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         bprm->interp = iname;   /* for binfmt_script */
 176
 177         interp_file = open_exec (iname);
 178         retval = PTR_ERR (interp_file);
 179         if (IS_ERR (interp_file))
 180                 goto _error;
 181
 182         bprm->file = interp_file;
 183         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 184                 /*
 185                  * No need to call prepare_binprm(), it's already been
 186                  * done.  bprm->buf is stale, update from interp_file.
 187                  */
 188                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 189                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 190         } else
 191                 retval = prepare_binprm (bprm);
 192
 193         if (retval < 0)
 194                 goto _error;
 195
 196         retval = search_binary_handler(bprm);
 197         if (retval < 0)
 198                 goto _error;
 199
 200 _ret:
 201         return retval;
 202 _error:
 203         if (fd_binary > 0)
 204                 sys_close(fd_binary);
 205         bprm->interp_flags = 0;
 206         bprm->interp_data = 0;
 207         goto _ret;
 208 }
 209
 210 /* Command parsers */
 211
 212 /*
 213  * parses and copies one argument enclosed in del from *sp to *dp,
 214  * recognising the \x special.
 215  * returns pointer to the copied argument or NULL in case of an
 216  * error (and sets err) or null argument length.
 217  */
 218 static char *scanarg(char *s, char del)
 219 {
 220         char c;
 221
 222         while ((c = *s++) != del) {
 223                 if (c == '\\' && *s == 'x') {
 224                         s++;
 225                         if (!isxdigit(*s++))
 226                                 return NULL;
 227                         if (!isxdigit(*s++))
 228                                 return NULL;
 229                 }
 230         }
 231         return s;
 232 }
 233
 234 static int unquote(char *from)
 235 {
 236         char c = 0, *s = from, *p = from;
 237
 238         while ((c = *s++) != '\0') {
 239                 if (c == '\\' && *s == 'x') {
 240                         s++;
 241                         c = toupper(*s++);
 242                         *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
 243                         c = toupper(*s++);
 244                         *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
 245                         continue;
 246                 }
 247                 *p++ = c;
 248         }
 249         return p - from;
 250 }
 251
 252 static char * check_special_flags (char * sfs, Node * e)
 253 {
 254         char * p = sfs;
 255         int cont = 1;
 256
 257         /* special flags */
 258         while (cont) {
 259                 switch (*p) {
 260                         case 'P':
 261                                 p++;
 262                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 263                                 break;
 264                         case 'O':
 265                                 p++;
 266                                 e->flags |= MISC_FMT_OPEN_BINARY;
 267                                 break;
 268                         case 'C':
 269                                 p++;
 270                                 /* this flags also implies the
 271                                    open-binary flag */
 272                                 e->flags |= (MISC_FMT_CREDENTIALS |
 273                                                 MISC_FMT_OPEN_BINARY);
 274                                 break;
 275                         default:
 276                                 cont = 0;
 277                 }
 278         }
 279
 280         return p;
 281 }
 282 /*
 283  * This registers a new binary format, it recognises the syntax
 284  * ':name:type:offset:magic:mask:interpreter:flags'
 285  * where the ':' is the IFS, that can be chosen with the first char
 286  */
 287 static Node *create_entry(const char __user *buffer, size_t count)
 288 {
 289         Node *e;
 290         int memsize, err;
 291         char *buf, *p;
 292         char del;
 293
 294         /* some sanity checks */
 295         err = -EINVAL;
 296         if ((count < 11) || (count > 256))
 297                 goto out;
 298
 299         err = -ENOMEM;
 300         memsize = sizeof(Node) + count + 8;
 301         e = kmalloc(memsize, GFP_USER);
 302         if (!e)
 303                 goto out;
 304
 305         p = buf = (char *)e + sizeof(Node);
 306
