expfs.c 13.8 KB
Newer Older
1 2 3 4 5 6 7 8
/*
 * Copyright (C) Neil Brown 2002
 * Copyright (C) Christoph Hellwig 2007
 *
 * This file contains the code mapping from inodes to NFS file handles,
 * and for mapping back from file handles to dentries.
 *
 * For details on why we do all the strange and hairy things in here
9
 * take a look at Documentation/filesystems/nfs/Exporting.
10
 */
11
#include <linux/exportfs.h>
Linus Torvalds's avatar
Linus Torvalds committed
12 13 14
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
15
#include <linux/mount.h>
Linus Torvalds's avatar
Linus Torvalds committed
16
#include <linux/namei.h>
17
#include <linux/sched.h>
Linus Torvalds's avatar
Linus Torvalds committed
18

19
#define dprintk(fmt, args...) do{}while(0)
Linus Torvalds's avatar
Linus Torvalds committed
20 21


22
static int get_name(const struct path *path, char *name, struct dentry *child);
23 24


25 26
static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
		char *name, struct dentry *child)
27
{
28
	const struct export_operations *nop = dir->d_sb->s_export_op;
29
	struct path path = {.mnt = mnt, .dentry = dir};
30 31 32 33

	if (nop->get_name)
		return nop->get_name(dir, name, child);
	else
34
		return get_name(&path, name, child);
35
}
Linus Torvalds's avatar
Linus Torvalds committed
36

37 38 39
/*
 * Check if the dentry or any of it's aliases is acceptable.
 */
40 41 42 43 44 45
static struct dentry *
find_acceptable_alias(struct dentry *result,
		int (*acceptable)(void *context, struct dentry *dentry),
		void *context)
{
	struct dentry *dentry, *toput = NULL;
46
	struct inode *inode;
47

48 49 50
	if (acceptable(context, result))
		return result;

51 52
	inode = result->d_inode;
	spin_lock(&inode->i_lock);
53
	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
54
		dget(dentry);
55
		spin_unlock(&inode->i_lock);
56 57 58 59 60 61
		if (toput)
			dput(toput);
		if (dentry != result && acceptable(context, dentry)) {
			dput(result);
			return dentry;
		}
62
		spin_lock(&inode->i_lock);
63 64
		toput = dentry;
	}
65
	spin_unlock(&inode->i_lock);
66 67 68 69 70 71

	if (toput)
		dput(toput);
	return NULL;
}

72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
static bool dentry_connected(struct dentry *dentry)
{
	dget(dentry);
	while (dentry->d_flags & DCACHE_DISCONNECTED) {
		struct dentry *parent = dget_parent(dentry);

		dput(dentry);
		if (IS_ROOT(dentry)) {
			dput(parent);
			return false;
		}
		dentry = parent;
	}
	dput(dentry);
	return true;
}

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106
static void clear_disconnected(struct dentry *dentry)
{
	dget(dentry);
	while (dentry->d_flags & DCACHE_DISCONNECTED) {
		struct dentry *parent = dget_parent(dentry);

		WARN_ON_ONCE(IS_ROOT(dentry));

		spin_lock(&dentry->d_lock);
		dentry->d_flags &= ~DCACHE_DISCONNECTED;
		spin_unlock(&dentry->d_lock);

		dput(dentry);
		dentry = parent;
	}
	dput(dentry);
}

107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
/*
 * Reconnect a directory dentry with its parent.
 *
 * This can return a dentry, or NULL, or an error.
 *
 * In the first case the returned dentry is the parent of the given
 * dentry, and may itself need to be reconnected to its parent.
 *
 * In the NULL case, a concurrent VFS operation has either renamed or
 * removed this directory.  The concurrent operation has reconnected our
 * dentry, so we no longer need to.
 */
static struct dentry *reconnect_one(struct vfsmount *mnt,
		struct dentry *dentry, char *nbuf)
{
	struct dentry *parent;
	struct dentry *tmp;
	int err;

