linux/fs/binfmt_misc.c
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   1/*
   2 *  binfmt_misc.c
   3 *
   4 *  Copyright (C) 1997 Richard G√ľnther
   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/magic.h>
  23#include <linux/binfmts.h>
  24#include <linux/slab.h>
  25#include <linux/ctype.h>
  26#include <linux/string_helpers.h>
  27#include <linux/file.h>
  28#include <linux/pagemap.h>
  29#include <linux/namei.h>
  30#include <linux/mount.h>
  31#include <linux/syscalls.h>
  32#include <linux/fs.h>
  33
  34#include <asm/uaccess.h>
  35
  36enum {
  37        VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  38};
  39
  40static LIST_HEAD(entries);
  41static int enabled = 1;
  42
  43enum {Enabled, Magic};
  44#define MISC_FMT_PRESERVE_ARGV0 (1<<31)
  45#define MISC_FMT_OPEN_BINARY (1<<30)
  46#define MISC_FMT_CREDENTIALS (1<<29)
  47
  48typedef struct {
  49        struct list_head list;
  50        unsigned long flags;            /* type, status, etc. */
  51        int offset;                     /* offset of magic */
  52        int size;                       /* size of magic/mask */
  53        char *magic;                    /* magic or filename extension */
  54        char *mask;                     /* mask, NULL for exact match */
  55        char *interpreter;              /* filename of interpreter */
  56        char *name;
  57        struct dentry *dentry;
  58} Node;
  59
  60static DEFINE_RWLOCK(entries_lock);
  61static struct file_system_type bm_fs_type;
  62static struct vfsmount *bm_mnt;
  63static int entry_count;
  64
  65/* 
  66 * Check if we support the binfmt
  67 * if we do, return the node, else NULL
  68 * locking is done in load_misc_binary
  69 */
  70static Node *check_file(struct linux_binprm *bprm)
  71{
  72        char *p = strrchr(bprm->interp, '.');
  73        struct list_head *l;
  74
  75        list_for_each(l, &entries) {
  76                Node *e = list_entry(l, Node, list);
  77                char *s;
  78                int j;
  79
  80                if (!test_bit(Enabled, &e->flags))
  81                        continue;
  82
  83                if (!test_bit(Magic, &e->flags)) {
  84                        if (p && !strcmp(e->magic, p + 1))
  85                                return e;
  86                        continue;
  87                }
  88
  89                s = bprm->buf + e->offset;
  90                if (e->mask) {
  91                        for (j = 0; j < e->size; j++)
  92                                if ((*s++ ^ e->magic[j]) & e->mask[j])
  93                                        break;
  94                } else {
  95                        for (j = 0; j < e->size; j++)
  96                                if ((*s++ ^ e->magic[j]))
  97                                        break;
  98                }
  99                if (j == e->size)
 100                        return e;
 101        }
 102        return NULL;
 103}
 104
 105/*
 106 * the loader itself
 107 */
 108static int load_misc_binary(struct linux_binprm *bprm)
 109{
 110        Node *fmt;
 111        struct file * interp_file = NULL;
 112        char iname[BINPRM_BUF_SIZE];
 113        const char *iname_addr = iname;
 114        int retval;
 115        int fd_binary = -1;
 116
 117        retval = -ENOEXEC;
 118        if (!enabled)
 119                goto _ret;
 120
 121        /* to keep locking time low, we copy the interpreter string */
 122        read_lock(&entries_lock);
 123        fmt = check_file(bprm);
 124        if (fmt)
 125                strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 126        read_unlock(&entries_lock);
 127        if (!fmt)
 128                goto _ret;
 129
 130        if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 131                retval = remove_arg_zero(bprm);
 132                if (retval)
 133                        goto _ret;
 134        }
 135
 136        if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 137
 138                /* if the binary should be opened on behalf of the
 139                 * interpreter than keep it open and assign descriptor
 140                 * to it */
 141                fd_binary = get_unused_fd();
 142                if (fd_binary < 0) {
 143                        retval = fd_binary;
 144                        goto _ret;
 145                }
 146                fd_install(fd_binary, bprm->file);
 147
 148                /* if the binary is not readable than enforce mm->dumpable=0
