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 #include <linux/fs.h>
  31
  32 #include <asm/uaccess.h>
  33
  34 enum {
  35         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  36 };
  37
  38 static LIST_HEAD(entries);
  39 static int enabled = 1;
  40
  41 enum {Enabled, Magic};
  42 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
  43 #define MISC_FMT_OPEN_BINARY (1<<30)
  44 #define MISC_FMT_CREDENTIALS (1<<29)
  45
  46 typedef struct {
  47         struct list_head list;
  48         unsigned long flags;            /* type, status, etc. */
  49         int offset;                     /* offset of magic */
  50         int size;                       /* size of magic/mask */
  51         char *magic;                    /* magic or filename extension */
  52         char *mask;                     /* mask, NULL for exact match */
  53         char *interpreter;              /* filename of interpreter */
  54         char *name;
  55         struct dentry *dentry;
  56 } Node;
  57
  58 static DEFINE_RWLOCK(entries_lock);
  59 static struct file_system_type bm_fs_type;
  60 static struct vfsmount *bm_mnt;
  61 static int entry_count;
  62
  63 /*
  64  * Check if we support the binfmt
  65  * if we do, return the node, else NULL
  66  * locking is done in load_misc_binary
  67  */
  68 static Node *check_file(struct linux_binprm *bprm)
  69 {
  70         char *p = strrchr(bprm->interp, '.');
  71         struct list_head *l;
  72
  73         list_for_each(l, &entries) {
  74                 Node *e = list_entry(l, Node, list);
  75                 char *s;
  76                 int j;
  77
  78                 if (!test_bit(Enabled, &e->flags))
  79                         continue;
  80
  81                 if (!test_bit(Magic, &e->flags)) {
  82                         if (p && !strcmp(e->magic, p + 1))
  83                                 return e;
  84                         continue;
  85                 }
  86
  87                 s = bprm->buf + e->offset;
  88                 if (e->mask) {
  89                         for (j = 0; j < e->size; j++)
  90                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
  91                                         break;
  92                 } else {
  93                         for (j = 0; j < e->size; j++)
  94                                 if ((*s++ ^ e->magic[j]))
  95                                         break;
  96                 }
  97                 if (j == e->size)
  98                         return e;
  99         }
 100         return NULL;
 101 }
 102
 103 /*
 104  * the loader itself
 105  */
 106 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 107 {
 108         Node *fmt;
 109         struct file * interp_file = NULL;
 110         char iname[BINPRM_BUF_SIZE];
 111         const char *iname_addr = iname;
 112         int retval;
 113         int fd_binary = -1;
 114
 115         retval = -ENOEXEC;
 116         if (!enabled)
 117                 goto _ret;
 118
 119         retval = -ENOEXEC;
 120         if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
 121                 goto _ret;
 122
 123         /* to keep locking time low, we copy the interpreter string */
 124         read_lock(&entries_lock);
 125         fmt = check_file(bprm);
 126         if (fmt)
 127                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 128         read_unlock(&entries_lock);
 129         if (!fmt)
 130                 goto _ret;
 131
 132         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 133                 retval = remove_arg_zero(bprm);
 134                 if (retval)
 135                         goto _ret;
 136         }
 137
 138         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 139
 140                 /* if the binary should be opened on behalf of the
 141                  * interpreter than keep it open and assign descriptor
 142                  * to it */
 143                 fd_binary = get_unused_fd();
 144                 if (fd_binary < 0) {
 145                         retval = fd_binary;
 146                         goto _ret;
 147                 }
 148                 fd_install(fd_binary, bprm->file);
 149
 150                 /* if the binary is not readable than enforce mm->dumpable=0
 151                    regardless of the interpreter's permissions */
 152                 if (file_permission(bprm->file, MAY_READ))
 153                         bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
 154
 155                 allow_write_access(bprm->file);
 156                 bprm->file = NULL;
 157
 158                 /* mark the bprm that fd should be passed to interp */
 159                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 160                 bprm->interp_data = fd_binary;
 161
 162         } else {
 163                 allow_write_access(bprm->file);
 164                 fput(bprm->file);
 165                 bprm->file = NULL;
 166         }
 167         /* make argv[1] be the path to the binary */
 168         retval = copy_strings_kernel (1, &bprm->interp, bprm);
 169         if (retval < 0)
 170                 goto _error;
 171         bprm->argc++;
 172
 173         /* add the interp as argv[0] */
 174         retval = copy_strings_kernel (1, &iname_addr, bprm);
 175         if (retval < 0)
 176                 goto _error;
 177         bprm->argc ++;
 178
 179         /* Update interp in case binfmt_script needs it. */
 180         retval = bprm_change_interp(iname, bprm);
 181         if (retval < 0)
 182                 goto _error;
 183
 184         interp_file = open_exec (iname);
 185         retval = PTR_ERR (interp_file);
 186         if (IS_ERR (interp_file))
 187                 goto _error;
 188
 189         bprm->file = interp_file;
 190         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 191                 /*
 192                  * No need to call prepare_binprm(), it's already been
 193                  * done.  bprm->buf is stale, update from interp_file.
