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/file.h>
  27#include <linux/pagemap.h>
  28#include <linux/namei.h>
  29#include <linux/mount.h>
  30#include <linux/syscalls.h>
  31#include <linux/fs.h>
  32
  33#include <asm/uaccess.h>
  34
  35enum {
  36        VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
  37};
  38
  39static LIST_HEAD(entries);
  40static int enabled = 1;
  41
  42enum {Enabled, Magic};
  43#define MISC_FMT_PRESERVE_ARGV0 (1<<31)
  44#define MISC_FMT_OPEN_BINARY (1<<30)
  45#define MISC_FMT_CREDENTIALS (1<<29)
  46
  47typedef struct {
  48        struct list_head list;
  49        unsigned long flags;            /* type, status, etc. */
  50        int offset;                     /* offset of magic */
  51        int size;                       /* size of magic/mask */
  52        char *magic;                    /* magic or filename extension */
  53        char *mask;                     /* mask, NULL for exact match */
  54        char *interpreter;              /* filename of interpreter */
  55        char *name;
  56        struct dentry *dentry;
  57} Node;
  58
  59static DEFINE_RWLOCK(entries_lock);
  60static struct file_system_type bm_fs_type;
  61static struct vfsmount *bm_mnt;
  62static int entry_count;
  63
  64/* 
  65 * Check if we support the binfmt
  66 * if we do, return the node, else NULL
  67 * locking is done in load_misc_binary
  68 */
  69static Node *check_file(struct linux_binprm *bprm)
  70{
  71        char *p = strrchr(bprm->interp, '.');
  72        struct list_head *l;
  73
  74        list_for_each(l, &entries) {
  75                Node *e = list_entry(l, Node, list);
  76                char *s;
  77                int j;
  78
  79                if (!test_bit(Enabled, &e->flags))
  80                        continue;
  81
  82                if (!test_bit(Magic, &e->flags)) {
  83                        if (p && !strcmp(e->magic, p + 1))
  84                                return e;
  85                        continue;
  86                }
  87
  88                s = bprm->buf + e->offset;
  89                if (e->mask) {
  90                        for (j = 0; j < e->size; j++)
  91                                if ((*s++ ^ e->magic[j]) & e->mask[j])
  92                                        break;
  93                } else {
  94                        for (j = 0; j < e->size; j++)
  95                                if ((*s++ ^ e->magic[j]))
  96                                        break;
  97                }
  98                if (j == e->size)
  99                        return e;
 100        }
 101        return NULL;
 102}
 103
 104/*
 105 * the loader itself
 106 */
 107static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 108{
 109        Node *fmt;
 110        struct file * interp_file = NULL;
 111        char iname[BINPRM_BUF_SIZE];
 112        const char *iname_addr = iname;
 113        int retval;
 114        int fd_binary = -1;
 115
 116        retval = -ENOEXEC;
 117        if (!enabled)
 118                goto _ret;
 119
 120        retval = -ENOEXEC;
 121        if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
 122                goto _ret;
 123
 124        /* to keep locking time low, we copy the interpreter string */
 125        read_lock(&entries_lock);
 126        fmt = check_file(bprm);
 127        if (fmt)
 128                strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
 129        read_unlock(&entries_lock);
 130        if (!fmt)
 131                goto _ret;
 132
 133        if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
 134                retval = remove_arg_zero(bprm);
 135                if (retval)
 136                        goto _ret;
 137        }
 138
 139        if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 140
 141                /* if the binary should be opened on behalf of the
 142                 * interpreter than keep it open and assign descriptor
 143                 * to it */
 144                fd_binary = get_unused_fd();
 145                if (fd_binary < 0) {
 146                        retval = fd_binary;
 147                        goto _ret;
 148                }
 149                fd_install(fd_binary, bprm->file);
 150
 151                /* if the binary is not readable than enforce mm->dumpable=0
 152                   regardless of the interpreter's permissions */
 153                would_dump(bprm, bprm->file);
 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 */
 227static 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
 243static 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
 261static 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 */
 296static 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
 402out:
 403        return ERR_PTR(err);
 404
 405Efault:
 406        kfree(e);
 407        return ERR_PTR(-EFAULT);
 408Einval:
 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 */
 417static 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
 440static 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
 496static 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
 509static void bm_evict_inode(struct inode *inode)
 510{
 511        clear_inode(inode);
 512        kfree(inode->i_private);
 513}
 514
 515static 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                drop_nlink(dentry->d_inode);
 529                d_drop(dentry);
 530                dput(dentry);
 531                simple_release_fs(&bm_mnt, &entry_count);
 532        }
 533}
 534
 535/* /<entry> */
 536
 537static ssize_t
 538bm_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
 555static 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.dentry->d_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
 580static 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
 588static 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.dentry->d_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;
 636out2:
 637        dput(dentry);
 638out:
 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
 649static const struct file_operations bm_register_operations = {
 650        .write          = bm_register_write,
 651        .llseek         = noop_llseek,
 652};
 653
 654/* /status */
 655
 656static ssize_t
 657bm_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
 664static 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.dentry->d_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
 686static 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
 694static const struct super_operations s_ops = {
 695        .statfs         = simple_statfs,
 696        .evict_inode    = bm_evict_inode,
 697};
 698
 699static 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, BINFMTFS_MAGIC, bm_files);
 707        if (!err)
 708                sb->s_op = &s_ops;
 709        return err;
 710}
 711
 712static 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
 718static struct linux_binfmt misc_format = {
 719        .module = THIS_MODULE,
 720        .load_binary = load_misc_binary,
 721};
 722
 723static 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
 730static int __init init_misc_binfmt(void)
 731{
 732        int err = register_filesystem(&bm_fs_type);
 733        if (!err)
 734                insert_binfmt(&misc_format);
 735        return err;
 736}
 737
 738static void __exit exit_misc_binfmt(void)
 739{
 740        unregister_binfmt(&misc_format);
 741        unregister_filesystem(&bm_fs_type);
 742}
 743
 744core_initcall(init_misc_binfmt);
 745module_exit(exit_misc_binfmt);
 746MODULE_LICENSE("GPL");
 747
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