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 | */ |
58 | struct 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 | |
75 | static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) |
76 | { |
77 | return is_dot_dotdot(name: str->name, len: 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 | */ |
92 | int 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: &iv, index: 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 | compl: crypto_req_done, data: &wait); |
122 | sg_init_one(&sg, out, olen); |
123 | skcipher_request_set_crypt(req, src: &sg, dst: &sg, cryptlen: olen, iv: &iv); |
124 | |
125 | /* Do the encryption */ |
126 | res = crypto_wait_req(err: crypto_skcipher_encrypt(req), wait: &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 | } |
135 | EXPORT_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 | */ |
147 | static 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 | compl: crypto_req_done, data: &wait); |
166 | |
167 | /* Initialize IV */ |
168 | fscrypt_generate_iv(iv: &iv, index: 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: &src_sg, dst: &dst_sg, cryptlen: iname->len, iv: &iv); |
174 | res = crypto_wait_req(err: crypto_skcipher_decrypt(req), wait: &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(p: oname->name, maxlen: iname->len); |
182 | return 0; |
183 | } |
184 | |
185 | static 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 | */ |
204 | static 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 | */ |
239 | static 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 | |
263 | bool __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 | */ |
293 | bool 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(policy: &inode->i_crypt_info->ci_policy, |
297 | orig_len, max_len, |
298 | encrypted_len_ret); |
299 | } |
300 | EXPORT_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 | */ |
313 | int 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(size: 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 | } |
325 | EXPORT_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 | */ |
333 | void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str) |
334 | { |
335 | if (!crypto_str) |
336 | return; |
337 | kfree(objp: crypto_str->name); |
338 | crypto_str->name = NULL; |
339 | } |
340 | EXPORT_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 | */ |
363 | int 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(str: &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(data: &iname->name[sizeof(nokey_name.bytes)], |
405 | len: iname->len - sizeof(nokey_name.bytes), |
406 | out: nokey_name.sha256); |
407 | size = FSCRYPT_NOKEY_NAME_MAX; |
408 | } |
409 | oname->len = fscrypt_base64url_encode(src: (const u8 *)&nokey_name, srclen: size, |
410 | dst: oname->name); |
411 | return 0; |
412 | } |
413 | EXPORT_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 | */ |
438 | int 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(str: 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(inode: dir, allow_unsupported: lookup); |
453 | if (ret) |
454 | return ret; |
455 | |
456 | if (fscrypt_has_encryption_key(inode: 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(size: 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(src: iname->name, srclen: iname->len, |
490 | dst: 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 | |
510 | errout: |
511 | kfree(objp: fname->crypto_buf.name); |
512 | return ret; |
513 | } |
514 | EXPORT_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 | */ |
530 | bool 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(p: de_name, q: fname->disk_name.name, size: de_name_len); |
541 | } |
542 | if (de_name_len <= sizeof(nokey_name->bytes)) |
543 | return false; |
544 | if (memcmp(p: de_name, q: nokey_name->bytes, size: sizeof(nokey_name->bytes))) |
545 | return false; |
546 | sha256(data: &de_name[sizeof(nokey_name->bytes)], |
547 | len: de_name_len - sizeof(nokey_name->bytes), out: digest); |
548 | return !memcmp(p: digest, q: nokey_name->sha256, size: sizeof(digest)); |
549 | } |
550 | EXPORT_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 | */ |
563 | u64 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(data: name->name, len: name->len, key: &ci->ci_dirhash_key); |
570 | } |
571 | EXPORT_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 | */ |
577 | int 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(inode: d_inode(dentry: dir), allow_unsupported: true); |
612 | valid = !fscrypt_has_encryption_key(inode: d_inode(dentry: dir)); |
613 | dput(dir); |
614 | |
615 | if (err < 0) |
616 | return err; |
617 | |
618 | return valid; |
619 | } |
620 | EXPORT_SYMBOL_GPL(fscrypt_d_revalidate); |
621 | |