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