Free Electrons

Embedded Linux Experts

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
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
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
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
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
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
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
/*
 *
 * Copyright (C) 2011 Novell Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/splice.h>
#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/uaccess.h>
#include <linux/sched/signal.h>
#include <linux/cred.h>
#include <linux/namei.h>
#include <linux/fdtable.h>
#include <linux/ratelimit.h>
#include <linux/exportfs.h>
#include "overlayfs.h"
#include "ovl_entry.h"

#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)

static bool __read_mostly ovl_check_copy_up;
module_param_named(check_copy_up, ovl_check_copy_up, bool,
		   S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(ovl_check_copy_up,
		 "Warn on copy-up when causing process also has a R/O fd open");

static int ovl_check_fd(const void *data, struct file *f, unsigned int fd)
{
	const struct dentry *dentry = data;

	if (file_inode(f) == d_inode(dentry))
		pr_warn_ratelimited("overlayfs: Warning: Copying up %pD, but open R/O on fd %u which will cease to be coherent [pid=%d %s]\n",
				    f, fd, current->pid, current->comm);
	return 0;
}

/*
 * Check the fds open by this process and warn if something like the following
 * scenario is about to occur:
 *
 *	fd1 = open("foo", O_RDONLY);
 *	fd2 = open("foo", O_RDWR);
 */
static void ovl_do_check_copy_up(struct dentry *dentry)
{
	if (ovl_check_copy_up)
		iterate_fd(current->files, 0, ovl_check_fd, dentry);
}

int ovl_copy_xattr(struct dentry *old, struct dentry *new)
{
	ssize_t list_size, size, value_size = 0;
	char *buf, *name, *value = NULL;
	int uninitialized_var(error);
	size_t slen;

	if (!(old->d_inode->i_opflags & IOP_XATTR) ||
	    !(new->d_inode->i_opflags & IOP_XATTR))
		return 0;

	list_size = vfs_listxattr(old, NULL, 0);
	if (list_size <= 0) {
		if (list_size == -EOPNOTSUPP)
			return 0;
		return list_size;
	}

	buf = kzalloc(list_size, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

	list_size = vfs_listxattr(old, buf, list_size);
	if (list_size <= 0) {
		error = list_size;
		goto out;
	}

	for (name = buf; list_size; name += slen) {
		slen = strnlen(name, list_size) + 1;

		/* underlying fs providing us with an broken xattr list? */
		if (WARN_ON(slen > list_size)) {
			error = -EIO;
			break;
		}
		list_size -= slen;

		if (ovl_is_private_xattr(name))
			continue;
retry:
		size = vfs_getxattr(old, name, value, value_size);
		if (size == -ERANGE)
			size = vfs_getxattr(old, name, NULL, 0);

		if (size < 0) {
			error = size;
			break;
		}

		if (size > value_size) {
			void *new;

			new = krealloc(value, size, GFP_KERNEL);
			if (!new) {
				error = -ENOMEM;
				break;
			}
			value = new;
			value_size = size;
			goto retry;
		}

		error = security_inode_copy_up_xattr(name);
		if (error < 0 && error != -EOPNOTSUPP)
			break;
		if (error == 1) {
			error = 0;
			continue; /* Discard */
		}
		error = vfs_setxattr(new, name, value, size, 0);
		if (error)
			break;
	}
	kfree(value);
out:
	kfree(buf);
	return error;
}

static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
{
	struct file *old_file;
	struct file *new_file;
	loff_t old_pos = 0;
	loff_t new_pos = 0;
	int error = 0;

	if (len == 0)
		return 0;

	old_file = ovl_path_open(old, O_LARGEFILE | O_RDONLY);
	if (IS_ERR(old_file))
		return PTR_ERR(old_file);

	new_file = ovl_path_open(new, O_LARGEFILE | O_WRONLY);
	if (IS_ERR(new_file)) {
		error = PTR_ERR(new_file);
		goto out_fput;
	}

	/* Try to use clone_file_range to clone up within the same fs */
	error = vfs_clone_file_range(old_file, 0, new_file, 0, len);
	if (!error)
		goto out;
	/* Couldn't clone, so now we try to copy the data */
	error = 0;

