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 <linux/ratelimit.h>
16 #include <crypto/skcipher.h>
17 #include "fscrypt_private.h"
18 
fscrypt_is_dot_dotdot(const struct qstr * str)19 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
20 {
21 	if (str->len == 1 && str->name[0] == '.')
22 		return true;
23 
24 	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
25 		return true;
26 
27 	return false;
28 }
29 
30 /**
31  * fname_encrypt() - encrypt a filename
32  *
33  * The output buffer must be at least as large as the input buffer.
34  * Any extra space is filled with NUL padding before encryption.
35  *
36  * Return: 0 on success, -errno on failure
37  */
fname_encrypt(struct inode * inode,const struct qstr * iname,u8 * out,unsigned int olen)38 int fname_encrypt(struct inode *inode, const struct qstr *iname,
39 		  u8 *out, unsigned int olen)
40 {
41 	struct skcipher_request *req = NULL;
42 	DECLARE_CRYPTO_WAIT(wait);
43 	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
44 	int res = 0;
45 	char iv[FS_CRYPTO_BLOCK_SIZE];
46 	struct scatterlist sg;
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 	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
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->i_sb,
75 			    "Filename encryption failed for inode %lu: %d",
76 			    inode->i_ino, res);
77 		return res;
78 	}
79 
80 	return 0;
81 }
82 
83 /**
84  * fname_decrypt() - decrypt a filename
85  *
86  * The caller must have allocated sufficient memory for the @oname string.
87  *
88  * Return: 0 on success, -errno on failure
89  */
fname_decrypt(struct inode * inode,const struct fscrypt_str * iname,struct fscrypt_str * oname)90 static int fname_decrypt(struct inode *inode,
91 				const struct fscrypt_str *iname,
92 				struct fscrypt_str *oname)
93 {
94 	struct skcipher_request *req = NULL;
95 	DECLARE_CRYPTO_WAIT(wait);
96 	struct scatterlist src_sg, dst_sg;
97 	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
98 	int res = 0;
99 	char iv[FS_CRYPTO_BLOCK_SIZE];
100 
101 	/* Allocate request */
102 	req = skcipher_request_alloc(tfm, GFP_NOFS);
103 	if (!req)
104 		return -ENOMEM;
105 	skcipher_request_set_callback(req,
106 		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
107 		crypto_req_done, &wait);
108 
109 	/* Initialize IV */
110 	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
111 
112 	/* Create decryption request */
113 	sg_init_one(&src_sg, iname->name, iname->len);
114 	sg_init_one(&dst_sg, oname->name, oname->len);
115 	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
116 	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
117 	skcipher_request_free(req);
118 	if (res < 0) {
119 		fscrypt_err(inode->i_sb,
120 			    "Filename decryption failed for inode %lu: %d",
121 			    inode->i_ino, res);
122 		return res;
123 	}
124 
125 	oname->len = strnlen(oname->name, iname->len);
126 	return 0;
127 }
128 
129 static const char *lookup_table =
130 	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
131 
132 #define BASE64_CHARS(nbytes)	DIV_ROUND_UP((nbytes) * 4, 3)
133 
134 /**
135  * digest_encode() -
136  *
137  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
138  * The encoded string is roughly 4/3 times the size of the input string.