 149                   regardless of the interpreter's permissions */
 150                would_dump(bprm, bprm->file);
 151
 152                allow_write_access(bprm->file);
 153                bprm->file = NULL;
 154
 155                /* mark the bprm that fd should be passed to interp */
 156                bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
 157                bprm->interp_data = fd_binary;
 158
 159        } else {
 160                allow_write_access(bprm->file);
 161                fput(bprm->file);
 162                bprm->file = NULL;
 163        }
 164        /* make argv[1] be the path to the binary */
 165        retval = copy_strings_kernel (1, &bprm->interp, bprm);
 166        if (retval < 0)
 167                goto _error;
 168        bprm->argc++;
 169
 170        /* add the interp as argv[0] */
 171        retval = copy_strings_kernel (1, &iname_addr, bprm);
 172        if (retval < 0)
 173                goto _error;
 174        bprm->argc ++;
 175
 176        /* Update interp in case binfmt_script needs it. */
 177        retval = bprm_change_interp(iname, bprm);
 178        if (retval < 0)
 179                goto _error;
 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        retval = search_binary_handler(bprm);
 201        if (retval < 0)
 202                goto _error;
 203
 204_ret:
 205        return retval;
 206_error:
 207        if (fd_binary > 0)
 208                sys_close(fd_binary);
 209        bprm->interp_flags = 0;
 210        bprm->interp_data = 0;
 211        goto _ret;
 212}
 213
 214/* Command parsers */
 215
 216/*
 217 * parses and copies one argument enclosed in del from *sp to *dp,
 218 * recognising the \x special.
 219 * returns pointer to the copied argument or NULL in case of an
 220 * error (and sets err) or null argument length.
 221 */
 222static char *scanarg(char *s, char del)
 223{
 224        char c;
 225
 226        while ((c = *s++) != del) {
 227                if (c == '\\' && *s == 'x') {
 228                        s++;
 229                        if (!isxdigit(*s++))
 230                                return NULL;
 231                        if (!isxdigit(*s++))
 232                                return NULL;
 233                }
 234        }
 235        return s;
 236}
 237
 238static char * check_special_flags (char * sfs, Node * e)
 239{
 240        char * p = sfs;
 241        int cont = 1;
 242
 243        /* special flags */
 244        while (cont) {
 245                switch (*p) {
 246                        case 'P':
 247                                p++;
 248                                e->flags |= MISC_FMT_PRESERVE_ARGV0;
 249                                break;
 250                        case 'O':
 251                                p++;
 252                                e->flags |= MISC_FMT_OPEN_BINARY;
 253                                break;
 254                        case 'C':
 255                                p++;
 256                                /* this flags also implies the
 257                                   open-binary flag */
 258                                e->flags |= (MISC_FMT_CREDENTIALS |
 259                                                MISC_FMT_OPEN_BINARY);
 260                                break;
 261                        default:
 262                                cont = 0;
 263                }
 264        }
 265
 266        return p;
 267}
 268/*
 269 * This registers a new binary format, it recognises the syntax
 270 * ':name:type:offset:magic:mask:interpreter:flags'
 271 * where the ':' is the IFS, that can be chosen with the first char
 272 */
 273static Node *create_entry(const char __user *buffer, size_t count)
 274{
 275        Node *e;
 276        int memsize, err;
 277        char *buf, *p;
 278        char del;
 279
 280        /* some sanity checks */
 281        err = -EINVAL;
 282        if ((count < 11) || (count > 256))
 283                goto out;
 284
 285        err = -ENOMEM;
 286        memsize = sizeof(Node) + count + 8;
 287        e = kmalloc(memsize, GFP_USER);
 288        if (!e)
 289                goto out;
 290
 291        p = buf = (char *)e + sizeof(Node);
 292
 293        memset(e, 0, sizeof(Node));
 294        if (copy_from_user(buf, buffer, count))
 295                goto Efault;
 296
 297        del = *p++;     /* delimeter */
 298
 299        memset(buf+count, del, 8);
 300