	/* FIXME: copy up sparse files efficiently */
	while (len) {
		size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
		long bytes;

		if (len < this_len)
			this_len = len;

		if (signal_pending_state(TASK_KILLABLE, current)) {
			error = -EINTR;
			break;
		}

		bytes = do_splice_direct(old_file, &old_pos,
					 new_file, &new_pos,
					 this_len, SPLICE_F_MOVE);
		if (bytes <= 0) {
			error = bytes;
			break;
		}
		WARN_ON(old_pos != new_pos);

		len -= bytes;
	}
out:
	if (!error)
		error = vfs_fsync(new_file, 0);
	fput(new_file);
out_fput:
	fput(old_file);
	return error;
}

static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
{
	struct iattr attr = {
		.ia_valid =
		     ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
		.ia_atime = stat->atime,
		.ia_mtime = stat->mtime,
	};

	return notify_change(upperdentry, &attr, NULL);
}

int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
{
	int err = 0;

	if (!S_ISLNK(stat->mode)) {
		struct iattr attr = {
			.ia_valid = ATTR_MODE,
			.ia_mode = stat->mode,
		};
		err = notify_change(upperdentry, &attr, NULL);
	}
	if (!err) {
		struct iattr attr = {
			.ia_valid = ATTR_UID | ATTR_GID,
			.ia_uid = stat->uid,
			.ia_gid = stat->gid,
		};
		err = notify_change(upperdentry, &attr, NULL);
	}
	if (!err)
		ovl_set_timestamps(upperdentry, stat);

	return err;
}

struct ovl_fh *ovl_encode_fh(struct dentry *lower, bool is_upper)
{
	struct ovl_fh *fh;
	int fh_type, fh_len, dwords;
	void *buf;
	int buflen = MAX_HANDLE_SZ;
	uuid_t *uuid = &lower->d_sb->s_uuid;

	buf = kmalloc(buflen, GFP_KERNEL);
	if (!buf)
		return ERR_PTR(-ENOMEM);

	/*
	 * We encode a non-connectable file handle for non-dir, because we
	 * only need to find the lower inode number and we don't want to pay
	 * the price or reconnecting the dentry.
	 */
	dwords = buflen >> 2;
	fh_type = exportfs_encode_fh(lower, buf, &dwords, 0);
	buflen = (dwords << 2);

	fh = ERR_PTR(-EIO);
	if (WARN_ON(fh_type < 0) ||
	    WARN_ON(buflen > MAX_HANDLE_SZ) ||
	    WARN_ON(fh_type == FILEID_INVALID))
		goto out;

	BUILD_BUG_ON(MAX_HANDLE_SZ + offsetof(struct ovl_fh, fid) > 255);
	fh_len = offsetof(struct ovl_fh, fid) + buflen;
	fh = kmalloc(fh_len, GFP_KERNEL);
	if (!fh) {
		fh = ERR_PTR(-ENOMEM);
		goto out;
	}

	fh->version = OVL_FH_VERSION;
	fh->magic = OVL_FH_MAGIC;
	fh->type = fh_type;
	fh->flags = OVL_FH_FLAG_CPU_ENDIAN;
	/*
	 * When we will want to decode an overlay dentry from this handle
	 * and all layers are on the same fs, if we get a disconncted real
	 * dentry when we decode fid, the only way to tell if we should assign
	 * it to upperdentry or to lowerstack is by checking this flag.
	 */
	if (is_upper)
		fh->flags |= OVL_FH_FLAG_PATH_UPPER;
	fh->len = fh_len;
	fh->uuid = *uuid;
	memcpy(fh->fid, buf, buflen);

out:
	kfree(buf);
	return fh;
}

static int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
			  struct dentry *upper)
{
	const struct ovl_fh *fh = NULL;
	int err;

	/*
	 * When lower layer doesn't support export operations store a 'null' fh,
	 * so we can use the overlay.origin xattr to distignuish between a copy
	 * up and a pure upper inode.
	 */
	if (ovl_can_decode_fh(lower->d_sb)) {
		fh = ovl_encode_fh(lower, false);
		if (IS_ERR(fh))
			return PTR_ERR(fh);
	}

	/*
	 * Do not fail when upper doesn't support xattrs.
	 */
	err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN, fh,
				 fh ? fh->len : 0, 0);
	kfree(fh);

	return err;
}

struct ovl_copy_up_ctx {
	struct dentry *parent;
	struct dentry *dentry;
	struct path lowerpath;
	struct kstat stat;
	struct kstat pstat;
	const char *link;
	struct dentry *destdir;
	struct qstr destname;
	struct dentry *workdir;
	bool tmpfile;
	bool origin;
};

static int ovl_link_up(struct ovl_copy_up_ctx *c)
{
	int err;
	struct dentry *upper;
	struct dentry *upperdir = ovl_dentry_upper(c->parent);
	struct inode *udir = d_inode(upperdir);

