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         const struct cred *old_cred;
  23
  24         parent = dget_parent(dentry);
  25         err = ovl_copy_up(parent);
  26         if (err)
  27                 goto out_dput_parent;
  28
  29         ovl_path_lower(dentry, &lowerpath);
  30
  31         old_cred = ovl_override_creds(dentry->d_sb);
  32         err = vfs_getattr(&lowerpath, &stat);
  33         if (!err) {
  34                 stat.size = 0;
  35                 err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
  36         }
  37         revert_creds(old_cred);
  38
  39 out_dput_parent:
  40         dput(parent);
  41         return err;
  42 }
  43
  44 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
  45 {
  46         int err;
  47         struct dentry *upperdentry;
  48         const struct cred *old_cred;
  49
  50         /*
  51          * Check for permissions before trying to copy-up.  This is redundant
  52          * since it will be rechecked later by ->setattr() on upper dentry.  But
  53          * without this, copy-up can be triggered by just about anybody.
  54          *
  55          * We don't initialize inode->size, which just means that
  56          * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
  57          * check for a swapfile (which this won't be anyway).
  58          */
  59         err = setattr_prepare(dentry, attr);
  60         if (err)
  61                 return err;
  62
  63         err = ovl_want_write(dentry);
  64         if (err)
  65                 goto out;
  66
  67         if (attr->ia_valid & ATTR_SIZE) {
  68                 struct inode *realinode = d_inode(ovl_dentry_real(dentry));
  69
  70                 err = -ETXTBSY;
  71                 if (atomic_read(&realinode->i_writecount) < 0)
  72                         goto out_drop_write;
  73         }
  74
  75         err = ovl_copy_up(dentry);
  76         if (!err) {
  77                 struct inode *winode = NULL;
  78
  79                 upperdentry = ovl_dentry_upper(dentry);
  80
  81                 if (attr->ia_valid & ATTR_SIZE) {
  82                         winode = d_inode(upperdentry);
  83                         err = get_write_access(winode);
  84                         if (err)
  85                                 goto out_drop_write;
  86                 }
  87
  88                 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
  89                         attr->ia_valid &= ~ATTR_MODE;
  90
  91                 inode_lock(upperdentry->d_inode);
  92                 old_cred = ovl_override_creds(dentry->d_sb);
  93                 err = notify_change(upperdentry, attr, NULL);
  94                 revert_creds(old_cred);
  95                 if (!err)
  96                         ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
  97                 inode_unlock(upperdentry->d_inode);
  98
  99                 if (winode)
 100                         put_write_access(winode);
 101         }
 102 out_drop_write:
 103         ovl_drop_write(dentry);
 104 out:
 105         return err;
 106 }
 107
 108 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 109                          struct kstat *stat)
 110 {
 111         struct path realpath;
 112         const struct cred *old_cred;
 113         int err;
 114
 115         ovl_path_real(dentry, &realpath);
 116         old_cred = ovl_override_creds(dentry->d_sb);
 117         err = vfs_getattr(&realpath, stat);
 118         revert_creds(old_cred);
 119         return err;
 120 }
 121
 122 int ovl_permission(struct inode *inode, int mask)
 123 {
 124         bool is_upper;
 125         struct inode *realinode = ovl_inode_real(inode, &is_upper);
 126         const struct cred *old_cred;
 127         int err;
 128
 129         /* Careful in RCU walk mode */
 130         if (!realinode) {
 131                 WARN_ON(!(mask & MAY_NOT_BLOCK));
 132                 return -ECHILD;
 133         }
 134
 135         /*
 136          * Check overlay inode with the creds of task and underlying inode
 137          * with creds of mounter
 138          */
 139         err = generic_permission(inode, mask);
 140         if (err)
 141                 return err;
 142
 143         old_cred = ovl_override_creds(inode->i_sb);
 144         if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) {
 145                 mask &= ~(MAY_WRITE | MAY_APPEND);
 146                 /* Make sure mounter can read file for copy up later */
 147                 mask |= MAY_READ;
 148         }
 149         err = inode_permission(realinode, mask);