 301        e->name = p;
 302        p = strchr(p, del);
 303        if (!p)
 304                goto Einval;
 305        *p++ = '\0';
 306        if (!e->name[0] ||
 307            !strcmp(e->name, ".") ||
 308            !strcmp(e->name, "..") ||
 309            strchr(e->name, '/'))
 310                goto Einval;
 311        switch (*p++) {
 312                case 'E': e->flags = 1<<Enabled; break;
 313                case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
 314                default: goto Einval;
 315        }
 316        if (*p++ != del)
 317                goto Einval;
 318        if (test_bit(Magic, &e->flags)) {
 319                char *s = strchr(p, del);
 320                if (!s)
 321                        goto Einval;
 322                *s++ = '\0';
 323                e->offset = simple_strtoul(p, &p, 10);
 324                if (*p++)
 325                        goto Einval;
 326                e->magic = p;
 327                p = scanarg(p, del);
 328                if (!p)
 329                        goto Einval;
 330                p[-1] = '\0';
 331                if (!e->magic[0])
 332                        goto Einval;
 333                e->mask = p;
 334                p = scanarg(p, del);
 335                if (!p)
 336                        goto Einval;
 337                p[-1] = '\0';
 338                if (!e->mask[0])
 339                        e->mask = NULL;
 340                e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
 341                if (e->mask &&
 342                    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
 343                        goto Einval;
 344                if (e->size + e->offset > BINPRM_BUF_SIZE)
 345                        goto Einval;
 346        } else {
 347                p = strchr(p, del);
 348                if (!p)
 349                        goto Einval;
 350                *p++ = '\0';
 351                e->magic = p;
 352                p = strchr(p, del);
 353                if (!p)
 354                        goto Einval;
 355                *p++ = '\0';
 356                if (!e->magic[0] || strchr(e->magic, '/'))
 357                        goto Einval;
 358                p = strchr(p, del);
 359                if (!p)
 360                        goto Einval;
 361                *p++ = '\0';
 362        }
 363        e->interpreter = p;
 364        p = strchr(p, del);
 365        if (!p)
 366                goto Einval;
 367        *p++ = '\0';
 368        if (!e->interpreter[0])
 369                goto Einval;
 370
 371
 372        p = check_special_flags (p, e);
 373
 374        if (*p == '\n')
 375                p++;
 376        if (p != buf + count)
 377                goto Einval;
 378        return e;
 379
 380out:
 381        return ERR_PTR(err);
 382
 383Efault:
 384        kfree(e);
 385        return ERR_PTR(-EFAULT);
 386Einval:
 387        kfree(e);
 388        return ERR_PTR(-EINVAL);
 389}
 390
 391/*
 392 * Set status of entry/binfmt_misc:
 393 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 394 */
 395static int parse_command(const char __user *buffer, size_t count)
 396{
 397        char s[4];
 398
 399        if (!count)
 400                return 0;
 401        if (count > 3)
 402                return -EINVAL;
 403        if (copy_from_user(s, buffer, count))
 404                return -EFAULT;
 405        if (s[count-1] == '\n')
 406                count--;
 407        if (count == 1 && s[0] == '0')
 408                return 1;
 409        if (count == 1 && s[0] == '1')
 410                return 2;
 411        if (count == 2 && s[0] == '-' && s[1] == '1')
 412                return 3;
 413        return -EINVAL;
 414}
 415
 416/* generic stuff */
 417
 418static void entry_status(Node *e, char *page)
 419{
 420        char *dp;
 421        char *status = "disabled";
 422        const char * flags = "flags: ";
 423
 424        if (test_bit(Enabled, &e->flags))
 425                status = "enabled";
 426
 427        if (!VERBOSE_STATUS) {
 428                sprintf(page, "%s\n", status);
 429                return;
 430        }
 431
 432        sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
 433        dp = page + strlen(page);
 434
 435        /* print the special flags */
 436        sprintf (dp, "%s", flags);
 437        dp += strlen (flags);
 438        if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
 439                *dp ++ = 'P';
 440        }
