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 static const char *ovl_get_link(struct dentry *dentry,
 135                                 struct inode *inode,
 136                                 struct delayed_call *done)
 137 {
 138         struct dentry *realdentry;
 139         struct inode *realinode;
 140
 141         if (!dentry)
 142                 return ERR_PTR(-ECHILD);
 143
 144         realdentry = ovl_dentry_real(dentry);
 145         realinode = realdentry->d_inode;
 146
 147         if (WARN_ON(!realinode->i_op->get_link))
 148                 return ERR_PTR(-EPERM);
 149
 150         return realinode->i_op->get_link(realdentry, realinode, done);
 151 }
 152
 153 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 154 {
 155         struct path realpath;
 156         struct inode *realinode;
 157
 158         ovl_path_real(dentry, &realpath);
 159         realinode = realpath.dentry->d_inode;
 160
 161         if (!realinode->i_op->readlink)
 162                 return -EINVAL;
 163
 164         touch_atime(&realpath);
 165
 166         return realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 167 }
 168
 169
 170 static bool ovl_is_private_xattr(const char *name)
 171 {
 172         return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 173 }
 174
 175 int ovl_setxattr(struct dentry *dentry, const char *name,
 176                  const void *value, size_t size, int flags)
 177 {
 178         int err;
 179         struct dentry *upperdentry;
 180
 181         err = ovl_want_write(dentry);
 182         if (err)
 183                 goto out;
 184
 185         err = -EPERM;
 186         if (ovl_is_private_xattr(name))
 187                 goto out_drop_write;
 188
 189         err = ovl_copy_up(dentry);
 190         if (err)
 191                 goto out_drop_write;
 192
 193         upperdentry = ovl_dentry_upper(dentry);
 194         err = vfs_setxattr(upperdentry, name, value, size, flags);
 195
 196 out_drop_write:
 197         ovl_drop_write(dentry);
 198 out:
 199         return err;
 200 }
 201
 202 static bool ovl_need_xattr_filter(struct dentry *dentry,
 203                                   enum ovl_path_type type)
 204 {
 205         if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
 206                 return S_ISDIR(dentry->d_inode->i_mode);
 207         else
 208                 return false;
 209 }
 210
 211 ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
 212                      void *value, size_t size)
 213 {
 214         struct path realpath;
 215         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 216
 217         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 218                 return -ENODATA;
 219
 220         return vfs_getxattr(realpath.dentry, name, value, size);
 221 }
 222
 223 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 224 {
 225         struct path realpath;
 226         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 227         ssize_t res;
 228         int off;
 229
 230         res = vfs_listxattr(realpath.dentry, list, size);
 231         if (res <= 0 || size == 0)
 232                 return res;
 233
 234         if (!ovl_need_xattr_filter(dentry, type))
 235                 return res;
 236
 237         /* filter out private xattrs */
 238         for (off = 0; off < res;) {
 239                 char *s = list + off;
 240                 size_t slen = strlen(s) + 1;
 241
 242                 BUG_ON(off + slen > res);
 243
 244                 if (ovl_is_private_xattr(s)) {
 245                         res -= slen;
 246                         memmove(s, s + slen, res - off);
 247                 } else {
 248                         off += slen;
 249                 }
 250         }
 251
 252         return res;
 253 }
 254
 255 int ovl_removexattr(struct dentry *dentry, const char *name)
 256 {
 257         int err;
 258         struct path realpath;
 259         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 260
 261         err = ovl_want_write(dentry);
 262         if (err)
 263                 goto out;
 264
 265         err = -ENODATA;
 266         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
 267                 goto out_drop_write;
 268
 269         if (!OVL_TYPE_UPPER(type)) {
 270                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 271                 if (err < 0)
 272                         goto out_drop_write;
 273
 274                 err = ovl_copy_up(dentry);
 275                 if (err)
 276                         goto out_drop_write;
 277
 278                 ovl_path_upper(dentry, &realpath);
 279         }
 280
 281         err = vfs_removexattr(realpath.dentry, name);
 282 out_drop_write:
 283         ovl_drop_write(dentry);
 284 out:
 285         return err;
 286 }
 287
 288 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 289                                   struct dentry *realdentry)
 290 {
 291         if (OVL_TYPE_UPPER(type))
 292                 return false;
 293
 294         if (special_file(realdentry->d_inode->i_mode))
 295                 return false;
 296
 297         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 298                 return false;
 299
 300         return true;
 301 }
 302
 303 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
 304 {
 305         int err;
 306         struct path realpath;
 307         enum ovl_path_type type;
 308
 309         if (d_is_dir(dentry))
 310                 return d_backing_inode(dentry);
 311
 312         type = ovl_path_real(dentry, &realpath);
 313         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 314                 err = ovl_want_write(dentry);
 315                 if (err)
 316                         return ERR_PTR(err);
 317
 318                 if (file_flags & O_TRUNC)
 319                         err = ovl_copy_up_truncate(dentry);
 320                 else
 321                         err = ovl_copy_up(dentry);
 322                 ovl_drop_write(dentry);
 323                 if (err)
 324                         return ERR_PTR(err);
 325
 326                 ovl_path_upper(dentry, &realpath);
 327         }
 328
 329         if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE)
 330                 return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags);
 331
 332         return d_backing_inode(realpath.dentry);
 333 }
 334
 335 static const struct inode_operations ovl_file_inode_operations = {
 336         .setattr        = ovl_setattr,
 337         .permission     = ovl_permission,
 338         .getattr        = ovl_getattr,
 339         .setxattr       = ovl_setxattr,
 340         .getxattr       = ovl_getxattr,
 341         .listxattr      = ovl_listxattr,
 342         .removexattr    = ovl_removexattr,
 343 };
 344
 345 static const struct inode_operations ovl_symlink_inode_operations = {
 346         .setattr        = ovl_setattr,
 347         .get_link       = ovl_get_link,
 348         .readlink       = ovl_readlink,
 349         .getattr        = ovl_getattr,
 350         .setxattr       = ovl_setxattr,
 351         .getxattr       = ovl_getxattr,
 352         .listxattr      = ovl_listxattr,
 353         .removexattr    = ovl_removexattr,
 354 };
 355
 356 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
 357                             struct ovl_entry *oe)
 358 {
 359         struct inode *inode;
 360
 361         inode = new_inode(sb);
 362         if (!inode)
 363                 return NULL;
 364
 365         mode &= S_IFMT;
 366
 367         inode->i_ino = get_next_ino();
 368         inode->i_mode = mode;
 369         inode->i_flags |= S_NOATIME | S_NOCMTIME;
 370
 371         switch (mode) {
 372         case S_IFDIR:
 373                 inode->i_private = oe;
 374                 inode->i_op = &ovl_dir_inode_operations;
 375                 inode->i_fop = &ovl_dir_operations;
 376                 break;
 377
 378         case S_IFLNK:
 379                 inode->i_op = &ovl_symlink_inode_operations;
 380                 break;
 381
 382         case S_IFREG:
 383         case S_IFSOCK:
 384         case S_IFBLK:
 385         case S_IFCHR:
 386         case S_IFIFO:
 387                 inode->i_op = &ovl_file_inode_operations;
 388                 break;
 389
 390         default:
 391                 WARN(1, "illegal file type: %i\n", mode);
 392                 iput(inode);
 393                 inode = NULL;
 394         }
 395
 396         return inode;
 397 }