fs/overlayfs/namei.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2011 Novell Inc.
   4  * Copyright (C) 2016 Red Hat, Inc.
   5  */
   6
   7 #include <linux/fs.h>
   8 #include <linux/cred.h>
   9 #include <linux/ctype.h>
  10 #include <linux/namei.h>
  11 #include <linux/xattr.h>
  12 #include <linux/ratelimit.h>
  13 #include <linux/mount.h>
  14 #include <linux/exportfs.h>
  15 #include "overlayfs.h"
  16
  17 #include "../internal.h"        /* for vfs_path_lookup */
  18
  19 struct ovl_lookup_data {
  20         struct super_block *sb;
  21         struct vfsmount *mnt;
  22         struct qstr name;
  23         bool is_dir;
  24         bool opaque;
  25         bool stop;
  26         bool last;
  27         char *redirect;
  28         int metacopy;
  29         /* Referring to last redirect xattr */
  30         bool absolute_redirect;
  31 };
  32
  33 static int ovl_check_redirect(const struct path *path, struct ovl_lookup_data *d,
  34                               size_t prelen, const char *post)
  35 {
  36         int res;
  37         char *buf;
  38         struct ovl_fs *ofs = OVL_FS(d->sb);
  39
  40         d->absolute_redirect = false;
  41         buf = ovl_get_redirect_xattr(ofs, path, prelen + strlen(post));
  42         if (IS_ERR_OR_NULL(buf))
  43                 return PTR_ERR(buf);
  44
  45         if (buf[0] == '/') {
  46                 d->absolute_redirect = true;
  47                 /*
  48                  * One of the ancestor path elements in an absolute path
  49                  * lookup in ovl_lookup_layer() could have been opaque and
  50                  * that will stop further lookup in lower layers (d->stop=true)
  51                  * But we have found an absolute redirect in descendant path
  52                  * element and that should force continue lookup in lower
  53                  * layers (reset d->stop).
  54                  */
  55                 d->stop = false;
  56         } else {
  57                 res = strlen(buf) + 1;
  58                 memmove(buf + prelen, buf, res);
  59                 memcpy(buf, d->name.name, prelen);
  60         }
  61
  62         strcat(buf, post);
  63         kfree(d->redirect);
  64         d->redirect = buf;
  65         d->name.name = d->redirect;
  66         d->name.len = strlen(d->redirect);
  67
  68         return 0;
  69 }
  70
  71 static int ovl_acceptable(void *ctx, struct dentry *dentry)
  72 {
  73         /*
  74          * A non-dir origin may be disconnected, which is fine, because
  75          * we only need it for its unique inode number.
  76          */
  77         if (!d_is_dir(dentry))
  78                 return 1;
  79
  80         /* Don't decode a deleted empty directory */
  81         if (d_unhashed(dentry))
  82                 return 0;
  83
  84         /* Check if directory belongs to the layer we are decoding from */
  85         return is_subdir(dentry, ((struct vfsmount *)ctx)->mnt_root);
  86 }
  87
  88 /*
  89  * Check validity of an overlay file handle buffer.
  90  *
  91  * Return 0 for a valid file handle.
  92  * Return -ENODATA for "origin unknown".
  93  * Return <0 for an invalid file handle.
  94  */
  95 int ovl_check_fb_len(struct ovl_fb *fb, int fb_len)
  96 {
  97         if (fb_len < sizeof(struct ovl_fb) || fb_len < fb->len)
  98                 return -EINVAL;
  99
 100         if (fb->magic != OVL_FH_MAGIC)
 101                 return -EINVAL;
 102
 103         /* Treat larger version and unknown flags as "origin unknown" */
 104         if (fb->version > OVL_FH_VERSION || fb->flags & ~OVL_FH_FLAG_ALL)
 105                 return -ENODATA;
 106
 107         /* Treat endianness mismatch as "origin unknown" */
 108         if (!(fb->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
 109             (fb->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
 110                 return -ENODATA;
 111
 112         return 0;
 113 }
 114
 115 static struct ovl_fh *ovl_get_fh(struct ovl_fs *ofs, struct dentry *upperdentry,
 116                                  enum ovl_xattr ox)
 117 {
 118         int res, err;
 119         struct ovl_fh *fh = NULL;
 120
 121         res = ovl_getxattr_upper(ofs, upperdentry, ox, NULL, 0);
 122         if (res < 0) {
 123                 if (res == -ENODATA || res == -EOPNOTSUPP)
 124                         return NULL;
 125                 goto fail;
 126         }
 127         /* Zero size value means "copied up but origin unknown" */
 128         if (res == 0)
 129                 return NULL;
 130
 131         fh = kzalloc(res + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
 132         if (!fh)
 133                 return ERR_PTR(-ENOMEM);
 134
 135         res = ovl_getxattr_upper(ofs, upperdentry, ox, fh->buf, res);
 136         if (res < 0)
 137                 goto fail;
 138
 139         err = ovl_check_fb_len(&fh->fb, res);
 140         if (err < 0) {
 141                 if (err == -ENODATA)
 142                         goto out;
 143                 goto invalid;
 144         }
 145
 146         return fh;
 147
 148 out:
 149         kfree(fh);
 150         return NULL;
 151
 152 fail:
 153         pr_warn_ratelimited("failed to get origin (%i)\n", res);
 154         goto out;
 155 invalid:
 156         pr_warn_ratelimited("invalid origin (%*phN)\n", res, fh);
 157         goto out;
 158 }
 159
 160 struct dentry *ovl_decode_real_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
 161                                   struct vfsmount *mnt, bool connected)
 162 {
 163         struct dentry *real;
 164         int bytes;
 165
 166         if (!capable(CAP_DAC_READ_SEARCH))
 167                 return NULL;
 168
 169         /*
 170          * Make sure that the stored uuid matches the uuid of the lower
 171          * layer where file handle will be decoded.
 172          * In case of uuid=off option just make sure that stored uuid is null.
 173          */
 174         if (ovl_origin_uuid(ofs) ?
