fs/overlayfs/namei.c

   1 /*
   2  * Copyright (C) 2011 Novell Inc.
   3  * Copyright (C) 2016 Red Hat, Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 as published by
   7  * the Free Software Foundation.
   8  */
   9
  10 #include <linux/fs.h>
  11 #include <linux/cred.h>
  12 #include <linux/ctype.h>
  13 #include <linux/namei.h>
  14 #include <linux/xattr.h>
  15 #include <linux/ratelimit.h>
  16 #include <linux/mount.h>
  17 #include <linux/exportfs.h>
  18 #include "overlayfs.h"
  19
  20 struct ovl_lookup_data {
  21         struct qstr name;
  22         bool is_dir;
  23         bool opaque;
  24         bool stop;
  25         bool last;
  26         char *redirect;
  27 };
  28
  29 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
  30                               size_t prelen, const char *post)
  31 {
  32         int res;
  33         char *s, *next, *buf = NULL;
  34
  35         res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
  36         if (res < 0) {
  37                 if (res == -ENODATA || res == -EOPNOTSUPP)
  38                         return 0;
  39                 goto fail;
  40         }
  41         buf = kzalloc(prelen + res + strlen(post) + 1, GFP_KERNEL);
  42         if (!buf)
  43                 return -ENOMEM;
  44
  45         if (res == 0)
  46                 goto invalid;
  47
  48         res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
  49         if (res < 0)
  50                 goto fail;
  51         if (res == 0)
  52                 goto invalid;
  53         if (buf[0] == '/') {
  54                 for (s = buf; *s++ == '/'; s = next) {
  55                         next = strchrnul(s, '/');
  56                         if (s == next)
  57                                 goto invalid;
  58                 }
  59                 /*
  60                  * One of the ancestor path elements in an absolute path
  61                  * lookup in ovl_lookup_layer() could have been opaque and
  62                  * that will stop further lookup in lower layers (d->stop=true)
  63                  * But we have found an absolute redirect in decendant path
  64                  * element and that should force continue lookup in lower
  65                  * layers (reset d->stop).
  66                  */
  67                 d->stop = false;
  68         } else {
  69                 if (strchr(buf, '/') != NULL)
  70                         goto invalid;
  71
  72                 memmove(buf + prelen, buf, res);
  73                 memcpy(buf, d->name.name, prelen);
  74         }
  75
  76         strcat(buf, post);
  77         kfree(d->redirect);
  78         d->redirect = buf;
  79         d->name.name = d->redirect;
  80         d->name.len = strlen(d->redirect);
  81
  82         return 0;
  83
  84 err_free:
  85         kfree(buf);
  86         return 0;
  87 fail:
  88         pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
  89         goto err_free;
  90 invalid:
  91         pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
  92         goto err_free;
  93 }
  94
  95 static int ovl_acceptable(void *ctx, struct dentry *dentry)
  96 {
  97         /*
  98          * A non-dir origin may be disconnected, which is fine, because
  99          * we only need it for its unique inode number.
 100          */
 101         if (!d_is_dir(dentry))
 102                 return 1;
 103
 104         /* Don't decode a deleted empty directory */
 105         if (d_unhashed(dentry))
 106                 return 0;
 107
 108         /* Check if directory belongs to the layer we are decoding from */
 109         return is_subdir(dentry, ((struct vfsmount *)ctx)->mnt_root);
 110 }
 111
 112 /*
 113  * Check validity of an overlay file handle buffer.
 114  *
 115  * Return 0 for a valid file handle.
 116  * Return -ENODATA for "origin unknown".
 117  * Return <0 for an invalid file handle.
