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 "fscrypt_private.h"
  14
  15 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  16 {
  17         struct fscrypt_completion_result *ecr = req->data;
  18
  19         if (rc == -EINPROGRESS)
  20                 return;
  21
  22         ecr->res = rc;
  23         complete(&ecr->completion);
  24 }
  25
  26 /**
  27  * derive_key_aes() - Derive a key using AES-128-ECB
  28  * @deriving_key: Encryption key used for derivation.
  29  * @source_key:   Source key to which to apply derivation.
  30  * @derived_key:  Derived key.
  31  *
  32  * Return: Zero on success; non-zero otherwise.
  33  */
  34 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  35                                 u8 source_key[FS_AES_256_XTS_KEY_SIZE],
  36                                 u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
  37 {
  38         int res = 0;
  39         struct skcipher_request *req = NULL;
  40         DECLARE_FS_COMPLETION_RESULT(ecr);
  41         struct scatterlist src_sg, dst_sg;
  42         struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
  43
  44         if (IS_ERR(tfm)) {
  45                 res = PTR_ERR(tfm);
  46                 tfm = NULL;
  47                 goto out;
  48         }
  49         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  50         req = skcipher_request_alloc(tfm, GFP_NOFS);
  51         if (!req) {
  52                 res = -ENOMEM;
  53                 goto out;
  54         }
  55         skcipher_request_set_callback(req,
  56                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  57                         derive_crypt_complete, &ecr);
  58         res = crypto_skcipher_setkey(tfm, deriving_key,
  59                                         FS_AES_128_ECB_KEY_SIZE);
  60         if (res < 0)
  61                 goto out;
  62
  63         sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
  64         sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
  65         skcipher_request_set_crypt(req, &src_sg, &dst_sg,
  66                                         FS_AES_256_XTS_KEY_SIZE, NULL);
  67         res = crypto_skcipher_encrypt(req);
  68         if (res == -EINPROGRESS || res == -EBUSY) {
  69                 wait_for_completion(&ecr.completion);
  70                 res = ecr.res;
  71         }
  72 out:
  73         skcipher_request_free(req);
  74         crypto_free_skcipher(tfm);
  75         return res;
  76 }
  77
  78 static int validate_user_key(struct fscrypt_info *crypt_info,
  79                         struct fscrypt_context *ctx, u8 *raw_key,
  80                         u8 *prefix, int prefix_size)
  81 {
  82         u8 *full_key_descriptor;
  83         struct key *keyring_key;
  84         struct fscrypt_key *master_key;
  85         const struct user_key_payload *ukp;
  86         int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
  87         int res;
  88
  89         full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
  90         if (!full_key_descriptor)
  91                 return -ENOMEM;
  92
  93         memcpy(full_key_descriptor, prefix, prefix_size);
  94         sprintf(full_key_descriptor + prefix_size,
  95                         "%*phN", FS_KEY_DESCRIPTOR_SIZE,
  96                         ctx->master_key_descriptor);
  97         full_key_descriptor[full_key_len - 1] = '\0';
  98         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
  99         kfree(full_key_descriptor);
 100         if (IS_ERR(keyring_key))
 101                 return PTR_ERR(keyring_key);
 102
 103         if (keyring_key->type != &key_type_logon) {
 104                 printk_once(KERN_WARNING
 105                                 "%s: key type must be logon\n", __func__);
 106                 res = -ENOKEY;
 107                 goto out;
 108         }
 109         down_read(&keyring_key->sem);
 110         ukp = user_key_payload(keyring_key);
 111         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 112                 res = -EINVAL;
 113                 up_read(&keyring_key->sem);
 114                 goto out;
 115         }
 116         master_key = (struct fscrypt_key *)ukp->data;
 117         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 118
 119         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 120                 printk_once(KERN_WARNING
 121                                 "%s: key size incorrect: %d\n",
 122                                 __func__, master_key->size);
 123                 res = -ENOKEY;
 124                 up_read(&keyring_key->sem);
 125                 goto out;
 126         }
 127         res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
 128         up_read(&keyring_key->sem);
 129         if (res)
 130                 goto out;
 131
 132         crypt_info->ci_keyring_key = keyring_key;
 133         return 0;
 134 out:
 135         key_put(keyring_key);
 136         return res;
 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         if (S_ISREG(inode->i_mode)) {
 143                 if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
 144                         *cipher_str_ret = "xts(aes)";
 145                         *keysize_ret = FS_AES_256_XTS_KEY_SIZE;
 146                         return 0;
 147                 }
 148                 pr_warn_once("fscrypto: unsupported contents encryption mode "
 149                              "%d for inode %lu\n",
 150                              ci->ci_data_mode, inode->i_ino);
 151                 return -ENOKEY;
 152         }
 153
 154         if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
 155                 if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
 156                         *cipher_str_ret = "cts(cbc(aes))";
 157                         *keysize_ret = FS_AES_256_CTS_KEY_SIZE;
 158                         return 0;
 159                 }
 160                 pr_warn_once("fscrypto: unsupported filenames encryption mode "
 161                              "%d for inode %lu\n",
 162                              ci->ci_filename_mode, inode->i_ino);
 163                 return -ENOKEY;
 164         }
 165
 166         pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
