
 151         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 152
 153                 /* if the binary should be opened on behalf of the
 154                  * interpreter than keep it open and assign descriptor
 155                  * to it */
 156                 fd_binary = get_unused_fd();
 157                 if (fd_binary < 0) {
 158                         retval = fd_binary;
 159                         goto _ret;
 160                 }
 161                 fd_install(fd_binary, bprm->file);
 162
 163                 /* if the binary is not readable than enforce mm->dumpable=0
 164                    regardless of the interpreter's permissions */
 165                 would_dump(bprm, bprm->file);
 166
 167                 allow_write_access(bprm->file);
 168                 bprm->file = NULL;
 169
 170                 /* mark the bprm that fd should be passed to interp */
 171                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 172                 bprm->interp_data = fd_binary;
 173
 174         } else {
 175                 allow_write_access(bprm->file);
 176                 fput(bprm->file);
 177                 bprm->file = NULL;
 178         }
 179         /* make argv[1] be the path to the binary */
 180         retval = copy_strings_kernel (1, &bprm->interp, bprm);
 181         if (retval < 0)
 182                 goto _error;
 183         bprm->argc++;
 184
 185         /* add the interp as argv[0] */
 186         retval = copy_strings_kernel (1, &iname_addr, bprm);
 187         if (retval < 0)
 188                 goto _error;
 189         bprm->argc ++;
 190
 191         /* Update interp in case binfmt_script needs it. */
 192         retval = bprm_change_interp(iname, bprm);
 193         if (retval < 0)
 194                 goto _error;
 195
 196         interp_file = open_exec (iname);
 197         retval = PTR_ERR (interp_file);
 198         if (IS_ERR (interp_file))
 199                 goto _error;
 200
 201         bprm->file = interp_file;
 202         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 203                 /*
 204                  * No need to call prepare_binprm(), it's already been
 205                  * done.  bprm->buf is stale, update from interp_file.
 206                  */
 207                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 208                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 209         } else
 210                 retval = prepare_binprm (bprm);
 211
 212         if (retval < 0)
 213                 goto _error;
 214
 215         retval = search_binary_handler(bprm);
 216         if (retval < 0)
 217                 goto _error;
 218
 219 _ret:
 220         return retval;
 221 _error:
 222         if (fd_binary > 0)
 223                 sys_close(fd_binary);
 224         bprm->interp_flags = 0;
 225         bprm->interp_data = 0;
 226         goto _ret;
 227 }
 228
 229 /* Command parsers */
 230
 231 /*
 232  * parses and copies one argument enclosed in del from *sp to *dp,
 233  * recognising the \x special.
 234  * returns pointer to the copied argument or NULL in case of an
 235  * error (and sets err) or null argument length.
 236  */
 237 static char *scanarg(char *s, char del)
 238 {
 239         char c;
 240
 241         while ((c = *s++) != del) {
 242                 if (c == '\\' && *s == 'x') {
 243                         s++;
 244                         if (!isxdigit(*s++))
 245                                 return NULL;
 246                         if (!isxdigit(*s++))
 247                                 return NULL;
 248                 }
 249         }
 250         return s;
 251 }
 252
 253 static char * check_special_flags (char * sfs, Node * e)
 254 {
 255         char * p = sfs;
 256         int cont = 1;
 257
 258         /* special flags */
 259         while (cont) {
 260                 switch (*p) {
 261                         case 'P':
 262                                 p++;
 263                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 264                                 break;
 265                         case 'O':
 266                                 p++;
 267                                 e->flags |= MISC_FMT_OPEN_BINARY;
 268                                 break;
 269                         case 'C':
 270                                 p++;
 271                                 /* this flags also implies the
 272                                    open-binary flag */
 273                                 e->flags |= (MISC_FMT_CREDENTIALS |
 274                                                 MISC_FMT_OPEN_BINARY);
 275                                 break;
 276                         default:
 277                                 cont = 0;
 278                 }
 279         }
 280
 281         return p;
 282 }
 283 /*
