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
  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         struct files_struct *files = NULL;
 114
 115         retval = -ENOEXEC;
 116         if (!enabled)
 117                 goto _ret;
 118
 119         /* to keep locking time low, we copy the interpreter string */
 120         read_lock(&entries_lock);
 121         fmt = check_file(bprm);
 122         if (fmt)
 123                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 124         read_unlock(&entries_lock);
 125         if (!fmt)
 126                 goto _ret;
 127
 128         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 129                 remove_arg_zero(bprm);
 130         }
 131
 132         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 133
 134                 files = current->files;
 135                 retval = unshare_files();
 136                 if (retval < 0)
 137                         goto _ret;
 138                 if (files == current->files) {
 139                         put_files_struct(files);
 140                         files = NULL;
 141                 }
 142                 /* if the binary should be opened on behalf of the
 143                  * interpreter than keep it open and assign descriptor
 144                  * to it */
 145                 fd_binary = get_unused_fd();
 146                 if (fd_binary < 0) {
 147                         retval = fd_binary;
 148                         goto _unshare;
 149                 }
 150                 fd_install(fd_binary, bprm->file);
 151
 152                 /* if the binary is not readable than enforce mm->dumpable=0
 153                    regardless of the interpreter's permissions */
 154                 if (file_permission(bprm->file, MAY_READ))
 155                         bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
 156
 157                 allow_write_access(bprm->file);
 158                 bprm->file = NULL;
 159
 160                 /* mark the bprm that fd should be passed to interp */
 161                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 162                 bprm->interp_data = fd_binary;
 163
 164         } else {
 165                 allow_write_access(bprm->file);
 166                 fput(bprm->file);
 167                 bprm->file = NULL;
 168         }
 169         /* make argv[1] be the path to the binary */
 170         retval = copy_strings_kernel (1, &bprm->interp, bprm);
 171         if (retval < 0)
 172                 goto _error;
 173         bprm->argc++;
 174
 175         /* add the interp as argv[0] */
 176         retval = copy_strings_kernel (1, &iname_addr, bprm);
 177         if (retval < 0)
 178                 goto _error;
 179         bprm->argc ++;
 180
 181         bprm->interp = iname;   /* for binfmt_script */
 182
 183         interp_file = open_exec (iname);
 184         retval = PTR_ERR (interp_file);
 185         if (IS_ERR (interp_file))
 186                 goto _error;
 187
 188         bprm->file = interp_file;
 189         if (fmt->flags & MISC_FMT_CREDENTIALS) {
 190                 /*
 191                  * No need to call prepare_binprm(), it's already been
 192                  * done.  bprm->buf is stale, update from interp_file.
 193                  */
 194                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 195                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
 196         } else
 197                 retval = prepare_binprm (bprm);
 198
 199         if (retval < 0)
 200                 goto _error;
 201
 202         retval = search_binary_handler (bprm, regs);
 203         if (retval < 0)
 204                 goto _error;
 205
 206         if (files) {
 207                 put_files_struct(files);
 208                 files = NULL;
 209         }
 210 _ret:
 211         return retval;
 212 _error:
 213         if (fd_binary > 0)
 214                 sys_close(fd_binary);
 215         bprm->interp_flags = 0;
 216         bprm->interp_data = 0;
 217 _unshare:
 218         if (files)
 219                 reset_files_struct(current, files);
 220         goto _ret;
 221 }
 222
 223 /* Command parsers */
 224
 225 /*
 226  * parses and copies one argument enclosed in del from *sp to *dp,
 227  * recognising the \x special.
 228  * returns pointer to the copied argument or NULL in case of an
 229  * error (and sets err) or null argument length.