 175             !uuid_equal(&fh->fb.uuid, &mnt->mnt_sb->s_uuid) :
 176             !uuid_is_null(&fh->fb.uuid))
 177                 return NULL;
 178
 179         bytes = (fh->fb.len - offsetof(struct ovl_fb, fid));
 180         real = exportfs_decode_fh(mnt, (struct fid *)fh->fb.fid,
 181                                   bytes >> 2, (int)fh->fb.type,
 182                                   connected ? ovl_acceptable : NULL, mnt);
 183         if (IS_ERR(real)) {
 184                 /*
 185                  * Treat stale file handle to lower file as "origin unknown".
 186                  * upper file handle could become stale when upper file is
 187                  * unlinked and this information is needed to handle stale
 188                  * index entries correctly.
 189                  */
 190                 if (real == ERR_PTR(-ESTALE) &&
 191                     !(fh->fb.flags & OVL_FH_FLAG_PATH_UPPER))
 192                         real = NULL;
 193                 return real;
 194         }
 195
 196         if (ovl_dentry_weird(real)) {
 197                 dput(real);
 198                 return NULL;
 199         }
 200
 201         return real;
 202 }
 203
 204 static bool ovl_is_opaquedir(struct ovl_fs *ofs, const struct path *path)
 205 {
 206         return ovl_path_check_dir_xattr(ofs, path, OVL_XATTR_OPAQUE);
 207 }
 208
 209 static struct dentry *ovl_lookup_positive_unlocked(struct ovl_lookup_data *d,
 210                                                    const char *name,
 211                                                    struct dentry *base, int len,
 212                                                    bool drop_negative)
 213 {
 214         struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->mnt), name, base, len);
 215
 216         if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
 217                 if (drop_negative && ret->d_lockref.count == 1) {
 218                         spin_lock(&ret->d_lock);
 219                         /* Recheck condition under lock */
 220                         if (d_is_negative(ret) && ret->d_lockref.count == 1)
 221                                 __d_drop(ret);
 222                         spin_unlock(&ret->d_lock);
 223                 }
 224                 dput(ret);
 225                 ret = ERR_PTR(-ENOENT);
 226         }
 227         return ret;
 228 }
 229
 230 static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 231                              const char *name, unsigned int namelen,
 232                              size_t prelen, const char *post,
 233                              struct dentry **ret, bool drop_negative)
 234 {
 235         struct dentry *this;
 236         struct path path;
 237         int err;
 238         bool last_element = !post[0];
 239
 240         this = ovl_lookup_positive_unlocked(d, name, base, namelen, drop_negative);
 241         if (IS_ERR(this)) {
 242                 err = PTR_ERR(this);
 243                 this = NULL;
 244                 if (err == -ENOENT || err == -ENAMETOOLONG)
 245                         goto out;
 246                 goto out_err;
 247         }
 248
 249         if (ovl_dentry_weird(this)) {
 250                 /* Don't support traversing automounts and other weirdness */
 251                 err = -EREMOTE;
 252                 goto out_err;
 253         }
 254         if (ovl_is_whiteout(this)) {
 255                 d->stop = d->opaque = true;
 256                 goto put_and_out;
 257         }
 258         /*
 259          * This dentry should be a regular file if previous layer lookup
 260          * found a metacopy dentry.
 261          */
 262         if (last_element && d->metacopy && !d_is_reg(this)) {
 263                 d->stop = true;
 264                 goto put_and_out;
 265         }
 266
 267         path.dentry = this;
 268         path.mnt = d->mnt;
 269         if (!d_can_lookup(this)) {
 270                 if (d->is_dir || !last_element) {
 271                         d->stop = true;
 272                         goto put_and_out;
 273                 }
 274                 err = ovl_check_metacopy_xattr(OVL_FS(d->sb), &path, NULL);
 275                 if (err < 0)
 276                         goto out_err;
 277
 278                 d->metacopy = err;
 279                 d->stop = !d->metacopy;
 280                 if (!d->metacopy || d->last)
 281                         goto out;
 282         } else {
 283                 if (ovl_lookup_trap_inode(d->sb, this)) {
 284                         /* Caught in a trap of overlapping layers */
 285                         err = -ELOOP;
 286                         goto out_err;
 287                 }
 288
 289                 if (last_element)
 290                         d->is_dir = true;
 291                 if (d->last)
 292                         goto out;
 293
 294                 if (ovl_is_opaquedir(OVL_FS(d->sb), &path)) {
 295                         d->stop = true;
 296                         if (last_element)
 297                                 d->opaque = true;
 298                         goto out;
 299                 }
 300         }
 301         err = ovl_check_redirect(&path, d, prelen, post);
 302         if (err)
 303                 goto out_err;
 304 out:
 305         *ret = this;
 306         return 0;
 307
 308 put_and_out:
 309         dput(this);
 310         this = NULL;
 311         goto out;
 312
 313 out_err:
 314         dput(this);
 315         return err;
 316 }
 317
 318 static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
 319                             struct dentry **ret, bool drop_negative)
 320 {
 321         /* Counting down from the end, since the prefix can change */
 322         size_t rem = d->name.len - 1;
 323         struct dentry *dentry = NULL;
 324         int err;
 325
 326         if (d->name.name[0] != '/')
 327                 return ovl_lookup_single(base, d, d->name.name, d->name.len,
 328                                          0, "", ret, drop_negative);
 329
 330         while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
 331                 const char *s = d->name.name + d->name.len - rem;
 332                 const char *next = strchrnul(s, '/');
 333                 size_t thislen = next - s;
 334                 bool end = !next[0];
 335
 336                 /* Verify we did not go off the rails */
 337                 if (WARN_ON(s[-1] != '/'))
 338                         return -EIO;
 339
 340                 err = ovl_lookup_single(base, d, s, thislen,
