1 // SPDX-License-Identifier: GPL-2.0
3 * This contains functions for filename crypto management
5 * Copyright (C) 2015, Google, Inc.
6 * Copyright (C) 2015, Motorola Mobility
8 * Written by Uday Savagaonkar, 2014.
9 * Modified by Jaegeuk Kim, 2015.
11 * This has not yet undergone a rigorous security audit.
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"
22 * struct fscrypt_nokey_name - identifier for directory entry when key is absent
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.
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.
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.
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).
51 struct fscrypt_nokey_name {
54 u8 sha256[SHA256_DIGEST_SIZE];
55 }; /* 189 bytes => 252 bytes base64-encoded, which is <= NAME_MAX (255) */
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.
62 #define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)
64 static struct crypto_shash *sha256_hash_tfm;
66 static int fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result)
68 struct crypto_shash *tfm = READ_ONCE(sha256_hash_tfm);
71 struct crypto_shash *prev_tfm;
73 tfm = crypto_alloc_shash("sha256", 0, 0);
76 "Error allocating SHA-256 transform: %ld",
80 prev_tfm = cmpxchg(&sha256_hash_tfm, NULL, tfm);
82 crypto_free_shash(tfm);
87 return crypto_shash_tfm_digest(tfm, data, data_len, result);
90 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
92 if (str->len == 1 && str->name[0] == '.')
95 if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
102 * fscrypt_fname_encrypt() - encrypt a filename
103 * @inode: inode of the parent directory (for regular filenames)
104 * or of the symlink (for symlink targets)
105 * @iname: the filename to encrypt
106 * @out: (output) the encrypted filename
107 * @olen: size of the encrypted filename. It must be at least @iname->len.
108 * Any extra space is filled with NUL padding before encryption.
110 * Return: 0 on success, -errno on failure
112 int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
113 u8 *out, unsigned int olen)
115 struct skcipher_request *req = NULL;
116 DECLARE_CRYPTO_WAIT(wait);
117 const struct fscrypt_info *ci = inode->i_crypt_info;
118 struct crypto_skcipher *tfm = ci->ci_ctfm;
120 struct scatterlist sg;
124 * Copy the filename to the output buffer for encrypting in-place and
125 * pad it with the needed number of NUL bytes.
127 if (WARN_ON(olen < iname->len))
129 memcpy(out, iname->name, iname->len);
130 memset(out + iname->len, 0, olen - iname->len);
132 /* Initialize the IV */
133 fscrypt_generate_iv(&iv, 0, ci);
135 /* Set up the encryption request */
136 req = skcipher_request_alloc(tfm, GFP_NOFS);
139 skcipher_request_set_callback(req,
140 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
141 crypto_req_done, &wait);
142 sg_init_one(&sg, out, olen);
143 skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
145 /* Do the encryption */
146 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
147 skcipher_request_free(req);
149 fscrypt_err(inode, "Filename encryption failed: %d", res);
157 * fname_decrypt() - decrypt a filename
158 * @inode: inode of the parent directory (for regular filenames)
159 * or of the symlink (for symlink targets)
160 * @iname: the encrypted filename to decrypt
161 * @oname: (output) the decrypted filename. The caller must have allocated
162 * enough space for this, e.g. using fscrypt_fname_alloc_buffer().
164 * Return: 0 on success, -errno on failure
166 static int fname_decrypt(const struct inode *inode,
167 const struct fscrypt_str *iname,
168 struct fscrypt_str *oname)
170 struct skcipher_request *req = NULL;
171 DECLARE_CRYPTO_WAIT(wait);
172 struct scatterlist src_sg, dst_sg;
173 const struct fscrypt_info *ci = inode->i_crypt_info;
174 struct crypto_skcipher *tfm = ci->ci_ctfm;
178 /* Allocate request */
179 req = skcipher_request_alloc(tfm, GFP_NOFS);
182 skcipher_request_set_callback(req,
183 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
184 crypto_req_done, &wait);
187 fscrypt_generate_iv(&iv, 0, ci);
189 /* Create decryption request */
190 sg_init_one(&src_sg, iname->name, iname->len);
191 sg_init_one(&dst_sg, oname->name, oname->len);
192 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
193 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
194 skcipher_request_free(req);
196 fscrypt_err(inode, "Filename decryption failed: %d", res);
200 oname->len = strnlen(oname->name, iname->len);
204 static const char lookup_table[65] =
205 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
207 #define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
210 * base64_encode() - base64-encode some bytes
211 * @src: the bytes to encode
212 * @len: number of bytes to encode
213 * @dst: (output) the base64-encoded string. Not NUL-terminated.
