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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This contains functions for filename crypto management
4 *
5 * Copyright (C) 2015, Google, Inc.
6 * Copyright (C) 2015, Motorola Mobility
7 *
8 * Written by Uday Savagaonkar, 2014.
9 * Modified by Jaegeuk Kim, 2015.
10 *
11 * This has not yet undergone a rigorous security audit.
12 */
13
14#include <linux/namei.h>
15#include <linux/scatterlist.h>
16#include <crypto/hash.h>
17#include <crypto/sha.h>
18#include <crypto/skcipher.h>
19#include "fscrypt_private.h"
20
21/*
22 * struct fscrypt_nokey_name - identifier for directory entry when key is absent
23 *
24 * When userspace lists an encrypted directory without access to the key, the
25 * filesystem must present a unique "no-key name" for each filename that allows
26 * it to find the directory entry again if requested. Naively, that would just
27 * mean using the ciphertext filenames. However, since the ciphertext filenames
28 * can contain illegal characters ('\0' and '/'), they must be encoded in some
29 * way. We use base64. But that can cause names to exceed NAME_MAX (255
30 * bytes), so we also need to use a strong hash to abbreviate long names.
31 *
32 * The filesystem may also need another kind of hash, the "dirhash", to quickly
33 * find the directory entry. Since filesystems normally compute the dirhash
34 * over the on-disk filename (i.e. the ciphertext), it's not computable from
35 * no-key names that abbreviate the ciphertext using the strong hash to fit in
36 * NAME_MAX. It's also not computable if it's a keyed hash taken over the
37 * plaintext (but it may still be available in the on-disk directory entry);
38 * casefolded directories use this type of dirhash. At least in these cases,
39 * each no-key name must include the name's dirhash too.
40 *
41 * To meet all these requirements, we base64-encode the following
42 * variable-length structure. It contains the dirhash, or 0's if the filesystem
43 * didn't provide one; up to 149 bytes of the ciphertext name; and for
44 * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
45 *
46 * This ensures that each no-key name contains everything needed to find the
47 * directory entry again, contains only legal characters, doesn't exceed
48 * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
49 * take the performance hit of SHA-256 on very long filenames (which are rare).
50 */
51struct fscrypt_nokey_name {
52 u32 dirhash[2];
53 u8 bytes[149];
54 u8 sha256[SHA256_DIGEST_SIZE];
55}; /* 189 bytes => 252 bytes base64-encoded, which is <= NAME_MAX (255) */
56
57/*
58 * Decoded size of max-size nokey name, i.e. a name that was abbreviated using
59 * the strong hash and thus includes the 'sha256' field. This isn't simply
60 * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
61 */
62#define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)
63
64static void fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result)
65{
66 struct sha256_state sctx;
67
68 sha256_init(&sctx);
69 sha256_update(&sctx, data, data_len);
70 sha256_final(&sctx, result);
71}
72
73static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
74{
75 if (str->len == 1 && str->name[0] == '.')
76 return true;
77
78 if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
79 return true;
80
81 return false;
82}
83
84/**
85 * fscrypt_fname_encrypt() - encrypt a filename
86 * @inode: inode of the parent directory (for regular filenames)
87 * or of the symlink (for symlink targets)
88 * @iname: the filename to encrypt
89 * @out: (output) the encrypted filename
90 * @olen: size of the encrypted filename. It must be at least @iname->len.
91 * Any extra space is filled with NUL padding before encryption.
92 *
93 * Return: 0 on success, -errno on failure
94 */
95int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
96 u8 *out, unsigned int olen)
97{
98 struct skcipher_request *req = NULL;
99 DECLARE_CRYPTO_WAIT(wait);
100 const struct fscrypt_info *ci = inode->i_crypt_info;
101 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
102 union fscrypt_iv iv;
103 struct scatterlist sg;
104 int res;
105
106 /*
107 * Copy the filename to the output buffer for encrypting in-place and
108 * pad it with the needed number of NUL bytes.
109 */
110 if (WARN_ON(olen < iname->len))
111 return -ENOBUFS;
112 memcpy(out, iname->name, iname->len);
113 memset(out + iname->len, 0, olen - iname->len);
114
115 /* Initialize the IV */
116 fscrypt_generate_iv(&iv, 0, ci);
117
118 /* Set up the encryption request */
119 req = skcipher_request_alloc(tfm, GFP_NOFS);
120 if (!req)
121 return -ENOMEM;
122 skcipher_request_set_callback(req,
123 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
124 crypto_req_done, &wait);
125 sg_init_one(&sg, out, olen);
126 skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
127
128 /* Do the encryption */
129 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
130 skcipher_request_free(req);
131 if (res < 0) {
132 fscrypt_err(inode, "Filename encryption failed: %d", res);
133 return res;
134 }
135
136 return 0;
137}
138
139/**
140 * fname_decrypt() - decrypt a filename
141 * @inode: inode of the parent directory (for regular filenames)
142 * or of the symlink (for symlink targets)
143 * @iname: the encrypted filename to decrypt
144 * @oname: (output) the decrypted filename. The caller must have allocated
145 * enough space for this, e.g. using fscrypt_fname_alloc_buffer().
