fs/overlayfs/file.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2017 Red Hat, Inc.
   4  */
   5
   6 #include <linux/cred.h>
   7 #include <linux/file.h>
   8 #include <linux/mount.h>
   9 #include <linux/xattr.h>
  10 #include <linux/uio.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/splice.h>
  13 #include <linux/security.h>
  14 #include <linux/mm.h>
  15 #include <linux/fs.h>
  16 #include "overlayfs.h"
  17
  18 struct ovl_aio_req {
  19         struct kiocb iocb;
  20         refcount_t ref;
  21         struct kiocb *orig_iocb;
  22 };
  23
  24 static struct kmem_cache *ovl_aio_request_cachep;
  25
  26 static char ovl_whatisit(struct inode *inode, struct inode *realinode)
  27 {
  28         if (realinode != ovl_inode_upper(inode))
  29                 return 'l';
  30         if (ovl_has_upperdata(inode))
  31                 return 'u';
  32         else
  33                 return 'm';
  34 }
  35
  36 /* No atime modification on underlying */
  37 #define OVL_OPEN_FLAGS (O_NOATIME)
  38
  39 static struct file *ovl_open_realfile(const struct file *file,
  40                                       const struct path *realpath)
  41 {
  42         struct inode *realinode = d_inode(realpath->dentry);
  43         struct inode *inode = file_inode(file);
  44         struct mnt_idmap *real_idmap;
  45         struct file *realfile;
  46         const struct cred *old_cred;
  47         int flags = file->f_flags | OVL_OPEN_FLAGS;
  48         int acc_mode = ACC_MODE(flags);
  49         int err;
  50
  51         if (flags & O_APPEND)
  52                 acc_mode |= MAY_APPEND;
  53
  54         old_cred = ovl_override_creds(inode->i_sb);
  55         real_idmap = mnt_idmap(realpath->mnt);
  56         err = inode_permission(real_idmap, realinode, MAY_OPEN | acc_mode);
  57         if (err) {
  58                 realfile = ERR_PTR(err);
  59         } else {
  60                 if (!inode_owner_or_capable(real_idmap, realinode))
  61                         flags &= ~O_NOATIME;
  62
  63                 realfile = backing_file_open(&file->f_path, flags, realpath,
  64                                              current_cred());
  65         }
  66         revert_creds(old_cred);
  67
  68         pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
  69                  file, file, ovl_whatisit(inode, realinode), file->f_flags,
  70                  realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
  71
  72         return realfile;
  73 }
  74
  75 #define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)
  76
  77 static int ovl_change_flags(struct file *file, unsigned int flags)
  78 {
  79         struct inode *inode = file_inode(file);
  80         int err;
  81
  82         flags &= OVL_SETFL_MASK;
  83
  84         if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
  85                 return -EPERM;
  86
  87         if ((flags & O_DIRECT) && !(file->f_mode & FMODE_CAN_ODIRECT))
  88                 return -EINVAL;
  89
  90         if (file->f_op->check_flags) {
  91                 err = file->f_op->check_flags(flags);
  92                 if (err)
  93                         return err;
  94         }
  95
  96         spin_lock(&file->f_lock);
  97         file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
  98         file->f_iocb_flags = iocb_flags(file);
  99         spin_unlock(&file->f_lock);
 100
 101         return 0;
 102 }
 103
 104 static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
 105                                bool allow_meta)
 106 {
 107         struct dentry *dentry = file_dentry(file);
 108         struct path realpath;
 109         int err;
 110
 111         real->flags = 0;
 112         real->file = file->private_data;
