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         if (attr->ia_valid & ATTR_SIZE) {
  65                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
  66
  67                 err = -ETXTBSY;
  68                 if (atomic_read(&realinode->i_writecount) < 0)
  69                         goto out_drop_write;
  70         }
  71
  72         err = ovl_copy_up(dentry);
  73         if (!err) {
  74                 struct inode *winode = NULL;
  75
  76                 upperdentry = ovl_dentry_upper(dentry);
  77
  78                 if (attr->ia_valid & ATTR_SIZE) {
  79                         winode = d_inode(upperdentry);
  80                         err = get_write_access(winode);
  81                         if (err)
  82                                 goto out_drop_write;
  83                 }
  84
  85                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  86                         attr->ia_valid &= ~ATTR_MODE;
  87
  88                 inode_lock(upperdentry->d_inode);
  89                 old_cred = ovl_override_creds(dentry->d_sb);
  90                 err = notify_change(upperdentry, attr, NULL);
  91                 revert_creds(old_cred);
  92                 if (!err)
  93                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  94                 inode_unlock(upperdentry->d_inode);
  95
  96                 if (winode)
  97                         put_write_access(winode);
  98         }
  99 out_drop_write:
 100         ovl_drop_write(dentry);
 101 out:
 102         return err;
 103 }
 104
 105 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 106                          struct kstat *stat)
 107 {
 108         struct path realpath;
 109         const struct cred *old_cred;
 110         int err;
 111
 112         ovl_path_real(dentry, &realpath);
 113         old_cred = ovl_override_creds(dentry->d_sb);
 114         err = vfs_getattr(&realpath, stat);
 115         revert_creds(old_cred);
 116         return err;
 117 }
 118
 119 int ovl_permission(struct inode *inode, int mask)
 120 {
 121         bool is_upper;
 122         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 123         const struct cred *old_cred;
 124         int err;
 125
 126         /* Careful in RCU walk mode */
 127         if (!realinode) {
 128                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 129                 return -ECHILD;
 130         }
 131
 132         /*
 133          * Check overlay inode with the creds of task and underlying inode
 134          * with creds of mounter
 135          */
 136         err = generic_permission(inode, mask);
 137         if (err)
 138                 return err;
 139
 140         old_cred = ovl_override_creds(inode->i_sb);
 141         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
 142                 mask &= ~(MAY_WRITE | MAY_APPEND);
 143                 /* Make sure mounter can read file for copy up later */
 144                 mask |= MAY_READ;
 145         }
 146         err = inode_permission(realinode, mask);
 147         revert_creds(old_cred);
 148
 149         return err;
 150 }
 151
 152 static const char *ovl_get_link(struct dentry *dentry,
 153                                 struct inode *inode,
 154                                 struct delayed_call *done)
 155 {
 156         struct dentry *realdentry;
 157         struct inode *realinode;
 158         const struct cred *old_cred;
 159         const char *p;
 160
 161         if (!dentry)
 162                 return ERR_PTR(-ECHILD);
 163
 164         realdentry = ovl_dentry_real(dentry);
 165         realinode = realdentry->d_inode;
 166
 167         if (WARN_ON(!realinode->i_op->get_link))
 168                 return ERR_PTR(-EPERM);
 169
 170         old_cred = ovl_override_creds(dentry->d_sb);
 171         p = realinode->i_op->get_link(realdentry, realinode, done);
 172         revert_creds(old_cred);
 173         return p;
 174 }
 175
 176 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 177 {
 178         struct path realpath;
 179         struct inode *realinode;
 180         const struct cred *old_cred;
 181         int err;
 182
 183         ovl_path_real(dentry, &realpath);
 184         realinode = realpath.dentry->d_inode;
 185
 186         if (!realinode->i_op->readlink)
 187                 return -EINVAL;
 188
