1 /* 2 * Copyright (C) Neil Brown 2002 3 * Copyright (C) Christoph Hellwig 2007 4 * 5 * This file contains the code mapping from inodes to NFS file handles, 6 * and for mapping back from file handles to dentries. 7 * 8 * For details on why we do all the strange and hairy things in here 9 * take a look at Documentation/filesystems/Exporting. 10 */ 11 #include <linux/exportfs.h> 12 #include <linux/fs.h> 13 #include <linux/file.h> 14 #include <linux/module.h> 15 #include <linux/mount.h> 16 #include <linux/namei.h> 17 18 #define dprintk(fmt, args...) do{}while(0) 19 20 21 static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name, 22 struct dentry *child); 23 24 25 static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir, 26 char *name, struct dentry *child) 27 { 28 const struct export_operations *nop = dir->d_sb->s_export_op; 29 30 if (nop->get_name) 31 return nop->get_name(dir, name, child); 32 else 33 return get_name(mnt, dir, name, child); 34 } 35 36 /* 37 * Check if the dentry or any of it's aliases is acceptable. 38 */ 39 static struct dentry * 40 find_acceptable_alias(struct dentry *result, 41 int (*acceptable)(void *context, struct dentry *dentry), 42 void *context) 43 { 44 struct dentry *dentry, *toput = NULL; 45 46 if (acceptable(context, result)) 47 return result; 48 49 spin_lock(&dcache_lock); 50 list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) { 51 dget_locked(dentry); 52 spin_unlock(&dcache_lock); 53 if (toput) 54 dput(toput); 55 if (dentry != result && acceptable(context, dentry)) { 56 dput(result); 57 return dentry; 58 } 59 spin_lock(&dcache_lock); 60 toput = dentry; 61 } 62 spin_unlock(&dcache_lock); 63 64 if (toput) 65 dput(toput); 66 return NULL; 67 } 68 69 /* 70 * Find root of a disconnected subtree and return a reference to it. 71 */ 72 static struct dentry * 73 find_disconnected_root(struct dentry *dentry) 74 { 75 dget(dentry); 76 spin_lock(&dentry->d_lock); 77 while (!IS_ROOT(dentry) && 78 (dentry->d_parent->d_flags & DCACHE_DISCONNECTED)) { 79 struct dentry *parent = dentry->d_parent; 80 dget(parent); 81 spin_unlock(&dentry->d_lock); 82 dput(dentry); 83 dentry = parent; 84 spin_lock(&dentry->d_lock); 85 } 86 spin_unlock(&dentry->d_lock); 87 return dentry; 88 } 89 90 91 /* 92 * Make sure target_dir is fully connected to the dentry tree. 93 * 94 * It may already be, as the flag isn't always updated when connection happens. 95 */ 96 static int 97 reconnect_path(struct vfsmount *mnt, struct dentry *target_dir) 98 { 99 char nbuf[NAME_MAX+1]; 100 int noprogress = 0; 101 int err = -ESTALE; 102 103 /* 104 * It is possible that a confused file system might not let us complete 105 * the path to the root. For example, if get_parent returns a directory 106 * in which we cannot find a name for the child. While this implies a 107 * very sick filesystem we don't want it to cause knfsd to spin. Hence 108 * the noprogress counter. If we go through the loop 10 times (2 is 109 * probably enough) without getting anywhere, we just give up 110 */ 111 while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) { 112 struct dentry *pd = find_disconnected_root(target_dir); 113 114 if (!IS_ROOT(pd)) { 115 /* must have found a connected parent - great */ 116 spin_lock(&pd->d_lock); 117 pd->d_flags &= ~DCACHE_DISCONNECTED; 118 spin_unlock(&pd->d_lock); 119 noprogress = 0; 120 } else if (pd == mnt->mnt_sb->s_root) { 121 printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n"); 122 spin_lock(&pd->d_lock); 123 pd->d_flags &= ~DCACHE_DISCONNECTED; 124 spin_unlock(&pd->d_lock); 125 noprogress = 0; 126 } else { 127 /* 128 * We have hit the top of a disconnected path, try to 129 * find parent and connect. 130 * 131 * Racing with some other process renaming a directory 132 * isn't much of a problem here. If someone renames 133 * the directory, it will end up properly connected, 134 * which is what we want 135 * 136 * Getting the parent can't be supported generically, 137 * the locking is too icky. 138 * 139 * Instead we just return EACCES. If server reboots 140 * or inodes get flushed, you lose 141 */ 142 struct dentry *ppd = ERR_PTR(-EACCES); 143 struct dentry *npd; 144 145 mutex_lock(&pd->d_inode->i_mutex); 146 if (mnt->mnt_sb->s_export_op->get_parent) 147 ppd = mnt->mnt_sb->s_export_op->get_parent(pd); 148 mutex_unlock(&pd->d_inode->i_mutex); 149 150 if (IS_ERR(ppd)) { 151 err = PTR_ERR(ppd); 152 dprintk("%s: get_parent of %ld failed, err %d\n", 153 __func__, pd->d_inode->i_ino, err); 154 dput(pd); 155 break; 156 } 157 158 dprintk("%s: find name of %lu in %lu\n", __func__, 159 pd->d_inode->i_ino, ppd->d_inode->i_ino); 160 err = exportfs_get_name(mnt, ppd, nbuf, pd); 161 if (err) { 162 dput(ppd); 163 dput(pd); 164 if (err == -ENOENT) 165 /* some race between get_parent and 166 * get_name? just try again 167 */ 168 continue; 169 break; 170 } 171 dprintk("%s: found name: %s\n", __func__, nbuf); 172 mutex_lock(&ppd->d_inode->i_mutex); 173 npd = lookup_one_len(nbuf, ppd, strlen(nbuf)); 174 mutex_unlock(&ppd->d_inode->i_mutex); 175 if (IS_ERR(npd)) { 176 err = PTR_ERR(npd); 177 dprintk("%s: lookup failed: %d\n", 178 __func__, err); 179 dput(ppd); 180 dput(pd); 181 break; 182 } 183 /* we didn't really want npd, we really wanted 184 * a side-effect of the lookup. 185 * hopefully, npd == pd, though it isn't really 186 * a problem if it isn't 187 */ 188 if (npd == pd) 189 noprogress = 0; 190 else 191 printk("%s: npd != pd\n", __func__); 192 dput(npd); 193 dput(ppd); 194 if (IS_ROOT(pd)) { 195 /* something went wrong, we have to give up */ 196 dput(pd); 197 break; 198 } 199 } 200 dput(pd); 201 } 202 203 if (target_dir->d_flags & DCACHE_DISCONNECTED) { 204 /* something went wrong - oh-well */ 205 if (!err) 206 err = -ESTALE; 207 return err; 208 } 209 210 return 0; 211 } 212 213 struct getdents_callback { 214 char *name; /* name that was found. It already points to a 215 buffer NAME_MAX+1 is size */ 216 unsigned long ino; /* the inum we are looking for */ 217 int found; /* inode matched? */ 218 int sequence; /* sequence counter */ 219 }; 220 221 /* 222 * A rather strange filldir function to capture 223 * the name matching the specified inode number. 224 */ 225 static int filldir_one(void * __buf, const char * name, int len, 226 loff_t pos, u64 ino, unsigned int d_type) 227 { 228 struct getdents_callback *buf = __buf; 229 int result = 0; 230 231 buf->sequence++; 232 if (buf->ino == ino) { 233 memcpy(buf->name, name, len); 234 buf->name[len] = '\0'; 235 buf->found = 1; 236 result = -1; 237 } 238 return result; 239 } 240 241 /** 242 * get_name - default export_operations->get_name function 243 * @dentry: the directory in which to find a name 244 * @name: a pointer to a %NAME_MAX+1 char buffer to store the name 245 * @child: the dentry for the child directory. 246 * 247 * calls readdir on the parent until it finds an entry with 248 * the same inode number as the child, and returns that. 249 */ 250 static int get_name(struct vfsmount *mnt, struct dentry *dentry, 251 char *name, struct dentry *child) 252 { 253 struct inode *dir = dentry->d_inode; 254 int error; 255 struct file *file; 256 struct getdents_callback buffer; 257 258 error = -ENOTDIR; 259 if (!dir || !S_ISDIR(dir->i_mode)) 260 goto out; 261 error = -EINVAL; 262 if (!dir->i_fop) 263 goto out; 264 /* 265 * Open the directory ... 266 */ 267 file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY); 268 error = PTR_ERR(file); 269 if (IS_ERR(file)) 270 goto out; 271 272 error = -EINVAL; 273 if (!file->f_op->readdir) 274 goto out_close; 275 276 buffer.name = name; 277 buffer.ino = child->d_inode->i_ino; 278 buffer.found = 0; 279 buffer.sequence = 0; 280 while (1) { 281 int old_seq = buffer.sequence; 282 283 error = vfs_readdir(file, filldir_one, &buffer); 284 285 if (error < 0) 286 break; 287 288 error = 0; 289 if (buffer.found) 290 break; 291 error = -ENOENT; 292 if (old_seq == buffer.sequence) 293 break; 294 } 295 296 out_close: 297 fput(file); 298 out: 299 return error; 300 } 301 302 /** 303 * export_encode_fh - default export_operations->encode_fh function 304 * @dentry: the dentry to encode 305 * @fh: where to store the file handle fragment 306 * @max_len: maximum length to store there 307 * @connectable: whether to store parent information 308 * 309 * This default encode_fh function assumes that the 32 inode number 310 * is suitable for locating an inode, and that the generation number 311 * can be used to check that it is still valid. It places them in the 312 * filehandle fragment where export_decode_fh expects to find them. 313 */ 314 static int export_encode_fh(struct dentry *dentry, struct fid *fid, 315 int *max_len, int connectable) 316 { 317 struct inode * inode = dentry->d_inode; 318 int len = *max_len; 319 int type = FILEID_INO32_GEN; 320 321 if (len < 2 || (connectable && len < 4)) 322 return 255; 323 324 len = 2; 325 fid->i32.ino = inode->i_ino; 326 fid->i32.gen = inode->i_generation; 327 if (connectable && !S_ISDIR(inode->i_mode)) { 328 struct inode *parent; 329 330 spin_lock(&dentry->d_lock); 331 parent = dentry->d_parent->d_inode; 332 fid->i32.parent_ino = parent->i_ino; 333 fid->i32.parent_gen = parent->i_generation; 334 spin_unlock(&dentry->d_lock); 335 len = 4; 336 type = FILEID_INO32_GEN_PARENT; 337 } 338 *max_len = len; 339 return type; 340 } 341 342 int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, 343 int connectable) 344 { 345 const struct export_operations *nop = dentry->d_sb->s_export_op; 346 int error; 347 348 if (nop->encode_fh) 349 error = nop->encode_fh(dentry, fid->raw, max_len, connectable); 350 else 351 error = export_encode_fh(dentry, fid, max_len, connectable); 352 353 return error; 354 } 355 EXPORT_SYMBOL_GPL(exportfs_encode_fh); 356 357 struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, 358 int fh_len, int fileid_type, 359 int (*acceptable)(void *, struct dentry *), void *context) 360 { 361 const struct export_operations *nop = mnt->mnt_sb->s_export_op; 362 struct dentry *result, *alias; 363 int err; 364 365 /* 366 * Try to get any dentry for the given file handle from the filesystem. 367 */ 368 result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type); 369 if (!result) 370 result = ERR_PTR(-ESTALE); 371 if (IS_ERR(result)) 372 return result; 373 374 if (S_ISDIR(result->d_inode->i_mode)) { 375 /* 376 * This request is for a directory. 377 * 378 * On the positive side there is only one dentry for each 379 * directory inode. On the negative side this implies that we 380 * to ensure our dentry is connected all the way up to the 381 * filesystem root. 382 */ 383 if (result->d_flags & DCACHE_DISCONNECTED) { 384 err = reconnect_path(mnt, result); 385 if (err) 386 goto err_result; 387 } 388 389 if (!acceptable(context, result)) { 390 err = -EACCES; 391 goto err_result; 392 } 393 394 return result; 395 } else { 396 /* 397 * It's not a directory. Life is a little more complicated. 398 */ 399 struct dentry *target_dir, *nresult; 400 char nbuf[NAME_MAX+1]; 401 402 /* 403 * See if either the dentry we just got from the filesystem 404 * or any alias for it is acceptable. This is always true 405 * if this filesystem is exported without the subtreecheck 406 * option. If the filesystem is exported with the subtree 407 * check option there's a fair chance we need to look at 408 * the parent directory in the file handle and make sure 409 * it's connected to the filesystem root. 410 */ 411 alias = find_acceptable_alias(result, acceptable, context); 412 if (alias) 413 return alias; 414 415 /* 416 * Try to extract a dentry for the parent directory from the 417 * file handle. If this fails we'll have to give up. 418 */ 419 err = -ESTALE; 420 if (!nop->fh_to_parent) 421 goto err_result; 422 423 target_dir = nop->fh_to_parent(mnt->mnt_sb, fid, 424 fh_len, fileid_type); 425 if (!target_dir) 426 goto err_result; 427 err = PTR_ERR(target_dir); 428 if (IS_ERR(target_dir)) 429 goto err_result; 430 431 /* 432 * And as usual we need to make sure the parent directory is 433 * connected to the filesystem root. The VFS really doesn't 434 * like disconnected directories.. 435 */ 436 err = reconnect_path(mnt, target_dir); 437 if (err) { 438 dput(target_dir); 439 goto err_result; 440 } 441 442 /* 443 * Now that we've got both a well-connected parent and a 444 * dentry for the inode we're after, make sure that our 445 * inode is actually connected to the parent. 446 */ 447 err = exportfs_get_name(mnt, target_dir, nbuf, result); 448 if (!err) { 449 mutex_lock(&target_dir->d_inode->i_mutex); 450 nresult = lookup_one_len(nbuf, target_dir, 451 strlen(nbuf)); 452 mutex_unlock(&target_dir->d_inode->i_mutex); 453 if (!IS_ERR(nresult)) { 454 if (nresult->d_inode) { 455 dput(result); 456 result = nresult; 457 } else 458 dput(nresult); 459 } 460 } 461 462 /* 463 * At this point we are done with the parent, but it's pinned 464 * by the child dentry anyway. 465 */ 466 dput(target_dir); 467 468 /* 469 * And finally make sure the dentry is actually acceptable 470 * to NFSD. 471 */ 472 alias = find_acceptable_alias(result, acceptable, context); 473 if (!alias) { 474 err = -EACCES; 475 goto err_result; 476 } 477 478 return alias; 479 } 480 481 err_result: 482 dput(result); 483 return ERR_PTR(err); 484 } 485 EXPORT_SYMBOL_GPL(exportfs_decode_fh); 486 487 MODULE_LICENSE("GPL"); 488