 118  */
 119 int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
 120 {
 121         if (fh_len < sizeof(struct ovl_fh) || fh_len < fh->len)
 122                 return -EINVAL;
 123
 124         if (fh->magic != OVL_FH_MAGIC)
 125                 return -EINVAL;
 126
 127         /* Treat larger version and unknown flags as "origin unknown" */
 128         if (fh->version > OVL_FH_VERSION || fh->flags & ~OVL_FH_FLAG_ALL)
 129                 return -ENODATA;
 130
 131         /* Treat endianness mismatch as "origin unknown" */
 132         if (!(fh->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
 133             (fh->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
 134                 return -ENODATA;
 135
 136         return 0;
 137 }
 138
 139 static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
 140 {
 141         int res, err;
 142         struct ovl_fh *fh = NULL;
 143
 144         res = vfs_getxattr(dentry, name, NULL, 0);
 145         if (res < 0) {
 146                 if (res == -ENODATA || res == -EOPNOTSUPP)
 147                         return NULL;
 148                 goto fail;
 149         }
 150         /* Zero size value means "copied up but origin unknown" */
 151         if (res == 0)
 152                 return NULL;
 153
 154         fh = kzalloc(res, GFP_KERNEL);
 155         if (!fh)
 156                 return ERR_PTR(-ENOMEM);
 157
 158         res = vfs_getxattr(dentry, name, fh, res);
 159         if (res < 0)
 160                 goto fail;
 161
 162         err = ovl_check_fh_len(fh, res);
 163         if (err < 0) {
 164                 if (err == -ENODATA)
 165                         goto out;
 166                 goto invalid;
 167         }
 168
 169         return fh;
 170
 171 out:
 172         kfree(fh);
 173         return NULL;
 174
 175 fail:
 176         pr_warn_ratelimited("overlayfs: failed to get origin (%i)\n", res);
 177         goto out;
 178 invalid:
 179         pr_warn_ratelimited("overlayfs: invalid origin (%*phN)\n", res, fh);
 180         goto out;
 181 }
 182
 183 struct dentry *ovl_decode_fh(struct ovl_fh *fh, struct vfsmount *mnt)
 184 {
 185         struct dentry *real;
 186         int bytes;
 187
 188         /*
 189          * Make sure that the stored uuid matches the uuid of the lower
 190          * layer where file handle will be decoded.
 191          */
 192         if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
 193                 return NULL;
 194
 195         bytes = (fh->len - offsetof(struct ovl_fh, fid));
 196         real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
 197                                   bytes >> 2, (int)fh->type,
 198                                   ovl_acceptable, mnt);
 199         if (IS_ERR(real)) {
 200                 /*
 201                  * Treat stale file handle to lower file as "origin unknown".
 202                  * upper file handle could become stale when upper file is
 203                  * unlinked and this information is needed to handle stale
 204                  * index entries correctly.
 205                  */
 206                 if (real == ERR_PTR(-ESTALE) &&
 207                     !(fh->flags & OVL_FH_FLAG_PATH_UPPER))
 208                         real = NULL;
 209                 return real;
 210         }
 211
 212         if (ovl_dentry_weird(real)) {
 213                 dput(real);
 214                 return NULL;
 215         }
 216
 217         return real;
 218 }
 219
 220 static bool ovl_is_opaquedir(struct dentry *dentry)
 221 {
 222         return ovl_check_dir_xattr(dentry, OVL_XATTR_OPAQUE);
 223 }
 224
 225 static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 226                              const char *name, unsigned int namelen,
 227                              size_t prelen, const char *post,
 228                              struct dentry **ret)
 229 {
 230         struct dentry *this;
 231         int err;
 232
 233         this = lookup_one_len_unlocked(name, base, namelen);
 234         if (IS_ERR(this)) {
 235                 err = PTR_ERR(this);
 236                 this = NULL;
 237                 if (err == -ENOENT || err == -ENAMETOOLONG)
 238                         goto out;
 239                 goto out_err;
 240         }
 241         if (!this->d_inode)
 242                 goto put_and_out;
 243
 244         if (ovl_dentry_weird(this)) {
 245                 /* Don't support traversing automounts and other weirdness */
 246                 err = -EREMOTE;
 247                 goto out_err;
 248         }
 249         if (ovl_is_whiteout(this)) {
 250                 d->stop = d->opaque = true;
 251                 goto put_and_out;
 252         }
 253         if (!d_can_lookup(this)) {
 254                 d->stop = true;
 255                 if (d->is_dir)
 256                         goto put_and_out;
 257                 goto out;
 258         }
 259         d->is_dir = true;
 260         if (!d->last && ovl_is_opaquedir(this)) {
 261                 d->stop = d->opaque = true;
 262                 goto out;
 263         }