 230  */
 231 static char *scanarg(char *s, char del)
 232 {
 233         char c;
 234
 235         while ((c = *s++) != del) {
 236                 if (c == '\\' && *s == 'x') {
 237                         s++;
 238                         if (!isxdigit(*s++))
 239                                 return NULL;
 240                         if (!isxdigit(*s++))
 241                                 return NULL;
 242                 }
 243         }
 244         return s;
 245 }
 246
 247 static int unquote(char *from)
 248 {
 249         char c = 0, *s = from, *p = from;
 250
 251         while ((c = *s++) != '\0') {
 252                 if (c == '\\' && *s == 'x') {
 253                         s++;
 254                         c = toupper(*s++);
 255                         *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
 256                         c = toupper(*s++);
 257                         *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
 258                         continue;
 259                 }
 260                 *p++ = c;
 261         }
 262         return p - from;
 263 }
 264
 265 static char * check_special_flags (char * sfs, Node * e)
 266 {
 267         char * p = sfs;
 268         int cont = 1;
 269
 270         /* special flags */
 271         while (cont) {
 272                 switch (*p) {
 273                         case 'P':
 274                                 p++;
 275                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
 276                                 break;
 277                         case 'O':
 278                                 p++;
 279                                 e->flags |= MISC_FMT_OPEN_BINARY;
 280                                 break;
 281                         case 'C':
 282                                 p++;
 283                                 /* this flags also implies the
 284                                    open-binary flag */
 285                                 e->flags |= (MISC_FMT_CREDENTIALS |
 286                                                 MISC_FMT_OPEN_BINARY);
 287                                 break;
 288                         default:
 289                                 cont = 0;
 290                 }
 291         }
 292
 293         return p;
 294 }
 295 /*
 296  * This registers a new binary format, it recognises the syntax
 297  * ':name:type:offset:magic:mask:interpreter:flags'
 298  * where the ':' is the IFS, that can be chosen with the first char
 299  */
 300 static Node *create_entry(const char __user *buffer, size_t count)
 301 {
 302         Node *e;
 303         int memsize, err;
 304         char *buf, *p;
 305         char del;
 306
 307         /* some sanity checks */
 308         err = -EINVAL;
 309         if ((count < 11) || (count > 256))
 310                 goto out;
 311
 312         err = -ENOMEM;
 313         memsize = sizeof(Node) + count + 8;
 314         e = kmalloc(memsize, GFP_USER);
 315         if (!e)
 316                 goto out;
 317
 318         p = buf = (char *)e + sizeof(Node);
 319
 320         memset(e, 0, sizeof(Node));
 321         if (copy_from_user(buf, buffer, count))
 322                 goto Efault;
 323
 324         del = *p++;     /* delimeter */
 325
 326         memset(buf+count, del, 8);
 327
 328         e->name = p;
 329         p = strchr(p, del);
 330         if (!p)
 331                 goto Einval;
 332         *p++ = '\0';
 333         if (!e->name[0] ||
 334             !strcmp(e->name, ".") ||
 335             !strcmp(e->name, "..") ||
 336             strchr(e->name, '/'))
 337                 goto Einval;
 338         switch (*p++) {
 339                 case 'E': e->flags = 1<<Enabled; break;
 340                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 341                 default: goto Einval;
 342         }
 343         if (*p++ != del)
 344                 goto Einval;
 345         if (test_bit(Magic, &e->flags)) {
 346                 char *s = strchr(p, del);
 347                 if (!s)
 348                         goto Einval;
 349                 *s++ = '\0';
 350                 e->offset = simple_strtoul(p, &p, 10);
 351                 if (*p++)
 352                         goto Einval;
 353                 e->magic = p;
 354                 p = scanarg(p, del);