215 * Encodes the input string using characters from the set [A-Za-z0-9+,].
216 * The encoded string is roughly 4/3 times the size of the input string.
218 * Return: length of the encoded string
220 static int base64_encode(const u8 *src, int len, char *dst)
222 int i, bits = 0, ac = 0;
225 for (i = 0; i < len; i++) {
226 ac += src[i] << bits;
229 *cp++ = lookup_table[ac & 0x3f];
235 *cp++ = lookup_table[ac & 0x3f];
239 static int base64_decode(const char *src, int len, u8 *dst)
241 int i, bits = 0, ac = 0;
245 for (i = 0; i < len; i++) {
246 p = strchr(lookup_table, src[i]);
247 if (p == NULL || src[i] == 0)
249 ac += (p - lookup_table) << bits;
262 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
263 u32 max_len, u32 *encrypted_len_ret)
265 const struct fscrypt_info *ci = inode->i_crypt_info;
266 int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
267 FSCRYPT_POLICY_FLAGS_PAD_MASK);
270 if (orig_len > max_len)
272 encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
273 encrypted_len = round_up(encrypted_len, padding);
274 *encrypted_len_ret = min(encrypted_len, max_len);
279 * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
280 * @inode: inode of the parent directory (for regular filenames)
281 * or of the symlink (for symlink targets)
282 * @max_encrypted_len: maximum length of encrypted filenames the buffer will be
284 * @crypto_str: (output) buffer to allocate
286 * Allocate a buffer that is large enough to hold any decrypted or encoded
287 * filename (null-terminated), for the given maximum encrypted filename length.
289 * Return: 0 on success, -errno on failure
291 int fscrypt_fname_alloc_buffer(const struct inode *inode,
292 u32 max_encrypted_len,
293 struct fscrypt_str *crypto_str)
295 const u32 max_encoded_len = BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX);
296 u32 max_presented_len;
298 max_presented_len = max(max_encoded_len, max_encrypted_len);
300 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
301 if (!crypto_str->name)
303 crypto_str->len = max_presented_len;
306 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
309 * fscrypt_fname_free_buffer() - free a buffer for presented filenames
310 * @crypto_str: the buffer to free
312 * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
314 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
318 kfree(crypto_str->name);
319 crypto_str->name = NULL;
321 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
324 * fscrypt_fname_disk_to_usr() - convert an encrypted filename to
325 * user-presentable form
326 * @inode: inode of the parent directory (for regular filenames)
327 * or of the symlink (for symlink targets)
328 * @hash: first part of the name's dirhash, if applicable. This only needs to
329 * be provided if the filename is located in an indexed directory whose
330 * encryption key may be unavailable. Not needed for symlink targets.
331 * @minor_hash: second part of the name's dirhash, if applicable
332 * @iname: encrypted filename to convert. May also be "." or "..", which
333 * aren't actually encrypted.
334 * @oname: output buffer for the user-presentable filename. The caller must
335 * have allocated enough space for this, e.g. using
336 * fscrypt_fname_alloc_buffer().
338 * If the key is available, we'll decrypt the disk name. Otherwise, we'll
339 * encode it for presentation in fscrypt_nokey_name format.
340 * See struct fscrypt_nokey_name for details.