 284  * This registers a new binary format, it recognises the syntax
 285  * ':name:type:offset:magic:mask:interpreter:flags'
 286  * where the ':' is the IFS, that can be chosen with the first char
 287  */
 288 static Node *create_entry(const char __user *buffer, size_t count)
 289 {
 290         Node *e;
 291         int memsize, err;
 292         char *buf, *p;
 293         char del;
 294
 295         /* some sanity checks */
 296         err = -EINVAL;
 297         if ((count < 11) || (count > MAX_REGISTER_LENGTH))
 298                 goto out;
 299
 300         err = -ENOMEM;
 301         memsize = sizeof(Node) + count + 8;
 302         e = kmalloc(memsize, GFP_USER);
 303         if (!e)
 304                 goto out;
 305
 306         p = buf = (char *)e + sizeof(Node);
 307
 308         memset(e, 0, sizeof(Node));
 309         if (copy_from_user(buf, buffer, count))
 310                 goto Efault;
 311
 312         del = *p++;     /* delimeter */
 313
 314         memset(buf+count, del, 8);
 315
 316         e->name = p;
 317         p = strchr(p, del);
 318         if (!p)
 319                 goto Einval;
 320         *p++ = '\0';
 321         if (!e->name[0] ||
 322             !strcmp(e->name, ".") ||
 323             !strcmp(e->name, "..") ||
 324             strchr(e->name, '/'))
 325                 goto Einval;
 326         switch (*p++) {
 327                 case 'E': e->flags = 1<<Enabled; break;
 328                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 329                 default: goto Einval;
 330         }
 331         if (*p++ != del)
 332                 goto Einval;
 333         if (test_bit(Magic, &e->flags)) {
 334                 char *s = strchr(p, del);
 335                 if (!s)
 336                         goto Einval;
 337                 *s++ = '\0';
 338                 e->offset = simple_strtoul(p, &p, 10);
 339                 if (*p++)
 340                         goto Einval;
 341                 e->magic = p;
 342                 p = scanarg(p, del);
 343                 if (!p)
 344                         goto Einval;
 345                 p[-1] = '\0';
 346                 if (!e->magic[0])
 347                         goto Einval;
 348                 e->mask = p;
 349                 p = scanarg(p, del);
 350                 if (!p)
 351                         goto Einval;
 352                 p[-1] = '\0';
 353                 if (!e->mask[0])
 354                         e->mask = NULL;
 355                 e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 356                 if (e->mask &&
 357                     string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 358                         goto Einval;
 359                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 360                         goto Einval;
 361         } else {
 362                 p = strchr(p, del);
 363                 if (!p)
 364                         goto Einval;
 365                 *p++ = '\0';
 366                 e->magic = p;
 367                 p = strchr(p, del);
 368                 if (!p)
 369                         goto Einval;
 370                 *p++ = '\0';
 371                 if (!e->magic[0] || strchr(e->magic, '/'))
 372                         goto Einval;
 373                 p = strchr(p, del);
 374                 if (!p)
 375                         goto Einval;
 376                 *p++ = '\0';
 377         }
 378         e->interpreter = p;
 379         p = strchr(p, del);
 380         if (!p)
 381                 goto Einval;
 382         *p++ = '\0';
 383         if (!e->interpreter[0])
 384                 goto Einval;
 385
 386
 387         p = check_special_flags (p, e);
 388
 389         if (*p == '\n')
 390                 p++;
 391         if (p != buf + count)
 392                 goto Einval;
 393         return e;
 394
 395 out:
 396         return ERR_PTR(err);
 397
 398 Efault:
 399         kfree(e);
 400         return ERR_PTR(-EFAULT);
 401 Einval:
 402         kfree(e);
 403         return ERR_PTR(-EINVAL);
 404 }
 405
 406 /*
 407  * Set status of entry/binfmt_misc:
 408  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 409  */
 410 static int parse_command(const char __user *buffer, size_t count)
 411 {
 412         char s[4];
 413
 414         if (count > 3)
 415                 return -EINVAL;
 416         if (copy_from_user(s, buffer, count))
 417                 return -EFAULT;
 418         if (!count)
 419                 return 0;
 420         if (s[count-1] == '\n')
 421                 count--;
 422         if (count == 1 && s[0] == '0')
 423                 return 1;
 424         if (count == 1 && s[0] == '1')
 425                 return 2;
 426         if (count == 2 && s[0] == '-' && s[1] == '1')
 427                 return 3;
 428         return -EINVAL;
 429 }
 430
 431 /* generic stuff */
 432
