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#include <linux/compat.h>
  34
  35#include "internal.h"
  36
  37int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
  38        struct file *filp)
  39{
  40        int ret;
  41        struct iattr newattrs;
  42
  43        /* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
  44        if (length < 0)
  45                return -EINVAL;
  46
  47        newattrs.ia_size = length;
  48        newattrs.ia_valid = ATTR_SIZE | time_attrs;
  49        if (filp) {
  50                newattrs.ia_file = filp;
  51                newattrs.ia_valid |= ATTR_FILE;
  52        }
  53
  54        /* Remove suid/sgid on truncate too */
  55        ret = should_remove_suid(dentry);
  56        if (ret)
  57                newattrs.ia_valid |= ret | ATTR_FORCE;
  58
  59        mutex_lock(&dentry->d_inode->i_mutex);
  60        ret = notify_change(dentry, &newattrs);
  61        mutex_unlock(&dentry->d_inode->i_mutex);
  62        return ret;
  63}
  64
  65long vfs_truncate(struct path *path, loff_t length)
  66{
  67        struct inode *inode;
  68        long error;
  69
  70        inode = path->dentry->d_inode;
  71
  72        /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
  73        if (S_ISDIR(inode->i_mode))
  74                return -EISDIR;
  75        if (!S_ISREG(inode->i_mode))
  76                return -EINVAL;
  77
  78        error = mnt_want_write(path->mnt);
  79        if (error)
  80                goto out;
  81
  82        error = inode_permission(inode, MAY_WRITE);
  83        if (error)
  84                goto mnt_drop_write_and_out;
  85
  86        error = -EPERM;
  87        if (IS_APPEND(inode))
  88                goto mnt_drop_write_and_out;
  89
  90        error = get_write_access(inode);
  91        if (error)
  92                goto mnt_drop_write_and_out;
  93
  94        /*
  95         * Make sure that there are no leases.  get_write_access() protects
  96         * against the truncate racing with a lease-granting setlease().
  97         */
  98        error = break_lease(inode, O_WRONLY);
  99        if (error)
 100                goto put_write_and_out;
 101
 102        error = locks_verify_truncate(inode, NULL, length);
 103        if (!error)
 104                error = security_path_truncate(path);
 105        if (!error)
 106                error = do_truncate(path->dentry, length, 0, NULL);
 107
 108put_write_and_out:
 109        put_write_access(inode);
 110mnt_drop_write_and_out:
 111        mnt_drop_write(path->mnt);
 112out:
 113        return error;
 114}
 115EXPORT_SYMBOL_GPL(vfs_truncate);
 116
 117static long do_sys_truncate(const char __user *pathname, loff_t length)
 118{
 119        unsigned int lookup_flags = LOOKUP_FOLLOW;
 120        struct path path;
 121        int error;
 122
 123        if (length < 0) /* sorry, but loff_t says... */
 124                return -EINVAL;
 125
 126retry:
 127        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 128        if (!error) {
 129                error = vfs_truncate(&path, length);
 130                path_put(&path);
 131        }
 132        if (retry_estale(error, lookup_flags)) {
 133                lookup_flags |= LOOKUP_REVAL;
 134                goto retry;
 135        }
 136        return error;
 137}
 138
 139SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
 140{
 141        return do_sys_truncate(path, length);
 142}
 143
 144#ifdef CONFIG_COMPAT
 145COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length)
 146{
 147        return do_sys_truncate(path, length);
 148}
 149#endif
 150
 151static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
 152{
 153        struct inode *inode;
 154        struct dentry *dentry;
 155        struct fd f;
 156        int error;
 157
 158        error = -EINVAL;
 159        if (length < 0)
 160                goto out;
 161        error = -EBADF;
 162        f = fdget(fd);
 163        if (!f.file)
 164                goto out;
 165
 166        /* explicitly opened as large or we are on 64-bit box */
 167        if (f.file->f_flags & O_LARGEFILE)
 168                small = 0;
 169
 170        dentry = f.file->f_path.dentry;
 171        inode = dentry->d_inode;
 172        error = -EINVAL;
 173        if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
 174                goto out_putf;
 175
 176        error = -EINVAL;
 177        /* Cannot ftruncate over 2^31 bytes without large file support */
 178        if (small && length > MAX_NON_LFS)
 179                goto out_putf;
 180
 181        error = -EPERM;
 182        if (IS_APPEND(inode))
 183                goto out_putf;
 184
 185        sb_start_write(inode->i_sb);
 186        error = locks_verify_truncate(inode, f.file, length);