 194                  */
 195                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 196                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 197         } else
 198                 retval = prepare_binprm (bprm);
 199
 200         if (retval < 0)
 201                 goto _error;
 202
 203         bprm->recursion_depth++;
 204
 205         retval = search_binary_handler (bprm, regs);
 206         if (retval < 0)
 207                 goto _error;
 208
 209 _ret:
 210         return retval;
 211 _error:
 212         if (fd_binary > 0)
 213                 sys_close(fd_binary);
 214         bprm->interp_flags = 0;
 215         bprm->interp_data = 0;
 216         goto _ret;
 217 }
 218
 219 /* Command parsers */
 220
 221 /*
 222  * parses and copies one argument enclosed in del from *sp to *dp,
 223  * recognising the \x special.
 224  * returns pointer to the copied argument or NULL in case of an
 225  * error (and sets err) or null argument length.
 226  */
 227 static char *scanarg(char *s, char del)
 228 {
 229         char c;
 230
 231         while ((c = *s++) != del) {
 232                 if (c == '\\' && *s == 'x') {
 233                         s++;
 234                         if (!isxdigit(*s++))
 235                                 return NULL;
 236                         if (!isxdigit(*s++))
 237                                 return NULL;
 238                 }
 239         }
 240         return s;
 241 }
 242
 243 static int unquote(char *from)
 244 {
 245         char c = 0, *s = from, *p = from;
 246
 247         while ((c = *s++) != '\0') {
 248                 if (c == '\\' && *s == 'x') {
 249                         s++;
 250                         c = toupper(*s++);
 251                         *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
 252                         c = toupper(*s++);
 253                         *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
 254                         continue;
 255                 }
 256                 *p++ = c;
 257         }
 258         return p - from;
 259 }
 260
 261 static char * check_special_flags (char * sfs, Node * e)
 262 {
 263         char * p = sfs;
 264         int cont = 1;
 265
 266         /* special flags */
 267         while (cont) {
 268                 switch (*p) {
 269                         case 'P':
 270                                 p++;
 271                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 272                                 break;
 273                         case 'O':
 274                                 p++;
 275                                 e->flags |= MISC_FMT_OPEN_BINARY;
 276                                 break;
 277                         case 'C':
 278                                 p++;
 279                                 /* this flags also implies the
 280                                    open-binary flag */
 281                                 e->flags |= (MISC_FMT_CREDENTIALS |
 282                                                 MISC_FMT_OPEN_BINARY);
 283                                 break;
 284                         default:
 285                                 cont = 0;
 286                 }
 287         }
 288
 289         return p;
 290 }
 291 /*
 292  * This registers a new binary format, it recognises the syntax
 293  * ':name:type:offset:magic:mask:interpreter:flags'
 294  * where the ':' is the IFS, that can be chosen with the first char
 295  */
 296 static Node *create_entry(const char __user *buffer, size_t count)
 297 {
 298         Node *e;
 299         int memsize, err;
 300         char *buf, *p;
 301         char del;
 302
 303         /* some sanity checks */
 304         err = -EINVAL;
 305         if ((count < 11) || (count > 256))
 306                 goto out;
 307
 308         err = -ENOMEM;
 309         memsize = sizeof(Node) + count + 8;
 310         e = kmalloc(memsize, GFP_USER);
 311         if (!e)
 312                 goto out;
 313
 314         p = buf = (char *)e + sizeof(Node);
 315
 316         memset(e, 0, sizeof(Node));
 317         if (copy_from_user(buf, buffer, count))
 318                 goto Efault;
 319
 320         del = *p++;     /* delimeter */
 321
 322         memset(buf+count, del, 8);
 323
 324         e->name = p;
 325         p = strchr(p, del);
 326         if (!p)
 327                 goto Einval;
 328         *p++ = '\0';
 329         if (!e->name[0] ||
 330             !strcmp(e->name, ".") ||
