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                         const char *prefix)
  81 {
  82         char *description;
  83         struct key *keyring_key;
  84         struct fscrypt_key *master_key;
  85         const struct user_key_payload *ukp;
  86         int res;
  87
  88         description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
  89                                 FS_KEY_DESCRIPTOR_SIZE,
  90                                 ctx->master_key_descriptor);
  91         if (!description)
  92                 return -ENOMEM;
  93
  94         keyring_key = request_key(&key_type_logon, description, NULL);
  95         kfree(description);
  96         if (IS_ERR(keyring_key))
  97                 return PTR_ERR(keyring_key);
  98
  99         if (keyring_key->type != &key_type_logon) {
 100                 printk_once(KERN_WARNING
 101                                 "%s: key type must be logon\n", __func__);
 102                 res = -ENOKEY;
 103                 goto out;
 104         }
 105         down_read(&keyring_key->sem);
 106         ukp = user_key_payload(keyring_key);
 107         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 108                 res = -EINVAL;
 109                 up_read(&keyring_key->sem);
 110                 goto out;
 111         }
 112         master_key = (struct fscrypt_key *)ukp->data;
 113         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 114
 115         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 116                 printk_once(KERN_WARNING
 117                                 "%s: key size incorrect: %d\n",
 118                                 __func__, master_key->size);
 119                 res = -ENOKEY;
 120                 up_read(&keyring_key->sem);
 121                 goto out;
 122         }
 123         res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
 124         up_read(&keyring_key->sem);
 125         if (res)
 126                 goto out;
 127
 128         crypt_info->ci_keyring_key = keyring_key;
 129         return 0;
 130 out:
 131         key_put(keyring_key);
 132         return res;
 133 }
 134
 135 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
 136                                  const char **cipher_str_ret, int *keysize_ret)
 137 {
 138         if (S_ISREG(inode->i_mode)) {
 139                 if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
 140                         *cipher_str_ret = "xts(aes)";
 141                         *keysize_ret = FS_AES_256_XTS_KEY_SIZE;
 142                         return 0;
 143                 }
 144                 pr_warn_once("fscrypto: unsupported contents encryption mode "
 145                              "%d for inode %lu\n",
 146                              ci->ci_data_mode, inode->i_ino);
 147                 return -ENOKEY;
 148         }
 149
 150         if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
 151                 if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
 152                         *cipher_str_ret = "cts(cbc(aes))";
 153                         *keysize_ret = FS_AES_256_CTS_KEY_SIZE;
 154                         return 0;
 155                 }
 156                 pr_warn_once("fscrypto: unsupported filenames encryption mode "
 157                              "%d for inode %lu\n",
 158                              ci->ci_filename_mode, inode->i_ino);
 159                 return -ENOKEY;
 160         }
 161
 162         pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
 163                      (inode->i_mode & S_IFMT), inode->i_ino);
 164         return -ENOKEY;
 165 }
 166
 167 static void put_crypt_info(struct fscrypt_info *ci)
 168 {
 169         if (!ci)
 170                 return;
 171
 172         key_put(ci->ci_keyring_key);
 173         crypto_free_skcipher(ci->ci_ctfm);
 174         kmem_cache_free(fscrypt_info_cachep, ci);
 175 }
 176
 177 int fscrypt_get_crypt_info(struct inode *inode)
 178 {
 179         struct fscrypt_info *crypt_info;
 180         struct fscrypt_context ctx;
 181         struct crypto_skcipher *ctfm;
 182         const char *cipher_str;
 183         int keysize;
 184         u8 *raw_key = NULL;
 185         int res;
 186
 187         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 188         if (res)
 189                 return res;
 190
 191         if (!inode->i_sb->s_cop->get_context)
 192                 return -EOPNOTSUPP;
 193 retry:
 194         crypt_info = ACCESS_ONCE(inode->i_crypt_info);
 195         if (crypt_info) {
 196                 if (!crypt_info->ci_keyring_key ||
 197                                 key_validate(crypt_info->ci_keyring_key) == 0)
 198                         return 0;
 199                 fscrypt_put_encryption_info(inode, crypt_info);
 200                 goto retry;
 201         }
 202
 203         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 204         if (res < 0) {
 205                 if (!fscrypt_dummy_context_enabled(inode) ||
 206                     inode->i_sb->s_cop->is_encrypted(inode))
 207                         return res;
 208                 /* Fake up a context for an unencrypted directory */
 209                 memset(&ctx, 0, sizeof(ctx));
 210                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 211                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 212                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 213                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 214                 res = sizeof(ctx);
 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         res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX);
 251         if (res && inode->i_sb->s_cop->key_prefix) {
 252                 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
 253                                              inode->i_sb->s_cop->key_prefix);
 254                 if (res2) {
 255                         if (res2 == -ENOKEY)
 256                                 res = -ENOKEY;
 257                         goto out;
 258                 }
 259         } else if (res) {
 260                 goto out;
 261         }
 262         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 263         if (!ctfm || IS_ERR(ctfm)) {
 264                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 265                 printk(KERN_DEBUG
 266                        "%s: error %d (inode %u) allocating crypto tfm\n",
 267                        __func__, res, (unsigned) inode->i_ino);
 268                 goto out;
 269         }
 270         crypt_info->ci_ctfm = ctfm;
 271         crypto_skcipher_clear_flags(ctfm, ~0);
 272         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 273         res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
 274         if (res)
 275                 goto out;
 276
 277         kzfree(raw_key);
 278         raw_key = NULL;
 279         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
 280                 put_crypt_info(crypt_info);
 281                 goto retry;
 282         }
 283         return 0;
 284
 285 out:
 286         if (res == -ENOKEY)
 287                 res = 0;
 288         put_crypt_info(crypt_info);
 289         kzfree(raw_key);
 290         return res;
 291 }
 292
 293 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 294 {
 295         struct fscrypt_info *prev;
 296
 297         if (ci == NULL)
 298                 ci = ACCESS_ONCE(inode->i_crypt_info);
 299         if (ci == NULL)
 300                 return;
 301
 302         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 303         if (prev != ci)
 304                 return;
 305
 306         put_crypt_info(ci);
 307 }
 308 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 309
 310 int fscrypt_get_encryption_info(struct inode *inode)
 311 {
 312         struct fscrypt_info *ci = inode->i_crypt_info;
 313
 314         if (!ci ||
 315                 (ci->ci_keyring_key &&
 316                  (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 317                                                (1 << KEY_FLAG_REVOKED) |
 318                                                (1 << KEY_FLAG_DEAD)))))
 319                 return fscrypt_get_crypt_info(inode);
 320         return 0;
 321 }
 322 EXPORT_SYMBOL(fscrypt_get_encryption_info);