security/keys/big_key.c

   1 /* Large capacity key type
   2  *
   3  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/init.h>
  13 #include <linux/seq_file.h>
  14 #include <linux/file.h>
  15 #include <linux/shmem_fs.h>
  16 #include <linux/err.h>
  17 #include <linux/scatterlist.h>
  18 #include <keys/user-type.h>
  19 #include <keys/big_key-type.h>
  20 #include <crypto/rng.h>
  21
  22 /*
  23  * Layout of key payload words.
  24  */
  25 enum {
  26         big_key_data,
  27         big_key_path,
  28         big_key_path_2nd_part,
  29         big_key_len,
  30 };
  31
  32 /*
  33  * Crypto operation with big_key data
  34  */
  35 enum big_key_op {
  36         BIG_KEY_ENC,
  37         BIG_KEY_DEC,
  38 };
  39
  40 /*
  41  * If the data is under this limit, there's no point creating a shm file to
  42  * hold it as the permanently resident metadata for the shmem fs will be at
  43  * least as large as the data.
  44  */
  45 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  46
  47 /*
  48  * Key size for big_key data encryption
  49  */
  50 #define ENC_KEY_SIZE    16
  51
  52 /*
  53  * big_key defined keys take an arbitrary string as the description and an
  54  * arbitrary blob of data as the payload
  55  */
  56 struct key_type key_type_big_key = {
  57         .name                   = "big_key",
  58         .preparse               = big_key_preparse,
  59         .free_preparse          = big_key_free_preparse,
  60         .instantiate            = generic_key_instantiate,
  61         .revoke                 = big_key_revoke,
  62         .destroy                = big_key_destroy,
  63         .describe               = big_key_describe,
  64         .read                   = big_key_read,
  65 };
  66
  67 /*
  68  * Crypto names for big_key data encryption
  69  */
  70 static const char big_key_rng_name[] = "stdrng";
  71 static const char big_key_alg_name[] = "ecb(aes)";
  72
  73 /*
  74  * Crypto algorithms for big_key data encryption
  75  */
  76 static struct crypto_rng *big_key_rng;
  77 static struct crypto_blkcipher *big_key_blkcipher;
  78
  79 /*
  80  * Generate random key to encrypt big_key data
  81  */
  82 static inline int big_key_gen_enckey(u8 *key)
  83 {
  84         return crypto_rng_get_bytes(big_key_rng, key, ENC_KEY_SIZE);
  85 }
  86
  87 /*
  88  * Encrypt/decrypt big_key data
  89  */
  90 static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
  91 {
  92         int ret = -EINVAL;
  93         struct scatterlist sgio;
  94         struct blkcipher_desc desc;
  95
  96         if (crypto_blkcipher_setkey(big_key_blkcipher, key, ENC_KEY_SIZE)) {
  97                 ret = -EAGAIN;
  98                 goto error;
  99         }
 100
 101         desc.flags = 0;
 102         desc.tfm = big_key_blkcipher;
 103
 104         sg_init_one(&sgio, data, datalen);
 105
 106         if (op == BIG_KEY_ENC)
 107                 ret = crypto_blkcipher_encrypt(&desc, &sgio, &sgio, datalen);
 108         else
 109                 ret = crypto_blkcipher_decrypt(&desc, &sgio, &sgio, datalen);
 110
 111 error:
 112         return ret;
 113 }
 114
 115 /*
 116  * Preparse a big key
 117  */
 118 int big_key_preparse(struct key_preparsed_payload *prep)
 119 {
 120         struct path *path = (struct path *)&prep->payload.data[big_key_path];
 121         struct file *file;
 122         u8 *enckey;
 123         u8 *data = NULL;
 124         ssize_t written;
 125         size_t datalen = prep->datalen;
 126         int ret;
 127
 128         ret = -EINVAL;
 129         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
 130                 goto error;
 131
 132         /* Set an arbitrary quota */
 133         prep->quotalen = 16;
 134
 135         prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
 136
 137         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 138                 /* Create a shmem file to store the data in.  This will permit the data
 139                  * to be swapped out if needed.
 140                  *
 141                  * File content is stored encrypted with randomly generated key.
 142                  */
 143                 size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));
 144
 145                 /* prepare aligned data to encrypt */
 146                 data = kmalloc(enclen, GFP_KERNEL);
 147                 if (!data)
 148                         return -ENOMEM;
 149
 150                 memcpy(data, prep->data, datalen);
 151                 memset(data + datalen, 0x00, enclen - datalen);
 152
 153                 /* generate random key */
 154                 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
 155                 if (!enckey) {
 156                         ret = -ENOMEM;
 157                         goto error;
 158                 }
 159
 160                 ret = big_key_gen_enckey(enckey);
 161                 if (ret)
 162                         goto err_enckey;
 163
 164                 /* encrypt aligned data */
 165                 ret = big_key_crypt(BIG_KEY_ENC, data, enclen, enckey);
 166                 if (ret)
 167                         goto err_enckey;
 168
 169                 /* save aligned data to file */
 170                 file = shmem_kernel_file_setup("", enclen, 0);
 171                 if (IS_ERR(file)) {
 172                         ret = PTR_ERR(file);
 173                         goto err_enckey;
 174                 }
 175
 176                 written = kernel_write(file, data, enclen, 0);
 177                 if (written != enclen) {
 178                         ret = written;
 179                         if (written >= 0)
 180                                 ret = -ENOMEM;
 181                         goto err_fput;
 182                 }
 183
 184                 /* Pin the mount and dentry to the key so that we can open it again
 185                  * later
 186                  */
 187                 prep->payload.data[big_key_data] = enckey;
 188                 *path = file->f_path;
 189                 path_get(path);
 190                 fput(file);
 191                 kfree(data);
 192         } else {
 193                 /* Just store the data in a buffer */
 194                 void *data = kmalloc(datalen, GFP_KERNEL);
 195
 196                 if (!data)
 197                         return -ENOMEM;
 198
 199                 prep->payload.data[big_key_data] = data;
 200                 memcpy(data, prep->data, prep->datalen);
 201         }
 202         return 0;
 203
 204 err_fput:
 205         fput(file);
 206 err_enckey:
 207         kfree(enckey);
 208 error:
 209         kfree(data);
 210         return ret;
 211 }
 212
 213 /*
 214  * Clear preparsement.