 187        if (!error)
 188                error = security_path_truncate(&f.file->f_path);
 189        if (!error)
 190                error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, f.file);
 191        sb_end_write(inode->i_sb);
 192out_putf:
 193        fdput(f);
 194out:
 195        return error;
 196}
 197
 198SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
 199{
 200        return do_sys_ftruncate(fd, length, 1);
 201}
 202
 203#ifdef CONFIG_COMPAT
 204COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_ulong_t, length)
 205{
 206        return do_sys_ftruncate(fd, length, 1);
 207}
 208#endif
 209
 210/* LFS versions of truncate are only needed on 32 bit machines */
 211#if BITS_PER_LONG == 32
 212SYSCALL_DEFINE2(truncate64, const char __user *, path, loff_t, length)
 213{
 214        return do_sys_truncate(path, length);
 215}
 216
 217SYSCALL_DEFINE2(ftruncate64, unsigned int, fd, loff_t, length)
 218{
 219        return do_sys_ftruncate(fd, length, 0);
 220}
 221#endif /* BITS_PER_LONG == 32 */
 222
 223
 224int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 225{
 226        struct inode *inode = file_inode(file);
 227        long ret;
 228
 229        if (offset < 0 || len <= 0)
 230                return -EINVAL;
 231
 232        /* Return error if mode is not supported */
 233        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
 234                return -EOPNOTSUPP;
 235
 236        /* Punch hole must have keep size set */
 237        if ((mode & FALLOC_FL_PUNCH_HOLE) &&
 238            !(mode & FALLOC_FL_KEEP_SIZE))
 239                return -EOPNOTSUPP;
 240
 241        if (!(file->f_mode & FMODE_WRITE))
 242                return -EBADF;
 243
 244        /* It's not possible punch hole on append only file */
 245        if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
 246                return -EPERM;
 247
 248        if (IS_IMMUTABLE(inode))
 249                return -EPERM;
 250
 251        /*
 252         * Revalidate the write permissions, in case security policy has
 253         * changed since the files were opened.
 254         */
 255        ret = security_file_permission(file, MAY_WRITE);
 256        if (ret)
 257                return ret;
 258
 259        if (S_ISFIFO(inode->i_mode))
 260                return -ESPIPE;
 261
 262        /*
 263         * Let individual file system decide if it supports preallocation
 264         * for directories or not.
 265         */
 266        if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
 267                return -ENODEV;
 268
 269        /* Check for wrap through zero too */
 270        if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
 271                return -EFBIG;
 272
 273        if (!file->f_op->fallocate)
 274                return -EOPNOTSUPP;
 275
 276        sb_start_write(inode->i_sb);
 277        ret = file->f_op->fallocate(file, mode, offset, len);
 278        sb_end_write(inode->i_sb);
 279        return ret;
 280}
 281
 282SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
 283{
 284        struct fd f = fdget(fd);
 285        int error = -EBADF;
 286
 287        if (f.file) {
 288                error = do_fallocate(f.file, mode, offset, len);
 289                fdput(f);
 290        }
 291        return error;
 292}
 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        unsigned int lookup_flags = LOOKUP_FOLLOW;
 307
 308        if (mode & ~S_IRWXO)    /* where's F_OK, X_OK, W_OK, R_OK? */
 309                return -EINVAL;
 310
 311        override_cred = prepare_creds();
 312        if (!override_cred)
 313                return -ENOMEM;
 314
 315        override_cred->fsuid = override_cred->uid;
 316        override_cred->fsgid = override_cred->gid;
 317
 318        if (!issecure(SECURE_NO_SETUID_FIXUP)) {
 319                /* Clear the capabilities if we switch to a non-root user */
 320                kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
 321                if (!uid_eq(override_cred->uid, root_uid))
 322                        cap_clear(override_cred->cap_effective);
 323                else
 324                        override_cred->cap_effective =
 325                                override_cred->cap_permitted;
 326        }
 327
 328        old_cred = override_creds(override_cred);
 329retry:
 330        res = user_path_at(dfd, filename, lookup_flags, &path);
 331        if (res)
 332                goto out;
 333
 334        inode = path.dentry->d_inode;
 335
 336        if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
 337                /*
 338                 * MAY_EXEC on regular files is denied if the fs is mounted
 339                 * with the "noexec" flag.
