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/binfmts.h>
  23 #include <linux/slab.h>
  24 #include <linux/ctype.h>
  25 #include <linux/file.h>
  26 #include <linux/pagemap.h>
  27 #include <linux/namei.h>
  28 #include <linux/mount.h>
  29 #include <linux/syscalls.h>
  30
  31 #include <asm/uaccess.h>
  32
  33 enum {
  34         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  35 };
  36
  37 static LIST_HEAD(entries);
  38 static int enabled = 1;
  39
  40 enum {Enabled, Magic};
  41 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
  42 #define MISC_FMT_OPEN_BINARY (1<<30)
  43 #define MISC_FMT_CREDENTIALS (1<<29)
  44
  45 typedef struct {
  46         struct list_head list;
  47         unsigned long flags;            /* type, status, etc. */
  48         int offset;                     /* offset of magic */
  49         int size;                       /* size of magic/mask */
  50         char *magic;                    /* magic or filename extension */
  51         char *mask;                     /* mask, NULL for exact match */
  52         char *interpreter;              /* filename of interpreter */
  53         char *name;
  54         struct dentry *dentry;
  55 } Node;
  56
  57 static DEFINE_RWLOCK(entries_lock);
  58 static struct file_system_type bm_fs_type;
  59 static struct vfsmount *bm_mnt;
  60 static int entry_count;
  61
  62 /*
  63  * Check if we support the binfmt
  64  * if we do, return the node, else NULL
  65  * locking is done in load_misc_binary
  66  */
  67 static Node *check_file(struct linux_binprm *bprm)
  68 {
  69         char *p = strrchr(bprm->interp, '.');
  70         struct list_head *l;
  71
  72         list_for_each(l, &entries) {
  73                 Node *e = list_entry(l, Node, list);
  74                 char *s;
  75                 int j;
  76
  77                 if (!test_bit(Enabled, &e->flags))
  78                         continue;
  79
  80                 if (!test_bit(Magic, &e->flags)) {
  81                         if (p && !strcmp(e->magic, p + 1))
  82                                 return e;
  83                         continue;
  84                 }
  85
  86                 s = bprm->buf + e->offset;
  87                 if (e->mask) {
  88                         for (j = 0; j < e->size; j++)
  89                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
  90                                         break;
  91                 } else {
  92                         for (j = 0; j < e->size; j++)
  93                                 if ((*s++ ^ e->magic[j]))
  94                                         break;
  95                 }
  96                 if (j == e->size)
  97                         return e;
  98         }
  99         return NULL;
 100 }
 101
 102 /*
 103  * the loader itself
 104  */
 105 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 106 {
 107         Node *fmt;
 108         struct file * interp_file = NULL;
 109         char iname[BINPRM_BUF_SIZE];
 110         char *iname_addr = iname;
 111         int retval;
 112         int fd_binary = -1;
 113
 114         retval = -ENOEXEC;
 115         if (!enabled)
 116                 goto _ret;
 117
 118         /* to keep locking time low, we copy the interpreter string */
 119         read_lock(&entries_lock);
 120         fmt = check_file(bprm);
 121         if (fmt)
 122                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 123         read_unlock(&entries_lock);
 124         if (!fmt)
 125                 goto _ret;
 126
 127         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 128                 retval = remove_arg_zero(bprm);
 129                 if (retval)
 130                         goto _ret;
 131         }
 132
 133         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 134
 135                 /* if the binary should be opened on behalf of the
 136                  * interpreter than keep it open and assign descriptor
 137                  * to it */
 138                 fd_binary = get_unused_fd();
 139                 if (fd_binary < 0) {
 140                         retval = fd_binary;
 141                         goto _ret;
 142                 }
 143                 fd_install(fd_binary, bprm->file);
 144
 145                 /* if the binary is not readable than enforce mm->dumpable=0
 146                    regardless of the interpreter's permissions */
 147                 if (file_permission(bprm->file, MAY_READ))
 148                         bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
 149
 150                 allow_write_access(bprm->file);
 151                 bprm->file = NULL;
 152
 153                 /* mark the bprm that fd should be passed to interp */
 154                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 155                 bprm->interp_data = fd_binary;
 156
 157         } else {
 158                 allow_write_access(bprm->file);
 159                 fput(bprm->file);
 160                 bprm->file = NULL;
 161         }
 162         /* make argv[1] be the path to the binary */
 163         retval = copy_strings_kernel (1, &bprm->interp, bprm);
 164         if (retval < 0)
 165                 goto _error;
 166         bprm->argc++;
 167
 168         /* add the interp as argv[0] */
 169         retval = copy_strings_kernel (1, &iname_addr, bprm);
 170         if (retval < 0)
 171                 goto _error;
 172         bprm->argc ++;
 173
 174         bprm->interp = iname;   /* for binfmt_script */
 175
 176         interp_file = open_exec (iname);
 177         retval = PTR_ERR (interp_file);
 178         if (IS_ERR (interp_file))
 179                 goto _error;
 180
 181         bprm->file = interp_file;
 182         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 183                 /*
 184                  * No need to call prepare_binprm(), it's already been
 185                  * done.  bprm->buf is stale, update from interp_file.
