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         retval = -ENOEXEC;
 119         if (bprm->misc_bang)
 120                 goto _ret;
 121
 122         bprm->misc_bang = 1;
 123
 124         /* to keep locking time low, we copy the interpreter string */
 125         read_lock(&entries_lock);
 126         fmt = check_file(bprm);
 127         if (fmt)
 128                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 129         read_unlock(&entries_lock);
 130         if (!fmt)
 131                 goto _ret;
 132
 133         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 134                 retval = remove_arg_zero(bprm);
 135                 if (retval)
 136                         goto _ret;
 137         }
 138
 139         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 140
 141                 /* if the binary should be opened on behalf of the
 142                  * interpreter than keep it open and assign descriptor
 143                  * to it */
 144                 fd_binary = get_unused_fd();
 145                 if (fd_binary < 0) {
 146                         retval = fd_binary;
 147                         goto _ret;
 148                 }
 149                 fd_install(fd_binary, bprm->file);
 150
 151                 /* if the binary is not readable than enforce mm->dumpable=0
 152                    regardless of the interpreter's permissions */
 153                 if (file_permission(bprm->file, MAY_READ))
 154                         bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
 155
 156                 allow_write_access(bprm->file);
 157                 bprm->file = NULL;
 158
 159                 /* mark the bprm that fd should be passed to interp */
 160                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 161                 bprm->interp_data = fd_binary;
 162
 163         } else {
 164                 allow_write_access(bprm->file);
 165                 fput(bprm->file);
 166                 bprm->file = NULL;
 167         }
 168         /* make argv[1] be the path to the binary */
 169         retval = copy_strings_kernel (1, &bprm->interp, bprm);
 170         if (retval < 0)
 171                 goto _error;
 172         bprm->argc++;
 173
 174         /* add the interp as argv[0] */
 175         retval = copy_strings_kernel (1, &iname_addr, bprm);
 176         if (retval < 0)
 177                 goto _error;
 178         bprm->argc ++;
 179
 180         bprm->interp = iname;   /* for binfmt_script */
 181
 182         interp_file = open_exec (iname);
 183         retval = PTR_ERR (interp_file);
 184         if (IS_ERR (interp_file))
 185                 goto _error;
 186
 187         bprm->file = interp_file;
 188         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 189                 /*
 190                  * No need to call prepare_binprm(), it's already been
 191                  * done.  bprm->buf is stale, update from interp_file.
 192                  */
 193                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 194                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 195         } else
 196                 retval = prepare_binprm (bprm);
 197
 198         if (retval < 0)
 199                 goto _error;
 200
 201         retval = search_binary_handler (bprm, regs);
 202         if (retval < 0)
 203                 goto _error;
 204
 205 _ret:
 206         return retval;
 207 _error:
 208         if (fd_binary > 0)
 209                 sys_close(fd_binary);
 210         bprm->interp_flags = 0;
 211         bprm->interp_data = 0;
 212         goto _ret;
 213 }
 214
 215 /* Command parsers */
 216
 217 /*
 218  * parses and copies one argument enclosed in del from *sp to *dp,
 219  * recognising the \x special.
 220  * returns pointer to the copied argument or NULL in case of an
 221  * error (and sets err) or null argument length.
 222  */
 223 static char *scanarg(char *s, char del)
 224 {
 225         char c;
 226
 227         while ((c = *s++) != del) {
 228                 if (c == '\\' && *s == 'x') {
 229                         s++;
 230                         if (!isxdigit(*s++))
 231                                 return NULL;
 232                         if (!isxdigit(*s++))
 233                                 return NULL;
 234                 }
 235         }
 236         return s;
 237 }
 238
 239 static int unquote(char *from)
 240 {
 241         char c = 0, *s = from, *p = from;
 242
 243         while ((c = *s++) != '\0') {
 244                 if (c == '\\' && *s == 'x') {
 245                         s++;
 246                         c = toupper(*s++);
 247                         *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
 248                         c = toupper(*s++);
 249                         *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
 250                         continue;
 251                 }
 252                 *p++ = c;
 253         }
 254         return p - from;
 255 }
 256
 257 static char * check_special_flags (char * sfs, Node * e)
 258 {
 259         char * p = sfs;
 260         int cont = 1;
 261
 262         /* special flags */
 263         while (cont) {
 264                 switch (*p) {
 265                         case 'P':
