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