1 /* Large capacity key type 2 * 3 * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. 4 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells@redhat.com) 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public Licence 9 * as published by the Free Software Foundation; either version 10 * 2 of the Licence, or (at your option) any later version. 11 */ 12 13 #define pr_fmt(fmt) "big_key: "fmt 14 #include <linux/init.h> 15 #include <linux/seq_file.h> 16 #include <linux/file.h> 17 #include <linux/shmem_fs.h> 18 #include <linux/err.h> 19 #include <linux/scatterlist.h> 20 #include <linux/random.h> 21 #include <keys/user-type.h> 22 #include <keys/big_key-type.h> 23 #include <crypto/aead.h> 24 25 /* 26 * Layout of key payload words. 27 */ 28 enum { 29 big_key_data, 30 big_key_path, 31 big_key_path_2nd_part, 32 big_key_len, 33 }; 34 35 /* 36 * Crypto operation with big_key data 37 */ 38 enum big_key_op { 39 BIG_KEY_ENC, 40 BIG_KEY_DEC, 41 }; 42 43 /* 44 * If the data is under this limit, there's no point creating a shm file to 45 * hold it as the permanently resident metadata for the shmem fs will be at 46 * least as large as the data. 47 */ 48 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry)) 49 50 /* 51 * Key size for big_key data encryption 52 */ 53 #define ENC_KEY_SIZE 32 54 55 /* 56 * Authentication tag length 57 */ 58 #define ENC_AUTHTAG_SIZE 16 59 60 /* 61 * big_key defined keys take an arbitrary string as the description and an 62 * arbitrary blob of data as the payload 63 */ 64 struct key_type key_type_big_key = { 65 .name = "big_key", 66 .preparse = big_key_preparse, 67 .free_preparse = big_key_free_preparse, 68 .instantiate = generic_key_instantiate, 69 .revoke = big_key_revoke, 70 .destroy = big_key_destroy, 71 .describe = big_key_describe, 72 .read = big_key_read, 73 /* no ->update(); don't add it without changing big_key_crypt() nonce */ 74 }; 75 76 /* 77 * Crypto names for big_key data authenticated encryption 78 */ 79 static const char big_key_alg_name[] = "gcm(aes)"; 80 81 /* 82 * Crypto algorithms for big_key data authenticated encryption 83 */ 84 static struct crypto_aead *big_key_aead; 85 86 /* 87 * Since changing the key affects the entire object, we need a mutex. 88 */ 89 static DEFINE_MUTEX(big_key_aead_lock); 90 91 /* 92 * Encrypt/decrypt big_key data 93 */ 94 static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key) 95 { 96 int ret; 97 struct scatterlist sgio; 98 struct aead_request *aead_req; 99 /* We always use a zero nonce. The reason we can get away with this is 100 * because we're using a different randomly generated key for every 101 * different encryption. Notably, too, key_type_big_key doesn't define 102 * an .update function, so there's no chance we'll wind up reusing the 103 * key to encrypt updated data. Simply put: one key, one encryption. 104 */ 105 u8 zero_nonce[crypto_aead_ivsize(big_key_aead)]; 106 107 aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL); 108 if (!aead_req) 109 return -ENOMEM; 110 111 memset(zero_nonce, 0, sizeof(zero_nonce)); 112 sg_init_one(&sgio, data, datalen + (op == BIG_KEY_ENC ? ENC_AUTHTAG_SIZE : 0)); 113 aead_request_set_crypt(aead_req, &sgio, &sgio, datalen, zero_nonce); 114 aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL); 115 aead_request_set_ad(aead_req, 0); 116 117 mutex_lock(&big_key_aead_lock); 118 if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) { 119 ret = -EAGAIN; 120 goto error; 121 } 122 if (op == BIG_KEY_ENC) 123 ret = crypto_aead_encrypt(aead_req); 124 else 125 ret = crypto_aead_decrypt(aead_req); 126 error: 127 mutex_unlock(&big_key_aead_lock); 128 aead_request_free(aead_req); 129 return ret; 130 } 131 132 /* 133 * Preparse a big key 134 */ 135 int big_key_preparse(struct key_preparsed_payload *prep) 136 { 137 struct path *path = (struct path *)&prep->payload.data[big_key_path]; 138 struct file *file; 139 u8 *enckey; 140 u8 *data = NULL; 141 ssize_t written; 142 size_t datalen = prep->datalen; 143 int ret; 144 145 ret = -EINVAL; 146 if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data) 147 goto error; 148 149 /* Set an arbitrary quota */ 150 prep->quotalen = 16; 151 152 prep->payload.data[big_key_len] = (void *)(unsigned long)datalen; 153 154 if (datalen > BIG_KEY_FILE_THRESHOLD) { 155 /* Create a shmem file to store the data in. This will permit the data 156 * to be swapped out if needed. 