146 *
147 * Return: 0 on success, -errno on failure
148 */
149static int fname_decrypt(const struct inode *inode,
150 const struct fscrypt_str *iname,
151 struct fscrypt_str *oname)
152{
153 struct skcipher_request *req = NULL;
154 DECLARE_CRYPTO_WAIT(wait);
155 struct scatterlist src_sg, dst_sg;
156 const struct fscrypt_info *ci = inode->i_crypt_info;
157 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
158 union fscrypt_iv iv;
159 int res;
160
161 /* Allocate request */
162 req = skcipher_request_alloc(tfm, GFP_NOFS);
163 if (!req)
164 return -ENOMEM;
165 skcipher_request_set_callback(req,
166 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
167 crypto_req_done, &wait);
168
169 /* Initialize IV */
170 fscrypt_generate_iv(&iv, 0, ci);
171
172 /* Create decryption request */
173 sg_init_one(&src_sg, iname->name, iname->len);
174 sg_init_one(&dst_sg, oname->name, oname->len);
175 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
176 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
177 skcipher_request_free(req);
178 if (res < 0) {
179 fscrypt_err(inode, "Filename decryption failed: %d", res);
180 return res;
181 }
182
183 oname->len = strnlen(oname->name, iname->len);
184 return 0;
185}
186
187static const char lookup_table[65] =
188 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
189
190#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
191
192/**
193 * base64_encode() - base64-encode some bytes
194 * @src: the bytes to encode
195 * @len: number of bytes to encode
196 * @dst: (output) the base64-encoded string. Not NUL-terminated.
197 *
198 * Encodes the input string using characters from the set [A-Za-z0-9+,].
199 * The encoded string is roughly 4/3 times the size of the input string.
200 *
201 * Return: length of the encoded string
202 */
203static int base64_encode(const u8 *src, int len, char *dst)
204{
205 int i, bits = 0, ac = 0;
206 char *cp = dst;
207
208 for (i = 0; i < len; i++) {
209 ac += src[i] << bits;
210 bits += 8;
211 do {
212 *cp++ = lookup_table[ac & 0x3f];
213 ac >>= 6;
214 bits -= 6;
215 } while (bits >= 6);
216 }
217 if (bits)
218 *cp++ = lookup_table[ac & 0x3f];
219 return cp - dst;
220}
221
222static int base64_decode(const char *src, int len, u8 *dst)
223{
224 int i, bits = 0, ac = 0;
225 const char *p;
226 u8 *cp = dst;
227
228 for (i = 0; i < len; i++) {
229 p = strchr(lookup_table, src[i]);
230 if (p == NULL || src[i] == 0)
231 return -2;
232 ac += (p - lookup_table) << bits;
233 bits += 6;
234 if (bits >= 8) {
235 *cp++ = ac & 0xff;
236 ac >>= 8;
237 bits -= 8;
238 }
239 }
240 if (ac)
241 return -1;
242 return cp - dst;
243}
244
245bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
246 u32 max_len, u32 *encrypted_len_ret)
247{
248 const struct fscrypt_info *ci = inode->i_crypt_info;
249 int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
250 FSCRYPT_POLICY_FLAGS_PAD_MASK);
251 u32 encrypted_len;
252
253 if (orig_len > max_len)
254 return false;
255 encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
256 encrypted_len = round_up(encrypted_len, padding);
257 *encrypted_len_ret = min(encrypted_len, max_len);
258 return true;
259}
260
261/**
262 * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
263 * @inode: inode of the parent directory (for regular filenames)
264 * or of the symlink (for symlink targets)
265 * @max_encrypted_len: maximum length of encrypted filenames the buffer will be
266 * used to present
267 * @crypto_str: (output) buffer to allocate
268 *
269 * Allocate a buffer that is large enough to hold any decrypted or encoded
270 * filename (null-terminated), for the given maximum encrypted filename length.
271 *
272 * Return: 0 on success, -errno on failure
273 */
274int fscrypt_fname_alloc_buffer(const struct inode *inode,
275 u32 max_encrypted_len,
276 struct fscrypt_str *crypto_str)
277{
278 const u32 max_encoded_len = BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX);
279 u32 max_presented_len;
280
281 max_presented_len = max(max_encoded_len, max_encrypted_len);
282
283 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
284 if (!crypto_str->name)
285 return -ENOMEM;
286 crypto_str->len = max_presented_len;
287 return 0;
288}
289EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
290
291/**
292 * fscrypt_fname_free_buffer() - free a buffer for presented filenames
293 * @crypto_str: the buffer to free
294 *
295 * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
296 */
297void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
298{
299 if (!crypto_str)
300 return;
301 kfree(crypto_str->name);
302 crypto_str->name = NULL;
303}
304EXPORT_SYMBOL(fscrypt_fname_free_buffer);
305
306/**
307 * fscrypt_fname_disk_to_usr() - convert an encrypted filename to
308 * user-presentable form
309 * @inode: inode of the parent directory (for regular filenames)
310 * or of the symlink (for symlink targets)
311 * @hash: first part of the name's dirhash, if applicable. This only needs to
312 * be provided if the filename is located in an indexed directory whose
313 * encryption key may be unavailable. Not needed for symlink targets.
314 * @minor_hash: second part of the name's dirhash, if applicable
315 * @iname: encrypted filename to convert. May also be "." or "..", which
316 * aren't actually encrypted.
