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
  45         err = ovl_want_write(dentry);
  46         if (err)
  47                 goto out;
  48
  49         err = ovl_copy_up(dentry);
  50         if (!err) {
  51                 upperdentry = ovl_dentry_upper(dentry);
  52
  53                 mutex_lock(&upperdentry->d_inode->i_mutex);
  54                 err = notify_change(upperdentry, attr, NULL);
  55                 mutex_unlock(&upperdentry->d_inode->i_mutex);
  56         }
  57         ovl_drop_write(dentry);
  58 out:
  59         return err;
  60 }
  61
  62 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
  63                          struct kstat *stat)
  64 {
  65         struct path realpath;
  66
  67         ovl_path_real(dentry, &realpath);
  68         return vfs_getattr(&realpath, stat);
  69 }
  70
  71 int ovl_permission(struct inode *inode, int mask)
  72 {
  73         struct ovl_entry *oe;
  74         struct dentry *alias = NULL;
  75         struct inode *realinode;
  76         struct dentry *realdentry;
  77         bool is_upper;
  78         int err;
  79
  80         if (S_ISDIR(inode->i_mode)) {
  81                 oe = inode->i_private;
  82         } else if (mask & MAY_NOT_BLOCK) {
  83                 return -ECHILD;
  84         } else {
  85                 /*
  86                  * For non-directories find an alias and get the info
  87                  * from there.
  88                  */
  89                 alias = d_find_any_alias(inode);
  90                 if (WARN_ON(!alias))
  91                         return -ENOENT;
  92
  93                 oe = alias->d_fsdata;
  94         }
  95
  96         realdentry = ovl_entry_real(oe, &is_upper);
  97
  98         /* Careful in RCU walk mode */
  99         realinode = ACCESS_ONCE(realdentry->d_inode);
 100         if (!realinode) {
 101                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 102                 err = -ENOENT;
 103                 goto out_dput;
 104         }
 105
 106         if (mask & MAY_WRITE) {
 107                 umode_t mode = realinode->i_mode;
 108
 109                 /*
 110                  * Writes will always be redirected to upper layer, so
 111                  * ignore lower layer being read-only.
 112                  *
 113                  * If the overlay itself is read-only then proceed
 114                  * with the permission check, don't return EROFS.
 115                  * This will only happen if this is the lower layer of
 116                  * another overlayfs.
 117                  *
 118                  * If upper fs becomes read-only after the overlay was
 119                  * constructed return EROFS to prevent modification of
 120                  * upper layer.
 121                  */
 122                 err = -EROFS;
 123                 if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
 124                     (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
 125                         goto out_dput;
 126         }
 127
 128         err = __inode_permission(realinode, mask);
 129 out_dput:
 130         dput(alias);
 131         return err;
 132 }
 133
 134
 135 struct ovl_link_data {
 136         struct dentry *realdentry;
 137         void *cookie;
 138 };
 139
 140 static const char *ovl_follow_link(struct dentry *dentry, void **cookie)
 141 {
 142         struct dentry *realdentry;
 143         struct inode *realinode;
 144         struct ovl_link_data *data = NULL;
 145         const char *ret;
 146
 147         realdentry = ovl_dentry_real(dentry);
 148         realinode = realdentry->d_inode;
 149
 150         if (WARN_ON(!realinode->i_op->follow_link))
 151                 return ERR_PTR(-EPERM);
 152
 153         if (realinode->i_op->put_link) {
 154                 data = kmalloc(sizeof(struct ovl_link_data), GFP_KERNEL);
 155                 if (!data)
 156                         return ERR_PTR(-ENOMEM);
 157                 data->realdentry = realdentry;
 158         }
 159
 160         ret = realinode->i_op->follow_link(realdentry, cookie);
 161         if (IS_ERR_OR_NULL(ret)) {
 162                 kfree(data);
 163                 return ret;
 164         }
 165
 166         if (data)
 167                 data->cookie = *cookie;
 168
 169         *cookie = data;
 170
 171         return ret;
 172 }
 173
 174 static void ovl_put_link(struct inode *unused, void *c)
 175 {
 176         struct inode *realinode;
 177         struct ovl_link_data *data = c;
 178
 179         if (!data)
 180                 return;
 181
 182         realinode = data->realdentry->d_inode;
 183         realinode->i_op->put_link(realinode, data->cookie);
 184         kfree(data);
 185 }
 186
 187 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 188 {
 189         struct path realpath;
 190         struct inode *realinode;
 191
 192         ovl_path_real(dentry, &realpath);
 193         realinode = realpath.dentry->d_inode;
 194
 195         if (!realinode->i_op->readlink)
 196                 return -EINVAL;
 197
 198         touch_atime(&realpath);
 199
 200         return realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 201 }
 202
 203
 204 static bool ovl_is_private_xattr(const char *name)
 205 {
 206         return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 207 }
 208
 209 int ovl_setxattr(struct dentry *dentry, const char *name,
 210                  const void *value, size_t size, int flags)
 211 {
 212         int err;
 213         struct dentry *upperdentry;
 214
 215         err = ovl_want_write(dentry);
 216         if (err)
 217                 goto out;
 218
 219         err = -EPERM;
 220         if (ovl_is_private_xattr(name))
 221                 goto out_drop_write;
 222
 223         err = ovl_copy_up(dentry);
 224         if (err)
 225                 goto out_drop_write;
 226
 227         upperdentry = ovl_dentry_upper(dentry);
 228         err = vfs_setxattr(upperdentry, name, value, size, flags);
 229
 230 out_drop_write:
 231         ovl_drop_write(dentry);
 232 out:
 233         return err;
 234 }
 235
 236 static bool ovl_need_xattr_filter(struct dentry *dentry,
 237                                   enum ovl_path_type type)
 238 {
 239         if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
