linux/fs/open.c
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   1/*
   2 *  linux/fs/open.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 */
   6
   7#include <linux/string.h>
   8#include <linux/mm.h>
   9#include <linux/file.h>
  10#include <linux/fdtable.h>
  11#include <linux/fsnotify.h>
  12#include <linux/module.h>
  13#include <linux/tty.h>
  14#include <linux/namei.h>
  15#include <linux/backing-dev.h>
  16#include <linux/capability.h>
  17#include <linux/securebits.h>
  18#include <linux/security.h>
  19#include <linux/mount.h>
  20#include <linux/fcntl.h>
  21#include <linux/slab.h>
  22#include <asm/uaccess.h>
  23#include <linux/fs.h>
  24#include <linux/personality.h>
  25#include <linux/pagemap.h>
  26#include <linux/syscalls.h>
  27#include <linux/rcupdate.h>
  28#include <linux/audit.h>
  29#include <linux/falloc.h>
  30#include <linux/fs_struct.h>
  31#include <linux/ima.h>
  32#include <linux/dnotify.h>
  33
  34#include "internal.h"
  35
  36int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
  37        struct file *filp)
  38{
  39        int ret;
  40        struct iattr newattrs;
  41
  42        /* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
  43        if (length < 0)
  44                return -EINVAL;
  45
  46        newattrs.ia_size = length;
  47        newattrs.ia_valid = ATTR_SIZE | time_attrs;
  48        if (filp) {
  49                newattrs.ia_file = filp;
  50                newattrs.ia_valid |= ATTR_FILE;
  51        }
  52
  53        /* Remove suid/sgid on truncate too */
  54        ret = should_remove_suid(dentry);
  55        if (ret)
  56                newattrs.ia_valid |= ret | ATTR_FORCE;
  57
  58        mutex_lock(&dentry->d_inode->i_mutex);
  59        ret = notify_change(dentry, &newattrs);
  60        mutex_unlock(&dentry->d_inode->i_mutex);
  61        return ret;
  62}
  63
  64static long do_sys_truncate(const char __user *pathname, loff_t length)
  65{
  66        struct path path;
  67        struct inode *inode;
  68        int error;
  69
  70        error = -EINVAL;
  71        if (length < 0) /* sorry, but loff_t says... */
  72                goto out;
  73
  74        error = user_path(pathname, &path);
  75        if (error)
  76                goto out;
  77        inode = path.dentry->d_inode;
  78
  79        /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
  80        error = -EISDIR;
  81        if (S_ISDIR(inode->i_mode))
  82                goto dput_and_out;
  83
  84        error = -EINVAL;
  85        if (!S_ISREG(inode->i_mode))
  86                goto dput_and_out;
  87
  88        error = mnt_want_write(path.mnt);
  89        if (error)
  90                goto dput_and_out;
  91
  92        error = inode_permission(inode, MAY_WRITE);
  93        if (error)
  94                goto mnt_drop_write_and_out;
  95
  96        error = -EPERM;
  97        if (IS_APPEND(inode))
  98                goto mnt_drop_write_and_out;
  99
 100        error = get_write_access(inode);
 101        if (error)
 102                goto mnt_drop_write_and_out;
 103
 104        /*
 105         * Make sure that there are no leases.  get_write_access() protects
 106         * against the truncate racing with a lease-granting setlease().
