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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  */
51 struct 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 
fscrypt_is_dot_dotdot(const struct qstr * str)64 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
65 {
66 	if (str->len == 1 && str->name[0] == '.')
67 		return true;
68 
69 	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
70 		return true;
71 
72 	return false;
73 }
74 
75 /**
76  * fscrypt_fname_encrypt() - encrypt a filename
77  * @inode: inode of the parent directory (for regular filenames)
78  *	   or of the symlink (for symlink targets)
79  * @iname: the filename to encrypt
80  * @out: (output) the encrypted filename
81  * @olen: size of the encrypted filename.  It must be at least @iname->len.
82  *	  Any extra space is filled with NUL padding before encryption.
83  *
84  * Return: 0 on success, -errno on failure
85  */
fscrypt_fname_encrypt(const struct inode * inode,const struct qstr * iname,u8 * out,unsigned int olen)86 int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
87 			  u8 *out, unsigned int olen)
88 {
89 	struct skcipher_request *req = NULL;
90 	DECLARE_CRYPTO_WAIT(wait);
91 	const struct fscrypt_info *ci = inode->i_crypt_info;
92 	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
93 	union fscrypt_iv iv;
94 	struct scatterlist sg;
95 	int res;
96 
97 	/*
98 	 * Copy the filename to the output buffer for encrypting in-place and
99 	 * pad it with the needed number of NUL bytes.
100 	 */
101 	if (WARN_ON(olen < iname->len))
102 		return -ENOBUFS;
103 	memcpy(out, iname->name, iname->len);
104 	memset(out + iname->len, 0, olen - iname->len);
105 
106 	/* Initialize the IV */
107 	fscrypt_generate_iv(&iv, 0, ci);
108 
109 	/* Set up the encryption request */
110 	req = skcipher_request_alloc(tfm, GFP_NOFS);
111 	if (!req)
112 		return -ENOMEM;
113 	skcipher_request_set_callback(req,
114 			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
115 			crypto_req_done, &wait);
116 	sg_init_one(&sg, out, olen);
117 	skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
118 
119 	/* Do the encryption */
120 	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
121 	skcipher_request_free(req);
122 	if (res < 0) {
123 		fscrypt_err(inode, "Filename encryption failed: %d", res);
124 		return res;
125 	}
126 
127 	return 0;
128 }
129 
130 /**
131  * fname_decrypt() - decrypt a filename
132  * @inode: inode of the parent directory (for regular filenames)
133  *	   or of the symlink (for symlink targets)
134  * @iname: the encrypted filename to decrypt
135  * @oname: (output) the decrypted filename.  The caller must have allocated
136  *	   enough space for this, e.g. using fscrypt_fname_alloc_buffer().
137  *
138  * Return: 0 on success, -errno on failure
139  */
fname_decrypt(const struct inode * inode,const struct fscrypt_str * iname,struct fscrypt_str * oname)140 static int fname_decrypt(const struct inode *inode,
141 			 const struct fscrypt_str *iname,
142 			 struct fscrypt_str *oname)
143 {
144 	struct skcipher_request *req = NULL;
145 	DECLARE_CRYPTO_WAIT(wait);
146 	struct scatterlist src_sg, dst_sg;
147 	const struct fscrypt_info *ci = inode->i_crypt_info;
148 	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
149 	union fscrypt_iv iv;
150 	int res;
151 
152 	/* Allocate request */
153 	req = skcipher_request_alloc(tfm, GFP_NOFS);
154 	if (!req)
155 		return -ENOMEM;
156 	skcipher_request_set_callback(req,
157 		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
158 		crypto_req_done, &wait);
159 
160 	/* Initialize IV */
161 	fscrypt_generate_iv(&iv, 0, ci);
162 
163 	/* Create decryption request */
164 	sg_init_one(&src_sg, iname->name, iname->len);
165 	sg_init_one(&dst_sg, oname->name, oname->len);
166 	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
167 	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
168 	skcipher_request_free(req);
169 	if (res < 0) {
170 		fscrypt_err(inode, "Filename decryption failed: %d", res);
171 		return res;
172 	}
173 
174 	oname->len = strnlen(oname->name, iname->len);
175 	return 0;
176 }
177 
178 static const char lookup_table[65] =
179 	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
180 
181 #define BASE64_CHARS(nbytes)	DIV_ROUND_UP((nbytes) * 4, 3)
182 
183 /**
184  * base64_encode() - base64-encode some bytes
185  * @src: the bytes to encode
186  * @len: number of bytes to encode
187  * @dst: (output) the base64-encoded string.  Not NUL-terminated.
