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1/*
2 * linux/fs/ext4/crypto_fname.c
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains functions for filename crypto management in ext4
7 *
8 * Written by Uday Savagaonkar, 2014.
9 *
10 * This has not yet undergone a rigorous security audit.
11 *
12 */
13
14#include <crypto/skcipher.h>
15#include <keys/encrypted-type.h>
16#include <keys/user-type.h>
17#include <linux/gfp.h>
18#include <linux/kernel.h>
19#include <linux/key.h>
20#include <linux/list.h>
21#include <linux/mempool.h>
22#include <linux/random.h>
23#include <linux/scatterlist.h>
24#include <linux/spinlock_types.h>
25
26#include "ext4.h"
27#include "ext4_crypto.h"
28#include "xattr.h"
29
30/**
31 * ext4_dir_crypt_complete() -
32 */
33static void ext4_dir_crypt_complete(struct crypto_async_request *req, int res)
34{
35 struct ext4_completion_result *ecr = req->data;
36
37 if (res == -EINPROGRESS)
38 return;
39 ecr->res = res;
40 complete(&ecr->completion);
41}
42
43bool ext4_valid_filenames_enc_mode(uint32_t mode)
44{
45 return (mode == EXT4_ENCRYPTION_MODE_AES_256_CTS);
46}
47
48static unsigned max_name_len(struct inode *inode)
49{
50 return S_ISLNK(inode->i_mode) ? inode->i_sb->s_blocksize :
51 EXT4_NAME_LEN;
52}
53
54/**
55 * ext4_fname_encrypt() -
56 *
57 * This function encrypts the input filename, and returns the length of the
58 * ciphertext. Errors are returned as negative numbers. We trust the caller to
59 * allocate sufficient memory to oname string.
60 */
61static int ext4_fname_encrypt(struct inode *inode,
62 const struct qstr *iname,
63 struct ext4_str *oname)
64{
65 u32 ciphertext_len;
66 struct skcipher_request *req = NULL;
67 DECLARE_EXT4_COMPLETION_RESULT(ecr);
68 struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
69 struct crypto_skcipher *tfm = ci->ci_ctfm;
70 int res = 0;
71 char iv[EXT4_CRYPTO_BLOCK_SIZE];
72 struct scatterlist src_sg, dst_sg;
73 int padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
74 char *workbuf, buf[32], *alloc_buf = NULL;
75 unsigned lim = max_name_len(inode);
76
77 if (iname->len <= 0 || iname->len > lim)
78 return -EIO;
79
80 ciphertext_len = (iname->len < EXT4_CRYPTO_BLOCK_SIZE) ?
81 EXT4_CRYPTO_BLOCK_SIZE : iname->len;
82 ciphertext_len = ext4_fname_crypto_round_up(ciphertext_len, padding);
83 ciphertext_len = (ciphertext_len > lim)
84 ? lim : ciphertext_len;
85
86 if (ciphertext_len <= sizeof(buf)) {
87 workbuf = buf;
88 } else {
89 alloc_buf = kmalloc(ciphertext_len, GFP_NOFS);
90 if (!alloc_buf)
91 return -ENOMEM;
92 workbuf = alloc_buf;
93 }
94
95 /* Allocate request */
96 req = skcipher_request_alloc(tfm, GFP_NOFS);
97 if (!req) {
98 printk_ratelimited(
99 KERN_ERR "%s: crypto_request_alloc() failed\n", __func__);
100 kfree(alloc_buf);
101 return -ENOMEM;
102 }
103 skcipher_request_set_callback(req,
104 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
105 ext4_dir_crypt_complete, &ecr);
106
107 /* Copy the input */
108 memcpy(workbuf, iname->name, iname->len);
109 if (iname->len < ciphertext_len)
110 memset(workbuf + iname->len, 0, ciphertext_len - iname->len);
111
112 /* Initialize IV */
113 memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
114
115 /* Create encryption request */
116 sg_init_one(&src_sg, workbuf, ciphertext_len);
117 sg_init_one(&dst_sg, oname->name, ciphertext_len);
118 skcipher_request_set_crypt(req, &src_sg, &dst_sg, ciphertext_len, iv);
119 res = crypto_skcipher_encrypt(req);
120 if (res == -EINPROGRESS || res == -EBUSY) {
121 wait_for_completion(&ecr.completion);
122 res = ecr.res;
123 }
124 kfree(alloc_buf);
125 skcipher_request_free(req);
126 if (res < 0) {
127 printk_ratelimited(
128 KERN_ERR "%s: Error (error code %d)\n", __func__, res);
129 }
130 oname->len = ciphertext_len;
131 return res;
132}
133
134/*
135 * ext4_fname_decrypt()
136 * This function decrypts the input filename, and returns
137 * the length of the plaintext.
