1 /* 2 * Copyright (C) 2011 Novell Inc. 3 * Copyright (C) 2016 Red Hat, 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/cred.h> 12 #include <linux/namei.h> 13 #include <linux/xattr.h> 14 #include <linux/ratelimit.h> 15 #include "overlayfs.h" 16 #include "ovl_entry.h" 17 18 struct ovl_lookup_data { 19 struct qstr name; 20 bool is_dir; 21 bool opaque; 22 bool stop; 23 bool last; 24 char *redirect; 25 }; 26 27 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d, 28 size_t prelen, const char *post) 29 { 30 int res; 31 char *s, *next, *buf = NULL; 32 33 res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0); 34 if (res < 0) { 35 if (res == -ENODATA || res == -EOPNOTSUPP) 36 return 0; 37 goto fail; 38 } 39 buf = kzalloc(prelen + res + strlen(post) + 1, GFP_TEMPORARY); 40 if (!buf) 41 return -ENOMEM; 42 43 if (res == 0) 44 goto invalid; 45 46 res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res); 47 if (res < 0) 48 goto fail; 49 if (res == 0) 50 goto invalid; 51 if (buf[0] == '/') { 52 for (s = buf; *s++ == '/'; s = next) { 53 next = strchrnul(s, '/'); 54 if (s == next) 55 goto invalid; 56 } 57 } else { 58 if (strchr(buf, '/') != NULL) 59 goto invalid; 60 61 memmove(buf + prelen, buf, res); 62 memcpy(buf, d->name.name, prelen); 63 } 64 65 strcat(buf, post); 66 kfree(d->redirect); 67 d->redirect = buf; 68 d->name.name = d->redirect; 69 d->name.len = strlen(d->redirect); 70 71 return 0; 72 73 err_free: 74 kfree(buf); 75 return 0; 76 fail: 77 pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res); 78 goto err_free; 79 invalid: 80 pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf); 81 goto err_free; 82 } 83 84 static bool ovl_is_opaquedir(struct dentry *dentry) 85 { 86 int res; 87 char val; 88 89 if (!d_is_dir(dentry)) 90 return false; 91 92 res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1); 93 if (res == 1 && val == 'y') 94 return true; 95 96 return false; 97 } 98 99 static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d, 100 const char *name, unsigned int namelen, 101 size_t prelen, const char *post, 102 struct dentry **ret) 103 { 104 struct dentry *this; 105 int err; 106 107 this = lookup_one_len_unlocked(name, base, namelen); 108 if (IS_ERR(this)) { 109 err = PTR_ERR(this); 110 this = NULL; 111 if (err == -ENOENT || err == -ENAMETOOLONG) 112 goto out; 113 goto out_err; 114 } 115 if (!this->d_inode) 116 goto put_and_out; 117 118 if (ovl_dentry_weird(this)) { 119 /* Don't support traversing automounts and other weirdness */ 120 err = -EREMOTE; 121 goto out_err; 122 } 123 if (ovl_is_whiteout(this)) { 124 d->stop = d->opaque = true; 125 goto put_and_out; 126 } 127 if (!d_can_lookup(this)) { 128 d->stop = true; 129 if (d->is_dir) 130 goto put_and_out; 131 goto out; 132 } 133 d->is_dir = true; 134 if (!d->last && ovl_is_opaquedir(this)) { 135 d->stop = d->opaque = true; 136 goto out; 137 } 138 err = ovl_check_redirect(this, d, prelen, post); 139 if (err) 140 goto out_err; 141 out: 142 *ret = this; 143 return 0; 144 145 put_and_out: 146 dput(this); 147 this = NULL; 148 goto out; 149 150 out_err: 151 dput(this); 152 return err; 153 } 154 155 static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d, 156 struct dentry **ret) 157 { 158 /* Counting down from the end, since the prefix can change */ 159 size_t rem = d->name.len - 1; 160 struct dentry *dentry = NULL; 161 int err; 162 163 if (d->name.name[0] != '/') 164 return ovl_lookup_single(base, d, d->name.name, d->name.len, 165 0, "", ret); 166 167 while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) { 168 const char *s = d->name.name + d->name.len - rem; 169 const char *next = strchrnul(s, '/'); 170 size_t thislen = next - s; 171 bool end = !next[0]; 172 173 /* Verify we did not go off the rails */ 174 if (WARN_ON(s[-1] != '/')) 175 return -EIO; 176 177 err = ovl_lookup_single(base, d, s, thislen, 178 d->name.len - rem, next, &base); 179 dput(dentry); 180 if (err) 181 return err; 182 dentry = base; 183 if (end) 184 break; 185 186 rem -= thislen + 1; 187 188 if (WARN_ON(rem >= d->name.len)) 189 return -EIO; 190 } 191 *ret = dentry; 192 return 0; 193 } 194 195 /* 196 * Returns next layer in stack starting from top. 197 * Returns -1 if this is the last layer. 198 */ 199 int ovl_path_next(int idx, struct dentry *dentry, struct path *path) 200 { 201 struct ovl_entry *oe = dentry->d_fsdata; 202 203 BUG_ON(idx < 0); 204 if (idx == 0) { 205 ovl_path_upper(dentry, path); 206 if (path->dentry) 207 return oe->numlower ? 