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_last(struct dentry *dentry, struct iattr *attr,
  16                             bool no_data)
  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         if (no_data)
  34                 stat.size = 0;
  35
  36         err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat, attr);
  37
  38 out_dput_parent:
  39         dput(parent);
  40         return err;
  41 }
  42
  43 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  44 {
  45         int err;
  46         struct dentry *upperdentry;
  47
  48         err = ovl_want_write(dentry);
  49         if (err)
  50                 goto out;
  51
  52         upperdentry = ovl_dentry_upper(dentry);
  53         if (upperdentry) {
  54                 mutex_lock(&upperdentry->d_inode->i_mutex);
  55                 err = notify_change(upperdentry, attr, NULL);
  56                 mutex_unlock(&upperdentry->d_inode->i_mutex);
  57         } else {
  58                 err = ovl_copy_up_last(dentry, attr, false);
  59         }
  60         ovl_drop_write(dentry);
  61 out:
  62         return err;
  63 }
  64
  65 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
  66                          struct kstat *stat)
  67 {
  68         struct path realpath;
  69
  70         ovl_path_real(dentry, &realpath);
  71         return vfs_getattr(&realpath, stat);
  72 }
  73
  74 int ovl_permission(struct inode *inode, int mask)
  75 {
  76         struct ovl_entry *oe;
  77         struct dentry *alias = NULL;
  78         struct inode *realinode;
  79         struct dentry *realdentry;
  80         bool is_upper;
  81         int err;
  82
  83         if (S_ISDIR(inode->i_mode)) {
  84                 oe = inode->i_private;
  85         } else if (mask & MAY_NOT_BLOCK) {
  86                 return -ECHILD;
  87         } else {
  88                 /*
  89                  * For non-directories find an alias and get the info
  90                  * from there.
  91                  */
  92                 alias = d_find_any_alias(inode);
  93                 if (WARN_ON(!alias))
  94                         return -ENOENT;
  95
  96                 oe = alias->d_fsdata;
  97         }
  98
  99         realdentry = ovl_entry_real(oe, &is_upper);
 100
 101         /* Careful in RCU walk mode */
 102         realinode = ACCESS_ONCE(realdentry->d_inode);
 103         if (!realinode) {
 104                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 105                 err = -ENOENT;
 106                 goto out_dput;
 107         }
 108
 109         if (mask & MAY_WRITE) {
 110                 umode_t mode = realinode->i_mode;
 111
 112                 /*
 113                  * Writes will always be redirected to upper layer, so
 114                  * ignore lower layer being read-only.
 115                  *
 116                  * If the overlay itself is read-only then proceed
 117                  * with the permission check, don't return EROFS.
 118                  * This will only happen if this is the lower layer of
 119                  * another overlayfs.
 120                  *
 121                  * If upper fs becomes read-only after the overlay was
 122                  * constructed return EROFS to prevent modification of
 123                  * upper layer.
 124                  */
 125                 err = -EROFS;
 126                 if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
 127                     (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
 128                         goto out_dput;
 129         }
 130
 131         err = __inode_permission(realinode, mask);
 132 out_dput:
 133         dput(alias);
 134         return err;
 135 }
 136
 137
 138 struct ovl_link_data {
 139         struct dentry *realdentry;
 140         void *cookie;
 141 };
 142
 143 static const char *ovl_follow_link(struct dentry *dentry, void **cookie)
 144 {
 145         struct dentry *realdentry;
 146         struct inode *realinode;
 147         struct ovl_link_data *data = NULL;
 148         const char *ret;
 149
 150         realdentry = ovl_dentry_real(dentry);
 151         realinode = realdentry->d_inode;
 152
 153         if (WARN_ON(!realinode->i_op->follow_link))
 154                 return ERR_PTR(-EPERM);
 155
 156         if (realinode->i_op->put_link) {
 157                 data = kmalloc(sizeof(struct ovl_link_data), GFP_KERNEL);
 158                 if (!data)
 159                         return ERR_PTR(-ENOMEM);
 160                 data->realdentry = realdentry;
 161         }
 162
 163         ret = realinode->i_op->follow_link(realdentry, cookie);
 164         if (IS_ERR_OR_NULL(ret)) {
 165                 kfree(data);
 166                 return ret;
 167         }
 168
 169         if (data)
 170                 data->cookie = *cookie;
 171
 172         *cookie = data;
 173
 174         return ret;
 175 }
 176
 177 static void ovl_put_link(struct inode *unused, void *c)
 178 {
 179         struct inode *realinode;
 180         struct ovl_link_data *data = c;
 181
 182         if (!data)
 183                 return;
 184
 185         realinode = data->realdentry->d_inode;
 186         realinode->i_op->put_link(realinode, data->cookie);
 187         kfree(data);
 188 }
 189
 190 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 191 {
 192         struct path realpath;