	parent = ERR_PTR(-EACCES);
Al Viro's avatar
Al Viro committed
127
	inode_lock(dentry->d_inode);
128 129
	if (mnt->mnt_sb->s_export_op->get_parent)
		parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
Al Viro's avatar
Al Viro committed
130
	inode_unlock(dentry->d_inode);
131 132 133 134 135 136 137 138 139 140 141 142 143 144 145

	if (IS_ERR(parent)) {
		dprintk("%s: get_parent of %ld failed, err %d\n",
			__func__, dentry->d_inode->i_ino, PTR_ERR(parent));
		return parent;
	}

	dprintk("%s: find name of %lu in %lu\n", __func__,
		dentry->d_inode->i_ino, parent->d_inode->i_ino);
	err = exportfs_get_name(mnt, parent, nbuf, dentry);
	if (err == -ENOENT)
		goto out_reconnected;
	if (err)
		goto out_err;
	dprintk("%s: found name: %s\n", __func__, nbuf);
146
	tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
147 148 149 150 151
	if (IS_ERR(tmp)) {
		dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
		goto out_err;
	}
	if (tmp != dentry) {
152 153 154 155 156 157
		/*
		 * Somebody has renamed it since exportfs_get_name();
		 * great, since it could've only been renamed if it
		 * got looked up and thus connected, and it would
		 * remain connected afterwards.  We are done.
		 */
158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190
		dput(tmp);
		goto out_reconnected;
	}
	dput(tmp);
	if (IS_ROOT(dentry)) {
		err = -ESTALE;
		goto out_err;
	}
	return parent;

out_err:
	dput(parent);
	return ERR_PTR(err);
out_reconnected:
	dput(parent);
	/*
	 * Someone must have renamed our entry into another parent, in
	 * which case it has been reconnected by the rename.
	 *
	 * Or someone removed it entirely, in which case filehandle
	 * lookup will succeed but the directory is now IS_DEAD and
	 * subsequent operations on it will fail.
	 *
	 * Alternatively, maybe there was no race at all, and the
	 * filesystem is just corrupt and gave us a parent that doesn't
	 * actually contain any entry pointing to this inode.  So,
	 * double check that this worked and return -ESTALE if not:
	 */
	if (!dentry_connected(dentry))
		return ERR_PTR(-ESTALE);
	return NULL;
}

191 192
/*
 * Make sure target_dir is fully connected to the dentry tree.
Linus Torvalds's avatar
Linus Torvalds committed
193
 *
194 195 196 197 198 199 200 201 202 203 204 205 206
 * On successful return, DCACHE_DISCONNECTED will be cleared on
 * target_dir, and target_dir->d_parent->...->d_parent will reach the
 * root of the filesystem.
 *
 * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
 * But the converse is not true: target_dir may have DCACHE_DISCONNECTED
 * set but already be connected.  In that case we'll verify the
 * connection to root and then clear the flag.
 *
 * Note that target_dir could be removed by a concurrent operation.  In
 * that case reconnect_path may still succeed with target_dir fully
 * connected, but further operations using the filehandle will fail when
 * necessary (due to S_DEAD being set on the directory).
Linus Torvalds's avatar
Linus Torvalds committed
207
 */
208
static int
209
reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
Linus Torvalds's avatar
Linus Torvalds committed
210
{
211
	struct dentry *dentry, *parent;
Linus Torvalds's avatar
Linus Torvalds committed
212

213
	dentry = dget(target_dir);
Linus Torvalds's avatar
Linus Torvalds committed
214

215
	while (dentry->d_flags & DCACHE_DISCONNECTED) {
216
		BUG_ON(dentry == mnt->mnt_sb->s_root);
217

218 219 220 221 222 223
		if (IS_ROOT(dentry))
			parent = reconnect_one(mnt, dentry, nbuf);
		else
			parent = dget_parent(dentry);

		if (!parent)
224
			break;
225
		dput(dentry);
226 227 228
		if (IS_ERR(parent))
			return PTR_ERR(parent);
		dentry = parent;
Linus Torvalds's avatar
Linus Torvalds committed
229
	}
230
	dput(dentry);
231
	clear_disconnected(target_dir);
232 233 234
	return 0;
}

