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         err = ovl_copy_up(dentry);
  65         if (!err) {
  66                 upperdentry = ovl_dentry_upper(dentry);
  67
  68                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  69                         attr->ia_valid &= ~ATTR_MODE;
  70
  71                 inode_lock(upperdentry->d_inode);
  72                 old_cred = ovl_override_creds(dentry->d_sb);
  73                 err = notify_change(upperdentry, attr, NULL);
  74                 revert_creds(old_cred);
  75                 if (!err)
  76                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  77                 inode_unlock(upperdentry->d_inode);
  78         }
  79         ovl_drop_write(dentry);
  80 out:
  81         return err;
  82 }
  83
  84 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
  85                          struct kstat *stat)
  86 {
  87         struct path realpath;
  88         const struct cred *old_cred;
  89         int err;
  90
  91         ovl_path_real(dentry, &realpath);
  92         old_cred = ovl_override_creds(dentry->d_sb);
  93         err = vfs_getattr(&realpath, stat);
  94         revert_creds(old_cred);
  95         return err;
  96 }
  97
  98 int ovl_permission(struct inode *inode, int mask)
  99 {
 100         bool is_upper;
 101         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 102         const struct cred *old_cred;
 103         int err;
 104
 105         /* Careful in RCU walk mode */
 106         if (!realinode) {
 107                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 108                 return -ECHILD;
 109         }
 110
 111         /*
 112          * Check overlay inode with the creds of task and underlying inode
 113          * with creds of mounter
 114          */
 115         err = generic_permission(inode, mask);
 116         if (err)
 117                 return err;
 118
 119         old_cred = ovl_override_creds(inode->i_sb);
 120         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
 121                 mask &= ~(MAY_WRITE | MAY_APPEND);
 122                 /* Make sure mounter can read file for copy up later */
 123                 mask |= MAY_READ;
 124         }
 125         err = inode_permission(realinode, mask);
 126         revert_creds(old_cred);
 127
 128         return err;
 129 }
 130
 131 static const char *ovl_get_link(struct dentry *dentry,
 132                                 struct inode *inode,
 133                                 struct delayed_call *done)
 134 {
 135         struct dentry *realdentry;
 136         struct inode *realinode;
 137         const struct cred *old_cred;
 138         const char *p;
 139
 140         if (!dentry)
 141                 return ERR_PTR(-ECHILD);
 142
 143         realdentry = ovl_dentry_real(dentry);
 144         realinode = realdentry->d_inode;
 145
 146         if (WARN_ON(!realinode->i_op->get_link))
 147                 return ERR_PTR(-EPERM);
 148
 149         old_cred = ovl_override_creds(dentry->d_sb);
 150         p = realinode->i_op->get_link(realdentry, realinode, done);
 151         revert_creds(old_cred);
 152         return p;
 153 }
 154
 155 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 156 {
 157         struct path realpath;
 158         struct inode *realinode;
 159         const struct cred *old_cred;
 160         int err;
 161
 162         ovl_path_real(dentry, &realpath);
 163         realinode = realpath.dentry->d_inode;
 164
 165         if (!realinode->i_op->readlink)
 166                 return -EINVAL;
 167
 168         old_cred = ovl_override_creds(dentry->d_sb);
 169         err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 170         revert_creds(old_cred);
 171         return err;
 172 }
 173
 174 bool ovl_is_private_xattr(const char *name)
 175 {
 176         return strncmp(name, OVL_XATTR_PREFIX,
 177                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 178 }
 179
 180 int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
 181                   size_t size, int flags)
 182 {
 183         int err;
 184         struct path realpath;
 185         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 186         const struct cred *old_cred;
 187
 188         err = ovl_want_write(dentry);
 189         if (err)
 190                 goto out;
 191
 192         if (!value && !OVL_TYPE_UPPER(type)) {
 193                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 194                 if (err < 0)
 195                         goto out_drop_write;
 196         }
 197
 198         err = ovl_copy_up(dentry);
 199         if (err)
 200                 goto out_drop_write;
 201
 202         if (!OVL_TYPE_UPPER(type))
 203                 ovl_path_upper(dentry, &realpath);
 204
 205         old_cred = ovl_override_creds(dentry->d_sb);
 206         if (value)
 207                 err = vfs_setxattr(realpath.dentry, name, value, size, flags);
 208         else {
 209                 WARN_ON(flags != XATTR_REPLACE);
 210                 err = vfs_removexattr(realpath.dentry, name);
 211         }
 212         revert_creds(old_cred);
 213
 214 out_drop_write:
 215         ovl_drop_write(dentry);
 216 out:
 217         return err;
 218 }
 219
 220 int ovl_xattr_get(struct dentry *dentry, const char *name,
 221                   void *value, size_t size)
 222 {
 223         struct dentry *realdentry = ovl_dentry_real(dentry);
 224         ssize_t res;
 225         const struct cred *old_cred;
 226
 227         old_cred = ovl_override_creds(dentry->d_sb);
 228         res = vfs_getxattr(realdentry, name, value, size);
 229         revert_creds(old_cred);
 230         return res;
 231 }
 232
 233 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 234 {
 235         struct dentry *realdentry = ovl_dentry_real(dentry);
 236         ssize_t res;
 237         size_t len;
 238         char *s;
 239         const struct cred *old_cred;
 240
 241         old_cred = ovl_override_creds(dentry->d_sb);
 242         res = vfs_listxattr(realdentry, list, size);
 243         revert_creds(old_cred);
 244         if (res <= 0 || size == 0)
 245                 return res;