 264         err = ovl_check_redirect(this, d, prelen, post);
 265         if (err)
 266                 goto out_err;
 267 out:
 268         *ret = this;
 269         return 0;
 270
 271 put_and_out:
 272         dput(this);
 273         this = NULL;
 274         goto out;
 275
 276 out_err:
 277         dput(this);
 278         return err;
 279 }
 280
 281 static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
 282                             struct dentry **ret)
 283 {
 284         /* Counting down from the end, since the prefix can change */
 285         size_t rem = d->name.len - 1;
 286         struct dentry *dentry = NULL;
 287         int err;
 288
 289         if (d->name.name[0] != '/')
 290                 return ovl_lookup_single(base, d, d->name.name, d->name.len,
 291                                          0, "", ret);
 292
 293         while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
 294                 const char *s = d->name.name + d->name.len - rem;
 295                 const char *next = strchrnul(s, '/');
 296                 size_t thislen = next - s;
 297                 bool end = !next[0];
 298
 299                 /* Verify we did not go off the rails */
 300                 if (WARN_ON(s[-1] != '/'))
 301                         return -EIO;
 302
 303                 err = ovl_lookup_single(base, d, s, thislen,
 304                                         d->name.len - rem, next, &base);
 305                 dput(dentry);
 306                 if (err)
 307                         return err;
 308                 dentry = base;
 309                 if (end)
 310                         break;
 311
 312                 rem -= thislen + 1;
 313
 314                 if (WARN_ON(rem >= d->name.len))
 315                         return -EIO;
 316         }
 317         *ret = dentry;
 318         return 0;
 319 }
 320
 321
 322 int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
 323                         struct dentry *upperdentry, struct ovl_path **stackp)
 324 {
 325         struct dentry *origin = NULL;
 326         int i;
 327
 328         for (i = 0; i < ofs->numlower; i++) {
 329                 origin = ovl_decode_fh(fh, ofs->lower_layers[i].mnt);
 330                 if (origin)
 331                         break;
 332         }
 333
 334         if (!origin)
 335                 return -ESTALE;
 336         else if (IS_ERR(origin))
 337                 return PTR_ERR(origin);
 338
 339         if (upperdentry && !ovl_is_whiteout(upperdentry) &&
 340             ((d_inode(origin)->i_mode ^ d_inode(upperdentry)->i_mode) & S_IFMT))
 341                 goto invalid;
 342
 343         if (!*stackp)
 344                 *stackp = kmalloc(sizeof(struct ovl_path), GFP_KERNEL);
 345         if (!*stackp) {
 346                 dput(origin);
 347                 return -ENOMEM;
 348         }
 349         **stackp = (struct ovl_path){
 350                 .dentry = origin,
 351                 .layer = &ofs->lower_layers[i]
 352         };
 353
 354         return 0;
 355
 356 invalid:
 357         pr_warn_ratelimited("overlayfs: invalid origin (%pd2, ftype=%x, origin ftype=%x).\n",
 358                             upperdentry, d_inode(upperdentry)->i_mode & S_IFMT,
 359                             d_inode(origin)->i_mode & S_IFMT);
 360         dput(origin);
 361         return -EIO;
 362 }
 363
 364 static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
 365                             struct ovl_path **stackp, unsigned int *ctrp)
 366 {
 367         struct ovl_fh *fh = ovl_get_fh(upperdentry, OVL_XATTR_ORIGIN);
 368         int err;
 369
 370         if (IS_ERR_OR_NULL(fh))
 371                 return PTR_ERR(fh);
 372
 373         err = ovl_check_origin_fh(ofs, fh, upperdentry, stackp);
 374         kfree(fh);
 375
 376         if (err) {
 377                 if (err == -ESTALE)
 378                         return 0;
 379                 return err;
 380         }
 381
 382         if (WARN_ON(*ctrp))
 383                 return -EIO;
 384
 385         *ctrp = 1;
 386         return 0;
 387 }
 388
 389 /*
 390  * Verify that @fh matches the file handle stored in xattr @name.
 391  * Return 0 on match, -ESTALE on mismatch, < 0 on error.
 392  */
 393 static int ovl_verify_fh(struct dentry *dentry, const char *name,
 394                          const struct ovl_fh *fh)
 395 {
 396         struct ovl_fh *ofh = ovl_get_fh(dentry, name);
 397         int err = 0;
 398
 399         if (!ofh)
 400                 return -ENODATA;
 401
 402         if (IS_ERR(ofh))
 403                 return PTR_ERR(ofh);
 404
 405         if (fh->len != ofh->len || memcmp(fh, ofh, fh->len))
 406                 err = -ESTALE;
 407
 408         kfree(ofh);
 409         return err;
 410 }
 411
 412 /*
 413  * Verify that @real dentry matches the file handle stored in xattr @name.
 414  *
 415  * If @set is true and there is no stored file handle, encode @real and store
 416  * file handle in xattr @name.
 417  *
 418  * Return 0 on match, -ESTALE on mismatch, -ENODATA on no xattr, < 0 on error.