	/* Mark parent "impure" because it may now contain non-pure upper */
	err = ovl_set_impure(c->parent, upperdir);
	if (err)
		return err;

	err = ovl_set_nlink_lower(c->dentry);
	if (err)
		return err;

	inode_lock_nested(udir, I_MUTEX_PARENT);
	upper = lookup_one_len(c->dentry->d_name.name, upperdir,
			       c->dentry->d_name.len);
	err = PTR_ERR(upper);
	if (!IS_ERR(upper)) {
		err = ovl_do_link(ovl_dentry_upper(c->dentry), udir, upper,
				  true);
		dput(upper);

		if (!err) {
			/* Restore timestamps on parent (best effort) */
			ovl_set_timestamps(upperdir, &c->pstat);
			ovl_dentry_set_upper_alias(c->dentry);
		}
	}
	inode_unlock(udir);
	ovl_set_nlink_upper(c->dentry);

	return err;
}

static int ovl_install_temp(struct ovl_copy_up_ctx *c, struct dentry *temp,
			    struct dentry **newdentry)
{
	int err;
	struct dentry *upper;
	struct inode *udir = d_inode(c->destdir);

	upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
	if (IS_ERR(upper))
		return PTR_ERR(upper);

	if (c->tmpfile)
		err = ovl_do_link(temp, udir, upper, true);
	else
		err = ovl_do_rename(d_inode(c->workdir), temp, udir, upper, 0);

	if (!err)
		*newdentry = dget(c->tmpfile ? upper : temp);
	dput(upper);

	return err;
}

static int ovl_get_tmpfile(struct ovl_copy_up_ctx *c, struct dentry **tempp)
{
	int err;
	struct dentry *temp;
	const struct cred *old_creds = NULL;
	struct cred *new_creds = NULL;
	struct cattr cattr = {
		/* Can't properly set mode on creation because of the umask */
		.mode = c->stat.mode & S_IFMT,
		.rdev = c->stat.rdev,
		.link = c->link
	};

	err = security_inode_copy_up(c->dentry, &new_creds);
	if (err < 0)
		goto out;

	if (new_creds)
		old_creds = override_creds(new_creds);

	if (c->tmpfile) {
		temp = ovl_do_tmpfile(c->workdir, c->stat.mode);
		if (IS_ERR(temp))
			goto temp_err;
	} else {
		temp = ovl_lookup_temp(c->workdir);
		if (IS_ERR(temp))
			goto temp_err;

		err = ovl_create_real(d_inode(c->workdir), temp, &cattr,
				      NULL, true);
		if (err) {
			dput(temp);
			goto out;
		}
	}
	err = 0;
	*tempp = temp;
out:
	if (new_creds) {
		revert_creds(old_creds);
		put_cred(new_creds);
	}

	return err;

temp_err:
	err = PTR_ERR(temp);
	goto out;
}

static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
{
	int err;

	if (S_ISREG(c->stat.mode)) {
		struct path upperpath;

		ovl_path_upper(c->dentry, &upperpath);
		BUG_ON(upperpath.dentry != NULL);
		upperpath.dentry = temp;

		err = ovl_copy_up_data(&c->lowerpath, &upperpath, c->stat.size);
		if (err)
			return err;
	}

	err = ovl_copy_xattr(c->lowerpath.dentry, temp);
	if (err)
		return err;

	inode_lock(temp->d_inode);
	err = ovl_set_attr(temp, &c->stat);
	inode_unlock(temp->d_inode);
	if (err)
		return err;

	/*
	 * Store identifier of lower inode in upper inode xattr to
	 * allow lookup of the copy up origin inode.
	 *
	 * Don't set origin when we are breaking the association with a lower
	 * hard link.
	 */
	if (c->origin) {
		err = ovl_set_origin(c->dentry, c->lowerpath.dentry, temp);
		if (err)
			return err;
	}

	return 0;
}

static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
{
	struct inode *udir = c->destdir->d_inode;
	struct dentry *newdentry = NULL;
	struct dentry *temp = NULL;
	int err;

	err = ovl_get_tmpfile(c, &temp);
	if (err)
		goto out;

	err = ovl_copy_up_inode(c, temp);
	if (err)
		goto out_cleanup;

	if (c->tmpfile) {
		inode_lock_nested(udir, I_MUTEX_PARENT);
		err = ovl_install_temp(c, temp, &newdentry);
		inode_unlock(udir);
	} else {
		err = ovl_install_temp(c, temp, &newdentry);
	}
	if (err)
		goto out_cleanup;

	ovl_inode_update(d_inode(c->dentry), newdentry);
out:
	dput(temp);
	return err;

out_cleanup:
	if (!c->tmpfile)
		ovl_cleanup(d_inode(c->workdir), temp);
	goto out;
}