 215  */
 216 void big_key_free_preparse(struct key_preparsed_payload *prep)
 217 {
 218         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 219                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
 220
 221                 path_put(path);
 222         }
 223         kfree(prep->payload.data[big_key_data]);
 224 }
 225
 226 /*
 227  * dispose of the links from a revoked keyring
 228  * - called with the key sem write-locked
 229  */
 230 void big_key_revoke(struct key *key)
 231 {
 232         struct path *path = (struct path *)&key->payload.data[big_key_path];
 233
 234         /* clear the quota */
 235         key_payload_reserve(key, 0);
 236         if (key_is_instantiated(key) &&
 237             (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
 238                 vfs_truncate(path, 0);
 239 }
 240
 241 /*
 242  * dispose of the data dangling from the corpse of a big_key key
 243  */
 244 void big_key_destroy(struct key *key)
 245 {
 246         size_t datalen = (size_t)key->payload.data[big_key_len];
 247
 248         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 249                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 250
 251                 path_put(path);
 252                 path->mnt = NULL;
 253                 path->dentry = NULL;
 254         }
 255         kfree(key->payload.data[big_key_data]);
 256         key->payload.data[big_key_data] = NULL;
 257 }
 258
 259 /*
 260  * describe the big_key key
 261  */
 262 void big_key_describe(const struct key *key, struct seq_file *m)
 263 {
 264         size_t datalen = (size_t)key->payload.data[big_key_len];
 265
 266         seq_puts(m, key->description);
 267
 268         if (key_is_instantiated(key))
 269                 seq_printf(m, ": %zu [%s]",
 270                            datalen,
 271                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 272 }
 273
 274 /*
 275  * read the key data
 276  * - the key's semaphore is read-locked
 277  */
 278 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 279 {
 280         size_t datalen = (size_t)key->payload.data[big_key_len];
 281         long ret;
 282
 283         if (!buffer || buflen < datalen)
 284                 return datalen;
 285
 286         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 287                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 288                 struct file *file;
 289                 u8 *data;
 290                 u8 *enckey = (u8 *)key->payload.data[big_key_data];
 291                 size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));
 292
 293                 data = kmalloc(enclen, GFP_KERNEL);
 294                 if (!data)
 295                         return -ENOMEM;
 296
 297                 file = dentry_open(path, O_RDONLY, current_cred());
 298                 if (IS_ERR(file)) {
 299                         ret = PTR_ERR(file);
 300                         goto error;
 301                 }
 302
 303                 /* read file to kernel and decrypt */
 304                 ret = kernel_read(file, 0, data, enclen);
 305                 if (ret >= 0 && ret != enclen) {
 306                         ret = -EIO;
 307                         goto err_fput;
 308                 }
 309
 310                 ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
 311                 if (ret)
 312                         goto err_fput;
 313
 314                 ret = datalen;
 315
 316                 /* copy decrypted data to user */
 317                 if (copy_to_user(buffer, data, datalen) != 0)
 318                         ret = -EFAULT;
 319
 320 err_fput:
 321                 fput(file);
 322 error:
 323                 kfree(data);
 324         } else {
 325                 ret = datalen;
 326                 if (copy_to_user(buffer, key->payload.data[big_key_data],
 327                                  datalen) != 0)
 328                         ret = -EFAULT;
 329         }
 330
 331         return ret;
 332 }
 333
 334 /*
 335  * Register key type
 336  */
 337 static int __init big_key_init(void)
 338 {
 339         return register_key_type(&key_type_big_key);
 340 }
 341
 342 /*
 343  * Initialize big_key crypto and RNG algorithms
 344  */
 345 static int __init big_key_crypto_init(void)
 346 {
 347         int ret = -EINVAL;
 348
 349         /* init RNG */
 350         big_key_rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
 351         if (IS_ERR(big_key_rng)) {
 352                 big_key_rng = NULL;
 353                 return -EFAULT;
 354         }
 355
 356         /* seed RNG */
 357         ret = crypto_rng_reset(big_key_rng, NULL, crypto_rng_seedsize(big_key_rng));
 358         if (ret)
 359                 goto error;
 360
 361         /* init block cipher */
 362         big_key_blkcipher = crypto_alloc_blkcipher(big_key_alg_name, 0, 0);
 363         if (IS_ERR(big_key_blkcipher)) {
 364                 big_key_blkcipher = NULL;
 365                 ret = -EFAULT;
 366                 goto error;
 367         }
 368
 369         return 0;
 370
 371 error:
 372         crypto_free_rng(big_key_rng);
 373         big_key_rng = NULL;
 374         return ret;
 375 }
 376
 377 device_initcall(big_key_init);
 378 late_initcall(big_key_crypto_init);