 107         */
 108        error = break_lease(inode, O_WRONLY);
 109        if (error)
 110                goto put_write_and_out;
 111
 112        error = locks_verify_truncate(inode, NULL, length);
 113        if (!error)
 114                error = security_path_truncate(&path);
 115        if (!error)
 116                error = do_truncate(path.dentry, length, 0, NULL);
 117
 118put_write_and_out:
 119        put_write_access(inode);
 120mnt_drop_write_and_out:
 121        mnt_drop_write(path.mnt);
 122dput_and_out:
 123        path_put(&path);
 124out:
 125        return error;
 126}
 127
 128SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
 129{
 130        return do_sys_truncate(path, length);
 131}
 132
 133static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
 134{
 135        struct inode * inode;
 136        struct dentry *dentry;
 137        struct file * file;
 138        int error;
 139
 140        error = -EINVAL;
 141        if (length < 0)
 142                goto out;
 143        error = -EBADF;
 144        file = fget(fd);
 145        if (!file)
 146                goto out;
 147
 148        /* explicitly opened as large or we are on 64-bit box */
 149        if (file->f_flags & O_LARGEFILE)
 150                small = 0;
 151
 152        dentry = file->f_path.dentry;
 153        inode = dentry->d_inode;
 154        error = -EINVAL;
 155        if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
 156                goto out_putf;
 157
 158        error = -EINVAL;
 159        /* Cannot ftruncate over 2^31 bytes without large file support */
 160        if (small && length > MAX_NON_LFS)
 161                goto out_putf;
 162
 163        error = -EPERM;
 164        if (IS_APPEND(inode))
 165                goto out_putf;
 166
 167        error = locks_verify_truncate(inode, file, length);
 168        if (!error)
 169                error = security_path_truncate(&file->f_path);
 170        if (!error)
 171                error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, file);
 172out_putf:
 173        fput(file);
 174out:
 175        return error;
 176}
 177
 178SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
 179{
 180        long ret = do_sys_ftruncate(fd, length, 1);
 181        /* avoid REGPARM breakage on x86: */
 182        asmlinkage_protect(2, ret, fd, length);
 183        return ret;
 184}
 185
 186/* LFS versions of truncate are only needed on 32 bit machines */
 187#if BITS_PER_LONG == 32
 188SYSCALL_DEFINE(truncate64)(const char __user * path, loff_t length)
 189{
 190        return do_sys_truncate(path, length);
 191}
 192#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
 193asmlinkage long SyS_truncate64(long path, loff_t length)
 194{
 195        return SYSC_truncate64((const char __user *) path, length);
 196}
 197SYSCALL_ALIAS(sys_truncate64, SyS_truncate64);
 198#endif
 199
 200SYSCALL_DEFINE(ftruncate64)(unsigned int fd, loff_t length)
 201{
 202        long ret = do_sys_ftruncate(fd, length, 0);
 203        /* avoid REGPARM breakage on x86: */
 204        asmlinkage_protect(2, ret, fd, length);
 205        return ret;
 206}
 207#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
 208asmlinkage long SyS_ftruncate64(long fd, loff_t length)
 209{
 210        return SYSC_ftruncate64((unsigned int) fd, length);
 211}
 212SYSCALL_ALIAS(sys_ftruncate64, SyS_ftruncate64);
 213#endif
 214#endif /* BITS_PER_LONG == 32 */
 215
 216
 217int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 218{
 219        struct inode *inode = file->f_path.dentry->d_inode;
 220        long ret;
 221
 222        if (offset < 0 || len <= 0)
 223                return -EINVAL;
 224
 225        /* Return error if mode is not supported */
 226        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
 227                return -EOPNOTSUPP;
 228
 229        /* Punch hole must have keep size set */
 230        if ((mode & FALLOC_FL_PUNCH_HOLE) &&
 231            !(mode & FALLOC_FL_KEEP_SIZE))
 232                return -EOPNOTSUPP;
 233
 234        if (!(file->f_mode & FMODE_WRITE))
 235                return -EBADF;
 236
 237        /* It's not possible punch hole on append only file */
 238        if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
 239                return -EPERM;
 240
 241        if (IS_IMMUTABLE(inode))
 242                return -EPERM;
 243
 244        /*
 245         * Revalidate the write permissions, in case security policy has
 246         * changed since the files were opened.
 247         */
 248        ret = security_file_permission(file, MAY_WRITE);
 249        if (ret)
 250                return ret;
 251
 252        if (S_ISFIFO(inode->i_mode))
 253                return -ESPIPE;
 254
 255        /*
 256         * Let individual file system decide if it supports preallocation
 257         * for directories or not.
 258         */
 259        if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
 260                return -ENODEV;
 261
 262        /* Check for wrap through zero too */
 263        if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
 264                return -EFBIG;
 265
 266        if (!file->f_op->fallocate)
 267                return -EOPNOTSUPP;
 268
 269        return file->f_op->fallocate(file, mode, offset, len);
 270}
 271
 272SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
 273{
 274        struct file *file;
 275        int error = -EBADF;
 276
 277        file = fget(fd);
 278        if (file) {
 279                error = do_fallocate(file, mode, offset, len);
 280                fput(file);
 281        }
 282
 283        return error;
 284}
 285
 286#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
 287asmlinkage long SyS_fallocate(long fd, long mode, loff_t offset, loff_t len)
 288{
 289        return SYSC_fallocate((int)fd, (int)mode, offset, len);
 290}
 291SYSCALL_ALIAS(sys_fallocate, SyS_fallocate);
 292#endif
 293
 294/*
 295 * access() needs to use the real uid/gid, not the effective uid/gid.
