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