 341                                         d->name.len - rem, next, &base,
 342                                         drop_negative);
 343                 dput(dentry);
 344                 if (err)
 345                         return err;
 346                 dentry = base;
 347                 if (end)
 348                         break;
 349
 350                 rem -= thislen + 1;
 351
 352                 if (WARN_ON(rem >= d->name.len))
 353                         return -EIO;
 354         }
 355         *ret = dentry;
 356         return 0;
 357 }
 358
 359 static int ovl_lookup_data_layer(struct dentry *dentry, const char *redirect,
 360                                  const struct ovl_layer *layer,
 361                                  struct path *datapath)
 362 {
 363         int err;
 364
 365         err = vfs_path_lookup(layer->mnt->mnt_root, layer->mnt, redirect,
 366                         LOOKUP_BENEATH | LOOKUP_NO_SYMLINKS | LOOKUP_NO_XDEV,
 367                         datapath);
 368         pr_debug("lookup lowerdata (%pd2, redirect=\"%s\", layer=%d, err=%i)\n",
 369                  dentry, redirect, layer->idx, err);
 370
 371         if (err)
 372                 return err;
 373
 374         err = -EREMOTE;
 375         if (ovl_dentry_weird(datapath->dentry))
 376                 goto out_path_put;
 377
 378         err = -ENOENT;
 379         /* Only regular file is acceptable as lower data */
 380         if (!d_is_reg(datapath->dentry))
 381                 goto out_path_put;
 382
 383         return 0;
 384
 385 out_path_put:
 386         path_put(datapath);
 387
 388         return err;
 389 }
 390
 391 /* Lookup in data-only layers by absolute redirect to layer root */
 392 static int ovl_lookup_data_layers(struct dentry *dentry, const char *redirect,
 393                                   struct ovl_path *lowerdata)
 394 {
 395         struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
 396         const struct ovl_layer *layer;
 397         struct path datapath;
 398         int err = -ENOENT;
 399         int i;
 400
 401         layer = &ofs->layers[ofs->numlayer - ofs->numdatalayer];
 402         for (i = 0; i < ofs->numdatalayer; i++, layer++) {
 403                 err = ovl_lookup_data_layer(dentry, redirect, layer, &datapath);
 404                 if (!err) {
 405                         mntput(datapath.mnt);
 406                         lowerdata->dentry = datapath.dentry;
 407                         lowerdata->layer = layer;
 408                         return 0;
 409                 }
 410         }
 411
 412         return err;
 413 }
 414
 415 int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
 416                         struct dentry *upperdentry, struct ovl_path **stackp)
 417 {
 418         struct dentry *origin = NULL;
 419         int i;
 420
 421         for (i = 1; i <= ovl_numlowerlayer(ofs); i++) {
 422                 /*
 423                  * If lower fs uuid is not unique among lower fs we cannot match
 424                  * fh->uuid to layer.
 425                  */
 426                 if (ofs->layers[i].fsid &&
 427                     ofs->layers[i].fs->bad_uuid)
 428                         continue;
 429
 430                 origin = ovl_decode_real_fh(ofs, fh, ofs->layers[i].mnt,
 431                                             connected);
 432                 if (origin)
 433                         break;
 434         }
 435
 436         if (!origin)
 437                 return -ESTALE;
 438         else if (IS_ERR(origin))
 439                 return PTR_ERR(origin);
 440
 441         if (upperdentry && !ovl_is_whiteout(upperdentry) &&
 442             inode_wrong_type(d_inode(upperdentry), d_inode(origin)->i_mode))
 443                 goto invalid;
 444
 445         if (!*stackp)
 446                 *stackp = kmalloc(sizeof(struct ovl_path), GFP_KERNEL);
 447         if (!*stackp) {
 448                 dput(origin);
 449                 return -ENOMEM;
 450         }
 451         **stackp = (struct ovl_path){
 452                 .dentry = origin,
 453                 .layer = &ofs->layers[i]
 454         };
 455
 456         return 0;
 457
 458 invalid:
 459         pr_warn_ratelimited("invalid origin (%pd2, ftype=%x, origin ftype=%x).\n",
 460                             upperdentry, d_inode(upperdentry)->i_mode & S_IFMT,
 461                             d_inode(origin)->i_mode & S_IFMT);
 462         dput(origin);
 463         return -ESTALE;
 464 }
 465
 466 static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
 467                             struct ovl_path **stackp)
 468 {
 469         struct ovl_fh *fh = ovl_get_fh(ofs, upperdentry, OVL_XATTR_ORIGIN);
 470         int err;
 471
 472         if (IS_ERR_OR_NULL(fh))
 473                 return PTR_ERR(fh);
 474
 475         err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
 476         kfree(fh);
 477
 478         if (err) {
 479                 if (err == -ESTALE)
 480                         return 0;
 481                 return err;
 482         }
 483
 484         return 0;
 485 }
 486
 487 /*
 488  * Verify that @fh matches the file handle stored in xattr @name.
 489  * Return 0 on match, -ESTALE on mismatch, < 0 on error.
 490  */
 491 static int ovl_verify_fh(struct ovl_fs *ofs, struct dentry *dentry,
 492                          enum ovl_xattr ox, const struct ovl_fh *fh)
 493 {
 494         struct ovl_fh *ofh = ovl_get_fh(ofs, dentry, ox);
 495         int err = 0;
 496
 497         if (!ofh)
 498                 return -ENODATA;
 499
 500         if (IS_ERR(ofh))
 501                 return PTR_ERR(ofh);
 502
 503         if (fh->fb.len != ofh->fb.len || memcmp(&fh->fb, &ofh->fb, fh->fb.len))
 504                 err = -ESTALE;
 505
 506         kfree(ofh);
 507         return err;
 508 }
 509
 510 int ovl_verify_set_fh(struct ovl_fs *ofs, struct dentry *dentry,
 511                       enum ovl_xattr ox, const struct ovl_fh *fh,
 512                       bool is_upper, bool set)
 513 {
 514         int err;
 515
 516         err = ovl_verify_fh(ofs, dentry, ox, fh);
 517         if (set && err == -ENODATA)
 518                 err = ovl_setxattr(ofs, dentry, ox, fh->buf, fh->fb.len);
 519
 520         return err;
 521 }
 522
 523 /*
 524  * Verify that @real dentry matches the file handle stored in xattr @name.
 525  *
 526  * If @set is true and there is no stored file handle, encode @real and store
 527  * file handle in xattr @name.
 528  *
 529  * Return 0 on match, -ESTALE on mismatch, -ENODATA on no xattr, < 0 on error.