317 * @oname: output buffer for the user-presentable filename. The caller must
318 * have allocated enough space for this, e.g. using
319 * fscrypt_fname_alloc_buffer().
320 *
321 * If the key is available, we'll decrypt the disk name. Otherwise, we'll
322 * encode it for presentation in fscrypt_nokey_name format.
323 * See struct fscrypt_nokey_name for details.
324 *
325 * Return: 0 on success, -errno on failure
326 */
327int fscrypt_fname_disk_to_usr(const struct inode *inode,
328 u32 hash, u32 minor_hash,
329 const struct fscrypt_str *iname,
330 struct fscrypt_str *oname)
331{
332 const struct qstr qname = FSTR_TO_QSTR(iname);
333 struct fscrypt_nokey_name nokey_name;
334 u32 size; /* size of the unencoded no-key name */
335
336 if (fscrypt_is_dot_dotdot(&qname)) {
337 oname->name[0] = '.';
338 oname->name[iname->len - 1] = '.';
339 oname->len = iname->len;
340 return 0;
341 }
342
343 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
344 return -EUCLEAN;
345
346 if (fscrypt_has_encryption_key(inode))
347 return fname_decrypt(inode, iname, oname);
348
349 /*
350 * Sanity check that struct fscrypt_nokey_name doesn't have padding
351 * between fields and that its encoded size never exceeds NAME_MAX.
352 */
353 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
354 offsetof(struct fscrypt_nokey_name, bytes));
355 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
356 offsetof(struct fscrypt_nokey_name, sha256));
357 BUILD_BUG_ON(BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) > NAME_MAX);
358
359 if (hash) {
360 nokey_name.dirhash[0] = hash;
361 nokey_name.dirhash[1] = minor_hash;
362 } else {
363 nokey_name.dirhash[0] = 0;
364 nokey_name.dirhash[1] = 0;
365 }
366 if (iname->len <= sizeof(nokey_name.bytes)) {
367 memcpy(nokey_name.bytes, iname->name, iname->len);
368 size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
369 } else {
370 memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
371 /* Compute strong hash of remaining part of name. */
372 fscrypt_do_sha256(&iname->name[sizeof(nokey_name.bytes)],
373 iname->len - sizeof(nokey_name.bytes),
374 nokey_name.sha256);
375 size = FSCRYPT_NOKEY_NAME_MAX;
376 }
377 oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name);
378 return 0;
379}
380EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
381
382/**
383 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
384 * @dir: the directory that will be searched
385 * @iname: the user-provided filename being searched for
386 * @lookup: 1 if we're allowed to proceed without the key because it's
387 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
388 * proceed without the key because we're going to create the dir_entry.
389 * @fname: the filename information to be filled in
390 *
391 * Given a user-provided filename @iname, this function sets @fname->disk_name
392 * to the name that would be stored in the on-disk directory entry, if possible.
393 * If the directory is unencrypted this is simply @iname. Else, if we have the
394 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
395 * get the disk_name.
396 *
397 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
398 * we decode it to get the fscrypt_nokey_name. Non-@lookup operations will be
399 * impossible in this case, so we fail them with ENOKEY.
400 *
401 * If successful, fscrypt_free_filename() must be called later to clean up.
402 *
403 * Return: 0 on success, -errno on failure
404 */
405int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
406 int lookup, struct fscrypt_name *fname)
407{
408 struct fscrypt_nokey_name *nokey_name;
409 int ret;
410
411 memset(fname, 0, sizeof(struct fscrypt_name));
412 fname->usr_fname = iname;
413
414 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
415 fname->disk_name.name = (unsigned char *)iname->name;
416 fname->disk_name.len = iname->len;
417 return 0;
418 }
419 ret = fscrypt_get_encryption_info(dir);
420 if (ret)
421 return ret;
422
423 if (fscrypt_has_encryption_key(dir)) {
424 if (!fscrypt_fname_encrypted_size(dir, iname->len,
425 dir->i_sb->s_cop->max_namelen,
426 &fname->crypto_buf.len))
427 return -ENAMETOOLONG;
428 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
429 GFP_NOFS);
430 if (!fname->crypto_buf.name)
431 return -ENOMEM;
432
433 ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
434 fname->crypto_buf.len);
435 if (ret)
436 goto errout;
437 fname->disk_name.name = fname->crypto_buf.name;
438 fname->disk_name.len = fname->crypto_buf.len;
439 return 0;
440 }
441 if (!lookup)
442 return -ENOKEY;
443 fname->is_ciphertext_name = true;
444
445 /*
446 * We don't have the key and we are doing a lookup; decode the
447 * user-supplied name
448 */
449
450 if (iname->len > BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX))
451 return -ENOENT;
452
453 fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
454 if (fname->crypto_buf.name == NULL)
455 return -ENOMEM;
456
457 ret = base64_decode(iname->name, iname->len, fname->crypto_buf.name);
458 if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
459 (ret > offsetof(struct fscrypt_nokey_name, sha256) &&
460 ret != FSCRYPT_NOKEY_NAME_MAX)) {
461 ret = -ENOENT;
462 goto errout;
463 }
464 fname->crypto_buf.len = ret;
465
466 nokey_name = (void *)fname->crypto_buf.name;
467 fname->hash = nokey_name->dirhash[0];
468 fname->minor_hash = nokey_name->dirhash[1];
469 if (ret != FSCRYPT_NOKEY_NAME_MAX) {
470 /* The full ciphertext filename is available. */
471 fname->disk_name.name = nokey_name->bytes;
472 fname->disk_name.len =
473 ret - offsetof(struct fscrypt_nokey_name, bytes);
474 }
475 return 0;
476
477errout:
478 kfree(fname->crypto_buf.name);
479 return ret;
480}
481EXPORT_SYMBOL(fscrypt_setup_filename);
482
483/**
484 * fscrypt_match_name() - test whether the given name matches a directory entry
485 * @fname: the name being searched for
486 * @de_name: the name from the directory entry
487 * @de_name_len: the length of @de_name in bytes
488 *
489 * Normally @fname->disk_name will be set, and in that case we simply compare
490 * that to the name stored in the directory entry. The only exception is that
491 * if we don't have the key for an encrypted directory and the name we're
492 * looking for is very long, then we won't have the full disk_name and instead
493 * we'll need to match against a fscrypt_nokey_name that includes a strong hash.