188  *
189  * Encodes the input string using characters from the set [A-Za-z0-9+,].
190  * The encoded string is roughly 4/3 times the size of the input string.
191  *
192  * Return: length of the encoded string
193  */
base64_encode(const u8 * src,int len,char * dst)194 static int base64_encode(const u8 *src, int len, char *dst)
195 {
196 	int i, bits = 0, ac = 0;
197 	char *cp = dst;
198 
199 	for (i = 0; i < len; i++) {
200 		ac += src[i] << bits;
201 		bits += 8;
202 		do {
203 			*cp++ = lookup_table[ac & 0x3f];
204 			ac >>= 6;
205 			bits -= 6;
206 		} while (bits >= 6);
207 	}
208 	if (bits)
209 		*cp++ = lookup_table[ac & 0x3f];
210 	return cp - dst;
211 }
212 
base64_decode(const char * src,int len,u8 * dst)213 static int base64_decode(const char *src, int len, u8 *dst)
214 {
215 	int i, bits = 0, ac = 0;
216 	const char *p;
217 	u8 *cp = dst;
218 
219 	for (i = 0; i < len; i++) {
220 		p = strchr(lookup_table, src[i]);
221 		if (p == NULL || src[i] == 0)
222 			return -2;
223 		ac += (p - lookup_table) << bits;
224 		bits += 6;
225 		if (bits >= 8) {
226 			*cp++ = ac & 0xff;
227 			ac >>= 8;
228 			bits -= 8;
229 		}
230 	}
231 	if (ac)
232 		return -1;
233 	return cp - dst;
234 }
235 
fscrypt_fname_encrypted_size(const union fscrypt_policy * policy,u32 orig_len,u32 max_len,u32 * encrypted_len_ret)236 bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
237 				  u32 orig_len, u32 max_len,
238 				  u32 *encrypted_len_ret)
239 {
240 	int padding = 4 << (fscrypt_policy_flags(policy) &
241 			    FSCRYPT_POLICY_FLAGS_PAD_MASK);
242 	u32 encrypted_len;
243 
244 	if (orig_len > max_len)
245 		return false;
246 	encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
247 	encrypted_len = round_up(encrypted_len, padding);
248 	*encrypted_len_ret = min(encrypted_len, max_len);
249 	return true;
250 }
251 
252 /**
253  * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
254  * @max_encrypted_len: maximum length of encrypted filenames the buffer will be
255  *		       used to present
256  * @crypto_str: (output) buffer to allocate
257  *
258  * Allocate a buffer that is large enough to hold any decrypted or encoded
259  * filename (null-terminated), for the given maximum encrypted filename length.