342 * Return: 0 on success, -errno on failure
344 int fscrypt_fname_disk_to_usr(const struct inode *inode,
345 u32 hash, u32 minor_hash,
346 const struct fscrypt_str *iname,
347 struct fscrypt_str *oname)
349 const struct qstr qname = FSTR_TO_QSTR(iname);
350 struct fscrypt_nokey_name nokey_name;
351 u32 size; /* size of the unencoded no-key name */
354 if (fscrypt_is_dot_dotdot(&qname)) {
355 oname->name[0] = '.';
356 oname->name[iname->len - 1] = '.';
357 oname->len = iname->len;
361 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
364 if (fscrypt_has_encryption_key(inode))
365 return fname_decrypt(inode, iname, oname);
368 * Sanity check that struct fscrypt_nokey_name doesn't have padding
369 * between fields and that its encoded size never exceeds NAME_MAX.
371 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
372 offsetof(struct fscrypt_nokey_name, bytes));
373 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
374 offsetof(struct fscrypt_nokey_name, sha256));
375 BUILD_BUG_ON(BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) > NAME_MAX);
378 nokey_name.dirhash[0] = hash;
379 nokey_name.dirhash[1] = minor_hash;
381 nokey_name.dirhash[0] = 0;
382 nokey_name.dirhash[1] = 0;
384 if (iname->len <= sizeof(nokey_name.bytes)) {
385 memcpy(nokey_name.bytes, iname->name, iname->len);
386 size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
388 memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
389 /* Compute strong hash of remaining part of name. */
390 err = fscrypt_do_sha256(&iname->name[sizeof(nokey_name.bytes)],
391 iname->len - sizeof(nokey_name.bytes),
395 size = FSCRYPT_NOKEY_NAME_MAX;
397 oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name);
400 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
403 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
404 * @dir: the directory that will be searched
405 * @iname: the user-provided filename being searched for
406 * @lookup: 1 if we're allowed to proceed without the key because it's
407 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
408 * proceed without the key because we're going to create the dir_entry.
409 * @fname: the filename information to be filled in
411 * Given a user-provided filename @iname, this function sets @fname->disk_name
412 * to the name that would be stored in the on-disk directory entry, if possible.
413 * If the directory is unencrypted this is simply @iname. Else, if we have the
414 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
417 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
418 * we decode it to get the fscrypt_nokey_name. Non-@lookup operations will be
419 * impossible in this case, so we fail them with ENOKEY.
421 * If successful, fscrypt_free_filename() must be called later to clean up.
423 * Return: 0 on success, -errno on failure
425 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
426 int lookup, struct fscrypt_name *fname)
428 struct fscrypt_nokey_name *nokey_name;
431 memset(fname, 0, sizeof(struct fscrypt_name));
432 fname->usr_fname = iname;
434 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
435 fname->disk_name.name = (unsigned char *)iname->name;
436 fname->disk_name.len = iname->len;
439 ret = fscrypt_get_encryption_info(dir);
443 if (fscrypt_has_encryption_key(dir)) {
444 if (!fscrypt_fname_encrypted_size(dir, iname->len,
445 dir->i_sb->s_cop->max_namelen,
446 &fname->crypto_buf.len))
447 return -ENAMETOOLONG;
448 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
450 if (!fname->crypto_buf.name)
453 ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
454 fname->crypto_buf.len);
457 fname->disk_name.name = fname->crypto_buf.name;
458 fname->disk_name.len = fname->crypto_buf.len;
463 fname->is_ciphertext_name = true;
466 * We don't have the key and we are doing a lookup; decode the
470 if (iname->len > BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX))
473 fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
474 if (fname->crypto_buf.name == NULL)
477 ret = base64_decode(iname->name, iname->len, fname->crypto_buf.name);
478 if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
479 (ret > offsetof(struct fscrypt_nokey_name, sha256) &&
480 ret != FSCRYPT_NOKEY_NAME_MAX)) {
484 fname->crypto_buf.len = ret;
486 nokey_name = (void *)fname->crypto_buf.name;
487 fname->hash = nokey_name->dirhash[0];
488 fname->minor_hash = nokey_name->dirhash[1];
489 if (ret != FSCRYPT_NOKEY_NAME_MAX) {
490 /* The full ciphertext filename is available. */
491 fname->disk_name.name = nokey_name->bytes;
492 fname->disk_name.len =
493 ret - offsetof(struct fscrypt_nokey_name, bytes);
498 kfree(fname->crypto_buf.name);
501 EXPORT_SYMBOL(fscrypt_setup_filename);
504 * fscrypt_match_name() - test whether the given name matches a directory entry
505 * @fname: the name being searched for
506 * @de_name: the name from the directory entry
507 * @de_name_len: the length of @de_name in bytes
509 * Normally @fname->disk_name will be set, and in that case we simply compare
510 * that to the name stored in the directory entry. The only exception is that
511 * if we don't have the key for an encrypted directory and the name we're
512 * looking for is very long, then we won't have the full disk_name and instead
513 * we'll need to match against a fscrypt_nokey_name that includes a strong hash.
