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/scatterlist.h>
15 #include <crypto/skcipher.h>
16 #include "fscrypt_private.h"
18 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
20 if (str->len == 1 && str->name[0] == '.')
23 if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
30 * fname_encrypt() - encrypt a filename
32 * The output buffer must be at least as large as the input buffer.
33 * Any extra space is filled with NUL padding before encryption.
35 * Return: 0 on success, -errno on failure
37 int fname_encrypt(struct inode *inode, const struct qstr *iname,
38 u8 *out, unsigned int olen)
40 struct skcipher_request *req = NULL;
41 DECLARE_CRYPTO_WAIT(wait);
42 struct fscrypt_info *ci = inode->i_crypt_info;
43 struct crypto_skcipher *tfm = ci->ci_ctfm;
45 struct scatterlist sg;
49 * Copy the filename to the output buffer for encrypting in-place and
50 * pad it with the needed number of NUL bytes.
52 if (WARN_ON(olen < iname->len))
54 memcpy(out, iname->name, iname->len);
55 memset(out + iname->len, 0, olen - iname->len);
57 /* Initialize the IV */
58 fscrypt_generate_iv(&iv, 0, ci);
60 /* Set up the encryption request */
61 req = skcipher_request_alloc(tfm, GFP_NOFS);
64 skcipher_request_set_callback(req,
65 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
66 crypto_req_done, &wait);
67 sg_init_one(&sg, out, olen);
68 skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
70 /* Do the encryption */
71 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
72 skcipher_request_free(req);
74 fscrypt_err(inode, "Filename encryption failed: %d", res);
82 * fname_decrypt() - decrypt a filename
84 * The caller must have allocated sufficient memory for the @oname string.
86 * Return: 0 on success, -errno on failure
88 static int fname_decrypt(struct inode *inode,
89 const struct fscrypt_str *iname,
90 struct fscrypt_str *oname)
92 struct skcipher_request *req = NULL;
93 DECLARE_CRYPTO_WAIT(wait);
94 struct scatterlist src_sg, dst_sg;
95 struct fscrypt_info *ci = inode->i_crypt_info;
96 struct crypto_skcipher *tfm = ci->ci_ctfm;
100 /* Allocate request */
101 req = skcipher_request_alloc(tfm, GFP_NOFS);
104 skcipher_request_set_callback(req,
105 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
106 crypto_req_done, &wait);
109 fscrypt_generate_iv(&iv, 0, ci);
111 /* Create decryption request */
112 sg_init_one(&src_sg, iname->name, iname->len);
113 sg_init_one(&dst_sg, oname->name, oname->len);
114 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
115 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
116 skcipher_request_free(req);
118 fscrypt_err(inode, "Filename decryption failed: %d", res);
122 oname->len = strnlen(oname->name, iname->len);
126 static const char lookup_table[65] =
127 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
129 #define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
134 * Encodes the input string using characters from the set [A-Za-z0-9+,].
135 * The encoded string is roughly 4/3 times the size of the input string.
137 * Return: length of the encoded string
139 static int base64_encode(const u8 *src, int len, char *dst)
141 int i, bits = 0, ac = 0;
144 for (i = 0; i < len; i++) {
145 ac += src[i] << bits;
148 *cp++ = lookup_table[ac & 0x3f];
154 *cp++ = lookup_table[ac & 0x3f];
158 static int base64_decode(const char *src, int len, u8 *dst)
160 int i, bits = 0, ac = 0;
164 for (i = 0; i < len; i++) {
165 p = strchr(lookup_table, src[i]);
166 if (p == NULL || src[i] == 0)
168 ac += (p - lookup_table) << bits;
181 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
182 u32 max_len, u32 *encrypted_len_ret)
184 int padding = 4 << (inode->i_crypt_info->ci_flags &
185 FSCRYPT_POLICY_FLAGS_PAD_MASK);
188 if (orig_len > max_len)
190 encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
191 encrypted_len = round_up(encrypted_len, padding);
192 *encrypted_len_ret = min(encrypted_len, max_len);
197 * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
199 * Allocate a buffer that is large enough to hold any decrypted or encoded
200 * filename (null-terminated), for the given maximum encrypted filename length.