 193         struct inode *realinode;
 194
 195         ovl_path_real(dentry, &realpath);
 196         realinode = realpath.dentry->d_inode;
 197
 198         if (!realinode->i_op->readlink)
 199                 return -EINVAL;
 200
 201         touch_atime(&realpath);
 202
 203         return realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 204 }
 205
 206
 207 static bool ovl_is_private_xattr(const char *name)
 208 {
 209         return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 210 }
 211
 212 int ovl_setxattr(struct dentry *dentry, const char *name,
 213                  const void *value, size_t size, int flags)
 214 {
 215         int err;
 216         struct dentry *upperdentry;
 217
 218         err = ovl_want_write(dentry);
 219         if (err)
 220                 goto out;
 221
 222         err = -EPERM;
 223         if (ovl_is_private_xattr(name))
 224                 goto out_drop_write;
 225
 226         err = ovl_copy_up(dentry);
 227         if (err)
 228                 goto out_drop_write;
 229
 230         upperdentry = ovl_dentry_upper(dentry);
 231         err = vfs_setxattr(upperdentry, name, value, size, flags);
 232
 233 out_drop_write:
 234         ovl_drop_write(dentry);
 235 out:
 236         return err;
 237 }
 238
 239 static bool ovl_need_xattr_filter(struct dentry *dentry,
 240                                   enum ovl_path_type type)
 241 {
 242         if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
 243                 return S_ISDIR(dentry->d_inode->i_mode);
 244         else
 245                 return false;
 246 }
 247
 248 ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
 249                      void *value, size_t size)
 250 {
 251         struct path realpath;
 252         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 253
 254         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 255                 return -ENODATA;
 256
 257         return vfs_getxattr(realpath.dentry, name, value, size);
 258 }
 259
 260 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 261 {
 262         struct path realpath;
 263         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 264         ssize_t res;
 265         int off;
 266
 267         res = vfs_listxattr(realpath.dentry, list, size);
 268         if (res <= 0 || size == 0)
 269                 return res;
 270
 271         if (!ovl_need_xattr_filter(dentry, type))
 272                 return res;
 273
 274         /* filter out private xattrs */
 275         for (off = 0; off < res;) {
 276                 char *s = list + off;
 277                 size_t slen = strlen(s) + 1;
 278
 279                 BUG_ON(off + slen > res);
 280
 281                 if (ovl_is_private_xattr(s)) {
 282                         res -= slen;
 283                         memmove(s, s + slen, res - off);
 284                 } else {
 285                         off += slen;
 286                 }
 287         }
 288
 289         return res;
 290 }
 291
 292 int ovl_removexattr(struct dentry *dentry, const char *name)
 293 {
 294         int err;
 295         struct path realpath;
 296         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 297
 298         err = ovl_want_write(dentry);
 299         if (err)
 300                 goto out;
 301
 302         err = -ENODATA;
 303         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 304                 goto out_drop_write;
 305
 306         if (!OVL_TYPE_UPPER(type)) {
 307                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 308                 if (err < 0)
 309                         goto out_drop_write;
 310
 311                 err = ovl_copy_up(dentry);
 312                 if (err)
 313                         goto out_drop_write;
 314
 315                 ovl_path_upper(dentry, &realpath);
 316         }
 317
 318         err = vfs_removexattr(realpath.dentry, name);
 319 out_drop_write:
 320         ovl_drop_write(dentry);
 321 out:
 322         return err;
 323 }
 324
 325 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 326                                   struct dentry *realdentry)
 327 {
 328         if (OVL_TYPE_UPPER(type))
 329                 return false;
 330
 331         if (special_file(realdentry->d_inode->i_mode))
 332                 return false;
 333
 334         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 335                 return false;
 336
 337         return true;
 338 }
 339
 340 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
 341 {
 342         int err;
 343         struct path realpath;
 344         enum ovl_path_type type;
 345
 346         if (d_is_dir(dentry))
 347                 return d_backing_inode(dentry);
 348
 349         type = ovl_path_real(dentry, &realpath);
 350         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 351                 err = ovl_want_write(dentry);
 352                 if (err)
 353                         return ERR_PTR(err);
 354
 355                 if (file_flags & O_TRUNC)
 356                         err = ovl_copy_up_last(dentry, NULL, true);
 357                 else
 358                         err = ovl_copy_up(dentry);
 359                 ovl_drop_write(dentry);
 360                 if (err)
 361                         return ERR_PTR(err);
 362
 363                 ovl_path_upper(dentry, &realpath);
 364         }
 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 }