138 * Errors are returned as negative numbers.
139 * We trust the caller to allocate sufficient memory to oname string.
140 */
141static int ext4_fname_decrypt(struct inode *inode,
142 const struct ext4_str *iname,
143 struct ext4_str *oname)
144{
145 struct ext4_str tmp_in[2], tmp_out[1];
146 struct skcipher_request *req = NULL;
147 DECLARE_EXT4_COMPLETION_RESULT(ecr);
148 struct scatterlist src_sg, dst_sg;
149 struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
150 struct crypto_skcipher *tfm = ci->ci_ctfm;
151 int res = 0;
152 char iv[EXT4_CRYPTO_BLOCK_SIZE];
153 unsigned lim = max_name_len(inode);
154
155 if (iname->len <= 0 || iname->len > lim)
156 return -EIO;
157
158 tmp_in[0].name = iname->name;
159 tmp_in[0].len = iname->len;
160 tmp_out[0].name = oname->name;
161
162 /* Allocate request */
163 req = skcipher_request_alloc(tfm, GFP_NOFS);
164 if (!req) {
165 printk_ratelimited(
166 KERN_ERR "%s: crypto_request_alloc() failed\n", __func__);
167 return -ENOMEM;
168 }
169 skcipher_request_set_callback(req,
170 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
171 ext4_dir_crypt_complete, &ecr);
172
173 /* Initialize IV */
174 memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
175
176 /* Create encryption request */
177 sg_init_one(&src_sg, iname->name, iname->len);
178 sg_init_one(&dst_sg, oname->name, oname->len);
179 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
180 res = crypto_skcipher_decrypt(req);
181 if (res == -EINPROGRESS || res == -EBUSY) {
182 wait_for_completion(&ecr.completion);
183 res = ecr.res;
184 }
185 skcipher_request_free(req);
186 if (res < 0) {
187 printk_ratelimited(
188 KERN_ERR "%s: Error in ext4_fname_encrypt (error code %d)\n",
189 __func__, res);
190 return res;
191 }
192
193 oname->len = strnlen(oname->name, iname->len);
194 return oname->len;
195}
196
197static const char *lookup_table =
198 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
199
200/**
201 * ext4_fname_encode_digest() -
202 *
203 * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
204 * The encoded string is roughly 4/3 times the size of the input string.
