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