 441        if (e->flags & MISC_FMT_OPEN_BINARY) {
 442                *dp ++ = 'O';
 443        }
 444        if (e->flags & MISC_FMT_CREDENTIALS) {
 445                *dp ++ = 'C';
 446        }
 447        *dp ++ = '\n';
 448
 449
 450        if (!test_bit(Magic, &e->flags)) {
 451                sprintf(dp, "extension .%s\n", e->magic);
 452        } else {
 453                int i;
 454
 455                sprintf(dp, "offset %i\nmagic ", e->offset);
 456                dp = page + strlen(page);
 457                for (i = 0; i < e->size; i++) {
 458                        sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
 459                        dp += 2;
 460                }
 461                if (e->mask) {
 462                        sprintf(dp, "\nmask ");
 463                        dp += 6;
 464                        for (i = 0; i < e->size; i++) {
 465                                sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
 466                                dp += 2;
 467                        }
 468                }
 469                *dp++ = '\n';
 470                *dp = '\0';
 471        }
 472}
 473
 474static struct inode *bm_get_inode(struct super_block *sb, int mode)
 475{
 476        struct inode * inode = new_inode(sb);
 477
 478        if (inode) {
 479                inode->i_ino = get_next_ino();
 480                inode->i_mode = mode;
 481                inode->i_atime = inode->i_mtime = inode->i_ctime =
 482                        current_fs_time(inode->i_sb);
 483        }
 484        return inode;
 485}
 486
 487static void bm_evict_inode(struct inode *inode)
 488{
 489        clear_inode(inode);
 490        kfree(inode->i_private);
 491}
 492
 493static void kill_node(Node *e)
 494{
 495        struct dentry *dentry;
 496
 497        write_lock(&entries_lock);
 498        dentry = e->dentry;
 499        if (dentry) {
 500                list_del_init(&e->list);
 501                e->dentry = NULL;
 502        }
 503        write_unlock(&entries_lock);
 504
 505        if (dentry) {
 506                drop_nlink(dentry->d_inode);
 507                d_drop(dentry);
 508                dput(dentry);
 509                simple_release_fs(&bm_mnt, &entry_count);
 510        }
 511}
 512
 513/* /<entry> */
 514
 515static ssize_t
 516bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 517{
 518        Node *e = file_inode(file)->i_private;
 519        ssize_t res;
 520        char *page;
 521
 522        if (!(page = (char*) __get_free_page(GFP_KERNEL)))
 523                return -ENOMEM;
 524
 525        entry_status(e, page);
 526
 527        res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
 528
 529        free_page((unsigned long) page);
 530        return res;
 531}
 532
 533static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 534                                size_t count, loff_t *ppos)
 535{
 536        struct dentry *root;
 537        Node *e = file_inode(file)->i_private;
 538        int res = parse_command(buffer, count);
 539
 540        switch (res) {
 541                case 1: clear_bit(Enabled, &e->flags);
 542                        break;
 543                case 2: set_bit(Enabled, &e->flags);
 544                        break;
 545                case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 546                        mutex_lock(&root->d_inode->i_mutex);
 547
 548                        kill_node(e);
 549
 550                        mutex_unlock(&root->d_inode->i_mutex);
 551                        dput(root);
 552                        break;
 553                default: return res;
 554        }
 555        return count;
 556}
 557
 558static const struct file_operations bm_entry_operations = {
 559        .read           = bm_entry_read,
 560        .write          = bm_entry_write,
 561        .llseek         = default_llseek,
 562};
 563
 564/* /register */
 565
 566static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 567                               size_t count, loff_t *ppos)
 568{
 569        Node *e;
 570        struct inode *inode;
 571        struct dentry *root, *dentry;
 572        struct super_block *sb = file->f_path.dentry->d_sb;
 573        int err = 0;
 574
 575        e = create_entry(buffer, count);
 576
 577        if (IS_ERR(e))
 578                return PTR_ERR(e);
 579
 580        root = dget(sb->s_root);
 581        mutex_lock(&root->d_inode->i_mutex);
