summaryrefslogtreecommitdiff
path: root/fs/overlayfs/namei.c
blob: 023bb0b03352f4440d893b4e713d7d9ed937a771 (plain)
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
/*
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, 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/fs.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"
#include "ovl_entry.h"

struct ovl_lookup_data {
	struct qstr name;
	bool is_dir;
	bool opaque;
	bool stop;
	bool last;
	char *redirect;
};

static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
			      size_t prelen, const char *post)
{
	int res;
	char *s, *next, *buf = NULL;

	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
	if (res < 0) {
		if (res == -ENODATA || res == -EOPNOTSUPP)
			return 0;
		goto fail;
	}
	buf = kzalloc(prelen + res + strlen(post) + 1, GFP_TEMPORARY);
	if (!buf)
		return -ENOMEM;

	if (res == 0)
		goto invalid;

	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
	if (res < 0)
		goto fail;
	if (res == 0)
		goto invalid;
	if (buf[0] == '/') {
		for (s = buf; *s++ == '/'; s = next) {
			next = strchrnul(s, '/');
			if (s == next)
				goto invalid;
		}
	} else {
		if (strchr(buf, '/') != NULL)
			goto invalid;

		memmove(buf + prelen, buf, res);
		memcpy(buf, d->name.name, prelen);
	}

	strcat(buf, post);
	kfree(d->redirect);
	d->redirect = buf;
	d->name.name = d->redirect;
	d->name.len = strlen(d->redirect);

	return 0;

err_free:
	kfree(buf);
	return 0;
fail:
	pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
	goto err_free;
invalid:
	pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
	goto err_free;
}

static bool ovl_is_opaquedir(struct dentry *dentry)
{
	int res;
	char val;

	if (!d_is_dir(dentry))
		return false;

	res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
	if (res == 1 && val == 'y')
		return true;

	return false;
}

static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
			     const char *name, unsigned int namelen,
			     size_t prelen, const char *post,
			     struct dentry **ret)
{
	struct dentry *this;
	int err;

	this = lookup_one_len_unlocked(name, base, namelen);
	if (IS_ERR(this)) {
		err = PTR_ERR(this);
		this = NULL;
		if (err == -ENOENT || err == -ENAMETOOLONG)
			goto out;
		goto out_err;
	}
	if (!this->d_inode)
		goto put_and_out;

	if (ovl_dentry_weird(this)) {
		/* Don't support traversing automounts and other weirdness */
		err = -EREMOTE;
		goto out_err;
	}
	if (ovl_is_whiteout(this)) {
		d->stop = d->opaque = true;
		goto put_and_out;
	}
	if (!d_can_lookup(this)) {
		d->stop = true;
		if (d->is_dir)
			goto put_and_out;
		goto out;
	}
	d->is_dir = true;
	if (!d->last && ovl_is_opaquedir(this)) {
		d->stop = d->opaque = true;
		goto out;
	}
	err = ovl_check_redirect(this, d, prelen, post);
	if (err)
		goto out_err;
out:
	*ret = this;
	return 0;

put_and_out:
	dput(this);
	this = NULL;
	goto out;

out_err:
	dput(this);
	return err;
}

static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
			    struct dentry **ret)
{
	/* Counting down from the end, since the prefix can change */
	size_t rem = d->name.len - 1;
	struct dentry *dentry = NULL;
	int err;

	if (d->name.name[0] != '/')
		return ovl_lookup_single(base, d, d->name.name, d->name.len,
					 0, "", ret);

	while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
		const char *s = d->name.name + d->name.len - rem;
		const char *next = strchrnul(s, '/');
		size_t thislen = next - s;
		bool end = !next[0];

		/* Verify we did not go off the rails */
		if (WARN_ON(s[-1] != '/'))
			return -EIO;

		err = ovl_lookup_single(base, d, s, thislen,
					d->name.len - rem, next, &base);
		dput(dentry);
		if (err)
			return err;
		dentry = base;
		if (end)
			break;

		rem -= thislen + 1;

		if (WARN_ON(rem >= d->name.len))
			return -EIO;
	}
	*ret = dentry;
	return 0;
}

/*
 * Returns next layer in stack starting from top.
 * Returns -1 if this is the last layer.
 */
int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	BUG_ON(idx < 0);
	if (idx == 0) {
		ovl_path_upper(dentry, path);
		if (path->dentry)
			return oe->numlower ? 1 : -1;
		idx++;
	}
	BUG_ON(idx > oe->numlower);
	*path = oe->lowerstack[idx - 1];

	return (idx < oe->numlower) ? idx + 1 : -1;
}

struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
			  unsigned int flags)
{
	struct ovl_entry *oe;
	const struct cred *old_cred;
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
	struct path *stack = NULL;
	struct dentry *upperdir, *upperdentry = NULL;
	unsigned int ctr = 0;
	struct inode *inode = NULL;
	bool upperopaque = false;
	char *upperredirect = NULL;
	struct dentry *this;
	unsigned int i;
	int err;
	struct ovl_lookup_data d = {
		.name = dentry->d_name,
		.is_dir = false,
		.opaque = false,
		.stop = false,
		.last = !poe->numlower,
		.redirect = NULL,
	};

