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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/scatterlist.h>
15#include <crypto/skcipher.h>
16#include "fscrypt_private.h"
17
18static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
19{
20 if (str->len == 1 && str->name[0] == '.')
21 return true;
22
23 if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
24 return true;
25
26 return false;
27}
28
29/**
30 * fname_encrypt() - encrypt a filename
31 *
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.
34 *
35 * Return: 0 on success, -errno on failure
36 */
37int fname_encrypt(struct inode *inode, const struct qstr *iname,
38 u8 *out, unsigned int olen)
39{
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;
44 union fscrypt_iv iv;
45 struct scatterlist sg;
46 int res;
47
48 /*
49 * Copy the filename to the output buffer for encrypting in-place and
50 * pad it with the needed number of NUL bytes.
51 */
52 if (WARN_ON(olen < iname->len))
53 return -ENOBUFS;
54 memcpy(out, iname->name, iname->len);
55 memset(out + iname->len, 0, olen - iname->len);
56
57 /* Initialize the IV */
58 fscrypt_generate_iv(&iv, 0, ci);
59
60 /* Set up the encryption request */
61 req = skcipher_request_alloc(tfm, GFP_NOFS);
62 if (!req)
63 return -ENOMEM;
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);
69
70 /* Do the encryption */
71 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
72 skcipher_request_free(req);
73 if (res < 0) {
74 fscrypt_err(inode, "Filename encryption failed: %d", res);
75 return res;
76 }
77
78 return 0;
79}
80
81/**
82 * fname_decrypt() - decrypt a filename
83 *
84 * The caller must have allocated sufficient memory for the @oname string.
85 *
86 * Return: 0 on success, -errno on failure
87 */
88static int fname_decrypt(struct inode *inode,
89 const struct fscrypt_str *iname,
90 struct fscrypt_str *oname)
91{
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;
97 union fscrypt_iv iv;
98 int res;
99
100 /* Allocate request */
101 req = skcipher_request_alloc(tfm, GFP_NOFS);
102 if (!req)
103 return -ENOMEM;
104 skcipher_request_set_callback(req,
105 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
106 crypto_req_done, &wait);
107
108 /* Initialize IV */
109 fscrypt_generate_iv(&iv, 0, ci);
110
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);
117 if (res < 0) {
118 fscrypt_err(inode, "Filename decryption failed: %d", res);
119 return res;
120 }
121
122 oname->len = strnlen(oname->name, iname->len);
123 return 0;
124}
125
126static const char lookup_table[65] =
127 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
128
129#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
130
131/**
132 * base64_encode() -
133 *
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.
136 *
137 * Return: length of the encoded string
138 */
139static int base64_encode(const u8 *src, int len, char *dst)
140{
141 int i, bits = 0, ac = 0;
142 char *cp = dst;
143
144 for (i = 0; i < len; i++) {
145 ac += src[i] << bits;
146 bits += 8;
147 do {
148 *cp++ = lookup_table[ac & 0x3f];
149 ac >>= 6;
150 bits -= 6;
151 } while (bits >= 6);
152 }
153 if (bits)
154 *cp++ = lookup_table[ac & 0x3f];
155 return cp - dst;
156}
157
158static int base64_decode(const char *src, int len, u8 *dst)
159{
160 int i, bits = 0, ac = 0;
161 const char *p;
162 u8 *cp = dst;
163
164 for (i = 0; i < len; i++) {
165 p = strchr(lookup_table, src[i]);
166 if (p == NULL || src[i] == 0)
167 return -2;
168 ac += (p - lookup_table) << bits;
169 bits += 6;
170 if (bits >= 8) {
171 *cp++ = ac & 0xff;
172 ac >>= 8;
173 bits -= 8;
174 }
175 }
176 if (ac)
177 return -1;
178 return cp - dst;
179}
180
181bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
182 u32 max_len, u32 *encrypted_len_ret)
183{
184 const struct fscrypt_info *ci = inode->i_crypt_info;
185 int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
186 FSCRYPT_POLICY_FLAGS_PAD_MASK);
187 u32 encrypted_len;
188
189 if (orig_len > max_len)
190 return false;
191 encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
192 encrypted_len = round_up(encrypted_len, padding);
193 *encrypted_len_ret = min(encrypted_len, max_len);
194 return true;
195}
196
197/**
198 * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
199 *
200 * Allocate a buffer that is large enough to hold any decrypted or encoded
201 * filename (null-terminated), for the given maximum encrypted filename length.
202 *
203 * Return: 0 on success, -errno on failure
204 */
205int fscrypt_fname_alloc_buffer(const struct inode *inode,
206 u32 max_encrypted_len,
207 struct fscrypt_str *crypto_str)
208{
209 const u32 max_encoded_len =
210 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
211 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
212 u32 max_presented_len;
213
214 max_presented_len = max(max_encoded_len, max_encrypted_len);
215
216 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
217 if (!crypto_str->name)
218 return -ENOMEM;
219 crypto_str->len = max_presented_len;
220 return 0;
221}
222EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
223
224/**
225 * fscrypt_fname_free_buffer - free the buffer for presented filenames
226 *
227 * Free the buffer allocated by fscrypt_fname_alloc_buffer().
