fs/overlayfs/inode.c

   1 /*
   2  *
   3  * Copyright (C) 2011 Novell 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/slab.h>
  12 #include <linux/xattr.h>
  13 #include <linux/posix_acl.h>
  14 #include "overlayfs.h"
  15
  16 static int ovl_copy_up_truncate(struct dentry *dentry)
  17 {
  18         int err;
  19         struct dentry *parent;
  20         struct kstat stat;
  21         struct path lowerpath;
  22
  23         parent = dget_parent(dentry);
  24         err = ovl_copy_up(parent);
  25         if (err)
  26                 goto out_dput_parent;
  27
  28         ovl_path_lower(dentry, &lowerpath);
  29         err = vfs_getattr(&lowerpath, &stat);
  30         if (err)
  31                 goto out_dput_parent;
  32
  33         stat.size = 0;
  34         err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
  35
  36 out_dput_parent:
  37         dput(parent);
  38         return err;
  39 }
  40
  41 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  42 {
  43         int err;
  44         struct dentry *upperdentry;
  45         const struct cred *old_cred;
  46
  47         /*
  48          * Check for permissions before trying to copy-up.  This is redundant
  49          * since it will be rechecked later by ->setattr() on upper dentry.  But
  50          * without this, copy-up can be triggered by just about anybody.
  51          *
  52          * We don't initialize inode->size, which just means that
  53          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
  54          * check for a swapfile (which this won't be anyway).
  55          */
  56         err = inode_change_ok(dentry->d_inode, attr);
  57         if (err)
  58                 return err;
  59
  60         err = ovl_want_write(dentry);
  61         if (err)
  62                 goto out;
  63
  64         if (attr->ia_valid & ATTR_SIZE) {
  65                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
  66
  67                 err = -ETXTBSY;
  68                 if (atomic_read(&realinode->i_writecount) < 0)
  69                         goto out_drop_write;
  70         }
  71
  72         err = ovl_copy_up(dentry);
  73         if (!err) {
  74                 struct inode *winode = NULL;
  75
  76                 upperdentry = ovl_dentry_upper(dentry);
  77
  78                 if (attr->ia_valid & ATTR_SIZE) {
  79                         winode = d_inode(upperdentry);
  80                         err = get_write_access(winode);
  81                         if (err)
  82                                 goto out_drop_write;
  83                 }
  84
  85                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  86                         attr->ia_valid &= ~ATTR_MODE;
  87
  88                 inode_lock(upperdentry->d_inode);
  89                 old_cred = ovl_override_creds(dentry->d_sb);
  90                 err = notify_change(upperdentry, attr, NULL);
  91                 revert_creds(old_cred);
  92                 if (!err)
  93                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  94                 inode_unlock(upperdentry->d_inode);
  95
  96                 if (winode)
  97                         put_write_access(winode);
  98         }
  99 out_drop_write:
 100         ovl_drop_write(dentry);
 101 out:
 102         return err;
 103 }
 104
 105 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 106                          struct kstat *stat)
 107 {
 108         struct path realpath;
 109         const struct cred *old_cred;
 110         int err;
 111
 112         ovl_path_real(dentry, &realpath);
 113         old_cred = ovl_override_creds(dentry->d_sb);
 114         err = vfs_getattr(&realpath, stat);
 115         revert_creds(old_cred);
 116         return err;
 117 }
 118
 119 int ovl_permission(struct inode *inode, int mask)
 120 {
 121         bool is_upper;
 122         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 123         const struct cred *old_cred;
 124         int err;
 125
 126         /* Careful in RCU walk mode */
 127         if (!realinode) {
 128                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 129                 return -ECHILD;
 130         }
 131
 132         /*
 133          * Check overlay inode with the creds of task and underlying inode
 134          * with creds of mounter
 135          */
 136         err = generic_permission(inode, mask);
 137         if (err)
 138                 return err;
 139
 140         old_cred = ovl_override_creds(inode->i_sb);
 141         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
 142                 mask &= ~(MAY_WRITE | MAY_APPEND);
 143                 /* Make sure mounter can read file for copy up later */
 144                 mask |= MAY_READ;
 145         }
 146         err = inode_permission(realinode, mask);
 147         revert_creds(old_cred);
 148
 149         return err;
 150 }
 151
 152 static const char *ovl_get_link(struct dentry *dentry,
 153                                 struct inode *inode,
 154                                 struct delayed_call *done)
 155 {
 156         struct dentry *realdentry;
 157         struct inode *realinode;
