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         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 300         if (is_sync_kiocb(iocb)) {
 301                 ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
 302                                     ovl_iocb_to_rwf(iocb->ki_flags));
 303         } else {
 304                 struct ovl_aio_req *aio_req;
 305
 306                 ret = -ENOMEM;
 307                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 308                 if (!aio_req)
 309                         goto out;
 310
 311                 aio_req->fd = real;
 312                 real.flags = 0;
 313                 aio_req->orig_iocb = iocb;
 314                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 315                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 316                 ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
 317                 if (ret != -EIOCBQUEUED)
 318                         ovl_aio_cleanup_handler(aio_req);
 319         }
 320 out:
 321         revert_creds(old_cred);
 322         ovl_file_accessed(file);
 323
 324         fdput(real);
 325
 326         return ret;
 327 }
 328
 329 static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 330 {
 331         struct file *file = iocb->ki_filp;
 332         struct inode *inode = file_inode(file);
 333         struct fd real;
 334         const struct cred *old_cred;
 335         ssize_t ret;
 336         int ifl = iocb->ki_flags;
 337
 338         if (!iov_iter_count(iter))
 339                 return 0;
 340
 341         inode_lock(inode);
 342         /* Update mode */
 343         ovl_copyattr(ovl_inode_real(inode), inode);
 344         ret = file_remove_privs(file);
 345         if (ret)
 346                 goto out_unlock;
 347
 348         ret = ovl_real_fdget(file, &real);
 349         if (ret)
 350                 goto out_unlock;
 351
 352         if (!ovl_should_sync(OVL_FS(inode->i_sb)))
 353                 ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
 354
 355         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 356         if (is_sync_kiocb(iocb)) {
 357                 file_start_write(real.file);
 358                 ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
 359                                      ovl_iocb_to_rwf(ifl));
 360                 file_end_write(real.file);
 361                 /* Update size */
 362                 ovl_copyattr(ovl_inode_real(inode), inode);
 363         } else {
 364                 struct ovl_aio_req *aio_req;
 365
 366                 ret = -ENOMEM;
 367                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 368                 if (!aio_req)
 369                         goto out;
 370
 371                 file_start_write(real.file);
 372                 /* Pacify lockdep, same trick as done in aio_write() */
 373                 __sb_writers_release(file_inode(real.file)->i_sb,
 374                                      SB_FREEZE_WRITE);
 375                 aio_req->fd = real;
 376                 real.flags = 0;
 377                 aio_req->orig_iocb = iocb;
 378                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 379                 aio_req->iocb.ki_flags = ifl;
 380                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 381                 ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
 382                 if (ret != -EIOCBQUEUED)
 383                         ovl_aio_cleanup_handler(aio_req);
 384         }
 385 out:
 386         revert_creds(old_cred);
 387         fdput(real);
 388
 389 out_unlock:
 390         inode_unlock(inode);
 391
 392         return ret;
 393 }
 394
 395 /*
 396  * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
 397  * due to lock order inversion between pipe->mutex in iter_file_splice_write()
 398  * and file_start_write(real.file) in ovl_write_iter().
 399  *
 400  * So do everything ovl_write_iter() does and call iter_file_splice_write() on
 401  * the real file.
 402  */
 403 static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 404                                 loff_t *ppos, size_t len, unsigned int flags)
 405 {
 406         struct fd real;
 407         const struct cred *old_cred;
 408         struct inode *inode = file_inode(out);
 409         struct inode *realinode = ovl_inode_real(inode);
 410         ssize_t ret;
 411
 412         inode_lock(inode);
 413         /* Update mode */
 414         ovl_copyattr(realinode, inode);
 415         ret = file_remove_privs(out);
 416         if (ret)
 417                 goto out_unlock;
 418
 419         ret = ovl_real_fdget(out, &real);
 420         if (ret)
 421                 goto out_unlock;
 422
 423         old_cred = ovl_override_creds(inode->i_sb);
 424         file_start_write(real.file);
 425
 426         ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
 427
 428         file_end_write(real.file);
 429         /* Update size */
 430         ovl_copyattr(realinode, inode);
 431         revert_creds(old_cred);
 432         fdput(real);
 433
 434 out_unlock:
 435         inode_unlock(inode);
 436
 437         return ret;
 438 }
 439
 440 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 441 {
 442         struct fd real;
 443         const struct cred *old_cred;
 444         int ret;
 445
 446         ret = ovl_sync_status(OVL_FS(file_inode(file)->i_sb));
 447         if (ret <= 0)
 448                 return ret;
 449
 450         ret = ovl_real_fdget_meta(file, &real, !datasync);
 451         if (ret)
 452                 return ret;
 453
 454         /* Don't sync lower file for fear of receiving EROFS error */
 455         if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 456                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 457                 ret = vfs_fsync_range(real.file, start, end, datasync);
 458                 revert_creds(old_cred);
 459         }
 460
 461         fdput(real);
 462
 463         return ret;
 464 }
 465
 466 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 467 {
 468         struct file *realfile = file->private_data;
 469         const struct cred *old_cred;
 470         int ret;
 471
 472         if (!realfile->f_op->mmap)
 473                 return -ENODEV;
 474
 475         if (WARN_ON(file != vma->vm_file))
 476                 return -EIO;
 477
 478         vma_set_file(vma, realfile);
 479