 340                 */
 341                res = -EACCES;
 342                if (path.mnt->mnt_flags & MNT_NOEXEC)
 343                        goto out_path_release;
 344        }
 345
 346        res = inode_permission(inode, mode | MAY_ACCESS);
 347        /* SuS v2 requires we report a read only fs too */
 348        if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
 349                goto out_path_release;
 350        /*
 351         * This is a rare case where using __mnt_is_readonly()
 352         * is OK without a mnt_want/drop_write() pair.  Since
 353         * no actual write to the fs is performed here, we do
 354         * not need to telegraph to that to anyone.
 355         *
 356         * By doing this, we accept that this access is
 357         * inherently racy and know that the fs may change
 358         * state before we even see this result.
 359         */
 360        if (__mnt_is_readonly(path.mnt))
 361                res = -EROFS;
 362
 363out_path_release:
 364        path_put(&path);
 365        if (retry_estale(res, lookup_flags)) {
 366                lookup_flags |= LOOKUP_REVAL;
 367                goto retry;
 368        }
 369out:
 370        revert_creds(old_cred);
 371        put_cred(override_cred);
 372        return res;
 373}
 374
 375SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
 376{
 377        return sys_faccessat(AT_FDCWD, filename, mode);
 378}
 379
 380SYSCALL_DEFINE1(chdir, const char __user *, filename)
 381{
 382        struct path path;
 383        int error;
 384        unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 385retry:
 386        error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
 387        if (error)
 388                goto out;
 389
 390        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 391        if (error)
 392                goto dput_and_out;
 393
 394        set_fs_pwd(current->fs, &path);
 395
 396dput_and_out:
 397        path_put(&path);
 398        if (retry_estale(error, lookup_flags)) {
 399                lookup_flags |= LOOKUP_REVAL;
 400                goto retry;
 401        }
 402out:
 403        return error;
 404}
 405
 406SYSCALL_DEFINE1(fchdir, unsigned int, fd)
 407{
 408        struct fd f = fdget_raw(fd);
 409        struct inode *inode;
 410        int error = -EBADF;
 411
 412        error = -EBADF;
 413        if (!f.file)
 414                goto out;
 415
 416        inode = file_inode(f.file);
 417
 418        error = -ENOTDIR;
 419        if (!S_ISDIR(inode->i_mode))
 420                goto out_putf;
 421
 422        error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
 423        if (!error)
 424                set_fs_pwd(current->fs, &f.file->f_path);
 425out_putf:
 426        fdput(f);
 427out:
 428        return error;
 429}
 430
 431SYSCALL_DEFINE1(chroot, const char __user *, filename)
 432{
 433        struct path path;
 434        int error;
 435        unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 436retry:
 437        error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
 438        if (error)
 439                goto out;
 440
 441        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 442        if (error)
 443                goto dput_and_out;
 444
 445        error = -EPERM;
 446        if (!ns_capable(current_user_ns(), CAP_SYS_CHROOT))
 447                goto dput_and_out;
 448        error = security_path_chroot(&path);
 449        if (error)
 450                goto dput_and_out;
 451
 452        set_fs_root(current->fs, &path);
 453        error = 0;
 454dput_and_out:
 455        path_put(&path);
 456        if (retry_estale(error, lookup_flags)) {
 457                lookup_flags |= LOOKUP_REVAL;
 458                goto retry;
 459        }
 460out:
 461        return error;
 462}
 463
 464static int chmod_common(struct path *path, umode_t mode)
 465{
 466        struct inode *inode = path->dentry->d_inode;
 467        struct iattr newattrs;
 468        int error;
 469
 470        error = mnt_want_write(path->mnt);
 471        if (error)
 472                return error;
 473        mutex_lock(&inode->i_mutex);
 474        error = security_path_chmod(path, mode);
 475        if (error)
 476                goto out_unlock;
 477        newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
 478        newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
 479        error = notify_change(path->dentry, &newattrs);
 480out_unlock:
 481        mutex_unlock(&inode->i_mutex);
 482        mnt_drop_write(path->mnt);
