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 <keys/encrypted-type.h>
  12 #include <keys/user-type.h>
  13 #include <linux/random.h>
  14 #include <linux/scatterlist.h>
  15 #include <uapi/linux/keyctl.h>
  16
  17 #include "ext4.h"
  18 #include "xattr.h"
  19
  20 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  21 {
  22         struct ext4_completion_result *ecr = req->data;
  23
  24         if (rc == -EINPROGRESS)
  25                 return;
  26
  27         ecr->res = rc;
  28         complete(&ecr->completion);
  29 }
  30
  31 /**
  32  * ext4_derive_key_aes() - Derive a key using AES-128-ECB
  33  * @deriving_key: Encryption key used for derivation.
  34  * @source_key:   Source key to which to apply derivation.
  35  * @derived_key:  Derived key.
  36  *
  37  * Return: Zero on success; non-zero otherwise.
  38  */
  39 static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
  40                                char source_key[EXT4_AES_256_XTS_KEY_SIZE],
  41                                char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
  42 {
  43         int res = 0;
  44         struct ablkcipher_request *req = NULL;
  45         DECLARE_EXT4_COMPLETION_RESULT(ecr);
  46         struct scatterlist src_sg, dst_sg;
  47         struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
  48                                                                 0);
  49
  50         if (IS_ERR(tfm)) {
  51                 res = PTR_ERR(tfm);
  52                 tfm = NULL;
  53                 goto out;
  54         }
  55         crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  56         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
  57         if (!req) {
  58                 res = -ENOMEM;
  59                 goto out;
  60         }
  61         ablkcipher_request_set_callback(req,
  62                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  63                         derive_crypt_complete, &ecr);
  64         res = crypto_ablkcipher_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         ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
  71                                      EXT4_AES_256_XTS_KEY_SIZE, NULL);
  72         res = crypto_ablkcipher_encrypt(req);
  73         if (res == -EINPROGRESS || res == -EBUSY) {
  74                 BUG_ON(req->base.data != &ecr);
  75                 wait_for_completion(&ecr.completion);
  76                 res = ecr.res;
  77         }
  78
  79 out:
  80         if (req)
  81                 ablkcipher_request_free(req);
  82         if (tfm)
  83                 crypto_free_ablkcipher(tfm);
  84         return res;
  85 }
  86
  87 void ext4_free_crypt_info(struct ext4_crypt_info *ci)
  88 {
  89         if (!ci)
  90                 return;
  91
  92         if (ci->ci_keyring_key)
  93                 key_put(ci->ci_keyring_key);
  94         crypto_free_ablkcipher(ci->ci_ctfm);
  95         kmem_cache_free(ext4_crypt_info_cachep, ci);
  96 }
  97
  98 void ext4_free_encryption_info(struct inode *inode,
  99                                struct ext4_crypt_info *ci)
 100 {
 101         struct ext4_inode_info *ei = EXT4_I(inode);
 102         struct ext4_crypt_info *prev;
 103
 104         if (ci == NULL)
 105                 ci = ACCESS_ONCE(ei->i_crypt_info);
 106         if (ci == NULL)
 107                 return;
 108         prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
 109         if (prev != ci)
 110                 return;
 111
 112         ext4_free_crypt_info(ci);
 113 }
 114
 115 int _ext4_get_encryption_info(struct inode *inode)
 116 {
 117         struct ext4_inode_info *ei = EXT4_I(inode);
 118         struct ext4_crypt_info *crypt_info;
 119         char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 120                                  (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
 121         struct key *keyring_key = NULL;
 122         struct ext4_encryption_key *master_key;
 123         struct ext4_encryption_context ctx;
 124         const struct user_key_payload *ukp;
 125         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 126         struct crypto_ablkcipher *ctfm;
 127         const char *cipher_str;
 128         char raw_key[EXT4_MAX_KEY_SIZE];
 129         char mode;
 130         int res;
 131
 132         if (!ext4_read_workqueue) {
 133                 res = ext4_init_crypto();
 134                 if (res)
 135                         return res;
 136         }
 137
 138 retry:
 139         crypt_info = ACCESS_ONCE(ei->i_crypt_info);
 140         if (crypt_info) {
 141                 if (!crypt_info->ci_keyring_key ||
 142                     key_validate(crypt_info->ci_keyring_key) == 0)
 143                         return 0;
 144                 ext4_free_encryption_info(inode, crypt_info);
 145                 goto retry;
 146         }
 147
 148         res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 149                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 150                                  &ctx, sizeof(ctx));
