fs/crypto/keyinfo.c

   1 /*
   2  * key management facility for FS encryption support.
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  *
   6  * This contains encryption key functions.
   7  *
   8  * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
   9  */
  10
  11 #include <keys/user-type.h>
  12 #include <linux/scatterlist.h>
  13 #include <linux/ratelimit.h>
  14 #include <crypto/aes.h>
  15 #include <crypto/sha.h>
  16 #include "fscrypt_private.h"
  17
  18 static struct crypto_shash *essiv_hash_tfm;
  19
  20 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  21 {
  22         struct fscrypt_completion_result *ecr = req->data;
  23
  24         if (rc == -EINPROGRESS)
  25                 return;
  26
  27         ecr->res = rc;
  28         complete(&ecr->completion);
  29 }
  30
  31 /**
  32  * derive_key_aes() - Derive a key using AES-128-ECB
  33  * @deriving_key: Encryption key used for derivation.
  34  * @source_key:   Source key to which to apply derivation.
  35  * @derived_raw_key:  Derived raw key.
  36  *
  37  * Return: Zero on success; non-zero otherwise.
  38  */
  39 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  40                                 const struct fscrypt_key *source_key,
  41                                 u8 derived_raw_key[FS_MAX_KEY_SIZE])
  42 {
  43         int res = 0;
  44         struct skcipher_request *req = NULL;
  45         DECLARE_FS_COMPLETION_RESULT(ecr);
  46         struct scatterlist src_sg, dst_sg;
  47         struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
  48
  49         if (IS_ERR(tfm)) {
  50                 res = PTR_ERR(tfm);
  51                 tfm = NULL;
  52                 goto out;
  53         }
  54         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  55         req = skcipher_request_alloc(tfm, GFP_NOFS);
  56         if (!req) {
  57                 res = -ENOMEM;
  58                 goto out;
  59         }
  60         skcipher_request_set_callback(req,
  61                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  62                         derive_crypt_complete, &ecr);
  63         res = crypto_skcipher_setkey(tfm, deriving_key,
  64                                         FS_AES_128_ECB_KEY_SIZE);
  65         if (res < 0)
  66                 goto out;
  67
  68         sg_init_one(&src_sg, source_key->raw, source_key->size);
  69         sg_init_one(&dst_sg, derived_raw_key, source_key->size);
  70         skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size,
  71                                    NULL);
  72         res = crypto_skcipher_encrypt(req);
  73         if (res == -EINPROGRESS || res == -EBUSY) {
  74                 wait_for_completion(&ecr.completion);
  75                 res = ecr.res;
  76         }
  77 out:
  78         skcipher_request_free(req);
  79         crypto_free_skcipher(tfm);
  80         return res;
  81 }
  82
  83 static int validate_user_key(struct fscrypt_info *crypt_info,
  84                         struct fscrypt_context *ctx, u8 *raw_key,
  85                         const char *prefix, int min_keysize)
  86 {
  87         char *description;
  88         struct key *keyring_key;
  89         struct fscrypt_key *master_key;
  90         const struct user_key_payload *ukp;
  91         int res;
  92
  93         description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
  94                                 FS_KEY_DESCRIPTOR_SIZE,
  95                                 ctx->master_key_descriptor);
  96         if (!description)
  97                 return -ENOMEM;
  98
  99         keyring_key = request_key(&key_type_logon, description, NULL);
 100         kfree(description);
 101         if (IS_ERR(keyring_key))
 102                 return PTR_ERR(keyring_key);
 103         down_read(&keyring_key->sem);
 104
 105         if (keyring_key->type != &key_type_logon) {
 106                 printk_once(KERN_WARNING
 107                                 "%s: key type must be logon\n", __func__);
 108                 res = -ENOKEY;
 109                 goto out;
 110         }
 111         ukp = user_key_payload_locked(keyring_key);
 112         if (!ukp) {
 113                 /* key was revoked before we acquired its semaphore */
 114                 res = -EKEYREVOKED;
 115                 goto out;
 116         }
 117         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 118                 res = -EINVAL;
 119                 goto out;
 120         }
 121         master_key = (struct fscrypt_key *)ukp->data;
 122         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 123