 530  */
 531 int ovl_verify_origin_xattr(struct ovl_fs *ofs, struct dentry *dentry,
 532                             enum ovl_xattr ox, struct dentry *real,
 533                             bool is_upper, bool set)
 534 {
 535         struct inode *inode;
 536         struct ovl_fh *fh;
 537         int err;
 538
 539         fh = ovl_encode_real_fh(ofs, real, is_upper);
 540         err = PTR_ERR(fh);
 541         if (IS_ERR(fh)) {
 542                 fh = NULL;
 543                 goto fail;
 544         }
 545
 546         err = ovl_verify_set_fh(ofs, dentry, ox, fh, is_upper, set);
 547         if (err)
 548                 goto fail;
 549
 550 out:
 551         kfree(fh);
 552         return err;
 553
 554 fail:
 555         inode = d_inode(real);
 556         pr_warn_ratelimited("failed to verify %s (%pd2, ino=%lu, err=%i)\n",
 557                             is_upper ? "upper" : "origin", real,
 558                             inode ? inode->i_ino : 0, err);
 559         goto out;
 560 }
 561
 562
 563 /* Get upper dentry from index */
 564 struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index,
 565                                bool connected)
 566 {
 567         struct ovl_fh *fh;
 568         struct dentry *upper;
 569
 570         if (!d_is_dir(index))
 571                 return dget(index);
 572
 573         fh = ovl_get_fh(ofs, index, OVL_XATTR_UPPER);
 574         if (IS_ERR_OR_NULL(fh))
 575                 return ERR_CAST(fh);
 576
 577         upper = ovl_decode_real_fh(ofs, fh, ovl_upper_mnt(ofs), connected);
 578         kfree(fh);
 579
 580         if (IS_ERR_OR_NULL(upper))
 581                 return upper ?: ERR_PTR(-ESTALE);
 582
 583         if (!d_is_dir(upper)) {
 584                 pr_warn_ratelimited("invalid index upper (%pd2, upper=%pd2).\n",
 585                                     index, upper);
 586                 dput(upper);
 587                 return ERR_PTR(-EIO);
 588         }
 589
 590         return upper;
 591 }
 592
 593 /*
 594  * Verify that an index entry name matches the origin file handle stored in
 595  * OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
 596  * Return 0 on match, -ESTALE on mismatch or stale origin, < 0 on error.
 597  */
 598 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 599 {
 600         struct ovl_fh *fh = NULL;
 601         size_t len;
 602         struct ovl_path origin = { };
 603         struct ovl_path *stack = &origin;
 604         struct dentry *upper = NULL;
 605         int err;
 606
 607         if (!d_inode(index))
 608                 return 0;
 609
 610         err = -EINVAL;
 611         if (index->d_name.len < sizeof(struct ovl_fb)*2)
 612                 goto fail;
 613
 614         err = -ENOMEM;
 615         len = index->d_name.len / 2;
 616         fh = kzalloc(len + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
 617         if (!fh)
 618                 goto fail;
 619
 620         err = -EINVAL;
 621         if (hex2bin(fh->buf, index->d_name.name, len))
 622                 goto fail;
 623
 624         err = ovl_check_fb_len(&fh->fb, len);
 625         if (err)
 626                 goto fail;
 627
 628         /*
 629          * Whiteout index entries are used as an indication that an exported
 630          * overlay file handle should be treated as stale (i.e. after unlink
 631          * of the overlay inode). These entries contain no origin xattr.
 632          */
 633         if (ovl_is_whiteout(index))
 634                 goto out;
 635
 636         /*
 637          * Verifying directory index entries are not stale is expensive, so
 638          * only verify stale dir index if NFS export is enabled.
 639          */
 640         if (d_is_dir(index) && !ofs->config.nfs_export)
 641                 goto out;
 642
 643         /*
 644          * Directory index entries should have 'upper' xattr pointing to the
 645          * real upper dir. Non-dir index entries are hardlinks to the upper
 646          * real inode. For non-dir index, we can read the copy up origin xattr
 647          * directly from the index dentry, but for dir index we first need to
 648          * decode the upper directory.
 649          */
 650         upper = ovl_index_upper(ofs, index, false);
 651         if (IS_ERR_OR_NULL(upper)) {
 652                 err = PTR_ERR(upper);
 653                 /*
 654                  * Directory index entries with no 'upper' xattr need to be
 655                  * removed. When dir index entry has a stale 'upper' xattr,
 656                  * we assume that upper dir was removed and we treat the dir
 657                  * index as orphan entry that needs to be whited out.
 658                  */
 659                 if (err == -ESTALE)
 660                         goto orphan;
 661                 else if (!err)
 662                         err = -ESTALE;
 663                 goto fail;
 664         }
 665
 666         err = ovl_verify_fh(ofs, upper, OVL_XATTR_ORIGIN, fh);
 667         dput(upper);
 668         if (err)
 669                 goto fail;
 670
 671         /* Check if non-dir index is orphan and don't warn before cleaning it */
 672         if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
 673                 err = ovl_check_origin_fh(ofs, fh, false, index, &stack);
 674                 if (err)
 675                         goto fail;
 676
 677                 if (ovl_get_nlink(ofs, origin.dentry, index, 0) == 0)
 678                         goto orphan;
 679         }
 680
 681 out:
 682         dput(origin.dentry);
 683         kfree(fh);
 684         return err;
 685
 686 fail:
 687         pr_warn_ratelimited("failed to verify index (%pd2, ftype=%x, err=%i)\n",
 688                             index, d_inode(index)->i_mode & S_IFMT, err);
 689         goto out;
 690
 691 orphan:
 692         pr_warn_ratelimited("orphan index entry (%pd2, ftype=%x, nlink=%u)\n",
 693                             index, d_inode(index)->i_mode & S_IFMT,
 694                             d_inode(index)->i_nlink);
 695         err = -ENOENT;
 696         goto out;
 697 }
 698
 699 int ovl_get_index_name_fh(const struct ovl_fh *fh, struct qstr *name)
 700 {
 701         char *n, *s;
 702
 703         n = kcalloc(fh->fb.len, 2, GFP_KERNEL);
 704         if (!n)
 705                 return -ENOMEM;
 706
 707         s  = bin2hex(n, fh->buf, fh->fb.len);
 708         *name = (struct qstr) QSTR_INIT(n, s - n);
 709
 710         return 0;
 711
 712 }
 713
 714 /*
 715  * Lookup in indexdir for the index entry of a lower real inode or a copy up
 716  * origin inode. The index entry name is the hex representation of the lower
 717  * inode file handle.
 718  *
 719  * If the index dentry in negative, then either no lower aliases have been
 720  * copied up yet, or aliases have been copied up in older kernels and are
 721  * not indexed.
