fs/overlayfs/file.c

   1 /*
   2  * Copyright (C) 2017 Red Hat, Inc.
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 as published by
   6  * the Free Software Foundation.
   7  */
   8
   9 #include <linux/cred.h>
  10 #include <linux/file.h>
  11 #include <linux/mount.h>
  12 #include <linux/xattr.h>
  13 #include <linux/uio.h>
  14 #include <linux/uaccess.h>
  15 #include "overlayfs.h"
  16
  17 static char ovl_whatisit(struct inode *inode, struct inode *realinode)
  18 {
  19         if (realinode != ovl_inode_upper(inode))
  20                 return 'l';
  21         if (ovl_has_upperdata(inode))
  22                 return 'u';
  23         else
  24                 return 'm';
  25 }
  26
  27 static struct file *ovl_open_realfile(const struct file *file,
  28                                       struct inode *realinode)
  29 {
  30         struct inode *inode = file_inode(file);
  31         struct file *realfile;
  32         const struct cred *old_cred;
  33         int flags = file->f_flags | O_NOATIME | FMODE_NONOTIFY;
  34
  35         old_cred = ovl_override_creds(inode->i_sb);
  36         realfile = open_with_fake_path(&file->f_path, flags, realinode,
  37                                        current_cred());
  38         revert_creds(old_cred);
  39
  40         pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
  41                  file, file, ovl_whatisit(inode, realinode), file->f_flags,
  42                  realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
  43
  44         return realfile;
  45 }
  46
  47 #define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)
  48
  49 static int ovl_change_flags(struct file *file, unsigned int flags)
  50 {
  51         struct inode *inode = file_inode(file);
  52         int err;
  53
  54         /* No atime modificaton on underlying */
  55         flags |= O_NOATIME | FMODE_NONOTIFY;
  56
  57         /* If some flag changed that cannot be changed then something's amiss */
  58         if (WARN_ON((file->f_flags ^ flags) & ~OVL_SETFL_MASK))
  59                 return -EIO;
  60
  61         flags &= OVL_SETFL_MASK;
  62
  63         if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
  64                 return -EPERM;
  65
  66         if (flags & O_DIRECT) {
  67                 if (!file->f_mapping->a_ops ||
  68                     !file->f_mapping->a_ops->direct_IO)
  69                         return -EINVAL;
  70         }
  71
  72         if (file->f_op->check_flags) {
  73                 err = file->f_op->check_flags(flags);
  74                 if (err)
  75                         return err;
  76         }
  77
  78         spin_lock(&file->f_lock);
  79         file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
  80         spin_unlock(&file->f_lock);
  81
  82         return 0;
  83 }
  84
  85 static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
  86                                bool allow_meta)
  87 {
  88         struct inode *inode = file_inode(file);
  89         struct inode *realinode;
  90
  91         real->flags = 0;
  92         real->file = file->private_data;
  93
  94         if (allow_meta)
  95                 realinode = ovl_inode_real(inode);
  96         else
  97                 realinode = ovl_inode_realdata(inode);
  98
  99         /* Has it been copied up since we'd opened it? */
 100         if (unlikely(file_inode(real->file) != realinode)) {
 101                 real->flags = FDPUT_FPUT;
 102                 real->file = ovl_open_realfile(file, realinode);
 103
 104                 return PTR_ERR_OR_ZERO(real->file);
 105         }
 106
 107         /* Did the flags change since open? */
 108         if (unlikely((file->f_flags ^ real->file->f_flags) & ~O_NOATIME))
 109                 return ovl_change_flags(real->file, file->f_flags);
 110
 111         return 0;
 112 }
 113
 114 static int ovl_real_fdget(const struct file *file, struct fd *real)
 115 {
 116         return ovl_real_fdget_meta(file, real, false);
 117 }
 118
 119 static int ovl_open(struct inode *inode, struct file *file)
 120 {
 121         struct file *realfile;
 122         int err;
 123
 124         err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
 125         if (err)
 126                 return err;
 127
 128         /* No longer need these flags, so don't pass them on to underlying fs */
 129         file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 130
 131         realfile = ovl_open_realfile(file, ovl_inode_realdata(inode));
 132         if (IS_ERR(realfile))
 133                 return PTR_ERR(realfile);
 134
 135         file->private_data = realfile;
 136
 137         return 0;
 138 }
 139
 140 static int ovl_release(struct inode *inode, struct file *file)
 141 {
 142         fput(file->private_data);
 143
 144         return 0;
 145 }
 146
 147 static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 148 {
 149         struct inode *inode = file_inode(file);
 150         struct fd real;
 151         const struct cred *old_cred;
 152         ssize_t ret;
 153
 154         /*
 155          * The two special cases below do not need to involve real fs,
 156          * so we can optimizing concurrent callers.