 150         revert_creds(old_cred);
 151
 152         return err;
 153 }
 154
 155 static const char *ovl_get_link(struct dentry *dentry,
 156                                 struct inode *inode,
 157                                 struct delayed_call *done)
 158 {
 159         const struct cred *old_cred;
 160         const char *p;
 161
 162         if (!dentry)
 163                 return ERR_PTR(-ECHILD);
 164
 165         old_cred = ovl_override_creds(dentry->d_sb);
 166         p = vfs_get_link(ovl_dentry_real(dentry), done);
 167         revert_creds(old_cred);
 168         return p;
 169 }
 170
 171 bool ovl_is_private_xattr(const char *name)
 172 {
 173         return strncmp(name, OVL_XATTR_PREFIX,
 174                        sizeof(OVL_XATTR_PREFIX) - 1) == 0;
 175 }
 176
 177 int ovl_xattr_set(struct dentry *dentry, const char *name, const void *value,
 178                   size_t size, int flags)
 179 {
 180         int err;
 181         struct path realpath;
 182         enum ovl_path_type type = ovl_path_real(dentry, &realpath);
 183         const struct cred *old_cred;
 184
 185         err = ovl_want_write(dentry);
 186         if (err)
 187                 goto out;
 188
 189         if (!value && !OVL_TYPE_UPPER(type)) {
 190                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
 191                 if (err < 0)
 192                         goto out_drop_write;
 193         }
 194
 195         err = ovl_copy_up(dentry);
 196         if (err)
 197                 goto out_drop_write;
 198
 199         if (!OVL_TYPE_UPPER(type))
 200                 ovl_path_upper(dentry, &realpath);
 201
 202         old_cred = ovl_override_creds(dentry->d_sb);
 203         if (value)
 204                 err = vfs_setxattr(realpath.dentry, name, value, size, flags);
 205         else {
 206                 WARN_ON(flags != XATTR_REPLACE);
 207                 err = vfs_removexattr(realpath.dentry, name);
 208         }
 209         revert_creds(old_cred);
 210
 211 out_drop_write:
 212         ovl_drop_write(dentry);
 213 out:
 214         return err;
 215 }
 216
 217 int ovl_xattr_get(struct dentry *dentry, const char *name,
 218                   void *value, size_t size)
 219 {
 220         struct dentry *realdentry = ovl_dentry_real(dentry);
 221         ssize_t res;
 222         const struct cred *old_cred;
 223
 224         old_cred = ovl_override_creds(dentry->d_sb);
 225         res = vfs_getxattr(realdentry, name, value, size);
 226         revert_creds(old_cred);
 227         return res;
 228 }
 229
 230 static bool ovl_can_list(const char *s)
 231 {
 232         /* List all non-trusted xatts */
 233         if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
 234                 return true;
 235
 236         /* Never list trusted.overlay, list other trusted for superuser only */
 237         return !ovl_is_private_xattr(s) &&
 238                ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
 239 }
 240
 241 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 242 {
 243         struct dentry *realdentry = ovl_dentry_real(dentry);
 244         ssize_t res;
 245         size_t len;
 246         char *s;
 247         const struct cred *old_cred;
 248
 249         old_cred = ovl_override_creds(dentry->d_sb);
 250         res = vfs_listxattr(realdentry, list, size);
 251         revert_creds(old_cred);
 252         if (res <= 0 || size == 0)
 253                 return res;
 254
 255         /* filter out private xattrs */
 256         for (s = list, len = res; len;) {
 257                 size_t slen = strnlen(s, len) + 1;
 258
 259                 /* underlying fs providing us with an broken xattr list? */
 260                 if (WARN_ON(slen > len))
 261                         return -EIO;
 262
 263                 len -= slen;
 264                 if (!ovl_can_list(s)) {
 265                         res -= slen;
 266                         memmove(s, s + slen, len);
 267                 } else {
 268                         s += slen;
 269                 }
 270         }
 271
 272         return res;
 273 }
 274
 275 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 276 {
 277         struct inode *realinode = ovl_inode_real(inode, NULL);
 278         const struct cred *old_cred;
 279         struct posix_acl *acl;
 280
 281         if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 282                 return NULL;
 283
 284         old_cred = ovl_override_creds(inode->i_sb);
 285         acl = get_acl(realinode, type);
 286         revert_creds(old_cred);