494 *
495 * Return: %true if the name matches, otherwise %false.
496 */
497bool fscrypt_match_name(const struct fscrypt_name *fname,
498 const u8 *de_name, u32 de_name_len)
499{
500 const struct fscrypt_nokey_name *nokey_name =
501 (const void *)fname->crypto_buf.name;
502 u8 sha256[SHA256_DIGEST_SIZE];
503
504 if (likely(fname->disk_name.name)) {
505 if (de_name_len != fname->disk_name.len)
506 return false;
507 return !memcmp(de_name, fname->disk_name.name, de_name_len);
508 }
509 if (de_name_len <= sizeof(nokey_name->bytes))
510 return false;
511 if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
512 return false;
513 fscrypt_do_sha256(&de_name[sizeof(nokey_name->bytes)],
514 de_name_len - sizeof(nokey_name->bytes), sha256);
515 return !memcmp(sha256, nokey_name->sha256, sizeof(sha256));
516}
517EXPORT_SYMBOL_GPL(fscrypt_match_name);
518
519/**
520 * fscrypt_fname_siphash() - calculate the SipHash of a filename
521 * @dir: the parent directory
522 * @name: the filename to calculate the SipHash of
523 *
524 * Given a plaintext filename @name and a directory @dir which uses SipHash as
525 * its dirhash method and has had its fscrypt key set up, this function
526 * calculates the SipHash of that name using the directory's secret dirhash key.
527 *
528 * Return: the SipHash of @name using the hash key of @dir
529 */
530u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
531{
532 const struct fscrypt_info *ci = dir->i_crypt_info;
533
534 WARN_ON(!ci->ci_dirhash_key_initialized);
535
536 return siphash(name->name, name->len, &ci->ci_dirhash_key);
537}
538EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
539
540/*
541 * Validate dentries in encrypted directories to make sure we aren't potentially
542 * caching stale dentries after a key has been added.
543 */
544static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
545{
546 struct dentry *dir;
547 int err;
548 int valid;
549
550 /*
551 * Plaintext names are always valid, since fscrypt doesn't support
552 * reverting to ciphertext names without evicting the directory's inode
553 * -- which implies eviction of the dentries in the directory.
554 */
555 if (!(dentry->d_flags & DCACHE_ENCRYPTED_NAME))
556 return 1;
557
558 /*
559 * Ciphertext name; valid if the directory's key is still unavailable.
560 *
561 * Although fscrypt forbids rename() on ciphertext names, we still must
562 * use dget_parent() here rather than use ->d_parent directly. That's
563 * because a corrupted fs image may contain directory hard links, which
564 * the VFS handles by moving the directory's dentry tree in the dcache
565 * each time ->lookup() finds the directory and it already has a dentry
566 * elsewhere. Thus ->d_parent can be changing, and we must safely grab
567 * a reference to some ->d_parent to prevent it from being freed.
568 */
569
570 if (flags & LOOKUP_RCU)
571 return -ECHILD;
572
573 dir = dget_parent(dentry);
574 err = fscrypt_get_encryption_info(d_inode(dir));
575 valid = !fscrypt_has_encryption_key(d_inode(dir));
576 dput(dir);
577
578 if (err < 0)
579 return err;
580
581 return valid;
582}
583
584const struct dentry_operations fscrypt_d_ops = {
585 .d_revalidate = fscrypt_d_revalidate,
586};
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This contains functions for filename crypto management
4 *
5 * Copyright (C) 2015, Google, Inc.
6 * Copyright (C) 2015, Motorola Mobility
7 *
8 * Written by Uday Savagaonkar, 2014.
9 * Modified by Jaegeuk Kim, 2015.
10 *
11 * This has not yet undergone a rigorous security audit.
12 */
13
14#include <linux/namei.h>
15#include <linux/scatterlist.h>
16#include <crypto/hash.h>
17#include <crypto/sha2.h>
18#include <crypto/skcipher.h>
19#include "fscrypt_private.h"
20
21/*
22 * The minimum message length (input and output length), in bytes, for all
23 * filenames encryption modes. Filenames shorter than this will be zero-padded
24 * before being encrypted.