 483        return error;
 484}
 485
 486SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
 487{
 488        struct fd f = fdget(fd);
 489        int err = -EBADF;
 490
 491        if (f.file) {
 492                audit_inode(NULL, f.file->f_path.dentry, 0);
 493                err = chmod_common(&f.file->f_path, mode);
 494                fdput(f);
 495        }
 496        return err;
 497}
 498
 499SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
 500{
 501        struct path path;
 502        int error;
 503        unsigned int lookup_flags = LOOKUP_FOLLOW;
 504retry:
 505        error = user_path_at(dfd, filename, lookup_flags, &path);
 506        if (!error) {
 507                error = chmod_common(&path, mode);
 508                path_put(&path);
 509                if (retry_estale(error, lookup_flags)) {
 510                        lookup_flags |= LOOKUP_REVAL;
 511                        goto retry;
 512                }
 513        }
 514        return error;
 515}
 516
 517SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
 518{
 519        return sys_fchmodat(AT_FDCWD, filename, mode);
 520}
 521
 522static int chown_common(struct path *path, uid_t user, gid_t group)
 523{
 524        struct inode *inode = path->dentry->d_inode;
 525        int error;
 526        struct iattr newattrs;
 527        kuid_t uid;
 528        kgid_t gid;
 529
 530        uid = make_kuid(current_user_ns(), user);
 531        gid = make_kgid(current_user_ns(), group);
 532
 533        newattrs.ia_valid =  ATTR_CTIME;
 534        if (user != (uid_t) -1) {
 535                if (!uid_valid(uid))
 536                        return -EINVAL;
 537                newattrs.ia_valid |= ATTR_UID;
 538                newattrs.ia_uid = uid;
 539        }
 540        if (group != (gid_t) -1) {
 541                if (!gid_valid(gid))
 542                        return -EINVAL;
 543                newattrs.ia_valid |= ATTR_GID;
 544                newattrs.ia_gid = gid;
 545        }
 546        if (!S_ISDIR(inode->i_mode))
 547                newattrs.ia_valid |=
 548                        ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
 549        mutex_lock(&inode->i_mutex);
 550        error = security_path_chown(path, uid, gid);
 551        if (!error)
 552                error = notify_change(path->dentry, &newattrs);
 553        mutex_unlock(&inode->i_mutex);
 554
 555        return error;
 556}
 557
 558SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 559                gid_t, group, int, flag)
 560{
 561        struct path path;
 562        int error = -EINVAL;
 563        int lookup_flags;
 564
 565        if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
 566                goto out;
 567
 568        lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
 569        if (flag & AT_EMPTY_PATH)
 570                lookup_flags |= LOOKUP_EMPTY;
 571retry:
 572        error = user_path_at(dfd, filename, lookup_flags, &path);
 573        if (error)
 574                goto out;
 575        error = mnt_want_write(path.mnt);
 576        if (error)
 577                goto out_release;
 578        error = chown_common(&path, user, group);
 579        mnt_drop_write(path.mnt);
 580out_release:
 581        path_put(&path);
 582        if (retry_estale(error, lookup_flags)) {
 583                lookup_flags |= LOOKUP_REVAL;
 584                goto retry;
 585        }
 586out:
 587        return error;
 588}
 589
 590SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
 591{
 592        return sys_fchownat(AT_FDCWD, filename, user, group, 0);
 593}
 594
 595SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
 596{
 597        return sys_fchownat(AT_FDCWD, filename, user, group,
 598                            AT_SYMLINK_NOFOLLOW);
 599}
 600
 601SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
 602{
 603        struct fd f = fdget(fd);
 604        int error = -EBADF;
 605
 606        if (!f.file)
 607                goto out;
 608
 609        error = mnt_want_write_file(f.file);
 610        if (error)
 611                goto out_fput;
 612        audit_inode(NULL, f.file->f_path.dentry, 0);
 613        error = chown_common(&f.file->f_path, user, group);
 614        mnt_drop_write_file(f.file);
 615out_fput:
 616        fdput(f);
 617out:
 618        return error;
 619}
 620
 621/*
 622 * You have to be very careful that these write
 623 * counts get cleaned up in error cases and
 624 * upon __fput().  This should probably never
 625 * be called outside of __dentry_open().