 158         const struct cred *old_cred;
 159         const char *p;
 160
 161         if (!dentry)
 162                 return ERR_PTR(-ECHILD);
 163
 164         realdentry = ovl_dentry_real(dentry);
 165         realinode = realdentry->d_inode;
 166
 167         if (WARN_ON(!realinode->i_op->get_link))
 168                 return ERR_PTR(-EPERM);
 169
 170         old_cred = ovl_override_creds(dentry->d_sb);
 171         p = realinode->i_op->get_link(realdentry, realinode, done);
 172         revert_creds(old_cred);
 173         return p;
 174 }
 175
 176 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 177 {
 178         struct path realpath;
 179         struct inode *realinode;
 180         const struct cred *old_cred;
 181         int err;
 182
 183         ovl_path_real(dentry, &realpath);
 184         realinode = realpath.dentry->d_inode;
 185
 186         if (!realinode->i_op->readlink)
 187                 return -EINVAL;
 188
 189         old_cred = ovl_override_creds(dentry->d_sb);
 190         err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 191         revert_creds(old_cred);
 192         return err;
 193 }
 194
 195 bool ovl_is_private_xattr(const char *name)
 196 {
 197         return strncmp(name, OVL_XATTR_PREFIX,
 198                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 199 }
 200
 201 int ovl_setxattr(struct dentry *dentry, struct inode *inode,
 202                  const char *name, const void *value,
 203                  size_t size, int flags)
 204 {
 205         int err;
 206         struct dentry *upperdentry;
 207         const struct cred *old_cred;
 208
 209         err = ovl_want_write(dentry);
 210         if (err)
 211                 goto out;
 212
 213         err = ovl_copy_up(dentry);
 214         if (err)
 215                 goto out_drop_write;
 216
 217         upperdentry = ovl_dentry_upper(dentry);
 218         old_cred = ovl_override_creds(dentry->d_sb);
 219         err = vfs_setxattr(upperdentry, name, value, size, flags);
 220         revert_creds(old_cred);
 221
 222 out_drop_write:
 223         ovl_drop_write(dentry);
 224 out:
 225         return err;
 226 }
 227
 228 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
 229                      const char *name, void *value, size_t size)
 230 {
 231         struct dentry *realdentry = ovl_dentry_real(dentry);
 232         ssize_t res;
 233         const struct cred *old_cred;
 234
 235         if (ovl_is_private_xattr(name))
 236                 return -ENODATA;
 237
 238         old_cred = ovl_override_creds(dentry->d_sb);
 239         res = vfs_getxattr(realdentry, name, value, size);
 240         revert_creds(old_cred);
 241         return res;
 242 }
 243
 244 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 245 {
 246         struct dentry *realdentry = ovl_dentry_real(dentry);
 247         ssize_t res;
 248         int off;
 249         const struct cred *old_cred;
 250
 251         old_cred = ovl_override_creds(dentry->d_sb);
 252         res = vfs_listxattr(realdentry, list, size);
 253         revert_creds(old_cred);
 254         if (res <= 0 || size == 0)
 255                 return res;
 256
 257         /* filter out private xattrs */
 258         for (off = 0; off < res;) {
 259                 char *s = list + off;
 260                 size_t slen = strlen(s) + 1;
 261
 262                 BUG_ON(off + slen > res);
 263
 264                 if (ovl_is_private_xattr(s)) {
 265                         res -= slen;
 266                         memmove(s, s + slen, res - off);
 267                 } else {
 268                         off += slen;
 269                 }
 270         }
 271
 272         return res;
 273 }
 274
 275 int ovl_removexattr(struct dentry *dentry, const char *name)
 276 {
 277         int err;
 278         struct path realpath;
 279         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 280         const struct cred *old_cred;
 281
 282         err = ovl_want_write(dentry);
 283         if (err)
 284                 goto out;
 285
 286         err = -ENODATA;
 287         if (ovl_is_private_xattr(name))
 288                 goto out_drop_write;
 289
 290         if (!OVL_TYPE_UPPER(type)) {
 291                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 292                 if (err < 0)
 293                         goto out_drop_write;
 294
 295                 err = ovl_copy_up(dentry);
 296                 if (err)
 297                         goto out_drop_write;
 298
 299                 ovl_path_upper(dentry, &realpath);
 300         }
 301
 302         old_cred = ovl_override_creds(dentry->d_sb);
 303         err = vfs_removexattr(realpath.dentry, name);
 304         revert_creds(old_cred);
 305 out_drop_write:
 306         ovl_drop_write(dentry);
 307 out:
 308         return err;
 309 }
 310
 311 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 312 {
 313         struct inode *realinode = ovl_inode_real(inode, NULL);
 314         const struct cred *old_cred;
 315         struct posix_acl *acl;
 316
 317         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 318                 return NULL;
 319