260  *
261  * Return: 0 on success, -errno on failure
262  */
fscrypt_fname_alloc_buffer(u32 max_encrypted_len,struct fscrypt_str * crypto_str)263 int fscrypt_fname_alloc_buffer(u32 max_encrypted_len,
264 			       struct fscrypt_str *crypto_str)
265 {
266 	const u32 max_encoded_len = BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX);
267 	u32 max_presented_len;
268 
269 	max_presented_len = max(max_encoded_len, max_encrypted_len);
270 
271 	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
272 	if (!crypto_str->name)
273 		return -ENOMEM;
274 	crypto_str->len = max_presented_len;
275 	return 0;
276 }
277 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
278 
279 /**
280  * fscrypt_fname_free_buffer() - free a buffer for presented filenames
281  * @crypto_str: the buffer to free
282  *
283  * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
284  */
fscrypt_fname_free_buffer(struct fscrypt_str * crypto_str)285 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
286 {
287 	if (!crypto_str)
288 		return;
289 	kfree(crypto_str->name);
290 	crypto_str->name = NULL;
291 }
292 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
293 
294 /**
295  * fscrypt_fname_disk_to_usr() - convert an encrypted filename to
296  *				 user-presentable form
297  * @inode: inode of the parent directory (for regular filenames)
298  *	   or of the symlink (for symlink targets)
299  * @hash: first part of the name's dirhash, if applicable.  This only needs to
300  *	  be provided if the filename is located in an indexed directory whose
301  *	  encryption key may be unavailable.  Not needed for symlink targets.
302  * @minor_hash: second part of the name's dirhash, if applicable
303  * @iname: encrypted filename to convert.  May also be "." or "..", which
304  *	   aren't actually encrypted.
305  * @oname: output buffer for the user-presentable filename.  The caller must
306  *	   have allocated enough space for this, e.g. using
307  *	   fscrypt_fname_alloc_buffer().
308  *
309  * If the key is available, we'll decrypt the disk name.  Otherwise, we'll
310  * encode it for presentation in fscrypt_nokey_name format.
311  * See struct fscrypt_nokey_name for details.
312  *
313  * Return: 0 on success, -errno on failure
314  */
fscrypt_fname_disk_to_usr(const struct inode * inode,u32 hash,u32 minor_hash,const struct fscrypt_str * iname,struct fscrypt_str * oname)315 int fscrypt_fname_disk_to_usr(const struct inode *inode,
316 			      u32 hash, u32 minor_hash,
317 			      const struct fscrypt_str *iname,
318 			      struct fscrypt_str *oname)
319 {
320 	const struct qstr qname = FSTR_TO_QSTR(iname);
321 	struct fscrypt_nokey_name nokey_name;
322 	u32 size; /* size of the unencoded no-key name */
323 
324 	if (fscrypt_is_dot_dotdot(&qname)) {
325 		oname->name[0] = '.';
326 		oname->name[iname->len - 1] = '.';
327 		oname->len = iname->len;
328 		return 0;
329 	}
330 
331 	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
332 		return -EUCLEAN;
333 
334 	if (fscrypt_has_encryption_key(inode))
335 		return fname_decrypt(inode, iname, oname);
336 
337 	/*
338 	 * Sanity check that struct fscrypt_nokey_name doesn't have padding
339 	 * between fields and that its encoded size never exceeds NAME_MAX.
340 	 */
341 	BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
342 		     offsetof(struct fscrypt_nokey_name, bytes));
343 	BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
344 		     offsetof(struct fscrypt_nokey_name, sha256));
345 	BUILD_BUG_ON(BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) > NAME_MAX);
346 
347 	nokey_name.dirhash[0] = hash;
348 	nokey_name.dirhash[1] = minor_hash;
349 
350 	if (iname->len <= sizeof(nokey_name.bytes)) {
351 		memcpy(nokey_name.bytes, iname->name, iname->len);
352 		size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
353 	} else {
354 		memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
355 		/* Compute strong hash of remaining part of name. */
356 		sha256(&iname->name[sizeof(nokey_name.bytes)],
357 		       iname->len - sizeof(nokey_name.bytes),
358 		       nokey_name.sha256);
359 		size = FSCRYPT_NOKEY_NAME_MAX;
360 	}
361 	oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name);
362 	return 0;
363 }
364 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
365 
366 /**
367  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
368  * @dir: the directory that will be searched
369  * @iname: the user-provided filename being searched for
370  * @lookup: 1 if we're allowed to proceed without the key because it's
371  *	->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
372  *	proceed without the key because we're going to create the dir_entry.
373  * @fname: the filename information to be filled in
374  *
375  * Given a user-provided filename @iname, this function sets @fname->disk_name
376  * to the name that would be stored in the on-disk directory entry, if possible.
