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/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 #include <linux/fscrypto.h>
  17
  18 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  19 {
  20         struct fscrypt_completion_result *ecr = req->data;
  21
  22         if (rc == -EINPROGRESS)
  23                 return;
  24
  25         ecr->res = rc;
  26         complete(&ecr->completion);
  27 }
  28
  29 /**
  30  * derive_key_aes() - Derive a key using AES-128-ECB
  31  * @deriving_key: Encryption key used for derivation.
  32  * @source_key:   Source key to which to apply derivation.
  33  * @derived_key:  Derived key.
  34  *
  35  * Return: Zero on success; non-zero otherwise.
  36  */
  37 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  38                                 u8 source_key[FS_AES_256_XTS_KEY_SIZE],
  39                                 u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
  40 {
  41         int res = 0;
  42         struct skcipher_request *req = NULL;
  43         DECLARE_FS_COMPLETION_RESULT(ecr);
  44         struct scatterlist src_sg, dst_sg;
  45         struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
  46
  47         if (IS_ERR(tfm)) {
  48                 res = PTR_ERR(tfm);
  49                 tfm = NULL;
  50                 goto out;
  51         }
  52         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  53         req = skcipher_request_alloc(tfm, GFP_NOFS);
  54         if (!req) {
  55                 res = -ENOMEM;
  56                 goto out;
  57         }
  58         skcipher_request_set_callback(req,
  59                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  60                         derive_crypt_complete, &ecr);
  61         res = crypto_skcipher_setkey(tfm, deriving_key,
  62                                         FS_AES_128_ECB_KEY_SIZE);
  63         if (res < 0)
  64                 goto out;
  65
  66         sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
  67         sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
  68         skcipher_request_set_crypt(req, &src_sg, &dst_sg,
  69                                         FS_AES_256_XTS_KEY_SIZE, NULL);
  70         res = crypto_skcipher_encrypt(req);
  71         if (res == -EINPROGRESS || res == -EBUSY) {
  72                 wait_for_completion(&ecr.completion);
  73                 res = ecr.res;
  74         }
  75 out:
  76         skcipher_request_free(req);
  77         crypto_free_skcipher(tfm);
  78         return res;
  79 }
  80
  81 static void put_crypt_info(struct fscrypt_info *ci)
  82 {
  83         if (!ci)
  84                 return;
  85
  86         key_put(ci->ci_keyring_key);
  87         crypto_free_skcipher(ci->ci_ctfm);
  88         kmem_cache_free(fscrypt_info_cachep, ci);
  89 }
  90
  91 int get_crypt_info(struct inode *inode)
  92 {
  93         struct fscrypt_info *crypt_info;
  94         u8 full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
  95                                 (FS_KEY_DESCRIPTOR_SIZE * 2) + 1];
  96         struct key *keyring_key = NULL;
  97         struct fscrypt_key *master_key;
  98         struct fscrypt_context ctx;
  99         const struct user_key_payload *ukp;
 100         struct crypto_skcipher *ctfm;
 101         const char *cipher_str;
 102         u8 raw_key[FS_MAX_KEY_SIZE];
 103         u8 mode;
 104         int res;
 105
 106         res = fscrypt_initialize();
 107         if (res)
 108                 return res;
 109
 110         if (!inode->i_sb->s_cop->get_context)
 111                 return -EOPNOTSUPP;
 112 retry:
 113         crypt_info = ACCESS_ONCE(inode->i_crypt_info);
 114         if (crypt_info) {
 115                 if (!crypt_info->ci_keyring_key ||
 116                                 key_validate(crypt_info->ci_keyring_key) == 0)
 117                         return 0;
 118                 fscrypt_put_encryption_info(inode, crypt_info);
 119                 goto retry;
 120         }
 121
 122         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 123         if (res < 0) {
 124                 if (!fscrypt_dummy_context_enabled(inode))
 125                         return res;
 126                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 127                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 128                 ctx.flags = 0;
 129         } else if (res != sizeof(ctx)) {
 130                 return -EINVAL;
 131         }
 132         res = 0;
 133
 134         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 135         if (!crypt_info)
 136                 return -ENOMEM;
 137
 138         crypt_info->ci_flags = ctx.flags;
 139         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 140         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 141         crypt_info->ci_ctfm = NULL;
 142         crypt_info->ci_keyring_key = NULL;
 143         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 144                                 sizeof(crypt_info->ci_master_key));
 145         if (S_ISREG(inode->i_mode))
 146                 mode = crypt_info->ci_data_mode;