 355                 if (!p)
 356                         goto Einval;
 357                 p[-1] = '\0';
 358                 if (!e->magic[0])
 359                         goto Einval;
 360                 e->mask = p;
 361                 p = scanarg(p, del);
 362                 if (!p)
 363                         goto Einval;
 364                 p[-1] = '\0';
 365                 if (!e->mask[0])
 366                         e->mask = NULL;
 367                 e->size = unquote(e->magic);
 368                 if (e->mask && unquote(e->mask) != e->size)
 369                         goto Einval;
 370                 if (e->size + e->offset > BINPRM_BUF_SIZE)
 371                         goto Einval;
 372         } else {
 373                 p = strchr(p, del);
 374                 if (!p)
 375                         goto Einval;
 376                 *p++ = '\0';
 377                 e->magic = p;
 378                 p = strchr(p, del);
 379                 if (!p)
 380                         goto Einval;
 381                 *p++ = '\0';
 382                 if (!e->magic[0] || strchr(e->magic, '/'))
 383                         goto Einval;
 384                 p = strchr(p, del);
 385                 if (!p)
 386                         goto Einval;
 387                 *p++ = '\0';
 388         }
 389         e->interpreter = p;
 390         p = strchr(p, del);
 391         if (!p)
 392                 goto Einval;
 393         *p++ = '\0';
 394         if (!e->interpreter[0])
 395                 goto Einval;
 396
 397
 398         p = check_special_flags (p, e);
 399
 400         if (*p == '\n')
 401                 p++;
 402         if (p != buf + count)
 403                 goto Einval;
 404         return e;
 405
 406 out:
 407         return ERR_PTR(err);
 408
 409 Efault:
 410         kfree(e);
 411         return ERR_PTR(-EFAULT);
 412 Einval:
 413         kfree(e);
 414         return ERR_PTR(-EINVAL);
 415 }
 416
 417 /*
 418  * Set status of entry/binfmt_misc:
 419  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 420  */
 421 static int parse_command(const char __user *buffer, size_t count)
 422 {
 423         char s[4];
 424
 425         if (!count)
 426                 return 0;
 427         if (count > 3)
 428                 return -EINVAL;
 429         if (copy_from_user(s, buffer, count))
 430                 return -EFAULT;
 431         if (s[count-1] == '\n')
 432                 count--;
 433         if (count == 1 && s[0] == '0')
 434                 return 1;
 435         if (count == 1 && s[0] == '1')
 436                 return 2;
 437         if (count == 2 && s[0] == '-' && s[1] == '1')
 438                 return 3;
 439         return -EINVAL;
 440 }
 441
 442 /* generic stuff */
 443
 444 static void entry_status(Node *e, char *page)
 445 {
 446         char *dp;
 447         char *status = "disabled";
 448         const char * flags = "flags: ";
 449
 450         if (test_bit(Enabled, &e->flags))
 451                 status = "enabled";
 452
 453         if (!VERBOSE_STATUS) {
 454                 sprintf(page, "%s\n", status);
 455                 return;
 456         }
 457
 458         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 459         dp = page + strlen(page);
 460
 461         /* print the special flags */
 462         sprintf (dp, "%s", flags);
 463         dp += strlen (flags);
 464         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 465                 *dp ++ = 'P';
 466         }
 467         if (e->flags & MISC_FMT_OPEN_BINARY) {
 468                 *dp ++ = 'O';
 469         }
 470         if (e->flags & MISC_FMT_CREDENTIALS) {
 471                 *dp ++ = 'C';
 472         }
 473         *dp ++ = '\n';
 474
 475
 476         if (!test_bit(Magic, &e->flags)) {
 477                 sprintf(dp, "extension .%s\n", e->magic);
 478         } else {
 479                 int i;
 480
 481                 sprintf(dp, "offset %i\nmagic ", e->offset);
 482                 dp = page + strlen(page);
 483                 for (i = 0; i < e->size; i++) {
 484                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 485                         dp += 2;
 486                 }
 487                 if (e->mask) {
 488                         sprintf(dp, "\nmask ");
 489                         dp += 6;