515 * Return: %true if the name matches, otherwise %false.
517 bool fscrypt_match_name(const struct fscrypt_name *fname,
518 const u8 *de_name, u32 de_name_len)
520 const struct fscrypt_nokey_name *nokey_name =
521 (const void *)fname->crypto_buf.name;
522 u8 sha256[SHA256_DIGEST_SIZE];
524 if (likely(fname->disk_name.name)) {
525 if (de_name_len != fname->disk_name.len)
527 return !memcmp(de_name, fname->disk_name.name, de_name_len);
529 if (de_name_len <= sizeof(nokey_name->bytes))
531 if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
533 if (fscrypt_do_sha256(&de_name[sizeof(nokey_name->bytes)],
534 de_name_len - sizeof(nokey_name->bytes), sha256))
536 return !memcmp(sha256, nokey_name->sha256, sizeof(sha256));
538 EXPORT_SYMBOL_GPL(fscrypt_match_name);
541 * fscrypt_fname_siphash() - calculate the SipHash of a filename
542 * @dir: the parent directory
543 * @name: the filename to calculate the SipHash of
545 * Given a plaintext filename @name and a directory @dir which uses SipHash as
546 * its dirhash method and has had its fscrypt key set up, this function
547 * calculates the SipHash of that name using the directory's secret dirhash key.
549 * Return: the SipHash of @name using the hash key of @dir
551 u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
553 const struct fscrypt_info *ci = dir->i_crypt_info;
555 WARN_ON(!ci->ci_dirhash_key_initialized);
557 return siphash(name->name, name->len, &ci->ci_dirhash_key);
559 EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
562 * Validate dentries in encrypted directories to make sure we aren't potentially
563 * caching stale dentries after a key has been added.
565 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
572 * Plaintext names are always valid, since fscrypt doesn't support
573 * reverting to ciphertext names without evicting the directory's inode
574 * -- which implies eviction of the dentries in the directory.
576 if (!(dentry->d_flags & DCACHE_ENCRYPTED_NAME))
580 * Ciphertext name; valid if the directory's key is still unavailable.
582 * Although fscrypt forbids rename() on ciphertext names, we still must
583 * use dget_parent() here rather than use ->d_parent directly. That's
584 * because a corrupted fs image may contain directory hard links, which
585 * the VFS handles by moving the directory's dentry tree in the dcache
586 * each time ->lookup() finds the directory and it already has a dentry
587 * elsewhere. Thus ->d_parent can be changing, and we must safely grab
588 * a reference to some ->d_parent to prevent it from being freed.
591 if (flags & LOOKUP_RCU)
594 dir = dget_parent(dentry);
595 err = fscrypt_get_encryption_info(d_inode(dir));
596 valid = !fscrypt_has_encryption_key(d_inode(dir));
605 const struct dentry_operations fscrypt_d_ops = {
606 .d_revalidate = fscrypt_d_revalidate,