 722  *
 723  * If the index dentry for a copy up origin inode is positive, but points
 724  * to an inode different than the upper inode, then either the upper inode
 725  * has been copied up and not indexed or it was indexed, but since then
 726  * index dir was cleared. Either way, that index cannot be used to identify
 727  * the overlay inode.
 728  */
 729 int ovl_get_index_name(struct ovl_fs *ofs, struct dentry *origin,
 730                        struct qstr *name)
 731 {
 732         struct ovl_fh *fh;
 733         int err;
 734
 735         fh = ovl_encode_real_fh(ofs, origin, false);
 736         if (IS_ERR(fh))
 737                 return PTR_ERR(fh);
 738
 739         err = ovl_get_index_name_fh(fh, name);
 740
 741         kfree(fh);
 742         return err;
 743 }
 744
 745 /* Lookup index by file handle for NFS export */
 746 struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
 747 {
 748         struct dentry *index;
 749         struct qstr name;
 750         int err;
 751
 752         err = ovl_get_index_name_fh(fh, &name);
 753         if (err)
 754                 return ERR_PTR(err);
 755
 756         index = lookup_positive_unlocked(name.name, ofs->indexdir, name.len);
 757         kfree(name.name);
 758         if (IS_ERR(index)) {
 759                 if (PTR_ERR(index) == -ENOENT)
 760                         index = NULL;
 761                 return index;
 762         }
 763
 764         if (ovl_is_whiteout(index))
 765                 err = -ESTALE;
 766         else if (ovl_dentry_weird(index))
 767                 err = -EIO;
 768         else
 769                 return index;
 770
 771         dput(index);
 772         return ERR_PTR(err);
 773 }
 774
 775 struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
 776                                 struct dentry *origin, bool verify)
 777 {
 778         struct dentry *index;
 779         struct inode *inode;
 780         struct qstr name;
 781         bool is_dir = d_is_dir(origin);
 782         int err;
 783
 784         err = ovl_get_index_name(ofs, origin, &name);
 785         if (err)
 786                 return ERR_PTR(err);
 787
 788         index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name.name,
 789                                              ofs->indexdir, name.len);
 790         if (IS_ERR(index)) {
 791                 err = PTR_ERR(index);
 792                 if (err == -ENOENT) {
 793                         index = NULL;
 794                         goto out;
 795                 }
 796                 pr_warn_ratelimited("failed inode index lookup (ino=%lu, key=%.*s, err=%i);\n"
 797                                     "overlayfs: mount with '-o index=off' to disable inodes index.\n",
 798                                     d_inode(origin)->i_ino, name.len, name.name,
 799                                     err);
 800                 goto out;
 801         }
 802
 803         inode = d_inode(index);
 804         if (ovl_is_whiteout(index) && !verify) {
 805                 /*
 806                  * When index lookup is called with !verify for decoding an
 807                  * overlay file handle, a whiteout index implies that decode
 808                  * should treat file handle as stale and no need to print a
 809                  * warning about it.
 810                  */
 811                 dput(index);
 812                 index = ERR_PTR(-ESTALE);
 813                 goto out;
 814         } else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
 815                    inode_wrong_type(inode, d_inode(origin)->i_mode)) {
 816                 /*
 817                  * Index should always be of the same file type as origin
 818                  * except for the case of a whiteout index. A whiteout
 819                  * index should only exist if all lower aliases have been
 820                  * unlinked, which means that finding a lower origin on lookup
 821                  * whose index is a whiteout should be treated as an error.
 822                  */
 823                 pr_warn_ratelimited("bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
 824                                     index, d_inode(index)->i_mode & S_IFMT,
 825                                     d_inode(origin)->i_mode & S_IFMT);
 826                 goto fail;
 827         } else if (is_dir && verify) {
 828                 if (!upper) {
 829                         pr_warn_ratelimited("suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
 830                                             origin, index);
 831                         goto fail;
 832                 }
 833
 834                 /* Verify that dir index 'upper' xattr points to upper dir */
 835                 err = ovl_verify_upper(ofs, index, upper, false);
 836                 if (err) {
 837                         if (err == -ESTALE) {
 838                                 pr_warn_ratelimited("suspected multiply redirected dir found (upper=%pd2, origin=%pd2, index=%pd2).\n",
 839                                                     upper, origin, index);
 840                         }
 841                         goto fail;
 842                 }
 843         } else if (upper && d_inode(upper) != inode) {
 844                 goto out_dput;
 845         }
 846 out:
 847         kfree(name.name);
 848         return index;
 849
 850 out_dput:
 851         dput(index);
 852         index = NULL;
 853         goto out;
 854
 855 fail:
 856         dput(index);
 857         index = ERR_PTR(-EIO);
 858         goto out;
 859 }
 860
 861 /*
 862  * Returns next layer in stack starting from top.
 863  * Returns -1 if this is the last layer.