/*
 * Copy up a single dentry
 *
 * All renames start with copy up of source if necessary.  The actual
 * rename will only proceed once the copy up was successful.  Copy up uses
 * upper parent i_mutex for exclusion.  Since rename can change d_parent it
 * is possible that the copy up will lock the old parent.  At that point
 * the file will have already been copied up anyway.
 */
static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
{
	int err;
	struct ovl_fs *ofs = c->dentry->d_sb->s_fs_info;
	bool indexed = false;

	if (ovl_indexdir(c->dentry->d_sb) && !S_ISDIR(c->stat.mode) &&
	    c->stat.nlink > 1)
		indexed = true;

	if (S_ISDIR(c->stat.mode) || c->stat.nlink == 1 || indexed)
		c->origin = true;

	if (indexed) {
		c->destdir = ovl_indexdir(c->dentry->d_sb);
		err = ovl_get_index_name(c->lowerpath.dentry, &c->destname);
		if (err)
			return err;
	} else {
		/*
		 * Mark parent "impure" because it may now contain non-pure
		 * upper
		 */
		err = ovl_set_impure(c->parent, c->destdir);
		if (err)
			return err;
	}

	/* Should we copyup with O_TMPFILE or with workdir? */
	if (S_ISREG(c->stat.mode) && ofs->tmpfile) {
		c->tmpfile = true;
		err = ovl_copy_up_locked(c);
	} else {
		err = ovl_lock_rename_workdir(c->workdir, c->destdir);
		if (!err) {
			err = ovl_copy_up_locked(c);
			unlock_rename(c->workdir, c->destdir);
		}
	}

	if (indexed) {
		if (!err)
			ovl_set_flag(OVL_INDEX, d_inode(c->dentry));
		kfree(c->destname.name);
	} else if (!err) {
		struct inode *udir = d_inode(c->destdir);

		/* Restore timestamps on parent (best effort) */
		inode_lock(udir);
		ovl_set_timestamps(c->destdir, &c->pstat);
		inode_unlock(udir);

		ovl_dentry_set_upper_alias(c->dentry);
	}

	return err;
}

static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
			   int flags)
{
	int err;
	DEFINE_DELAYED_CALL(done);
	struct path parentpath;
	struct ovl_copy_up_ctx ctx = {
		.parent = parent,
		.dentry = dentry,
		.workdir = ovl_workdir(dentry),
	};

	if (WARN_ON(!ctx.workdir))
		return -EROFS;

	ovl_path_lower(dentry, &ctx.lowerpath);
	err = vfs_getattr(&ctx.lowerpath, &ctx.stat,
			  STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
	if (err)
		return err;

	ovl_path_upper(parent, &parentpath);
	ctx.destdir = parentpath.dentry;
	ctx.destname = dentry->d_name;

	err = vfs_getattr(&parentpath, &ctx.pstat,
			  STATX_ATIME | STATX_MTIME, AT_STATX_SYNC_AS_STAT);
	if (err)
		return err;

	/* maybe truncate regular file. this has no effect on dirs */
	if (flags & O_TRUNC)
		ctx.stat.size = 0;

	if (S_ISLNK(ctx.stat.mode)) {
		ctx.link = vfs_get_link(ctx.lowerpath.dentry, &done);
		if (IS_ERR(ctx.link))
			return PTR_ERR(ctx.link);
	}
	ovl_do_check_copy_up(ctx.lowerpath.dentry);

	err = ovl_copy_up_start(dentry);
	/* err < 0: interrupted, err > 0: raced with another copy-up */
	if (unlikely(err)) {
		if (err > 0)
			err = 0;
	} else {
		if (!ovl_dentry_upper(dentry))
			err = ovl_do_copy_up(&ctx);
		if (!err && !ovl_dentry_has_upper_alias(dentry))
			err = ovl_link_up(&ctx);
		ovl_copy_up_end(dentry);
	}
	do_delayed_call(&done);

	return err;
}

int ovl_copy_up_flags(struct dentry *dentry, int flags)
{
	int err = 0;
	const struct cred *old_cred = ovl_override_creds(dentry->d_sb);

	while (!err) {
		struct dentry *next;
		struct dentry *parent;

		/*
		 * Check if copy-up has happened as well as for upper alias (in
		 * case of hard links) is there.
		 *
		 * Both checks are lockless:
		 *  - false negatives: will recheck under oi->lock
		 *  - false positives:
		 *    + ovl_dentry_upper() uses memory barriers to ensure the
		 *      upper dentry is up-to-date
		 *    + ovl_dentry_has_upper_alias() relies on locking of
		 *      upper parent i_rwsem to prevent reordering copy-up
		 *      with rename.
		 */
		if (ovl_dentry_upper(dentry) &&
		    ovl_dentry_has_upper_alias(dentry))
			break;

		next = dget(dentry);
		/* find the topmost dentry not yet copied up */
		for (;;) {
			parent = dget_parent(next);

			if (ovl_dentry_upper(parent))
				break;

			dput(next);
			next = parent;
		}

		err = ovl_copy_up_one(parent, next, flags);

		dput(parent);
		dput(next);
	}
	revert_creds(old_cred);

	return err;
}

int ovl_copy_up(struct dentry *dentry)
{
	return ovl_copy_up_flags(dentry, 0);
}