 151         if (res < 0) {
 152                 if (!DUMMY_ENCRYPTION_ENABLED(sbi))
 153                         return res;
 154                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 155                 ctx.filenames_encryption_mode =
 156                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 157                 ctx.flags = 0;
 158         } else if (res != sizeof(ctx))
 159                 return -EINVAL;
 160         res = 0;
 161
 162         crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
 163         if (!crypt_info)
 164                 return -ENOMEM;
 165
 166         crypt_info->ci_flags = ctx.flags;
 167         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 168         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 169         crypt_info->ci_ctfm = NULL;
 170         crypt_info->ci_keyring_key = NULL;
 171         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 172                sizeof(crypt_info->ci_master_key));
 173         if (S_ISREG(inode->i_mode))
 174                 mode = crypt_info->ci_data_mode;
 175         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 176                 mode = crypt_info->ci_filename_mode;
 177         else
 178                 BUG();
 179         switch (mode) {
 180         case EXT4_ENCRYPTION_MODE_AES_256_XTS:
 181                 cipher_str = "xts(aes)";
 182                 break;
 183         case EXT4_ENCRYPTION_MODE_AES_256_CTS:
 184                 cipher_str = "cts(cbc(aes))";
 185                 break;
 186         default:
 187                 printk_once(KERN_WARNING
 188                             "ext4: unsupported key mode %d (ino %u)\n",
 189                             mode, (unsigned) inode->i_ino);
 190                 res = -ENOKEY;
 191                 goto out;
 192         }
 193         if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
 194                 memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
 195                 goto got_key;
 196         }
 197         memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 198                EXT4_KEY_DESC_PREFIX_SIZE);
 199         sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
 200                 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
 201                 ctx.master_key_descriptor);
 202         full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 203                             (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
 204         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 205         if (IS_ERR(keyring_key)) {
 206                 res = PTR_ERR(keyring_key);
 207                 keyring_key = NULL;
 208                 goto out;
 209         }
 210         crypt_info->ci_keyring_key = keyring_key;
 211         BUG_ON(keyring_key->type != &key_type_logon);
 212         ukp = user_key_payload(keyring_key);
 213         if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 214                 res = -EINVAL;
 215                 goto out;
 216         }
 217         master_key = (struct ext4_encryption_key *)ukp->data;
 218         BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
 219                      EXT4_KEY_DERIVATION_NONCE_SIZE);
 220         BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
 221         res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 222                                   raw_key);
 223         if (res)
 224                 goto out;
 225 got_key:
 226         ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
 227         if (!ctfm || IS_ERR(ctfm)) {
 228                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 229                 printk(KERN_DEBUG
 230                        "%s: error %d (inode %u) allocating crypto tfm\n",
 231                        __func__, res, (unsigned) inode->i_ino);
 232                 goto out;
 233         }
 234         crypt_info->ci_ctfm = ctfm;
 235         crypto_ablkcipher_clear_flags(ctfm, ~0);
 236         crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
 237                              CRYPTO_TFM_REQ_WEAK_KEY);
 238         res = crypto_ablkcipher_setkey(ctfm, raw_key,
 239                                        ext4_encryption_key_size(mode));
 240         if (res)
 241                 goto out;
 242         memzero_explicit(raw_key, sizeof(raw_key));
 243         if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
 244                 ext4_free_crypt_info(crypt_info);
 245                 goto retry;
 246         }
 247         return 0;
 248
 249 out:
 250         if (res == -ENOKEY)
 251                 res = 0;
 252         ext4_free_crypt_info(crypt_info);
 253         memzero_explicit(raw_key, sizeof(raw_key));
 254         return res;
 255 }
 256
 257 int ext4_has_encryption_key(struct inode *inode)
 258 {
 259         struct ext4_inode_info *ei = EXT4_I(inode);
 260
 261         return (ei->i_crypt_info != NULL);
 262 }