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->i_sb,
75 "Filename encryption failed for inode %lu: %d",
84 * fname_decrypt() - decrypt a filename
86 * The caller must have allocated sufficient memory for the @oname string.
88 * Return: 0 on success, -errno on failure
90 static int fname_decrypt(struct inode *inode,
91 const struct fscrypt_str *iname,
92 struct fscrypt_str *oname)
94 struct skcipher_request *req = NULL;
95 DECLARE_CRYPTO_WAIT(wait);
96 struct scatterlist src_sg, dst_sg;
97 struct fscrypt_info *ci = inode->i_crypt_info;
98 struct crypto_skcipher *tfm = ci->ci_ctfm;
102 /* Allocate request */
103 req = skcipher_request_alloc(tfm, GFP_NOFS);
106 skcipher_request_set_callback(req,
107 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
108 crypto_req_done, &wait);
111 fscrypt_generate_iv(&iv, 0, ci);
113 /* Create decryption request */
114 sg_init_one(&src_sg, iname->name, iname->len);
115 sg_init_one(&dst_sg, oname->name, oname->len);
116 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
117 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
118 skcipher_request_free(req);
120 fscrypt_err(inode->i_sb,
121 "Filename decryption failed for inode %lu: %d",
126 oname->len = strnlen(oname->name, iname->len);
130 static const char *lookup_table =
131 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
133 #define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
138 * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
139 * The encoded string is roughly 4/3 times the size of the input string.
141 static int digest_encode(const char *src, int len, char *dst)
143 int i = 0, bits = 0, ac = 0;
147 ac += (((unsigned char) src[i]) << bits);
150 *cp++ = lookup_table[ac & 0x3f];
157 *cp++ = lookup_table[ac & 0x3f];
161 static int digest_decode(const char *src, int len, char *dst)
163 int i = 0, bits = 0, ac = 0;
168 p = strchr(lookup_table, src[i]);
169 if (p == NULL || src[i] == 0)
171 ac += (p - lookup_table) << bits;
185 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
186 u32 max_len, u32 *encrypted_len_ret)
188 int padding = 4 << (inode->i_crypt_info->ci_flags &
189 FS_POLICY_FLAGS_PAD_MASK);
192 if (orig_len > max_len)
194 encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
195 encrypted_len = round_up(encrypted_len, padding);
196 *encrypted_len_ret = min(encrypted_len, max_len);
201 * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
203 * Allocate a buffer that is large enough to hold any decrypted or encoded
204 * filename (null-terminated), for the given maximum encrypted filename length.
206 * Return: 0 on success, -errno on failure
208 int fscrypt_fname_alloc_buffer(const struct inode *inode,
209 u32 max_encrypted_len,
210 struct fscrypt_str *crypto_str)
212 const u32 max_encoded_len =
213 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
214 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
215 u32 max_presented_len;
217 max_presented_len = max(max_encoded_len, max_encrypted_len);
219 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
220 if (!crypto_str->name)
222 crypto_str->len = max_presented_len;
225 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
228 * fscrypt_fname_free_buffer - free the buffer for presented filenames
230 * Free the buffer allocated by fscrypt_fname_alloc_buffer().
232 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
236 kfree(crypto_str->name);
237 crypto_str->name = NULL;
239 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
242 * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
245 * The caller must have allocated sufficient memory for the @oname string.
247 * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
248 * it for presentation. Short names are directly base64-encoded, while long
249 * names are encoded in fscrypt_digested_name format.
251 * Return: 0 on success, -errno on failure
253 int fscrypt_fname_disk_to_usr(struct inode *inode,
254 u32 hash, u32 minor_hash,
255 const struct fscrypt_str *iname,
256 struct fscrypt_str *oname)
258 const struct qstr qname = FSTR_TO_QSTR(iname);
259 struct fscrypt_digested_name digested_name;
261 if (fscrypt_is_dot_dotdot(&qname)) {
262 oname->name[0] = '.';
263 oname->name[iname->len - 1] = '.';
264 oname->len = iname->len;
268 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
271 if (fscrypt_has_encryption_key(inode))
272 return fname_decrypt(inode, iname, oname);
274 if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
275 oname->len = digest_encode(iname->name, iname->len,
280 digested_name.hash = hash;
281 digested_name.minor_hash = minor_hash;
283 digested_name.hash = 0;
284 digested_name.minor_hash = 0;
286 memcpy(digested_name.digest,
287 FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
288 FSCRYPT_FNAME_DIGEST_SIZE);
289 oname->name[0] = '_';
290 oname->len = 1 + digest_encode((const char *)&digested_name,
291 sizeof(digested_name), oname->name + 1);
294 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
297 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
298 * @dir: the directory that will be searched
299 * @iname: the user-provided filename being searched for
300 * @lookup: 1 if we're allowed to proceed without the key because it's
301 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
302 * proceed without the key because we're going to create the dir_entry.
303 * @fname: the filename information to be filled in
305 * Given a user-provided filename @iname, this function sets @fname->disk_name
306 * to the name that would be stored in the on-disk directory entry, if possible.
307 * If the directory is unencrypted this is simply @iname. Else, if we have the
308 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
311 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
312 * we decode it to get either the ciphertext disk_name (for short names) or the
313 * fscrypt_digested_name (for long names). Non-@lookup operations will be
314 * impossible in this case, so we fail them with ENOKEY.
316 * If successful, fscrypt_free_filename() must be called later to clean up.
318 * Return: 0 on success, -errno on failure
320 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
321 int lookup, struct fscrypt_name *fname)
326 memset(fname, 0, sizeof(struct fscrypt_name));
327 fname->usr_fname = iname;
329 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
330 fname->disk_name.name = (unsigned char *)iname->name;
331 fname->disk_name.len = iname->len;
334 ret = fscrypt_get_encryption_info(dir);
338 if (fscrypt_has_encryption_key(dir)) {
339 if (!fscrypt_fname_encrypted_size(dir, iname->len,
340 dir->i_sb->s_cop->max_namelen,
341 &fname->crypto_buf.len))
342 return -ENAMETOOLONG;
343 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
345 if (!fname->crypto_buf.name)
348 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
349 fname->crypto_buf.len);
352 fname->disk_name.name = fname->crypto_buf.name;
353 fname->disk_name.len = fname->crypto_buf.len;
358 fname->is_ciphertext_name = true;
361 * We don't have the key and we are doing a lookup; decode the
364 if (iname->name[0] == '_') {
366 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
371 BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
376 fname->crypto_buf.name =
377 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
378 sizeof(struct fscrypt_digested_name)),
380 if (fname->crypto_buf.name == NULL)
383 ret = digest_decode(iname->name + digested, iname->len - digested,
384 fname->crypto_buf.name);
389 fname->crypto_buf.len = ret;
391 const struct fscrypt_digested_name *n =
392 (const void *)fname->crypto_buf.name;
393 fname->hash = n->hash;
394 fname->minor_hash = n->minor_hash;
396 fname->disk_name.name = fname->crypto_buf.name;
397 fname->disk_name.len = fname->crypto_buf.len;
402 kfree(fname->crypto_buf.name);
405 EXPORT_SYMBOL(fscrypt_setup_filename);