Linus Torvalds's avatar
Linus Torvalds committed
235
struct getdents_callback {
236
	struct dir_context ctx;
Linus Torvalds's avatar
Linus Torvalds committed
237 238
	char *name;		/* name that was found. It already points to a
				   buffer NAME_MAX+1 is size */
239
	u64 ino;		/* the inum we are looking for */
Linus Torvalds's avatar
Linus Torvalds committed
240 241 242 243 244 245 246 247
	int found;		/* inode matched? */
	int sequence;		/* sequence counter */
};

/*
 * A rather strange filldir function to capture
 * the name matching the specified inode number.
 */
248
static int filldir_one(struct dir_context *ctx, const char *name, int len,
249
			loff_t pos, u64 ino, unsigned int d_type)
Linus Torvalds's avatar
Linus Torvalds committed
250
{
251 252
	struct getdents_callback *buf =
		container_of(ctx, struct getdents_callback, ctx);
Linus Torvalds's avatar
Linus Torvalds committed
253 254 255
	int result = 0;

	buf->sequence++;
256
	if (buf->ino == ino && len <= NAME_MAX) {
Linus Torvalds's avatar
Linus Torvalds committed
257 258 259 260 261 262 263 264 265 266
		memcpy(buf->name, name, len);
		buf->name[len] = '\0';
		buf->found = 1;
		result = -1;
	}
	return result;
}

/**
 * get_name - default export_operations->get_name function
267
 * @path:   the directory in which to find a name
Linus Torvalds's avatar
Linus Torvalds committed
268 269 270 271 272 273
 * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 * @child:  the dentry for the child directory.
 *
 * calls readdir on the parent until it finds an entry with
 * the same inode number as the child, and returns that.
 */
274
static int get_name(const struct path *path, char *name, struct dentry *child)
Linus Torvalds's avatar
Linus Torvalds committed
275
{
276
	const struct cred *cred = current_cred();
277
	struct inode *dir = path->dentry->d_inode;
Linus Torvalds's avatar
Linus Torvalds committed
278 279
	int error;
	struct file *file;
280 281 282 283 284
	struct kstat stat;
	struct path child_path = {
		.mnt = path->mnt,
		.dentry = child,
	};
Al Viro's avatar
Al Viro committed
285 286 287 288
	struct getdents_callback buffer = {
		.ctx.actor = filldir_one,
		.name = name,
	};
Linus Torvalds's avatar
Linus Torvalds committed
289 290 291 292 293 294 295

	error = -ENOTDIR;
	if (!dir || !S_ISDIR(dir->i_mode))
		goto out;
	error = -EINVAL;
	if (!dir->i_fop)
		goto out;
296 297 298 299 300 301 302 303 304 305
	/*
	 * inode->i_ino is unsigned long, kstat->ino is u64, so the
	 * former would be insufficient on 32-bit hosts when the
	 * filesystem supports 64-bit inode numbers.  So we need to
	 * actually call ->getattr, not just read i_ino:
	 */
	error = vfs_getattr_nosec(&child_path, &stat);
	if (error)
		return error;
	buffer.ino = stat.ino;
Linus Torvalds's avatar
Linus Torvalds committed
306 307 308
	/*
	 * Open the directory ...
	 */
309
	file = dentry_open(path, O_RDONLY, cred);
Linus Torvalds's avatar
Linus Torvalds committed
310 311 312 313 314
	error = PTR_ERR(file);
	if (IS_ERR(file))
		goto out;

	error = -EINVAL;
315
	if (!file->f_op->iterate && !file->f_op->iterate_shared)
Linus Torvalds's avatar
Linus Torvalds committed
316 317 318 319 320 321
		goto out_close;

	buffer.sequence = 0;
	while (1) {
		int old_seq = buffer.sequence;

