fs/ext4/crypto_key.c

   1 /*
   2  * linux/fs/ext4/crypto_key.c
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  *
   6  * This contains encryption key functions for ext4
   7  *
   8  * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
   9  */
  10
  11 #include <crypto/skcipher.h>
  12 #include <keys/encrypted-type.h>
  13 #include <keys/user-type.h>
  14 #include <linux/random.h>
  15 #include <linux/scatterlist.h>
  16 #include <uapi/linux/keyctl.h>
  17
  18 #include "ext4.h"
  19 #include "xattr.h"
  20
  21 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  22 {
  23         struct ext4_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  * ext4_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_key:  Derived key.
  37  *
  38  * Return: Zero on success; non-zero otherwise.
  39  */
  40 static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
  41                                char source_key[EXT4_AES_256_XTS_KEY_SIZE],
  42                                char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
  43 {
  44         int res = 0;
  45         struct skcipher_request *req = NULL;
  46         DECLARE_EXT4_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                                      EXT4_AES_128_ECB_KEY_SIZE);
  66         if (res < 0)
  67                 goto out;
  68         sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
  69         sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
  70         skcipher_request_set_crypt(req, &src_sg, &dst_sg,
  71                                    EXT4_AES_256_XTS_KEY_SIZE, NULL);
  72         res = crypto_skcipher_encrypt(req);
  73         if (res == -EINPROGRESS || res == -EBUSY) {
  74                 wait_for_completion(&ecr.completion);
  75                 res = ecr.res;
  76         }
  77
  78 out:
  79         skcipher_request_free(req);
  80         crypto_free_skcipher(tfm);
  81         return res;
  82 }
  83
  84 void ext4_free_crypt_info(struct ext4_crypt_info *ci)
  85 {
  86         if (!ci)
  87                 return;
  88
  89         if (ci->ci_keyring_key)
  90                 key_put(ci->ci_keyring_key);
  91         crypto_free_skcipher(ci->ci_ctfm);
  92         kmem_cache_free(ext4_crypt_info_cachep, ci);
  93 }
  94
  95 void ext4_free_encryption_info(struct inode *inode,
  96                                struct ext4_crypt_info *ci)
  97 {
  98         struct ext4_inode_info *ei = EXT4_I(inode);
  99         struct ext4_crypt_info *prev;
 100
 101         if (ci == NULL)
 102                 ci = ACCESS_ONCE(ei->i_crypt_info);
 103         if (ci == NULL)
 104                 return;
 105         prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
 106         if (prev != ci)
 107                 return;
 108
 109         ext4_free_crypt_info(ci);
 110 }
 111
 112 int _ext4_get_encryption_info(struct inode *inode)
 113 {
 114         struct ext4_inode_info *ei = EXT4_I(inode);
 115         struct ext4_crypt_info *crypt_info;
 116         char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 117                                  (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
 118         struct key *keyring_key = NULL;
 119         struct ext4_encryption_key *master_key;
 120         struct ext4_encryption_context ctx;
 121         const struct user_key_payload *ukp;
 122         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 123         struct crypto_skcipher *ctfm;
 124         const char *cipher_str;
 125         char raw_key[EXT4_MAX_KEY_SIZE];
 126         char mode;
 127         int res;
 128
 129         if (!ext4_read_workqueue) {
 130                 res = ext4_init_crypto();
 131                 if (res)
 132                         return res;
 133         }
 134
 135 retry:
 136         crypt_info = ACCESS_ONCE(ei->i_crypt_info);
 137         if (crypt_info) {
 138                 if (!crypt_info->ci_keyring_key ||
 139                     key_validate(crypt_info->ci_keyring_key) == 0)
 140                         return 0;
 141                 ext4_free_encryption_info(inode, crypt_info);
 142                 goto retry;
 143         }
 144
 145         res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 146                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 147                                  &ctx, sizeof(ctx));
 148         if (res < 0) {
 149                 if (!DUMMY_ENCRYPTION_ENABLED(sbi))
 150                         return res;
 151                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 152                 ctx.filenames_encryption_mode =
 153                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 154                 ctx.flags = 0;
 155         } else if (res != sizeof(ctx))
 156                 return -EINVAL;
 157         res = 0;
 158
 159         crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
 160         if (!crypt_info)
 161                 return -ENOMEM;