 157          */
 158         if (offset == 0) {
 159                 if (whence == SEEK_CUR)
 160                         return file->f_pos;
 161
 162                 if (whence == SEEK_SET)
 163                         return vfs_setpos(file, 0, 0);
 164         }
 165
 166         ret = ovl_real_fdget(file, &real);
 167         if (ret)
 168                 return ret;
 169
 170         /*
 171          * Overlay file f_pos is the master copy that is preserved
 172          * through copy up and modified on read/write, but only real
 173          * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
 174          * limitations that are more strict than ->s_maxbytes for specific
 175          * files, so we use the real file to perform seeks.
 176          */
 177         inode_lock(inode);
 178         real.file->f_pos = file->f_pos;
 179
 180         old_cred = ovl_override_creds(inode->i_sb);
 181         ret = vfs_llseek(real.file, offset, whence);
 182         revert_creds(old_cred);
 183
 184         file->f_pos = real.file->f_pos;
 185         inode_unlock(inode);
 186
 187         fdput(real);
 188
 189         return ret;
 190 }
 191
 192 static void ovl_file_accessed(struct file *file)
 193 {
 194         struct inode *inode, *upperinode;
 195
 196         if (file->f_flags & O_NOATIME)
 197                 return;
 198
 199         inode = file_inode(file);
 200         upperinode = ovl_inode_upper(inode);
 201
 202         if (!upperinode)
 203                 return;
 204
 205         if ((!timespec64_equal(&inode->i_mtime, &upperinode->i_mtime) ||
 206              !timespec64_equal(&inode->i_ctime, &upperinode->i_ctime))) {
 207                 inode->i_mtime = upperinode->i_mtime;
 208                 inode->i_ctime = upperinode->i_ctime;
 209         }
 210
 211         touch_atime(&file->f_path);
 212 }
 213
 214 static rwf_t ovl_iocb_to_rwf(struct kiocb *iocb)
 215 {
 216         int ifl = iocb->ki_flags;
 217         rwf_t flags = 0;
 218
 219         if (ifl & IOCB_NOWAIT)
 220                 flags |= RWF_NOWAIT;
 221         if (ifl & IOCB_HIPRI)
 222                 flags |= RWF_HIPRI;
 223         if (ifl & IOCB_DSYNC)
 224                 flags |= RWF_DSYNC;
 225         if (ifl & IOCB_SYNC)
 226                 flags |= RWF_SYNC;
 227
 228         return flags;
 229 }
 230
 231 static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 232 {
 233         struct file *file = iocb->ki_filp;
 234         struct fd real;
 235         const struct cred *old_cred;
 236         ssize_t ret;
 237
 238         if (!iov_iter_count(iter))
 239                 return 0;
 240
 241         ret = ovl_real_fdget(file, &real);
 242         if (ret)
 243                 return ret;
 244
 245         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 246         ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
 247                             ovl_iocb_to_rwf(iocb));
 248         revert_creds(old_cred);
 249
 250         ovl_file_accessed(file);
 251
 252         fdput(real);
 253
 254         return ret;
 255 }
 256
 257 static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 258 {
 259         struct file *file = iocb->ki_filp;
 260         struct inode *inode = file_inode(file);
 261         struct fd real;
 262         const struct cred *old_cred;
 263         ssize_t ret;
 264
 265         if (!iov_iter_count(iter))
 266                 return 0;
 267
 268         inode_lock(inode);
 269         /* Update mode */
 270         ovl_copyattr(ovl_inode_real(inode), inode);
 271         ret = file_remove_privs(file);
 272         if (ret)
 273                 goto out_unlock;
 274
 275         ret = ovl_real_fdget(file, &real);
 276         if (ret)
 277                 goto out_unlock;
 278
 279         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 280         file_start_write(real.file);
 281         ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
 282                              ovl_iocb_to_rwf(iocb));
 283         file_end_write(real.file);
 284         revert_creds(old_cred);
 285
 286         /* Update size */
 287         ovl_copyattr(ovl_inode_real(inode), inode);
 288
 289         fdput(real);
 290
 291 out_unlock:
 292         inode_unlock(inode);
 293
 294         return ret;
 295 }
 296
 297 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 298 {
 299         struct fd real;
 300         const struct cred *old_cred;
 301         int ret;
 302
 303         ret = ovl_real_fdget_meta(file, &real, !datasync);
 304         if (ret)
 305                 return ret;
 306
 307         /* Don't sync lower file for fear of receiving EROFS error */
 308         if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 309                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 310                 ret = vfs_fsync_range(real.file, start, end, datasync);