 296 * We do this by temporarily clearing all FS-related capabilities and
 297 * switching the fsuid/fsgid around to the real ones.
 298 */
 299SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
 300{
 301        const struct cred *old_cred;
 302        struct cred *override_cred;
 303        struct path path;
 304        struct inode *inode;
 305        int res;
 306
 307        if (mode & ~S_IRWXO)    /* where's F_OK, X_OK, W_OK, R_OK? */
 308                return -EINVAL;
 309
 310        override_cred = prepare_creds();
 311        if (!override_cred)
 312                return -ENOMEM;
 313
 314        override_cred->fsuid = override_cred->uid;
 315        override_cred->fsgid = override_cred->gid;
 316
 317        if (!issecure(SECURE_NO_SETUID_FIXUP)) {
 318                /* Clear the capabilities if we switch to a non-root user */
 319                if (override_cred->uid)
 320                        cap_clear(override_cred->cap_effective);
 321                else
 322                        override_cred->cap_effective =
 323                                override_cred->cap_permitted;
 324        }
 325
 326        old_cred = override_creds(override_cred);
 327
 328        res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
 329        if (res)
 330                goto out;
 331
 332        inode = path.dentry->d_inode;
 333
 334        if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
 335                /*
 336                 * MAY_EXEC on regular files is denied if the fs is mounted
 337                 * with the "noexec" flag.
 338                 */
 339                res = -EACCES;
 340                if (path.mnt->mnt_flags & MNT_NOEXEC)
 341                        goto out_path_release;
 342        }
 343
 344        res = inode_permission(inode, mode | MAY_ACCESS);
 345        /* SuS v2 requires we report a read only fs too */
 346        if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
 347                goto out_path_release;
 348        /*
 349         * This is a rare case where using __mnt_is_readonly()
 350         * is OK without a mnt_want/drop_write() pair.  Since
 351         * no actual write to the fs is performed here, we do
 352         * not need to telegraph to that to anyone.
 353         *
 354         * By doing this, we accept that this access is
 355         * inherently racy and know that the fs may change
 356         * state before we even see this result.
 357         */
 358        if (__mnt_is_readonly(path.mnt))
 359                res = -EROFS;
 360
 361out_path_release:
 362        path_put(&path);
 363out:
 364        revert_creds(old_cred);
 365        put_cred(override_cred);
 366        return res;
 367}
 368
 369SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
 370{
 371        return sys_faccessat(AT_FDCWD, filename, mode);
 372}
 373
 374SYSCALL_DEFINE1(chdir, const char __user *, filename)
 375{
 376        struct path path;
 377        int error;
 378
 379        error = user_path_dir(filename, &path);
 380        if (error)
 381                goto out;
 382
 383        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 384        if (error)
 385                goto dput_and_out;
 386
 387        set_fs_pwd(current->fs, &path);
 388
 389dput_and_out:
 390        path_put(&path);
 391out:
 392        return error;
 393}
 394
 395SYSCALL_DEFINE1(fchdir, unsigned int, fd)
 396{
 397        struct file *file;
 398        struct inode *inode;
 399        int error;
 400
 401        error = -EBADF;
 402        file = fget(fd);
 403        if (!file)
 404                goto out;
 405
 406        inode = file->f_path.dentry->d_inode;
 407
 408        error = -ENOTDIR;
 409        if (!S_ISDIR(inode->i_mode))
 410                goto out_putf;
 411
 412        error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
 413        if (!error)
 414                set_fs_pwd(current->fs, &file->f_path);
 415out_putf:
 416        fput(file);
 417out:
 418        return error;
 419}
 420
 421SYSCALL_DEFINE1(chroot, const char __user *, filename)
 422{
 423        struct path path;
 424        int error;
 425
 426        error = user_path_dir(filename, &path);
 427        if (error)
 428                goto out;
 429
 430        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 431        if (error)
 432                goto dput_and_out;
 433
 434        error = -EPERM;
 435        if (!capable(CAP_SYS_CHROOT))
 436                goto dput_and_out;
 437        error = security_path_chroot(&path);
 438        if (error)
 439                goto dput_and_out;
 440
 441        set_fs_root(current->fs, &path);
 442        error = 0;
 443dput_and_out:
 444        path_put(&path);
 445out:
 446        return error;
 447}
 448
 449static int chmod_common(struct path *path, umode_t mode)
 450{
 451        struct inode *inode = path->dentry->d_inode;
 452        struct iattr newattrs;
 453        int error;
 454
 455        error = mnt_want_write(path->mnt);
 456        if (error)
 457                return error;
 458        mutex_lock(&inode->i_mutex);
