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/namei.h>
  13 #include <linux/xattr.h>
  14 #include <linux/ratelimit.h>
  15 #include "overlayfs.h"
  16 #include "ovl_entry.h"
  17
  18 struct ovl_lookup_data {
  19         struct qstr name;
  20         bool is_dir;
  21         bool opaque;
  22         bool stop;
  23         bool last;
  24         char *redirect;
  25 };
  26
  27 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
  28                               size_t prelen, const char *post)
  29 {
  30         int res;
  31         char *s, *next, *buf = NULL;
  32
  33         res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
  34         if (res < 0) {
  35                 if (res == -ENODATA || res == -EOPNOTSUPP)
  36                         return 0;
  37                 goto fail;
  38         }
  39         buf = kzalloc(prelen + res + strlen(post) + 1, GFP_TEMPORARY);
  40         if (!buf)
  41                 return -ENOMEM;
  42
  43         if (res == 0)
  44                 goto invalid;
  45
  46         res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
  47         if (res < 0)
  48                 goto fail;
  49         if (res == 0)
  50                 goto invalid;
  51         if (buf[0] == '/') {
  52                 for (s = buf; *s++ == '/'; s = next) {
  53                         next = strchrnul(s, '/');
  54                         if (s == next)
  55                                 goto invalid;
  56                 }
  57         } else {
  58                 if (strchr(buf, '/') != NULL)
  59                         goto invalid;
  60
  61                 memmove(buf + prelen, buf, res);
  62                 memcpy(buf, d->name.name, prelen);
  63         }
  64
  65         strcat(buf, post);
  66         kfree(d->redirect);
  67         d->redirect = buf;
  68         d->name.name = d->redirect;
  69         d->name.len = strlen(d->redirect);
  70
  71         return 0;
  72
  73 err_free:
  74         kfree(buf);
  75         return 0;
  76 fail:
  77         pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
  78         goto err_free;
  79 invalid:
  80         pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
  81         goto err_free;
  82 }
  83
  84 static bool ovl_is_opaquedir(struct dentry *dentry)
  85 {
  86         int res;
  87         char val;
  88
  89         if (!d_is_dir(dentry))
  90                 return false;
  91
  92         res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
  93         if (res == 1 && val == 'y')
  94                 return true;
  95
  96         return false;
  97 }
  98
  99 static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 100                              const char *name, unsigned int namelen,
 101                              size_t prelen, const char *post,
 102                              struct dentry **ret)
 103 {
 104         struct dentry *this;
 105         int err;
 106
 107         this = lookup_one_len_unlocked(name, base, namelen);
 108         if (IS_ERR(this)) {
 109                 err = PTR_ERR(this);
 110                 this = NULL;
 111                 if (err == -ENOENT || err == -ENAMETOOLONG)
 112                         goto out;
 113                 goto out_err;
 114         }
 115         if (!this->d_inode)
 116                 goto put_and_out;
 117
 118         if (ovl_dentry_weird(this)) {
 119                 /* Don't support traversing automounts and other weirdness */
 120                 err = -EREMOTE;
 121                 goto out_err;
 122         }
 123         if (ovl_is_whiteout(this)) {
 124                 d->stop = d->opaque = true;
 125                 goto put_and_out;
 126         }
 127         if (!d_can_lookup(this)) {
 128                 d->stop = true;
 129                 if (d->is_dir)
 130                         goto put_and_out;
 131                 goto out;
 132         }
 133         d->is_dir = true;
 134         if (!d->last && ovl_is_opaquedir(this)) {
 135                 d->stop = d->opaque = true;
 136                 goto out;
 137         }
 138         err = ovl_check_redirect(this, d, prelen, post);
 139         if (err)
 140                 goto out_err;
 141 out:
 142         *ret = this;
 143         return 0;
 144
 145 put_and_out:
 146         dput(this);
 147         this = NULL;
 148         goto out;
 149
 150 out_err:
 151         dput(this);
 152         return err;
 153 }
 154
 155 static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
 156                             struct dentry **ret)
 157 {
 158         /* Counting down from the end, since the prefix can change */
 159         size_t rem = d->name.len - 1;
 160         struct dentry *dentry = NULL;
 161         int err;
 162
 163         if (d->name.name[0] != '/')
 164                 return ovl_lookup_single(base, d, d->name.name, d->name.len,
 165                                          0, "", ret);
 166
 167         while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
 168                 const char *s = d->name.name + d->name.len - rem;
 169                 const char *next = strchrnul(s, '/');
 170                 size_t thislen = next - s;
 171                 bool end = !next[0];
 172
 173                 /* Verify we did not go off the rails */
 174                 if (WARN_ON(s[-1] != '/'))
 175                         return -EIO;
 176
 177                 err = ovl_lookup_single(base, d, s, thislen,
 178                                         d->name.len - rem, next, &base);
 179                 dput(dentry);
 180                 if (err)
 181                         return err;
 182                 dentry = base;
 183                 if (end)
 184                         break;
 185
 186                 rem -= thislen + 1;
 187
 188                 if (WARN_ON(rem >= d->name.len))
 189                         return -EIO;
 190         }
 191         *ret = dentry;
 192         return 0;
 193 }
 194
 195 /*
 196  * Returns next layer in stack starting from top.