 307         memset(e, 0, sizeof(Node));
 308         if (copy_from_user(buf, buffer, count))
 309                 goto Efault;
 310
 311         del = *p++;     /* delimeter */
 312
 313         memset(buf+count, del, 8);
 314
 315         e->name = p;
 316         p = strchr(p, del);
 317         if (!p)
 318                 goto Einval;
 319         *p++ = '\0';
 320         if (!e->name[0] ||
 321             !strcmp(e->name, ".") ||
 322             !strcmp(e->name, "..") ||
 323             strchr(e->name, '/'))
 324                 goto Einval;
 325         switch (*p++) {
 326                 case 'E': e->flags = 1<<Enabled; break;
 327                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 328                 default: goto Einval;
 329         }
 330         if (*p++ != del)
 331                 goto Einval;
 332         if (test_bit(Magic, &e->flags)) {
 333                 char *s = strchr(p, del);
 334                 if (!s)
 335                         goto Einval;
 336                 *s++ = '\0';
 337                 e->offset = simple_strtoul(p, &p, 10);
 338                 if (*p++)
 339                         goto Einval;
 340                 e->magic = p;
 341                 p = scanarg(p, del);
 342                 if (!p)
 343                         goto Einval;
 344                 p[-1] = '\0';
 345                 if (!e->magic[0])
 346                         goto Einval;
 347                 e->mask = p;
 348                 p = scanarg(p, del);
 349                 if (!p)
 350                         goto Einval;
 351                 p[-1] = '\0';
 352                 if (!e->mask[0])
 353                         e->mask = NULL;
 354                 e->size = unquote(e->magic);
 355                 if (e->mask && unquote(e->mask) != e->size)
 356                         goto Einval;
 357                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 358                         goto Einval;
 359         } else {
 360                 p = strchr(p, del);
 361                 if (!p)
 362                         goto Einval;
 363                 *p++ = '\0';
 364                 e->magic = p;
 365                 p = strchr(p, del);
 366                 if (!p)
 367                         goto Einval;
 368                 *p++ = '\0';
 369                 if (!e->magic[0] || strchr(e->magic, '/'))
 370                         goto Einval;
 371                 p = strchr(p, del);
 372                 if (!p)
 373                         goto Einval;
 374                 *p++ = '\0';
 375         }
 376         e->interpreter = p;
 377         p = strchr(p, del);
 378         if (!p)
 379                 goto Einval;
 380         *p++ = '\0';
 381         if (!e->interpreter[0])
 382                 goto Einval;
 383
 384
 385         p = check_special_flags (p, e);
 386
 387         if (*p == '\n')
 388                 p++;
 389         if (p != buf + count)
 390                 goto Einval;
 391         return e;
 392
 393 out:
 394         return ERR_PTR(err);
 395
 396 Efault:
 397         kfree(e);
 398         return ERR_PTR(-EFAULT);
 399 Einval:
 400         kfree(e);
 401         return ERR_PTR(-EINVAL);
 402 }
 403
 404 /*
 405  * Set status of entry/binfmt_misc:
 406  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 407  */
 408 static int parse_command(const char __user *buffer, size_t count)
 409 {
 410         char s[4];
 411
 412         if (!count)
 413                 return 0;
 414         if (count > 3)
 415                 return -EINVAL;
 416         if (copy_from_user(s, buffer, count))
 417                 return -EFAULT;
 418         if (s[count-1] == '\n')
 419                 count--;
 420         if (count == 1 && s[0] == '0')
 421                 return 1;
 422         if (count == 1 && s[0] == '1')
 423                 return 2;
 424         if (count == 2 && s[0] == '-' && s[1] == '1')
 425                 return 3;
 426         return -EINVAL;
 427 }
 428
 429 /* generic stuff */
 430
 431 static void entry_status(Node *e, char *page)
 432 {
 433         char *dp;
 434         char *status = "disabled";
 435         const char * flags = "flags: ";
 436
 437         if (test_bit(Enabled, &e->flags))
 438                 status = "enabled";
 439
 440         if (!VERBOSE_STATUS) {
 441                 sprintf(page, "%s\n", status);
 442                 return;
 443         }
 444
 445         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 446         dp = page + strlen(page);
 447
 448         /* print the special flags */
 449         sprintf (dp, "%s", flags);