 419  */
 420 int ovl_verify_set_fh(struct dentry *dentry, const char *name,
 421                       struct dentry *real, bool is_upper, bool set)
 422 {
 423         struct inode *inode;
 424         struct ovl_fh *fh;
 425         int err;
 426
 427         fh = ovl_encode_fh(real, is_upper);
 428         err = PTR_ERR(fh);
 429         if (IS_ERR(fh))
 430                 goto fail;
 431
 432         err = ovl_verify_fh(dentry, name, fh);
 433         if (set && err == -ENODATA)
 434                 err = ovl_do_setxattr(dentry, name, fh, fh->len, 0);
 435         if (err)
 436                 goto fail;
 437
 438 out:
 439         kfree(fh);
 440         return err;
 441
 442 fail:
 443         inode = d_inode(real);
 444         pr_warn_ratelimited("overlayfs: failed to verify %s (%pd2, ino=%lu, err=%i)\n",
 445                             is_upper ? "upper" : "origin", real,
 446                             inode ? inode->i_ino : 0, err);
 447         goto out;
 448 }
 449
 450 /* Get upper dentry from index */
 451 struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index)
 452 {
 453         struct ovl_fh *fh;
 454         struct dentry *upper;
 455
 456         if (!d_is_dir(index))
 457                 return dget(index);
 458
 459         fh = ovl_get_fh(index, OVL_XATTR_UPPER);
 460         if (IS_ERR_OR_NULL(fh))
 461                 return ERR_CAST(fh);
 462
 463         upper = ovl_decode_fh(fh, ofs->upper_mnt);
 464         kfree(fh);
 465
 466         if (IS_ERR_OR_NULL(upper))
 467                 return upper ?: ERR_PTR(-ESTALE);
 468
 469         if (!d_is_dir(upper)) {
 470                 pr_warn_ratelimited("overlayfs: invalid index upper (%pd2, upper=%pd2).\n",
 471                                     index, upper);
 472                 dput(upper);
 473                 return ERR_PTR(-EIO);
 474         }
 475
 476         return upper;
 477 }
 478
 479 /* Is this a leftover from create/whiteout of directory index entry? */
 480 static bool ovl_is_temp_index(struct dentry *index)
 481 {
 482         return index->d_name.name[0] == '#';
 483 }
 484
 485 /*
 486  * Verify that an index entry name matches the origin file handle stored in
 487  * OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
 488  * Return 0 on match, -ESTALE on mismatch or stale origin, < 0 on error.
 489  */
 490 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 491 {
 492         struct ovl_fh *fh = NULL;
 493         size_t len;
 494         struct ovl_path origin = { };
 495         struct ovl_path *stack = &origin;
 496         struct dentry *upper = NULL;
 497         int err;
 498
 499         if (!d_inode(index))
 500                 return 0;
 501
 502         /* Cleanup leftover from index create/cleanup attempt */
 503         err = -ESTALE;
 504         if (ovl_is_temp_index(index))
 505                 goto fail;
 506
 507         err = -EINVAL;
 508         if (index->d_name.len < sizeof(struct ovl_fh)*2)
 509                 goto fail;
 510
 511         err = -ENOMEM;
 512         len = index->d_name.len / 2;
 513         fh = kzalloc(len, GFP_KERNEL);
 514         if (!fh)
 515                 goto fail;
 516
 517         err = -EINVAL;
 518         if (hex2bin((u8 *)fh, index->d_name.name, len))
 519                 goto fail;
 520
 521         err = ovl_check_fh_len(fh, len);
 522         if (err)
 523                 goto fail;
 524
 525         /*
 526          * Whiteout index entries are used as an indication that an exported
 527          * overlay file handle should be treated as stale (i.e. after unlink
 528          * of the overlay inode). These entries contain no origin xattr.
 529          */
 530         if (ovl_is_whiteout(index))
 531                 goto out;
 532
 533         /*
 534          * Verifying directory index entries are not stale is expensive, so
 535          * only verify stale dir index if NFS export is enabled.
 536          */
 537         if (d_is_dir(index) && !ofs->config.nfs_export)
 538                 goto out;
 539
 540         /*
 541          * Directory index entries should have 'upper' xattr pointing to the
 542          * real upper dir. Non-dir index entries are hardlinks to the upper
 543          * real inode. For non-dir index, we can read the copy up origin xattr
 544          * directly from the index dentry, but for dir index we first need to
 545          * decode the upper directory.
 546          */
 547         upper = ovl_index_upper(ofs, index);
 548         if (IS_ERR_OR_NULL(upper)) {
 549                 err = PTR_ERR(upper);
 550                 /*
 551                  * Directory index entries with no 'upper' xattr need to be
 552                  * removed. When dir index entry has a stale 'upper' xattr,
 553                  * we assume that upper dir was removed and we treat the dir
 554                  * index as orphan entry that needs to be whited out.