 287
 288         return acl;
 289 }
 290
 291 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 292                                   struct dentry *realdentry)
 293 {
 294         if (OVL_TYPE_UPPER(type))
 295                 return false;
 296
 297         if (special_file(realdentry->d_inode->i_mode))
 298                 return false;
 299
 300         if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
 301                 return false;
 302
 303         return true;
 304 }
 305
 306 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 307 {
 308         int err = 0;
 309         struct path realpath;
 310         enum ovl_path_type type;
 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                         if (file_flags & O_TRUNC)
 317                                 err = ovl_copy_up_truncate(dentry);
 318                         else
 319                                 err = ovl_copy_up(dentry);
 320                         ovl_drop_write(dentry);
 321                 }
 322         }
 323
 324         return err;
 325 }
 326
 327 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags)
 328 {
 329         struct dentry *alias;
 330         struct path upperpath;
 331
 332         if (!(flags & S_ATIME))
 333                 return 0;
 334
 335         alias = d_find_any_alias(inode);
 336         if (!alias)
 337                 return 0;
 338
 339         ovl_path_upper(alias, &upperpath);
 340         if (upperpath.dentry) {
 341                 touch_atime(&upperpath);
 342                 inode->i_atime = d_inode(upperpath.dentry)->i_atime;
 343         }
 344
 345         dput(alias);
 346
 347         return 0;
 348 }
 349
 350 static const struct inode_operations ovl_file_inode_operations = {
 351         .setattr        = ovl_setattr,
 352         .permission     = ovl_permission,
 353         .getattr        = ovl_getattr,
 354         .listxattr      = ovl_listxattr,
 355         .get_acl        = ovl_get_acl,
 356         .update_time    = ovl_update_time,
 357 };
 358
 359 static const struct inode_operations ovl_symlink_inode_operations = {
 360         .setattr        = ovl_setattr,
 361         .get_link       = ovl_get_link,
 362         .readlink       = generic_readlink,
 363         .getattr        = ovl_getattr,
 364         .listxattr      = ovl_listxattr,
 365         .update_time    = ovl_update_time,
 366 };
 367
 368 static void ovl_fill_inode(struct inode *inode, umode_t mode)
 369 {
 370         inode->i_ino = get_next_ino();
 371         inode->i_mode = mode;
 372         inode->i_flags |= S_NOCMTIME;
 373 #ifdef CONFIG_FS_POSIX_ACL
 374         inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
 375 #endif
 376
 377         mode &= S_IFMT;
 378         switch (mode) {
 379         case S_IFDIR:
 380                 inode->i_op = &ovl_dir_inode_operations;
 381                 inode->i_fop = &ovl_dir_operations;
 382                 break;
 383
 384         case S_IFLNK:
 385                 inode->i_op = &ovl_symlink_inode_operations;
 386                 break;
 387
 388         default:
 389                 WARN(1, "illegal file type: %i\n", mode);
 390                 /* Fall through */
 391
 392         case S_IFREG:
 393         case S_IFSOCK:
 394         case S_IFBLK:
 395         case S_IFCHR:
 396         case S_IFIFO:
 397                 inode->i_op = &ovl_file_inode_operations;
 398                 break;
 399         }
 400 }
 401
 402 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 403 {
 404         struct inode *inode;
 405
 406         inode = new_inode(sb);
 407         if (inode)
 408                 ovl_fill_inode(inode, mode);
 409
 410         return inode;
 411 }
 412
 413 static int ovl_inode_test(struct inode *inode, void *data)
 414 {
 415         return ovl_inode_real(inode, NULL) == data;
 416 }
 417
 418 static int ovl_inode_set(struct inode *inode, void *data)
 419 {
 420         inode->i_private = (void *) (((unsigned long) data) | OVL_ISUPPER_MASK);
 421         return 0;
 422 }
 423
 424 struct inode *ovl_get_inode(struct super_block *sb, struct inode *realinode)
 425
 426 {
 427         struct inode *inode;
 428
 429         inode = iget5_locked(sb, (unsigned long) realinode,
 430                              ovl_inode_test, ovl_inode_set, realinode);
 431         if (inode && inode->i_state & I_NEW) {
 432                 ovl_fill_inode(inode, realinode->i_mode);
 433                 set_nlink(inode, realinode->i_nlink);
 434                 unlock_new_inode(inode);
 435         }
 436
 437         return inode;
 438 }