 197  * Returns -1 if this is the last layer.
 198  */
 199 int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
 200 {
 201         struct ovl_entry *oe = dentry->d_fsdata;
 202
 203         BUG_ON(idx < 0);
 204         if (idx == 0) {
 205                 ovl_path_upper(dentry, path);
 206                 if (path->dentry)
 207                         return oe->numlower ? 1 : -1;
 208                 idx++;
 209         }
 210         BUG_ON(idx > oe->numlower);
 211         *path = oe->lowerstack[idx - 1];
 212
 213         return (idx < oe->numlower) ? idx + 1 : -1;
 214 }
 215
 216 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 217                           unsigned int flags)
 218 {
 219         struct ovl_entry *oe;
 220         const struct cred *old_cred;
 221         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 222         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 223         struct path *stack = NULL;
 224         struct dentry *upperdir, *upperdentry = NULL;
 225         unsigned int ctr = 0;
 226         struct inode *inode = NULL;
 227         bool upperopaque = false;
 228         char *upperredirect = NULL;
 229         struct dentry *this;
 230         unsigned int i;
 231         int err;
 232         struct ovl_lookup_data d = {
 233                 .name = dentry->d_name,
 234                 .is_dir = false,
 235                 .opaque = false,
 236                 .stop = false,
 237                 .last = !poe->numlower,
 238                 .redirect = NULL,
 239         };
 240
 241         if (dentry->d_name.len > ofs->namelen)
 242                 return ERR_PTR(-ENAMETOOLONG);
 243
 244         old_cred = ovl_override_creds(dentry->d_sb);
 245         upperdir = ovl_upperdentry_dereference(poe);
 246         if (upperdir) {
 247                 err = ovl_lookup_layer(upperdir, &d, &upperdentry);
 248                 if (err)
 249                         goto out;
 250
 251                 if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
 252                         dput(upperdentry);
 253                         err = -EREMOTE;
 254                         goto out;
 255                 }
 256
 257                 if (d.redirect) {
 258                         upperredirect = kstrdup(d.redirect, GFP_KERNEL);
 259                         if (!upperredirect)
 260                                 goto out_put_upper;
 261                         if (d.redirect[0] == '/')
 262                                 poe = dentry->d_sb->s_root->d_fsdata;
 263                 }
 264                 upperopaque = d.opaque;
 265         }
 266
 267         if (!d.stop && poe->numlower) {
 268                 err = -ENOMEM;
 269                 stack = kcalloc(ofs->numlower, sizeof(struct path),
 270                                 GFP_TEMPORARY);
 271                 if (!stack)
 272                         goto out_put_upper;
 273         }
 274
 275         for (i = 0; !d.stop && i < poe->numlower; i++) {
 276                 struct path lowerpath = poe->lowerstack[i];
 277
 278                 d.last = i == poe->numlower - 1;
 279                 err = ovl_lookup_layer(lowerpath.dentry, &d, &this);
 280                 if (err)
 281                         goto out_put;
 282
 283                 if (!this)
 284                         continue;
 285
 286                 stack[ctr].dentry = this;
 287                 stack[ctr].mnt = lowerpath.mnt;
 288                 ctr++;
 289
 290                 if (d.stop)
 291                         break;
 292
 293                 if (d.redirect &&
 294                     d.redirect[0] == '/' &&
 295                     poe != dentry->d_sb->s_root->d_fsdata) {
 296                         poe = dentry->d_sb->s_root->d_fsdata;
 297
 298                         /* Find the current layer on the root dentry */
 299                         for (i = 0; i < poe->numlower; i++)
 300                                 if (poe->lowerstack[i].mnt == lowerpath.mnt)
 301                                         break;