 864  */
 865 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 866 {
 867         struct ovl_entry *oe = OVL_E(dentry);
 868         struct ovl_path *lowerstack = ovl_lowerstack(oe);
 869
 870         BUG_ON(idx < 0);
 871         if (idx == 0) {
 872                 ovl_path_upper(dentry, path);
 873                 if (path->dentry)
 874                         return ovl_numlower(oe) ? 1 : -1;
 875                 idx++;
 876         }
 877         BUG_ON(idx > ovl_numlower(oe));
 878         path->dentry = lowerstack[idx - 1].dentry;
 879         path->mnt = lowerstack[idx - 1].layer->mnt;
 880
 881         return (idx < ovl_numlower(oe)) ? idx + 1 : -1;
 882 }
 883
 884 /* Fix missing 'origin' xattr */
 885 static int ovl_fix_origin(struct ovl_fs *ofs, struct dentry *dentry,
 886                           struct dentry *lower, struct dentry *upper)
 887 {
 888         const struct ovl_fh *fh;
 889         int err;
 890
 891         if (ovl_check_origin_xattr(ofs, upper))
 892                 return 0;
 893
 894         fh = ovl_get_origin_fh(ofs, lower);
 895         if (IS_ERR(fh))
 896                 return PTR_ERR(fh);
 897
 898         err = ovl_want_write(dentry);
 899         if (err)
 900                 goto out;
 901
 902         err = ovl_set_origin_fh(ofs, fh, upper);
 903         if (!err)
 904                 err = ovl_set_impure(dentry->d_parent, upper->d_parent);
 905
 906         ovl_drop_write(dentry);
 907 out:
 908         kfree(fh);
 909         return err;
 910 }
 911
 912 static int ovl_maybe_validate_verity(struct dentry *dentry)
 913 {
 914         struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
 915         struct inode *inode = d_inode(dentry);
 916         struct path datapath, metapath;
 917         int err;
 918
 919         if (!ofs->config.verity_mode ||
 920             !ovl_is_metacopy_dentry(dentry) ||
 921             ovl_test_flag(OVL_VERIFIED_DIGEST, inode))
 922                 return 0;
 923
 924         if (!ovl_test_flag(OVL_HAS_DIGEST, inode)) {
 925                 if (ofs->config.verity_mode == OVL_VERITY_REQUIRE) {
 926                         pr_warn_ratelimited("metacopy file '%pd' has no digest specified\n",
 927                                             dentry);
 928                         return -EIO;
 929                 }
 930                 return 0;
 931         }
 932
 933         ovl_path_lowerdata(dentry, &datapath);
 934         if (!datapath.dentry)
 935                 return -EIO;
 936
 937         ovl_path_real(dentry, &metapath);
 938         if (!metapath.dentry)
 939                 return -EIO;
 940
 941         err = ovl_inode_lock_interruptible(inode);
 942         if (err)
 943                 return err;
 944
 945         if (!ovl_test_flag(OVL_VERIFIED_DIGEST, inode)) {
 946                 const struct cred *old_cred;
 947
 948                 old_cred = ovl_override_creds(dentry->d_sb);
 949
 950                 err = ovl_validate_verity(ofs, &metapath, &datapath);
 951                 if (err == 0)
 952                         ovl_set_flag(OVL_VERIFIED_DIGEST, inode);
 953
 954                 revert_creds(old_cred);
 955         }
 956
 957         ovl_inode_unlock(inode);
 958
 959         return err;
 960 }
 961
 962 /* Lazy lookup of lowerdata */
 963 static int ovl_maybe_lookup_lowerdata(struct dentry *dentry)
 964 {
 965         struct inode *inode = d_inode(dentry);
 966         const char *redirect = ovl_lowerdata_redirect(inode);
 967         struct ovl_path datapath = {};
 968         const struct cred *old_cred;
 969         int err;
 970
 971         if (!redirect || ovl_dentry_lowerdata(dentry))
 972                 return 0;
 973
 974         if (redirect[0] != '/')
 975                 return -EIO;
 976
 977         err = ovl_inode_lock_interruptible(inode);
 978         if (err)
 979                 return err;
 980
 981         err = 0;
 982         /* Someone got here before us? */
 983         if (ovl_dentry_lowerdata(dentry))
 984                 goto out;
 985
 986         old_cred = ovl_override_creds(dentry->d_sb);
 987         err = ovl_lookup_data_layers(dentry, redirect, &datapath);
 988         revert_creds(old_cred);
 989         if (err)
 990                 goto out_err;
 991
 992         err = ovl_dentry_set_lowerdata(dentry, &datapath);
 993         if (err)
 994                 goto out_err;
 995
 996 out:
 997         ovl_inode_unlock(inode);
 998         dput(datapath.dentry);
 999
1000         return err;
1001
1002 out_err:
1003         pr_warn_ratelimited("lazy lowerdata lookup failed (%pd2, err=%i)\n",
1004                             dentry, err);
1005         goto out;
1006 }
1007
1008 int ovl_verify_lowerdata(struct dentry *dentry)
1009 {
1010         int err;
1011
1012         err = ovl_maybe_lookup_lowerdata(dentry);
1013         if (err)
1014                 return err;
1015
1016         return ovl_maybe_validate_verity(dentry);
1017 }
1018
1019 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
1020                           unsigned int flags)
1021 {
1022         struct ovl_entry *oe = NULL;
1023         const struct cred *old_cred;
1024         struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
1025         struct ovl_entry *poe = OVL_E(dentry->d_parent);
1026         struct ovl_entry *roe = OVL_E(dentry->d_sb->s_root);
1027         struct ovl_path *stack = NULL, *origin_path = NULL;
1028         struct dentry *upperdir, *upperdentry = NULL;
1029         struct dentry *origin = NULL;
1030         struct dentry *index = NULL;
1031         unsigned int ctr = 0;
1032         struct inode *inode = NULL;
1033         bool upperopaque = false;
1034         char *upperredirect = NULL;
1035         struct dentry *this;
1036         unsigned int i;
1037         int err;
1038         bool uppermetacopy = false;
1039         int metacopy_size = 0;
1040         struct ovl_lookup_data d = {
1041                 .sb = dentry->d_sb,
1042                 .name = dentry->d_name,
1043                 .is_dir = false,
1044                 .opaque = false,
1045                 .stop = false,
1046                 .last = ovl_redirect_follow(ofs) ? false : !ovl_numlower(poe),
1047                 .redirect = NULL,
1048                 .metacopy = 0,
1049         };
1050
1051         if (dentry->d_name.len > ofs->namelen)
1052                 return ERR_PTR(-ENAMETOOLONG);
1053
1054         old_cred = ovl_override_creds(dentry->d_sb);
1055         upperdir = ovl_dentry_upper(dentry->d_parent);
1056         if (upperdir) {
1057                 d.mnt = ovl_upper_mnt(ofs);
1058                 err = ovl_lookup_layer(upperdir, &d, &upperdentry, true);
1059                 if (err)
1060                         goto out;
1061
1062                 if (upperdentry && upperdentry->d_flags & DCACHE_OP_REAL) {
1063                         dput(upperdentry);
1064                         err = -EREMOTE;
1065                         goto out;
1066                 }
1067                 if (upperdentry && !d.is_dir) {
1068                         /*
1069                          * Lookup copy up origin by decoding origin file handle.
1070                          * We may get a disconnected dentry, which is fine,
1071                          * because we only need to hold the origin inode in
1072                          * cache and use its inode number.  We may even get a
1073                          * connected dentry, that is not under any of the lower
1074                          * layers root.  That is also fine for using it's inode
1075                          * number - it's the same as if we held a reference
1076                          * to a dentry in lower layer that was moved under us.