 459        error = security_path_chmod(path->dentry, path->mnt, mode);
 460        if (error)
 461                goto out_unlock;
 462        newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
 463        newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
 464        error = notify_change(path->dentry, &newattrs);
 465out_unlock:
 466        mutex_unlock(&inode->i_mutex);
 467        mnt_drop_write(path->mnt);
 468        return error;
 469}
 470
 471SYSCALL_DEFINE2(fchmod, unsigned int, fd, mode_t, mode)
 472{
 473        struct file * file;
 474        int err = -EBADF;
 475
 476        file = fget(fd);
 477        if (file) {
 478                audit_inode(NULL, file->f_path.dentry);
 479                err = chmod_common(&file->f_path, mode);
 480                fput(file);
 481        }
 482        return err;
 483}
 484
 485SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, mode_t, mode)
 486{
 487        struct path path;
 488        int error;
 489
 490        error = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
 491        if (!error) {
 492                error = chmod_common(&path, mode);
 493                path_put(&path);
 494        }
 495        return error;
 496}
 497
 498SYSCALL_DEFINE2(chmod, const char __user *, filename, mode_t, mode)
 499{
 500        return sys_fchmodat(AT_FDCWD, filename, mode);
 501}
 502
 503static int chown_common(struct path *path, uid_t user, gid_t group)
 504{
 505        struct inode *inode = path->dentry->d_inode;
 506        int error;
 507        struct iattr newattrs;
 508
 509        newattrs.ia_valid =  ATTR_CTIME;
 510        if (user != (uid_t) -1) {
 511                newattrs.ia_valid |= ATTR_UID;
 512                newattrs.ia_uid = user;
 513        }
 514        if (group != (gid_t) -1) {
 515                newattrs.ia_valid |= ATTR_GID;
 516                newattrs.ia_gid = group;
 517        }
 518        if (!S_ISDIR(inode->i_mode))
 519                newattrs.ia_valid |=
 520                        ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
 521        mutex_lock(&inode->i_mutex);
 522        error = security_path_chown(path, user, group);
 523        if (!error)
 524                error = notify_change(path->dentry, &newattrs);
 525        mutex_unlock(&inode->i_mutex);
 526
 527        return error;
 528}
 529
 530SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
 531{
 532        struct path path;
 533        int error;
 534
 535        error = user_path(filename, &path);
 536        if (error)
 537                goto out;
 538        error = mnt_want_write(path.mnt);
 539        if (error)
 540                goto out_release;
 541        error = chown_common(&path, user, group);
 542        mnt_drop_write(path.mnt);
 543out_release:
 544        path_put(&path);
 545out:
 546        return error;
 547}
 548
 549SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 550                gid_t, group, int, flag)
 551{
 552        struct path path;
 553        int error = -EINVAL;
 554        int lookup_flags;
 555
 556        if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
 557                goto out;
 558
 559        lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
 560        if (flag & AT_EMPTY_PATH)
 561                lookup_flags |= LOOKUP_EMPTY;
 562        error = user_path_at(dfd, filename, lookup_flags, &path);
 563        if (error)
 564                goto out;
 565        error = mnt_want_write(path.mnt);
 566        if (error)
 567                goto out_release;
 568        error = chown_common(&path, user, group);
 569        mnt_drop_write(path.mnt);
 570out_release:
 571        path_put(&path);
 572out:
 573        return error;
 574}
 575
 576SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
 577{
 578        struct path path;
 579        int error;
 580
 581        error = user_lpath(filename, &path);
 582        if (error)
 583                goto out;
 584        error = mnt_want_write(path.mnt);
 585        if (error)
 586                goto out_release;
 587        error = chown_common(&path, user, group);
 588        mnt_drop_write(path.mnt);
 589out_release:
 590        path_put(&path);
 591out:
 592        return error;
 593}
 594
 595SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
 596{
 597        struct file * file;
 598        int error = -EBADF;
 599        struct dentry * dentry;
 600
 601        file = fget(fd);
 602        if (!file)
 603                goto out;
 604
 605        error = mnt_want_write_file(file);
 606        if (error)
 607                goto out_fput;
 608        dentry = file->f_path.dentry;
 609        audit_inode(NULL, dentry);
 610        error = chown_common(&file->f_path, user, group);
 611        mnt_drop_write(file->f_path.mnt);
 612out_fput:
 613        fput(file);
 614out:
 615        return error;
 616}
 617
 618/*
 619 * You have to be very careful that these write
 620 * counts get cleaned up in error cases and
 621 * upon __fput().  This should probably never
 622 * be called outside of __dentry_open().