139  */
digest_encode(const char * src,int len,char * dst)140 static int digest_encode(const char *src, int len, char *dst)
141 {
142 	int i = 0, bits = 0, ac = 0;
143 	char *cp = dst;
144 
145 	while (i < len) {
146 		ac += (((unsigned char) src[i]) << bits);
147 		bits += 8;
148 		do {
149 			*cp++ = lookup_table[ac & 0x3f];
150 			ac >>= 6;
151 			bits -= 6;
152 		} while (bits >= 6);
153 		i++;
154 	}
155 	if (bits)
156 		*cp++ = lookup_table[ac & 0x3f];
157 	return cp - dst;
158 }
159 
digest_decode(const char * src,int len,char * dst)160 static int digest_decode(const char *src, int len, char *dst)
161 {
162 	int i = 0, bits = 0, ac = 0;
163 	const char *p;
164 	char *cp = dst;
165 
166 	while (i < len) {
167 		p = strchr(lookup_table, src[i]);
168 		if (p == NULL || src[i] == 0)
169 			return -2;
170 		ac += (p - lookup_table) << bits;
171 		bits += 6;
172 		if (bits >= 8) {
173 			*cp++ = ac & 0xff;
174 			ac >>= 8;
175 			bits -= 8;
176 		}
177 		i++;
178 	}
179 	if (ac)
180 		return -1;
181 	return cp - dst;
182 }
183 
fscrypt_fname_encrypted_size(const struct inode * inode,u32 orig_len,u32 max_len,u32 * encrypted_len_ret)184 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
185 				  u32 max_len, u32 *encrypted_len_ret)
186 {
187 	int padding = 4 << (inode->i_crypt_info->ci_flags &
188 			    FS_POLICY_FLAGS_PAD_MASK);
189 	u32 encrypted_len;
190 
191 	if (orig_len > max_len)
192 		return false;
193 	encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
194 	encrypted_len = round_up(encrypted_len, padding);
195 	*encrypted_len_ret = min(encrypted_len, max_len);
196 	return true;
197 }
198 
199 /**
200  * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
201  *
202  * Allocate a buffer that is large enough to hold any decrypted or encoded
203  * filename (null-terminated), for the given maximum encrypted filename length.
204  *
205  * Return: 0 on success, -errno on failure
206  */
fscrypt_fname_alloc_buffer(const struct inode * inode,u32 max_encrypted_len,struct fscrypt_str * crypto_str)207 int fscrypt_fname_alloc_buffer(const struct inode *inode,
208 			       u32 max_encrypted_len,
209 			       struct fscrypt_str *crypto_str)
210 {
211 	const u32 max_encoded_len =
212 		max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
213 		      1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
214 	u32 max_presented_len;
215 
216 	max_presented_len = max(max_encoded_len, max_encrypted_len);
217 
218 	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
219 	if (!crypto_str->name)
220 		return -ENOMEM;
221 	crypto_str->len = max_presented_len;
222 	return 0;
223 }
224 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
225 
226 /**
227  * fscrypt_fname_free_buffer - free the buffer for presented filenames
228  *
229  * Free the buffer allocated by fscrypt_fname_alloc_buffer().
230  */
fscrypt_fname_free_buffer(struct fscrypt_str * crypto_str)231 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
232 {
233 	if (!crypto_str)
234 		return;
235 	kfree(crypto_str->name);
236 	crypto_str->name = NULL;
237 }
238 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
239 
240 /**
241  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
242  * space
243  *
244  * The caller must have allocated sufficient memory for the @oname string.
245  *
246  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
247  * it for presentation.  Short names are directly base64-encoded, while long
248  * names are encoded in fscrypt_digested_name format.
249  *
250  * Return: 0 on success, -errno on failure
251  */
fscrypt_fname_disk_to_usr(struct inode * inode,u32 hash,u32 minor_hash,const struct fscrypt_str * iname,struct fscrypt_str * oname)252 int fscrypt_fname_disk_to_usr(struct inode *inode,
253 			u32 hash, u32 minor_hash,
254 			const struct fscrypt_str *iname,
255 			struct fscrypt_str *oname)
256 {
257 	const struct qstr qname = FSTR_TO_QSTR(iname);
258 	struct fscrypt_digested_name digested_name;
259 
260 	if (fscrypt_is_dot_dotdot(&qname)) {
261 		oname->name[0] = '.';
262 		oname->name[iname->len - 1] = '.';
263 		oname->len = iname->len;
264 		return 0;
265 	}
266 
267 	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
268 		return -EUCLEAN;
269 
270 	if (inode->i_crypt_info)
271 		return fname_decrypt(inode, iname, oname);
272 
273 	if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
274 		oname->len = digest_encode(iname->name, iname->len,
275 					   oname->name);
276 		return 0;
277 	}
278 	digested_name.hash = hash;
279 	digested_name.minor_hash = minor_hash;
280 	memcpy(digested_name.digest,
281 	       FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
282 	       FSCRYPT_FNAME_DIGEST_SIZE);
283 	oname->name[0] = '_';
284 	oname->len = 1 + digest_encode((const char *)&digested_name,
285 				       sizeof(digested_name), oname->name + 1);
286 	return 0;
287 }
288 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
289 
290 /**
291  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
292  * @dir: the directory that will be searched
293  * @iname: the user-provided filename being searched for
294  * @lookup: 1 if we're allowed to proceed without the key because it's
295  *	->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
296  *	proceed without the key because we're going to create the dir_entry.