25 */
26#define FSCRYPT_FNAME_MIN_MSG_LEN 16
27
28/*
29 * struct fscrypt_nokey_name - identifier for directory entry when key is absent
30 *
31 * When userspace lists an encrypted directory without access to the key, the
32 * filesystem must present a unique "no-key name" for each filename that allows
33 * it to find the directory entry again if requested. Naively, that would just
34 * mean using the ciphertext filenames. However, since the ciphertext filenames
35 * can contain illegal characters ('\0' and '/'), they must be encoded in some
36 * way. We use base64url. But that can cause names to exceed NAME_MAX (255
37 * bytes), so we also need to use a strong hash to abbreviate long names.
38 *
39 * The filesystem may also need another kind of hash, the "dirhash", to quickly
40 * find the directory entry. Since filesystems normally compute the dirhash
41 * over the on-disk filename (i.e. the ciphertext), it's not computable from
42 * no-key names that abbreviate the ciphertext using the strong hash to fit in
43 * NAME_MAX. It's also not computable if it's a keyed hash taken over the
44 * plaintext (but it may still be available in the on-disk directory entry);
45 * casefolded directories use this type of dirhash. At least in these cases,
46 * each no-key name must include the name's dirhash too.
47 *
48 * To meet all these requirements, we base64url-encode the following
49 * variable-length structure. It contains the dirhash, or 0's if the filesystem
50 * didn't provide one; up to 149 bytes of the ciphertext name; and for
51 * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
52 *
53 * This ensures that each no-key name contains everything needed to find the
54 * directory entry again, contains only legal characters, doesn't exceed
55 * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
56 * take the performance hit of SHA-256 on very long filenames (which are rare).
57 */
58struct fscrypt_nokey_name {
59 u32 dirhash[2];
60 u8 bytes[149];
61 u8 sha256[SHA256_DIGEST_SIZE];
62}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
63
64/*
65 * Decoded size of max-size no-key name, i.e. a name that was abbreviated using
66 * the strong hash and thus includes the 'sha256' field. This isn't simply
67 * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
68 */
69#define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)
70
71/* Encoded size of max-size no-key name */
72#define FSCRYPT_NOKEY_NAME_MAX_ENCODED \
73 FSCRYPT_BASE64URL_CHARS(FSCRYPT_NOKEY_NAME_MAX)
74
75static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
76{
77 return is_dot_dotdot(str->name, str->len);
78}
79
80/**
81 * fscrypt_fname_encrypt() - encrypt a filename
82 * @inode: inode of the parent directory (for regular filenames)
83 * or of the symlink (for symlink targets). Key must already be
84 * set up.
85 * @iname: the filename to encrypt
86 * @out: (output) the encrypted filename
87 * @olen: size of the encrypted filename. It must be at least @iname->len.
88 * Any extra space is filled with NUL padding before encryption.
89 *
90 * Return: 0 on success, -errno on failure
91 */
92int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
93 u8 *out, unsigned int olen)
94{
95 struct skcipher_request *req = NULL;
96 DECLARE_CRYPTO_WAIT(wait);
97 const struct fscrypt_inode_info *ci = inode->i_crypt_info;
98 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
99 union fscrypt_iv iv;
100 struct scatterlist sg;
101 int res;
102
103 /*
104 * Copy the filename to the output buffer for encrypting in-place and
105 * pad it with the needed number of NUL bytes.
106 */
107 if (WARN_ON_ONCE(olen < iname->len))
108 return -ENOBUFS;
109 memcpy(out, iname->name, iname->len);
110 memset(out + iname->len, 0, olen - iname->len);
111
112 /* Initialize the IV */
113 fscrypt_generate_iv(&iv, 0, ci);
114
115 /* Set up the encryption request */
116 req = skcipher_request_alloc(tfm, GFP_NOFS);
117 if (!req)
118 return -ENOMEM;
119 skcipher_request_set_callback(req,
120 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
121 crypto_req_done, &wait);
122 sg_init_one(&sg, out, olen);
123 skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
124
125 /* Do the encryption */
126 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
127 skcipher_request_free(req);
128 if (res < 0) {
129 fscrypt_err(inode, "Filename encryption failed: %d", res);
130 return res;
131 }
132
133 return 0;
134}
135EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);
136
137/**
138 * fname_decrypt() - decrypt a filename
139 * @inode: inode of the parent directory (for regular filenames)
140 * or of the symlink (for symlink targets)
141 * @iname: the encrypted filename to decrypt
142 * @oname: (output) the decrypted filename. The caller must have allocated
143 * enough space for this, e.g. using fscrypt_fname_alloc_buffer().
144 *
145 * Return: 0 on success, -errno on failure
146 */
147static int fname_decrypt(const struct inode *inode,
148 const struct fscrypt_str *iname,
149 struct fscrypt_str *oname)
150{
151 struct skcipher_request *req = NULL;
152 DECLARE_CRYPTO_WAIT(wait);
153 struct scatterlist src_sg, dst_sg;
154 const struct fscrypt_inode_info *ci = inode->i_crypt_info;
155 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
156 union fscrypt_iv iv;
157 int res;
158
159 /* Allocate request */
160 req = skcipher_request_alloc(tfm, GFP_NOFS);
161 if (!req)
162 return -ENOMEM;
163 skcipher_request_set_callback(req,
164 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
165 crypto_req_done, &wait);
166
167 /* Initialize IV */
168 fscrypt_generate_iv(&iv, 0, ci);
169
170 /* Create decryption request */
171 sg_init_one(&src_sg, iname->name, iname->len);
172 sg_init_one(&dst_sg, oname->name, oname->len);
173 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
174 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
175 skcipher_request_free(req);
176 if (res < 0) {
177 fscrypt_err(inode, "Filename decryption failed: %d", res);
178 return res;
179 }
180
181 oname->len = strnlen(oname->name, iname->len);
182 return 0;
183}
184
185static const char base64url_table[65] =
186 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
187
188#define FSCRYPT_BASE64URL_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
189
190/**
191 * fscrypt_base64url_encode() - base64url-encode some binary data
192 * @src: the binary data to encode
193 * @srclen: the length of @src in bytes
194 * @dst: (output) the base64url-encoded string. Not NUL-terminated.