 623 */
 624static inline int __get_file_write_access(struct inode *inode,
 625                                          struct vfsmount *mnt)
 626{
 627        int error;
 628        error = get_write_access(inode);
 629        if (error)
 630                return error;
 631        /*
 632         * Do not take mount writer counts on
 633         * special files since no writes to
 634         * the mount itself will occur.
 635         */
 636        if (!special_file(inode->i_mode)) {
 637                /*
 638                 * Balanced in __fput()
 639                 */
 640                error = mnt_want_write(mnt);
 641                if (error)
 642                        put_write_access(inode);
 643        }
 644        return error;
 645}
 646
 647static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
 648                                        struct file *f,
 649                                        int (*open)(struct inode *, struct file *),
 650                                        const struct cred *cred)
 651{
 652        static const struct file_operations empty_fops = {};
 653        struct inode *inode;
 654        int error;
 655
 656        f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
 657                                FMODE_PREAD | FMODE_PWRITE;
 658
 659        if (unlikely(f->f_flags & O_PATH))
 660                f->f_mode = FMODE_PATH;
 661
 662        inode = dentry->d_inode;
 663        if (f->f_mode & FMODE_WRITE) {
 664                error = __get_file_write_access(inode, mnt);
 665                if (error)
 666                        goto cleanup_file;
 667                if (!special_file(inode->i_mode))
 668                        file_take_write(f);
 669        }
 670
 671        f->f_mapping = inode->i_mapping;
 672        f->f_path.dentry = dentry;
 673        f->f_path.mnt = mnt;
 674        f->f_pos = 0;
 675        file_sb_list_add(f, inode->i_sb);
 676
 677        if (unlikely(f->f_mode & FMODE_PATH)) {
 678                f->f_op = &empty_fops;
 679                return f;
 680        }
 681
 682        f->f_op = fops_get(inode->i_fop);
 683
 684        error = security_dentry_open(f, cred);
 685        if (error)
 686                goto cleanup_all;
 687
 688        if (!open && f->f_op)
 689                open = f->f_op->open;
 690        if (open) {
 691                error = open(inode, f);
 692                if (error)
 693                        goto cleanup_all;
 694        }
 695        if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 696                i_readcount_inc(inode);
 697
 698        f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 699
 700        file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
 701
 702        /* NB: we're sure to have correct a_ops only after f_op->open */
 703        if (f->f_flags & O_DIRECT) {
 704                if (!f->f_mapping->a_ops ||
 705                    ((!f->f_mapping->a_ops->direct_IO) &&
 706                    (!f->f_mapping->a_ops->get_xip_mem))) {
 707                        fput(f);
 708                        f = ERR_PTR(-EINVAL);
 709                }
 710        }
 711
 712        return f;
 713
 714cleanup_all:
 715        fops_put(f->f_op);
 716        if (f->f_mode & FMODE_WRITE) {
 717                put_write_access(inode);
 718                if (!special_file(inode->i_mode)) {
 719                        /*
 720                         * We don't consider this a real
 721                         * mnt_want/drop_write() pair
 722                         * because it all happenend right
 723                         * here, so just reset the state.
 724                         */
 725                        file_reset_write(f);
 726                        mnt_drop_write(mnt);
 727                }
 728        }
 729        file_sb_list_del(f);
 730        f->f_path.dentry = NULL;
 731        f->f_path.mnt = NULL;
 732cleanup_file:
 733        put_filp(f);
 734        dput(dentry);
 735        mntput(mnt);
 736        return ERR_PTR(error);
 737}
 738
 739/**
 740 * lookup_instantiate_filp - instantiates the open intent filp
 741 * @nd: pointer to nameidata
 742 * @dentry: pointer to dentry
 743 * @open: open callback
 744 *
 745 * Helper for filesystems that want to use lookup open intents and pass back
 746 * a fully instantiated struct file to the caller.
 747 * This function is meant to be called from within a filesystem's
 748 * lookup method.