 490                         for (i = 0; i < e->size; i++) {
 491                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 492                                 dp += 2;
 493                         }
 494                 }
 495                 *dp++ = '\n';
 496                 *dp = '\0';
 497         }
 498 }
 499
 500 static struct inode *bm_get_inode(struct super_block *sb, int mode)
 501 {
 502         struct inode * inode = new_inode(sb);
 503
 504         if (inode) {
 505                 inode->i_mode = mode;
 506                 inode->i_uid = 0;
 507                 inode->i_gid = 0;
 508                 inode->i_blocks = 0;
 509                 inode->i_atime = inode->i_mtime = inode->i_ctime =
 510                         current_fs_time(inode->i_sb);
 511         }
 512         return inode;
 513 }
 514
 515 static void bm_clear_inode(struct inode *inode)
 516 {
 517         kfree(inode->i_private);
 518 }
 519
 520 static void kill_node(Node *e)
 521 {
 522         struct dentry *dentry;
 523
 524         write_lock(&entries_lock);
 525         dentry = e->dentry;
 526         if (dentry) {
 527                 list_del_init(&e->list);
 528                 e->dentry = NULL;
 529         }
 530         write_unlock(&entries_lock);
 531
 532         if (dentry) {
 533                 dentry->d_inode->i_nlink--;
 534                 d_drop(dentry);
 535                 dput(dentry);
 536                 simple_release_fs(&bm_mnt, &entry_count);
 537         }
 538 }
 539
 540 /* /<entry> */
 541
 542 static ssize_t
 543 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 544 {
 545         Node *e = file->f_path.dentry->d_inode->i_private;
 546         loff_t pos = *ppos;
 547         ssize_t res;
 548         char *page;
 549         int len;
 550
 551         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 552                 return -ENOMEM;
 553
 554         entry_status(e, page);
 555         len = strlen(page);
 556
 557         res = -EINVAL;
 558         if (pos < 0)
 559                 goto out;
 560         res = 0;
 561         if (pos >= len)
 562                 goto out;
 563         if (len < pos + nbytes)
 564                 nbytes = len - pos;
 565         res = -EFAULT;
 566         if (copy_to_user(buf, page + pos, nbytes))
 567                 goto out;
 568         *ppos = pos + nbytes;
 569         res = nbytes;
 570 out:
 571         free_page((unsigned long) page);
 572         return res;
 573 }
 574
 575 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 576                                 size_t count, loff_t *ppos)
 577 {
 578         struct dentry *root;
 579         Node *e = file->f_path.dentry->d_inode->i_private;
 580         int res = parse_command(buffer, count);
 581
 582         switch (res) {
 583                 case 1: clear_bit(Enabled, &e->flags);
 584                         break;
 585                 case 2: set_bit(Enabled, &e->flags);
 586                         break;
 587                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 588                         mutex_lock(&root->d_inode->i_mutex);
 589
 590                         kill_node(e);
 591
 592                         mutex_unlock(&root->d_inode->i_mutex);
 593                         dput(root);
 594                         break;
 595                 default: return res;
 596         }
 597         return count;
 598 }
 599
 600 static const struct file_operations bm_entry_operations = {
 601         .read           = bm_entry_read,
 602         .write          = bm_entry_write,
 603 };
 604
 605 /* /register */
 606
 607 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 608                                size_t count, loff_t *ppos)
 609 {
 610         Node *e;
 611         struct inode *inode;
 612         struct dentry *root, *dentry;
 613         struct super_block *sb = file->f_path.mnt->mnt_sb;
 614         int err = 0;
 615
 616         e = create_entry(buffer, count);
 617
 618         if (IS_ERR(e))
 619                 return PTR_ERR(e);
 620
 621         root = dget(sb->s_root);
 622         mutex_lock(&root->d_inode->i_mutex);
 623         dentry = lookup_one_len(e->name, root, strlen(e->name));
 624         err = PTR_ERR(dentry);
 625         if (IS_ERR(dentry))
 626                 goto out;
