aboutsummaryrefslogtreecommitdiffstats
path: root/fs/crypto/fname.c
blob: e33f3d3c5ade8ce6e647e6b5021f7e51f00a96c1 (plain) (blame)
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
// SPDX-License-Identifier: GPL-2.0
/*
 * This contains functions for filename crypto management
 *
 * Copyright (C) 2015, Google, Inc.
 * Copyright (C) 2015, Motorola Mobility
 *
 * Written by Uday Savagaonkar, 2014.
 * Modified by Jaegeuk Kim, 2015.
 *
 * This has not yet undergone a rigorous security audit.
 */

#include <linux/scatterlist.h>
#include <linux/ratelimit.h>
#include <crypto/skcipher.h>
#include "fscrypt_private.h"

static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
{
	if (str->len == 1 && str->name[0] == '.')
		return true;

	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
		return true;

	return false;
}

/**
 * fname_encrypt() - encrypt a filename
 *
 * The output buffer must be at least as large as the input buffer.
 * Any extra space is filled with NUL padding before encryption.
 *
 * Return: 0 on success, -errno on failure
 */
int fname_encrypt(struct inode *inode, const struct qstr *iname,
		  u8 *out, unsigned int olen)
{
	struct skcipher_request *req = NULL;
	DECLARE_CRYPTO_WAIT(wait);
	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
	int res = 0;
	char iv[FS_CRYPTO_BLOCK_SIZE];
	struct scatterlist sg;

	/*
	 * Copy the filename to the output buffer for encrypting in-place and
	 * pad it with the needed number of NUL bytes.
	 */
	if (WARN_ON(olen < iname->len))
		return -ENOBUFS;
	memcpy(out, iname->name, iname->len);
	memset(out + iname->len, 0, olen - iname->len);

	/* Initialize the IV */
	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

	/* Set up the encryption request */
	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req) {
		printk_ratelimited(KERN_ERR
			"%s: skcipher_request_alloc() failed\n", __func__);
		return -ENOMEM;
	}
	skcipher_request_set_callback(req,
			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
			crypto_req_done, &wait);
	sg_init_one(&sg, out, olen);
	skcipher_request_set_crypt(req, &sg, &sg, olen, iv);

	/* Do the encryption */
	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
	skcipher_request_free(req);
	if (res < 0) {
		printk_ratelimited(KERN_ERR
				"%s: Error (error code %d)\n", __func__, res);
		return res;
	}

	return 0;
}

/**
 * fname_decrypt() - decrypt a filename
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * Return: 0 on success, -errno on failure
 */
static int fname_decrypt(struct inode *inode,
				const struct fscrypt_str *iname,
				struct fscrypt_str *oname)
{
	struct skcipher_request *req = NULL;
	DECLARE_CRYPTO_WAIT(wait);
	struct scatterlist src_sg, dst_sg;
	struct fscrypt_info *ci = inode->i_crypt_info;
	struct crypto_skcipher *tfm = ci->ci_ctfm;
	int res = 0;
	char iv[FS_CRYPTO_BLOCK_SIZE];
	unsigned lim;

	lim = inode->i_sb->s_cop->max_namelen(inode);
	if (iname->len <= 0 || iname->len > lim)
		return -EIO;

	/* Allocate request */
	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req) {
		printk_ratelimited(KERN_ERR
			"%s: crypto_request_alloc() failed\n",  __func__);
		return -ENOMEM;
	}
	skcipher_request_set_callback(req,
		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
		crypto_req_done, &wait);

	/* Initialize IV */
	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

	/* Create decryption request */
	sg_init_one(&src_sg, iname->name, iname->len);
	sg_init_one(&dst_sg, oname->name, oname->len);
	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
	skcipher_request_free(req);
	if (res < 0) {
		printk_ratelimited(KERN_ERR
				"%s: Error (error code %d)\n", __func__, res);
		return res;
	}

	oname->len = strnlen(oname->name, iname->len);
	return 0;
}

static const char *lookup_table =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";

#define BASE64_CHARS(nbytes)	DIV_ROUND_UP((nbytes) * 4, 3)

/**
 * digest_encode() -
 *
 * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 * The encoded string is roughly 4/3 times the size of the input string.
 */
static int digest_encode(const char *src, int len, char *dst)
{
	int i = 0, bits = 0, ac = 0;
	char *cp = dst;

	while (i < len) {
		ac += (((unsigned char) src[i]) << bits);
		bits += 8;
		do {
			*cp++ = lookup_table[ac & 0x3f];
			ac >>= 6;
			bits -= 6;
		} while (bits >= 6);
		i++;
	}
	if (bits)
		*cp++ = lookup_table[ac & 0x3f];
	return cp - dst;
}

static int digest_decode(const char *src, int len, char *dst)
{
	int i = 0, bits = 0, ac = 0;
	const char *p;
	char *cp = dst;

	while (i < len) {
		p = strchr(lookup_table, src[i]);
		if (p == NULL || src[i] == 0)
			return -2;
		ac += (p - lookup_table) << bits;
		bits += 6;
		if (bits >= 8) {
			*cp++ = ac & 0xff;
			ac >>= 8;
			bits -= 8;
		}
		i++;
	}
	if (ac)
		return -1;
	return cp - dst;
}

bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
				  u32 max_len, u32 *encrypted_len_ret)
{
	int padding = 4 << (inode->i_crypt_info->ci_flags &
			    FS_POLICY_FLAGS_PAD_MASK);
	u32 encrypted_len;

	if (orig_len > max_len)
		return false;
	encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
	encrypted_len = round_up(encrypted_len, padding);
	*encrypted_len_ret = min(encrypted_len, max_len);
	return true;
}

