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