195 *
196 * Encodes data using base64url encoding, i.e. the "Base 64 Encoding with URL
197 * and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't used,
198 * as it's unneeded and not required by the RFC. base64url is used instead of
199 * base64 to avoid the '/' character, which isn't allowed in filenames.
200 *
201 * Return: the length of the resulting base64url-encoded string in bytes.
202 * This will be equal to FSCRYPT_BASE64URL_CHARS(srclen).
203 */
204static int fscrypt_base64url_encode(const u8 *src, int srclen, char *dst)
205{
206 u32 ac = 0;
207 int bits = 0;
208 int i;
209 char *cp = dst;
210
211 for (i = 0; i < srclen; i++) {
212 ac = (ac << 8) | src[i];
213 bits += 8;
214 do {
215 bits -= 6;
216 *cp++ = base64url_table[(ac >> bits) & 0x3f];
217 } while (bits >= 6);
218 }
219 if (bits)
220 *cp++ = base64url_table[(ac << (6 - bits)) & 0x3f];
221 return cp - dst;
222}
223
224/**
225 * fscrypt_base64url_decode() - base64url-decode a string
226 * @src: the string to decode. Doesn't need to be NUL-terminated.
227 * @srclen: the length of @src in bytes
228 * @dst: (output) the decoded binary data
229 *
230 * Decodes a string using base64url encoding, i.e. the "Base 64 Encoding with
231 * URL and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't
232 * accepted, nor are non-encoding characters such as whitespace.
233 *
234 * This implementation hasn't been optimized for performance.
235 *
236 * Return: the length of the resulting decoded binary data in bytes,
237 * or -1 if the string isn't a valid base64url string.
238 */
239static int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
240{
241 u32 ac = 0;
242 int bits = 0;
243 int i;
244 u8 *bp = dst;
245
246 for (i = 0; i < srclen; i++) {
247 const char *p = strchr(base64url_table, src[i]);
248
249 if (p == NULL || src[i] == 0)
250 return -1;
251 ac = (ac << 6) | (p - base64url_table);
252 bits += 6;
253 if (bits >= 8) {
254 bits -= 8;
255 *bp++ = (u8)(ac >> bits);
256 }
257 }
258 if (ac & ((1 << bits) - 1))
259 return -1;
260 return bp - dst;
261}
262
263bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
264 u32 orig_len, u32 max_len,
265 u32 *encrypted_len_ret)
266{
267 int padding = 4 << (fscrypt_policy_flags(policy) &
268 FSCRYPT_POLICY_FLAGS_PAD_MASK);
269 u32 encrypted_len;
270
271 if (orig_len > max_len)
272 return false;
273 encrypted_len = max_t(u32, orig_len, FSCRYPT_FNAME_MIN_MSG_LEN);
274 encrypted_len = round_up(encrypted_len, padding);
275 *encrypted_len_ret = min(encrypted_len, max_len);
276 return true;
277}
278
279/**
280 * fscrypt_fname_encrypted_size() - calculate length of encrypted filename
281 * @inode: parent inode of dentry name being encrypted. Key must
282 * already be set up.
283 * @orig_len: length of the original filename
284 * @max_len: maximum length to return
285 * @encrypted_len_ret: where calculated length should be returned (on success)
286 *
287 * Filenames that are shorter than the maximum length may have their lengths
288 * increased slightly by encryption, due to padding that is applied.
289 *
290 * Return: false if the orig_len is greater than max_len. Otherwise, true and
291 * fill out encrypted_len_ret with the length (up to max_len).
292 */
293bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
294 u32 max_len, u32 *encrypted_len_ret)
295{
296 return __fscrypt_fname_encrypted_size(&inode->i_crypt_info->ci_policy,
297 orig_len, max_len,
298 encrypted_len_ret);
299}
300EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size);
301
302/**
303 * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
304 * @max_encrypted_len: maximum length of encrypted filenames the buffer will be
305 * used to present
306 * @crypto_str: (output) buffer to allocate
307 *
308 * Allocate a buffer that is large enough to hold any decrypted or encoded
309 * filename (null-terminated), for the given maximum encrypted filename length.
