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