1077                          */
1078                         err = ovl_check_origin(ofs, upperdentry, &origin_path);
1079                         if (err)
1080                                 goto out_put_upper;
1081
1082                         if (d.metacopy)
1083                                 uppermetacopy = true;
1084                         metacopy_size = d.metacopy;
1085                 }
1086
1087                 if (d.redirect) {
1088                         err = -ENOMEM;
1089                         upperredirect = kstrdup(d.redirect, GFP_KERNEL);
1090                         if (!upperredirect)
1091                                 goto out_put_upper;
1092                         if (d.redirect[0] == '/')
1093                                 poe = roe;
1094                 }
1095                 upperopaque = d.opaque;
1096         }
1097
1098         if (!d.stop && ovl_numlower(poe)) {
1099                 err = -ENOMEM;
1100                 stack = ovl_stack_alloc(ofs->numlayer - 1);
1101                 if (!stack)
1102                         goto out_put_upper;
1103         }
1104
1105         for (i = 0; !d.stop && i < ovl_numlower(poe); i++) {
1106                 struct ovl_path lower = ovl_lowerstack(poe)[i];
1107
1108                 if (!ovl_redirect_follow(ofs))
1109                         d.last = i == ovl_numlower(poe) - 1;
1110                 else if (d.is_dir || !ofs->numdatalayer)
1111                         d.last = lower.layer->idx == ovl_numlower(roe);
1112
1113                 d.mnt = lower.layer->mnt;
1114                 err = ovl_lookup_layer(lower.dentry, &d, &this, false);
1115                 if (err)
1116                         goto out_put;
1117
1118                 if (!this)
1119                         continue;
1120
1121                 if ((uppermetacopy || d.metacopy) && !ofs->config.metacopy) {
1122                         dput(this);
1123                         err = -EPERM;
1124                         pr_warn_ratelimited("refusing to follow metacopy origin for (%pd2)\n", dentry);
1125                         goto out_put;
1126                 }
1127
1128                 /*
1129                  * If no origin fh is stored in upper of a merge dir, store fh
1130                  * of lower dir and set upper parent "impure".
1131                  */
1132                 if (upperdentry && !ctr && !ofs->noxattr && d.is_dir) {
1133                         err = ovl_fix_origin(ofs, dentry, this, upperdentry);
1134                         if (err) {
1135                                 dput(this);
1136                                 goto out_put;
1137                         }
1138                 }
1139
1140                 /*
1141                  * When "verify_lower" feature is enabled, do not merge with a
1142                  * lower dir that does not match a stored origin xattr. In any
1143                  * case, only verified origin is used for index lookup.
1144                  *
1145                  * For non-dir dentry, if index=on, then ensure origin
1146                  * matches the dentry found using path based lookup,
1147                  * otherwise error out.
1148                  */
1149                 if (upperdentry && !ctr &&
1150                     ((d.is_dir && ovl_verify_lower(dentry->d_sb)) ||
1151                      (!d.is_dir && ofs->config.index && origin_path))) {
1152                         err = ovl_verify_origin(ofs, upperdentry, this, false);
1153                         if (err) {
1154                                 dput(this);
1155                                 if (d.is_dir)
1156                                         break;
1157                                 goto out_put;
1158                         }
1159                         origin = this;
1160                 }
1161
1162                 if (!upperdentry && !d.is_dir && !ctr && d.metacopy)
1163                         metacopy_size = d.metacopy;
1164
1165                 if (d.metacopy && ctr) {
1166                         /*
1167                          * Do not store intermediate metacopy dentries in
1168                          * lower chain, except top most lower metacopy dentry.
1169                          * Continue the loop so that if there is an absolute
1170                          * redirect on this dentry, poe can be reset to roe.
1171                          */
1172                         dput(this);
1173                         this = NULL;
1174                 } else {
1175                         stack[ctr].dentry = this;
1176                         stack[ctr].layer = lower.layer;
1177                         ctr++;
1178                 }
1179
1180                 /*
1181                  * Following redirects can have security consequences: it's like
1182                  * a symlink into the lower layer without the permission checks.
1183                  * This is only a problem if the upper layer is untrusted (e.g
1184                  * comes from an USB drive).  This can allow a non-readable file
1185                  * or directory to become readable.
1186                  *
1187                  * Only following redirects when redirects are enabled disables
1188                  * this attack vector when not necessary.
1189                  */
1190                 err = -EPERM;
1191                 if (d.redirect && !ovl_redirect_follow(ofs)) {
1192                         pr_warn_ratelimited("refusing to follow redirect for (%pd2)\n",
1193                                             dentry);
1194                         goto out_put;
1195                 }
1196
1197                 if (d.stop)
1198                         break;
1199
1200                 if (d.redirect && d.redirect[0] == '/' && poe != roe) {
1201                         poe = roe;
1202                         /* Find the current layer on the root dentry */
1203                         i = lower.layer->idx - 1;
1204                 }
1205         }
1206
1207         /* Defer lookup of lowerdata in data-only layers to first access */
1208         if (d.metacopy && ctr && ofs->numdatalayer && d.absolute_redirect) {
1209                 d.metacopy = 0;
1210                 ctr++;
1211         }
1212
1213         /*
1214          * For regular non-metacopy upper dentries, there is no lower
1215          * path based lookup, hence ctr will be zero. If a dentry is found
1216          * using ORIGIN xattr on upper, install it in stack.
1217          *
1218          * For metacopy dentry, path based lookup will find lower dentries.
1219          * Just make sure a corresponding data dentry has been found.
1220          */
1221         if (d.metacopy || (uppermetacopy && !ctr)) {
1222                 pr_warn_ratelimited("metacopy with no lower data found - abort lookup (%pd2)\n",
1223                                     dentry);
1224                 err = -EIO;
1225                 goto out_put;
1226         } else if (!d.is_dir && upperdentry && !ctr && origin_path) {
1227                 if (WARN_ON(stack != NULL)) {
1228                         err = -EIO;
1229                         goto out_put;
1230                 }
1231                 stack = origin_path;
1232                 ctr = 1;
1233                 origin = origin_path->dentry;
1234                 origin_path = NULL;
1235         }
1236
1237         /*
1238          * Always lookup index if there is no-upperdentry.
1239          *
1240          * For the case of upperdentry, we have set origin by now if it
1241          * needed to be set. There are basically three cases.