310 *
311 * Return: 0 on success, -errno on failure
312 */
313int fscrypt_fname_alloc_buffer(u32 max_encrypted_len,
314 struct fscrypt_str *crypto_str)
315{
316 u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED,
317 max_encrypted_len);
318
319 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
320 if (!crypto_str->name)
321 return -ENOMEM;
322 crypto_str->len = max_presented_len;
323 return 0;
324}
325EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
326
327/**
328 * fscrypt_fname_free_buffer() - free a buffer for presented filenames
329 * @crypto_str: the buffer to free
330 *
331 * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
332 */
333void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
334{
335 if (!crypto_str)
336 return;
337 kfree(crypto_str->name);
338 crypto_str->name = NULL;
339}
340EXPORT_SYMBOL(fscrypt_fname_free_buffer);
341
342/**
343 * fscrypt_fname_disk_to_usr() - convert an encrypted filename to
344 * user-presentable form
345 * @inode: inode of the parent directory (for regular filenames)
346 * or of the symlink (for symlink targets)
347 * @hash: first part of the name's dirhash, if applicable. This only needs to
348 * be provided if the filename is located in an indexed directory whose
349 * encryption key may be unavailable. Not needed for symlink targets.
350 * @minor_hash: second part of the name's dirhash, if applicable
351 * @iname: encrypted filename to convert. May also be "." or "..", which
352 * aren't actually encrypted.
353 * @oname: output buffer for the user-presentable filename. The caller must
354 * have allocated enough space for this, e.g. using
355 * fscrypt_fname_alloc_buffer().
356 *
357 * If the key is available, we'll decrypt the disk name. Otherwise, we'll
358 * encode it for presentation in fscrypt_nokey_name format.
359 * See struct fscrypt_nokey_name for details.
360 *
361 * Return: 0 on success, -errno on failure
362 */
363int fscrypt_fname_disk_to_usr(const struct inode *inode,
364 u32 hash, u32 minor_hash,
365 const struct fscrypt_str *iname,
366 struct fscrypt_str *oname)
367{
368 const struct qstr qname = FSTR_TO_QSTR(iname);
369 struct fscrypt_nokey_name nokey_name;
370 u32 size; /* size of the unencoded no-key name */
371
372 if (fscrypt_is_dot_dotdot(&qname)) {
373 oname->name[0] = '.';
374 oname->name[iname->len - 1] = '.';
375 oname->len = iname->len;
376 return 0;
377 }
378
379 if (iname->len < FSCRYPT_FNAME_MIN_MSG_LEN)
380 return -EUCLEAN;
381
382 if (fscrypt_has_encryption_key(inode))
383 return fname_decrypt(inode, iname, oname);
384
385 /*
386 * Sanity check that struct fscrypt_nokey_name doesn't have padding
387 * between fields and that its encoded size never exceeds NAME_MAX.
388 */
389 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
390 offsetof(struct fscrypt_nokey_name, bytes));
391 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
392 offsetof(struct fscrypt_nokey_name, sha256));
393 BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX);
394
395 nokey_name.dirhash[0] = hash;
396 nokey_name.dirhash[1] = minor_hash;
397
398 if (iname->len <= sizeof(nokey_name.bytes)) {
399 memcpy(nokey_name.bytes, iname->name, iname->len);
400 size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
401 } else {
402 memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
403 /* Compute strong hash of remaining part of name. */
404 sha256(&iname->name[sizeof(nokey_name.bytes)],
405 iname->len - sizeof(nokey_name.bytes),
406 nokey_name.sha256);
407 size = FSCRYPT_NOKEY_NAME_MAX;
408 }
409 oname->len = fscrypt_base64url_encode((const u8 *)&nokey_name, size,
410 oname->name);
411 return 0;
412}
413EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
414
415/**
416 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
417 * @dir: the directory that will be searched
418 * @iname: the user-provided filename being searched for
419 * @lookup: 1 if we're allowed to proceed without the key because it's
420 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
421 * proceed without the key because we're going to create the dir_entry.
422 * @fname: the filename information to be filled in
423 *
424 * Given a user-provided filename @iname, this function sets @fname->disk_name
425 * to the name that would be stored in the on-disk directory entry, if possible.
426 * If the directory is unencrypted this is simply @iname. Else, if we have the
427 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
428 * get the disk_name.
429 *
430 * Else, for keyless @lookup operations, @iname should be a no-key name, so we
431 * decode it to get the struct fscrypt_nokey_name. Non-@lookup operations will
432 * be impossible in this case, so we fail them with ENOKEY.
433 *
434 * If successful, fscrypt_free_filename() must be called later to clean up.