 331             !strcmp(e->name, "..") ||
 332             strchr(e->name, '/'))
 333                 goto Einval;
 334         switch (*p++) {
 335                 case 'E': e->flags = 1<<Enabled; break;
 336                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 337                 default: goto Einval;
 338         }
 339         if (*p++ != del)
 340                 goto Einval;
 341         if (test_bit(Magic, &e->flags)) {
 342                 char *s = strchr(p, del);
 343                 if (!s)
 344                         goto Einval;
 345                 *s++ = '\0';
 346                 e->offset = simple_strtoul(p, &p, 10);
 347                 if (*p++)
 348                         goto Einval;
 349                 e->magic = p;
 350                 p = scanarg(p, del);
 351                 if (!p)
 352                         goto Einval;
 353                 p[-1] = '\0';
 354                 if (!e->magic[0])
 355                         goto Einval;
 356                 e->mask = p;
 357                 p = scanarg(p, del);
 358                 if (!p)
 359                         goto Einval;
 360                 p[-1] = '\0';
 361                 if (!e->mask[0])
 362                         e->mask = NULL;
 363                 e->size = unquote(e->magic);
 364                 if (e->mask && unquote(e->mask) != e->size)
 365                         goto Einval;
 366                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 367                         goto Einval;
 368         } else {
 369                 p = strchr(p, del);
 370                 if (!p)
 371                         goto Einval;
 372                 *p++ = '\0';
 373                 e->magic = p;
 374                 p = strchr(p, del);
 375                 if (!p)
 376                         goto Einval;
 377                 *p++ = '\0';
 378                 if (!e->magic[0] || strchr(e->magic, '/'))
 379                         goto Einval;
 380                 p = strchr(p, del);
 381                 if (!p)
 382                         goto Einval;
 383                 *p++ = '\0';
 384         }
 385         e->interpreter = p;
 386         p = strchr(p, del);
 387         if (!p)
 388                 goto Einval;
 389         *p++ = '\0';
 390         if (!e->interpreter[0])
 391                 goto Einval;
 392
 393
 394         p = check_special_flags (p, e);
 395
 396         if (*p == '\n')
 397                 p++;
 398         if (p != buf + count)
 399                 goto Einval;
 400         return e;
 401
 402 out:
 403         return ERR_PTR(err);
 404
 405 Efault:
 406         kfree(e);
 407         return ERR_PTR(-EFAULT);
 408 Einval:
 409         kfree(e);
 410         return ERR_PTR(-EINVAL);
 411 }
 412
 413 /*
 414  * Set status of entry/binfmt_misc:
 415  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 416  */
 417 static int parse_command(const char __user *buffer, size_t count)
 418 {
 419         char s[4];
 420
 421         if (!count)
 422                 return 0;
 423         if (count > 3)
 424                 return -EINVAL;
 425         if (copy_from_user(s, buffer, count))
 426                 return -EFAULT;
 427         if (s[count-1] == '\n')
 428                 count--;
 429         if (count == 1 && s[0] == '0')
 430                 return 1;
 431         if (count == 1 && s[0] == '1')
 432                 return 2;
 433         if (count == 2 && s[0] == '-' && s[1] == '1')
 434                 return 3;
 435         return -EINVAL;
 436 }
 437
 438 /* generic stuff */
 439
 440 static void entry_status(Node *e, char *page)
 441 {
 442         char *dp;
 443         char *status = "disabled";
 444         const char * flags = "flags: ";
 445
 446         if (test_bit(Enabled, &e->flags))
 447                 status = "enabled";
 448
 449         if (!VERBOSE_STATUS) {
 450                 sprintf(page, "%s\n", status);
 451                 return;
 452         }
 453
 454         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 455         dp = page + strlen(page);
 456
 457         /* print the special flags */
 458         sprintf (dp, "%s", flags);
 459         dp += strlen (flags);
 460         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 461                 *dp ++ = 'P';
 462         }
 463         if (e->flags & MISC_FMT_OPEN_BINARY) {
 464                 *dp ++ = 'O';
 465         }
 466         if (e->flags & MISC_FMT_CREDENTIALS) {