 113
 114         if (allow_meta) {
 115                 ovl_path_real(dentry, &realpath);
 116         } else {
 117                 /* lazy lookup and verify of lowerdata */
 118                 err = ovl_verify_lowerdata(dentry);
 119                 if (err)
 120                         return err;
 121
 122                 ovl_path_realdata(dentry, &realpath);
 123         }
 124         if (!realpath.dentry)
 125                 return -EIO;
 126
 127         /* Has it been copied up since we'd opened it? */
 128         if (unlikely(file_inode(real->file) != d_inode(realpath.dentry))) {
 129                 real->flags = FDPUT_FPUT;
 130                 real->file = ovl_open_realfile(file, &realpath);
 131
 132                 return PTR_ERR_OR_ZERO(real->file);
 133         }
 134
 135         /* Did the flags change since open? */
 136         if (unlikely((file->f_flags ^ real->file->f_flags) & ~OVL_OPEN_FLAGS))
 137                 return ovl_change_flags(real->file, file->f_flags);
 138
 139         return 0;
 140 }
 141
 142 static int ovl_real_fdget(const struct file *file, struct fd *real)
 143 {
 144         if (d_is_dir(file_dentry(file))) {
 145                 real->flags = 0;
 146                 real->file = ovl_dir_real_file(file, false);
 147
 148                 return PTR_ERR_OR_ZERO(real->file);
 149         }
 150
 151         return ovl_real_fdget_meta(file, real, false);
 152 }
 153
 154 static int ovl_open(struct inode *inode, struct file *file)
 155 {
 156         struct dentry *dentry = file_dentry(file);
 157         struct file *realfile;
 158         struct path realpath;
 159         int err;
 160
 161         /* lazy lookup and verify lowerdata */
 162         err = ovl_verify_lowerdata(dentry);
 163         if (err)
 164                 return err;
 165
 166         err = ovl_maybe_copy_up(dentry, file->f_flags);
 167         if (err)
 168                 return err;
 169
 170         /* No longer need these flags, so don't pass them on to underlying fs */
 171         file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 172
 173         ovl_path_realdata(dentry, &realpath);
 174         if (!realpath.dentry)
 175                 return -EIO;
 176
 177         realfile = ovl_open_realfile(file, &realpath);
 178         if (IS_ERR(realfile))
 179                 return PTR_ERR(realfile);
 180
 181         file->private_data = realfile;
 182
 183         return 0;
 184 }
 185
 186 static int ovl_release(struct inode *inode, struct file *file)
 187 {
 188         fput(file->private_data);
 189
 190         return 0;
 191 }
 192
 193 static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 194 {
 195         struct inode *inode = file_inode(file);
 196         struct fd real;
 197         const struct cred *old_cred;
 198         loff_t ret;
 199
 200         /*
 201          * The two special cases below do not need to involve real fs,
 202          * so we can optimizing concurrent callers.
 203          */
 204         if (offset == 0) {
 205                 if (whence == SEEK_CUR)
 206                         return file->f_pos;
 207
 208                 if (whence == SEEK_SET)
 209                         return vfs_setpos(file, 0, 0);
 210         }
 211
 212         ret = ovl_real_fdget(file, &real);
 213         if (ret)
 214                 return ret;
 215
 216         /*
 217          * Overlay file f_pos is the master copy that is preserved
 218          * through copy up and modified on read/write, but only real
 219          * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
 220          * limitations that are more strict than ->s_maxbytes for specific
 221          * files, so we use the real file to perform seeks.
