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                 wait_for_completion(&ecr.completion);
  75                 res = ecr.res;
  76         }
  77
  78 out:
  79         if (req)
  80                 ablkcipher_request_free(req);
  81         if (tfm)
  82                 crypto_free_ablkcipher(tfm);
  83         return res;
  84 }
  85
  86 void ext4_free_crypt_info(struct ext4_crypt_info *ci)
  87 {
  88         if (!ci)
  89                 return;
  90
  91         if (ci->ci_keyring_key)
  92                 key_put(ci->ci_keyring_key);
  93         crypto_free_ablkcipher(ci->ci_ctfm);
  94         kmem_cache_free(ext4_crypt_info_cachep, ci);
  95 }
  96
  97 void ext4_free_encryption_info(struct inode *inode,
  98                                struct ext4_crypt_info *ci)
  99 {
 100         struct ext4_inode_info *ei = EXT4_I(inode);
 101         struct ext4_crypt_info *prev;
 102
 103         if (ci == NULL)
 104                 ci = ACCESS_ONCE(ei->i_crypt_info);
 105         if (ci == NULL)
 106                 return;
 107         prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
 108         if (prev != ci)
 109                 return;
 110
 111         ext4_free_crypt_info(ci);
 112 }
 113
 114 int _ext4_get_encryption_info(struct inode *inode)
 115 {
 116         struct ext4_inode_info *ei = EXT4_I(inode);
 117         struct ext4_crypt_info *crypt_info;
 118         char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 119                                  (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
 120         struct key *keyring_key = NULL;
 121         struct ext4_encryption_key *master_key;
 122         struct ext4_encryption_context ctx;
 123         const struct user_key_payload *ukp;
 124         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 125         struct crypto_ablkcipher *ctfm;
 126         const char *cipher_str;
 127         char raw_key[EXT4_MAX_KEY_SIZE];
 128         char mode;
 129         int res;
 130
 131         if (!ext4_read_workqueue) {
 132                 res = ext4_init_crypto();
 133                 if (res)
 134                         return res;
 135         }
 136
 137 retry:
 138         crypt_info = ACCESS_ONCE(ei->i_crypt_info);
 139         if (crypt_info) {
 140                 if (!crypt_info->ci_keyring_key ||
 141                     key_validate(crypt_info->ci_keyring_key) == 0)
 142                         return 0;
 143                 ext4_free_encryption_info(inode, crypt_info);
 144                 goto retry;
 145         }
 146
 147         res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 148                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 149                                  &ctx, sizeof(ctx));
 150         if (res < 0) {
 151                 if (!DUMMY_ENCRYPTION_ENABLED(sbi))
 152                         return res;
 153                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 154                 ctx.filenames_encryption_mode =
 155                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 156                 ctx.flags = 0;
 157         } else if (res != sizeof(ctx))
 158                 return -EINVAL;
 159         res = 0;
 160
 161         crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
 162         if (!crypt_info)
 163                 return -ENOMEM;
 164
 165         crypt_info->ci_flags = ctx.flags;
 166         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 167         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 168         crypt_info->ci_ctfm = NULL;
 169         crypt_info->ci_keyring_key = NULL;
 170         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 171                sizeof(crypt_info->ci_master_key));
 172         if (S_ISREG(inode->i_mode))
 173                 mode = crypt_info->ci_data_mode;
 174         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 175                 mode = crypt_info->ci_filename_mode;
 176         else
 177                 BUG();
 178         switch (mode) {
 179         case EXT4_ENCRYPTION_MODE_AES_256_XTS:
 180                 cipher_str = "xts(aes)";
 181                 break;
 182         case EXT4_ENCRYPTION_MODE_AES_256_CTS:
 183                 cipher_str = "cts(cbc(aes))";
 184                 break;
 185         default:
 186                 printk_once(KERN_WARNING
 187                             "ext4: unsupported key mode %d (ino %u)\n",
 188                             mode, (unsigned) inode->i_ino);
 189                 res = -ENOKEY;
 190                 goto out;
 191         }
 192         if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
 193                 memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
 194                 goto got_key;
 195         }
 196         memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 197                EXT4_KEY_DESC_PREFIX_SIZE);
 198         sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
 199                 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
 200                 ctx.master_key_descriptor);
 201         full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 202                             (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
 203         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 204         if (IS_ERR(keyring_key)) {
 205                 res = PTR_ERR(keyring_key);
 206                 keyring_key = NULL;
 207                 goto out;
 208         }
 209         crypt_info->ci_keyring_key = keyring_key;
 210         if (keyring_key->type != &key_type_logon) {
 211                 printk_once(KERN_WARNING
 212                             "ext4: key type must be logon\n");
 213                 res = -ENOKEY;
 214                 goto out;
 215         }
 216         ukp = user_key_payload(keyring_key);
 217         if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 218                 res = -EINVAL;
 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                 goto out;
 230         }
 231         res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 232                                   raw_key);
 233         if (res)
 234                 goto out;
 235 got_key:
 236         ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
 237         if (!ctfm || IS_ERR(ctfm)) {
 238                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 239                 printk(KERN_DEBUG
 240                        "%s: error %d (inode %u) allocating crypto tfm\n",
 241                        __func__, res, (unsigned) inode->i_ino);
 242                 goto out;
 243         }
 244         crypt_info->ci_ctfm = ctfm;
 245         crypto_ablkcipher_clear_flags(ctfm, ~0);
 246         crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
 247                              CRYPTO_TFM_REQ_WEAK_KEY);
 248         res = crypto_ablkcipher_setkey(ctfm, raw_key,
 249                                        ext4_encryption_key_size(mode));
 250         if (res)
 251                 goto out;
 252         memzero_explicit(raw_key, sizeof(raw_key));
 253         if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
 254                 ext4_free_crypt_info(crypt_info);
 255                 goto retry;
 256         }
 257         return 0;
 258
 259 out:
 260         if (res == -ENOKEY)
 261                 res = 0;
 262         ext4_free_crypt_info(crypt_info);
 263         memzero_explicit(raw_key, sizeof(raw_key));
 264         return res;
 265 }
 266
 267 int ext4_has_encryption_key(struct inode *inode)
 268 {
 269         struct ext4_inode_info *ei = EXT4_I(inode);
 270
 271         return (ei->i_crypt_info != NULL);
 272 }