 240                 return S_ISDIR(dentry->d_inode->i_mode);
 241         else
 242                 return false;
 243 }
 244
 245 ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
 246                      void *value, size_t size)
 247 {
 248         struct path realpath;
 249         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 250
 251         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 252                 return -ENODATA;
 253
 254         return vfs_getxattr(realpath.dentry, name, value, size);
 255 }
 256
 257 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 258 {
 259         struct path realpath;
 260         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 261         ssize_t res;
 262         int off;
 263
 264         res = vfs_listxattr(realpath.dentry, list, size);
 265         if (res <= 0 || size == 0)
 266                 return res;
 267
 268         if (!ovl_need_xattr_filter(dentry, type))
 269                 return res;
 270
 271         /* filter out private xattrs */
 272         for (off = 0; off < res;) {
 273                 char *s = list + off;
 274                 size_t slen = strlen(s) + 1;
 275
 276                 BUG_ON(off + slen > res);
 277
 278                 if (ovl_is_private_xattr(s)) {
 279                         res -= slen;
 280                         memmove(s, s + slen, res - off);
 281                 } else {
 282                         off += slen;
 283                 }
 284         }
 285
 286         return res;
 287 }
 288
 289 int ovl_removexattr(struct dentry *dentry, const char *name)
 290 {
 291         int err;
 292         struct path realpath;
 293         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 294
 295         err = ovl_want_write(dentry);
 296         if (err)
 297                 goto out;
 298
 299         err = -ENODATA;
 300         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 301                 goto out_drop_write;
 302
 303         if (!OVL_TYPE_UPPER(type)) {
 304                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 305                 if (err < 0)
 306                         goto out_drop_write;
 307
 308                 err = ovl_copy_up(dentry);
 309                 if (err)
 310                         goto out_drop_write;
 311
 312                 ovl_path_upper(dentry, &realpath);
 313         }
 314
 315         err = vfs_removexattr(realpath.dentry, name);
 316 out_drop_write:
 317         ovl_drop_write(dentry);
 318 out:
 319         return err;
 320 }
 321
 322 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 323                                   struct dentry *realdentry)
 324 {
 325         if (OVL_TYPE_UPPER(type))
 326                 return false;
 327
 328         if (special_file(realdentry->d_inode->i_mode))
 329                 return false;
 330
 331         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 332                 return false;
 333
 334         return true;
 335 }
 336
 337 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
 338 {
 339         int err;
 340         struct path realpath;
 341         enum ovl_path_type type;
 342
 343         if (d_is_dir(dentry))
 344                 return d_backing_inode(dentry);
 345
 346         type = ovl_path_real(dentry, &realpath);
 347         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 348                 err = ovl_want_write(dentry);
 349                 if (err)
 350                         return ERR_PTR(err);
 351
 352                 if (file_flags & O_TRUNC)
 353                         err = ovl_copy_up_truncate(dentry);
 354                 else
 355                         err = ovl_copy_up(dentry);
 356                 ovl_drop_write(dentry);
 357                 if (err)
 358                         return ERR_PTR(err);
 359
 360                 ovl_path_upper(dentry, &realpath);
 361         }
 362
 363         if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE)
 364                 return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags);
 365
 366         return d_backing_inode(realpath.dentry);
 367 }
 368
 369 static const struct inode_operations ovl_file_inode_operations = {
 370         .setattr        = ovl_setattr,
 371         .permission     = ovl_permission,
 372         .getattr        = ovl_getattr,
 373         .setxattr       = ovl_setxattr,
 374         .getxattr       = ovl_getxattr,
 375         .listxattr      = ovl_listxattr,
 376         .removexattr    = ovl_removexattr,
 377 };
 378
 379 static const struct inode_operations ovl_symlink_inode_operations = {
 380         .setattr        = ovl_setattr,
 381         .follow_link    = ovl_follow_link,
 382         .put_link       = ovl_put_link,
 383         .readlink       = ovl_readlink,
 384         .getattr        = ovl_getattr,
 385         .setxattr       = ovl_setxattr,
 386         .getxattr       = ovl_getxattr,
 387         .listxattr      = ovl_listxattr,
 388         .removexattr    = ovl_removexattr,
 389 };
 390
 391 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
 392                             struct ovl_entry *oe)
 393 {
 394         struct inode *inode;
 395
 396         inode = new_inode(sb);
 397         if (!inode)
 398                 return NULL;
 399
 400         mode &= S_IFMT;
 401
 402         inode->i_ino = get_next_ino();
 403         inode->i_mode = mode;
 404         inode->i_flags |= S_NOATIME | S_NOCMTIME;
 405
 406         switch (mode) {
 407         case S_IFDIR:
 408                 inode->i_private = oe;
 409                 inode->i_op = &ovl_dir_inode_operations;
 410                 inode->i_fop = &ovl_dir_operations;
 411                 break;
 412
 413         case S_IFLNK:
 414                 inode->i_op = &ovl_symlink_inode_operations;
 415                 break;
 416
 417         case S_IFREG:
 418         case S_IFSOCK:
 419         case S_IFBLK:
 420         case S_IFCHR:
 421         case S_IFIFO:
 422                 inode->i_op = &ovl_file_inode_operations;
 423                 break;
 424
 425         default:
 426                 WARN(1, "illegal file type: %i\n", mode);
 427                 iput(inode);
 428                 inode = NULL;
 429         }
 430
 431         return inode;
 432 }