 467                 *dp ++ = 'C';
 468         }
 469         *dp ++ = '\n';
 470
 471
 472         if (!test_bit(Magic, &e->flags)) {
 473                 sprintf(dp, "extension .%s\n", e->magic);
 474         } else {
 475                 int i;
 476
 477                 sprintf(dp, "offset %i\nmagic ", e->offset);
 478                 dp = page + strlen(page);
 479                 for (i = 0; i < e->size; i++) {
 480                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 481                         dp += 2;
 482                 }
 483                 if (e->mask) {
 484                         sprintf(dp, "\nmask ");
 485                         dp += 6;
 486                         for (i = 0; i < e->size; i++) {
 487                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 488                                 dp += 2;
 489                         }
 490                 }
 491                 *dp++ = '\n';
 492                 *dp = '\0';
 493         }
 494 }
 495
 496 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 497 {
 498         struct inode * inode = new_inode(sb);
 499
 500         if (inode) {
 501                 inode->i_ino = get_next_ino();
 502                 inode->i_mode = mode;
 503                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 504                         current_fs_time(inode->i_sb);
 505         }
 506         return inode;
 507 }
 508
 509 static void bm_evict_inode(struct inode *inode)
 510 {
 511         end_writeback(inode);
 512         kfree(inode->i_private);
 513 }
 514
 515 static void kill_node(Node *e)
 516 {
 517         struct dentry *dentry;
 518
 519         write_lock(&entries_lock);
 520         dentry = e->dentry;
 521         if (dentry) {
 522                 list_del_init(&e->list);
 523                 e->dentry = NULL;
 524         }
 525         write_unlock(&entries_lock);
 526
 527         if (dentry) {
 528                 dentry->d_inode->i_nlink--;
 529                 d_drop(dentry);
 530                 dput(dentry);
 531                 simple_release_fs(&bm_mnt, &entry_count);
 532         }
 533 }
 534
 535 /* /<entry> */
 536
 537 static ssize_t
 538 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 539 {
 540         Node *e = file->f_path.dentry->d_inode->i_private;
 541         ssize_t res;
 542         char *page;
 543
 544         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 545                 return -ENOMEM;
 546
 547         entry_status(e, page);
 548
 549         res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 550
 551         free_page((unsigned long) page);
 552         return res;
 553 }
 554
 555 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 556                                 size_t count, loff_t *ppos)
 557 {
 558         struct dentry *root;
 559         Node *e = file->f_path.dentry->d_inode->i_private;
 560         int res = parse_command(buffer, count);
 561
 562         switch (res) {
 563                 case 1: clear_bit(Enabled, &e->flags);
 564                         break;
 565                 case 2: set_bit(Enabled, &e->flags);
 566                         break;
 567                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 568                         mutex_lock(&root->d_inode->i_mutex);
 569
 570                         kill_node(e);
 571
 572                         mutex_unlock(&root->d_inode->i_mutex);
 573                         dput(root);
 574                         break;
 575                 default: return res;
 576         }
 577         return count;
 578 }
 579
 580 static const struct file_operations bm_entry_operations = {
 581         .read           = bm_entry_read,
 582         .write          = bm_entry_write,
 583         .llseek         = default_llseek,
 584 };
 585
 586 /* /register */
 587
 588 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 589                                size_t count, loff_t *ppos)
 590 {
 591         Node *e;
 592         struct inode *inode;
 593         struct dentry *root, *dentry;
 594         struct super_block *sb = file->f_path.mnt->mnt_sb;
 595         int err = 0;
 596
 597         e = create_entry(buffer, count);
 598
 599         if (IS_ERR(e))
 600                 return PTR_ERR(e);
 601
 602         root = dget(sb->s_root);
 603         mutex_lock(&root->d_inode->i_mutex);
 604         dentry = lookup_one_len(e->name, root, strlen(e->name));
 605         err = PTR_ERR(dentry);