 246
 247         /* filter out private xattrs */
 248         for (s = list, len = res; len;) {
 249                 size_t slen = strnlen(s, len) + 1;
 250
 251                 /* underlying fs providing us with an broken xattr list? */
 252                 if (WARN_ON(slen > len))
 253                         return -EIO;
 254
 255                 len -= slen;
 256                 if (ovl_is_private_xattr(s)) {
 257                         res -= slen;
 258                         memmove(s, s + slen, len);
 259                 } else {
 260                         s += slen;
 261                 }
 262         }
 263
 264         return res;
 265 }
 266
 267 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 268 {
 269         struct inode *realinode = ovl_inode_real(inode, NULL);
 270         const struct cred *old_cred;
 271         struct posix_acl *acl;
 272
 273         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 274                 return NULL;
 275
 276         if (!realinode->i_op->get_acl)
 277                 return NULL;
 278
 279         old_cred = ovl_override_creds(inode->i_sb);
 280         acl = get_acl(realinode, type);
 281         revert_creds(old_cred);
 282
 283         return acl;
 284 }
 285
 286 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 287                                   struct dentry *realdentry)
 288 {
 289         if (OVL_TYPE_UPPER(type))
 290                 return false;
 291
 292         if (special_file(realdentry->d_inode->i_mode))
 293                 return false;
 294
 295         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 296                 return false;
 297
 298         return true;
 299 }
 300
 301 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 302 {
 303         int err = 0;
 304         struct path realpath;
 305         enum ovl_path_type type;
 306
 307         type = ovl_path_real(dentry, &realpath);
 308         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 309                 err = ovl_want_write(dentry);
 310                 if (!err) {
 311                         if (file_flags & O_TRUNC)
 312                                 err = ovl_copy_up_truncate(dentry);
 313                         else
 314                                 err = ovl_copy_up(dentry);
 315                         ovl_drop_write(dentry);
 316                 }
 317         }
 318
 319         return err;
 320 }
 321
 322 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 323 {
 324         struct dentry *alias;
 325         struct path upperpath;
 326
 327         if (!(flags & S_ATIME))
 328                 return 0;
 329
 330         alias = d_find_any_alias(inode);
 331         if (!alias)
 332                 return 0;
 333
 334         ovl_path_upper(alias, &upperpath);
 335         if (upperpath.dentry) {
 336                 touch_atime(&upperpath);
 337                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 338         }
 339
 340         dput(alias);
 341
 342         return 0;
 343 }
 344
 345 static const struct inode_operations ovl_file_inode_operations = {
 346         .setattr        = ovl_setattr,
 347         .permission     = ovl_permission,
 348         .getattr        = ovl_getattr,
 349         .setxattr       = generic_setxattr,
 350         .getxattr       = generic_getxattr,
 351         .listxattr      = ovl_listxattr,
 352         .removexattr    = generic_removexattr,
 353         .get_acl        = ovl_get_acl,
 354         .update_time    = ovl_update_time,
 355 };
 356
 357 static const struct inode_operations ovl_symlink_inode_operations = {
 358         .setattr        = ovl_setattr,
 359         .get_link       = ovl_get_link,
 360         .readlink       = ovl_readlink,
 361         .getattr        = ovl_getattr,
 362         .setxattr       = generic_setxattr,
 363         .getxattr       = generic_getxattr,
 364         .listxattr      = ovl_listxattr,
 365         .removexattr    = generic_removexattr,
 366         .update_time    = ovl_update_time,
 367 };
 368
 369 static void ovl_fill_inode(struct inode *inode, umode_t mode)
 370 {
 371         inode->i_ino = get_next_ino();
 372         inode->i_mode = mode;
 373         inode->i_flags |= S_NOCMTIME;
 374 #ifdef CONFIG_FS_POSIX_ACL
 375         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
 376 #endif
 377
 378         mode &= S_IFMT;
 379         switch (mode) {
 380         case S_IFDIR:
 381                 inode->i_op = &ovl_dir_inode_operations;
 382                 inode->i_fop = &ovl_dir_operations;
 383                 break;
 384
 385         case S_IFLNK:
 386                 inode->i_op = &ovl_symlink_inode_operations;
 387                 break;
 388
 389         default:
 390                 WARN(1, "illegal file type: %i\n", mode);
 391                 /* Fall through */
 392
 393         case S_IFREG:
 394         case S_IFSOCK:
 395         case S_IFBLK:
 396         case S_IFCHR:
 397         case S_IFIFO:
 398                 inode->i_op = &ovl_file_inode_operations;
 399                 break;
 400         }
 401 }
 402
 403 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 404 {
 405         struct inode *inode;
 406
 407         inode = new_inode(sb);
 408         if (inode)
 409                 ovl_fill_inode(inode, mode);
 410
 411         return inode;
 412 }
 413
 414 static int ovl_inode_test(struct inode *inode, void *data)
 415 {
 416         return ovl_inode_real(inode, NULL) == data;
 417 }
 418
 419 static int ovl_inode_set(struct inode *inode, void *data)
 420 {
 421         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 422         return 0;
 423 }
 424
 425 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 426
 427 {
 428         struct inode *inode;
 429
 430         inode = iget5_locked(sb, (unsigned long) realinode,
 431                              ovl_inode_test, ovl_inode_set, realinode);
 432         if (inode && inode->i_state & I_NEW) {
 433                 ovl_fill_inode(inode, realinode->i_mode);
 434                 set_nlink(inode, realinode->i_nlink);
 435                 unlock_new_inode(inode);
 436         }
 437
 438         return inode;
 439 }