 626 */
 627static inline int __get_file_write_access(struct inode *inode,
 628                                          struct vfsmount *mnt)
 629{
 630        int error;
 631        error = get_write_access(inode);
 632        if (error)
 633                return error;
 634        /*
 635         * Do not take mount writer counts on
 636         * special files since no writes to
 637         * the mount itself will occur.
 638         */
 639        if (!special_file(inode->i_mode)) {
 640                /*
 641                 * Balanced in __fput()
 642                 */
 643                error = __mnt_want_write(mnt);
 644                if (error)
 645                        put_write_access(inode);
 646        }
 647        return error;
 648}
 649
 650int open_check_o_direct(struct file *f)
 651{
 652        /* NB: we're sure to have correct a_ops only after f_op->open */
 653        if (f->f_flags & O_DIRECT) {
 654                if (!f->f_mapping->a_ops ||
 655                    ((!f->f_mapping->a_ops->direct_IO) &&
 656                    (!f->f_mapping->a_ops->get_xip_mem))) {
 657                        return -EINVAL;
 658                }
 659        }
 660        return 0;
 661}
 662
 663static int do_dentry_open(struct file *f,
 664                          int (*open)(struct inode *, struct file *),
 665                          const struct cred *cred)
 666{
 667        static const struct file_operations empty_fops = {};
 668        struct inode *inode;
 669        int error;
 670
 671        f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
 672                                FMODE_PREAD | FMODE_PWRITE;
 673
 674        if (unlikely(f->f_flags & O_PATH))
 675                f->f_mode = FMODE_PATH;
 676
 677        path_get(&f->f_path);
 678        inode = f->f_inode = f->f_path.dentry->d_inode;
 679        if (f->f_mode & FMODE_WRITE) {
 680                error = __get_file_write_access(inode, f->f_path.mnt);
 681                if (error)
 682                        goto cleanup_file;
 683                if (!special_file(inode->i_mode))
 684                        file_take_write(f);
 685        }
 686
 687        f->f_mapping = inode->i_mapping;
 688        file_sb_list_add(f, inode->i_sb);
 689
 690        if (unlikely(f->f_mode & FMODE_PATH)) {
 691                f->f_op = &empty_fops;
 692                return 0;
 693        }
 694
 695        f->f_op = fops_get(inode->i_fop);
 696
 697        error = security_file_open(f, cred);
 698        if (error)
 699                goto cleanup_all;
 700
 701        error = break_lease(inode, f->f_flags);
 702        if (error)
 703                goto cleanup_all;
 704
 705        if (!open && f->f_op)
 706                open = f->f_op->open;
 707        if (open) {
 708                error = open(inode, f);
 709                if (error)
 710                        goto cleanup_all;
 711        }
 712        if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 713                i_readcount_inc(inode);
 714
 715        f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 716
 717        file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
 718
 719        return 0;
 720
 721cleanup_all:
 722        fops_put(f->f_op);
 723        file_sb_list_del(f);
 724        if (f->f_mode & FMODE_WRITE) {
 725                put_write_access(inode);
 726                if (!special_file(inode->i_mode)) {
 727                        /*
 728                         * We don't consider this a real
 729                         * mnt_want/drop_write() pair
 730                         * because it all happenend right
 731                         * here, so just reset the state.
