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