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 err = ovl_copy_up(dentry); 63 if (!err) { 64 upperdentry = ovl_dentry_upper(dentry); 65 66 inode_lock(upperdentry->d_inode); 67 err = notify_change(upperdentry, attr, NULL); 68 if (!err) 69 ovl_copyattr(upperdentry->d_inode, dentry->d_inode); 70 inode_unlock(upperdentry->d_inode); 71 } 72 ovl_drop_write(dentry); 73 out: 74 return err; 75 } 76 77 static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry, 78 struct kstat *stat) 79 { 80 struct path realpath; 81 82 ovl_path_real(dentry, &realpath); 83 return vfs_getattr(&realpath, stat); 84 } 85 86 int ovl_permission(struct inode *inode, int mask) 87 { 88 struct ovl_entry *oe; 89 struct dentry *alias = NULL; 90 struct inode *realinode; 91 struct dentry *realdentry; 92 bool is_upper; 93 int err; 94 95 if (S_ISDIR(inode->i_mode)) { 96 oe = inode->i_private; 97 } else if (mask & MAY_NOT_BLOCK) { 98 return -ECHILD; 99 } else { 100 /* 101 * For non-directories find an alias and get the info 102 * from there. 103 */ 104 alias = d_find_any_alias(inode); 105 if (WARN_ON(!alias)) 106 return -ENOENT; 107 108 oe = alias->d_fsdata; 109 } 110 111 realdentry = ovl_entry_real(oe, &is_upper); 112 113 if (ovl_is_default_permissions(inode)) { 114 struct kstat stat; 115 struct path realpath = { .dentry = realdentry }; 116 117 if (mask & MAY_NOT_BLOCK) 118 return -ECHILD; 119 120 realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper); 121 122 err = vfs_getattr(&realpath, &stat); 123 if (err) 124 return err; 125 126 if ((stat.mode ^ inode->i_mode) & S_IFMT) 127 return -ESTALE; 128 129 inode->i_mode = stat.mode; 130 inode->i_uid = stat.uid; 131 inode->i_gid = stat.gid; 132 133 return generic_permission(inode, mask); 134 } 135 136 /* Careful in RCU walk mode */ 137 realinode = ACCESS_ONCE(realdentry->d_inode); 138 if (!realinode) { 139 WARN_ON(!(mask & MAY_NOT_BLOCK)); 140 err = -ENOENT; 141 goto out_dput; 142 } 143 144 if (mask & MAY_WRITE) { 145 umode_t mode = realinode->i_mode; 146 147 /* 148 * Writes will always be redirected to upper layer, so 149 * ignore lower layer being read-only. 150 * 151 * If the overlay itself is read-only then proceed 152 * with the permission check, don't return EROFS. 153 * This will only happen if this is the lower layer of 154 * another overlayfs. 155 * 156 * If upper fs becomes read-only after the overlay was 157 * constructed return EROFS to prevent modification of 158 * upper layer. 159 */ 160 err = -EROFS; 161 if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) && 162 (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) 163 goto out_dput; 164 } 165 166 err = __inode_permission(realinode, mask); 167 out_dput: 168 dput(alias); 169 return err; 170 } 171 172 static const char *ovl_get_link(struct dentry *dentry, 173 struct inode *inode, 174 struct delayed_call *done) 175 { 176 struct dentry *realdentry; 177 struct inode *realinode; 178 179 if (!dentry) 180 return ERR_PTR(-ECHILD); 181 182 realdentry = ovl_dentry_real(dentry); 183 realinode = realdentry->d_inode; 184 185 if (WARN_ON(!realinode->i_op->get_link)) 186 return ERR_PTR(-EPERM); 187 188 return realinode->i_op->get_link(realdentry, realinode, done); 189 } 190 191 static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz) 192 { 193 struct path realpath; 194 struct inode *realinode; 195 196 ovl_path_real(dentry, &realpath); 197 realinode = realpath.dentry->d_inode; 198 199 if (!realinode->i_op->readlink) 200 return -EINVAL; 201 202 touch_atime(&realpath); 203 204 return realinode->i_op->readlink(realpath.dentry, buf, bufsiz); 205 } 206 207 208 static bool ovl_is_private_xattr(const char *name) 209 { 210 return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0; 211 } 212 213 int ovl_setxattr(struct dentry *dentry, struct inode *inode, 214 const char *name, const void *value, 215 size_t size, int flags) 216 { 217 int err; 218 struct dentry *upperdentry; 219 220 err = ovl_want_write(dentry); 221 if (err) 222 goto out; 223 224 err = -EPERM; 225 if (ovl_is_private_xattr(name)) 226 goto out_drop_write; 227 228 err = ovl_copy_up(dentry); 229 if (err) 230 goto out_drop_write; 231 232 upperdentry = ovl_dentry_upper(dentry); 233 err = vfs_setxattr(upperdentry, name, value, size, flags); 234 235 out_drop_write: 236 