1242          *
1243          * For directories, lookup index by lower inode and verify it matches
1244          * upper inode. We only trust dir index if we verified that lower dir
1245          * matches origin, otherwise dir index entries may be inconsistent
1246          * and we ignore them.
1247          *
1248          * For regular upper, we already set origin if upper had ORIGIN
1249          * xattr. There is no verification though as there is no path
1250          * based dentry lookup in lower in this case.
1251          *
1252          * For metacopy upper, we set a verified origin already if index
1253          * is enabled and if upper had an ORIGIN xattr.
1254          *
1255          */
1256         if (!upperdentry && ctr)
1257                 origin = stack[0].dentry;
1258
1259         if (origin && ovl_indexdir(dentry->d_sb) &&
1260             (!d.is_dir || ovl_index_all(dentry->d_sb))) {
1261                 index = ovl_lookup_index(ofs, upperdentry, origin, true);
1262                 if (IS_ERR(index)) {
1263                         err = PTR_ERR(index);
1264                         index = NULL;
1265                         goto out_put;
1266                 }
1267         }
1268
1269         if (ctr) {
1270                 oe = ovl_alloc_entry(ctr);
1271                 err = -ENOMEM;
1272                 if (!oe)
1273                         goto out_put;
1274
1275                 ovl_stack_cpy(ovl_lowerstack(oe), stack, ctr);
1276         }
1277
1278         if (upperopaque)
1279                 ovl_dentry_set_opaque(dentry);
1280
1281         if (upperdentry)
1282                 ovl_dentry_set_upper_alias(dentry);
1283         else if (index) {
1284                 struct path upperpath = {
1285                         .dentry = upperdentry = dget(index),
1286                         .mnt = ovl_upper_mnt(ofs),
1287                 };
1288
1289                 /*
1290                  * It's safe to assign upperredirect here: the previous
1291                  * assignment of happens only if upperdentry is non-NULL, and
1292                  * this one only if upperdentry is NULL.
1293                  */
1294                 upperredirect = ovl_get_redirect_xattr(ofs, &upperpath, 0);
1295                 if (IS_ERR(upperredirect)) {
1296                         err = PTR_ERR(upperredirect);
1297                         upperredirect = NULL;
1298                         goto out_free_oe;
1299                 }
1300                 err = ovl_check_metacopy_xattr(ofs, &upperpath, NULL);
1301                 if (err < 0)
1302                         goto out_free_oe;
1303                 uppermetacopy = err;
1304                 metacopy_size = err;
1305         }
1306
1307         if (upperdentry || ctr) {
1308                 struct ovl_inode_params oip = {
1309                         .upperdentry = upperdentry,
1310                         .oe = oe,
1311                         .index = index,
1312                         .redirect = upperredirect,
1313                 };
1314
1315                 /* Store lowerdata redirect for lazy lookup */
1316                 if (ctr > 1 && !d.is_dir && !stack[ctr - 1].dentry) {
1317                         oip.lowerdata_redirect = d.redirect;
1318                         d.redirect = NULL;
1319                 }
1320                 inode = ovl_get_inode(dentry->d_sb, &oip);
1321                 err = PTR_ERR(inode);
1322                 if (IS_ERR(inode))
1323                         goto out_free_oe;
1324                 if (upperdentry && !uppermetacopy)
1325                         ovl_set_flag(OVL_UPPERDATA, inode);
1326
1327                 if (metacopy_size > OVL_METACOPY_MIN_SIZE)
1328                         ovl_set_flag(OVL_HAS_DIGEST, inode);
1329         }
1330
1331         ovl_dentry_init_reval(dentry, upperdentry, OVL_I_E(inode));
1332
1333         revert_creds(old_cred);
1334         if (origin_path) {
1335                 dput(origin_path->dentry);
1336                 kfree(origin_path);
1337         }
1338         dput(index);
1339         ovl_stack_free(stack, ctr);
1340         kfree(d.redirect);
1341         return d_splice_alias(inode, dentry);
1342
1343 out_free_oe:
1344         ovl_free_entry(oe);
1345 out_put:
1346         dput(index);
1347         ovl_stack_free(stack, ctr);
1348 out_put_upper:
1349         if (origin_path) {
1350                 dput(origin_path->dentry);
1351                 kfree(origin_path);
1352         }
1353         dput(upperdentry);
1354         kfree(upperredirect);
1355 out:
1356         kfree(d.redirect);
1357         revert_creds(old_cred);
1358         return ERR_PTR(err);
1359 }
1360
1361 bool ovl_lower_positive(struct dentry *dentry)
1362 {
1363         struct ovl_entry *poe = OVL_E(dentry->d_parent);
1364         const struct qstr *name = &dentry->d_name;
1365         const struct cred *old_cred;
1366         unsigned int i;
1367         bool positive = false;
1368         bool done = false;
1369
1370         /*
1371          * If dentry is negative, then lower is positive iff this is a
1372          * whiteout.
1373          */
1374         if (!dentry->d_inode)
1375                 return ovl_dentry_is_opaque(dentry);
1376
1377         /* Negative upper -> positive lower */
1378         if (!ovl_dentry_upper(dentry))
1379                 return true;
1380
1381         old_cred = ovl_override_creds(dentry->d_sb);
1382         /* Positive upper -> have to look up lower to see whether it exists */
1383         for (i = 0; !done && !positive && i < ovl_numlower(poe); i++) {
1384                 struct dentry *this;
1385                 struct ovl_path *parentpath = &ovl_lowerstack(poe)[i];
1386
1387                 this = lookup_one_positive_unlocked(
1388                                 mnt_idmap(parentpath->layer->mnt),
1389                                 name->name, parentpath->dentry, name->len);
1390                 if (IS_ERR(this)) {
1391                         switch (PTR_ERR(this)) {
1392                         case -ENOENT:
1393                         case -ENAMETOOLONG:
1394                                 break;
1395
1396                         default:
1397                                 /*
1398                                  * Assume something is there, we just couldn't
1399                                  * access it.
1400                                  */
1401                                 positive = true;
1402                                 break;
1403                         }
1404                 } else {
1405                         positive = !ovl_is_whiteout(this);
1406                         done = true;
1407                         dput(this);
1408                 }
1409         }
1410         revert_creds(old_cred);
1411
1412         return positive;
1413 }