377  * If the directory is unencrypted this is simply @iname.  Else, if we have the
378  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
379  * get the disk_name.
380  *
381  * Else, for keyless @lookup operations, @iname should be a no-key name, so we
382  * decode it to get the struct fscrypt_nokey_name.  Non-@lookup operations will
383  * be impossible in this case, so we fail them with ENOKEY.
384  *
385  * If successful, fscrypt_free_filename() must be called later to clean up.
386  *
387  * Return: 0 on success, -errno on failure
388  */
fscrypt_setup_filename(struct inode * dir,const struct qstr * iname,int lookup,struct fscrypt_name * fname)389 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
390 			      int lookup, struct fscrypt_name *fname)
391 {
392 	struct fscrypt_nokey_name *nokey_name;
393 	int ret;
394 
395 	memset(fname, 0, sizeof(struct fscrypt_name));
396 	fname->usr_fname = iname;
397 
398 	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
399 		fname->disk_name.name = (unsigned char *)iname->name;
400 		fname->disk_name.len = iname->len;
401 		return 0;
402 	}
403 	ret = fscrypt_get_encryption_info(dir);
404 	if (ret)
405 		return ret;
406 
407 	if (fscrypt_has_encryption_key(dir)) {
408 		if (!fscrypt_fname_encrypted_size(&dir->i_crypt_info->ci_policy,
409 						  iname->len,
410 						  dir->i_sb->s_cop->max_namelen,
411 						  &fname->crypto_buf.len))
412 			return -ENAMETOOLONG;
413 		fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
414 						 GFP_NOFS);
415 		if (!fname->crypto_buf.name)
416 			return -ENOMEM;
417 
418 		ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
419 					    fname->crypto_buf.len);
420 		if (ret)
421 			goto errout;
422 		fname->disk_name.name = fname->crypto_buf.name;
423 		fname->disk_name.len = fname->crypto_buf.len;
424 		return 0;
425 	}
426 	if (!lookup)
427 		return -ENOKEY;
428 	fname->is_nokey_name = true;
429 
430 	/*
431 	 * We don't have the key and we are doing a lookup; decode the
432 	 * user-supplied name
433 	 */
434 
435 	if (iname->len > BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX))
436 		return -ENOENT;
437 
438 	fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
439 	if (fname->crypto_buf.name == NULL)
440 		return -ENOMEM;
441 
442 	ret = base64_decode(iname->name, iname->len, fname->crypto_buf.name);
443 	if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
444 	    (ret > offsetof(struct fscrypt_nokey_name, sha256) &&
445 	     ret != FSCRYPT_NOKEY_NAME_MAX)) {
446 		ret = -ENOENT;
447 		goto errout;
448 	}
449 	fname->crypto_buf.len = ret;
450 
451 	nokey_name = (void *)fname->crypto_buf.name;
452 	fname->hash = nokey_name->dirhash[0];
453 	fname->minor_hash = nokey_name->dirhash[1];
454 	if (ret != FSCRYPT_NOKEY_NAME_MAX) {
455 		/* The full ciphertext filename is available. */
456 		fname->disk_name.name = nokey_name->bytes;
457 		fname->disk_name.len =
458 			ret - offsetof(struct fscrypt_nokey_name, bytes);
459 	}
460 	return 0;
461 
462 errout:
463 	kfree(fname->crypto_buf.name);
464 	return ret;
465 }
466 EXPORT_SYMBOL(fscrypt_setup_filename);
467 
468 /**
469  * fscrypt_match_name() - test whether the given name matches a directory entry
470  * @fname: the name being searched for
471  * @de_name: the name from the directory entry
472  * @de_name_len: the length of @de_name in bytes
473  *
474  * Normally @fname->disk_name will be set, and in that case we simply compare
475  * that to the name stored in the directory entry.  The only exception is that
476  * if we don't have the key for an encrypted directory and the name we're
477  * looking for is very long, then we won't have the full disk_name and instead
478  * we'll need to match against a fscrypt_nokey_name that includes a strong hash.