 222          */
 223         ovl_inode_lock(inode);
 224         real.file->f_pos = file->f_pos;
 225
 226         old_cred = ovl_override_creds(inode->i_sb);
 227         ret = vfs_llseek(real.file, offset, whence);
 228         revert_creds(old_cred);
 229
 230         file->f_pos = real.file->f_pos;
 231         ovl_inode_unlock(inode);
 232
 233         fdput(real);
 234
 235         return ret;
 236 }
 237
 238 static void ovl_file_accessed(struct file *file)
 239 {
 240         struct inode *inode, *upperinode;
 241         struct timespec64 ctime, uctime;
 242         struct timespec64 mtime, umtime;
 243
 244         if (file->f_flags & O_NOATIME)
 245                 return;
 246
 247         inode = file_inode(file);
 248         upperinode = ovl_inode_upper(inode);
 249
 250         if (!upperinode)
 251                 return;
 252
 253         ctime = inode_get_ctime(inode);
 254         uctime = inode_get_ctime(upperinode);
 255         mtime = inode_get_mtime(inode);
 256         umtime = inode_get_mtime(upperinode);
 257         if ((!timespec64_equal(&mtime, &umtime)) ||
 258              !timespec64_equal(&ctime, &uctime)) {
 259                 inode_set_mtime_to_ts(inode, inode_get_mtime(upperinode));
 260                 inode_set_ctime_to_ts(inode, uctime);
 261         }
 262
 263         touch_atime(&file->f_path);
 264 }
 265
 266 static rwf_t ovl_iocb_to_rwf(int ifl)
 267 {
 268         rwf_t flags = 0;
 269
 270         if (ifl & IOCB_NOWAIT)
 271                 flags |= RWF_NOWAIT;
 272         if (ifl & IOCB_HIPRI)
 273                 flags |= RWF_HIPRI;
 274         if (ifl & IOCB_DSYNC)
 275                 flags |= RWF_DSYNC;
 276         if (ifl & IOCB_SYNC)
 277                 flags |= RWF_SYNC;
 278
 279         return flags;
 280 }
 281
 282 static inline void ovl_aio_put(struct ovl_aio_req *aio_req)
 283 {
 284         if (refcount_dec_and_test(&aio_req->ref)) {
 285                 fput(aio_req->iocb.ki_filp);
 286                 kmem_cache_free(ovl_aio_request_cachep, aio_req);
 287         }
 288 }
 289
 290 static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
 291 {
 292         struct kiocb *iocb = &aio_req->iocb;
 293         struct kiocb *orig_iocb = aio_req->orig_iocb;
 294
 295         if (iocb->ki_flags & IOCB_WRITE) {
 296                 struct inode *inode = file_inode(orig_iocb->ki_filp);
 297
 298                 kiocb_end_write(iocb);
 299                 ovl_copyattr(inode);
 300         }
 301
 302         orig_iocb->ki_pos = iocb->ki_pos;
 303         ovl_aio_put(aio_req);
 304 }
 305
 306 static void ovl_aio_rw_complete(struct kiocb *iocb, long res)
 307 {
 308         struct ovl_aio_req *aio_req = container_of(iocb,
 309                                                    struct ovl_aio_req, iocb);
 310         struct kiocb *orig_iocb = aio_req->orig_iocb;
 311
 312         ovl_aio_cleanup_handler(aio_req);
 313         orig_iocb->ki_complete(orig_iocb, res);
 314 }
 315
 316 static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 317 {
 318         struct file *file = iocb->ki_filp;
 319         struct fd real;
 320         const struct cred *old_cred;
 321         ssize_t ret;
 322
 323         if (!iov_iter_count(iter))
 324                 return 0;
 325
 326         ret = ovl_real_fdget(file, &real);
 327         if (ret)
 328                 return ret;
 329
 330         ret = -EINVAL;
 331         if (iocb->ki_flags & IOCB_DIRECT &&
 332             !(real.file->f_mode & FMODE_CAN_ODIRECT))
 333                 goto out_fdput;
 334
 335         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 336         if (is_sync_kiocb(iocb)) {
 337                 ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
 338                                     ovl_iocb_to_rwf(iocb->ki_flags));
 339         } else {
 340                 struct ovl_aio_req *aio_req;
 341
 342                 ret = -ENOMEM;
 343                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 344                 if (!aio_req)
 345                         goto out;
 346
 347                 aio_req->orig_iocb = iocb;
 348                 kiocb_clone(&aio_req->iocb, iocb, get_file(real.file));