 266                                 p++;
 267                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 268                                 break;
 269                         case 'O':
 270                                 p++;
 271                                 e->flags |= MISC_FMT_OPEN_BINARY;
 272                                 break;
 273                         case 'C':
 274                                 p++;
 275                                 /* this flags also implies the
 276                                    open-binary flag */
 277                                 e->flags |= (MISC_FMT_CREDENTIALS |
 278                                                 MISC_FMT_OPEN_BINARY);
 279                                 break;
 280                         default:
 281                                 cont = 0;
 282                 }
 283         }
 284
 285         return p;
 286 }
 287 /*
 288  * This registers a new binary format, it recognises the syntax
 289  * ':name:type:offset:magic:mask:interpreter:flags'
 290  * where the ':' is the IFS, that can be chosen with the first char
 291  */
 292 static Node *create_entry(const char __user *buffer, size_t count)
 293 {
 294         Node *e;
 295         int memsize, err;
 296         char *buf, *p;
 297         char del;
 298
 299         /* some sanity checks */
 300         err = -EINVAL;
 301         if ((count < 11) || (count > 256))
 302                 goto out;
 303
 304         err = -ENOMEM;
 305         memsize = sizeof(Node) + count + 8;
 306         e = kmalloc(memsize, GFP_USER);
 307         if (!e)
 308                 goto out;
 309
 310         p = buf = (char *)e + sizeof(Node);
 311
 312         memset(e, 0, sizeof(Node));
 313         if (copy_from_user(buf, buffer, count))
 314                 goto Efault;
 315
 316         del = *p++;     /* delimeter */
 317
 318         memset(buf+count, del, 8);
 319
 320         e->name = p;
 321         p = strchr(p, del);
 322         if (!p)
 323                 goto Einval;
 324         *p++ = '\0';
 325         if (!e->name[0] ||
 326             !strcmp(e->name, ".") ||
 327             !strcmp(e->name, "..") ||
 328             strchr(e->name, '/'))
 329                 goto Einval;
 330         switch (*p++) {
 331                 case 'E': e->flags = 1<<Enabled; break;
 332                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 333                 default: goto Einval;
 334         }
 335         if (*p++ != del)
 336                 goto Einval;
 337         if (test_bit(Magic, &e->flags)) {
 338                 char *s = strchr(p, del);
 339                 if (!s)
 340                         goto Einval;
 341                 *s++ = '\0';
 342                 e->offset = simple_strtoul(p, &p, 10);
 343                 if (*p++)
 344                         goto Einval;
 345                 e->magic = p;
 346                 p = scanarg(p, del);
 347                 if (!p)
 348                         goto Einval;
 349                 p[-1] = '\0';
 350                 if (!e->magic[0])
 351                         goto Einval;
 352                 e->mask = p;
 353                 p = scanarg(p, del);
 354                 if (!p)
 355                         goto Einval;
 356                 p[-1] = '\0';
 357                 if (!e->mask[0])
 358                         e->mask = NULL;
 359                 e->size = unquote(e->magic);
 360                 if (e->mask && unquote(e->mask) != e->size)
 361                         goto Einval;
 362                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 363                         goto Einval;
 364         } else {
 365                 p = strchr(p, del);
 366                 if (!p)
 367                         goto Einval;
 368                 *p++ = '\0';
 369                 e->magic = p;
 370                 p = strchr(p, del);
 371                 if (!p)
 372                         goto Einval;
 373                 *p++ = '\0';
 374                 if (!e->magic[0] || strchr(e->magic, '/'))
 375                         goto Einval;
 376                 p = strchr(p, del);
 377                 if (!p)
 378                         goto Einval;
 379                 *p++ = '\0';
 380         }
 381         e->interpreter = p;
 382         p = strchr(p, del);
 383         if (!p)
 384                 goto Einval;
 385         *p++ = '\0';
 386         if (!e->interpreter[0])
 387                 goto Einval;
 388
 389
 390         p = check_special_flags (p, e);
 391
 392         if (*p == '\n')
 393                 p++;
 394         if (p != buf + count)
 395                 goto Einval;
 396         return e;
 397
 398 out:
 399         return ERR_PTR(err);
 400
 401 Efault:
 402         kfree(e);
 403         return ERR_PTR(-EFAULT);
 404 Einval:
 405         kfree(e);
 406         return ERR_PTR(-EINVAL);
 407 }
 408
 409 /*
 410  * Set status of entry/binfmt_misc:
 411  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 412  */
 413 static int parse_command(const char __user *buffer, size_t count)
 414 {
 415         char s[4];
 416
 417         if (!count)
 418                 return 0;
 419         if (count > 3)
 420                 return -EINVAL;
 421         if (copy_from_user(s, buffer, count))