202 * Return: 0 on success, -errno on failure
204 int fscrypt_fname_alloc_buffer(const struct inode *inode,
205 u32 max_encrypted_len,
206 struct fscrypt_str *crypto_str)
208 const u32 max_encoded_len =
209 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
210 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
211 u32 max_presented_len;
213 max_presented_len = max(max_encoded_len, max_encrypted_len);
215 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
216 if (!crypto_str->name)
218 crypto_str->len = max_presented_len;
221 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
224 * fscrypt_fname_free_buffer - free the buffer for presented filenames
226 * Free the buffer allocated by fscrypt_fname_alloc_buffer().
228 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
232 kfree(crypto_str->name);
233 crypto_str->name = NULL;
235 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
238 * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
241 * The caller must have allocated sufficient memory for the @oname string.
243 * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
244 * it for presentation. Short names are directly base64-encoded, while long
245 * names are encoded in fscrypt_digested_name format.
247 * Return: 0 on success, -errno on failure
249 int fscrypt_fname_disk_to_usr(struct inode *inode,
250 u32 hash, u32 minor_hash,
251 const struct fscrypt_str *iname,
252 struct fscrypt_str *oname)
254 const struct qstr qname = FSTR_TO_QSTR(iname);
255 struct fscrypt_digested_name digested_name;
257 if (fscrypt_is_dot_dotdot(&qname)) {
258 oname->name[0] = '.';
259 oname->name[iname->len - 1] = '.';
260 oname->len = iname->len;
264 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
267 if (fscrypt_has_encryption_key(inode))
268 return fname_decrypt(inode, iname, oname);
270 if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
271 oname->len = base64_encode(iname->name, iname->len,
276 digested_name.hash = hash;
277 digested_name.minor_hash = minor_hash;
279 digested_name.hash = 0;
280 digested_name.minor_hash = 0;
282 memcpy(digested_name.digest,
283 FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
284 FSCRYPT_FNAME_DIGEST_SIZE);
285 oname->name[0] = '_';
286 oname->len = 1 + base64_encode((const u8 *)&digested_name,
287 sizeof(digested_name), oname->name + 1);
290 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
293 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
294 * @dir: the directory that will be searched
295 * @iname: the user-provided filename being searched for
296 * @lookup: 1 if we're allowed to proceed without the key because it's
297 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
298 * proceed without the key because we're going to create the dir_entry.
299 * @fname: the filename information to be filled in
301 * Given a user-provided filename @iname, this function sets @fname->disk_name
302 * to the name that would be stored in the on-disk directory entry, if possible.
303 * If the directory is unencrypted this is simply @iname. Else, if we have the
304 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
307 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
308 * we decode it to get either the ciphertext disk_name (for short names) or the
309 * fscrypt_digested_name (for long names). Non-@lookup operations will be
310 * impossible in this case, so we fail them with ENOKEY.
312 * If successful, fscrypt_free_filename() must be called later to clean up.
314 * Return: 0 on success, -errno on failure
316 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
317 int lookup, struct fscrypt_name *fname)
322 memset(fname, 0, sizeof(struct fscrypt_name));
323 fname->usr_fname = iname;
325 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
326 fname->disk_name.name = (unsigned char *)iname->name;
327 fname->disk_name.len = iname->len;
330 ret = fscrypt_get_encryption_info(dir);
334 if (fscrypt_has_encryption_key(dir)) {
335 if (!fscrypt_fname_encrypted_size(dir, iname->len,
336 dir->i_sb->s_cop->max_namelen,
337 &fname->crypto_buf.len))
338 return -ENAMETOOLONG;
339 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
341 if (!fname->crypto_buf.name)
344 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
345 fname->crypto_buf.len);
348 fname->disk_name.name = fname->crypto_buf.name;
349 fname->disk_name.len = fname->crypto_buf.len;
354 fname->is_ciphertext_name = true;
357 * We don't have the key and we are doing a lookup; decode the
360 if (iname->name[0] == '_') {
362 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
367 BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
372 fname->crypto_buf.name =
373 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
374 sizeof(struct fscrypt_digested_name)),
376 if (fname->crypto_buf.name == NULL)
379 ret = base64_decode(iname->name + digested, iname->len - digested,
380 fname->crypto_buf.name);
385 fname->crypto_buf.len = ret;
387 const struct fscrypt_digested_name *n =
388 (const void *)fname->crypto_buf.name;
389 fname->hash = n->hash;
390 fname->minor_hash = n->minor_hash;
392 fname->disk_name.name = fname->crypto_buf.name;
393 fname->disk_name.len = fname->crypto_buf.len;
398 kfree(fname->crypto_buf.name);
401 EXPORT_SYMBOL(fscrypt_setup_filename);