 349                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 350                 refcount_set(&aio_req->ref, 2);
 351                 ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
 352                 ovl_aio_put(aio_req);
 353                 if (ret != -EIOCBQUEUED)
 354                         ovl_aio_cleanup_handler(aio_req);
 355         }
 356 out:
 357         revert_creds(old_cred);
 358         ovl_file_accessed(file);
 359 out_fdput:
 360         fdput(real);
 361
 362         return ret;
 363 }
 364
 365 static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 366 {
 367         struct file *file = iocb->ki_filp;
 368         struct inode *inode = file_inode(file);
 369         struct fd real;
 370         const struct cred *old_cred;
 371         ssize_t ret;
 372         int ifl = iocb->ki_flags;
 373
 374         if (!iov_iter_count(iter))
 375                 return 0;
 376
 377         inode_lock(inode);
 378         /* Update mode */
 379         ovl_copyattr(inode);
 380         ret = file_remove_privs(file);
 381         if (ret)
 382                 goto out_unlock;
 383
 384         ret = ovl_real_fdget(file, &real);
 385         if (ret)
 386                 goto out_unlock;
 387
 388         ret = -EINVAL;
 389         if (iocb->ki_flags & IOCB_DIRECT &&
 390             !(real.file->f_mode & FMODE_CAN_ODIRECT))
 391                 goto out_fdput;
 392
 393         if (!ovl_should_sync(OVL_FS(inode->i_sb)))
 394                 ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
 395
 396         /*
 397          * Overlayfs doesn't support deferred completions, don't copy
 398          * this property in case it is set by the issuer.
 399          */
 400         ifl &= ~IOCB_DIO_CALLER_COMP;
 401
 402         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 403         if (is_sync_kiocb(iocb)) {
 404                 file_start_write(real.file);
 405                 ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
 406                                      ovl_iocb_to_rwf(ifl));
 407                 file_end_write(real.file);
 408                 /* Update size */
 409                 ovl_copyattr(inode);
 410         } else {
 411                 struct ovl_aio_req *aio_req;
 412
 413                 ret = -ENOMEM;
 414                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 415                 if (!aio_req)
 416                         goto out;
 417
 418                 aio_req->orig_iocb = iocb;
 419                 kiocb_clone(&aio_req->iocb, iocb, get_file(real.file));
 420                 aio_req->iocb.ki_flags = ifl;
 421                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 422                 refcount_set(&aio_req->ref, 2);
 423                 kiocb_start_write(&aio_req->iocb);
 424                 ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
 425                 ovl_aio_put(aio_req);
 426                 if (ret != -EIOCBQUEUED)
 427                         ovl_aio_cleanup_handler(aio_req);
 428         }
 429 out:
 430         revert_creds(old_cred);
 431 out_fdput:
 432         fdput(real);
 433
 434 out_unlock:
 435         inode_unlock(inode);
 436
 437         return ret;
 438 }
 439
 440 static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
 441                                struct pipe_inode_info *pipe, size_t len,
 442                                unsigned int flags)
 443 {
 444         const struct cred *old_cred;
 445         struct fd real;
 446         ssize_t ret;
 447
 448         ret = ovl_real_fdget(in, &real);
 449         if (ret)
 450                 return ret;
 451
 452         old_cred = ovl_override_creds(file_inode(in)->i_sb);
 453         ret = vfs_splice_read(real.file, ppos, pipe, len, flags);
 454         revert_creds(old_cred);
 455         ovl_file_accessed(in);
 456
 457         fdput(real);
 458         return ret;
 459 }
 460
 461 /*
 462  * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
 463  * due to lock order inversion between pipe->mutex in iter_file_splice_write()
 464  * and file_start_write(real.file) in ovl_write_iter().
 465  *
 466  * So do everything ovl_write_iter() does and call iter_file_splice_write() on
 467  * the real file.