 422                 return -EFAULT;
 423         if (s[count-1] == '\n')
 424                 count--;
 425         if (count == 1 && s[0] == '0')
 426                 return 1;
 427         if (count == 1 && s[0] == '1')
 428                 return 2;
 429         if (count == 2 && s[0] == '-' && s[1] == '1')
 430                 return 3;
 431         return -EINVAL;
 432 }
 433
 434 /* generic stuff */
 435
 436 static void entry_status(Node *e, char *page)
 437 {
 438         char *dp;
 439         char *status = "disabled";
 440         const char * flags = "flags: ";
 441
 442         if (test_bit(Enabled, &e->flags))
 443                 status = "enabled";
 444
 445         if (!VERBOSE_STATUS) {
 446                 sprintf(page, "%s\n", status);
 447                 return;
 448         }
 449
 450         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 451         dp = page + strlen(page);
 452
 453         /* print the special flags */
 454         sprintf (dp, "%s", flags);
 455         dp += strlen (flags);
 456         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 457                 *dp ++ = 'P';
 458         }
 459         if (e->flags & MISC_FMT_OPEN_BINARY) {
 460                 *dp ++ = 'O';
 461         }
 462         if (e->flags & MISC_FMT_CREDENTIALS) {
 463                 *dp ++ = 'C';
 464         }
 465         *dp ++ = '\n';
 466
 467
 468         if (!test_bit(Magic, &e->flags)) {
 469                 sprintf(dp, "extension .%s\n", e->magic);
 470         } else {
 471                 int i;
 472
 473                 sprintf(dp, "offset %i\nmagic ", e->offset);
 474                 dp = page + strlen(page);
 475                 for (i = 0; i < e->size; i++) {
 476                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 477                         dp += 2;
 478                 }
 479                 if (e->mask) {
 480                         sprintf(dp, "\nmask ");
 481                         dp += 6;
 482                         for (i = 0; i < e->size; i++) {
 483                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 484                                 dp += 2;
 485                         }
 486                 }
 487                 *dp++ = '\n';
 488                 *dp = '\0';
 489         }
 490 }
 491
 492 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 493 {
 494         struct inode * inode = new_inode(sb);
 495
 496         if (inode) {
 497                 inode->i_mode = mode;
 498                 inode->i_uid = 0;
 499                 inode->i_gid = 0;
 500                 inode->i_blocks = 0;
 501                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 502                         current_fs_time(inode->i_sb);
 503         }
 504         return inode;
 505 }
 506
 507 static void bm_clear_inode(struct inode *inode)
 508 {
 509         kfree(inode->i_private);
 510 }
 511
 512 static void kill_node(Node *e)
 513 {
 514         struct dentry *dentry;
 515
 516         write_lock(&entries_lock);
 517         dentry = e->dentry;
 518         if (dentry) {
 519                 list_del_init(&e->list);
 520                 e->dentry = NULL;
 521         }
 522         write_unlock(&entries_lock);
 523
 524         if (dentry) {
 525                 dentry->d_inode->i_nlink--;
 526                 d_drop(dentry);
 527                 dput(dentry);
 528                 simple_release_fs(&bm_mnt, &entry_count);
 529         }
 530 }
 531
 532 /* /<entry> */
 533
 534 static ssize_t
 535 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 536 {
 537         Node *e = file->f_path.dentry->d_inode->i_private;
 538         loff_t pos = *ppos;
 539         ssize_t res;
 540         char *page;
 541         int len;
 542
 543         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 544                 return -ENOMEM;
 545
 546         entry_status(e, page);
 547         len = strlen(page);
 548
 549         res = -EINVAL;
 550         if (pos < 0)
 551                 goto out;
 552         res = 0;
 553         if (pos >= len)
 554                 goto out;
 555         if (len < pos + nbytes)
 556                 nbytes = len - pos;
 557         res = -EFAULT;
 558         if (copy_to_user(buf, page + pos, nbytes))
 559                 goto out;
 560         *ppos = pos + nbytes;
 561         res = nbytes;
 562 out:
 563         free_page((unsigned long) page);
 564         return res;
 565 }
 566
 567 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 568                                 size_t count, loff_t *ppos)
 569 {
 570         struct dentry *root;
 571         Node *e = file->f_path.dentry->d_inode->i_private;
 572         int res = parse_command(buffer, count);
 573
 574         switch (res) {
 575                 case 1: clear_bit(Enabled, &e->flags);
 576                         break;
 577                 case 2: set_bit(Enabled, &e->flags);
 578                         break;
 579                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 580                         mutex_lock(&root->d_inode->i_mutex);
 581
 582                         kill_node(e);
 583
 584                         mutex_unlock(&root->d_inode->i_mutex);
 585                         dput(root);
 586                         break;