 555                  */
 556                 if (err == -ESTALE)
 557                         goto orphan;
 558                 else if (!err)
 559                         err = -ESTALE;
 560                 goto fail;
 561         }
 562
 563         err = ovl_verify_fh(upper, OVL_XATTR_ORIGIN, fh);
 564         dput(upper);
 565         if (err)
 566                 goto fail;
 567
 568         /* Check if non-dir index is orphan and don't warn before cleaning it */
 569         if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
 570                 err = ovl_check_origin_fh(ofs, fh, index, &stack);
 571                 if (err)
 572                         goto fail;
 573
 574                 if (ovl_get_nlink(origin.dentry, index, 0) == 0)
 575                         goto orphan;
 576         }
 577
 578 out:
 579         dput(origin.dentry);
 580         kfree(fh);
 581         return err;
 582
 583 fail:
 584         pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, ftype=%x, err=%i)\n",
 585                             index, d_inode(index)->i_mode & S_IFMT, err);
 586         goto out;
 587
 588 orphan:
 589         pr_warn_ratelimited("overlayfs: orphan index entry (%pd2, ftype=%x, nlink=%u)\n",
 590                             index, d_inode(index)->i_mode & S_IFMT,
 591                             d_inode(index)->i_nlink);
 592         err = -ENOENT;
 593         goto out;
 594 }
 595
 596 static int ovl_get_index_name_fh(struct ovl_fh *fh, struct qstr *name)
 597 {
 598         char *n, *s;
 599
 600         n = kzalloc(fh->len * 2, GFP_KERNEL);
 601         if (!n)
 602                 return -ENOMEM;
 603
 604         s  = bin2hex(n, fh, fh->len);
 605         *name = (struct qstr) QSTR_INIT(n, s - n);
 606
 607         return 0;
 608
 609 }
 610
 611 /*
 612  * Lookup in indexdir for the index entry of a lower real inode or a copy up
 613  * origin inode. The index entry name is the hex representation of the lower
 614  * inode file handle.
 615  *
 616  * If the index dentry in negative, then either no lower aliases have been
 617  * copied up yet, or aliases have been copied up in older kernels and are
 618  * not indexed.
 619  *
 620  * If the index dentry for a copy up origin inode is positive, but points
 621  * to an inode different than the upper inode, then either the upper inode
 622  * has been copied up and not indexed or it was indexed, but since then
 623  * index dir was cleared. Either way, that index cannot be used to indentify
 624  * the overlay inode.
 625  */
 626 int ovl_get_index_name(struct dentry *origin, struct qstr *name)
 627 {
 628         struct ovl_fh *fh;
 629         int err;
 630
 631         fh = ovl_encode_fh(origin, false);
 632         if (IS_ERR(fh))
 633                 return PTR_ERR(fh);
 634
 635         err = ovl_get_index_name_fh(fh, name);
 636
 637         kfree(fh);
 638         return err;
 639 }
 640
 641 /* Lookup index by file handle for NFS export */
 642 struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
 643 {
 644         struct dentry *index;
 645         struct qstr name;
 646         int err;
 647
 648         err = ovl_get_index_name_fh(fh, &name);
 649         if (err)
 650                 return ERR_PTR(err);
 651
 652         index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
 653         kfree(name.name);
 654         if (IS_ERR(index)) {
 655                 if (PTR_ERR(index) == -ENOENT)
 656                         index = NULL;
 657                 return index;
 658         }
 659
 660         if (d_is_negative(index))
 661                 err = 0;
 662         else if (ovl_is_whiteout(index))
 663                 err = -ESTALE;
 664         else if (ovl_dentry_weird(index))
 665                 err = -EIO;
 666         else
 667                 return index;
 668
 669         dput(index);
 670         return ERR_PTR(err);
 671 }
 672
 673 struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
 674                                 struct dentry *origin, bool verify)
 675 {
 676         struct dentry *index;
 677         struct inode *inode;
 678         struct qstr name;
 679         bool is_dir = d_is_dir(origin);
 680         int err;
 681
 682         err = ovl_get_index_name(origin, &name);
 683         if (err)
 684                 return ERR_PTR(err);
 685
 686         index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
 687         if (IS_ERR(index)) {
 688                 err = PTR_ERR(index);
 689                 if (err == -ENOENT) {
 690                         index = NULL;
 691                         goto out;
 692                 }
 693                 pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%*s, err=%i);\n"
 694                                     "overlayfs: mount with '-o index=off' to disable inodes index.\n",
 695                                     d_inode(origin)->i_ino, name.len, name.name,
 696                                     err);
 697                 goto out;
 698         }
 699
 700         inode = d_inode(index);
 701         if (d_is_negative(index)) {
 702                 goto out_dput;
 703         } else if (ovl_is_whiteout(index) && !verify) {
 704                 /*
 705                  * When index lookup is called with !verify for decoding an
 706                  * overlay file handle, a whiteout index implies that decode
 707                  * should treat file handle as stale and no need to print a
 708                  * warning about it.