 468  */
 469 static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 470                                 loff_t *ppos, size_t len, unsigned int flags)
 471 {
 472         struct fd real;
 473         const struct cred *old_cred;
 474         struct inode *inode = file_inode(out);
 475         ssize_t ret;
 476
 477         inode_lock(inode);
 478         /* Update mode */
 479         ovl_copyattr(inode);
 480         ret = file_remove_privs(out);
 481         if (ret)
 482                 goto out_unlock;
 483
 484         ret = ovl_real_fdget(out, &real);
 485         if (ret)
 486                 goto out_unlock;
 487
 488         old_cred = ovl_override_creds(inode->i_sb);
 489         file_start_write(real.file);
 490
 491         ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
 492
 493         file_end_write(real.file);
 494         /* Update size */
 495         ovl_copyattr(inode);
 496         revert_creds(old_cred);
 497         fdput(real);
 498
 499 out_unlock:
 500         inode_unlock(inode);
 501
 502         return ret;
 503 }
 504
 505 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 506 {
 507         struct fd real;
 508         const struct cred *old_cred;
 509         int ret;
 510
 511         ret = ovl_sync_status(OVL_FS(file_inode(file)->i_sb));
 512         if (ret <= 0)
 513                 return ret;
 514
 515         ret = ovl_real_fdget_meta(file, &real, !datasync);
 516         if (ret)
 517                 return ret;
 518
 519         /* Don't sync lower file for fear of receiving EROFS error */
 520         if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 521                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 522                 ret = vfs_fsync_range(real.file, start, end, datasync);
 523                 revert_creds(old_cred);
 524         }
 525
 526         fdput(real);
 527
 528         return ret;
 529 }
 530
 531 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 532 {
 533         struct file *realfile = file->private_data;
 534         const struct cred *old_cred;
 535         int ret;
 536
 537         if (!realfile->f_op->mmap)
 538                 return -ENODEV;
 539
 540         if (WARN_ON(file != vma->vm_file))
 541                 return -EIO;
 542
 543         vma_set_file(vma, realfile);
 544
 545         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 546         ret = call_mmap(vma->vm_file, vma);
 547         revert_creds(old_cred);
 548         ovl_file_accessed(file);
 549
 550         return ret;
 551 }
 552
 553 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 554 {
 555         struct inode *inode = file_inode(file);
 556         struct fd real;
 557         const struct cred *old_cred;
 558         int ret;
 559
 560         inode_lock(inode);
 561         /* Update mode */
 562         ovl_copyattr(inode);
 563         ret = file_remove_privs(file);
 564         if (ret)
 565                 goto out_unlock;
 566
 567         ret = ovl_real_fdget(file, &real);
 568         if (ret)
 569                 goto out_unlock;
 570
 571         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 572         ret = vfs_fallocate(real.file, mode, offset, len);
 573         revert_creds(old_cred);
 574
 575         /* Update size */
 576         ovl_copyattr(inode);
 577
 578         fdput(real);
 579
 580 out_unlock:
 581         inode_unlock(inode);
 582
 583         return ret;
 584 }
 585
 586 static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 587 {
 588         struct fd real;
 589         const struct cred *old_cred;
 590         int ret;
 591
 592         ret = ovl_real_fdget(file, &real);
 593         if (ret)
 594                 return ret;
 595
 596         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 597         ret = vfs_fadvise(real.file, offset, len, advice);
 598         revert_creds(old_cred);
 599
 600         fdput(real);
 601
 602         return ret;
 603 }
 604
 605 enum ovl_copyop {
 606         OVL_COPY,
 607         OVL_CLONE,
 608         OVL_DEDUPE,
 609 };
 610
 611 static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 612                             struct file *file_out, loff_t pos_out,
 613                             loff_t len, unsigned int flags, enum ovl_copyop op)
 614 {
 615         struct inode *inode_out = file_inode(file_out);
 616         struct fd real_in, real_out;
 617         const struct cred *old_cred;
 618         loff_t ret;
 619
 620         inode_lock(inode_out);
 621         if (op != OVL_DEDUPE) {
 622                 /* Update mode */
 623                 ovl_copyattr(inode_out);
 624                 ret = file_remove_privs(file_out);