 732                         */
 733                        file_reset_write(f);
 734                        __mnt_drop_write(f->f_path.mnt);
 735                }
 736        }
 737cleanup_file:
 738        path_put(&f->f_path);
 739        f->f_path.mnt = NULL;
 740        f->f_path.dentry = NULL;
 741        f->f_inode = NULL;
 742        return error;
 743}
 744
 745/**
 746 * finish_open - finish opening a file
 747 * @file: file pointer
 748 * @dentry: pointer to dentry
 749 * @open: open callback
 750 * @opened: state of open
 751 *
 752 * This can be used to finish opening a file passed to i_op->atomic_open().
 753 *
 754 * If the open callback is set to NULL, then the standard f_op->open()
 755 * filesystem callback is substituted.
 756 *
 757 * NB: the dentry reference is _not_ consumed.  If, for example, the dentry is
 758 * the return value of d_splice_alias(), then the caller needs to perform dput()
 759 * on it after finish_open().
 760 *
 761 * On successful return @file is a fully instantiated open file.  After this, if
 762 * an error occurs in ->atomic_open(), it needs to clean up with fput().
 763 *
 764 * Returns zero on success or -errno if the open failed.
 765 */
 766int finish_open(struct file *file, struct dentry *dentry,
 767                int (*open)(struct inode *, struct file *),
 768                int *opened)
 769{
 770        int error;
 771        BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
 772
 773        file->f_path.dentry = dentry;
 774        error = do_dentry_open(file, open, current_cred());
 775        if (!error)
 776                *opened |= FILE_OPENED;
 777
 778        return error;
 779}
 780EXPORT_SYMBOL(finish_open);
 781
 782/**
 783 * finish_no_open - finish ->atomic_open() without opening the file
 784 *
 785 * @file: file pointer
 786 * @dentry: dentry or NULL (as returned from ->lookup())
 787 *
 788 * This can be used to set the result of a successful lookup in ->atomic_open().
 789 *
 790 * NB: unlike finish_open() this function does consume the dentry reference and
 791 * the caller need not dput() it.
 792 *
 793 * Returns "1" which must be the return value of ->atomic_open() after having
 794 * called this function.
 795 */
 796int finish_no_open(struct file *file, struct dentry *dentry)
 797{
 798        file->f_path.dentry = dentry;
 799        return 1;
 800}
 801EXPORT_SYMBOL(finish_no_open);
 802
 803struct file *dentry_open(const struct path *path, int flags,
 804                         const struct cred *cred)
 805{
 806        int error;
 807        struct file *f;
 808
 809        validate_creds(cred);
 810
 811        /* We must always pass in a valid mount pointer. */
 812        BUG_ON(!path->mnt);
 813
 814        f = get_empty_filp();
 815        if (!IS_ERR(f)) {
 816                f->f_flags = flags;
 817                f->f_path = *path;
 818                error = do_dentry_open(f, NULL, cred);
 819                if (!error) {
 820                        /* from now on we need fput() to dispose of f */
 821                        error = open_check_o_direct(f);
 822                        if (error) {
 823                                fput(f);
 824                                f = ERR_PTR(error);
 825                        }
 826                } else { 
 827                        put_filp(f);
 828                        f = ERR_PTR(error);
 829                }
 830        }
 831        return f;
 832}
 833EXPORT_SYMBOL(dentry_open);
 834
 835static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
 836{
 837        int lookup_flags = 0;
 838        int acc_mode;
 839
 840        if (flags & (O_CREAT | __O_TMPFILE))
 841                op->mode = (mode & S_IALLUGO) | S_IFREG;
 842        else
 843                op->mode = 0;
 844
 845        /* Must never be set by userspace */
 846        flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC;
 847
 848        /*
 849         * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
 850         * check for O_DSYNC if the need any syncing at all we enforce it's
 851         * always set instead of having to deal with possibly weird behaviour
 852         * for malicious applications setting only __O_SYNC.