 480         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 481         ret = call_mmap(vma->vm_file, vma);
 482         revert_creds(old_cred);
 483         ovl_file_accessed(file);
 484
 485         return ret;
 486 }
 487
 488 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 489 {
 490         struct inode *inode = file_inode(file);
 491         struct fd real;
 492         const struct cred *old_cred;
 493         int ret;
 494
 495         ret = ovl_real_fdget(file, &real);
 496         if (ret)
 497                 return ret;
 498
 499         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 500         ret = vfs_fallocate(real.file, mode, offset, len);
 501         revert_creds(old_cred);
 502
 503         /* Update size */
 504         ovl_copyattr(ovl_inode_real(inode), inode);
 505
 506         fdput(real);
 507
 508         return ret;
 509 }
 510
 511 static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 512 {
 513         struct fd real;
 514         const struct cred *old_cred;
 515         int ret;
 516
 517         ret = ovl_real_fdget(file, &real);
 518         if (ret)
 519                 return ret;
 520
 521         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 522         ret = vfs_fadvise(real.file, offset, len, advice);
 523         revert_creds(old_cred);
 524
 525         fdput(real);
 526
 527         return ret;
 528 }
 529
 530 enum ovl_copyop {
 531         OVL_COPY,
 532         OVL_CLONE,
 533         OVL_DEDUPE,
 534 };
 535
 536 static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 537                             struct file *file_out, loff_t pos_out,
 538                             loff_t len, unsigned int flags, enum ovl_copyop op)
 539 {
 540         struct inode *inode_out = file_inode(file_out);
 541         struct fd real_in, real_out;
 542         const struct cred *old_cred;
 543         loff_t ret;
 544
 545         ret = ovl_real_fdget(file_out, &real_out);
 546         if (ret)
 547                 return ret;
 548
 549         ret = ovl_real_fdget(file_in, &real_in);
 550         if (ret) {
 551                 fdput(real_out);
 552                 return ret;
 553         }
 554
 555         old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
 556         switch (op) {
 557         case OVL_COPY:
 558                 ret = vfs_copy_file_range(real_in.file, pos_in,
 559                                           real_out.file, pos_out, len, flags);
 560                 break;
 561
 562         case OVL_CLONE:
 563                 ret = vfs_clone_file_range(real_in.file, pos_in,
 564                                            real_out.file, pos_out, len, flags);
 565                 break;
 566
 567         case OVL_DEDUPE:
 568                 ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
 569                                                 real_out.file, pos_out, len,
 570                                                 flags);
 571                 break;
 572         }
 573         revert_creds(old_cred);
 574
 575         /* Update size */
 576         ovl_copyattr(ovl_inode_real(inode_out), inode_out);
 577
 578         fdput(real_in);
 579         fdput(real_out);
 580
 581         return ret;
 582 }
 583
 584 static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
 585                                    struct file *file_out, loff_t pos_out,
 586                                    size_t len, unsigned int flags)
 587 {
 588         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
 589                             OVL_COPY);
 590 }
 591
 592 static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
 593                                    struct file *file_out, loff_t pos_out,
 594                                    loff_t len, unsigned int remap_flags)
 595 {
 596         enum ovl_copyop op;
 597
 598         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 599                 return -EINVAL;
 600
 601         if (remap_flags & REMAP_FILE_DEDUP)
 602                 op = OVL_DEDUPE;
 603         else
 604                 op = OVL_CLONE;
 605
 606         /*
 607          * Don't copy up because of a dedupe request, this wouldn't make sense
 608          * most of the time (data would be duplicated instead of deduplicated).
 609          */
 610         if (op == OVL_DEDUPE &&
 611             (!ovl_inode_upper(file_inode(file_in)) ||
 612              !ovl_inode_upper(file_inode(file_out))))
 613                 return -EPERM;
 614
 615         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
 616                             remap_flags, op);
 617 }
 618
 619 static int ovl_flush(struct file *file, fl_owner_t id)
 620 {
 621         struct fd real;
 622         const struct cred *old_cred;
 623         int err;
 624
 625         err = ovl_real_fdget(file, &real);
 626         if (err)
 627                 return err;
 628
 629         if (real.file->f_op->flush) {
 630                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 631                 err = real.file->f_op->flush(real.file, id);
 632                 revert_creds(old_cred);
 633         }
 634         fdput(real);
 635
 636         return err;
 637 }
 638
 639 const struct file_operations ovl_file_operations = {
 640         .open           = ovl_open,
 641         .release        = ovl_release,
 642         .llseek         = ovl_llseek,
 643         .read_iter      = ovl_read_iter,
 644         .write_iter     = ovl_write_iter,
 645         .fsync          = ovl_fsync,
 646         .mmap           = ovl_mmap,
 647         .fallocate      = ovl_fallocate,
 648         .fadvise        = ovl_fadvise,
 649         .flush          = ovl_flush,
 650         .splice_read    = generic_file_splice_read,
 651         .splice_write   = ovl_splice_write,
 652
 653         .copy_file_range        = ovl_copy_file_range,
 654         .remap_file_range       = ovl_remap_file_range,
 655 };
 656
 657 int __init ovl_aio_request_cache_init(void)
 658 {
 659         ovl_aio_request_cachep = kmem_cache_create("ovl_aio_req",
 660                                                    sizeof(struct ovl_aio_req),
 661                                                    0, SLAB_HWCACHE_ALIGN, NULL);
 662         if (!ovl_aio_request_cachep)
 663                 return -ENOMEM;
 664
 665         return 0;
 666 }
 667
 668 void ovl_aio_request_cache_destroy(void)
 669 {
 670         kmem_cache_destroy(ovl_aio_request_cachep);
 671 }