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 if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) 84 attr->ia_valid &= ~ATTR_MODE; 85 86 inode_lock(upperdentry->d_inode); 87 err = notify_change(upperdentry, attr, NULL); 88 if (!err) 89 ovl_copyattr(upperdentry->d_inode, dentry->d_inode); 90 inode_unlock(upperdentry->d_inode); 91 92 if (winode) 93 put_write_access(winode); 94 } 95 out_drop_write: 96 ovl_drop_write(dentry); 97 out: 98 return err; 99 } 100 101 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry, 102 struct kstat *stat) 103 { 104 struct path realpath; 105 106 ovl_path_real(dentry, &realpath); 107 return vfs_getattr(&realpath, stat); 108 } 109 110 int ovl_permission(struct inode *inode, int mask) 111 { 112 struct ovl_entry *oe; 113 struct dentry *alias = NULL; 114 struct inode *realinode; 115 struct dentry *realdentry; 116 bool is_upper; 117 int err; 118 119 if (S_ISDIR(inode->i_mode)) { 120 oe = inode->i_private; 121 } else if (mask & MAY_NOT_BLOCK) { 122 return -ECHILD; 123 } else { 124 /* 125 * For non-directories find an alias and get the info 126 * from there. 127 */ 128 alias = d_find_any_alias(inode); 129 if (WARN_ON(!alias)) 130 return -ENOENT; 131 132 oe = alias->d_fsdata; 133 } 134 135 realdentry = ovl_entry_real(oe, &is_upper); 136 137 if (ovl_is_default_permissions(inode)) { 138 struct kstat stat; 139 struct path realpath = { .dentry = realdentry }; 140 141 if (mask & MAY_NOT_BLOCK) 142 return -ECHILD; 143 144 realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper); 145 146 err = vfs_getattr(&realpath, &stat); 147 if (err) 148 goto out_dput; 149 150 err = -ESTALE; 151 if ((stat.mode ^ inode->i_mode) & S_IFMT) 152 goto out_dput; 153 154 inode->i_mode = stat.mode; 155 inode->i_uid = stat.uid; 156 inode->i_gid = stat.gid; 157 158 err = generic_permission(inode, mask); 159 goto out_dput; 160 } 161 162 /* Careful in RCU walk mode */ 163 realinode = ACCESS_ONCE(realdentry->d_inode); 164 if (!realinode) { 165 WARN_ON(!(mask & MAY_NOT_BLOCK)); 166 err = -ENOENT; 167 goto out_dput; 168 } 169 170 if (mask & MAY_WRITE) { 171 umode_t mode = realinode->i_mode; 172 173 /* 174 * Writes will always be redirected to upper layer, so 175 * ignore lower layer being read-only. 176 * 177 * If the overlay itself is read-only then proceed 178 * with the permission check, don't return EROFS. 179 * This will only happen if this is the lower layer of 180 * another overlayfs. 181 * 182 * If upper fs becomes read-only after the overlay was 183 * constructed return EROFS to prevent modification of 184 * upper layer. 185 */ 186 err = -EROFS; 187 if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) && 188 (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) 189 goto out_dput; 190 } 191 192 err = __inode_permission(realinode, mask); 193 out_dput: 194 dput(alias); 195 return err; 196 } 197 198 static const char *ovl_get_link(struct dentry *dentry, 199 struct inode *inode, 200 struct delayed_call *done) 201 { 202 struct dentry *realdentry; 203 struct inode *realinode; 204 205 if (!dentry) 206 return ERR_PTR(-ECHILD); 207 208 realdentry = ovl_dentry_real(dentry); 209 realinode = realdentry->d_inode; 210 211 if (WARN_ON(!realinode->i_op->get_link)) 212 return ERR_PTR(-EPERM); 213 214 return realinode->i_op->get_link(realdentry, realinode, done); 215 } 216 217 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz) 218 { 219 struct path realpath; 220 struct inode *realinode; 221 222 ovl_path_real(dentry, &realpath); 223 realinode = realpath.dentry->d_inode; 224 225 if (!realinode->i_op->readlink) 226 return -EINVAL; 227 228 touch_atime(&realpath); 229 230 return realinode->i_op->readlink(realpath.dentry, buf, bufsiz); 231 } 232 233 234 static bool ovl_is_private_xattr(const char *name) 235 { 236 return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0; 237 } 238 239 int ovl_setxattr(struct dentry *dentry, struct inode *inode, 240 const char *name, const void *value, 241 size_t size, int flags) 242 { 243 int err; 244 struct dentry *upperdentry; 245 246 err = ovl_want_write(dentry); 247 if (err) 248 goto out; 249 250 err = -EPERM; 251 if (ovl_is_private_xattr(name)) 252 goto out_drop_write; 253 254 err = ovl_copy_up(dentry); 255 if (err) 256 goto out_drop_write; 257 258 upperdentry = ovl_dentry_upper(dentry); 259 err = vfs_setxattr(upperdentry, name, value, size, flags); 260 261 out_drop_write: 262 ovl_drop_write(dentry); 263 out: 264 return err; 265 } 266 267 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode, 268 const char *name, void *value, size_t size) 269 { 270 struct dentry *realdentry = ovl_dentry_real(dentry); 271 272 if (ovl_is_private_xattr(name)) 273 return -ENODATA; 274 275 return vfs_getxattr(realdentry, name, value, size); 276 } 277 278 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size) 279 { 280 struct dentry *realdentry = ovl_dentry_real(dentry); 281 ssize_t res; 282 int off; 283 284 res = vfs_listxattr(realdentry, list, size); 285 if (res <= 0 || size == 0) 286 return res; 287 288 /* filter out private xattrs */ 289 for (off = 0; off < res;) { 290 char *s = list + off; 291 size_t slen = strlen(s) + 1; 292 293 BUG_ON(off + slen > res); 294 295 if (ovl_is_private_xattr(s)) { 296 res -= slen; 297 memmove(s, s + slen, res - off); 298 } else { 299 off += slen; 300 } 301 } 302 303 return res; 304 } 305 306 int ovl_removexattr(struct dentry *dentry, const char *name) 307 { 308 int err; 309 struct path realpath; 310 enum ovl_path_type type = ovl_path_real(dentry, &realpath); 311 312 err = ovl_want_write(dentry); 313 if (err) 314 goto out; 315 316 err = -ENODATA; 317 if (ovl_is_private_xattr(name)) 318 goto out_drop_write; 319 320 if (!OVL_TYPE_UPPER(type)) { 321 err = vfs_getxattr(realpath.dentry, name, NULL, 0); 322 if (err < 0) 323 goto out_drop_write; 324 325 err = ovl_copy_up(dentry); 326 if (err) 327 goto out_drop_write; 328 329 ovl_path_upper(dentry, &realpath); 330 } 331 332 err = vfs_removexattr(realpath.dentry, name); 333 out_drop_write: 334 ovl_drop_write(dentry); 335 out: 336 return err; 337 } 338 339 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type, 340 struct dentry *realdentry) 341 { 342 if (OVL_TYPE_UPPER(type)) 343 return false; 344 345 if (special_file(realdentry->d_inode->i_mode)) 346 return false; 347 348 if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC)) 349 return false; 350 351 return true; 352 } 353 354 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags) 355 { 356 int err; 357 struct path realpath; 358 enum ovl_path_type type; 359 360 if (d_is_dir(dentry)) 361 return d_backing_inode(dentry); 362 363 type = ovl_path_real(dentry, &realpath); 364 if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) { 365 err = ovl_want_write(dentry); 366 if (err) 367 return ERR_PTR(err); 368 369 if (file_flags & O_TRUNC) 370 err = ovl_copy_up_truncate(dentry); 371 else 372 err = ovl_copy_up(dentry); 373 ovl_drop_write(dentry); 374 if (err) 375 return ERR_PTR(err); 376 377 ovl_path_upper(dentry, &realpath); 378 } 379 380 if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE) 381 return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags); 382 383 return d_backing_inode(realpath.dentry); 384 } 385 386 static const struct inode_operations ovl_file_inode_operations = { 387 .setattr = ovl_setattr, 388 .permission = ovl_permission, 389 .getattr = ovl_getattr, 390 .setxattr = ovl_setxattr, 391 .getxattr = ovl_getxattr, 392 .listxattr = ovl_listxattr, 393 .removexattr = ovl_removexattr, 394 }; 395 396 static const struct inode_operations ovl_symlink_inode_operations = { 397 .setattr = ovl_setattr, 398 .get_link = ovl_get_link, 399 .readlink = ovl_readlink, 400 .getattr = ovl_getattr, 401 .setxattr = ovl_setxattr, 402 .getxattr = ovl_getxattr, 403 .listxattr = ovl_listxattr, 404 .removexattr = ovl_removexattr, 405 }; 406 407 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, 408 struct ovl_entry *oe) 409 { 410 struct inode *inode; 411 412 inode = new_inode(sb); 413 if (!inode) 414 return NULL; 415 416 inode->i_ino = get_next_ino(); 417 inode->i_mode = mode; 418 inode->i_flags |= S_NOATIME | S_NOCMTIME; 419 420 mode &= S_IFMT; 421 switch (mode) { 422 case S_IFDIR: 423 inode->i_private = oe; 424 inode->i_op = &ovl_dir_inode_operations; 425 inode->i_fop = &ovl_dir_operations; 426 break; 427 428 case S_IFLNK: 429 inode->i_op = &ovl_symlink_inode_operations; 430 break; 431 432 case S_IFREG: 433 case S_IFSOCK: 434 case S_IFBLK: 435 case S_IFCHR: 436 case S_IFIFO: 437 inode->i_op = &ovl_file_inode_operations; 438 break; 439 440 default: 441 WARN(1, "illegal file type: %i\n", mode); 442 iput(inode); 443 inode = NULL; 444 } 445 446 return inode; 447 } 448