 749 * Beware of calling it for non-regular files! Those ->open methods might block
 750 * (e.g. in fifo_open), leaving you with parent locked (and in case of fifo,
 751 * leading to a deadlock, as nobody can open that fifo anymore, because
 752 * another process to open fifo will block on locked parent when doing lookup).
 753 * Note that in case of error, nd->intent.open.file is destroyed, but the
 754 * path information remains valid.
 755 * If the open callback is set to NULL, then the standard f_op->open()
 756 * filesystem callback is substituted.
 757 */
 758struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
 759                int (*open)(struct inode *, struct file *))
 760{
 761        const struct cred *cred = current_cred();
 762
 763        if (IS_ERR(nd->intent.open.file))
 764                goto out;
 765        if (IS_ERR(dentry))
 766                goto out_err;
 767        nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->path.mnt),
 768                                             nd->intent.open.file,
 769                                             open, cred);
 770out:
 771        return nd->intent.open.file;
 772out_err:
 773        release_open_intent(nd);
 774        nd->intent.open.file = ERR_CAST(dentry);
 775        goto out;
 776}
 777EXPORT_SYMBOL_GPL(lookup_instantiate_filp);
 778
 779/**
 780 * nameidata_to_filp - convert a nameidata to an open filp.
 781 * @nd: pointer to nameidata
 782 * @flags: open flags
 783 *
 784 * Note that this function destroys the original nameidata
 785 */
 786struct file *nameidata_to_filp(struct nameidata *nd)
 787{
 788        const struct cred *cred = current_cred();
 789        struct file *filp;
 790
 791        /* Pick up the filp from the open intent */
 792        filp = nd->intent.open.file;
 793        nd->intent.open.file = NULL;
 794
 795        /* Has the filesystem initialised the file for us? */
 796        if (filp->f_path.dentry == NULL) {
 797                path_get(&nd->path);
 798                filp = __dentry_open(nd->path.dentry, nd->path.mnt, filp,
 799                                     NULL, cred);
 800        }
 801        return filp;
 802}
 803
 804/*
 805 * dentry_open() will have done dput(dentry) and mntput(mnt) if it returns an
 806 * error.
 807 */
 808struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
 809                         const struct cred *cred)
 810{
 811        int error;
 812        struct file *f;
 813
 814        validate_creds(cred);
 815
 816        /* We must always pass in a valid mount pointer. */
 817        BUG_ON(!mnt);
 818
 819        error = -ENFILE;
 820        f = get_empty_filp();
 821        if (f == NULL) {
 822                dput(dentry);
 823                mntput(mnt);
 824                return ERR_PTR(error);
 825        }
 826
 827        f->f_flags = flags;
 828        return __dentry_open(dentry, mnt, f, NULL, cred);
 829}
 830EXPORT_SYMBOL(dentry_open);
 831
 832static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 833{
 834        struct fdtable *fdt = files_fdtable(files);
 835        __FD_CLR(fd, fdt->open_fds);
 836        if (fd < files->next_fd)
 837                files->next_fd = fd;
 838}
 839
 840void put_unused_fd(unsigned int fd)
 841{
 842        struct files_struct *files = current->files;
 843        spin_lock(&files->file_lock);
 844        __put_unused_fd(files, fd);
 845        spin_unlock(&files->file_lock);
 846}
 847
 848EXPORT_SYMBOL(put_unused_fd);
 849
 850/*
 851 * Install a file pointer in the fd array.
 852 *
 853 * The VFS is full of places where we drop the files lock between
 854 * setting the open_fds bitmap and installing the file in the file
 855 * array.  At any such point, we are vulnerable to a dup2() race
 856 * installing a file in the array before us.  We need to detect this and
 857 * fput() the struct file we are about to overwrite in this case.
 858 *
 859 * It should never happen - if we allow dup2() do it, _really_ bad things
 860 * will follow.
 861 */
 862
 863void fd_install(unsigned int fd, struct file *file)
 864{
 865        struct files_struct *files = current->files;
 866        struct fdtable *fdt;
 867        spin_lock(&files->file_lock);
 868        fdt = files_fdtable(files);
 869        BUG_ON(fdt->fd[fd] != NULL);
 870        rcu_assign_pointer(fdt->fd[fd], file);
 871        spin_unlock(&files->file_lock);
 872}
 873
 874EXPORT_SYMBOL(fd_install);
 875
 876static inline int build_open_flags(int flags, int mode, struct open_flags *op)
 877{
 878        int lookup_flags = 0;
 879        int acc_mode;
 880
 881        if (!(flags & O_CREAT))
 882                mode = 0;
 883        op->mode = mode;
 884
 885        /* Must never be set by userspace */
 886        flags &= ~FMODE_NONOTIFY;
 887
 888        /*
 889         * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
 890         * check for O_DSYNC if the need any syncing at all we enforce it's
 891         * always set instead of having to deal with possibly weird behaviour
 892         * for malicious applications setting only __O_SYNC.