 450         dp += strlen (flags);
 451         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 452                 *dp ++ = 'P';
 453         }
 454         if (e->flags & MISC_FMT_OPEN_BINARY) {
 455                 *dp ++ = 'O';
 456         }
 457         if (e->flags & MISC_FMT_CREDENTIALS) {
 458                 *dp ++ = 'C';
 459         }
 460         *dp ++ = '\n';
 461
 462
 463         if (!test_bit(Magic, &e->flags)) {
 464                 sprintf(dp, "extension .%s\n", e->magic);
 465         } else {
 466                 int i;
 467
 468                 sprintf(dp, "offset %i\nmagic ", e->offset);
 469                 dp = page + strlen(page);
 470                 for (i = 0; i < e->size; i++) {
 471                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 472                         dp += 2;
 473                 }
 474                 if (e->mask) {
 475                         sprintf(dp, "\nmask ");
 476                         dp += 6;
 477                         for (i = 0; i < e->size; i++) {
 478                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 479                                 dp += 2;
 480                         }
 481                 }
 482                 *dp++ = '\n';
 483                 *dp = '\0';
 484         }
 485 }
 486
 487 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 488 {
 489         struct inode * inode = new_inode(sb);
 490
 491         if (inode) {
 492                 inode->i_ino = get_next_ino();
 493                 inode->i_mode = mode;
 494                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 495                         current_fs_time(inode->i_sb);
 496         }
 497         return inode;
 498 }
 499
 500 static void bm_evict_inode(struct inode *inode)
 501 {
 502         clear_inode(inode);
 503         kfree(inode->i_private);
 504 }
 505
 506 static void kill_node(Node *e)
 507 {
 508         struct dentry *dentry;
 509
 510         write_lock(&entries_lock);
 511         dentry = e->dentry;
 512         if (dentry) {
 513                 list_del_init(&e->list);
 514                 e->dentry = NULL;
 515         }
 516         write_unlock(&entries_lock);
 517
 518         if (dentry) {
 519                 drop_nlink(dentry->d_inode);
 520                 d_drop(dentry);
 521                 dput(dentry);
 522                 simple_release_fs(&bm_mnt, &entry_count);
 523         }
 524 }
 525
 526 /* /<entry> */
 527
 528 static ssize_t
 529 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 530 {
 531         Node *e = file->f_path.dentry->d_inode->i_private;
 532         ssize_t res;
 533         char *page;
 534
 535         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 536                 return -ENOMEM;
 537
 538         entry_status(e, page);
 539
 540         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 541
 542         free_page((unsigned long) page);
 543         return res;
 544 }
 545
 546 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 547                                 size_t count, loff_t *ppos)
 548 {
 549         struct dentry *root;
 550         Node *e = file->f_path.dentry->d_inode->i_private;
 551         int res = parse_command(buffer, count);
 552
 553         switch (res) {
 554                 case 1: clear_bit(Enabled, &e->flags);
 555                         break;
 556                 case 2: set_bit(Enabled, &e->flags);
 557                         break;
 558                 case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 559                         mutex_lock(&root->d_inode->i_mutex);
 560
 561                         kill_node(e);
 562
 563                         mutex_unlock(&root->d_inode->i_mutex);
 564                         dput(root);
 565                         break;
 566                 default: return res;
 567         }
 568         return count;
 569 }
 570
 571 static const struct file_operations bm_entry_operations = {
 572         .read           = bm_entry_read,
 573         .write          = bm_entry_write,
 574         .llseek         = default_llseek,
 575 };
 576
 577 /* /register */
 578
 579 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 580                                size_t count, loff_t *ppos)
 581 {
 582         Node *e;
 583         struct inode *inode;
 584         struct dentry *root, *dentry;
 585         struct super_block *sb = file->f_path.dentry->d_sb;
 586         int err = 0;
 587
 588         e = create_entry(buffer, count);
 589
 590         if (IS_ERR(e))
