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         struct kiocb *orig_iocb;
  21         struct fd fd;
  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 modificaton nor notify on underlying */
  37 #define OVL_OPEN_FLAGS (O_NOATIME | FMODE_NONOTIFY)
  38
  39 static struct file *ovl_open_realfile(const struct file *file,
  40                                       struct inode *realinode)
  41 {
  42         struct inode *inode = file_inode(file);
  43         struct file *realfile;
  44         const struct cred *old_cred;
  45         int flags = file->f_flags | OVL_OPEN_FLAGS;
  46         int acc_mode = ACC_MODE(flags);
  47         int err;
  48
  49         if (flags & O_APPEND)
  50                 acc_mode |= MAY_APPEND;
  51
  52         old_cred = ovl_override_creds(inode->i_sb);
  53         err = inode_permission(&init_user_ns, realinode, MAY_OPEN | acc_mode);
  54         if (err) {
  55                 realfile = ERR_PTR(err);
  56         } else {
  57                 if (!inode_owner_or_capable(&init_user_ns, realinode))
  58                         flags &= ~O_NOATIME;
  59
  60                 realfile = open_with_fake_path(&file->f_path, flags, realinode,
  61                                                current_cred());
  62         }
  63         revert_creds(old_cred);
  64
  65         pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
  66                  file, file, ovl_whatisit(inode, realinode), file->f_flags,
  67                  realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
  68
  69         return realfile;
  70 }
  71
  72 #define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)
  73
  74 static int ovl_change_flags(struct file *file, unsigned int flags)
  75 {
  76         struct inode *inode = file_inode(file);
  77         int err;
  78
  79         flags &= OVL_SETFL_MASK;
  80
  81         if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
  82                 return -EPERM;
  83
  84         if (flags & O_DIRECT) {
  85                 if (!file->f_mapping->a_ops ||
  86                     !file->f_mapping->a_ops->direct_IO)
  87                         return -EINVAL;
  88         }
  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         spin_unlock(&file->f_lock);
  99
 100         return 0;
 101 }
 102
 103 static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
 104                                bool allow_meta)
 105 {
 106         struct inode *inode = file_inode(file);
 107         struct inode *realinode;
 108
 109         real->flags = 0;
 110         real->file = file->private_data;
 111
 112         if (allow_meta)
 113                 realinode = ovl_inode_real(inode);
 114         else
 115                 realinode = ovl_inode_realdata(inode);
 116
 117         /* Has it been copied up since we'd opened it? */
 118         if (unlikely(file_inode(real->file) != realinode)) {
 119                 real->flags = FDPUT_FPUT;
 120                 real->file = ovl_open_realfile(file, realinode);
 121
 122                 return PTR_ERR_OR_ZERO(real->file);
 123         }
 124
 125         /* Did the flags change since open? */
 126         if (unlikely((file->f_flags ^ real->file->f_flags) & ~OVL_OPEN_FLAGS))
 127                 return ovl_change_flags(real->file, file->f_flags);
 128
 129         return 0;
 130 }
 131
 132 static int ovl_real_fdget(const struct file *file, struct fd *real)
 133 {
 134         if (d_is_dir(file_dentry(file))) {
 135                 real->flags = 0;
 136                 real->file = ovl_dir_real_file(file, false);
 137
 138                 return PTR_ERR_OR_ZERO(real->file);
 139         }
 140
 141         return ovl_real_fdget_meta(file, real, false);
 142 }
 143
 144 static int ovl_open(struct inode *inode, struct file *file)
 145 {
 146         struct file *realfile;
 147         int err;
 148
 149         err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
 150         if (err)
 151                 return err;
 152
 153         /* No longer need these flags, so don't pass them on to underlying fs */
 154         file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 155
 156         realfile = ovl_open_realfile(file, ovl_inode_realdata(inode));
 157         if (IS_ERR(realfile))
 158                 return PTR_ERR(realfile);
 159
 160         file->private_data = realfile;
 161
 162         return 0;
 163 }
 164
 165 static int ovl_release(struct inode *inode, struct file *file)
 166 {
 167         fput(file->private_data);
 168
 169         return 0;
 170 }
 171
 172 static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 173 {
 174         struct inode *inode = file_inode(file);
 175         struct fd real;
 176         const struct cred *old_cred;
 177         loff_t ret;
 178
 179         /*
 180          * The two special cases below do not need to involve real fs,
 181          * so we can optimizing concurrent callers.