 893         */
 894        if (flags & __O_SYNC)
 895                flags |= O_DSYNC;
 896
 897        /*
 898         * If we have O_PATH in the open flag. Then we
 899         * cannot have anything other than the below set of flags
 900         */
 901        if (flags & O_PATH) {
 902                flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
 903                acc_mode = 0;
 904        } else {
 905                acc_mode = MAY_OPEN | ACC_MODE(flags);
 906        }
 907
 908        op->open_flag = flags;
 909
 910        /* O_TRUNC implies we need access checks for write permissions */
 911        if (flags & O_TRUNC)
 912                acc_mode |= MAY_WRITE;
 913
 914        /* Allow the LSM permission hook to distinguish append
 915           access from general write access. */
 916        if (flags & O_APPEND)
 917                acc_mode |= MAY_APPEND;
 918
 919        op->acc_mode = acc_mode;
 920
 921        op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
 922
 923        if (flags & O_CREAT) {
 924                op->intent |= LOOKUP_CREATE;
 925                if (flags & O_EXCL)
 926                        op->intent |= LOOKUP_EXCL;
 927        }
 928
 929        if (flags & O_DIRECTORY)
 930                lookup_flags |= LOOKUP_DIRECTORY;
 931        if (!(flags & O_NOFOLLOW))
 932                lookup_flags |= LOOKUP_FOLLOW;
 933        return lookup_flags;
 934}
 935
 936/**
 937 * filp_open - open file and return file pointer
 938 *
 939 * @filename:   path to open
 940 * @flags:      open flags as per the open(2) second argument
 941 * @mode:       mode for the new file if O_CREAT is set, else ignored
 942 *
 943 * This is the helper to open a file from kernelspace if you really
 944 * have to.  But in generally you should not do this, so please move
 945 * along, nothing to see here..
 946 */
 947struct file *filp_open(const char *filename, int flags, int mode)
 948{
 949        struct open_flags op;
 950        int lookup = build_open_flags(flags, mode, &op);
 951        return do_filp_open(AT_FDCWD, filename, &op, lookup);
 952}
 953EXPORT_SYMBOL(filp_open);
 954
 955struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
 956                            const char *filename, int flags)
 957{
 958        struct open_flags op;
 959        int lookup = build_open_flags(flags, 0, &op);
 960        if (flags & O_CREAT)
 961                return ERR_PTR(-EINVAL);
 962        if (!filename && (flags & O_DIRECTORY))
 963                if (!dentry->d_inode->i_op->lookup)
 964                        return ERR_PTR(-ENOTDIR);
 965        return do_file_open_root(dentry, mnt, filename, &op, lookup);
 966}
 967EXPORT_SYMBOL(file_open_root);
 968
 969long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
 970{
 971        struct open_flags op;
 972        int lookup = build_open_flags(flags, mode, &op);
 973        char *tmp = getname(filename);
 974        int fd = PTR_ERR(tmp);
 975
 976        if (!IS_ERR(tmp)) {
 977                fd = get_unused_fd_flags(flags);
 978                if (fd >= 0) {
 979                        struct file *f = do_filp_open(dfd, tmp, &op, lookup);
 980                        if (IS_ERR(f)) {
 981                                put_unused_fd(fd);
 982                                fd = PTR_ERR(f);
 983                        } else {
 984                                fsnotify_open(f);
 985                                fd_install(fd, f);
 986                        }
 987                }
 988                putname(tmp);
 989        }
 990        return fd;
 991}
 992
 993SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, int, mode)
 994{
 995        long ret;
 996
 997        if (force_o_largefile())
 998                flags |= O_LARGEFILE;
 999
1000        ret = do_sys_open(AT_FDCWD, filename, flags, mode);
1001        /* avoid REGPARM breakage on x86: */
1002        asmlinkage_protect(3, ret, filename, flags, mode);
1003        return ret;
1004}
1005
1006SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
1007                int, mode)
1008{
1009        long ret;
1010
1011        if (force_o_largefile())
1012                flags |= O_LARGEFILE;
1013
1014        ret = do_sys_open(dfd, filename, flags, mode);
1015        /* avoid REGPARM breakage on x86: */
1016        asmlinkage_protect(4, ret, dfd, filename, flags, mode);
1017        return ret;
1018}
1019
1020#ifndef __alpha__
1021
1022/*
1023 * For backward compatibility?  Maybe this should be moved
1024 * into arch/i386 instead?