 591                 return PTR_ERR(e);
 592
 593         root = dget(sb->s_root);
 594         mutex_lock(&root->d_inode->i_mutex);
 595         dentry = lookup_one_len(e->name, root, strlen(e->name));
 596         err = PTR_ERR(dentry);
 597         if (IS_ERR(dentry))
 598                 goto out;
 599
 600         err = -EEXIST;
 601         if (dentry->d_inode)
 602                 goto out2;
 603
 604         inode = bm_get_inode(sb, S_IFREG | 0644);
 605
 606         err = -ENOMEM;
 607         if (!inode)
 608                 goto out2;
 609
 610         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 611         if (err) {
 612                 iput(inode);
 613                 inode = NULL;
 614                 goto out2;
 615         }
 616
 617         e->dentry = dget(dentry);
 618         inode->i_private = e;
 619         inode->i_fop = &bm_entry_operations;
 620
 621         d_instantiate(dentry, inode);
 622         write_lock(&entries_lock);
 623         list_add(&e->list, &entries);
 624         write_unlock(&entries_lock);
 625
 626         err = 0;
 627 out2:
 628         dput(dentry);
 629 out:
 630         mutex_unlock(&root->d_inode->i_mutex);
 631         dput(root);
 632
 633         if (err) {
 634                 kfree(e);
 635                 return -EINVAL;
 636         }
 637         return count;
 638 }
 639
 640 static const struct file_operations bm_register_operations = {
 641         .write          = bm_register_write,
 642         .llseek         = noop_llseek,
 643 };
 644
 645 /* /status */
 646
 647 static ssize_t
 648 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 649 {
 650         char *s = enabled ? "enabled\n" : "disabled\n";
 651
 652         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 653 }
 654
 655 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 656                 size_t count, loff_t *ppos)
 657 {
 658         int res = parse_command(buffer, count);
 659         struct dentry *root;
 660
 661         switch (res) {
 662                 case 1: enabled = 0; break;
 663                 case 2: enabled = 1; break;
 664                 case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 665                         mutex_lock(&root->d_inode->i_mutex);
 666
 667                         while (!list_empty(&entries))
 668                                 kill_node(list_entry(entries.next, Node, list));
 669
 670                         mutex_unlock(&root->d_inode->i_mutex);
 671                         dput(root);
 672                 default: return res;
 673         }
 674         return count;
 675 }
 676
 677 static const struct file_operations bm_status_operations = {
 678         .read           = bm_status_read,
 679         .write          = bm_status_write,
 680         .llseek         = default_llseek,
 681 };
 682
 683 /* Superblock handling */
 684
 685 static const struct super_operations s_ops = {
 686         .statfs         = simple_statfs,
 687         .evict_inode    = bm_evict_inode,
 688 };
 689
 690 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 691 {
 692         static struct tree_descr bm_files[] = {
 693                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 694                 [3] = {"register", &bm_register_operations, S_IWUSR},
 695                 /* last one */ {""}
 696         };
 697         int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 698         if (!err)
 699                 sb->s_op = &s_ops;
 700         return err;
 701 }
 702
 703 static struct dentry *bm_mount(struct file_system_type *fs_type,
 704         int flags, const char *dev_name, void *data)
 705 {
 706         return mount_single(fs_type, flags, data, bm_fill_super);
 707 }
 708
 709 static struct linux_binfmt misc_format = {
 710         .module = THIS_MODULE,
 711         .load_binary = load_misc_binary,
 712 };
 713
 714 static struct file_system_type bm_fs_type = {
 715         .owner          = THIS_MODULE,
 716         .name           = "binfmt_misc",
 717         .mount          = bm_mount,
 718         .kill_sb        = kill_litter_super,
 719 };
 720
 721 static int __init init_misc_binfmt(void)
 722 {
 723         int err = register_filesystem(&bm_fs_type);
 724         if (!err)
 725                 insert_binfmt(&misc_format);
 726         return err;
 727 }
 728
 729 static void __exit exit_misc_binfmt(void)
 730 {
 731         unregister_binfmt(&misc_format);
 732         unregister_filesystem(&bm_fs_type);
 733 }
 734
 735 core_initcall(init_misc_binfmt);
 736 module_exit(exit_misc_binfmt);
 737 MODULE_LICENSE("GPL");