 186                  */
 187                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 188                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 189         } else
 190                 retval = prepare_binprm (bprm);
 191
 192         if (retval < 0)
 193                 goto _error;
 194
 195         retval = search_binary_handler (bprm, regs);
 196         if (retval < 0)
 197                 goto _error;
 198
 199 _ret:
 200         return retval;
 201 _error:
 202         if (fd_binary > 0)
 203                 sys_close(fd_binary);
 204         bprm->interp_flags = 0;
 205         bprm->interp_data = 0;
 206         goto _ret;
 207 }
 208
 209 /* Command parsers */
 210
 211 /*
 212  * parses and copies one argument enclosed in del from *sp to *dp,
 213  * recognising the \x special.
 214  * returns pointer to the copied argument or NULL in case of an
 215  * error (and sets err) or null argument length.
 216  */
 217 static char *scanarg(char *s, char del)
 218 {
 219         char c;
 220
 221         while ((c = *s++) != del) {
 222                 if (c == '\\' && *s == 'x') {
 223                         s++;
 224                         if (!isxdigit(*s++))
 225                                 return NULL;
 226                         if (!isxdigit(*s++))
 227                                 return NULL;
 228                 }
 229         }
 230         return s;
 231 }
 232
 233 static int unquote(char *from)
 234 {
 235         char c = 0, *s = from, *p = from;
 236
 237         while ((c = *s++) != '\0') {
 238                 if (c == '\\' && *s == 'x') {
 239                         s++;
 240                         c = toupper(*s++);
 241                         *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
 242                         c = toupper(*s++);
 243                         *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
 244                         continue;
 245                 }
 246                 *p++ = c;
 247         }
 248         return p - from;
 249 }
 250
 251 static char * check_special_flags (char * sfs, Node * e)
 252 {
 253         char * p = sfs;
 254         int cont = 1;
 255
 256         /* special flags */
 257         while (cont) {
 258                 switch (*p) {
 259                         case 'P':
 260                                 p++;
 261                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 262                                 break;
 263                         case 'O':
 264                                 p++;
 265                                 e->flags |= MISC_FMT_OPEN_BINARY;
 266                                 break;
 267                         case 'C':
 268                                 p++;
 269                                 /* this flags also implies the
 270                                    open-binary flag */
 271                                 e->flags |= (MISC_FMT_CREDENTIALS |
 272                                                 MISC_FMT_OPEN_BINARY);
 273                                 break;
 274                         default:
 275                                 cont = 0;
 276                 }
 277         }
 278
 279         return p;
 280 }
 281 /*
 282  * This registers a new binary format, it recognises the syntax
 283  * ':name:type:offset:magic:mask:interpreter:flags'
 284  * where the ':' is the IFS, that can be chosen with the first char
 285  */
 286 static Node *create_entry(const char __user *buffer, size_t count)
 287 {
 288         Node *e;
 289         int memsize, err;
 290         char *buf, *p;
 291         char del;
 292
 293         /* some sanity checks */
 294         err = -EINVAL;
 295         if ((count < 11) || (count > 256))
 296                 goto out;
 297
 298         err = -ENOMEM;
 299         memsize = sizeof(Node) + count + 8;
 300         e = kmalloc(memsize, GFP_USER);
 301         if (!e)
 302                 goto out;
 303
 304         p = buf = (char *)e + sizeof(Node);
 305
 306         memset(e, 0, sizeof(Node));
 307         if (copy_from_user(buf, buffer, count))
 308                 goto Efault;
 309
 310         del = *p++;     /* delimeter */
 311
 312         memset(buf+count, del, 8);
 313
 314         e->name = p;
 315         p = strchr(p, del);
 316         if (!p)
 317                 goto Einval;
 318         *p++ = '\0';