 147         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 148                 mode = crypt_info->ci_filename_mode;
 149         else
 150                 BUG();
 151
 152         switch (mode) {
 153         case FS_ENCRYPTION_MODE_AES_256_XTS:
 154                 cipher_str = "xts(aes)";
 155                 break;
 156         case FS_ENCRYPTION_MODE_AES_256_CTS:
 157                 cipher_str = "cts(cbc(aes))";
 158                 break;
 159         default:
 160                 printk_once(KERN_WARNING
 161                             "%s: unsupported key mode %d (ino %u)\n",
 162                             __func__, mode, (unsigned) inode->i_ino);
 163                 res = -ENOKEY;
 164                 goto out;
 165         }
 166         if (fscrypt_dummy_context_enabled(inode)) {
 167                 memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
 168                 goto got_key;
 169         }
 170         memcpy(full_key_descriptor, FS_KEY_DESC_PREFIX,
 171                                         FS_KEY_DESC_PREFIX_SIZE);
 172         sprintf(full_key_descriptor + FS_KEY_DESC_PREFIX_SIZE,
 173                                         "%*phN", FS_KEY_DESCRIPTOR_SIZE,
 174                                         ctx.master_key_descriptor);
 175         full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
 176                                         (2 * FS_KEY_DESCRIPTOR_SIZE)] = '\0';
 177         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 178         if (IS_ERR(keyring_key)) {
 179                 res = PTR_ERR(keyring_key);
 180                 keyring_key = NULL;
 181                 goto out;
 182         }
 183         crypt_info->ci_keyring_key = keyring_key;
 184         if (keyring_key->type != &key_type_logon) {
 185                 printk_once(KERN_WARNING
 186                                 "%s: key type must be logon\n", __func__);
 187                 res = -ENOKEY;
 188                 goto out;
 189         }
 190         down_read(&keyring_key->sem);
 191         ukp = user_key_payload(keyring_key);
 192         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 193                 res = -EINVAL;
 194                 up_read(&keyring_key->sem);
 195                 goto out;
 196         }
 197         master_key = (struct fscrypt_key *)ukp->data;
 198         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 199
 200         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 201                 printk_once(KERN_WARNING
 202                                 "%s: key size incorrect: %d\n",
 203                                 __func__, master_key->size);
 204                 res = -ENOKEY;
 205                 up_read(&keyring_key->sem);
 206                 goto out;
 207         }
 208         res = derive_key_aes(ctx.nonce, master_key->raw, raw_key);
 209         up_read(&keyring_key->sem);
 210         if (res)
 211                 goto out;
 212 got_key:
 213         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 214         if (!ctfm || IS_ERR(ctfm)) {
 215                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 216                 printk(KERN_DEBUG
 217                        "%s: error %d (inode %u) allocating crypto tfm\n",
 218                        __func__, res, (unsigned) inode->i_ino);
 219                 goto out;
 220         }
 221         crypt_info->ci_ctfm = ctfm;
 222         crypto_skcipher_clear_flags(ctfm, ~0);
 223         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 224         res = crypto_skcipher_setkey(ctfm, raw_key, fscrypt_key_size(mode));
 225         if (res)
 226                 goto out;
 227
 228         memzero_explicit(raw_key, sizeof(raw_key));
 229         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
 230                 put_crypt_info(crypt_info);
 231                 goto retry;
 232         }
 233         return 0;
 234
 235 out:
 236         if (res == -ENOKEY)
 237                 res = 0;
 238         put_crypt_info(crypt_info);
 239         memzero_explicit(raw_key, sizeof(raw_key));
 240         return res;
 241 }
 242
 243 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 244 {
 245         struct fscrypt_info *prev;
 246
 247         if (ci == NULL)
 248                 ci = ACCESS_ONCE(inode->i_crypt_info);
 249         if (ci == NULL)
 250                 return;
 251
 252         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 253         if (prev != ci)
 254                 return;
 255
 256         put_crypt_info(ci);
 257 }
 258 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 259
 260 int fscrypt_get_encryption_info(struct inode *inode)
 261 {
 262         struct fscrypt_info *ci = inode->i_crypt_info;
 263
 264         if (!ci ||
 265                 (ci->ci_keyring_key &&
 266                  (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 267                                                (1 << KEY_FLAG_REVOKED) |
 268                                                (1 << KEY_FLAG_DEAD)))))
 269                 return get_crypt_info(inode);
 270         return 0;
 271 }
 272 EXPORT_SYMBOL(fscrypt_get_encryption_info);