 167                      (inode->i_mode & S_IFMT), inode->i_ino);
 168         return -ENOKEY;
 169 }
 170
 171 static void put_crypt_info(struct fscrypt_info *ci)
 172 {
 173         if (!ci)
 174                 return;
 175
 176         key_put(ci->ci_keyring_key);
 177         crypto_free_skcipher(ci->ci_ctfm);
 178         kmem_cache_free(fscrypt_info_cachep, ci);
 179 }
 180
 181 int fscrypt_get_crypt_info(struct inode *inode)
 182 {
 183         struct fscrypt_info *crypt_info;
 184         struct fscrypt_context ctx;
 185         struct crypto_skcipher *ctfm;
 186         const char *cipher_str;
 187         int keysize;
 188         u8 *raw_key = NULL;
 189         int res;
 190
 191         res = fscrypt_initialize();
 192         if (res)
 193                 return res;
 194
 195         if (!inode->i_sb->s_cop->get_context)
 196                 return -EOPNOTSUPP;
 197 retry:
 198         crypt_info = ACCESS_ONCE(inode->i_crypt_info);
 199         if (crypt_info) {
 200                 if (!crypt_info->ci_keyring_key ||
 201                                 key_validate(crypt_info->ci_keyring_key) == 0)
 202                         return 0;
 203                 fscrypt_put_encryption_info(inode, crypt_info);
 204                 goto retry;
 205         }
 206
 207         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 208         if (res < 0) {
 209                 if (!fscrypt_dummy_context_enabled(inode))
 210                         return res;
 211                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 212                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 213                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 214                 ctx.flags = 0;
 215         } else if (res != sizeof(ctx)) {
 216                 return -EINVAL;
 217         }
 218
 219         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 220                 return -EINVAL;
 221
 222         if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
 223                 return -EINVAL;
 224
 225         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 226         if (!crypt_info)
 227                 return -ENOMEM;
 228
 229         crypt_info->ci_flags = ctx.flags;
 230         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 231         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 232         crypt_info->ci_ctfm = NULL;
 233         crypt_info->ci_keyring_key = NULL;
 234         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 235                                 sizeof(crypt_info->ci_master_key));
 236
 237         res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
 238         if (res)
 239                 goto out;
 240
 241         /*
 242          * This cannot be a stack buffer because it is passed to the scatterlist
 243          * crypto API as part of key derivation.
 244          */
 245         res = -ENOMEM;
 246         raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
 247         if (!raw_key)
 248                 goto out;
 249
 250         if (fscrypt_dummy_context_enabled(inode)) {
 251                 memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
 252                 goto got_key;
 253         }
 254
 255         res = validate_user_key(crypt_info, &ctx, raw_key,
 256                         FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
 257         if (res && inode->i_sb->s_cop->key_prefix) {
 258                 u8 *prefix = NULL;
 259                 int prefix_size, res2;
 260
 261                 prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
 262                 res2 = validate_user_key(crypt_info, &ctx, raw_key,
 263                                                         prefix, prefix_size);
 264                 if (res2) {
 265                         if (res2 == -ENOKEY)
 266                                 res = -ENOKEY;
 267                         goto out;
 268                 }
 269         } else if (res) {
 270                 goto out;
 271         }
 272 got_key:
 273         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 274         if (!ctfm || IS_ERR(ctfm)) {
 275                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 276                 printk(KERN_DEBUG
 277                        "%s: error %d (inode %u) allocating crypto tfm\n",
 278                        __func__, res, (unsigned) inode->i_ino);
 279                 goto out;
 280         }
 281         crypt_info->ci_ctfm = ctfm;
 282         crypto_skcipher_clear_flags(ctfm, ~0);
 283         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 284         res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
 285         if (res)
 286                 goto out;
 287
 288         kzfree(raw_key);
 289         raw_key = NULL;
 290         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
 291                 put_crypt_info(crypt_info);
 292                 goto retry;
 293         }
 294         return 0;
 295
 296 out:
 297         if (res == -ENOKEY)
 298                 res = 0;
 299         put_crypt_info(crypt_info);
 300         kzfree(raw_key);
 301         return res;
 302 }
 303
 304 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 305 {
 306         struct fscrypt_info *prev;
 307
 308         if (ci == NULL)
 309                 ci = ACCESS_ONCE(inode->i_crypt_info);
 310         if (ci == NULL)
 311                 return;
 312
 313         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 314         if (prev != ci)
 315                 return;
 316
 317         put_crypt_info(ci);
 318 }
 319 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 320
 321 int fscrypt_get_encryption_info(struct inode *inode)
 322 {
 323         struct fscrypt_info *ci = inode->i_crypt_info;
 324
 325         if (!ci ||
 326                 (ci->ci_keyring_key &&
 327                  (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 328                                                (1 << KEY_FLAG_REVOKED) |
 329                                                (1 << KEY_FLAG_DEAD)))))
 330                 return fscrypt_get_crypt_info(inode);
 331         return 0;
 332 }
 333 EXPORT_SYMBOL(fscrypt_get_encryption_info);