479  *
480  * Return: %true if the name matches, otherwise %false.
481  */
fscrypt_match_name(const struct fscrypt_name * fname,const u8 * de_name,u32 de_name_len)482 bool fscrypt_match_name(const struct fscrypt_name *fname,
483 			const u8 *de_name, u32 de_name_len)
484 {
485 	const struct fscrypt_nokey_name *nokey_name =
486 		(const void *)fname->crypto_buf.name;
487 	u8 digest[SHA256_DIGEST_SIZE];
488 
489 	if (likely(fname->disk_name.name)) {
490 		if (de_name_len != fname->disk_name.len)
491 			return false;
492 		return !memcmp(de_name, fname->disk_name.name, de_name_len);
493 	}
494 	if (de_name_len <= sizeof(nokey_name->bytes))
495 		return false;
496 	if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
497 		return false;
498 	sha256(&de_name[sizeof(nokey_name->bytes)],
499 	       de_name_len - sizeof(nokey_name->bytes), digest);
500 	return !memcmp(digest, nokey_name->sha256, sizeof(digest));
501 }
502 EXPORT_SYMBOL_GPL(fscrypt_match_name);
503 
504 /**
505  * fscrypt_fname_siphash() - calculate the SipHash of a filename
506  * @dir: the parent directory
507  * @name: the filename to calculate the SipHash of
508  *
509  * Given a plaintext filename @name and a directory @dir which uses SipHash as
510  * its dirhash method and has had its fscrypt key set up, this function
511  * calculates the SipHash of that name using the directory's secret dirhash key.
512  *
513  * Return: the SipHash of @name using the hash key of @dir
514  */
fscrypt_fname_siphash(const struct inode * dir,const struct qstr * name)515 u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
516 {
517 	const struct fscrypt_info *ci = dir->i_crypt_info;
518 
519 	WARN_ON(!ci->ci_dirhash_key_initialized);
520 
521 	return siphash(name->name, name->len, &ci->ci_dirhash_key);
522 }
523 EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
524 
525 /*
526  * Validate dentries in encrypted directories to make sure we aren't potentially
527  * caching stale dentries after a key has been added.
528  */
fscrypt_d_revalidate(struct dentry * dentry,unsigned int flags)529 int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
530 {
531 	struct dentry *dir;
532 	int err;
533 	int valid;
534 
535 	/*
536 	 * Plaintext names are always valid, since fscrypt doesn't support
537 	 * reverting to no-key names without evicting the directory's inode
538 	 * -- which implies eviction of the dentries in the directory.
539 	 */
540 	if (!(dentry->d_flags & DCACHE_NOKEY_NAME))
541 		return 1;
542 
543 	/*
544 	 * No-key name; valid if the directory's key is still unavailable.
545 	 *
546 	 * Although fscrypt forbids rename() on no-key names, we still must use
547 	 * dget_parent() here rather than use ->d_parent directly.  That's
548 	 * because a corrupted fs image may contain directory hard links, which
549 	 * the VFS handles by moving the directory's dentry tree in the dcache
550 	 * each time ->lookup() finds the directory and it already has a dentry
551 	 * elsewhere.  Thus ->d_parent can be changing, and we must safely grab
552 	 * a reference to some ->d_parent to prevent it from being freed.
553 	 */
554 
555 	if (flags & LOOKUP_RCU)
556 		return -ECHILD;
557 
558 	dir = dget_parent(dentry);
559 	err = fscrypt_get_encryption_info(d_inode(dir));
560 	valid = !fscrypt_has_encryption_key(d_inode(dir));
561 	dput(dir);
562 
563 	if (err < 0)
564 		return err;
565 
566 	return valid;
567 }
568 EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
569 
570 const struct dentry_operations fscrypt_d_ops = {
571 	.d_revalidate = fscrypt_d_revalidate,
572 };
573