157 * 158 * File content is stored encrypted with randomly generated key. 159 */ 160 size_t enclen = datalen + ENC_AUTHTAG_SIZE; 161 loff_t pos = 0; 162 163 data = kmalloc(enclen, GFP_KERNEL); 164 if (!data) 165 return -ENOMEM; 166 memcpy(data, prep->data, datalen); 167 168 /* generate random key */ 169 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL); 170 if (!enckey) { 171 ret = -ENOMEM; 172 goto error; 173 } 174 ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE); 175 if (unlikely(ret)) 176 goto err_enckey; 177 178 /* encrypt aligned data */ 179 ret = big_key_crypt(BIG_KEY_ENC, data, datalen, enckey); 180 if (ret) 181 goto err_enckey; 182 183 /* save aligned data to file */ 184 file = shmem_kernel_file_setup("", enclen, 0); 185 if (IS_ERR(file)) { 186 ret = PTR_ERR(file); 187 goto err_enckey; 188 } 189 190 written = kernel_write(file, data, enclen, &pos); 191 if (written != enclen) { 192 ret = written; 193 if (written >= 0) 194 ret = -ENOMEM; 195 goto err_fput; 196 } 197 198 /* Pin the mount and dentry to the key so that we can open it again 199 * later 200 */ 201 prep->payload.data[big_key_data] = enckey; 202 *path = file->f_path; 203 path_get(path); 204 fput(file); 205 kzfree(data); 206 } else { 207 /* Just store the data in a buffer */ 208 void *data = kmalloc(datalen, GFP_KERNEL); 209 210 if (!data) 211 return -ENOMEM; 212 213 prep->payload.data[big_key_data] = data; 214 memcpy(data, prep->data, prep->datalen); 215 } 216 return 0; 217 218 err_fput: 219 fput(file); 220 err_enckey: 221 kzfree(enckey); 222 error: 223 kzfree(data); 224 return ret; 225 } 226 227 /* 228 * Clear preparsement. 229 */ 230 void big_key_free_preparse(struct key_preparsed_payload *prep) 231 { 232 if (prep->datalen > BIG_KEY_FILE_THRESHOLD) { 233 struct path *path = (struct path *)&prep->payload.data[big_key_path]; 234 235 path_put(path); 236 } 237 kzfree(prep->payload.data[big_key_data]); 238 } 239 240 /* 241 * dispose of the links from a revoked keyring 242 * - called with the key sem write-locked 243 */ 244 void big_key_revoke(struct key *key) 245 { 246 struct path *path = (struct path *)&key->payload.data[big_key_path]; 247 248 /* clear the quota */ 249 key_payload_reserve(key, 0); 250 if (key_is_instantiated(key) && 251 (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD) 252 vfs_truncate(path, 0); 253 } 254 255 /* 256 * dispose of the data dangling from the corpse of a big_key key 257 */ 258 void big_key_destroy(struct key *key) 259 { 260 size_t datalen = (size_t)key->payload.data[big_key_len]; 261 262 if (datalen > BIG_KEY_FILE_THRESHOLD) { 263 struct path *path = (struct path *)&key->payload.data[big_key_path]; 264 265 path_put(path); 266 path->mnt = NULL; 267 path->dentry = NULL; 268 } 269 kzfree(key->payload.data[big_key_data]); 270 key->payload.data[big_key_data] = NULL; 271 } 272 273 /* 274 * describe the big_key key 275 */ 276 void big_key_describe(const struct key *key, struct seq_file *m) 277 { 278 size_t datalen = (size_t)key->payload.data[big_key_len]; 279 280 seq_puts(m, key->description); 281 282 if (key_is_instantiated(key)) 283 seq_printf(m, ": %zu [%s]", 284 datalen, 285 datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff"); 286 } 287 288 /* 289 * read the key data 290 * - the key's semaphore is read-locked 291 */ 292 long big_key_read(const struct key *key, char __user *buffer, size_t buflen) 293 { 294 size_t datalen = (size_t)key->payload.data[big_key_len]; 295 long ret; 296 297 if (!buffer || buflen < datalen) 298 return datalen; 299 300 if (datalen > BIG_KEY_FILE_THRESHOLD) { 301 struct path *path = (struct path *)&key->payload.data[big_key_path]; 302 struct file *file; 303 u8 *data; 304 u8 *enckey = (u8 *)key->payload.data[big_key_data]; 305 size_t enclen = datalen + ENC_AUTHTAG_SIZE; 306 loff_t pos = 0; 307 308 data = kmalloc(enclen, GFP_KERNEL); 309 if (!data) 310 return -ENOMEM; 311 312 file = dentry_open(path, O_RDONLY, current_cred()); 313 if (IS_ERR(file)) { 314 ret = PTR_ERR(file); 315 goto error; 316 } 317 318 /* read file to kernel and decrypt */ 319 ret = kernel_read(file, data, enclen, &pos); 320 if (ret >= 0 && ret != enclen) { 321 ret = -EIO; 322 goto err_fput; 323 } 324 325 ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey); 326 if (ret) 327 goto err_fput; 328 329 ret = datalen; 330 331 /* copy decrypted data to user */ 332 if (copy_to_user(buffer, data, datalen) != 0) 333 ret = -EFAULT; 334 335 err_fput: 336 fput(file); 337 error: 338 kzfree(data); 339 } else { 340 ret = datalen; 341 if (copy_to_user(buffer, key->payload.data[big_key_data], 342 datalen) != 0) 343 ret = -EFAULT; 344 } 345 346 return ret; 347 } 348 349 /* 350 * Register key type 351 */ 352 static int __init big_key_init(void) 353 { 354 int ret; 355 356 /* init block cipher */ 357 big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC); 358 if (IS_ERR(big_key_aead)) { 359 ret = PTR_ERR(big_key_aead); 360 pr_err("Can't alloc crypto: %d\n", ret); 361 return ret; 362 } 363 ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE); 364 if (ret < 0) { 365 pr_err("Can't set crypto auth tag len: %d\n", ret); 366 goto free_aead; 367 } 368 369 ret = register_key_type(&key_type_big_key); 370 if (ret < 0) { 371 pr_err("Can't register type: %d\n", ret); 372 goto free_aead; 373 } 374 375 return 0; 376 377 free_aead: 378 crypto_free_aead(big_key_aead); 379 return ret; 380 } 381 382 late_initcall(big_key_init); 383