 302                         if (WARN_ON(i == poe->numlower))
 303                                 break;
 304                 }
 305         }
 306
 307         oe = ovl_alloc_entry(ctr);
 308         err = -ENOMEM;
 309         if (!oe)
 310                 goto out_put;
 311
 312         if (upperdentry || ctr) {
 313                 struct dentry *realdentry;
 314                 struct inode *realinode;
 315
 316                 realdentry = upperdentry ? upperdentry : stack[0].dentry;
 317                 realinode = d_inode(realdentry);
 318
 319                 err = -ENOMEM;
 320                 if (upperdentry && !d_is_dir(upperdentry)) {
 321                         inode = ovl_get_inode(dentry->d_sb, realinode);
 322                 } else {
 323                         inode = ovl_new_inode(dentry->d_sb, realinode->i_mode,
 324                                               realinode->i_rdev);
 325                         if (inode)
 326                                 ovl_inode_init(inode, realinode, !!upperdentry);
 327                 }
 328                 if (!inode)
 329                         goto out_free_oe;
 330                 ovl_copyattr(realdentry->d_inode, inode);
 331         }
 332
 333         revert_creds(old_cred);
 334         oe->opaque = upperopaque;
 335         oe->redirect = upperredirect;
 336         oe->__upperdentry = upperdentry;
 337         memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 338         kfree(stack);
 339         kfree(d.redirect);
 340         dentry->d_fsdata = oe;
 341         d_add(dentry, inode);
 342
 343         return NULL;
 344
 345 out_free_oe:
 346         kfree(oe);
 347 out_put:
 348         for (i = 0; i < ctr; i++)
 349                 dput(stack[i].dentry);
 350         kfree(stack);
 351 out_put_upper:
 352         dput(upperdentry);
 353         kfree(upperredirect);
 354 out:
 355         kfree(d.redirect);
 356         revert_creds(old_cred);
 357         return ERR_PTR(err);
 358 }
 359
 360 bool ovl_lower_positive(struct dentry *dentry)
 361 {
 362         struct ovl_entry *oe = dentry->d_fsdata;
 363         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 364         const struct qstr *name = &dentry->d_name;
 365         unsigned int i;
 366         bool positive = false;
 367         bool done = false;
 368
 369         /*
 370          * If dentry is negative, then lower is positive iff this is a
 371          * whiteout.
 372          */
 373         if (!dentry->d_inode)
 374                 return oe->opaque;
 375
 376         /* Negative upper -> positive lower */
 377         if (!oe->__upperdentry)
 378                 return true;
 379
 380         /* Positive upper -> have to look up lower to see whether it exists */
 381         for (i = 0; !done && !positive && i < poe->numlower; i++) {
 382                 struct dentry *this;
 383                 struct dentry *lowerdir = poe->lowerstack[i].dentry;
 384
 385                 this = lookup_one_len_unlocked(name->name, lowerdir,
 386                                                name->len);
 387                 if (IS_ERR(this)) {
 388                         switch (PTR_ERR(this)) {
 389                         case -ENOENT:
 390                         case -ENAMETOOLONG:
 391                                 break;
 392
 393                         default:
 394                                 /*
 395                                  * Assume something is there, we just couldn't
 396                                  * access it.
 397                                  */
 398                                 positive = true;
 399                                 break;
 400                         }
 401                 } else {
 402                         if (this->d_inode) {
 403                                 positive = !ovl_is_whiteout(this);
 404                                 done = true;
 405                         }
 406                         dput(this);
 407                 }
 408         }
 409
 410         return positive;
 411 }