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 /* 46 * Check for permissions before trying to copy-up. This is redundant 47 * since it will be rechecked later by ->setattr() on upper dentry. But 48 * without this, copy-up can be triggered by just about anybody. 49 * 50 * We don't initialize inode->size, which just means that 51 * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not 52 * check for a swapfile (which this won't be anyway). 53 */ 54 err = inode_change_ok(dentry->d_inode, attr); 55 if (err) 56 return err; 57 58 err = ovl_want_write(dentry); 59 if (err) 60 goto out; 61 62 if (attr->ia_valid & ATTR_SIZE) { 63 struct inode *realinode = d_inode(ovl_dentry_real(dentry)); 64 65 err = -ETXTBSY; 66 if (atomic_read(&realinode->i_writecount) < 0) 67 goto out_drop_write; 68 } 69 70 err = ovl_copy_up(dentry); 71 if (!err) { 72 struct inode *winode = NULL; 73 74 upperdentry = ovl_dentry_upper(dentry); 75 76 if (attr->ia_valid & ATTR_SIZE) { 77 winode = d_inode(upperdentry); 78 err = get_write_access(winode); 79 if (err) 80 goto out_drop_write; 81 } 82 83 inode_lock(upperdentry->d_inode); 84 err = notify_change(upperdentry, attr, NULL); 85 if (!err) 86 ovl_copyattr(upperdentry->d_inode, dentry->d_inode); 87 inode_unlock(upperdentry->d_inode); 88 89 if (winode) 90 put_write_access(winode); 91 } 92 out_drop_write: 93 ovl_drop_write(dentry); 94 out: 95 return err; 96 } 97 98 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry, 99 struct kstat *stat) 100 { 101 struct path realpath; 102 103 ovl_path_real(dentry, &realpath); 104 return vfs_getattr(&realpath, stat); 105 } 106 107 int ovl_permission(struct inode *inode, int mask) 108 { 109 struct ovl_entry *oe; 110 struct dentry *alias = NULL; 111 struct inode *realinode; 112 struct dentry *realdentry; 113 bool is_upper; 114 int err; 115 116 if (S_ISDIR(inode->i_mode)) { 117 oe = inode->i_private; 118 } else if (mask & MAY_NOT_BLOCK) { 119 return -ECHILD; 120 } else { 121 /* 122 * For non-directories find an alias and get the info 123 * from there. 124 */ 125 alias = d_find_any_alias(inode); 126 if (WARN_ON(!alias)) 127 return -ENOENT; 128 129 oe = alias->d_fsdata; 130 } 131 132 realdentry = ovl_entry_real(oe, &is_upper); 133 134 if (ovl_is_default_permissions(inode)) { 135 struct kstat stat; 136 struct path realpath = { .dentry = realdentry }; 137 138 if (mask & MAY_NOT_BLOCK) 139 return -ECHILD; 140 141 realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper); 142 143 err = vfs_getattr(&realpath, &stat); 144 if (err) 145 goto out_dput; 146 147 err = -ESTALE; 148 if ((stat.mode ^ inode->i_mode) & S_IFMT) 149 goto out_dput; 150 151 inode->i_mode = stat.mode; 152 inode->i_uid = stat.uid; 153 inode->i_gid = stat.gid; 154 155 err = generic_permission(inode, mask); 156 goto out_dput; 157 } 158 159 /* Careful in RCU walk mode */ 160 realinode = ACCESS_ONCE(realdentry->d_inode); 161 if (!realinode) { 162 WARN_ON(!(mask & MAY_NOT_BLOCK)); 163 err = -ENOENT; 164 goto out_dput; 165 } 166 167 if (mask & MAY_WRITE) { 168 umode_t mode = realinode->i_mode; 169 170 /* 171 * Writes will always be redirected to upper layer, so 172 * ignore lower layer being read-only. 173 * 174 * If the overlay itself is read-only then proceed 175 * with the permission check, don't return EROFS. 176 * This will only happen if this is the lower layer of 177 * another overlayfs. 178 * 179 * If upper fs becomes read-only after the overlay was 180 * constructed return EROFS to prevent modification of 181 * upper layer. 182 */ 183 err = -EROFS; 184 if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) && 185 (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) 186 goto out_dput; 187 } 188 189 err = __inode_permission(realinode, mask); 190 out_dput: 191 dput(alias); 192 return err; 193 } 194 195 static const char *ovl_get_link(struct dentry *dentry, 196 struct inode *inode, 197 struct delayed_call *done) 198 { 199 struct dentry *realdentry; 200 struct inode *realinode; 201 202 if (!dentry) 203 return ERR_PTR(-ECHILD); 204 205 realdentry = ovl_dentry_real(dentry); 206 realinode = realdentry->d_inode; 207 208 if (WARN_ON(!realinode->i_op->get_link)) 209 return ERR_PTR(-EPERM); 210 211 return realinode->i_op->get_link(realdentry, realinode, done); 212 } 213 214 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz) 215 { 216 struct path realpath; 217 struct inode *realinode; 218 219 ovl_path_real(dentry, &realpath); 220 realinode = realpath.dentry->d_inode; 221 222 if (!realinode->i_op->readlink) 223 return -EINVAL; 224 225 touch_atime(&realpath); 226 227 return realinode->i_op->readlink(realpath.dentry, buf, bufsiz); 228 } 229 230 231 static bool ovl_is_private_xattr(const char *name) 232 { 233 return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0; 234 } 235 236 int ovl_setxattr(struct