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 "overlayfs.h"
  14
  15 static int ovl_copy_up_truncate(struct dentry *dentry)
  16 {
  17         int err;
  18         struct dentry *parent;
  19         struct kstat stat;
  20         struct path lowerpath;
  21
  22         parent = dget_parent(dentry);
  23         err = ovl_copy_up(parent);
  24         if (err)
  25                 goto out_dput_parent;
  26
  27         ovl_path_lower(dentry, &lowerpath);
  28         err = vfs_getattr(&lowerpath, &stat);
  29         if (err)
  30                 goto out_dput_parent;
  31
  32         stat.size = 0;
  33         err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
  34
  35 out_dput_parent:
  36         dput(parent);
  37         return err;
  38 }
  39
  40 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  41 {
  42         int err;
  43         struct dentry *upperdentry;
  44         const struct cred *old_cred;
  45
  46         /*
  47          * Check for permissions before trying to copy-up.  This is redundant
  48          * since it will be rechecked later by ->setattr() on upper dentry.  But
  49          * without this, copy-up can be triggered by just about anybody.
  50          *
  51          * We don't initialize inode->size, which just means that
  52          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
  53          * check for a swapfile (which this won't be anyway).
  54          */
  55         err = inode_change_ok(dentry->d_inode, attr);
  56         if (err)
  57                 return err;
  58
  59         err = ovl_want_write(dentry);
  60         if (err)
  61                 goto out;
  62
  63         if (attr->ia_valid & ATTR_SIZE) {
  64                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
  65
  66                 err = -ETXTBSY;
  67                 if (atomic_read(&realinode->i_writecount) < 0)
  68                         goto out_drop_write;
  69         }
  70
  71         err = ovl_copy_up(dentry);
  72         if (!err) {
  73                 struct inode *winode = NULL;
  74
  75                 upperdentry = ovl_dentry_upper(dentry);
  76
  77                 if (attr->ia_valid & ATTR_SIZE) {
  78                         winode = d_inode(upperdentry);
  79                         err = get_write_access(winode);
  80                         if (err)
  81                                 goto out_drop_write;
  82                 }
  83
  84                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  85                         attr->ia_valid &= ~ATTR_MODE;
  86
  87                 inode_lock(upperdentry->d_inode);
  88                 old_cred = ovl_override_creds(dentry->d_sb);
  89                 err = notify_change(upperdentry, attr, NULL);
  90                 revert_creds(old_cred);
  91                 if (!err)
  92                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  93                 inode_unlock(upperdentry->d_inode);
  94
  95                 if (winode)
  96                         put_write_access(winode);
  97         }
  98 out_drop_write:
  99         ovl_drop_write(dentry);
 100 out:
 101         return err;
 102 }
 103
 104 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 105                          struct kstat *stat)
 106 {
 107         struct path realpath;
 108         const struct cred *old_cred;
 109         int err;
 110
 111         ovl_path_real(dentry, &realpath);
 112         old_cred = ovl_override_creds(dentry->d_sb);
 113         err = vfs_getattr(&realpath, stat);
 114         revert_creds(old_cred);
 115         return err;
 116 }
 117
 118 int ovl_permission(struct inode *inode, int mask)
 119 {
 120         bool is_upper;
 121         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 122         const struct cred *old_cred;
 123         int err;
 124
 125         /* Careful in RCU walk mode */
 126         if (!realinode) {
 127                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 128                 return -ECHILD;
 129         }
 130
 131         /*
 132          * Check overlay inode with the creds of task and underlying inode
 133          * with creds of mounter
 134          */
 135         err = generic_permission(inode, mask);
 136         if (err)
 137                 return err;
 138
 139         old_cred = ovl_override_creds(inode->i_sb);
 140         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
 141                 mask &= ~(MAY_WRITE | MAY_APPEND);
 142                 /* Make sure mounter can read file for copy up later */
 143                 mask |= MAY_READ;
 144         }
 145         err = inode_permission(realinode, mask);
 146         revert_creds(old_cred);
 147
 148         return err;
 149 }
 150
 151 static const char *ovl_get_link(struct dentry *dentry,
 152                                 struct inode *inode,
 153                                 struct delayed_call *done)
 154 {
 155         struct dentry *realdentry;
 156         struct inode *realinode;
 157         const struct cred *old_cred;
 158         const char *p;
 159
 160         if (!dentry)
 161                 return ERR_PTR(-ECHILD);
 162
 163         realdentry = ovl_dentry_real(dentry);
 164         realinode = realdentry->d_inode;
 165
 166         if (WARN_ON(!realinode->i_op->get_link))
 167                 return ERR_PTR(-EPERM);
 168
 169         old_cred = ovl_override_creds(dentry->d_sb);
 170         p = realinode->i_op->get_link(realdentry, realinode, done);
 171         revert_creds(old_cred);
 172         return p;
 173 }
 174
 175 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 176 {
 177         struct path realpath;
 178         struct inode *realinode;
 179         const struct cred *old_cred;
 180         int err;
 181
 182         ovl_path_real(dentry, &realpath);
 183         realinode = realpath.dentry->d_inode;
 184
 185         if (!realinode->i_op->readlink)
 186                 return -EINVAL;
 187
 188         old_cred = ovl_override_creds(dentry->d_sb);
 189         err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 190         revert_creds(old_cred);
 191         return err;
 192 }
 193
 194 static bool ovl_is_private_xattr(const char *name)
 195 {
 196 #define OVL_XATTR_PRE_NAME OVL_XATTR_PREFIX "."
 197         return strncmp(name, OVL_XATTR_PRE_NAME,
 198                        sizeof(OVL_XATTR_PRE_NAME) - 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_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 = realinode->i_op->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
 419         mode &= S_IFMT;
 420         switch (mode) {
 421         case S_IFDIR:
 422                 inode->i_op = &ovl_dir_inode_operations;
 423                 inode->i_fop = &ovl_dir_operations;
 424                 break;
 425
 426         case S_IFLNK:
 427                 inode->i_op = &ovl_symlink_inode_operations;
 428                 break;
 429
 430         default:
 431                 WARN(1, "illegal file type: %i\n", mode);
 432                 /* Fall through */
 433
 434         case S_IFREG:
 435         case S_IFSOCK:
 436         case S_IFBLK:
 437         case S_IFCHR:
 438         case S_IFIFO:
 439                 inode->i_op = &ovl_file_inode_operations;
 440                 break;
 441         }
 442 }
 443
 444 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 445 {
 446         struct inode *inode;
 447
 448         inode = new_inode(sb);
 449         if (inode)
 450                 ovl_fill_inode(inode, mode);
 451
 452         return inode;
 453 }
 454
 455 static int ovl_inode_test(struct inode *inode, void *data)
 456 {
 457         return ovl_inode_real(inode, NULL) == data;
 458 }
 459
 460 static int ovl_inode_set(struct inode *inode, void *data)
 461 {
 462         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 463         return 0;
 464 }
 465
 466 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 467
 468 {
 469         struct inode *inode;
 470
 471         inode = iget5_locked(sb, (unsigned long) realinode,
 472                              ovl_inode_test, ovl_inode_set, realinode);
 473         if (inode && inode->i_state & I_NEW) {
 474                 ovl_fill_inode(inode, realinode->i_mode);
 475                 set_nlink(inode, realinode->i_nlink);
 476                 unlock_new_inode(inode);
 477         }
 478
 479         return inode;
 480 }