ovl_drop_write(dentry); 237 out: 238 return err; 239 } 240 241 ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode, 242 const char *name, void *value, size_t size) 243 { 244 struct dentry *realdentry = ovl_dentry_real(dentry); 245 246 if (ovl_is_private_xattr(name)) 247 return -ENODATA; 248 249 return vfs_getxattr(realdentry, name, value, size); 250 } 251 252 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size) 253 { 254 struct dentry *realdentry = ovl_dentry_real(dentry); 255 ssize_t res; 256 int off; 257 258 res = vfs_listxattr(realdentry, list, size); 259 if (res <= 0 || size == 0) 260 return res; 261 262 /* filter out private xattrs */ 263 for (off = 0; off < res;) { 264 char *s = list + off; 265 size_t slen = strlen(s) + 1; 266 267 BUG_ON(off + slen > res); 268 269 if (ovl_is_private_xattr(s)) { 270 res -= slen; 271 memmove(s, s + slen, res - off); 272 } else { 273 off += slen; 274 } 275 } 276 277 return res; 278 } 279 280 int ovl_removexattr(struct dentry *dentry, const char *name) 281 { 282 int err; 283 struct path realpath; 284 enum ovl_path_type type = ovl_path_real(dentry, &realpath); 285 286 err = ovl_want_write(dentry); 287 if (err) 288 goto out; 289 290 err = -ENODATA; 291 if (ovl_is_private_xattr(name)) 292 goto out_drop_write; 293 294 if (!OVL_TYPE_UPPER(type)) { 295 err = vfs_getxattr(realpath.dentry, name, NULL, 0); 296 if (err < 0) 297 goto out_drop_write; 298 299 err = ovl_copy_up(dentry); 300 if (err) 301 goto out_drop_write; 302 303 ovl_path_upper(dentry, &realpath); 304 } 305 306 err = vfs_removexattr(realpath.dentry, name); 307 out_drop_write: 308 ovl_drop_write(dentry); 309 out: 310 return err; 311 } 312 313 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type, 314 struct dentry *realdentry) 315 { 316 if (OVL_TYPE_UPPER(type)) 317 return false; 318 319 if (special_file(realdentry->d_inode->i_mode)) 320 return false; 321 322 if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC)) 323 return false; 324 325 return true; 326 } 327 328 struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags) 329 { 330 int err; 331 struct path realpath; 332 enum ovl_path_type type; 333 334 if (d_is_dir(dentry)) 335 return d_backing_inode(dentry); 336 337 type = ovl_path_real(dentry, &realpath); 338 if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) { 339 err = ovl_want_write(dentry); 340 if (err) 341 return ERR_PTR(err); 342 343 if (file_flags & O_TRUNC) 344 err = ovl_copy_up_truncate(dentry); 345 else 346 err = ovl_copy_up(dentry); 347 ovl_drop_write(dentry); 348 if (err) 349 return ERR_PTR(err); 350 351 ovl_path_upper(dentry, &realpath); 352 } 353 354 if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE) 355 return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags); 356 357 return d_backing_inode(realpath.dentry); 358 } 359 360 static const struct inode_operations ovl_file_inode_operations = { 361 .setattr = ovl_setattr, 362 .permission = ovl_permission, 363 .getattr = ovl_getattr, 364 .setxattr = ovl_setxattr, 365 .getxattr = ovl_getxattr, 366 .listxattr = ovl_listxattr, 367 .removexattr = ovl_removexattr, 368 }; 369 370 static const struct inode_operations ovl_symlink_inode_operations = { 371 .setattr = ovl_setattr, 372 .get_link = ovl_get_link, 373 .readlink = ovl_readlink, 374 .getattr = ovl_getattr, 375 .setxattr = ovl_setxattr, 376 .getxattr = ovl_getxattr, 377 .listxattr = ovl_listxattr, 378 .removexattr = ovl_removexattr, 379 }; 380 381 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, 382 struct ovl_entry *oe) 383 { 384 struct inode *inode; 385 386 inode = new_inode(sb); 387 if (!inode) 388 return NULL; 389 390 mode &= S_IFMT; 391 392 inode->i_ino = get_next_ino(); 393 inode->i_mode = mode; 394 inode->i_flags |= S_NOATIME | S_NOCMTIME; 395 396 switch (mode) { 397 case S_IFDIR: 398 inode->i_private = oe; 399 inode->i_op = &ovl_dir_inode_operations; 400 inode->i_fop = &ovl_dir_operations; 401 break; 402 403 case S_IFLNK: 404 inode->i_op = &ovl_symlink_inode_operations; 405 break; 406 407 case S_IFREG: 408 case S_IFSOCK: 409 case S_IFBLK: 410 case S_IFCHR: 411 case S_IFIFO: 412 inode->i_op = &ovl_file_inode_operations; 413 break; 414 415 default: 416 WARN(1, "illegal file type: %i\n", mode); 417 iput(inode); 418 inode = NULL; 419 } 420 421 return inode; 422 } 423