 319         if (!e->name[0] ||
 320             !strcmp(e->name, ".") ||
 321             !strcmp(e->name, "..") ||
 322             strchr(e->name, '/'))
 323                 goto Einval;
 324         switch (*p++) {
 325                 case 'E': e->flags = 1<<Enabled; break;
 326                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 327                 default: goto Einval;
 328         }
 329         if (*p++ != del)
 330                 goto Einval;
 331         if (test_bit(Magic, &e->flags)) {
 332                 char *s = strchr(p, del);
 333                 if (!s)
 334                         goto Einval;
 335                 *s++ = '\0';
 336                 e->offset = simple_strtoul(p, &p, 10);
 337                 if (*p++)
 338                         goto Einval;
 339                 e->magic = p;
 340                 p = scanarg(p, del);
 341                 if (!p)
 342                         goto Einval;
 343                 p[-1] = '\0';
 344                 if (!e->magic[0])
 345                         goto Einval;
 346                 e->mask = p;
 347                 p = scanarg(p, del);
 348                 if (!p)
 349                         goto Einval;
 350                 p[-1] = '\0';
 351                 if (!e->mask[0])
 352                         e->mask = NULL;
 353                 e->size = unquote(e->magic);
 354                 if (e->mask && unquote(e->mask) != e->size)
 355                         goto Einval;
 356                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 357                         goto Einval;
 358         } else {
 359                 p = strchr(p, del);
 360                 if (!p)
 361                         goto Einval;
 362                 *p++ = '\0';
 363                 e->magic = p;
 364                 p = strchr(p, del);
 365                 if (!p)
 366                         goto Einval;
 367                 *p++ = '\0';
 368                 if (!e->magic[0] || strchr(e->magic, '/'))
 369                         goto Einval;
 370                 p = strchr(p, del);
 371                 if (!p)
 372                         goto Einval;
 373                 *p++ = '\0';
 374         }
 375         e->interpreter = p;
 376         p = strchr(p, del);
 377         if (!p)
 378                 goto Einval;
 379         *p++ = '\0';
 380         if (!e->interpreter[0])
 381                 goto Einval;
 382
 383
 384         p = check_special_flags (p, e);
 385
 386         if (*p == '\n')
 387                 p++;
 388         if (p != buf + count)
 389                 goto Einval;
 390         return e;
 391
 392 out:
 393         return ERR_PTR(err);
 394
 395 Efault:
 396         kfree(e);
 397         return ERR_PTR(-EFAULT);
 398 Einval:
 399         kfree(e);
 400         return ERR_PTR(-EINVAL);
 401 }
 402
 403 /*
 404  * Set status of entry/binfmt_misc:
 405  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 406  */
 407 static int parse_command(const char __user *buffer, size_t count)
 408 {
 409         char s[4];
 410
 411         if (!count)
 412                 return 0;
 413         if (count > 3)
 414                 return -EINVAL;
 415         if (copy_from_user(s, buffer, count))
 416                 return -EFAULT;
 417         if (s[count-1] == '\n')
 418                 count--;
 419         if (count == 1 && s[0] == '0')
 420                 return 1;
 421         if (count == 1 && s[0] == '1')
 422                 return 2;
 423         if (count == 2 && s[0] == '-' && s[1] == '1')
 424                 return 3;
 425         return -EINVAL;
 426 }
 427
 428 /* generic stuff */
 429
 430 static void entry_status(Node *e, char *page)
 431 {
 432         char *dp;
 433         char *status = "disabled";
 434         const char * flags = "flags: ";
 435
 436         if (test_bit(Enabled, &e->flags))
 437                 status = "enabled";
 438
 439         if (!VERBOSE_STATUS) {
 440                 sprintf(page, "%s\n", status);
 441                 return;
 442         }
 443
 444         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 445         dp = page + strlen(page);
 446
 447         /* print the special flags */
 448         sprintf (dp, "%s", flags);
 449         dp += strlen (flags);
 450         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 451                 *dp ++ = 'P';
 452         }