 582        dentry = lookup_one_len(e->name, root, strlen(e->name));
 583        err = PTR_ERR(dentry);
 584        if (IS_ERR(dentry))
 585                goto out;
 586
 587        err = -EEXIST;
 588        if (dentry->d_inode)
 589                goto out2;
 590
 591        inode = bm_get_inode(sb, S_IFREG | 0644);
 592
 593        err = -ENOMEM;
 594        if (!inode)
 595                goto out2;
 596
 597        err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
 598        if (err) {
 599                iput(inode);
 600                inode = NULL;
 601                goto out2;
 602        }
 603
 604        e->dentry = dget(dentry);
 605        inode->i_private = e;
 606        inode->i_fop = &bm_entry_operations;
 607
 608        d_instantiate(dentry, inode);
 609        write_lock(&entries_lock);
 610        list_add(&e->list, &entries);
 611        write_unlock(&entries_lock);
 612
 613        err = 0;
 614out2:
 615        dput(dentry);
 616out:
 617        mutex_unlock(&root->d_inode->i_mutex);
 618        dput(root);
 619
 620        if (err) {
 621                kfree(e);
 622                return -EINVAL;
 623        }
 624        return count;
 625}
 626
 627static const struct file_operations bm_register_operations = {
 628        .write          = bm_register_write,
 629        .llseek         = noop_llseek,
 630};
 631
 632/* /status */
 633
 634static ssize_t
 635bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 636{
 637        char *s = enabled ? "enabled\n" : "disabled\n";
 638
 639        return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 640}
 641
 642static ssize_t bm_status_write(struct file * file, const char __user * buffer,
 643                size_t count, loff_t *ppos)
 644{
 645        int res = parse_command(buffer, count);
 646        struct dentry *root;
 647
 648        switch (res) {
 649                case 1: enabled = 0; break;
 650                case 2: enabled = 1; break;
 651                case 3: root = dget(file->f_path.dentry->d_sb->s_root);
 652                        mutex_lock(&root->d_inode->i_mutex);
 653
 654                        while (!list_empty(&entries))
 655                                kill_node(list_entry(entries.next, Node, list));
 656
 657                        mutex_unlock(&root->d_inode->i_mutex);
 658                        dput(root);
 659                default: return res;
 660        }
 661        return count;
 662}
 663
 664static const struct file_operations bm_status_operations = {
 665        .read           = bm_status_read,
 666        .write          = bm_status_write,
 667        .llseek         = default_llseek,
 668};
 669
 670/* Superblock handling */
 671
 672static const struct super_operations s_ops = {
 673        .statfs         = simple_statfs,
 674        .evict_inode    = bm_evict_inode,
 675};
 676
 677static int bm_fill_super(struct super_block * sb, void * data, int silent)
 678{
 679        static struct tree_descr bm_files[] = {
 680                [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
 681                [3] = {"register", &bm_register_operations, S_IWUSR},
 682                /* last one */ {""}
 683        };
 684        int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 685        if (!err)
 686                sb->s_op = &s_ops;
 687        return err;
 688}
 689
 690static struct dentry *bm_mount(struct file_system_type *fs_type,
 691        int flags, const char *dev_name, void *data)
 692{
 693        return mount_single(fs_type, flags, data, bm_fill_super);
 694}
 695
 696static struct linux_binfmt misc_format = {
 697        .module = THIS_MODULE,
 698        .load_binary = load_misc_binary,
 699};
 700
 701static struct file_system_type bm_fs_type = {
 702        .owner          = THIS_MODULE,
 703        .name           = "binfmt_misc",
 704        .mount          = bm_mount,
 705        .kill_sb        = kill_litter_super,
 706};
 707MODULE_ALIAS_FS("binfmt_misc");
 708
 709static int __init init_misc_binfmt(void)
 710{
 711        int err = register_filesystem(&bm_fs_type);
 712        if (!err)
 713                insert_binfmt(&misc_format);
 714        return err;
 715}
 716
 717static void __exit exit_misc_binfmt(void)
 718{
 719        unregister_binfmt(&misc_format);
 720        unregister_filesystem(&bm_fs_type);
 721}
 722
 723core_initcall(init_misc_binfmt);
 724module_exit(exit_misc_binfmt);
 725MODULE_LICENSE("GPL");
 726
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