fs/crypto/keyinfo.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * key management facility for FS encryption support.
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  *
   7  * This contains encryption key functions.
   8  *
   9  * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
  10  */
  11
  12 #include <keys/user-type.h>
  13 #include <linux/scatterlist.h>
  14 #include <linux/ratelimit.h>
  15 #include <crypto/aes.h>
  16 #include <crypto/sha.h>
  17 #include "fscrypt_private.h"
  18
  19 static struct crypto_shash *essiv_hash_tfm;
  20
  21 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  22 {
  23         struct fscrypt_completion_result *ecr = req->data;
  24
  25         if (rc == -EINPROGRESS)
  26                 return;
  27
  28         ecr->res = rc;
  29         complete(&ecr->completion);
  30 }
  31
  32 /**
  33  * derive_key_aes() - Derive a key using AES-128-ECB
  34  * @deriving_key: Encryption key used for derivation.
  35  * @source_key:   Source key to which to apply derivation.
  36  * @derived_raw_key:  Derived raw key.
  37  *
  38  * Return: Zero on success; non-zero otherwise.
  39  */
  40 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  41                                 const struct fscrypt_key *source_key,
  42                                 u8 derived_raw_key[FS_MAX_KEY_SIZE])
  43 {
  44         int res = 0;
  45         struct skcipher_request *req = NULL;
  46         DECLARE_FS_COMPLETION_RESULT(ecr);
  47         struct scatterlist src_sg, dst_sg;
  48         struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
  49
  50         if (IS_ERR(tfm)) {
  51                 res = PTR_ERR(tfm);
  52                 tfm = NULL;
  53                 goto out;
  54         }
  55         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  56         req = skcipher_request_alloc(tfm, GFP_NOFS);
  57         if (!req) {
  58                 res = -ENOMEM;
  59                 goto out;
  60         }
  61         skcipher_request_set_callback(req,
  62                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  63                         derive_crypt_complete, &ecr);
  64         res = crypto_skcipher_setkey(tfm, deriving_key,
  65                                         FS_AES_128_ECB_KEY_SIZE);
  66         if (res < 0)
  67                 goto out;
  68
  69         sg_init_one(&src_sg, source_key->raw, source_key->size);
  70         sg_init_one(&dst_sg, derived_raw_key, source_key->size);
  71         skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size,
  72                                    NULL);
  73         res = crypto_skcipher_encrypt(req);
  74         if (res == -EINPROGRESS || res == -EBUSY) {
  75                 wait_for_completion(&ecr.completion);
  76                 res = ecr.res;
  77         }
  78 out:
  79         skcipher_request_free(req);
  80         crypto_free_skcipher(tfm);
  81         return res;
  82 }
  83
  84 static int validate_user_key(struct fscrypt_info *crypt_info,
  85                         struct fscrypt_context *ctx, u8 *raw_key,
  86                         const char *prefix, int min_keysize)
  87 {
  88         char *description;
  89         struct key *keyring_key;
  90         struct fscrypt_key *master_key;
  91         const struct user_key_payload *ukp;
  92         int res;
  93
  94         description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
  95                                 FS_KEY_DESCRIPTOR_SIZE,
  96                                 ctx->master_key_descriptor);
  97         if (!description)
  98                 return -ENOMEM;
  99
 100         keyring_key = request_key(&key_type_logon, description, NULL);
 101         kfree(description);
 102         if (IS_ERR(keyring_key))
 103                 return PTR_ERR(keyring_key);
 104         down_read(&keyring_key->sem);
 105
 106         if (keyring_key->type != &key_type_logon) {
 107                 printk_once(KERN_WARNING
 108                                 "%s: key type must be logon\n", __func__);
 109                 res = -ENOKEY;
 110                 goto out;
 111         }
 112         ukp = user_key_payload_locked(keyring_key);
 113         if (!ukp) {
 114                 /* key was revoked before we acquired its semaphore */
 115                 res = -EKEYREVOKED;
 116                 goto out;
 117         }
 118         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 119                 res = -EINVAL;
 120                 goto out;
 121         }
 122         master_key = (struct fscrypt_key *)ukp->data;
 123         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 124