 453         if (e->flags & MISC_FMT_OPEN_BINARY) {
 454                 *dp ++ = 'O';
 455         }
 456         if (e->flags & MISC_FMT_CREDENTIALS) {
 457                 *dp ++ = 'C';
 458         }
 459         *dp ++ = '\n';
 460
 461
 462         if (!test_bit(Magic, &e->flags)) {
 463                 sprintf(dp, "extension .%s\n", e->magic);
 464         } else {
 465                 int i;
 466
 467                 sprintf(dp, "offset %i\nmagic ", e->offset);
 468                 dp = page + strlen(page);
 469                 for (i = 0; i < e->size; i++) {
 470                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 471                         dp += 2;
 472                 }
 473                 if (e->mask) {
 474                         sprintf(dp, "\nmask ");
 475                         dp += 6;
 476                         for (i = 0; i < e->size; i++) {
 477                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 478                                 dp += 2;
 479                         }
 480                 }
 481                 *dp++ = '\n';
 482                 *dp = '\0';
 483         }
 484 }
 485
 486 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 487 {
 488         struct inode * inode = new_inode(sb);
 489
 490         if (inode) {
 491                 inode->i_mode = mode;
 492                 inode->i_uid = 0;
 493                 inode->i_gid = 0;
 494                 inode->i_blocks = 0;
 495                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 496                         current_fs_time(inode->i_sb);
 497         }
 498         return inode;
 499 }
 500
 501 static void bm_clear_inode(struct inode *inode)
 502 {
 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                 dentry->d_inode->i_nlink--;
 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         loff_t pos = *ppos;
 533         ssize_t res;
 534         char *page;
 535         int len;
 536
 537         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 538                 return -ENOMEM;
 539
 540         entry_status(e, page);
 541         len = strlen(page);
 542
 543         res = -EINVAL;
 544         if (pos < 0)
 545                 goto out;
 546         res = 0;
 547         if (pos >= len)
 548                 goto out;
 549         if (len < pos + nbytes)
 550                 nbytes = len - pos;
 551         res = -EFAULT;
 552         if (copy_to_user(buf, page + pos, nbytes))
 553                 goto out;
 554         *ppos = pos + nbytes;
 555         res = nbytes;
 556 out:
 557         free_page((unsigned long) page);
 558         return res;
 559 }
 560
 561 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 562                                 size_t count, loff_t *ppos)
 563 {
 564         struct dentry *root;
 565         Node *e = file->f_path.dentry->d_inode->i_private;
 566         int res = parse_command(buffer, count);
 567
 568         switch (res) {
 569                 case 1: clear_bit(Enabled, &e->flags);
 570                         break;
 571                 case 2: set_bit(Enabled, &e->flags);
 572                         break;
 573                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 574                         mutex_lock(&root->d_inode->i_mutex);
 575
 576                         kill_node(e);
 577
 578                         mutex_unlock(&root->d_inode->i_mutex);
 579                         dput(root);
 580                         break;
 581                 default: return res;
 582         }
 583         return count;
 584 }
 585
 586 static const struct file_operations bm_entry_operations = {
 587         .read           = bm_entry_read,
 588         .write          = bm_entry_write,
 589 };
 590
 591 /* /register */
 592
 593 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 594                                size_t count, loff_t *ppos)
 595 {
 596         Node *e;
 597         struct inode *inode;
 598         struct dentry *root, *dentry;
 599         struct super_block *sb = file->f_path.mnt->mnt_sb;
 600         int err = 0;
 601
 602         e = create_entry(buffer, count);
 603
 604         if (IS_ERR(e))
 605                 return PTR_ERR(e);
 606
 607         root = dget(sb->s_root);
 608         mutex_lock(&root->d_inode->i_mutex);
 609         dentry = lookup_one_len(e->name, root, strlen(e->name));
 610         err = PTR_ERR(dentry);