 182          */
 183         if (offset == 0) {
 184                 if (whence == SEEK_CUR)
 185                         return file->f_pos;
 186
 187                 if (whence == SEEK_SET)
 188                         return vfs_setpos(file, 0, 0);
 189         }
 190
 191         ret = ovl_real_fdget(file, &real);
 192         if (ret)
 193                 return ret;
 194
 195         /*
 196          * Overlay file f_pos is the master copy that is preserved
 197          * through copy up and modified on read/write, but only real
 198          * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
 199          * limitations that are more strict than ->s_maxbytes for specific
 200          * files, so we use the real file to perform seeks.
 201          */
 202         ovl_inode_lock(inode);
 203         real.file->f_pos = file->f_pos;
 204
 205         old_cred = ovl_override_creds(inode->i_sb);
 206         ret = vfs_llseek(real.file, offset, whence);
 207         revert_creds(old_cred);
 208
 209         file->f_pos = real.file->f_pos;
 210         ovl_inode_unlock(inode);
 211
 212         fdput(real);
 213
 214         return ret;
 215 }
 216
 217 static void ovl_file_accessed(struct file *file)
 218 {
 219         struct inode *inode, *upperinode;
 220
 221         if (file->f_flags & O_NOATIME)
 222                 return;
 223
 224         inode = file_inode(file);
 225         upperinode = ovl_inode_upper(inode);
 226
 227         if (!upperinode)
 228                 return;
 229
 230         if ((!timespec64_equal(&inode->i_mtime, &upperinode->i_mtime) ||
 231              !timespec64_equal(&inode->i_ctime, &upperinode->i_ctime))) {
 232                 inode->i_mtime = upperinode->i_mtime;
 233                 inode->i_ctime = upperinode->i_ctime;
 234         }
 235
 236         touch_atime(&file->f_path);
 237 }
 238
 239 static rwf_t ovl_iocb_to_rwf(int ifl)
 240 {
 241         rwf_t flags = 0;
 242
 243         if (ifl & IOCB_NOWAIT)
 244                 flags |= RWF_NOWAIT;
 245         if (ifl & IOCB_HIPRI)
 246                 flags |= RWF_HIPRI;
 247         if (ifl & IOCB_DSYNC)
 248                 flags |= RWF_DSYNC;
 249         if (ifl & IOCB_SYNC)
 250                 flags |= RWF_SYNC;
 251
 252         return flags;
 253 }
 254
 255 static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
 256 {
 257         struct kiocb *iocb = &aio_req->iocb;
 258         struct kiocb *orig_iocb = aio_req->orig_iocb;
 259
 260         if (iocb->ki_flags & IOCB_WRITE) {
 261                 struct inode *inode = file_inode(orig_iocb->ki_filp);
 262
 263                 /* Actually acquired in ovl_write_iter() */
 264                 __sb_writers_acquired(file_inode(iocb->ki_filp)->i_sb,
 265                                       SB_FREEZE_WRITE);
 266                 file_end_write(iocb->ki_filp);
 267                 ovl_copyattr(ovl_inode_real(inode), inode);
 268         }
 269
 270         orig_iocb->ki_pos = iocb->ki_pos;
 271         fdput(aio_req->fd);
 272         kmem_cache_free(ovl_aio_request_cachep, aio_req);
 273 }
 274
 275 static void ovl_aio_rw_complete(struct kiocb *iocb, long res, long res2)
 276 {
 277         struct ovl_aio_req *aio_req = container_of(iocb,
 278                                                    struct ovl_aio_req, iocb);
 279         struct kiocb *orig_iocb = aio_req->orig_iocb;
 280
 281         ovl_aio_cleanup_handler(aio_req);
 282         orig_iocb->ki_complete(orig_iocb, res, res2);
 283 }
 284
 285 static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 286 {
 287         struct file *file = iocb->ki_filp;
 288         struct fd real;
 289         const struct cred *old_cred;
 290         ssize_t ret;
 291
 292         if (!iov_iter_count(iter))
 293                 return 0;
 294
 295         ret = ovl_real_fdget(file, &real);
 296         if (ret)
 297                 return ret;
 298
 299         ret = -EINVAL;
 300         if (iocb->ki_flags & IOCB_DIRECT &&
 301             (!real.file->f_mapping->a_ops ||
 302              !real.file->f_mapping->a_ops->direct_IO))
 303                 goto out_fdput;