 189         old_cred = ovl_override_creds(dentry->d_sb);
 190         err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
 191         revert_creds(old_cred);
 192         return err;
 193 }
 194
 195 bool ovl_is_private_xattr(const char *name)
 196 {
 197         return strncmp(name, OVL_XATTR_PREFIX,
 198                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 199 }
 200
 201 int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
 202                   size_t size, int flags)
 203 {
 204         int err;
 205         struct path realpath;
 206         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 207         const struct cred *old_cred;
 208
 209         err = ovl_want_write(dentry);
 210         if (err)
 211                 goto out;
 212
 213         if (!value && !OVL_TYPE_UPPER(type)) {
 214                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 215                 if (err < 0)
 216                         goto out_drop_write;
 217         }
 218
 219         err = ovl_copy_up(dentry);
 220         if (err)
 221                 goto out_drop_write;
 222
 223         if (!OVL_TYPE_UPPER(type))
 224                 ovl_path_upper(dentry, &realpath);
 225
 226         old_cred = ovl_override_creds(dentry->d_sb);
 227         if (value)
 228                 err = vfs_setxattr(realpath.dentry, name, value, size, flags);
 229         else {
 230                 WARN_ON(flags != XATTR_REPLACE);
 231                 err = vfs_removexattr(realpath.dentry, name);
 232         }
 233         revert_creds(old_cred);
 234
 235 out_drop_write:
 236         ovl_drop_write(dentry);
 237 out:
 238         return err;
 239 }
 240
 241 int ovl_xattr_get(struct dentry *dentry, const char *name,
 242                   void *value, size_t size)
 243 {
 244         struct dentry *realdentry = ovl_dentry_real(dentry);
 245         ssize_t res;
 246         const struct cred *old_cred;
 247
 248         old_cred = ovl_override_creds(dentry->d_sb);
 249         res = vfs_getxattr(realdentry, name, value, size);
 250         revert_creds(old_cred);
 251         return res;
 252 }
 253
 254 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 255 {
 256         struct dentry *realdentry = ovl_dentry_real(dentry);
 257         ssize_t res;
 258         size_t len;
 259         char *s;
 260         const struct cred *old_cred;
 261
 262         old_cred = ovl_override_creds(dentry->d_sb);
 263         res = vfs_listxattr(realdentry, list, size);
 264         revert_creds(old_cred);
 265         if (res <= 0 || size == 0)
 266                 return res;
 267
 268         /* filter out private xattrs */
 269         for (s = list, len = res; len;) {
 270                 size_t slen = strnlen(s, len) + 1;
 271
 272                 /* underlying fs providing us with an broken xattr list? */
 273                 if (WARN_ON(slen > len))
 274                         return -EIO;
 275
 276                 len -= slen;
 277                 if (ovl_is_private_xattr(s)) {
 278                         res -= slen;
 279                         memmove(s, s + slen, len);
 280                 } else {
 281                         s += slen;
 282                 }
 283         }
 284
 285         return res;
 286 }
 287
 288 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 289 {
 290         struct inode *realinode = ovl_inode_real(inode, NULL);
 291         const struct cred *old_cred;
 292         struct posix_acl *acl;
 293
 294         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 295                 return NULL;
 296
 297         if (!realinode->i_op->get_acl)
 298                 return NULL;
 299
 300         old_cred = ovl_override_creds(inode->i_sb);
 301         acl = get_acl(realinode, type);
 302         revert_creds(old_cred);
 303
 304         return acl;
 305 }
 306
 307 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 308                                   struct dentry *realdentry)
 309 {
 310         if (OVL_TYPE_UPPER(type))
 311                 return false;
 312
 313         if (special_file(realdentry->d_inode->i_mode))
 314                 return false;
 315
 316         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 317                 return false;
 318
 319         return true;
 320 }
 321
 322 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 323 {
 324         int err = 0;