 611         if (IS_ERR(dentry))
 612                 goto out;
 613
 614         err = -EEXIST;
 615         if (dentry->d_inode)
 616                 goto out2;
 617
 618         inode = bm_get_inode(sb, S_IFREG | 0644);
 619
 620         err = -ENOMEM;
 621         if (!inode)
 622                 goto out2;
 623
 624         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 625         if (err) {
 626                 iput(inode);
 627                 inode = NULL;
 628                 goto out2;
 629         }
 630
 631         e->dentry = dget(dentry);
 632         inode->i_private = e;
 633         inode->i_fop = &bm_entry_operations;
 634
 635         d_instantiate(dentry, inode);
 636         write_lock(&entries_lock);
 637         list_add(&e->list, &entries);
 638         write_unlock(&entries_lock);
 639
 640         err = 0;
 641 out2:
 642         dput(dentry);
 643 out:
 644         mutex_unlock(&root->d_inode->i_mutex);
 645         dput(root);
 646
 647         if (err) {
 648                 kfree(e);
 649                 return -EINVAL;
 650         }
 651         return count;
 652 }
 653
 654 static const struct file_operations bm_register_operations = {
 655         .write          = bm_register_write,
 656 };
 657
 658 /* /status */
 659
 660 static ssize_t
 661 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 662 {
 663         char *s = enabled ? "enabled" : "disabled";
 664
 665         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 666 }
 667
 668 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 669                 size_t count, loff_t *ppos)
 670 {
 671         int res = parse_command(buffer, count);
 672         struct dentry *root;
 673
 674         switch (res) {
 675                 case 1: enabled = 0; break;
 676                 case 2: enabled = 1; break;
 677                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 678                         mutex_lock(&root->d_inode->i_mutex);
 679
 680                         while (!list_empty(&entries))
 681                                 kill_node(list_entry(entries.next, Node, list));
 682
 683                         mutex_unlock(&root->d_inode->i_mutex);
 684                         dput(root);
 685                 default: return res;
 686         }
 687         return count;
 688 }
 689
 690 static const struct file_operations bm_status_operations = {
 691         .read           = bm_status_read,
 692         .write          = bm_status_write,
 693 };
 694
 695 /* Superblock handling */
 696
 697 static const struct super_operations s_ops = {
 698         .statfs         = simple_statfs,
 699         .clear_inode    = bm_clear_inode,
 700 };
 701
 702 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 703 {
 704         static struct tree_descr bm_files[] = {
 705                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 706                 [3] = {"register", &bm_register_operations, S_IWUSR},
 707                 /* last one */ {""}
 708         };
 709         int err = simple_fill_super(sb, 0x42494e4d, bm_files);
 710         if (!err)
 711                 sb->s_op = &s_ops;
 712         return err;
 713 }
 714
 715 static int bm_get_sb(struct file_system_type *fs_type,
 716         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 717 {
 718         return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
 719 }
 720
 721 static struct linux_binfmt misc_format = {
 722         .module = THIS_MODULE,
 723         .load_binary = load_misc_binary,
 724 };
 725
 726 static struct file_system_type bm_fs_type = {
 727         .owner          = THIS_MODULE,
 728         .name           = "binfmt_misc",
 729         .get_sb         = bm_get_sb,
 730         .kill_sb        = kill_litter_super,
 731 };
 732
 733 static int __init init_misc_binfmt(void)
 734 {
 735         int err = register_filesystem(&bm_fs_type);
 736         if (!err) {
 737                 err = register_binfmt(&misc_format);
 738                 if (err)
 739                         unregister_filesystem(&bm_fs_type);
 740         }
 741         return err;
 742 }
 743
 744 static void __exit exit_misc_binfmt(void)
 745 {
 746         unregister_binfmt(&misc_format);
 747         unregister_filesystem(&bm_fs_type);
 748 }
 749
 750 core_initcall(init_misc_binfmt);
 751 module_exit(exit_misc_binfmt);
 752 MODULE_LICENSE("GPL");