 304
 305         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 306         if (is_sync_kiocb(iocb)) {
 307                 ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
 308                                     ovl_iocb_to_rwf(iocb->ki_flags));
 309         } else {
 310                 struct ovl_aio_req *aio_req;
 311
 312                 ret = -ENOMEM;
 313                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 314                 if (!aio_req)
 315                         goto out;
 316
 317                 aio_req->fd = real;
 318                 real.flags = 0;
 319                 aio_req->orig_iocb = iocb;
 320                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 321                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 322                 ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
 323                 if (ret != -EIOCBQUEUED)
 324                         ovl_aio_cleanup_handler(aio_req);
 325         }
 326 out:
 327         revert_creds(old_cred);
 328         ovl_file_accessed(file);
 329 out_fdput:
 330         fdput(real);
 331
 332         return ret;
 333 }
 334
 335 static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 336 {
 337         struct file *file = iocb->ki_filp;
 338         struct inode *inode = file_inode(file);
 339         struct fd real;
 340         const struct cred *old_cred;
 341         ssize_t ret;
 342         int ifl = iocb->ki_flags;
 343
 344         if (!iov_iter_count(iter))
 345                 return 0;
 346
 347         inode_lock(inode);
 348         /* Update mode */
 349         ovl_copyattr(ovl_inode_real(inode), inode);
 350         ret = file_remove_privs(file);
 351         if (ret)
 352                 goto out_unlock;
 353
 354         ret = ovl_real_fdget(file, &real);
 355         if (ret)
 356                 goto out_unlock;
 357
 358         ret = -EINVAL;
 359         if (iocb->ki_flags & IOCB_DIRECT &&
 360             (!real.file->f_mapping->a_ops ||
 361              !real.file->f_mapping->a_ops->direct_IO))
 362                 goto out_fdput;
 363
 364         if (!ovl_should_sync(OVL_FS(inode->i_sb)))
 365                 ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
 366
 367         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 368         if (is_sync_kiocb(iocb)) {
 369                 file_start_write(real.file);
 370                 ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
 371                                      ovl_iocb_to_rwf(ifl));
 372                 file_end_write(real.file);
 373                 /* Update size */
 374                 ovl_copyattr(ovl_inode_real(inode), inode);
 375         } else {
 376                 struct ovl_aio_req *aio_req;
 377
 378                 ret = -ENOMEM;
 379                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 380                 if (!aio_req)
 381                         goto out;
 382
 383                 file_start_write(real.file);
 384                 /* Pacify lockdep, same trick as done in aio_write() */
 385                 __sb_writers_release(file_inode(real.file)->i_sb,
 386                                      SB_FREEZE_WRITE);
 387                 aio_req->fd = real;
 388                 real.flags = 0;
 389                 aio_req->orig_iocb = iocb;
 390                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 391                 aio_req->iocb.ki_flags = ifl;
 392                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 393                 ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
 394                 if (ret != -EIOCBQUEUED)
 395                         ovl_aio_cleanup_handler(aio_req);
 396         }
 397 out:
 398         revert_creds(old_cred);
 399 out_fdput:
 400         fdput(real);
 401
 402 out_unlock:
 403         inode_unlock(inode);
 404
 405         return ret;
 406 }
 407
 408 /*
 409  * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
 410  * due to lock order inversion between pipe->mutex in iter_file_splice_write()
 411  * and file_start_write(real.file) in ovl_write_iter().