 853         */
 854        if (flags & __O_SYNC)
 855                flags |= O_DSYNC;
 856
 857        if (flags & __O_TMPFILE) {
 858                if ((flags & O_TMPFILE_MASK) != O_TMPFILE)
 859                        return -EINVAL;
 860                acc_mode = MAY_OPEN | ACC_MODE(flags);
 861                if (!(acc_mode & MAY_WRITE))
 862                        return -EINVAL;
 863        } else if (flags & O_PATH) {
 864                /*
 865                 * If we have O_PATH in the open flag. Then we
 866                 * cannot have anything other than the below set of flags
 867                 */
 868                flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
 869                acc_mode = 0;
 870        } else {
 871                acc_mode = MAY_OPEN | ACC_MODE(flags);
 872        }
 873
 874        op->open_flag = flags;
 875
 876        /* O_TRUNC implies we need access checks for write permissions */
 877        if (flags & O_TRUNC)
 878                acc_mode |= MAY_WRITE;
 879
 880        /* Allow the LSM permission hook to distinguish append
 881           access from general write access. */
 882        if (flags & O_APPEND)
 883                acc_mode |= MAY_APPEND;
 884
 885        op->acc_mode = acc_mode;
 886
 887        op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
 888
 889        if (flags & O_CREAT) {
 890                op->intent |= LOOKUP_CREATE;
 891                if (flags & O_EXCL)
 892                        op->intent |= LOOKUP_EXCL;
 893        }
 894
 895        if (flags & O_DIRECTORY)
 896                lookup_flags |= LOOKUP_DIRECTORY;
 897        if (!(flags & O_NOFOLLOW))
 898                lookup_flags |= LOOKUP_FOLLOW;
 899        op->lookup_flags = lookup_flags;
 900        return 0;
 901}
 902
 903/**
 904 * file_open_name - open file and return file pointer
 905 *
 906 * @name:       struct filename containing path to open
 907 * @flags:      open flags as per the open(2) second argument
 908 * @mode:       mode for the new file if O_CREAT is set, else ignored
 909 *
 910 * This is the helper to open a file from kernelspace if you really
 911 * have to.  But in generally you should not do this, so please move
 912 * along, nothing to see here..
 913 */
 914struct file *file_open_name(struct filename *name, int flags, umode_t mode)
 915{
 916        struct open_flags op;
 917        int err = build_open_flags(flags, mode, &op);
 918        return err ? ERR_PTR(err) : do_filp_open(AT_FDCWD, name, &op);
 919}
 920
 921/**
 922 * filp_open - open file and return file pointer
 923 *
 924 * @filename:   path to open
 925 * @flags:      open flags as per the open(2) second argument
 926 * @mode:       mode for the new file if O_CREAT is set, else ignored
 927 *
 928 * This is the helper to open a file from kernelspace if you really
 929 * have to.  But in generally you should not do this, so please move
 930 * along, nothing to see here..
 931 */
 932struct file *filp_open(const char *filename, int flags, umode_t mode)
 933{
 934        struct filename name = {.name = filename};
 935        return file_open_name(&name, flags, mode);
 936}
 937EXPORT_SYMBOL(filp_open);
 938
 939struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
 940                            const char *filename, int flags)
 941{
 942        struct open_flags op;
 943        int err = build_open_flags(flags, 0, &op);
 944        if (err)
 945                return ERR_PTR(err);
 946        if (flags & O_CREAT)
 947                return ERR_PTR(-EINVAL);
 948        if (!filename && (flags & O_DIRECTORY))
 949                if (!dentry->d_inode->i_op->lookup)
 950                        return ERR_PTR(-ENOTDIR);
 951        return do_file_open_root(dentry, mnt, filename, &op);
 952}
 953EXPORT_SYMBOL(file_open_root);
 954
 955long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
 956{
 957        struct open_flags op;
 958        int fd = build_open_flags(flags, mode, &op);
 959        struct filename *tmp;
 960
 961        if (fd)
 962                return fd;
 963
 964        tmp = getname(filename);
 965        if (IS_ERR(tmp))
 966                return PTR_ERR(tmp);
 967
 968        fd = get_unused_fd_flags(flags);
 969        if (fd >= 0) {
 970                struct file *f = do_filp_open(dfd, tmp, &op);
 971                if (IS_ERR(f)) {
 972                        put_unused_fd(fd);
 973                        fd = PTR_ERR(f);
 974                } else {
 975                        fsnotify_open(f);
 976                        fd_install(fd, f);
 977                }
 978        }
 979        putname(tmp);
 980        return fd;
 981}
 982
 983SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
 984{
 985        if (force_o_largefile())
 986                flags |= O_LARGEFILE;
 987
 988        return do_sys_open(AT_FDCWD, filename, flags, mode);
 989}
 990
 991SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
 992                umode_t, mode)
 993{
 994        if (force_o_largefile())
 995                flags |= O_LARGEFILE;
 996
 997        return do_sys_open(dfd, filename, flags, mode);
 998}
 999
1000#ifndef __alpha__
1001
1002/*
1003 * For backward compatibility?  Maybe this should be moved
1004 * into arch/i386 instead?