 709                  */
 710                 dput(index);
 711                 index = ERR_PTR(-ESTALE);
 712                 goto out;
 713         } else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
 714                    ((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
 715                 /*
 716                  * Index should always be of the same file type as origin
 717                  * except for the case of a whiteout index. A whiteout
 718                  * index should only exist if all lower aliases have been
 719                  * unlinked, which means that finding a lower origin on lookup
 720                  * whose index is a whiteout should be treated as an error.
 721                  */
 722                 pr_warn_ratelimited("overlayfs: bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
 723                                     index, d_inode(index)->i_mode & S_IFMT,
 724                                     d_inode(origin)->i_mode & S_IFMT);
 725                 goto fail;
 726         } else if (is_dir && verify) {
 727                 if (!upper) {
 728                         pr_warn_ratelimited("overlayfs: suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
 729                                             origin, index);
 730                         goto fail;
 731                 }
 732
 733                 /* Verify that dir index 'upper' xattr points to upper dir */
 734                 err = ovl_verify_upper(index, upper, false);
 735                 if (err) {
 736                         if (err == -ESTALE) {
 737                                 pr_warn_ratelimited("overlayfs: suspected multiply redirected dir found (upper=%pd2, origin=%pd2, index=%pd2).\n",
 738                                                     upper, origin, index);
 739                         }
 740                         goto fail;
 741                 }
 742         } else if (upper && d_inode(upper) != inode) {
 743                 goto out_dput;
 744         }
 745 out:
 746         kfree(name.name);
 747         return index;
 748
 749 out_dput:
 750         dput(index);
 751         index = NULL;
 752         goto out;
 753
 754 fail:
 755         dput(index);
 756         index = ERR_PTR(-EIO);
 757         goto out;
 758 }
 759
 760 /*
 761  * Returns next layer in stack starting from top.
 762  * Returns -1 if this is the last layer.
 763  */
 764 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 765 {
 766         struct ovl_entry *oe = dentry->d_fsdata;
 767
 768         BUG_ON(idx < 0);
 769         if (idx == 0) {
 770                 ovl_path_upper(dentry, path);
 771                 if (path->dentry)
 772                         return oe->numlower ? 1 : -1;
 773                 idx++;
 774         }
 775         BUG_ON(idx > oe->numlower);
 776         path->dentry = oe->lowerstack[idx - 1].dentry;
 777         path->mnt = oe->lowerstack[idx - 1].layer->mnt;
 778
 779         return (idx < oe->numlower) ? idx + 1 : -1;
 780 }
 781
 782 /* Fix missing 'origin' xattr */
 783 static int ovl_fix_origin(struct dentry *dentry, struct dentry *lower,
 784                           struct dentry *upper)
 785 {
 786         int err;
 787
 788         if (ovl_check_origin_xattr(upper))
 789                 return 0;
 790
 791         err = ovl_want_write(dentry);
 792         if (err)
 793                 return err;
 794
 795         err = ovl_set_origin(dentry, lower, upper);
 796         if (!err)
 797                 err = ovl_set_impure(dentry->d_parent, upper->d_parent);
 798
 799         ovl_drop_write(dentry);
 800         return err;
 801 }
 802
 803 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 804                           unsigned int flags)
 805 {
 806         struct ovl_entry *oe;
 807         const struct cred *old_cred;
 808         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 809         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 810         struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
 811         struct ovl_path *stack = NULL;
 812         struct dentry *upperdir, *upperdentry = NULL;
 813         struct dentry *origin = NULL;
 814         struct dentry *index = NULL;
 815         unsigned int ctr = 0;
 816         struct inode *inode = NULL;
 817         bool upperopaque = false;
 818         char *upperredirect = NULL;
 819         struct dentry *this;
 820         unsigned int i;
 821         int err;
 822         struct ovl_lookup_data d = {
 823                 .name = dentry->d_name,
 824                 .is_dir = false,
 825                 .opaque = false,
 826                 .stop = false,
 827                 .last = ofs->config.redirect_follow ? false : !poe->numlower,
 828                 .redirect = NULL,
 829         };
 830
 831         if (dentry->d_name.len > ofs->namelen)
 832                 return ERR_PTR(-ENAMETOOLONG);
 833
 834         old_cred = ovl_override_creds(dentry->d_sb);
 835         upperdir = ovl_dentry_upper(dentry->d_parent);
 836         if (upperdir) {
 837                 err = ovl_lookup_layer(upperdir, &d, &upperdentry);
 838                 if (err)
 839                         goto out;
 840
 841                 if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
 842                         dput(upperdentry);
 843                         err = -EREMOTE;
 844                         goto out;
 845                 }
 846                 if (upperdentry && !d.is_dir) {
 847                         BUG_ON(!d.stop || d.redirect);
 848                         /*
 849                          * Lookup copy up origin by decoding origin file handle.