 412  *
 413  * So do everything ovl_write_iter() does and call iter_file_splice_write() on
 414  * the real file.
 415  */
 416 static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 417                                 loff_t *ppos, size_t len, unsigned int flags)
 418 {
 419         struct fd real;
 420         const struct cred *old_cred;
 421         struct inode *inode = file_inode(out);
 422         struct inode *realinode = ovl_inode_real(inode);
 423         ssize_t ret;
 424
 425         inode_lock(inode);
 426         /* Update mode */
 427         ovl_copyattr(realinode, inode);
 428         ret = file_remove_privs(out);
 429         if (ret)
 430                 goto out_unlock;
 431
 432         ret = ovl_real_fdget(out, &real);
 433         if (ret)
 434                 goto out_unlock;
 435
 436         old_cred = ovl_override_creds(inode->i_sb);
 437         file_start_write(real.file);
 438
 439         ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
 440
 441         file_end_write(real.file);
 442         /* Update size */
 443         ovl_copyattr(realinode, inode);
 444         revert_creds(old_cred);
 445         fdput(real);
 446
 447 out_unlock:
 448         inode_unlock(inode);
 449
 450         return ret;
 451 }
 452
 453 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 454 {
 455         struct fd real;
 456         const struct cred *old_cred;
 457         int ret;
 458
 459         ret = ovl_sync_status(OVL_FS(file_inode(file)->i_sb));
 460         if (ret <= 0)
 461                 return ret;
 462
 463         ret = ovl_real_fdget_meta(file, &real, !datasync);
 464         if (ret)
 465                 return ret;
 466
 467         /* Don't sync lower file for fear of receiving EROFS error */
 468         if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 469                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 470                 ret = vfs_fsync_range(real.file, start, end, datasync);
 471                 revert_creds(old_cred);
 472         }
 473
 474         fdput(real);
 475
 476         return ret;
 477 }
 478
 479 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 480 {
 481         struct file *realfile = file->private_data;
 482         const struct cred *old_cred;
 483         int ret;
 484
 485         if (!realfile->f_op->mmap)
 486                 return -ENODEV;
 487
 488         if (WARN_ON(file != vma->vm_file))
 489                 return -EIO;
 490
 491         vma_set_file(vma, realfile);
 492
 493         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 494         ret = call_mmap(vma->vm_file, vma);
 495         revert_creds(old_cred);
 496         ovl_file_accessed(file);
 497
 498         return ret;
 499 }
 500
 501 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 502 {
 503         struct inode *inode = file_inode(file);
 504         struct fd real;
 505         const struct cred *old_cred;
 506         int ret;
 507
 508         ret = ovl_real_fdget(file, &real);
 509         if (ret)
 510                 return ret;
 511
 512         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 513         ret = vfs_fallocate(real.file, mode, offset, len);
 514         revert_creds(old_cred);
 515
 516         /* Update size */
 517         ovl_copyattr(ovl_inode_real(inode), inode);
 518
 519         fdput(real);
 520
 521         return ret;
 522 }
 523
 524 static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 525 {
 526         struct fd real;
 527         const struct cred *old_cred;
 528         int ret;
 529
 530         ret = ovl_real_fdget(file, &real);
 531         if (ret)
 532                 return ret;
 533
 534         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 535         ret = vfs_fadvise(real.file, offset, len, advice);
 536         revert_creds(old_cred);
 537
 538         fdput(real);
 539
 540         return ret;
 541 }
 542
 543 enum ovl_copyop {
 544         OVL_COPY,
 545         OVL_CLONE,
 546         OVL_DEDUPE,
 547 };
 548
 549 static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 550                             struct file *file_out, loff_t pos_out,
 551                             loff_t len, unsigned int flags, enum ovl_copyop op)
 552 {
 553         struct inode *inode_out = file_inode(file_out);
 554         struct fd real_in, real_out;
 555         const struct cred *old_cred;
 556         loff_t ret;
 557
 558         ret = ovl_real_fdget(file_out, &real_out);
 559         if (ret)