205 */
206static int digest_encode(const char *src, int len, char *dst)
207{
208 int i = 0, bits = 0, ac = 0;
209 char *cp = dst;
210
211 while (i < len) {
212 ac += (((unsigned char) src[i]) << bits);
213 bits += 8;
214 do {
215 *cp++ = lookup_table[ac & 0x3f];
216 ac >>= 6;
217 bits -= 6;
218 } while (bits >= 6);
219 i++;
220 }
221 if (bits)
222 *cp++ = lookup_table[ac & 0x3f];
223 return cp - dst;
224}
225
226static int digest_decode(const char *src, int len, char *dst)
227{
228 int i = 0, bits = 0, ac = 0;
229 const char *p;
230 char *cp = dst;
231
232 while (i < len) {
233 p = strchr(lookup_table, src[i]);
234 if (p == NULL || src[i] == 0)
235 return -2;
236 ac += (p - lookup_table) << bits;
237 bits += 6;
238 if (bits >= 8) {
239 *cp++ = ac & 0xff;
240 ac >>= 8;
241 bits -= 8;
242 }
243 i++;
244 }
245 if (ac)
246 return -1;
247 return cp - dst;
248}
249
250/**
251 * ext4_fname_crypto_round_up() -
252 *
253 * Return: The next multiple of block size
254 */
255u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
256{
257 return ((size+blksize-1)/blksize)*blksize;
258}
259
260unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen)
261{
262 struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
263 int padding = 32;
264
265 if (ci)
266 padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
267 if (ilen < EXT4_CRYPTO_BLOCK_SIZE)
268 ilen = EXT4_CRYPTO_BLOCK_SIZE;
269 return ext4_fname_crypto_round_up(ilen, padding);
270}
271
272/*
273 * ext4_fname_crypto_alloc_buffer() -
274 *
275 * Allocates an output buffer that is sufficient for the crypto operation
276 * specified by the context and the direction.
277 */
278int ext4_fname_crypto_alloc_buffer(struct inode *inode,
279 u32 ilen, struct ext4_str *crypto_str)
280{
281 unsigned int olen = ext4_fname_encrypted_size(inode, ilen);
282
283 crypto_str->len = olen;
284 if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
285 olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
286 /* Allocated buffer can hold one more character to null-terminate the
287 * string */
288 crypto_str->name = kmalloc(olen+1, GFP_NOFS);
289 if (!(crypto_str->name))
290 return -ENOMEM;
291 return 0;
292}
293
294/**
295 * ext4_fname_crypto_free_buffer() -
296 *
297 * Frees the buffer allocated for crypto operation.
298 */
299void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str)
300{
301 if (!crypto_str)
302 return;
303 kfree(crypto_str->name);
304 crypto_str->name = NULL;
305}
306
307/**
308 * ext4_fname_disk_to_usr() - converts a filename from disk space to user space
309 */
310int _ext4_fname_disk_to_usr(struct inode *inode,
311 struct dx_hash_info *hinfo,
312 const struct ext4_str *iname,
313 struct ext4_str *oname)
314{
315 char buf[24];
316 int ret;
317
318 if (iname->len < 3) {
319 /*Check for . and .. */
320 if (iname->name[0] == '.' && iname->name[iname->len-1] == '.') {
321 oname->name[0] = '.';
322 oname->name[iname->len-1] = '.';
323 oname->len = iname->len;
324 return oname->len;
325 }
326 }
327 if (iname->len < EXT4_CRYPTO_BLOCK_SIZE) {
328 EXT4_ERROR_INODE(inode, "encrypted inode too small");
329 return -EUCLEAN;
330 }
331 if (EXT4_I(inode)->i_crypt_info)
332 return ext4_fname_decrypt(inode, iname, oname);
333
334 if (iname->len <= EXT4_FNAME_CRYPTO_DIGEST_SIZE) {
335 ret = digest_encode(iname->name, iname->len, oname->name);
336 oname->len = ret;
337 return ret;
338 }
339 if (hinfo) {
340 memcpy(buf, &hinfo->hash, 4);
341 memcpy(buf+4, &hinfo->minor_hash, 4);
342 } else
343 memset(buf, 0, 8);