1005 */
1006SYSCALL_DEFINE2(creat, const char __user *, pathname, umode_t, mode)
1007{
1008        return sys_open(pathname, O_CREAT | O_WRONLY | O_TRUNC, mode);
1009}
1010
1011#endif
1012
1013/*
1014 * "id" is the POSIX thread ID. We use the
1015 * files pointer for this..
1016 */
1017int filp_close(struct file *filp, fl_owner_t id)
1018{
1019        int retval = 0;
1020
1021        if (!file_count(filp)) {
1022                printk(KERN_ERR "VFS: Close: file count is 0\n");
1023                return 0;
1024        }
1025
1026        if (filp->f_op && filp->f_op->flush)
1027                retval = filp->f_op->flush(filp, id);
1028
1029        if (likely(!(filp->f_mode & FMODE_PATH))) {
1030                dnotify_flush(filp, id);
1031                locks_remove_posix(filp, id);
1032        }
1033        fput(filp);
1034        return retval;
1035}
1036
1037EXPORT_SYMBOL(filp_close);
1038
1039/*
1040 * Careful here! We test whether the file pointer is NULL before
1041 * releasing the fd. This ensures that one clone task can't release
1042 * an fd while another clone is opening it.
1043 */
1044SYSCALL_DEFINE1(close, unsigned int, fd)
1045{
1046        int retval = __close_fd(current->files, fd);
1047
1048        /* can't restart close syscall because file table entry was cleared */
1049        if (unlikely(retval == -ERESTARTSYS ||
1050                     retval == -ERESTARTNOINTR ||
1051                     retval == -ERESTARTNOHAND ||
1052                     retval == -ERESTART_RESTARTBLOCK))
1053                retval = -EINTR;
1054
1055        return retval;
1056}
1057EXPORT_SYMBOL(sys_close);
1058
1059/*
1060 * This routine simulates a hangup on the tty, to arrange that users
1061 * are given clean terminals at login time.
1062 */
1063SYSCALL_DEFINE0(vhangup)
1064{
1065        if (capable(CAP_SYS_TTY_CONFIG)) {
1066                tty_vhangup_self();
1067                return 0;
1068        }
1069        return -EPERM;
1070}
1071
1072/*
1073 * Called when an inode is about to be open.
1074 * We use this to disallow opening large files on 32bit systems if
1075 * the caller didn't specify O_LARGEFILE.  On 64bit systems we force
1076 * on this flag in sys_open.
1077 */
1078int generic_file_open(struct inode * inode, struct file * filp)
1079{
1080        if (!(filp->f_flags & O_LARGEFILE) && i_size_read(inode) > MAX_NON_LFS)
1081                return -EOVERFLOW;
1082        return 0;
1083}
1084
1085EXPORT_SYMBOL(generic_file_open);
1086
1087/*
1088 * This is used by subsystems that don't want seekable
1089 * file descriptors. The function is not supposed to ever fail, the only
1090 * reason it returns an 'int' and not 'void' is so that it can be plugged
1091 * directly into file_operations structure.
1092 */
1093int nonseekable_open(struct inode *inode, struct file *filp)
1094{
1095        filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
1096        return 0;
1097}
1098
1099EXPORT_SYMBOL(nonseekable_open);
1100
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