322
		error = iterate_dir(file, &buffer.ctx);
323 324 325 326
		if (buffer.found) {
			error = 0;
			break;
		}
Linus Torvalds's avatar
Linus Torvalds committed
327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343

		if (error < 0)
			break;

		error = -ENOENT;
		if (old_seq == buffer.sequence)
			break;
	}

out_close:
	fput(file);
out:
	return error;
}

/**
 * export_encode_fh - default export_operations->encode_fh function
Al Viro's avatar
Al Viro committed
344
 * @inode:   the object to encode
345
 * @fid:     where to store the file handle fragment
Linus Torvalds's avatar
Linus Torvalds committed
346
 * @max_len: maximum length to store there
Al Viro's avatar
Al Viro committed
347
 * @parent:  parent directory inode, if wanted
Linus Torvalds's avatar
Linus Torvalds committed
348 349 350 351 352 353
 *
 * This default encode_fh function assumes that the 32 inode number
 * is suitable for locating an inode, and that the generation number
 * can be used to check that it is still valid.  It places them in the
 * filehandle fragment where export_decode_fh expects to find them.
 */
Al Viro's avatar
Al Viro committed
354 355
static int export_encode_fh(struct inode *inode, struct fid *fid,
		int *max_len, struct inode *parent)
Linus Torvalds's avatar
Linus Torvalds committed
356 357
{
	int len = *max_len;
Christoph Hellwig's avatar
Christoph Hellwig committed
358
	int type = FILEID_INO32_GEN;
359

Al Viro's avatar
Al Viro committed
360
	if (parent && (len < 4)) {
361
		*max_len = 4;
362
		return FILEID_INVALID;
363 364
	} else if (len < 2) {
		*max_len = 2;
365
		return FILEID_INVALID;
366
	}
Linus Torvalds's avatar
Linus Torvalds committed
367 368

	len = 2;
Christoph Hellwig's avatar
Christoph Hellwig committed
369 370
	fid->i32.ino = inode->i_ino;
	fid->i32.gen = inode->i_generation;
Al Viro's avatar
Al Viro committed
371
	if (parent) {
Christoph Hellwig's avatar
Christoph Hellwig committed
372 373
		fid->i32.parent_ino = parent->i_ino;
		fid->i32.parent_gen = parent->i_generation;
Linus Torvalds's avatar
Linus Torvalds committed
374
		len = 4;
Christoph Hellwig's avatar
Christoph Hellwig committed
375
		type = FILEID_INO32_GEN_PARENT;
Linus Torvalds's avatar
Linus Torvalds committed
376 377 378 379 380
	}
	*max_len = len;
	return type;
}

381 382 383 384 385 386 387 388 389 390 391 392
int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
			     int *max_len, struct inode *parent)
{
	const struct export_operations *nop = inode->i_sb->s_export_op;

	if (nop && nop->encode_fh)
		return nop->encode_fh(inode, fid->raw, max_len, parent);

	return export_encode_fh(inode, fid, max_len, parent);
}
EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);

Christoph Hellwig's avatar
Christoph Hellwig committed
393
int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
394 395
		int connectable)
{
396
	int error;
Al Viro's avatar
Al Viro committed
397 398
	struct dentry *p = NULL;
	struct inode *inode = dentry->d_inode, *parent = NULL;
399

Al Viro's avatar
Al Viro committed
400 401 402 403 404 405 406 407
	if (connectable && !S_ISDIR(inode->i_mode)) {
		p = dget_parent(dentry);
		/*
		 * note that while p might've ceased to be our parent already,
		 * it's still pinned by and still positive.
		 */
		parent = p->d_inode;
	}
408 409

	error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
Al Viro's avatar
Al Viro committed
410
	dput(p);
411 412

	return error;
413 414 415
}
EXPORT_SYMBOL_GPL(exportfs_encode_fh);

Christoph Hellwig's avatar
Christoph Hellwig committed
416 417 418
struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
		int fh_len, int fileid_type,
		int (*acceptable)(void *, struct dentry *), void *context)
419
{
420
	const struct export_operations *nop = mnt->mnt_sb->s_export_op;
421
	struct dentry *result, *alias;
422
	char nbuf[NAME_MAX+1];
423
	int err;
424