dentry *dentry, struct inode *inode, 237 const char *name, const void *value, 238 size_t size, int flags) 239 { 240 int err; 241 struct dentry *upperdentry; 242 243 err = ovl_want_write(dentry); 244 if (err) 245 goto out; 246 247 err = -EPERM; 248 if (ovl_is_private_xattr(name)) 249 goto out_drop_write; 250 251 err = ovl_copy_up(dentry); 252 if (err) 253 goto out_drop_write; 254 255 upperdentry = ovl_dentry_upper(dentry); 256 err = vfs_setxattr(upperdentry, name, value, size, flags); 257 258 out_drop_write: 259 ovl_drop_write(dentry); 260 out: 261 return err; 262 } 263 264 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode, 265 const char *name, void *value, size_t size) 266 { 267 struct dentry *realdentry = ovl_dentry_real(dentry); 268 269 if (ovl_is_private_xattr(name)) 270 return -ENODATA; 271 272 return vfs_getxattr(realdentry, name, value, size); 273 } 274 275 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size) 276 { 277 struct dentry *realdentry = ovl_dentry_real(dentry); 278 ssize_t res; 279 int off; 280 281 res = vfs_listxattr(realdentry, list, size); 282 if (res <= 0 || size == 0) 283 return res; 284 285 /* filter out private xattrs */ 286 for (off = 0; off < res;) { 287 char *s = list + off; 288 size_t slen = strlen(s) + 1; 289 290 BUG_ON(off + slen > res); 291 292 if (ovl_is_private_xattr(s)) { 293 res -= slen; 294 memmove(s, s + slen, res - off); 295 } else { 296 off += slen; 297 } 298 } 299 300 return res; 301 } 302 303 int ovl_removexattr(struct dentry *dentry, const char *name) 304 { 305 int err; 306 struct path realpath; 307 enum ovl_path_type type = ovl_path_real(dentry, &realpath); 308 309 err = ovl_want_write(dentry); 310 if (err) 311 goto out; 312 313 err = -ENODATA; 314 if (ovl_is_private_xattr(name)) 315 goto out_drop_write; 316 317 if (!OVL_TYPE_UPPER(type)) { 318 err = vfs_getxattr(realpath.dentry, name, NULL, 0); 319 if (err < 0) 320 goto out_drop_write; 321 322 err = ovl_copy_up(dentry); 323 if (err) 324 goto out_drop_write; 325 326 ovl_path_upper(dentry, &realpath); 327 } 328 329 err = vfs_removexattr(realpath.dentry, name); 330 out_drop_write: 331 ovl_drop_write(dentry); 332 out: 333 return err; 334 } 335 336 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type, 337 struct dentry *realdentry) 338 { 339 if (OVL_TYPE_UPPER(type)) 340 return false; 341 342 if (special_file(realdentry->d_inode->i_mode)) 343 return false; 344 345 if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC)) 346 return false; 347 348 return true; 349 } 350 351 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags) 352 { 353 int err; 354 struct path realpath; 355 enum ovl_path_type type; 356 357 if (d_is_dir(dentry)) 358 return d_backing_inode(dentry); 359 360 type = ovl_path_real(dentry, &realpath); 361 if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) { 362 err = ovl_want_write(dentry); 363 if (err) 364 return ERR_PTR(err); 365 366 if (file_flags & O_TRUNC) 367 err = ovl_copy_up_truncate(dentry); 368 else 369 err = ovl_copy_up(dentry); 370 ovl_drop_write(dentry); 371 if (err) 372 return ERR_PTR(err); 373 374 ovl_path_upper(dentry, &realpath); 375 } 376 377 if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE) 378 return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags); 379 380 return d_backing_inode(realpath.dentry); 381 } 382 383 static const struct inode_operations ovl_file_inode_operations = { 384 .setattr = ovl_setattr, 385 .permission = ovl_permission, 386 .getattr = ovl_getattr, 387 .setxattr = ovl_setxattr, 388 .getxattr = ovl_getxattr, 389 .listxattr = ovl_listxattr, 390 .removexattr = ovl_removexattr, 391 }; 392 393 static const struct inode_operations ovl_symlink_inode_operations = { 394 .setattr = ovl_setattr, 395 .get_link = ovl_get_link, 396 .readlink = ovl_readlink, 397 .getattr = ovl_getattr, 398 .setxattr = ovl_setxattr, 399 .getxattr = ovl_getxattr, 400 .listxattr = ovl_listxattr, 401 .removexattr = ovl_removexattr, 402 }; 403 404 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, 405 struct ovl_entry *oe) 406 { 407 struct inode *inode; 408 409 inode = new_inode(sb); 410 if (!inode) 411 return NULL; 412 413 mode &= S_IFMT; 414 415 inode->i_ino = get_next_ino(); 416 inode->i_mode = mode; 417 inode->i_flags |= S_NOATIME | S_NOCMTIME; 418 419 switch (mode) { 420 case S_IFDIR: 421 inode->i_private = oe; 422 inode->i_op = &ovl_dir_inode_operations; 423 inode->i_fop = &ovl_dir_operations; 424 break; 425 426 case S_IFLNK: 427 inode->i_op = &ovl_symlink_inode_operations; 428 break; 429 430 case S_IFREG: 431 case S_IFSOCK: 432 case S_IFBLK: 433 case S_IFCHR: 434 case S_IFIFO: 435 inode->i_op = &ovl_file_inode_operations; 436 break; 437 438 default: 439 WARN(1, "illegal file type: %i\n", mode); 440 iput(inode); 441 inode = NULL; 442 } 443 444 return inode; 445 } 446