 627
 628         err = -EEXIST;
 629         if (dentry->d_inode)
 630                 goto out2;
 631
 632         inode = bm_get_inode(sb, S_IFREG | 0644);
 633
 634         err = -ENOMEM;
 635         if (!inode)
 636                 goto out2;
 637
 638         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 639         if (err) {
 640                 iput(inode);
 641                 inode = NULL;
 642                 goto out2;
 643         }
 644
 645         e->dentry = dget(dentry);
 646         inode->i_private = e;
 647         inode->i_fop = &bm_entry_operations;
 648
 649         d_instantiate(dentry, inode);
 650         write_lock(&entries_lock);
 651         list_add(&e->list, &entries);
 652         write_unlock(&entries_lock);
 653
 654         err = 0;
 655 out2:
 656         dput(dentry);
 657 out:
 658         mutex_unlock(&root->d_inode->i_mutex);
 659         dput(root);
 660
 661         if (err) {
 662                 kfree(e);
 663                 return -EINVAL;
 664         }
 665         return count;
 666 }
 667
 668 static const struct file_operations bm_register_operations = {
 669         .write          = bm_register_write,
 670 };
 671
 672 /* /status */
 673
 674 static ssize_t
 675 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 676 {
 677         char *s = enabled ? "enabled" : "disabled";
 678
 679         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 680 }
 681
 682 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 683                 size_t count, loff_t *ppos)
 684 {
 685         int res = parse_command(buffer, count);
 686         struct dentry *root;
 687
 688         switch (res) {
 689                 case 1: enabled = 0; break;
 690                 case 2: enabled = 1; break;
 691                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
 692                         mutex_lock(&root->d_inode->i_mutex);
 693
 694                         while (!list_empty(&entries))
 695                                 kill_node(list_entry(entries.next, Node, list));
 696
 697                         mutex_unlock(&root->d_inode->i_mutex);
 698                         dput(root);
 699                 default: return res;
 700         }
 701         return count;
 702 }
 703
 704 static const struct file_operations bm_status_operations = {
 705         .read           = bm_status_read,
 706         .write          = bm_status_write,
 707 };
 708
 709 /* Superblock handling */
 710
 711 static const struct super_operations s_ops = {
 712         .statfs         = simple_statfs,
 713         .clear_inode    = bm_clear_inode,
 714 };
 715
 716 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 717 {
 718         static struct tree_descr bm_files[] = {
 719                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 720                 [3] = {"register", &bm_register_operations, S_IWUSR},
 721                 /* last one */ {""}
 722         };
 723         int err = simple_fill_super(sb, 0x42494e4d, bm_files);
 724         if (!err)
 725                 sb->s_op = &s_ops;
 726         return err;
 727 }
 728
 729 static int bm_get_sb(struct file_system_type *fs_type,
 730         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 731 {
 732         return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
 733 }
 734
 735 static struct linux_binfmt misc_format = {
 736         .module = THIS_MODULE,
 737         .load_binary = load_misc_binary,
 738 };
 739
 740 static struct file_system_type bm_fs_type = {
 741         .owner          = THIS_MODULE,
 742         .name           = "binfmt_misc",
 743         .get_sb         = bm_get_sb,
 744         .kill_sb        = kill_litter_super,
 745 };
 746
 747 static int __init init_misc_binfmt(void)
 748 {
 749         int err = register_filesystem(&bm_fs_type);
 750         if (!err) {
 751                 err = register_binfmt(&misc_format);
 752                 if (err)
 753                         unregister_filesystem(&bm_fs_type);
 754         }
 755         return err;
 756 }
 757
 758 static void __exit exit_misc_binfmt(void)
 759 {
 760         unregister_binfmt(&misc_format);
 761         unregister_filesystem(&bm_fs_type);
 762 }
 763
 764 core_initcall(init_misc_binfmt);
 765 module_exit(exit_misc_binfmt);
 766 MODULE_LICENSE("GPL");