425 426 427
	/*
	 * Try to get any dentry for the given file handle from the filesystem.
	 */
428 429
	if (!nop || !nop->fh_to_dentry)
		return ERR_PTR(-ESTALE);
430
	result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
431 432 433 434
	if (PTR_ERR(result) == -ENOMEM)
		return ERR_CAST(result);
	if (IS_ERR_OR_NULL(result))
		return ERR_PTR(-ESTALE);
435

436
	if (d_is_dir(result)) {
437 438 439 440 441 442 443 444 445
		/*
		 * This request is for a directory.
		 *
		 * On the positive side there is only one dentry for each
		 * directory inode.  On the negative side this implies that we
		 * to ensure our dentry is connected all the way up to the
		 * filesystem root.
		 */
		if (result->d_flags & DCACHE_DISCONNECTED) {
446
			err = reconnect_path(mnt, result, nbuf);
447 448 449 450 451 452 453 454 455 456
			if (err)
				goto err_result;
		}

		if (!acceptable(context, result)) {
			err = -EACCES;
			goto err_result;
		}

		return result;
457
	} else {
458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485
		/*
		 * It's not a directory.  Life is a little more complicated.
		 */
		struct dentry *target_dir, *nresult;

		/*
		 * See if either the dentry we just got from the filesystem
		 * or any alias for it is acceptable.  This is always true
		 * if this filesystem is exported without the subtreecheck
		 * option.  If the filesystem is exported with the subtree
		 * check option there's a fair chance we need to look at
		 * the parent directory in the file handle and make sure
		 * it's connected to the filesystem root.
		 */
		alias = find_acceptable_alias(result, acceptable, context);
		if (alias)
			return alias;

		/*
		 * Try to extract a dentry for the parent directory from the
		 * file handle.  If this fails we'll have to give up.
		 */
		err = -ESTALE;
		if (!nop->fh_to_parent)
			goto err_result;

		target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
				fh_len, fileid_type);
486 487
		if (!target_dir)
			goto err_result;
488 489 490 491 492 493 494 495 496
		err = PTR_ERR(target_dir);
		if (IS_ERR(target_dir))
			goto err_result;

		/*
		 * And as usual we need to make sure the parent directory is
		 * connected to the filesystem root.  The VFS really doesn't
		 * like disconnected directories..
		 */
497
		err = reconnect_path(mnt, target_dir, nbuf);
498 499 500 501 502 503 504 505 506 507
		if (err) {
			dput(target_dir);
			goto err_result;
		}

		/*
		 * Now that we've got both a well-connected parent and a
		 * dentry for the inode we're after, make sure that our
		 * inode is actually connected to the parent.
		 */
508
		err = exportfs_get_name(mnt, target_dir, nbuf, result);
509
		if (!err) {
Al Viro's avatar
Al Viro committed
510
			inode_lock(target_dir->d_inode);
511 512
			nresult = lookup_one_len(nbuf, target_dir,
						 strlen(nbuf));
Al Viro's avatar
Al Viro committed
513
			inode_unlock(target_dir->d_inode);
514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539
			if (!IS_ERR(nresult)) {
				if (nresult->d_inode) {
					dput(result);
					result = nresult;
				} else
					dput(nresult);
			}
		}

		/*
		 * At this point we are done with the parent, but it's pinned
		 * by the child dentry anyway.
		 */
		dput(target_dir);

		/*
		 * And finally make sure the dentry is actually acceptable
		 * to NFSD.
		 */
		alias = find_acceptable_alias(result, acceptable, context);
		if (!alias) {
			err = -EACCES;
			goto err_result;
		}

		return alias;
540 541
	}

542 543
 err_result:
	dput(result);
544 545
	if (err != -ENOMEM)
		err = -ESTALE;
546
	return ERR_PTR(err);
547 548 549
}
EXPORT_SYMBOL_GPL(exportfs_decode_fh);

Linus Torvalds's avatar
Linus Torvalds committed
550
MODULE_LICENSE("GPL");