 125         if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE
 126             || master_key->size % AES_BLOCK_SIZE != 0) {
 127                 printk_once(KERN_WARNING
 128                                 "%s: key size incorrect: %d\n",
 129                                 __func__, master_key->size);
 130                 res = -ENOKEY;
 131                 goto out;
 132         }
 133         res = derive_key_aes(ctx->nonce, master_key, raw_key);
 134 out:
 135         up_read(&keyring_key->sem);
 136         key_put(keyring_key);
 137         return res;
 138 }
 139
 140 static const struct {
 141         const char *cipher_str;
 142         int keysize;
 143 } available_modes[] = {
 144         [FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)",
 145                                              FS_AES_256_XTS_KEY_SIZE },
 146         [FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))",
 147                                              FS_AES_256_CTS_KEY_SIZE },
 148         [FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)",
 149                                              FS_AES_128_CBC_KEY_SIZE },
 150         [FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))",
 151                                              FS_AES_128_CTS_KEY_SIZE },
 152 };
 153
 154 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
 155                                  const char **cipher_str_ret, int *keysize_ret)
 156 {
 157         u32 mode;
 158
 159         if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
 160                 pr_warn_ratelimited("fscrypt: inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)\n",
 161                                     inode->i_ino,
 162                                     ci->ci_data_mode, ci->ci_filename_mode);
 163                 return -EINVAL;
 164         }
 165
 166         if (S_ISREG(inode->i_mode)) {
 167                 mode = ci->ci_data_mode;
 168         } else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
 169                 mode = ci->ci_filename_mode;
 170         } else {
 171                 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
 172                           inode->i_ino, (inode->i_mode & S_IFMT));
 173                 return -EINVAL;
 174         }
 175
 176         *cipher_str_ret = available_modes[mode].cipher_str;
 177         *keysize_ret = available_modes[mode].keysize;
 178         return 0;
 179 }
 180
 181 static void put_crypt_info(struct fscrypt_info *ci)
 182 {
 183         if (!ci)
 184                 return;
 185
 186         crypto_free_skcipher(ci->ci_ctfm);
 187         crypto_free_cipher(ci->ci_essiv_tfm);
 188         kmem_cache_free(fscrypt_info_cachep, ci);
 189 }
 190
 191 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
 192 {
 193         struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
 194
 195         /* init hash transform on demand */
 196         if (unlikely(!tfm)) {
 197                 struct crypto_shash *prev_tfm;
 198
 199                 tfm = crypto_alloc_shash("sha256", 0, 0);
 200                 if (IS_ERR(tfm)) {
 201                         pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld\n",
 202                                             PTR_ERR(tfm));
 203                         return PTR_ERR(tfm);
 204                 }
 205                 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
 206                 if (prev_tfm) {
 207                         crypto_free_shash(tfm);
 208                         tfm = prev_tfm;
 209                 }
 210         }
 211
 212         {
 213                 SHASH_DESC_ON_STACK(desc, tfm);
 214                 desc->tfm = tfm;
 215                 desc->flags = 0;
 216
 217                 return crypto_shash_digest(desc, key, keysize, salt);
 218         }
 219 }
 220
 221 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
 222                                 int keysize)
 223 {
 224         int err;
 225         struct crypto_cipher *essiv_tfm;
 226         u8 salt[SHA256_DIGEST_SIZE];
 227
 228         essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
 229         if (IS_ERR(essiv_tfm))
 230                 return PTR_ERR(essiv_tfm);
 231
 232         ci->ci_essiv_tfm = essiv_tfm;
 233
 234         err = derive_essiv_salt(raw_key, keysize, salt);
 235         if (err)
 236                 goto out;
 237
 238         /*
 239          * Using SHA256 to derive the salt/key will result in AES-256 being
 240          * used for IV generation. File contents encryption will still use the
 241          * configured keysize (AES-128) nevertheless.