 162
 163         crypt_info->ci_flags = ctx.flags;
 164         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 165         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 166         crypt_info->ci_ctfm = NULL;
 167         crypt_info->ci_keyring_key = NULL;
 168         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 169                sizeof(crypt_info->ci_master_key));
 170         if (S_ISREG(inode->i_mode))
 171                 mode = crypt_info->ci_data_mode;
 172         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 173                 mode = crypt_info->ci_filename_mode;
 174         else
 175                 BUG();
 176         switch (mode) {
 177         case EXT4_ENCRYPTION_MODE_AES_256_XTS:
 178                 cipher_str = "xts(aes)";
 179                 break;
 180         case EXT4_ENCRYPTION_MODE_AES_256_CTS:
 181                 cipher_str = "cts(cbc(aes))";
 182                 break;
 183         default:
 184                 printk_once(KERN_WARNING
 185                             "ext4: unsupported key mode %d (ino %u)\n",
 186                             mode, (unsigned) inode->i_ino);
 187                 res = -ENOKEY;
 188                 goto out;
 189         }
 190         if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
 191                 memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
 192                 goto got_key;
 193         }
 194         memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 195                EXT4_KEY_DESC_PREFIX_SIZE);
 196         sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
 197                 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
 198                 ctx.master_key_descriptor);
 199         full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 200                             (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
 201         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 202         if (IS_ERR(keyring_key)) {
 203                 res = PTR_ERR(keyring_key);
 204                 keyring_key = NULL;
 205                 goto out;
 206         }
 207         crypt_info->ci_keyring_key = keyring_key;
 208         if (keyring_key->type != &key_type_logon) {
 209                 printk_once(KERN_WARNING
 210                             "ext4: key type must be logon\n");
 211                 res = -ENOKEY;
 212                 goto out;
 213         }
 214         down_read(&keyring_key->sem);
 215         ukp = user_key_payload(keyring_key);
 216         if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 217                 res = -EINVAL;
 218                 up_read(&keyring_key->sem);
 219                 goto out;
 220         }
 221         master_key = (struct ext4_encryption_key *)ukp->data;
 222         BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
 223                      EXT4_KEY_DERIVATION_NONCE_SIZE);
 224         if (master_key->size != EXT4_AES_256_XTS_KEY_SIZE) {
 225                 printk_once(KERN_WARNING
 226                             "ext4: key size incorrect: %d\n",
 227                             master_key->size);
 228                 res = -ENOKEY;
 229                 up_read(&keyring_key->sem);
 230                 goto out;
 231         }
 232         res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 233                                   raw_key);
 234         up_read(&keyring_key->sem);
 235         if (res)
 236                 goto out;
 237 got_key:
 238         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 239         if (!ctfm || IS_ERR(ctfm)) {
 240                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 241                 printk(KERN_DEBUG
 242                        "%s: error %d (inode %u) allocating crypto tfm\n",
 243                        __func__, res, (unsigned) inode->i_ino);
 244                 goto out;
 245         }
 246         crypt_info->ci_ctfm = ctfm;
 247         crypto_skcipher_clear_flags(ctfm, ~0);
 248         crypto_tfm_set_flags(crypto_skcipher_tfm(ctfm),
 249                              CRYPTO_TFM_REQ_WEAK_KEY);
 250         res = crypto_skcipher_setkey(ctfm, raw_key,
 251                                      ext4_encryption_key_size(mode));
 252         if (res)
 253                 goto out;
 254         memzero_explicit(raw_key, sizeof(raw_key));
 255         if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
 256                 ext4_free_crypt_info(crypt_info);
 257                 goto retry;
 258         }
 259         return 0;
 260
 261 out:
 262         if (res == -ENOKEY)
 263                 res = 0;
 264         ext4_free_crypt_info(crypt_info);
 265         memzero_explicit(raw_key, sizeof(raw_key));
 266         return res;
 267 }
 268
 269 int ext4_has_encryption_key(struct inode *inode)
 270 {
 271         struct ext4_inode_info *ei = EXT4_I(inode);
 272
 273         return (ei->i_crypt_info != NULL);
 274 }