 560                 return ret;
 561
 562         ret = ovl_real_fdget(file_in, &real_in);
 563         if (ret) {
 564                 fdput(real_out);
 565                 return ret;
 566         }
 567
 568         old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
 569         switch (op) {
 570         case OVL_COPY:
 571                 ret = vfs_copy_file_range(real_in.file, pos_in,
 572                                           real_out.file, pos_out, len, flags);
 573                 break;
 574
 575         case OVL_CLONE:
 576                 ret = vfs_clone_file_range(real_in.file, pos_in,
 577                                            real_out.file, pos_out, len, flags);
 578                 break;
 579
 580         case OVL_DEDUPE:
 581                 ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
 582                                                 real_out.file, pos_out, len,
 583                                                 flags);
 584                 break;
 585         }
 586         revert_creds(old_cred);
 587
 588         /* Update size */
 589         ovl_copyattr(ovl_inode_real(inode_out), inode_out);
 590
 591         fdput(real_in);
 592         fdput(real_out);
 593
 594         return ret;
 595 }
 596
 597 static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
 598                                    struct file *file_out, loff_t pos_out,
 599                                    size_t len, unsigned int flags)
 600 {
 601         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
 602                             OVL_COPY);
 603 }
 604
 605 static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
 606                                    struct file *file_out, loff_t pos_out,
 607                                    loff_t len, unsigned int remap_flags)
 608 {
 609         enum ovl_copyop op;
 610
 611         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 612                 return -EINVAL;
 613
 614         if (remap_flags & REMAP_FILE_DEDUP)
 615                 op = OVL_DEDUPE;
 616         else
 617                 op = OVL_CLONE;
 618
 619         /*
 620          * Don't copy up because of a dedupe request, this wouldn't make sense
 621          * most of the time (data would be duplicated instead of deduplicated).
 622          */
 623         if (op == OVL_DEDUPE &&
 624             (!ovl_inode_upper(file_inode(file_in)) ||
 625              !ovl_inode_upper(file_inode(file_out))))
 626                 return -EPERM;
 627
 628         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
 629                             remap_flags, op);
 630 }
 631
 632 static int ovl_flush(struct file *file, fl_owner_t id)
 633 {
 634         struct fd real;
 635         const struct cred *old_cred;
 636         int err;
 637
 638         err = ovl_real_fdget(file, &real);
 639         if (err)
 640                 return err;
 641
 642         if (real.file->f_op->flush) {
 643                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 644                 err = real.file->f_op->flush(real.file, id);
 645                 revert_creds(old_cred);
 646         }
 647         fdput(real);
 648
 649         return err;
 650 }
 651
 652 const struct file_operations ovl_file_operations = {
 653         .open           = ovl_open,
 654         .release        = ovl_release,
 655         .llseek         = ovl_llseek,
 656         .read_iter      = ovl_read_iter,
 657         .write_iter     = ovl_write_iter,
 658         .fsync          = ovl_fsync,
 659         .mmap           = ovl_mmap,
 660         .fallocate      = ovl_fallocate,
 661         .fadvise        = ovl_fadvise,
 662         .flush          = ovl_flush,
 663         .splice_read    = generic_file_splice_read,
 664         .splice_write   = ovl_splice_write,
 665
 666         .copy_file_range        = ovl_copy_file_range,
 667         .remap_file_range       = ovl_remap_file_range,
 668 };
 669
 670 int __init ovl_aio_request_cache_init(void)
 671 {
 672         ovl_aio_request_cachep = kmem_cache_create("ovl_aio_req",
 673                                                    sizeof(struct ovl_aio_req),
 674                                                    0, SLAB_HWCACHE_ALIGN, NULL);
 675         if (!ovl_aio_request_cachep)
 676                 return -ENOMEM;
 677
 678         return 0;
 679 }
 680
 681 void ovl_aio_request_cache_destroy(void)
 682 {
 683         kmem_cache_destroy(ovl_aio_request_cachep);
 684 }