 850                          * We may get a disconnected dentry, which is fine,
 851                          * because we only need to hold the origin inode in
 852                          * cache and use its inode number.  We may even get a
 853                          * connected dentry, that is not under any of the lower
 854                          * layers root.  That is also fine for using it's inode
 855                          * number - it's the same as if we held a reference
 856                          * to a dentry in lower layer that was moved under us.
 857                          */
 858                         err = ovl_check_origin(ofs, upperdentry, &stack, &ctr);
 859                         if (err)
 860                                 goto out_put_upper;
 861                 }
 862
 863                 if (d.redirect) {
 864                         err = -ENOMEM;
 865                         upperredirect = kstrdup(d.redirect, GFP_KERNEL);
 866                         if (!upperredirect)
 867                                 goto out_put_upper;
 868                         if (d.redirect[0] == '/')
 869                                 poe = roe;
 870                 }
 871                 upperopaque = d.opaque;
 872         }
 873
 874         if (!d.stop && poe->numlower) {
 875                 err = -ENOMEM;
 876                 stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
 877                                 GFP_KERNEL);
 878                 if (!stack)
 879                         goto out_put_upper;
 880         }
 881
 882         for (i = 0; !d.stop && i < poe->numlower; i++) {
 883                 struct ovl_path lower = poe->lowerstack[i];
 884
 885                 if (!ofs->config.redirect_follow)
 886                         d.last = i == poe->numlower - 1;
 887                 else
 888                         d.last = lower.layer->idx == roe->numlower;
 889
 890                 err = ovl_lookup_layer(lower.dentry, &d, &this);
 891                 if (err)
 892                         goto out_put;
 893
 894                 if (!this)
 895                         continue;
 896
 897                 /*
 898                  * If no origin fh is stored in upper of a merge dir, store fh
 899                  * of lower dir and set upper parent "impure".
 900                  */
 901                 if (upperdentry && !ctr && !ofs->noxattr) {
 902                         err = ovl_fix_origin(dentry, this, upperdentry);
 903                         if (err) {
 904                                 dput(this);
 905                                 goto out_put;
 906                         }
 907                 }
 908
 909                 /*
 910                  * When "verify_lower" feature is enabled, do not merge with a
 911                  * lower dir that does not match a stored origin xattr. In any
 912                  * case, only verified origin is used for index lookup.
 913                  */
 914                 if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
 915                         err = ovl_verify_origin(upperdentry, this, false);
 916                         if (err) {
 917                                 dput(this);
 918                                 break;
 919                         }
 920
 921                         /* Bless lower dir as verified origin */
 922                         origin = this;
 923                 }
 924
 925                 stack[ctr].dentry = this;
 926                 stack[ctr].layer = lower.layer;
 927                 ctr++;
 928
 929                 /*
 930                  * Following redirects can have security consequences: it's like
 931                  * a symlink into the lower layer without the permission checks.
 932                  * This is only a problem if the upper layer is untrusted (e.g
 933                  * comes from an USB drive).  This can allow a non-readable file
 934                  * or directory to become readable.
 935                  *
 936                  * Only following redirects when redirects are enabled disables
 937                  * this attack vector when not necessary.
 938                  */
 939                 err = -EPERM;
 940                 if (d.redirect && !ofs->config.redirect_follow) {
 941                         pr_warn_ratelimited("overlayfs: refusing to follow redirect for (%pd2)\n",
 942                                             dentry);
 943                         goto out_put;
 944                 }
 945
 946                 if (d.stop)
 947                         break;
 948
 949                 if (d.redirect && d.redirect[0] == '/' && poe != roe) {
 950                         poe = roe;
 951                         /* Find the current layer on the root dentry */
 952                         i = lower.layer->idx - 1;
 953                 }
 954         }
 955
 956         /*
 957          * Lookup index by lower inode and verify it matches upper inode.