 606         if (IS_ERR(dentry))
 607                 goto out;
 608
 609         err = -EEXIST;
 610         if (dentry->d_inode)
 611                 goto out2;
 612
 613         inode = bm_get_inode(sb, S_IFREG | 0644);
 614
 615         err = -ENOMEM;
 616         if (!inode)
 617                 goto out2;
 618
 619         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 620         if (err) {
 621                 iput(inode);
 622                 inode = NULL;
 623                 goto out2;
 624         }
 625
 626         e->dentry = dget(dentry);
 627         inode->i_private = e;
 628         inode->i_fop = &bm_entry_operations;
 629
 630         d_instantiate(dentry, inode);
 631         write_lock(&entries_lock);
 632         list_add(&e->list, &entries);
 633         write_unlock(&entries_lock);
 634
 635         err = 0;
 636 out2:
 637         dput(dentry);
 638 out:
 639         mutex_unlock(&root->d_inode->i_mutex);
 640         dput(root);
 641
 642         if (err) {
 643                 kfree(e);
 644                 return -EINVAL;
 645         }
 646         return count;
 647 }
 648
 649 static const struct file_operations bm_register_operations = {
 650         .write          = bm_register_write,
 651         .llseek         = noop_llseek,
 652 };
 653
 654 /* /status */
 655
 656 static ssize_t
 657 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 658 {
 659         char *s = enabled ? "enabled\n" : "disabled\n";
 660
 661         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 662 }
 663
 664 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 665                 size_t count, loff_t *ppos)
 666 {
 667         int res = parse_command(buffer, count);
 668         struct dentry *root;
 669
 670         switch (res) {
 671                 case 1: enabled = 0; break;
 672                 case 2: enabled = 1; break;
 673                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 674                         mutex_lock(&root->d_inode->i_mutex);
 675
 676                         while (!list_empty(&entries))
 677                                 kill_node(list_entry(entries.next, Node, list));
 678
 679                         mutex_unlock(&root->d_inode->i_mutex);
 680                         dput(root);
 681                 default: return res;
 682         }
 683         return count;
 684 }
 685
 686 static const struct file_operations bm_status_operations = {
 687         .read           = bm_status_read,
 688         .write          = bm_status_write,
 689         .llseek         = default_llseek,
 690 };
 691
 692 /* Superblock handling */
 693
 694 static const struct super_operations s_ops = {
 695         .statfs         = simple_statfs,
 696         .evict_inode    = bm_evict_inode,
 697 };
 698
 699 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 700 {
 701         static struct tree_descr bm_files[] = {
 702                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 703                 [3] = {"register", &bm_register_operations, S_IWUSR},
 704                 /* last one */ {""}
 705         };
 706         int err = simple_fill_super(sb, 0x42494e4d, bm_files);
 707         if (!err)
 708                 sb->s_op = &s_ops;
 709         return err;
 710 }
 711
 712 static struct dentry *bm_mount(struct file_system_type *fs_type,
 713         int flags, const char *dev_name, void *data)
 714 {
 715         return mount_single(fs_type, flags, data, bm_fill_super);
 716 }
 717
 718 static struct linux_binfmt misc_format = {
 719         .module = THIS_MODULE,
 720         .load_binary = load_misc_binary,
 721 };
 722
 723 static struct file_system_type bm_fs_type = {
 724         .owner          = THIS_MODULE,
 725         .name           = "binfmt_misc",
 726         .mount          = bm_mount,
 727         .kill_sb        = kill_litter_super,
 728 };
 729
 730 static int __init init_misc_binfmt(void)
 731 {
 732         int err = register_filesystem(&bm_fs_type);
 733         if (!err) {
 734                 err = insert_binfmt(&misc_format);
 735                 if (err)
 736                         unregister_filesystem(&bm_fs_type);
 737         }
 738         return err;
 739 }
 740
 741 static void __exit exit_misc_binfmt(void)
 742 {
 743         unregister_binfmt(&misc_format);
 744         unregister_filesystem(&bm_fs_type);
 745 }
 746
 747 core_initcall(init_misc_binfmt);
 748 module_exit(exit_misc_binfmt);
 749 MODULE_LICENSE("GPL");