 124         if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE
 125             || master_key->size % AES_BLOCK_SIZE != 0) {
 126                 printk_once(KERN_WARNING
 127                                 "%s: key size incorrect: %d\n",
 128                                 __func__, master_key->size);
 129                 res = -ENOKEY;
 130                 goto out;
 131         }
 132         res = derive_key_aes(ctx->nonce, master_key, raw_key);
 133 out:
 134         up_read(&keyring_key->sem);
 135         key_put(keyring_key);
 136         return res;
 137 }
 138
 139 static const struct {
 140         const char *cipher_str;
 141         int keysize;
 142 } available_modes[] = {
 143         [FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)",
 144                                              FS_AES_256_XTS_KEY_SIZE },
 145         [FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))",
 146                                              FS_AES_256_CTS_KEY_SIZE },
 147         [FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)",
 148                                              FS_AES_128_CBC_KEY_SIZE },
 149         [FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))",
 150                                              FS_AES_128_CTS_KEY_SIZE },
 151 };
 152
 153 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
 154                                  const char **cipher_str_ret, int *keysize_ret)
 155 {
 156         u32 mode;
 157
 158         if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
 159                 pr_warn_ratelimited("fscrypt: inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)\n",
 160                                     inode->i_ino,
 161                                     ci->ci_data_mode, ci->ci_filename_mode);
 162                 return -EINVAL;
 163         }
 164
 165         if (S_ISREG(inode->i_mode)) {
 166                 mode = ci->ci_data_mode;
 167         } else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
 168                 mode = ci->ci_filename_mode;
 169         } else {
 170                 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
 171                           inode->i_ino, (inode->i_mode & S_IFMT));
 172                 return -EINVAL;
 173         }
 174
 175         *cipher_str_ret = available_modes[mode].cipher_str;
 176         *keysize_ret = available_modes[mode].keysize;
 177         return 0;
 178 }
 179
 180 static void put_crypt_info(struct fscrypt_info *ci)
 181 {
 182         if (!ci)
 183                 return;
 184
 185         crypto_free_skcipher(ci->ci_ctfm);
 186         crypto_free_cipher(ci->ci_essiv_tfm);
 187         kmem_cache_free(fscrypt_info_cachep, ci);
 188 }
 189
 190 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
 191 {
 192         struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
 193
 194         /* init hash transform on demand */
 195         if (unlikely(!tfm)) {
 196                 struct crypto_shash *prev_tfm;
 197
 198                 tfm = crypto_alloc_shash("sha256", 0, 0);
 199                 if (IS_ERR(tfm)) {
 200                         pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld\n",
 201                                             PTR_ERR(tfm));
 202                         return PTR_ERR(tfm);
 203                 }
 204                 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
 205                 if (prev_tfm) {
 206                         crypto_free_shash(tfm);
 207                         tfm = prev_tfm;
 208                 }
 209         }
 210
 211         {
 212                 SHASH_DESC_ON_STACK(desc, tfm);
 213                 desc->tfm = tfm;
 214                 desc->flags = 0;
 215
 216                 return crypto_shash_digest(desc, key, keysize, salt);
 217         }
 218 }
 219
 220 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
 221                                 int keysize)
 222 {
 223         int err;
 224         struct crypto_cipher *essiv_tfm;
 225         u8 salt[SHA256_DIGEST_SIZE];
 226
 227         essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
 228         if (IS_ERR(essiv_tfm))
 229                 return PTR_ERR(essiv_tfm);
 230
 231         ci->ci_essiv_tfm = essiv_tfm;
 232
 233         err = derive_essiv_salt(raw_key, keysize, salt);
 234         if (err)
 235                 goto out;
 236
 237         /*
 238          * Using SHA256 to derive the salt/key will result in AES-256 being
 239          * used for IV generation. File contents encryption will still use the
 240          * configured keysize (AES-128) nevertheless.
