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         crypto_free_ablkcipher(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_ablkcipher *ctfm;
 124         const char *cipher_str;
 125         char raw_key[EXT4_MAX_KEY_SIZE];
 126         char mode;
 127         int res;
 128
 129         if (ei->i_crypt_info)
 130                 return 0;
 131
 132         res = ext4_init_crypto();
 133         if (res)
 134                 return res;
 135
 136         res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 137                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 138                                  &ctx, sizeof(ctx));
 139         if (res < 0) {
 140                 if (!DUMMY_ENCRYPTION_ENABLED(sbi))
 141                         return res;
 142                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 143                 ctx.filenames_encryption_mode =
 144                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 145                 ctx.flags = 0;
 146         } else if (res != sizeof(ctx))
 147                 return -EINVAL;
 148         res = 0;
 149
 150         crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
 151         if (!crypt_info)
 152                 return -ENOMEM;
 153
 154         crypt_info->ci_flags = ctx.flags;
 155         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 156         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 157         crypt_info->ci_ctfm = NULL;
 158         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 159                sizeof(crypt_info->ci_master_key));
 160         if (S_ISREG(inode->i_mode))
 161                 mode = crypt_info->ci_data_mode;
 162         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 163                 mode = crypt_info->ci_filename_mode;
 164         else
 165                 BUG();
 166         switch (mode) {
 167         case EXT4_ENCRYPTION_MODE_AES_256_XTS:
 168                 cipher_str = "xts(aes)";
 169                 break;
 170         case EXT4_ENCRYPTION_MODE_AES_256_CTS:
 171                 cipher_str = "cts(cbc(aes))";
 172                 break;
 173         default:
 174                 printk_once(KERN_WARNING
 175                             "ext4: unsupported key mode %d (ino %u)\n",
 176                             mode, (unsigned) inode->i_ino);
 177                 res = -ENOKEY;
 178                 goto out;
 179         }
 180         if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
 181                 memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
 182                 goto got_key;
 183         }
 184         memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 185                EXT4_KEY_DESC_PREFIX_SIZE);
 186         sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
 187                 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
 188                 ctx.master_key_descriptor);
 189         full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 190                             (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
 191         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 192         if (IS_ERR(keyring_key)) {
 193                 res = PTR_ERR(keyring_key);
 194                 keyring_key = NULL;
 195                 goto out;
 196         }
 197         if (keyring_key->type != &key_type_logon) {
 198                 printk_once(KERN_WARNING
 199                             "ext4: key type must be logon\n");
 200                 res = -ENOKEY;
 201                 goto out;
 202         }
 203         down_read(&keyring_key->sem);
 204         ukp = user_key_payload(keyring_key);
 205         if (!ukp) {
 206                 /* key was revoked before we acquired its semaphore */
 207                 res = -EKEYREVOKED;
 208                 up_read(&keyring_key->sem);
 209                 goto out;
 210         }
 211         if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 212                 res = -EINVAL;
 213                 up_read(&keyring_key->sem);
 214                 goto out;
 215         }
 216         master_key = (struct ext4_encryption_key *)ukp->data;
 217         BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
 218                      EXT4_KEY_DERIVATION_NONCE_SIZE);
 219         if (master_key->size != EXT4_AES_256_XTS_KEY_SIZE) {
 220                 printk_once(KERN_WARNING
 221                             "ext4: key size incorrect: %d\n",
 222                             master_key->size);
 223                 res = -ENOKEY;
 224                 up_read(&keyring_key->sem);
 225                 goto out;
 226         }
 227         res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 228                                   raw_key);
 229         up_read(&keyring_key->sem);
 230         if (res)
 231                 goto out;
 232 got_key:
 233         ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
 234         if (!ctfm || IS_ERR(ctfm)) {
 235                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 236                 printk(KERN_DEBUG
 237                        "%s: error %d (inode %u) allocating crypto tfm\n",
 238                        __func__, res, (unsigned) inode->i_ino);
 239                 goto out;
 240         }
 241         crypt_info->ci_ctfm = ctfm;
 242         crypto_ablkcipher_clear_flags(ctfm, ~0);
 243         crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
 244                              CRYPTO_TFM_REQ_WEAK_KEY);
 245         res = crypto_ablkcipher_setkey(ctfm, raw_key,
 246                                        ext4_encryption_key_size(mode));
 247         if (res)
 248                 goto out;
 249
 250         if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) == NULL)
 251                 crypt_info = NULL;
 252 out:
 253         if (res == -ENOKEY)
 254                 res = 0;
 255         key_put(keyring_key);
 256         ext4_free_crypt_info(crypt_info);
 257         memzero_explicit(raw_key, sizeof(raw_key));
 258         return res;
 259 }
 260
 261 int ext4_has_encryption_key(struct inode *inode)
 262 {
 263         struct ext4_inode_info *ei = EXT4_I(inode);
 264
 265         return (ei->i_crypt_info != NULL);
 266 }