 433 static void entry_status(Node *e, char *page)
 434 {
 435         char *dp;
 436         char *status = "disabled";
 437         const char * flags = "flags: ";
 438
 439         if (test_bit(Enabled, &e->flags))
 440                 status = "enabled";
 441
 442         if (!VERBOSE_STATUS) {
 443                 sprintf(page, "%s\n", status);
 444                 return;
 445         }
 446
 447         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 448         dp = page + strlen(page);
 449
 450         /* print the special flags */
 451         sprintf (dp, "%s", flags);
 452         dp += strlen (flags);
 453         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 454                 *dp ++ = 'P';
 455         }
 456         if (e->flags & MISC_FMT_OPEN_BINARY) {
 457                 *dp ++ = 'O';
 458         }
 459         if (e->flags & MISC_FMT_CREDENTIALS) {
 460                 *dp ++ = 'C';
 461         }
 462         *dp ++ = '\n';
 463
 464
 465         if (!test_bit(Magic, &e->flags)) {
 466                 sprintf(dp, "extension .%s\n", e->magic);
 467         } else {
 468                 int i;
 469
 470                 sprintf(dp, "offset %i\nmagic ", e->offset);
 471                 dp = page + strlen(page);
 472                 for (i = 0; i < e->size; i++) {
 473                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 474                         dp += 2;
 475                 }
 476                 if (e->mask) {
 477                         sprintf(dp, "\nmask ");
 478                         dp += 6;
 479                         for (i = 0; i < e->size; i++) {
 480                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 481                                 dp += 2;
 482                         }
 483                 }
 484                 *dp++ = '\n';
 485                 *dp = '\0';
 486         }
 487 }
 488
 489 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 490 {
 491         struct inode * inode = new_inode(sb);
 492
 493         if (inode) {
 494                 inode->i_ino = get_next_ino();
 495                 inode->i_mode = mode;
 496                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 497                         current_fs_time(inode->i_sb);
 498         }
 499         return inode;
 500 }
 501
 502 static void bm_evict_inode(struct inode *inode)
 503 {
 504         clear_inode(inode);
 505         kfree(inode->i_private);
 506 }
 507
 508 static void kill_node(Node *e)
 509 {
 510         struct dentry *dentry;
 511
 512         write_lock(&entries_lock);
 513         dentry = e->dentry;
 514         if (dentry) {
 515                 list_del_init(&e->list);
 516                 e->dentry = NULL;
 517         }
 518         write_unlock(&entries_lock);
 519
 520         if (dentry) {
 521                 drop_nlink(dentry->d_inode);
 522                 d_drop(dentry);
 523                 dput(dentry);
 524                 simple_release_fs(&bm_mnt, &entry_count);
 525         }
 526 }
 527
 528 /* /<entry> */
 529
 530 static ssize_t
 531 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 532 {
 533         Node *e = file_inode(file)->i_private;
 534         ssize_t res;
 535         char *page;
 536
 537         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 538                 return -ENOMEM;
 539
 540         entry_status(e, page);
 541
 542         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 543
 544         free_page((unsigned long) page);
 545         return res;
 546 }
 547
 548 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 549                                 size_t count, loff_t *ppos)
 550 {
 551         struct dentry *root;
 552         Node *e = file_inode(file)->i_private;
 553         int res = parse_command(buffer, count);
 554
 555         switch (res) {
 556                 case 1: clear_bit(Enabled, &e->flags);
 557                         break;
 558                 case 2: set_bit(Enabled, &e->flags);
 559                         break;
 560                 case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 561                         mutex_lock(&root->d_inode->i_mutex);
 562
 563                         kill_node(e);
 564
 565                         mutex_unlock(&root->d_inode->i_mutex);
 566                         dput(root);
 567                         break;
 568                 default: return res;
 569         }
 570         return count;
 571 }
 572
 573 static const struct file_operations bm_entry_operations = {
 574         .read           = bm_entry_read,
 575         .write          = bm_entry_write,
 576         .llseek         = default_llseek,
 577 };
 578
 579 /* /register */
 580
 581 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 582                                size_t count, loff_t *ppos)
 583 {
 584         Node *e;
 585         struct inode *inode;