 625                 if (ret)
 626                         goto out_unlock;
 627         }
 628
 629         ret = ovl_real_fdget(file_out, &real_out);
 630         if (ret)
 631                 goto out_unlock;
 632
 633         ret = ovl_real_fdget(file_in, &real_in);
 634         if (ret) {
 635                 fdput(real_out);
 636                 goto out_unlock;
 637         }
 638
 639         old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
 640         switch (op) {
 641         case OVL_COPY:
 642                 ret = vfs_copy_file_range(real_in.file, pos_in,
 643                                           real_out.file, pos_out, len, flags);
 644                 break;
 645
 646         case OVL_CLONE:
 647                 ret = vfs_clone_file_range(real_in.file, pos_in,
 648                                            real_out.file, pos_out, len, flags);
 649                 break;
 650
 651         case OVL_DEDUPE:
 652                 ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
 653                                                 real_out.file, pos_out, len,
 654                                                 flags);
 655                 break;
 656         }
 657         revert_creds(old_cred);
 658
 659         /* Update size */
 660         ovl_copyattr(inode_out);
 661
 662         fdput(real_in);
 663         fdput(real_out);
 664
 665 out_unlock:
 666         inode_unlock(inode_out);
 667
 668         return ret;
 669 }
 670
 671 static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
 672                                    struct file *file_out, loff_t pos_out,
 673                                    size_t len, unsigned int flags)
 674 {
 675         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
 676                             OVL_COPY);
 677 }
 678
 679 static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
 680                                    struct file *file_out, loff_t pos_out,
 681                                    loff_t len, unsigned int remap_flags)
 682 {
 683         enum ovl_copyop op;
 684
 685         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 686                 return -EINVAL;
 687
 688         if (remap_flags & REMAP_FILE_DEDUP)
 689                 op = OVL_DEDUPE;
 690         else
 691                 op = OVL_CLONE;
 692
 693         /*
 694          * Don't copy up because of a dedupe request, this wouldn't make sense
 695          * most of the time (data would be duplicated instead of deduplicated).
 696          */
 697         if (op == OVL_DEDUPE &&
 698             (!ovl_inode_upper(file_inode(file_in)) ||
 699              !ovl_inode_upper(file_inode(file_out))))
 700                 return -EPERM;
 701
 702         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
 703                             remap_flags, op);
 704 }
 705
 706 static int ovl_flush(struct file *file, fl_owner_t id)
 707 {
 708         struct fd real;
 709         const struct cred *old_cred;
 710         int err;
 711
 712         err = ovl_real_fdget(file, &real);
 713         if (err)
 714                 return err;
 715
 716         if (real.file->f_op->flush) {
 717                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 718                 err = real.file->f_op->flush(real.file, id);
 719                 revert_creds(old_cred);
 720         }
 721         fdput(real);
 722
 723         return err;
 724 }
 725
 726 const struct file_operations ovl_file_operations = {
 727         .open           = ovl_open,
 728         .release        = ovl_release,
 729         .llseek         = ovl_llseek,
 730         .read_iter      = ovl_read_iter,
 731         .write_iter     = ovl_write_iter,
 732         .fsync          = ovl_fsync,
 733         .mmap           = ovl_mmap,
 734         .fallocate      = ovl_fallocate,
 735         .fadvise        = ovl_fadvise,
 736         .flush          = ovl_flush,
 737         .splice_read    = ovl_splice_read,
 738         .splice_write   = ovl_splice_write,
 739
 740         .copy_file_range        = ovl_copy_file_range,
 741         .remap_file_range       = ovl_remap_file_range,
 742 };
 743
 744 int __init ovl_aio_request_cache_init(void)
 745 {
 746         ovl_aio_request_cachep = kmem_cache_create("ovl_aio_req",
 747                                                    sizeof(struct ovl_aio_req),
 748                                                    0, SLAB_HWCACHE_ALIGN, NULL);
 749         if (!ovl_aio_request_cachep)
 750                 return -ENOMEM;
 751
 752         return 0;
 753 }
 754
 755 void ovl_aio_request_cache_destroy(void)
 756 {
 757         kmem_cache_destroy(ovl_aio_request_cachep);
 758 }