1 : -1; 208 idx++; 209 } 210 BUG_ON(idx > oe->numlower); 211 *path = oe->lowerstack[idx - 1]; 212 213 return (idx < oe->numlower) ? idx + 1 : -1; 214 } 215 216 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, 217 unsigned int flags) 218 { 219 struct ovl_entry *oe; 220 const struct cred *old_cred; 221 struct ovl_fs *ofs = dentry->d_sb->s_fs_info; 222 struct ovl_entry *poe = dentry->d_parent->d_fsdata; 223 struct path *stack = NULL; 224 struct dentry *upperdir, *upperdentry = NULL; 225 unsigned int ctr = 0; 226 struct inode *inode = NULL; 227 bool upperopaque = false; 228 char *upperredirect = NULL; 229 struct dentry *this; 230 unsigned int i; 231 int err; 232 struct ovl_lookup_data d = { 233 .name = dentry->d_name, 234 .is_dir = false, 235 .opaque = false, 236 .stop = false, 237 .last = !poe->numlower, 238 .redirect = NULL, 239 }; 240 241 if (dentry->d_name.len > ofs->namelen) 242 return ERR_PTR(-ENAMETOOLONG); 243 244 old_cred = ovl_override_creds(dentry->d_sb); 245 upperdir = ovl_upperdentry_dereference(poe); 246 if (upperdir) { 247 err = ovl_lookup_layer(upperdir, &d, &upperdentry); 248 if (err) 249 goto out; 250 251 if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) { 252 dput(upperdentry); 253 err = -EREMOTE; 254 goto out; 255 } 256 257 if (d.redirect) { 258 upperredirect = kstrdup(d.redirect, GFP_KERNEL); 259 if (!upperredirect) 260 goto out_put_upper; 261 if (d.redirect[0] == '/') 262 poe = dentry->d_sb->s_root->d_fsdata; 263 } 264 upperopaque = d.opaque; 265 } 266 267 if (!d.stop && poe->numlower) { 268 err = -ENOMEM; 269 stack = kcalloc(ofs->numlower, sizeof(struct path), 270 GFP_TEMPORARY); 271 if (!stack) 272 goto out_put_upper; 273 } 274 275 for (i = 0; !d.stop && i < poe->numlower; i++) { 276 struct path lowerpath = poe->lowerstack[i]; 277 278 d.last = i == poe->numlower - 1; 279 err = ovl_lookup_layer(lowerpath.dentry, &d, &this); 280 if (err) 281 goto out_put; 282 283 if (!this) 284 continue; 285 286 stack[ctr].dentry = this; 287 stack[ctr].mnt = lowerpath.mnt; 288 ctr++; 289 290 if (d.stop) 291 break; 292 293 if (d.redirect && 294 d.redirect[0] == '/' && 295 poe != dentry->d_sb->s_root->d_fsdata) { 296 poe = dentry->d_sb->s_root->d_fsdata; 297 298 /* Find the current layer on the root dentry */ 299 for (i = 0; i < poe->numlower; i++) 300 if (poe->lowerstack[i].mnt == lowerpath.mnt) 301 break; 302 if (WARN_ON(i == poe->numlower)) 303 break; 304 } 305 } 306 307 oe = ovl_alloc_entry(ctr); 308 err = -ENOMEM; 309 if (!oe) 310 goto out_put; 311 312 if (upperdentry || ctr) { 313 struct dentry *realdentry; 314 struct inode *realinode; 315 316 realdentry = upperdentry ? upperdentry : stack[0].dentry; 317 realinode = d_inode(realdentry); 318 319 err = -ENOMEM; 320 if (upperdentry && !d_is_dir(upperdentry)) { 321 inode = ovl_get_inode(dentry->d_sb, realinode); 322 } else { 323 inode = ovl_new_inode(dentry->d_sb, realinode->i_mode, 324 realinode->i_rdev); 325 if (inode) 326 ovl_inode_init(inode, realinode, !!upperdentry); 327 } 328 if (!inode) 329 goto out_free_oe; 330 ovl_copyattr(realdentry->d_inode, inode); 331 } 332 333 revert_creds(old_cred); 334 oe->opaque = upperopaque; 335 oe->redirect = upperredirect; 336 oe->__upperdentry = upperdentry; 337 memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr); 338 kfree(stack); 339 kfree(d.redirect); 340 dentry->d_fsdata = oe; 341 d_add(dentry, inode); 342 343 return NULL; 344 345 out_free_oe: 346 kfree(oe); 347 out_put: 348 for (i = 0; i < ctr; i++) 349 dput(stack[i].dentry); 350 kfree(stack); 351 out_put_upper: 352 dput(upperdentry); 353 kfree(upperredirect); 354 out: 355 kfree(d.redirect); 356 revert_creds(old_cred); 357 return ERR_PTR(err); 358 } 359 360 bool ovl_lower_positive(struct dentry *dentry) 361 { 362 struct ovl_entry *oe = dentry->d_fsdata; 363 struct ovl_entry *poe = dentry->d_parent->d_fsdata; 364 const struct qstr *name = &dentry->d_name; 365 unsigned int i; 366 bool positive = false; 367 bool done = false; 368 369 /* 370 * If dentry is negative, then lower is positive iff this is a 371 * whiteout. 372 */ 373 if (!dentry->d_inode) 374 return oe->opaque; 375 376 /* Negative upper -> positive lower */ 377 if (!oe->__upperdentry) 378 return true; 379 380 /* Positive upper -> have to look up lower to see whether it exists */ 381 for (i = 0; !done && !positive && i < poe->numlower; i++) { 382 struct dentry *this; 383 struct dentry *lowerdir = poe->lowerstack[i].dentry; 384 385 this = lookup_one_len_unlocked(name->name, lowerdir, 386 name->len); 387 if (IS_ERR(this)) { 388 switch (PTR_ERR(this)) { 389 case -ENOENT: 390 case -ENAMETOOLONG: 391 break; 392 393 default: 394 /* 395 * Assume something is there, we just couldn't 396 * access it. 397 */ 398 positive = true; 399 break; 400 } 401 } else { 402 if (this->d_inode) { 403 positive = !ovl_is_whiteout(this); 404 done = true; 405 } 406 dput(this); 407 } 408 } 409 410 return positive; 411 } 412