344 memcpy(buf + 8, iname->name + iname->len - 16, 16);
345 oname->name[0] = '_';
346 ret = digest_encode(buf, 24, oname->name+1);
347 oname->len = ret + 1;
348 return ret + 1;
349}
350
351int ext4_fname_disk_to_usr(struct inode *inode,
352 struct dx_hash_info *hinfo,
353 const struct ext4_dir_entry_2 *de,
354 struct ext4_str *oname)
355{
356 struct ext4_str iname = {.name = (unsigned char *) de->name,
357 .len = de->name_len };
358
359 return _ext4_fname_disk_to_usr(inode, hinfo, &iname, oname);
360}
361
362
363/**
364 * ext4_fname_usr_to_disk() - converts a filename from user space to disk space
365 */
366int ext4_fname_usr_to_disk(struct inode *inode,
367 const struct qstr *iname,
368 struct ext4_str *oname)
369{
370 int res;
371 struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
372
373 if (iname->len < 3) {
374 /*Check for . and .. */
375 if (iname->name[0] == '.' &&
376 iname->name[iname->len-1] == '.') {
377 oname->name[0] = '.';
378 oname->name[iname->len-1] = '.';
379 oname->len = iname->len;
380 return oname->len;
381 }
382 }
383 if (ci) {
384 res = ext4_fname_encrypt(inode, iname, oname);
385 return res;
386 }
387 /* Without a proper key, a user is not allowed to modify the filenames
388 * in a directory. Consequently, a user space name cannot be mapped to
389 * a disk-space name */
390 return -EACCES;
391}
392
393int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
394 int lookup, struct ext4_filename *fname)
395{
396 struct ext4_crypt_info *ci;
397 int ret = 0, bigname = 0;
398
399 memset(fname, 0, sizeof(struct ext4_filename));
400 fname->usr_fname = iname;
401
402 if (!ext4_encrypted_inode(dir) ||
403 ((iname->name[0] == '.') &&
404 ((iname->len == 1) ||
405 ((iname->name[1] == '.') && (iname->len == 2))))) {
406 fname->disk_name.name = (unsigned char *) iname->name;
407 fname->disk_name.len = iname->len;
408 return 0;
409 }
410 ret = ext4_get_encryption_info(dir);
411 if (ret)
412 return ret;
413 ci = EXT4_I(dir)->i_crypt_info;
414 if (ci) {
415 ret = ext4_fname_crypto_alloc_buffer(dir, iname->len,
416 &fname->crypto_buf);
417 if (ret < 0)
418 return ret;
419 ret = ext4_fname_encrypt(dir, iname, &fname->crypto_buf);
420 if (ret < 0)
421 goto errout;
422 fname->disk_name.name = fname->crypto_buf.name;
423 fname->disk_name.len = fname->crypto_buf.len;
424 return 0;
425 }
426 if (!lookup)
427 return -EACCES;
428
429 /* We don't have the key and we are doing a lookup; decode the
430 * user-supplied name
431 */
432 if (iname->name[0] == '_')
433 bigname = 1;
434 if ((bigname && (iname->len != 33)) ||
435 (!bigname && (iname->len > 43)))
436 return -ENOENT;
437
438 fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
439 if (fname->crypto_buf.name == NULL)
440 return -ENOMEM;
441 ret = digest_decode(iname->name + bigname, iname->len - bigname,
442 fname->crypto_buf.name);
443 if (ret < 0) {
444 ret = -ENOENT;
445 goto errout;
446 }
447 fname->crypto_buf.len = ret;
448 if (bigname) {
449 memcpy(&fname->hinfo.hash, fname->crypto_buf.name, 4);
450 memcpy(&fname->hinfo.minor_hash, fname->crypto_buf.name + 4, 4);
451 } else {
452 fname->disk_name.name = fname->crypto_buf.name;
453 fname->disk_name.len = fname->crypto_buf.len;
454 }
455 return 0;
456errout:
457 kfree(fname->crypto_buf.name);
458 fname->crypto_buf.name = NULL;
459 return ret;
460}
461
462void ext4_fname_free_filename(struct ext4_filename *fname)
463{
464 kfree(fname->crypto_buf.name);
465 fname->crypto_buf.name = NULL;
466 fname->usr_fname = NULL;
467 fname->disk_name.name = NULL;
468}