/**
 * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
 *
 * Allocate a buffer that is large enough to hold any decrypted or encoded
 * filename (null-terminated), for the given maximum encrypted filename length.
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_fname_alloc_buffer(const struct inode *inode,
			       u32 max_encrypted_len,
			       struct fscrypt_str *crypto_str)
{
	const u32 max_encoded_len =
		max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
		      1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
	u32 max_presented_len;

	max_presented_len = max(max_encoded_len, max_encrypted_len);

	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
	if (!crypto_str->name)
		return -ENOMEM;
	crypto_str->len = max_presented_len;
	return 0;
}
EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);

/**
 * fscrypt_fname_free_buffer - free the buffer for presented filenames
 *
 * Free the buffer allocated by fscrypt_fname_alloc_buffer().
 */
void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
{
	if (!crypto_str)
		return;
	kfree(crypto_str->name);
	crypto_str->name = NULL;
}
EXPORT_SYMBOL(fscrypt_fname_free_buffer);

/**
 * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 * space
 *
 * The caller must have allocated sufficient memory for the @oname string.
 *
 * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 * it for presentation.  Short names are directly base64-encoded, while long
 * names are encoded in fscrypt_digested_name format.
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_fname_disk_to_usr(struct inode *inode,
			u32 hash, u32 minor_hash,
			const struct fscrypt_str *iname,
			struct fscrypt_str *oname)
{
	const struct qstr qname = FSTR_TO_QSTR(iname);
	struct fscrypt_digested_name digested_name;

	if (fscrypt_is_dot_dotdot(&qname)) {
		oname->name[0] = '.';
		oname->name[iname->len - 1] = '.';
		oname->len = iname->len;
		return 0;
	}

	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
		return -EUCLEAN;

	if (inode->i_crypt_info)
		return fname_decrypt(inode, iname, oname);

	if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
		oname->len = digest_encode(iname->name, iname->len,
					   oname->name);
		return 0;
	}
	if (hash) {
		digested_name.hash = hash;
		digested_name.minor_hash = minor_hash;
	} else {
		digested_name.hash = 0;
		digested_name.minor_hash = 0;
	}
	memcpy(digested_name.digest,
	       FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
	       FSCRYPT_FNAME_DIGEST_SIZE);
	oname->name[0] = '_';
	oname->len = 1 + digest_encode((const char *)&digested_name,
				       sizeof(digested_name), oname->name + 1);
	return 0;
}
EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);

/**
 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 * @dir: the directory that will be searched
 * @iname: the user-provided filename being searched for
 * @lookup: 1 if we're allowed to proceed without the key because it's
 *	->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 *	proceed without the key because we're going to create the dir_entry.
 * @fname: the filename information to be filled in
 *
 * Given a user-provided filename @iname, this function sets @fname->disk_name
 * to the name that would be stored in the on-disk directory entry, if possible.
 * If the directory is unencrypted this is simply @iname.  Else, if we have the
 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 * get the disk_name.
 *
 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 * we decode it to get either the ciphertext disk_name (for short names) or the
 * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 * impossible in this case, so we fail them with ENOKEY.
 *
 * If successful, fscrypt_free_filename() must be called later to clean up.
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
			      int lookup, struct fscrypt_name *fname)
{
	int ret;
	int digested;

	memset(fname, 0, sizeof(struct fscrypt_name));
	fname->usr_fname = iname;

	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
		fname->disk_name.name = (unsigned char *)iname->name;
		fname->disk_name.len = iname->len;
		return 0;
	}
	ret = fscrypt_get_encryption_info(dir);
	if (ret && ret != -EOPNOTSUPP)
		return ret;

	if (dir->i_crypt_info) {
		if (!fscrypt_fname_encrypted_size(dir, iname->len,
						  dir->i_sb->s_cop->max_namelen(dir),
						  &fname->crypto_buf.len))
			return -ENAMETOOLONG;
		fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
						 GFP_NOFS);
		if (!fname->crypto_buf.name)
			return -ENOMEM;

		ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
				    fname->crypto_buf.len);
		if (ret)
			goto errout;
		fname->disk_name.name = fname->crypto_buf.name;
		fname->disk_name.len = fname->crypto_buf.len;
		return 0;
	}
	if (!lookup)
		return -ENOKEY;

	/*
	 * We don't have the key and we are doing a lookup; decode the
	 * user-supplied name
	 */
	if (iname->name[0] == '_') {
		if (iname->len !=
		    1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
			return -ENOENT;
		digested = 1;
	} else {
		if (iname->len >
		    BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
			return -ENOENT;
		digested = 0;
	}

	fname->crypto_buf.name =
		kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
			      sizeof(struct fscrypt_digested_name)),
			GFP_KERNEL);
	if (fname->crypto_buf.name == NULL)
		return -ENOMEM;

	ret = digest_decode(iname->name + digested, iname->len - digested,
				fname->crypto_buf.name);
	if (ret < 0) {
		ret = -ENOENT;
		goto errout;
	}
	fname->crypto_buf.len = ret;
	if (digested) {
		const struct fscrypt_digested_name *n =
			(const void *)fname->crypto_buf.name;
		fname->hash = n->hash;
		fname->minor_hash = n->minor_hash;
	} else {
		fname->disk_name.name = fname->crypto_buf.name;
		fname->disk_name.len = fname->crypto_buf.len;
	}
	return 0;

errout:
	kfree(fname->crypto_buf.name);
	return ret;
}
EXPORT_SYMBOL(fscrypt_setup_filename);