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         struct ovl_entry *oe = inode->i_private;
 121         bool is_upper;
 122         struct dentry *realdentry = ovl_entry_real(oe, &is_upper);
 123         struct inode *realinode;
 124         const struct cred *old_cred;
 125         int err;
 126
 127         /* Careful in RCU walk mode */
 128         realinode = d_inode_rcu(realdentry);
 129         if (!realinode) {
 130                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 131                 return -ECHILD;
 132         }
 133
 134         /*
 135          * Check overlay inode with the creds of task and underlying inode
 136          * with creds of mounter
 137          */
 138         err = generic_permission(inode, mask);
 139         if (err)
 140                 return err;
 141
 142         old_cred = ovl_override_creds(inode->i_sb);
 143         if (!is_upper)
 144                 mask &= ~(MAY_WRITE | MAY_APPEND);
 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         return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 197 }
 198
 199 int ovl_setxattr(struct dentry *dentry, struct inode *inode,
 200                  const char *name, const void *value,
 201                  size_t size, int flags)
 202 {
 203         int err;
 204         struct dentry *upperdentry;
 205         const struct cred *old_cred;
 206
 207         err = ovl_want_write(dentry);
 208         if (err)
 209                 goto out;
 210
 211         err = -EPERM;
 212         if (ovl_is_private_xattr(name))
 213                 goto out_drop_write;
 214
 215         err = ovl_copy_up(dentry);
 216         if (err)
 217                 goto out_drop_write;
 218
 219         upperdentry = ovl_dentry_upper(dentry);
 220         old_cred = ovl_override_creds(dentry->d_sb);
 221         err = vfs_setxattr(upperdentry, name, value, size, flags);
 222         revert_creds(old_cred);
 223
 224 out_drop_write:
 225         ovl_drop_write(dentry);
 226 out:
 227         return err;
 228 }
 229
 230 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
 231                      const char *name, void *value, size_t size)
 232 {
 233         struct dentry *realdentry = ovl_dentry_real(dentry);
 234         ssize_t res;
 235         const struct cred *old_cred;
 236
 237         if (ovl_is_private_xattr(name))
 238                 return -ENODATA;
 239
 240         old_cred = ovl_override_creds(dentry->d_sb);
 241         res = vfs_getxattr(realdentry, name, value, size);
 242         revert_creds(old_cred);
 243         return res;
 244 }
 245
 246 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 247 {
 248         struct dentry *realdentry = ovl_dentry_real(dentry);
 249         ssize_t res;
 250         int off;
 251         const struct cred *old_cred;
 252
 253         old_cred = ovl_override_creds(dentry->d_sb);
 254         res = vfs_listxattr(realdentry, list, size);
 255         revert_creds(old_cred);
 256         if (res <= 0 || size == 0)
 257                 return res;
 258
 259         /* filter out private xattrs */
 260         for (off = 0; off < res;) {
 261                 char *s = list + off;
 262                 size_t slen = strlen(s) + 1;
 263
 264                 BUG_ON(off + slen > res);
 265
 266                 if (ovl_is_private_xattr(s)) {
 267                         res -= slen;
 268                         memmove(s, s + slen, res - off);
 269                 } else {
 270                         off += slen;
 271                 }
 272         }
 273
 274         return res;
 275 }
 276
 277 int ovl_removexattr(struct dentry *dentry, const char *name)
 278 {
 279         int err;
 280         struct path realpath;
 281         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 282         const struct cred *old_cred;
 283
 284         err = ovl_want_write(dentry);
 285         if (err)
 286                 goto out;
 287
 288         err = -ENODATA;
 289         if (ovl_is_private_xattr(name))
 290                 goto out_drop_write;
 291
 292         if (!OVL_TYPE_UPPER(type)) {
 293                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 294                 if (err < 0)
 295                         goto out_drop_write;
 296
 297                 err = ovl_copy_up(dentry);
 298                 if (err)
 299                         goto out_drop_write;
 300
 301                 ovl_path_upper(dentry, &realpath);
 302         }
 303
 304         old_cred = ovl_override_creds(dentry->d_sb);
 305         err = vfs_removexattr(realpath.dentry, name);
 306         revert_creds(old_cred);
 307 out_drop_write:
 308         ovl_drop_write(dentry);
 309 out:
 310         return err;
 311 }
 312
 313 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 314 {
 315         struct inode *realinode = ovl_inode_real(inode);
 316         const struct cred *old_cred;
 317         struct posix_acl *acl;
 318
 319         if (!IS_POSIXACL(realinode))
 320                 return NULL;
 321
 322         if (!realinode->i_op->get_acl)
 323                 return NULL;
 324
 325         old_cred = ovl_override_creds(inode->i_sb);
 326         acl = realinode->i_op->get_acl(realinode, type);
 327         revert_creds(old_cred);
 328
 329         return acl;
 330 }
 331
 332 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 333                                   struct dentry *realdentry)
 334 {
 335         if (OVL_TYPE_UPPER(type))
 336                 return false;
 337
 338         if (special_file(realdentry->d_inode->i_mode))
 339                 return false;
 340
 341         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 342                 return false;
 343
 344         return true;
 345 }
 346
 347 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 348 {
 349         int err = 0;
 350         struct path realpath;
 351         enum ovl_path_type type;
 352
 353         type = ovl_path_real(dentry, &realpath);
 354         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 355                 err = ovl_want_write(dentry);
 356                 if (!err) {
 357                         if (file_flags & O_TRUNC)
 358                                 err = ovl_copy_up_truncate(dentry);
 359                         else
 360                                 err = ovl_copy_up(dentry);
 361                         ovl_drop_write(dentry);
 362                 }
 363         }
 364
 365         return err;
 366 }
 367
 368 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 369 {
 370         struct dentry *alias;
 371         struct path upperpath;
 372
 373         if (!(flags & S_ATIME))
 374                 return 0;
 375
 376         alias = d_find_any_alias(inode);
 377         if (!alias)
 378                 return 0;
 379
 380         ovl_path_upper(alias, &upperpath);
 381         if (upperpath.dentry) {
 382                 touch_atime(&upperpath);
 383                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 384         }
 385
 386         dput(alias);
 387
 388         return 0;
 389 }
 390
 391 static const struct inode_operations ovl_file_inode_operations = {
 392         .setattr        = ovl_setattr,
 393         .permission     = ovl_permission,
 394         .getattr        = ovl_getattr,
 395         .setxattr       = ovl_setxattr,
 396         .getxattr       = ovl_getxattr,
 397         .listxattr      = ovl_listxattr,
 398         .removexattr    = ovl_removexattr,
 399         .get_acl        = ovl_get_acl,
 400         .update_time    = ovl_update_time,
 401 };
 402
 403 static const struct inode_operations ovl_symlink_inode_operations = {
 404         .setattr        = ovl_setattr,
 405         .get_link       = ovl_get_link,
 406         .readlink       = ovl_readlink,
 407         .getattr        = ovl_getattr,
 408         .setxattr       = ovl_setxattr,
 409         .getxattr       = ovl_getxattr,
 410         .listxattr      = ovl_listxattr,
 411         .removexattr    = ovl_removexattr,
 412         .update_time    = ovl_update_time,
 413 };
 414
 415 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
 416                             struct ovl_entry *oe)
 417 {
 418         struct inode *inode;
 419
 420         inode = new_inode(sb);
 421         if (!inode)
 422                 return NULL;
 423
 424         inode->i_ino = get_next_ino();
 425         inode->i_mode = mode;
 426         inode->i_flags |= S_NOCMTIME;
 427         inode->i_private = oe;
 428
 429         mode &= S_IFMT;
 430         switch (mode) {
 431         case S_IFDIR:
 432                 inode->i_op = &ovl_dir_inode_operations;
 433                 inode->i_fop = &ovl_dir_operations;
 434                 break;
 435
 436         case S_IFLNK:
 437                 inode->i_op = &ovl_symlink_inode_operations;
 438                 break;
 439
 440         case S_IFREG:
 441         case S_IFSOCK:
 442         case S_IFBLK:
 443         case S_IFCHR:
 444         case S_IFIFO:
 445                 inode->i_op = &ovl_file_inode_operations;
 446                 break;
 447
 448         default:
 449                 WARN(1, "illegal file type: %i\n", mode);
 450                 iput(inode);
 451                 inode = NULL;
 452         }
 453
 454         return inode;
 455 }