297  * @fname: the filename information to be filled in
298  *
299  * Given a user-provided filename @iname, this function sets @fname->disk_name
300  * to the name that would be stored in the on-disk directory entry, if possible.
301  * If the directory is unencrypted this is simply @iname.  Else, if we have the
302  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
303  * get the disk_name.
304  *
305  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
306  * we decode it to get either the ciphertext disk_name (for short names) or the
307  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
308  * impossible in this case, so we fail them with ENOKEY.
309  *
310  * If successful, fscrypt_free_filename() must be called later to clean up.
311  *
312  * Return: 0 on success, -errno on failure
313  */
fscrypt_setup_filename(struct inode * dir,const struct qstr * iname,int lookup,struct fscrypt_name * fname)314 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
315 			      int lookup, struct fscrypt_name *fname)
316 {
317 	int ret;
318 	int digested;
319 
320 	memset(fname, 0, sizeof(struct fscrypt_name));
321 	fname->usr_fname = iname;
322 
323 	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
324 		fname->disk_name.name = (unsigned char *)iname->name;
325 		fname->disk_name.len = iname->len;
326 		return 0;
327 	}
328 	ret = fscrypt_get_encryption_info(dir);
329 	if (ret)
330 		return ret;
331 
332 	if (dir->i_crypt_info) {
333 		if (!fscrypt_fname_encrypted_size(dir, iname->len,
334 						  dir->i_sb->s_cop->max_namelen,
335 						  &fname->crypto_buf.len))
336 			return -ENAMETOOLONG;
337 		fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
338 						 GFP_NOFS);
339 		if (!fname->crypto_buf.name)
340 			return -ENOMEM;
341 
342 		ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
343 				    fname->crypto_buf.len);
344 		if (ret)
345 			goto errout;
346 		fname->disk_name.name = fname->crypto_buf.name;
347 		fname->disk_name.len = fname->crypto_buf.len;
348 		return 0;
349 	}
350 	if (!lookup)
351 		return -ENOKEY;
352 	fname->is_ciphertext_name = true;
353 
354 	/*
355 	 * We don't have the key and we are doing a lookup; decode the
356 	 * user-supplied name
357 	 */
358 	if (iname->name[0] == '_') {
359 		if (iname->len !=
360 		    1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
361 			return -ENOENT;
362 		digested = 1;
363 	} else {
364 		if (iname->len >
365 		    BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
366 			return -ENOENT;
367 		digested = 0;
368 	}
369 
370 	fname->crypto_buf.name =
371 		kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
372 			      sizeof(struct fscrypt_digested_name)),
373 			GFP_KERNEL);
374 	if (fname->crypto_buf.name == NULL)
375 		return -ENOMEM;
376 
377 	ret = digest_decode(iname->name + digested, iname->len - digested,
378 				fname->crypto_buf.name);
379 	if (ret < 0) {
380 		ret = -ENOENT;
381 		goto errout;
382 	}
383 	fname->crypto_buf.len = ret;
384 	if (digested) {
385 		const struct fscrypt_digested_name *n =
386 			(const void *)fname->crypto_buf.name;
387 		fname->hash = n->hash;
388 		fname->minor_hash = n->minor_hash;
389 	} else {
390 		fname->disk_name.name = fname->crypto_buf.name;
391 		fname->disk_name.len = fname->crypto_buf.len;
392 	}
393 	return 0;
394 
395 errout:
396 	kfree(fname->crypto_buf.name);
397 	return ret;
398 }
399 EXPORT_SYMBOL(fscrypt_setup_filename);
400