 241          */
 242         err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
 243         if (err)
 244                 goto out;
 245
 246 out:
 247         memzero_explicit(salt, sizeof(salt));
 248         return err;
 249 }
 250
 251 void __exit fscrypt_essiv_cleanup(void)
 252 {
 253         crypto_free_shash(essiv_hash_tfm);
 254 }
 255
 256 int fscrypt_get_encryption_info(struct inode *inode)
 257 {
 258         struct fscrypt_info *crypt_info;
 259         struct fscrypt_context ctx;
 260         struct crypto_skcipher *ctfm;
 261         const char *cipher_str;
 262         int keysize;
 263         u8 *raw_key = NULL;
 264         int res;
 265
 266         if (inode->i_crypt_info)
 267                 return 0;
 268
 269         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 270         if (res)
 271                 return res;
 272
 273         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 274         if (res < 0) {
 275                 if (!fscrypt_dummy_context_enabled(inode) ||
 276                     inode->i_sb->s_cop->is_encrypted(inode))
 277                         return res;
 278                 /* Fake up a context for an unencrypted directory */
 279                 memset(&ctx, 0, sizeof(ctx));
 280                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 281                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 282                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 283                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 284         } else if (res != sizeof(ctx)) {
 285                 return -EINVAL;
 286         }
 287
 288         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 289                 return -EINVAL;
 290
 291         if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
 292                 return -EINVAL;
 293
 294         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 295         if (!crypt_info)
 296                 return -ENOMEM;
 297
 298         crypt_info->ci_flags = ctx.flags;
 299         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 300         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 301         crypt_info->ci_ctfm = NULL;
 302         crypt_info->ci_essiv_tfm = NULL;
 303         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 304                                 sizeof(crypt_info->ci_master_key));
 305
 306         res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
 307         if (res)
 308                 goto out;
 309
 310         /*
 311          * This cannot be a stack buffer because it is passed to the scatterlist
 312          * crypto API as part of key derivation.
 313          */
 314         res = -ENOMEM;
 315         raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
 316         if (!raw_key)
 317                 goto out;
 318
 319         res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX,
 320                                 keysize);
 321         if (res && inode->i_sb->s_cop->key_prefix) {
 322                 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
 323                                              inode->i_sb->s_cop->key_prefix,
 324                                              keysize);
 325                 if (res2) {
 326                         if (res2 == -ENOKEY)
 327                                 res = -ENOKEY;
 328                         goto out;
 329                 }
 330         } else if (res) {
 331                 goto out;
 332         }
 333         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 334         if (!ctfm || IS_ERR(ctfm)) {
 335                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 336                 pr_debug("%s: error %d (inode %lu) allocating crypto tfm\n",
 337                          __func__, res, inode->i_ino);
 338                 goto out;
 339         }
 340         crypt_info->ci_ctfm = ctfm;
 341         crypto_skcipher_clear_flags(ctfm, ~0);
 342         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 343         /*
 344          * if the provided key is longer than keysize, we use the first
 345          * keysize bytes of the derived key only
 346          */
 347         res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
 348         if (res)
 349                 goto out;
 350
 351         if (S_ISREG(inode->i_mode) &&
 352             crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) {
 353                 res = init_essiv_generator(crypt_info, raw_key, keysize);
 354                 if (res) {
 355                         pr_debug("%s: error %d (inode %lu) allocating essiv tfm\n",
 356                                  __func__, res, inode->i_ino);
 357                         goto out;
 358                 }
 359         }
 360         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
 361                 crypt_info = NULL;
 362 out:
 363         if (res == -ENOKEY)
 364                 res = 0;
 365         put_crypt_info(crypt_info);
 366         kzfree(raw_key);
 367         return res;
 368 }
 369 EXPORT_SYMBOL(fscrypt_get_encryption_info);
 370
 371 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 372 {
 373         struct fscrypt_info *prev;
 374
 375         if (ci == NULL)
 376                 ci = ACCESS_ONCE(inode->i_crypt_info);
 377         if (ci == NULL)
 378                 return;
 379
 380         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 381         if (prev != ci)
 382                 return;
 383
 384         put_crypt_info(ci);
 385 }
 386 EXPORT_SYMBOL(fscrypt_put_encryption_info);