 587                 default: return res;
 588         }
 589         return count;
 590 }
 591
 592 static const struct file_operations bm_entry_operations = {
 593         .read           = bm_entry_read,
 594         .write          = bm_entry_write,
 595 };
 596
 597 /* /register */
 598
 599 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 600                                size_t count, loff_t *ppos)
 601 {
 602         Node *e;
 603         struct inode *inode;
 604         struct dentry *root, *dentry;
 605         struct super_block *sb = file->f_path.mnt->mnt_sb;
 606         int err = 0;
 607
 608         e = create_entry(buffer, count);
 609
 610         if (IS_ERR(e))
 611                 return PTR_ERR(e);
 612
 613         root = dget(sb->s_root);
 614         mutex_lock(&root->d_inode->i_mutex);
 615         dentry = lookup_one_len(e->name, root, strlen(e->name));
 616         err = PTR_ERR(dentry);
 617         if (IS_ERR(dentry))
 618                 goto out;
 619
 620         err = -EEXIST;
 621         if (dentry->d_inode)
 622                 goto out2;
 623
 624         inode = bm_get_inode(sb, S_IFREG | 0644);
 625
 626         err = -ENOMEM;
 627         if (!inode)
 628                 goto out2;
 629
 630         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 631         if (err) {
 632                 iput(inode);
 633                 inode = NULL;
 634                 goto out2;
 635         }
 636
 637         e->dentry = dget(dentry);
 638         inode->i_private = e;
 639         inode->i_fop = &bm_entry_operations;
 640
 641         d_instantiate(dentry, inode);
 642         write_lock(&entries_lock);
 643         list_add(&e->list, &entries);
 644         write_unlock(&entries_lock);
 645
 646         err = 0;
 647 out2:
 648         dput(dentry);
 649 out:
 650         mutex_unlock(&root->d_inode->i_mutex);
 651         dput(root);
 652
 653         if (err) {
 654                 kfree(e);
 655                 return -EINVAL;
 656         }
 657         return count;
 658 }
 659
 660 static const struct file_operations bm_register_operations = {
 661         .write          = bm_register_write,
 662 };
 663
 664 /* /status */
 665
 666 static ssize_t
 667 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 668 {
 669         char *s = enabled ? "enabled" : "disabled";
 670
 671         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 672 }
 673
 674 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 675                 size_t count, loff_t *ppos)
 676 {
 677         int res = parse_command(buffer, count);
 678         struct dentry *root;
 679
 680         switch (res) {
 681                 case 1: enabled = 0; break;
 682                 case 2: enabled = 1; break;
 683                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 684                         mutex_lock(&root->d_inode->i_mutex);
 685
 686                         while (!list_empty(&entries))
 687                                 kill_node(list_entry(entries.next, Node, list));
 688
 689                         mutex_unlock(&root->d_inode->i_mutex);
 690                         dput(root);
 691                 default: return res;
 692         }
 693         return count;
 694 }
 695
 696 static const struct file_operations bm_status_operations = {
 697         .read           = bm_status_read,
 698         .write          = bm_status_write,
 699 };
 700
 701 /* Superblock handling */
 702
 703 static const struct super_operations s_ops = {
 704         .statfs         = simple_statfs,
 705         .clear_inode    = bm_clear_inode,
 706 };
 707
 708 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 709 {
 710         static struct tree_descr bm_files[] = {
 711                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 712                 [3] = {"register", &bm_register_operations, S_IWUSR},
 713                 /* last one */ {""}
 714         };
 715         int err = simple_fill_super(sb, 0x42494e4d, bm_files);
 716         if (!err)
 717                 sb->s_op = &s_ops;
 718         return err;
 719 }
 720
 721 static int bm_get_sb(struct file_system_type *fs_type,
 722         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 723 {
 724         return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
 725 }
 726
 727 static struct linux_binfmt misc_format = {
 728         .module = THIS_MODULE,
 729         .load_binary = load_misc_binary,
 730 };
 731
 732 static struct file_system_type bm_fs_type = {
 733         .owner          = THIS_MODULE,
 734         .name           = "binfmt_misc",
 735         .get_sb         = bm_get_sb,
 736         .kill_sb        = kill_litter_super,
 737 };
 738
 739 static int __init init_misc_binfmt(void)
 740 {
 741         int err = register_filesystem(&bm_fs_type);
 742         if (!err) {
 743                 err = register_binfmt(&misc_format);
 744                 if (err)
 745                         unregister_filesystem(&bm_fs_type);
 746         }
 747         return err;
 748 }
 749
 750 static void __exit exit_misc_binfmt(void)
 751 {
 752         unregister_binfmt(&misc_format);
 753         unregister_filesystem(&bm_fs_type);
 754 }
 755
 756 core_initcall(init_misc_binfmt);
 757 module_exit(exit_misc_binfmt);
 758 MODULE_LICENSE("GPL");