 586         struct dentry *root, *dentry;
 587         struct super_block *sb = file->f_path.dentry->d_sb;
 588         int err = 0;
 589
 590         e = create_entry(buffer, count);
 591
 592         if (IS_ERR(e))
 593                 return PTR_ERR(e);
 594
 595         root = dget(sb->s_root);
 596         mutex_lock(&root->d_inode->i_mutex);
 597         dentry = lookup_one_len(e->name, root, strlen(e->name));
 598         err = PTR_ERR(dentry);
 599         if (IS_ERR(dentry))
 600                 goto out;
 601
 602         err = -EEXIST;
 603         if (dentry->d_inode)
 604                 goto out2;
 605
 606         inode = bm_get_inode(sb, S_IFREG | 0644);
 607
 608         err = -ENOMEM;
 609         if (!inode)
 610                 goto out2;
 611
 612         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 613         if (err) {
 614                 iput(inode);
 615                 inode = NULL;
 616                 goto out2;
 617         }
 618
 619         e->dentry = dget(dentry);
 620         inode->i_private = e;
 621         inode->i_fop = &bm_entry_operations;
 622
 623         d_instantiate(dentry, inode);
 624         write_lock(&entries_lock);
 625         list_add(&e->list, &entries);
 626         write_unlock(&entries_lock);
 627
 628         err = 0;
 629 out2:
 630         dput(dentry);
 631 out:
 632         mutex_unlock(&root->d_inode->i_mutex);
 633         dput(root);
 634
 635         if (err) {
 636                 kfree(e);
 637                 return -EINVAL;
 638         }
 639         return count;
 640 }
 641
 642 static const struct file_operations bm_register_operations = {
 643         .write          = bm_register_write,
 644         .llseek         = noop_llseek,
 645 };
 646
 647 /* /status */
 648
 649 static ssize_t
 650 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 651 {
 652         char *s = enabled ? "enabled\n" : "disabled\n";
 653
 654         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 655 }
 656
 657 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 658                 size_t count, loff_t *ppos)
 659 {
 660         int res = parse_command(buffer, count);
 661         struct dentry *root;
 662
 663         switch (res) {
 664                 case 1: enabled = 0; break;
 665                 case 2: enabled = 1; break;
 666                 case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 667                         mutex_lock(&root->d_inode->i_mutex);
 668
 669                         while (!list_empty(&entries))
 670                                 kill_node(list_entry(entries.next, Node, list));
 671
 672                         mutex_unlock(&root->d_inode->i_mutex);
 673                         dput(root);
 674                         break;
 675                 default: return res;
 676         }
 677         return count;
 678 }
 679
 680 static const struct file_operations bm_status_operations = {
 681         .read           = bm_status_read,
 682         .write          = bm_status_write,
 683         .llseek         = default_llseek,
 684 };
 685
 686 /* Superblock handling */
 687
 688 static const struct super_operations s_ops = {
 689         .statfs         = simple_statfs,
 690         .evict_inode    = bm_evict_inode,
 691 };
 692
 693 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 694 {
 695         static struct tree_descr bm_files[] = {
 696                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 697                 [3] = {"register", &bm_register_operations, S_IWUSR},
 698                 /* last one */ {""}
 699         };
 700         int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 701         if (!err)
 702                 sb->s_op = &s_ops;
 703         return err;
 704 }
 705
 706 static struct dentry *bm_mount(struct file_system_type *fs_type,
 707         int flags, const char *dev_name, void *data)
 708 {
 709         return mount_single(fs_type, flags, data, bm_fill_super);
 710 }
 711
 712 static struct linux_binfmt misc_format = {
 713         .module = THIS_MODULE,
 714         .load_binary = load_misc_binary,
 715 };
 716
 717 static struct file_system_type bm_fs_type = {
 718         .owner          = THIS_MODULE,
 719         .name           = "binfmt_misc",
 720         .mount          = bm_mount,
 721         .kill_sb        = kill_litter_super,
 722 };
 723 MODULE_ALIAS_FS("binfmt_misc");
 724
 725 static int __init init_misc_binfmt(void)
 726 {
 727         int err = register_filesystem(&bm_fs_type);
 728         if (!err)
 729                 insert_binfmt(&misc_format);
 730         return err;
 731 }
 732
 733 static void __exit exit_misc_binfmt(void)
 734 {
 735         unregister_binfmt(&misc_format);
 736         unregister_filesystem(&bm_fs_type);
 737 }
 738
 739 core_initcall(init_misc_binfmt);
 740 module_exit(exit_misc_binfmt);
 741 MODULE_LICENSE("GPL");