 311                 revert_creds(old_cred);
 312         }
 313
 314         fdput(real);
 315
 316         return ret;
 317 }
 318
 319 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 320 {
 321         struct file *realfile = file->private_data;
 322         const struct cred *old_cred;
 323         int ret;
 324
 325         if (!realfile->f_op->mmap)
 326                 return -ENODEV;
 327
 328         if (WARN_ON(file != vma->vm_file))
 329                 return -EIO;
 330
 331         vma->vm_file = get_file(realfile);
 332
 333         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 334         ret = call_mmap(vma->vm_file, vma);
 335         revert_creds(old_cred);
 336
 337         if (ret) {
 338                 /* Drop reference count from new vm_file value */
 339                 fput(realfile);
 340         } else {
 341                 /* Drop reference count from previous vm_file value */
 342                 fput(file);
 343         }
 344
 345         ovl_file_accessed(file);
 346
 347         return ret;
 348 }
 349
 350 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 351 {
 352         struct inode *inode = file_inode(file);
 353         struct fd real;
 354         const struct cred *old_cred;
 355         int ret;
 356
 357         ret = ovl_real_fdget(file, &real);
 358         if (ret)
 359                 return ret;
 360
 361         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 362         ret = vfs_fallocate(real.file, mode, offset, len);
 363         revert_creds(old_cred);
 364
 365         /* Update size */
 366         ovl_copyattr(ovl_inode_real(inode), inode);
 367
 368         fdput(real);
 369
 370         return ret;
 371 }
 372
 373 static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 374 {
 375         struct fd real;
 376         const struct cred *old_cred;
 377         int ret;
 378
 379         ret = ovl_real_fdget(file, &real);
 380         if (ret)
 381                 return ret;
 382
 383         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 384         ret = vfs_fadvise(real.file, offset, len, advice);
 385         revert_creds(old_cred);
 386
 387         fdput(real);
 388
 389         return ret;
 390 }
 391
 392 static long ovl_real_ioctl(struct file *file, unsigned int cmd,
 393                            unsigned long arg)
 394 {
 395         struct fd real;
 396         const struct cred *old_cred;
 397         long ret;
 398
 399         ret = ovl_real_fdget(file, &real);
 400         if (ret)
 401                 return ret;
 402
 403         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 404         ret = vfs_ioctl(real.file, cmd, arg);
 405         revert_creds(old_cred);
 406
 407         fdput(real);
 408
 409         return ret;
 410 }
 411
 412 static unsigned int ovl_get_inode_flags(struct inode *inode)
 413 {
 414         unsigned int flags = READ_ONCE(inode->i_flags);
 415         unsigned int ovl_iflags = 0;
 416
 417         if (flags & S_SYNC)
 418                 ovl_iflags |= FS_SYNC_FL;
 419         if (flags & S_APPEND)
 420                 ovl_iflags |= FS_APPEND_FL;
 421         if (flags & S_IMMUTABLE)
 422                 ovl_iflags |= FS_IMMUTABLE_FL;
 423         if (flags & S_NOATIME)
 424                 ovl_iflags |= FS_NOATIME_FL;
 425
 426         return ovl_iflags;
 427 }
 428
 429 static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd,
 430                                 unsigned long arg)
 431 {
 432         long ret;
 433         struct inode *inode = file_inode(file);
 434         unsigned int flags;
 435         unsigned int old_flags;
 436
 437         if (!inode_owner_or_capable(inode))
 438                 return -EACCES;
 439
 440         if (get_user(flags, (int __user *) arg))
 441                 return -EFAULT;
 442
 443         ret = mnt_want_write_file(file);
 444         if (ret)
 445                 return ret;
 446
 447         inode_lock(inode);
 448
 449         /* Check the capability before cred override */
 450         ret = -EPERM;
 451         old_flags = ovl_get_inode_flags(inode);
 452         if (((flags ^ old_flags) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) &&
 453             !capable(CAP_LINUX_IMMUTABLE))
 454                 goto unlock;
 455
 456         ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY);
 457         if (ret)
 458                 goto unlock;
 459
 460         ret = ovl_real_ioctl(file, cmd, arg);
 461
 462         ovl_copyflags(ovl_inode_real(inode), inode);
 463 unlock:
 464         inode_unlock(inode);
 465
 466         mnt_drop_write_file(file);
 467
 468         return ret;
 469
 470 }
 471
 472 static long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 473 {
 474         long ret;
 475
 476         switch (cmd) {
 477         case FS_IOC_GETFLAGS:
 478         case FS_IOC_FSGETXATTR:
 479                 ret = ovl_real_ioctl(file, cmd, arg);
 480                 break;
 481
 482         case FS_IOC_SETFLAGS:
 483         case FS_IOC_FSSETXATTR:
 484                 ret = ovl_ioctl_set_flags(file, cmd, arg);
 485                 break;
 486
 487         default:
 488                 ret = -ENOTTY;
 489         }
 490
 491         return ret;
 492 }
 493
 494 static long ovl_compat_ioctl(struct file *file, unsigned int cmd,
 495                              unsigned long arg)
 496 {
 497         switch (cmd) {
 498         case FS_IOC32_GETFLAGS:
 499                 cmd = FS_IOC_GETFLAGS;
 500                 break;
 501
 502         case FS_IOC32_SETFLAGS:
 503                 cmd = FS_IOC_SETFLAGS;
 504                 break;
 505
 506         default:
 507                 return -ENOIOCTLCMD;
 508         }
 509
 510         return ovl_ioctl(file, cmd, arg);
 511 }
 512
 513 enum ovl_copyop {
 514         OVL_COPY,
 515         OVL_CLONE,
 516         OVL_DEDUPE,
 517 };
 518
 519 static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 520                             struct file *file_out, loff_t pos_out,
 521                             loff_t len, unsigned int flags, enum ovl_copyop op)
 522 {
 523         struct inode *inode_out = file_inode(file_out);
 524         struct fd real_in, real_out;
 525         const struct cred *old_cred;
 526         loff_t ret;
 527
 528         ret = ovl_real_fdget(file_out, &real_out);
 529         if (ret)
 530                 return ret;
 531
 532         ret = ovl_real_fdget(file_in, &real_in);
 533         if (ret) {
 534                 fdput(real_out);
 535                 return ret;
 536         }
 537
 538         old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
 539         switch (op) {
 540         case OVL_COPY:
 541                 ret = vfs_copy_file_range(real_in.file, pos_in,
 542                                           real_out.file, pos_out, len, flags);
 543                 break;
 544
 545         case OVL_CLONE:
 546                 ret = vfs_clone_file_range(real_in.file, pos_in,
 547                                            real_out.file, pos_out, len, flags);
 548                 break;
 549
 550         case OVL_DEDUPE:
 551                 ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
 552                                                 real_out.file, pos_out, len,
 553                                                 flags);
 554                 break;
 555         }
 556         revert_creds(old_cred);
 557
 558         /* Update size */
 559         ovl_copyattr(ovl_inode_real(inode_out), inode_out);
 560
 561         fdput(real_in);
 562         fdput(real_out);
 563
 564         return ret;
 565 }
 566
 567 static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
 568                                    struct file *file_out, loff_t pos_out,
 569                                    size_t len, unsigned int flags)
 570 {
 571         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
 572                             OVL_COPY);
 573 }
 574
 575 static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
 576                                    struct file *file_out, loff_t pos_out,
 577                                    loff_t len, unsigned int remap_flags)
 578 {
 579         enum ovl_copyop op;
 580
 581         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 582                 return -EINVAL;
 583
 584         if (remap_flags & REMAP_FILE_DEDUP)
 585                 op = OVL_DEDUPE;
 586         else
 587                 op = OVL_CLONE;
 588
 589         /*
 590          * Don't copy up because of a dedupe request, this wouldn't make sense
 591          * most of the time (data would be duplicated instead of deduplicated).
 592          */
 593         if (op == OVL_DEDUPE &&
 594             (!ovl_inode_upper(file_inode(file_in)) ||
 595              !ovl_inode_upper(file_inode(file_out))))
 596                 return -EPERM;
 597
 598         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
 599                             remap_flags, op);
 600 }
 601
 602 const struct file_operations ovl_file_operations = {
 603         .open           = ovl_open,
 604         .release        = ovl_release,
 605         .llseek         = ovl_llseek,
 606         .read_iter      = ovl_read_iter,
 607         .write_iter     = ovl_write_iter,
 608         .fsync          = ovl_fsync,
 609         .mmap           = ovl_mmap,
 610         .fallocate      = ovl_fallocate,
 611         .fadvise        = ovl_fadvise,
 612         .unlocked_ioctl = ovl_ioctl,
 613         .compat_ioctl   = ovl_compat_ioctl,
 614
 615         .copy_file_range        = ovl_copy_file_range,
 616         .remap_file_range       = ovl_remap_file_range,
 617 };