 958          * We only trust dir index if we verified that lower dir matches
 959          * origin, otherwise dir index entries may be inconsistent and we
 960          * ignore them. Always lookup index of non-dir and non-upper.
 961          */
 962         if (ctr && (!upperdentry || !d.is_dir))
 963                 origin = stack[0].dentry;
 964
 965         if (origin && ovl_indexdir(dentry->d_sb) &&
 966             (!d.is_dir || ovl_index_all(dentry->d_sb))) {
 967                 index = ovl_lookup_index(ofs, upperdentry, origin, true);
 968                 if (IS_ERR(index)) {
 969                         err = PTR_ERR(index);
 970                         index = NULL;
 971                         goto out_put;
 972                 }
 973         }
 974
 975         oe = ovl_alloc_entry(ctr);
 976         err = -ENOMEM;
 977         if (!oe)
 978                 goto out_put;
 979
 980         memcpy(oe->lowerstack, stack, sizeof(struct ovl_path) * ctr);
 981         dentry->d_fsdata = oe;
 982
 983         if (upperopaque)
 984                 ovl_dentry_set_opaque(dentry);
 985
 986         if (upperdentry)
 987                 ovl_dentry_set_upper_alias(dentry);
 988         else if (index)
 989                 upperdentry = dget(index);
 990
 991         if (upperdentry || ctr) {
 992                 if (ctr)
 993                         origin = stack[0].dentry;
 994                 inode = ovl_get_inode(dentry->d_sb, upperdentry, origin, index,
 995                                       ctr);
 996                 err = PTR_ERR(inode);
 997                 if (IS_ERR(inode))
 998                         goto out_free_oe;
 999
1000                 OVL_I(inode)->redirect = upperredirect;
1001                 if (index)
1002                         ovl_set_flag(OVL_INDEX, inode);
1003         }
1004
1005         revert_creds(old_cred);
1006         dput(index);
1007         kfree(stack);
1008         kfree(d.redirect);
1009         return d_splice_alias(inode, dentry);
1010
1011 out_free_oe:
1012         dentry->d_fsdata = NULL;
1013         kfree(oe);
1014 out_put:
1015         dput(index);
1016         for (i = 0; i < ctr; i++)
1017                 dput(stack[i].dentry);
1018         kfree(stack);
1019 out_put_upper:
1020         dput(upperdentry);
1021         kfree(upperredirect);
1022 out:
1023         kfree(d.redirect);
1024         revert_creds(old_cred);
1025         return ERR_PTR(err);
1026 }
1027
1028 bool ovl_lower_positive(struct dentry *dentry)
1029 {
1030         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
1031         const struct qstr *name = &dentry->d_name;
1032         const struct cred *old_cred;
1033         unsigned int i;
1034         bool positive = false;
1035         bool done = false;
1036
1037         /*
1038          * If dentry is negative, then lower is positive iff this is a
1039          * whiteout.
1040          */
1041         if (!dentry->d_inode)
1042                 return ovl_dentry_is_opaque(dentry);
1043
1044         /* Negative upper -> positive lower */
1045         if (!ovl_dentry_upper(dentry))
1046                 return true;
1047
1048         old_cred = ovl_override_creds(dentry->d_sb);
1049         /* Positive upper -> have to look up lower to see whether it exists */
1050         for (i = 0; !done && !positive && i < poe->numlower; i++) {
1051                 struct dentry *this;
1052                 struct dentry *lowerdir = poe->lowerstack[i].dentry;
1053
1054                 this = lookup_one_len_unlocked(name->name, lowerdir,
1055                                                name->len);
1056                 if (IS_ERR(this)) {
1057                         switch (PTR_ERR(this)) {
1058                         case -ENOENT:
1059                         case -ENAMETOOLONG:
1060                                 break;
1061
1062                         default:
1063                                 /*
1064                                  * Assume something is there, we just couldn't
1065                                  * access it.
1066                                  */
1067                                 positive = true;
1068                                 break;
1069                         }
1070                 } else {
1071                         if (this->d_inode) {
1072                                 positive = !ovl_is_whiteout(this);
1073                                 done = true;
1074                         }
1075                         dput(this);
1076                 }
1077         }
1078         revert_creds(old_cred);
1079
1080         return positive;
1081 }