435 *
436 * Return: 0 on success, -errno on failure
437 */
438int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
439 int lookup, struct fscrypt_name *fname)
440{
441 struct fscrypt_nokey_name *nokey_name;
442 int ret;
443
444 memset(fname, 0, sizeof(struct fscrypt_name));
445 fname->usr_fname = iname;
446
447 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
448 fname->disk_name.name = (unsigned char *)iname->name;
449 fname->disk_name.len = iname->len;
450 return 0;
451 }
452 ret = fscrypt_get_encryption_info(dir, lookup);
453 if (ret)
454 return ret;
455
456 if (fscrypt_has_encryption_key(dir)) {
457 if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX,
458 &fname->crypto_buf.len))
459 return -ENAMETOOLONG;
460 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
461 GFP_NOFS);
462 if (!fname->crypto_buf.name)
463 return -ENOMEM;
464
465 ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
466 fname->crypto_buf.len);
467 if (ret)
468 goto errout;
469 fname->disk_name.name = fname->crypto_buf.name;
470 fname->disk_name.len = fname->crypto_buf.len;
471 return 0;
472 }
473 if (!lookup)
474 return -ENOKEY;
475 fname->is_nokey_name = true;
476
477 /*
478 * We don't have the key and we are doing a lookup; decode the
479 * user-supplied name
480 */
481
482 if (iname->len > FSCRYPT_NOKEY_NAME_MAX_ENCODED)
483 return -ENOENT;
484
485 fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
486 if (fname->crypto_buf.name == NULL)
487 return -ENOMEM;
488
489 ret = fscrypt_base64url_decode(iname->name, iname->len,
490 fname->crypto_buf.name);
491 if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
492 (ret > offsetof(struct fscrypt_nokey_name, sha256) &&
493 ret != FSCRYPT_NOKEY_NAME_MAX)) {
494 ret = -ENOENT;
495 goto errout;
496 }
497 fname->crypto_buf.len = ret;
498
499 nokey_name = (void *)fname->crypto_buf.name;
500 fname->hash = nokey_name->dirhash[0];
501 fname->minor_hash = nokey_name->dirhash[1];
502 if (ret != FSCRYPT_NOKEY_NAME_MAX) {
503 /* The full ciphertext filename is available. */
504 fname->disk_name.name = nokey_name->bytes;
505 fname->disk_name.len =
506 ret - offsetof(struct fscrypt_nokey_name, bytes);
507 }
508 return 0;
509
510errout:
511 kfree(fname->crypto_buf.name);
512 return ret;
513}
514EXPORT_SYMBOL(fscrypt_setup_filename);
515
516/**
517 * fscrypt_match_name() - test whether the given name matches a directory entry
518 * @fname: the name being searched for
519 * @de_name: the name from the directory entry
520 * @de_name_len: the length of @de_name in bytes
521 *
522 * Normally @fname->disk_name will be set, and in that case we simply compare
523 * that to the name stored in the directory entry. The only exception is that
524 * if we don't have the key for an encrypted directory and the name we're
525 * looking for is very long, then we won't have the full disk_name and instead
526 * we'll need to match against a fscrypt_nokey_name that includes a strong hash.
527 *
528 * Return: %true if the name matches, otherwise %false.
529 */
530bool fscrypt_match_name(const struct fscrypt_name *fname,
531 const u8 *de_name, u32 de_name_len)
532{
533 const struct fscrypt_nokey_name *nokey_name =
534 (const void *)fname->crypto_buf.name;
535 u8 digest[SHA256_DIGEST_SIZE];
536
537 if (likely(fname->disk_name.name)) {
538 if (de_name_len != fname->disk_name.len)
539 return false;
540 return !memcmp(de_name, fname->disk_name.name, de_name_len);
541 }
542 if (de_name_len <= sizeof(nokey_name->bytes))
543 return false;
544 if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
545 return false;
546 sha256(&de_name[sizeof(nokey_name->bytes)],
547 de_name_len - sizeof(nokey_name->bytes), digest);
548 return !memcmp(digest, nokey_name->sha256, sizeof(digest));
549}
550EXPORT_SYMBOL_GPL(fscrypt_match_name);
551
552/**
553 * fscrypt_fname_siphash() - calculate the SipHash of a filename
554 * @dir: the parent directory
555 * @name: the filename to calculate the SipHash of
556 *
557 * Given a plaintext filename @name and a directory @dir which uses SipHash as
558 * its dirhash method and has had its fscrypt key set up, this function
559 * calculates the SipHash of that name using the directory's secret dirhash key.
560 *
561 * Return: the SipHash of @name using the hash key of @dir
562 */
563u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
564{
565 const struct fscrypt_inode_info *ci = dir->i_crypt_info;
566
567 WARN_ON_ONCE(!ci->ci_dirhash_key_initialized);
568
569 return siphash(name->name, name->len, &ci->ci_dirhash_key);
570}
571EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
572
573/*
574 * Validate dentries in encrypted directories to make sure we aren't potentially
575 * caching stale dentries after a key has been added.
576 */
577int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
578{
579 struct dentry *dir;
580 int err;
581 int valid;
582
583 /*
584 * Plaintext names are always valid, since fscrypt doesn't support
585 * reverting to no-key names without evicting the directory's inode
586 * -- which implies eviction of the dentries in the directory.
587 */
588 if (!(dentry->d_flags & DCACHE_NOKEY_NAME))
589 return 1;
590
591 /*
592 * No-key name; valid if the directory's key is still unavailable.
593 *
594 * Although fscrypt forbids rename() on no-key names, we still must use
595 * dget_parent() here rather than use ->d_parent directly. That's
596 * because a corrupted fs image may contain directory hard links, which
597 * the VFS handles by moving the directory's dentry tree in the dcache
598 * each time ->lookup() finds the directory and it already has a dentry
599 * elsewhere. Thus ->d_parent can be changing, and we must safely grab
600 * a reference to some ->d_parent to prevent it from being freed.
601 */
602
603 if (flags & LOOKUP_RCU)
604 return -ECHILD;
605
606 dir = dget_parent(dentry);
607 /*
608 * Pass allow_unsupported=true, so that files with an unsupported
609 * encryption policy can be deleted.
610 */
611 err = fscrypt_get_encryption_info(d_inode(dir), true);
612 valid = !fscrypt_has_encryption_key(d_inode(dir));
613 dput(dir);
614
615 if (err < 0)
616 return err;
617
618 return valid;
619}
620EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);