 242          */
 243         err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
 244         if (err)
 245                 goto out;
 246
 247 out:
 248         memzero_explicit(salt, sizeof(salt));
 249         return err;
 250 }
 251
 252 void __exit fscrypt_essiv_cleanup(void)
 253 {
 254         crypto_free_shash(essiv_hash_tfm);
 255 }
 256
 257 int fscrypt_get_encryption_info(struct inode *inode)
 258 {
 259         struct fscrypt_info *crypt_info;
 260         struct fscrypt_context ctx;
 261         struct crypto_skcipher *ctfm;
 262         const char *cipher_str;
 263         int keysize;
 264         u8 *raw_key = NULL;
 265         int res;
 266
 267         if (inode->i_crypt_info)
 268                 return 0;
 269
 270         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 271         if (res)
 272                 return res;
 273
 274         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 275         if (res < 0) {
 276                 if (!fscrypt_dummy_context_enabled(inode) ||
 277                     inode->i_sb->s_cop->is_encrypted(inode))
 278                         return res;
 279                 /* Fake up a context for an unencrypted directory */
 280                 memset(&ctx, 0, sizeof(ctx));
 281                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 282                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 283                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 284                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 285         } else if (res != sizeof(ctx)) {
 286                 return -EINVAL;
 287         }
 288
 289         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 290                 return -EINVAL;
 291
 292         if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
 293                 return -EINVAL;
 294
 295         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 296         if (!crypt_info)
 297                 return -ENOMEM;
 298
 299         crypt_info->ci_flags = ctx.flags;
 300         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 301         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 302         crypt_info->ci_ctfm = NULL;
 303         crypt_info->ci_essiv_tfm = NULL;
 304         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 305                                 sizeof(crypt_info->ci_master_key));
 306
 307         res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
 308         if (res)
 309                 goto out;
 310
 311         /*
 312          * This cannot be a stack buffer because it is passed to the scatterlist
 313          * crypto API as part of key derivation.
 314          */
 315         res = -ENOMEM;
 316         raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
 317         if (!raw_key)
 318                 goto out;
 319
 320         res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX,
 321                                 keysize);
 322         if (res && inode->i_sb->s_cop->key_prefix) {
 323                 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
 324                                              inode->i_sb->s_cop->key_prefix,
 325                                              keysize);
 326                 if (res2) {
 327                         if (res2 == -ENOKEY)
 328                                 res = -ENOKEY;
 329                         goto out;
 330                 }
 331         } else if (res) {
 332                 goto out;
 333         }
 334         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 335         if (!ctfm || IS_ERR(ctfm)) {
 336                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 337                 pr_debug("%s: error %d (inode %lu) allocating crypto tfm\n",
 338                          __func__, res, inode->i_ino);
 339                 goto out;
 340         }
 341         crypt_info->ci_ctfm = ctfm;
 342         crypto_skcipher_clear_flags(ctfm, ~0);
 343         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 344         /*
 345          * if the provided key is longer than keysize, we use the first
 346          * keysize bytes of the derived key only
 347          */
 348         res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
 349         if (res)
 350                 goto out;
 351
 352         if (S_ISREG(inode->i_mode) &&
 353             crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) {
 354                 res = init_essiv_generator(crypt_info, raw_key, keysize);
 355                 if (res) {
 356                         pr_debug("%s: error %d (inode %lu) allocating essiv tfm\n",
 357                                  __func__, res, inode->i_ino);
 358                         goto out;
 359                 }
 360         }
 361         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
 362                 crypt_info = NULL;
 363 out:
 364         if (res == -ENOKEY)
 365                 res = 0;
 366         put_crypt_info(crypt_info);
 367         kzfree(raw_key);
 368         return res;
 369 }
 370 EXPORT_SYMBOL(fscrypt_get_encryption_info);
 371
 372 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 373 {
 374         struct fscrypt_info *prev;
 375
 376         if (ci == NULL)
 377                 ci = ACCESS_ONCE(inode->i_crypt_info);
 378         if (ci == NULL)
 379                 return;
 380
 381         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 382         if (prev != ci)
 383                 return;
 384
 385         put_crypt_info(ci);
 386 }
 387 EXPORT_SYMBOL(fscrypt_put_encryption_info);