	if (dentry->d_name.len > ofs->namelen)
		return ERR_PTR(-ENAMETOOLONG);

	old_cred = ovl_override_creds(dentry->d_sb);
	upperdir = ovl_upperdentry_dereference(poe);
	if (upperdir) {
		err = ovl_lookup_layer(upperdir, &d, &upperdentry);
		if (err)
			goto out;

		if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
			dput(upperdentry);
			err = -EREMOTE;
			goto out;
		}

		if (d.redirect) {
			upperredirect = kstrdup(d.redirect, GFP_KERNEL);
			if (!upperredirect)
				goto out_put_upper;
			if (d.redirect[0] == '/')
				poe = dentry->d_sb->s_root->d_fsdata;
		}
		upperopaque = d.opaque;
	}

	if (!d.stop && poe->numlower) {
		err = -ENOMEM;
		stack = kcalloc(ofs->numlower, sizeof(struct path),
				GFP_TEMPORARY);
		if (!stack)
			goto out_put_upper;
	}

	for (i = 0; !d.stop && i < poe->numlower; i++) {
		struct path lowerpath = poe->lowerstack[i];

		d.last = i == poe->numlower - 1;
		err = ovl_lookup_layer(lowerpath.dentry, &d, &this);
		if (err)
			goto out_put;

		if (!this)
			continue;

		stack[ctr].dentry = this;
		stack[ctr].mnt = lowerpath.mnt;
		ctr++;

		if (d.stop)
			break;

		if (d.redirect &&
		    d.redirect[0] == '/' &&
		    poe != dentry->d_sb->s_root->d_fsdata) {
			poe = dentry->d_sb->s_root->d_fsdata;

			/* Find the current layer on the root dentry */
			for (i = 0; i < poe->numlower; i++)
				if (poe->lowerstack[i].mnt == lowerpath.mnt)
					break;
			if (WARN_ON(i == poe->numlower))
				break;
		}
	}

	oe = ovl_alloc_entry(ctr);
	err = -ENOMEM;
	if (!oe)
		goto out_put;

	if (upperdentry || ctr) {
		struct dentry *realdentry;
		struct inode *realinode;

		realdentry = upperdentry ? upperdentry : stack[0].dentry;
		realinode = d_inode(realdentry);

		err = -ENOMEM;
		if (upperdentry && !d_is_dir(upperdentry)) {
			inode = ovl_get_inode(dentry->d_sb, realinode);
		} else {
			inode = ovl_new_inode(dentry->d_sb, realinode->i_mode,
					      realinode->i_rdev);
			if (inode)
				ovl_inode_init(inode, realinode, !!upperdentry);
		}
		if (!inode)
			goto out_free_oe;
		ovl_copyattr(realdentry->d_inode, inode);
	}

	revert_creds(old_cred);
	oe->opaque = upperopaque;
	oe->redirect = upperredirect;
	oe->__upperdentry = upperdentry;
	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
	kfree(stack);
	kfree(d.redirect);
	dentry->d_fsdata = oe;
	d_add(dentry, inode);

	return NULL;

out_free_oe:
	kfree(oe);
out_put:
	for (i = 0; i < ctr; i++)
		dput(stack[i].dentry);
	kfree(stack);
out_put_upper:
	dput(upperdentry);
	kfree(upperredirect);
out:
	kfree(d.redirect);
	revert_creds(old_cred);
	return ERR_PTR(err);
}

bool ovl_lower_positive(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
	const struct qstr *name = &dentry->d_name;
	unsigned int i;
	bool positive = false;
	bool done = false;

	/*
	 * If dentry is negative, then lower is positive iff this is a
	 * whiteout.
	 */
	if (!dentry->d_inode)
		return oe->opaque;

	/* Negative upper -> positive lower */
	if (!oe->__upperdentry)
		return true;

	/* Positive upper -> have to look up lower to see whether it exists */
	for (i = 0; !done && !positive && i < poe->numlower; i++) {
		struct dentry *this;
		struct dentry *lowerdir = poe->lowerstack[i].dentry;

		this = lookup_one_len_unlocked(name->name, lowerdir,
					       name->len);
		if (IS_ERR(this)) {
			switch (PTR_ERR(this)) {
			case -ENOENT:
			case -ENAMETOOLONG:
				break;

			default:
				/*
				 * Assume something is there, we just couldn't
				 * access it.
				 */
				positive = true;
				break;
			}
		} else {
			if (this->d_inode) {
				positive = !ovl_is_whiteout(this);
				done = true;
			}
			dput(this);
		}
	}

	return positive;
}