1025 */
1026SYSCALL_DEFINE2(creat, const char __user *, pathname, int, mode)
1027{
1028        return sys_open(pathname, O_CREAT | O_WRONLY | O_TRUNC, mode);
1029}
1030
1031#endif
1032
1033/*
1034 * "id" is the POSIX thread ID. We use the
1035 * files pointer for this..
1036 */
1037int filp_close(struct file *filp, fl_owner_t id)
1038{
1039        int retval = 0;
1040
1041        if (!file_count(filp)) {
1042                printk(KERN_ERR "VFS: Close: file count is 0\n");
1043                return 0;
1044        }
1045
1046        if (filp->f_op && filp->f_op->flush)
1047                retval = filp->f_op->flush(filp, id);
1048
1049        if (likely(!(filp->f_mode & FMODE_PATH))) {
1050                dnotify_flush(filp, id);
1051                locks_remove_posix(filp, id);
1052        }
1053        fput(filp);
1054        return retval;
1055}
1056
1057EXPORT_SYMBOL(filp_close);
1058
1059/*
1060 * Careful here! We test whether the file pointer is NULL before
1061 * releasing the fd. This ensures that one clone task can't release
1062 * an fd while another clone is opening it.
1063 */
1064SYSCALL_DEFINE1(close, unsigned int, fd)
1065{
1066        struct file * filp;
1067        struct files_struct *files = current->files;
1068        struct fdtable *fdt;
1069        int retval;
1070
1071        spin_lock(&files->file_lock);
1072        fdt = files_fdtable(files);
1073        if (fd >= fdt->max_fds)
1074                goto out_unlock;
1075        filp = fdt->fd[fd];
1076        if (!filp)
1077                goto out_unlock;
1078        rcu_assign_pointer(fdt->fd[fd], NULL);
1079        FD_CLR(fd, fdt->close_on_exec);
1080        __put_unused_fd(files, fd);
1081        spin_unlock(&files->file_lock);
1082        retval = filp_close(filp, files);
1083
1084        /* can't restart close syscall because file table entry was cleared */
1085        if (unlikely(retval == -ERESTARTSYS ||
1086                     retval == -ERESTARTNOINTR ||
1087                     retval == -ERESTARTNOHAND ||
1088                     retval == -ERESTART_RESTARTBLOCK))
1089                retval = -EINTR;
1090
1091        return retval;
1092
1093out_unlock:
1094        spin_unlock(&files->file_lock);
1095        return -EBADF;
1096}
1097EXPORT_SYMBOL(sys_close);
1098
1099/*
1100 * This routine simulates a hangup on the tty, to arrange that users
1101 * are given clean terminals at login time.
1102 */
1103SYSCALL_DEFINE0(vhangup)
1104{
1105        if (capable(CAP_SYS_TTY_CONFIG)) {
1106                tty_vhangup_self();
1107                return 0;
1108        }
1109        return -EPERM;
1110}
1111
1112/*
1113 * Called when an inode is about to be open.
1114 * We use this to disallow opening large files on 32bit systems if
1115 * the caller didn't specify O_LARGEFILE.  On 64bit systems we force
1116 * on this flag in sys_open.
1117 */
1118int generic_file_open(struct inode * inode, struct file * filp)
1119{
1120        if (!(filp->f_flags & O_LARGEFILE) && i_size_read(inode) > MAX_NON_LFS)
1121                return -EOVERFLOW;
1122        return 0;
1123}
1124
1125EXPORT_SYMBOL(generic_file_open);
1126
1127/*
1128 * This is used by subsystems that don't want seekable
1129 * file descriptors. The function is not supposed to ever fail, the only
1130 * reason it returns an 'int' and not 'void' is so that it can be plugged
1131 * directly into file_operations structure.
1132 */
1133int nonseekable_open(struct inode *inode, struct file *filp)
1134{
1135        filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
1136        return 0;
1137}
1138
1139EXPORT_SYMBOL(nonseekable_open);
1140
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