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 void fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result)
66 struct sha256_state sctx;
69 sha256_update(&sctx, data, data_len);
70 sha256_final(&sctx, result);
73 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
75 if (str->len == 1 && str->name[0] == '.')
78 if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
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.
93 * Return: 0 on success, -errno on failure
95 int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
96 u8 *out, unsigned int olen)
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;
103 struct scatterlist sg;
107 * Copy the filename to the output buffer for encrypting in-place and
108 * pad it with the needed number of NUL bytes.
110 if (WARN_ON(olen < iname->len))
112 memcpy(out, iname->name, iname->len);
113 memset(out + iname->len, 0, olen - iname->len);
115 /* Initialize the IV */
116 fscrypt_generate_iv(&iv, 0, ci);
118 /* Set up the encryption request */
119 req = skcipher_request_alloc(tfm, GFP_NOFS);
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);
128 /* Do the encryption */
129 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
130 skcipher_request_free(req);
132 fscrypt_err(inode, "Filename encryption failed: %d", res);
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().
147 * Return: 0 on success, -errno on failure
149 static int fname_decrypt(const struct inode *inode,
150 const struct fscrypt_str *iname,
151 struct fscrypt_str *oname)
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;
161 /* Allocate request */
162 req = skcipher_request_alloc(tfm, GFP_NOFS);
165 skcipher_request_set_callback(req,
166 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
167 crypto_req_done, &wait);
170 fscrypt_generate_iv(&iv, 0, ci);
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);
179 fscrypt_err(inode, "Filename decryption failed: %d", res);
183 oname->len = strnlen(oname->name, iname->len);
187 static const char lookup_table[65] =
188 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
190 #define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
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.
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.
201 * Return: length of the encoded string
203 static int base64_encode(const u8 *src, int len, char *dst)
205 int i, bits = 0, ac = 0;
208 for (i = 0; i < len; i++) {
209 ac += src[i] << bits;
212 *cp++ = lookup_table[ac & 0x3f];
218 *cp++ = lookup_table[ac & 0x3f];
222 static int base64_decode(const char *src, int len, u8 *dst)
224 int i, bits = 0, ac = 0;
228 for (i = 0; i < len; i++) {
229 p = strchr(lookup_table, src[i]);
230 if (p == NULL || src[i] == 0)
232 ac += (p - lookup_table) << bits;
245 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
246 u32 max_len, u32 *encrypted_len_ret)
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);
253 if (orig_len > max_len)
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);
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
267 * @crypto_str: (output) buffer to allocate
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.
272 * Return: 0 on success, -errno on failure
274 int fscrypt_fname_alloc_buffer(const struct inode *inode,
275 u32 max_encrypted_len,
276 struct fscrypt_str *crypto_str)
278 const u32 max_encoded_len = BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX);
279 u32 max_presented_len;
281 max_presented_len = max(max_encoded_len, max_encrypted_len);
283 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
284 if (!crypto_str->name)
286 crypto_str->len = max_presented_len;
289 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
292 * fscrypt_fname_free_buffer() - free a buffer for presented filenames
293 * @crypto_str: the buffer to free
295 * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
297 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
301 kfree(crypto_str->name);
302 crypto_str->name = NULL;
304 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
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().
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.
325 * Return: 0 on success, -errno on failure
327 int 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)
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 */
336 if (fscrypt_is_dot_dotdot(&qname)) {
337 oname->name[0] = '.';
338 oname->name[iname->len - 1] = '.';
339 oname->len = iname->len;
343 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
346 if (fscrypt_has_encryption_key(inode))
347 return fname_decrypt(inode, iname, oname);
350 * Sanity check that struct fscrypt_nokey_name doesn't have padding
351 * between fields and that its encoded size never exceeds NAME_MAX.
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);
360 nokey_name.dirhash[0] = hash;
361 nokey_name.dirhash[1] = minor_hash;
363 nokey_name.dirhash[0] = 0;
364 nokey_name.dirhash[1] = 0;
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]);
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),
375 size = FSCRYPT_NOKEY_NAME_MAX;
377 oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name);
380 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
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
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
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.
401 * If successful, fscrypt_free_filename() must be called later to clean up.
403 * Return: 0 on success, -errno on failure
405 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
406 int lookup, struct fscrypt_name *fname)
408 struct fscrypt_nokey_name *nokey_name;
411 memset(fname, 0, sizeof(struct fscrypt_name));
412 fname->usr_fname = iname;
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;
419 ret = fscrypt_get_encryption_info(dir);
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,
430 if (!fname->crypto_buf.name)
433 ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
434 fname->crypto_buf.len);
437 fname->disk_name.name = fname->crypto_buf.name;
438 fname->disk_name.len = fname->crypto_buf.len;
443 fname->is_ciphertext_name = true;
446 * We don't have the key and we are doing a lookup; decode the
450 if (iname->len > BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX))
453 fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
454 if (fname->crypto_buf.name == NULL)
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)) {
464 fname->crypto_buf.len = ret;
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);
478 kfree(fname->crypto_buf.name);
481 EXPORT_SYMBOL(fscrypt_setup_filename);
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
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.
495 * Return: %true if the name matches, otherwise %false.
497 bool fscrypt_match_name(const struct fscrypt_name *fname,
498 const u8 *de_name, u32 de_name_len)
500 const struct fscrypt_nokey_name *nokey_name =
501 (const void *)fname->crypto_buf.name;
502 u8 sha256[SHA256_DIGEST_SIZE];
504 if (likely(fname->disk_name.name)) {
505 if (de_name_len != fname->disk_name.len)
507 return !memcmp(de_name, fname->disk_name.name, de_name_len);
509 if (de_name_len <= sizeof(nokey_name->bytes))
511 if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
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));
517 EXPORT_SYMBOL_GPL(fscrypt_match_name);
520 * fscrypt_fname_siphash() - calculate the SipHash of a filename
521 * @dir: the parent directory
522 * @name: the filename to calculate the SipHash of
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.
528 * Return: the SipHash of @name using the hash key of @dir
530 u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
532 const struct fscrypt_info *ci = dir->i_crypt_info;
534 WARN_ON(!ci->ci_dirhash_key_initialized);
536 return siphash(name->name, name->len, &ci->ci_dirhash_key);
538 EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
541 * Validate dentries in encrypted directories to make sure we aren't potentially
542 * caching stale dentries after a key has been added.
544 static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
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.
555 if (!(dentry->d_flags & DCACHE_ENCRYPTED_NAME))
559 * Ciphertext name; valid if the directory's key is still unavailable.
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.
570 if (flags & LOOKUP_RCU)
573 dir = dget_parent(dentry);
574 err = fscrypt_get_encryption_info(d_inode(dir));
575 valid = !fscrypt_has_encryption_key(d_inode(dir));
584 const struct dentry_operations fscrypt_d_ops = {
585 .d_revalidate = fscrypt_d_revalidate,