228 */
229void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
230{
231 if (!crypto_str)
232 return;
233 kfree(crypto_str->name);
234 crypto_str->name = NULL;
235}
236EXPORT_SYMBOL(fscrypt_fname_free_buffer);
237
238/**
239 * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
240 * space
241 *
242 * The caller must have allocated sufficient memory for the @oname string.
243 *
244 * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
245 * it for presentation. Short names are directly base64-encoded, while long
246 * names are encoded in fscrypt_digested_name format.
247 *
248 * Return: 0 on success, -errno on failure
249 */
250int fscrypt_fname_disk_to_usr(struct inode *inode,
251 u32 hash, u32 minor_hash,
252 const struct fscrypt_str *iname,
253 struct fscrypt_str *oname)
254{
255 const struct qstr qname = FSTR_TO_QSTR(iname);
256 struct fscrypt_digested_name digested_name;
257
258 if (fscrypt_is_dot_dotdot(&qname)) {
259 oname->name[0] = '.';
260 oname->name[iname->len - 1] = '.';
261 oname->len = iname->len;
262 return 0;
263 }
264
265 if (iname->len < FS_CRYPTO_BLOCK_SIZE)
266 return -EUCLEAN;
267
268 if (fscrypt_has_encryption_key(inode))
269 return fname_decrypt(inode, iname, oname);
270
271 if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
272 oname->len = base64_encode(iname->name, iname->len,
273 oname->name);
274 return 0;
275 }
276 if (hash) {
277 digested_name.hash = hash;
278 digested_name.minor_hash = minor_hash;
279 } else {
280 digested_name.hash = 0;
281 digested_name.minor_hash = 0;
282 }
283 memcpy(digested_name.digest,
284 FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
285 FSCRYPT_FNAME_DIGEST_SIZE);
286 oname->name[0] = '_';
287 oname->len = 1 + base64_encode((const u8 *)&digested_name,
288 sizeof(digested_name), oname->name + 1);
289 return 0;
290}
291EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
292
293/**
294 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
295 * @dir: the directory that will be searched
296 * @iname: the user-provided filename being searched for
297 * @lookup: 1 if we're allowed to proceed without the key because it's
298 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
299 * proceed without the key because we're going to create the dir_entry.
300 * @fname: the filename information to be filled in
301 *
302 * Given a user-provided filename @iname, this function sets @fname->disk_name
303 * to the name that would be stored in the on-disk directory entry, if possible.
304 * If the directory is unencrypted this is simply @iname. Else, if we have the
305 * directory's encryption key, then @iname is the plaintext, so we encrypt it to
306 * get the disk_name.
307 *
308 * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
309 * we decode it to get either the ciphertext disk_name (for short names) or the
310 * fscrypt_digested_name (for long names). Non-@lookup operations will be
311 * impossible in this case, so we fail them with ENOKEY.
312 *
313 * If successful, fscrypt_free_filename() must be called later to clean up.
314 *
315 * Return: 0 on success, -errno on failure
316 */
317int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
318 int lookup, struct fscrypt_name *fname)
319{
320 int ret;
321 int digested;
322
323 memset(fname, 0, sizeof(struct fscrypt_name));
324 fname->usr_fname = iname;
325
326 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
327 fname->disk_name.name = (unsigned char *)iname->name;
328 fname->disk_name.len = iname->len;
329 return 0;
330 }
331 ret = fscrypt_get_encryption_info(dir);
332 if (ret)
333 return ret;
334
335 if (fscrypt_has_encryption_key(dir)) {
336 if (!fscrypt_fname_encrypted_size(dir, iname->len,
337 dir->i_sb->s_cop->max_namelen,
338 &fname->crypto_buf.len))
339 return -ENAMETOOLONG;
340 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
341 GFP_NOFS);
342 if (!fname->crypto_buf.name)
343 return -ENOMEM;
344
345 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
346 fname->crypto_buf.len);
347 if (ret)
348 goto errout;
349 fname->disk_name.name = fname->crypto_buf.name;
350 fname->disk_name.len = fname->crypto_buf.len;
351 return 0;
352 }
353 if (!lookup)
354 return -ENOKEY;
355 fname->is_ciphertext_name = true;
356
357 /*
358 * We don't have the key and we are doing a lookup; decode the
359 * user-supplied name
360 */
361 if (iname->name[0] == '_') {
362 if (iname->len !=
363 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
364 return -ENOENT;
365 digested = 1;
366 } else {
367 if (iname->len >
368 BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
369 return -ENOENT;
370 digested = 0;
371 }
372
373 fname->crypto_buf.name =
374 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
375 sizeof(struct fscrypt_digested_name)),
376 GFP_KERNEL);
377 if (fname->crypto_buf.name == NULL)
378 return -ENOMEM;
379
380 ret = base64_decode(iname->name + digested, iname->len - digested,
381 fname->crypto_buf.name);
382 if (ret < 0) {
383 ret = -ENOENT;
384 goto errout;
385 }
386 fname->crypto_buf.len = ret;
387 if (digested) {
388 const struct fscrypt_digested_name *n =
389 (const void *)fname->crypto_buf.name;
390 fname->hash = n->hash;
391 fname->minor_hash = n->minor_hash;
392 } else {
393 fname->disk_name.name = fname->crypto_buf.name;
394 fname->disk_name.len = fname->crypto_buf.len;
395 }
396 return 0;
397
398errout:
399 kfree(fname->crypto_buf.name);
400 return ret;
401}
402EXPORT_SYMBOL(fscrypt_setup_filename);