 325         struct path realpath;
 326         enum ovl_path_type type;
 327
 328         type = ovl_path_real(dentry, &realpath);
 329         if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 330                 err = ovl_want_write(dentry);
 331                 if (!err) {
 332                         if (file_flags & O_TRUNC)
 333                                 err = ovl_copy_up_truncate(dentry);
 334                         else
 335                                 err = ovl_copy_up(dentry);
 336                         ovl_drop_write(dentry);
 337                 }
 338         }
 339
 340         return err;
 341 }
 342
 343 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 344 {
 345         struct dentry *alias;
 346         struct path upperpath;
 347
 348         if (!(flags & S_ATIME))
 349                 return 0;
 350
 351         alias = d_find_any_alias(inode);
 352         if (!alias)
 353                 return 0;
 354
 355         ovl_path_upper(alias, &upperpath);
 356         if (upperpath.dentry) {
 357                 touch_atime(&upperpath);
 358                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 359         }
 360
 361         dput(alias);
 362
 363         return 0;
 364 }
 365
 366 static const struct inode_operations ovl_file_inode_operations = {
 367         .setattr        = ovl_setattr,
 368         .permission     = ovl_permission,
 369         .getattr        = ovl_getattr,
 370         .setxattr       = generic_setxattr,
 371         .getxattr       = generic_getxattr,
 372         .listxattr      = ovl_listxattr,
 373         .removexattr    = generic_removexattr,
 374         .get_acl        = ovl_get_acl,
 375         .update_time    = ovl_update_time,
 376 };
 377
 378 static const struct inode_operations ovl_symlink_inode_operations = {
 379         .setattr        = ovl_setattr,
 380         .get_link       = ovl_get_link,
 381         .readlink       = ovl_readlink,
 382         .getattr        = ovl_getattr,
 383         .setxattr       = generic_setxattr,
 384         .getxattr       = generic_getxattr,
 385         .listxattr      = ovl_listxattr,
 386         .removexattr    = generic_removexattr,
 387         .update_time    = ovl_update_time,
 388 };
 389
 390 static void ovl_fill_inode(struct inode *inode, umode_t mode)
 391 {
 392         inode->i_ino = get_next_ino();
 393         inode->i_mode = mode;
 394         inode->i_flags |= S_NOCMTIME;
 395 #ifdef CONFIG_FS_POSIX_ACL
 396         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
 397 #endif
 398
 399         mode &= S_IFMT;
 400         switch (mode) {
 401         case S_IFDIR:
 402                 inode->i_op = &ovl_dir_inode_operations;
 403                 inode->i_fop = &ovl_dir_operations;
 404                 break;
 405
 406         case S_IFLNK:
 407                 inode->i_op = &ovl_symlink_inode_operations;
 408                 break;
 409
 410         default:
 411                 WARN(1, "illegal file type: %i\n", mode);
 412                 /* Fall through */
 413
 414         case S_IFREG:
 415         case S_IFSOCK:
 416         case S_IFBLK:
 417         case S_IFCHR:
 418         case S_IFIFO:
 419                 inode->i_op = &ovl_file_inode_operations;
 420                 break;
 421         }
 422 }
 423
 424 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 425 {
 426         struct inode *inode;
 427
 428         inode = new_inode(sb);
 429         if (inode)
 430                 ovl_fill_inode(inode, mode);
 431
 432         return inode;
 433 }
 434
 435 static int ovl_inode_test(struct inode *inode, void *data)
 436 {
 437         return ovl_inode_real(inode, NULL) == data;
 438 }
 439
 440 static int ovl_inode_set(struct inode *inode, void *data)
 441 {
 442         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 443         return 0;
 444 }
 445
 446 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 447
 448 {
 449         struct inode *inode;
 450
 451         inode = iget5_locked(sb, (unsigned long) realinode,
 452                              ovl_inode_test, ovl_inode_set, realinode);
 453         if (inode && inode->i_state & I_NEW) {
 454                 ovl_fill_inode(inode, realinode->i_mode);
 455                 set_nlink(inode, realinode->i_nlink);
 456                 unlock_new_inode(inode);
 457         }
 458
 459         return inode;
 460 }