 320         if (!realinode->i_op->get_acl)
 321                 return NULL;
 322
 323         old_cred = ovl_override_creds(inode->i_sb);
 324         acl = get_acl(realinode, type);
 325         revert_creds(old_cred);
 326
 327         return acl;
 328 }
 329
 330 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 331                                   struct dentry *realdentry)
 332 {
 333         if (OVL_TYPE_UPPER(type))
 334                 return false;
 335
 336         if (special_file(realdentry->d_inode->i_mode))
 337                 return false;
 338
 339         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 340                 return false;
 341
 342         return true;
 343 }
 344
 345 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 346 {
 347         int err = 0;
 348         struct path realpath;
 349         enum ovl_path_type type;
 350
 351         type = ovl_path_real(dentry, &realpath);
 352         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 353                 err = ovl_want_write(dentry);
 354                 if (!err) {
 355                         if (file_flags & O_TRUNC)
 356                                 err = ovl_copy_up_truncate(dentry);
 357                         else
 358                                 err = ovl_copy_up(dentry);
 359                         ovl_drop_write(dentry);
 360                 }
 361         }
 362
 363         return err;
 364 }
 365
 366 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 367 {
 368         struct dentry *alias;
 369         struct path upperpath;
 370
 371         if (!(flags & S_ATIME))
 372                 return 0;
 373
 374         alias = d_find_any_alias(inode);
 375         if (!alias)
 376                 return 0;
 377
 378         ovl_path_upper(alias, &upperpath);
 379         if (upperpath.dentry) {
 380                 touch_atime(&upperpath);
 381                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 382         }
 383
 384         dput(alias);
 385
 386         return 0;
 387 }
 388
 389 static const struct inode_operations ovl_file_inode_operations = {
 390         .setattr        = ovl_setattr,
 391         .permission     = ovl_permission,
 392         .getattr        = ovl_getattr,
 393         .setxattr       = generic_setxattr,
 394         .getxattr       = ovl_getxattr,
 395         .listxattr      = ovl_listxattr,
 396         .removexattr    = ovl_removexattr,
 397         .get_acl        = ovl_get_acl,
 398         .update_time    = ovl_update_time,
 399 };
 400
 401 static const struct inode_operations ovl_symlink_inode_operations = {
 402         .setattr        = ovl_setattr,
 403         .get_link       = ovl_get_link,
 404         .readlink       = ovl_readlink,
 405         .getattr        = ovl_getattr,
 406         .setxattr       = generic_setxattr,
 407         .getxattr       = ovl_getxattr,
 408         .listxattr      = ovl_listxattr,
 409         .removexattr    = ovl_removexattr,
 410         .update_time    = ovl_update_time,
 411 };
 412
 413 static void ovl_fill_inode(struct inode *inode, umode_t mode)
 414 {
 415         inode->i_ino = get_next_ino();
 416         inode->i_mode = mode;
 417         inode->i_flags |= S_NOCMTIME;
 418 #ifdef CONFIG_FS_POSIX_ACL
 419         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
 420 #endif
 421
 422         mode &= S_IFMT;
 423         switch (mode) {
 424         case S_IFDIR:
 425                 inode->i_op = &ovl_dir_inode_operations;
 426                 inode->i_fop = &ovl_dir_operations;
 427                 break;
 428
 429         case S_IFLNK:
 430                 inode->i_op = &ovl_symlink_inode_operations;
 431                 break;
 432
 433         default:
 434                 WARN(1, "illegal file type: %i\n", mode);
 435                 /* Fall through */
 436
 437         case S_IFREG:
 438         case S_IFSOCK:
 439         case S_IFBLK:
 440         case S_IFCHR:
 441         case S_IFIFO:
 442                 inode->i_op = &ovl_file_inode_operations;
 443                 break;
 444         }
 445 }
 446
 447 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 448 {
 449         struct inode *inode;
 450
 451         inode = new_inode(sb);
 452         if (inode)
 453                 ovl_fill_inode(inode, mode);
 454
 455         return inode;
 456 }
 457
 458 static int ovl_inode_test(struct inode *inode, void *data)
 459 {
 460         return ovl_inode_real(inode, NULL) == data;
 461 }
 462
 463 static int ovl_inode_set(struct inode *inode, void *data)
 464 {
 465         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 466         return 0;
 467 }
 468
 469 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 470
 471 {
 472         struct inode *inode;
 473
 474         inode = iget5_locked(sb, (unsigned long) realinode,
 475                              ovl_inode_test, ovl_inode_set, realinode);
 476         if (inode && inode->i_state & I_NEW) {
 477                 ovl_fill_inode(inode, realinode->i_mode);
 478                 set_nlink(inode, realinode->i_nlink);
 479                 unlock_new_inode(inode);
 480         }
 481
 482         return inode;
 483 }