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 <crypto/hash.h>
  17 #include <linux/fscrypto.h>
  18
  19 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  20 {
  21         struct fscrypt_completion_result *ecr = req->data;
  22
  23         if (rc == -EINPROGRESS)
  24                 return;
  25
  26         ecr->res = rc;
  27         complete(&ecr->completion);
  28 }
  29
  30 /**
  31  * derive_key_aes() - Derive a key using AES-128-ECB
  32  * @deriving_key: Encryption key used for derivation.
  33  * @source_key:   Source key to which to apply derivation.
  34  * @derived_key:  Derived key.
  35  *
  36  * Return: Zero on success; non-zero otherwise.
  37  */
  38 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  39                                 u8 source_key[FS_AES_256_XTS_KEY_SIZE],
  40                                 u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
  41 {
  42         int res = 0;
  43         struct ablkcipher_request *req = NULL;
  44         DECLARE_FS_COMPLETION_RESULT(ecr);
  45         struct scatterlist src_sg, dst_sg;
  46         struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
  47                                                                 0);
  48
  49         if (IS_ERR(tfm)) {
  50                 res = PTR_ERR(tfm);
  51                 tfm = NULL;
  52                 goto out;
  53         }
  54         crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  55         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
  56         if (!req) {
  57                 res = -ENOMEM;
  58                 goto out;
  59         }
  60         ablkcipher_request_set_callback(req,
  61                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  62                         derive_crypt_complete, &ecr);
  63         res = crypto_ablkcipher_setkey(tfm, deriving_key,
  64                                         FS_AES_128_ECB_KEY_SIZE);
  65         if (res < 0)
  66                 goto out;
  67
  68         sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
  69         sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
  70         ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
  71                                         FS_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 out:
  78         if (req)
  79                 ablkcipher_request_free(req);
  80         if (tfm)
  81                 crypto_free_ablkcipher(tfm);
  82         return res;
  83 }
  84
  85 static void put_crypt_info(struct fscrypt_info *ci)
  86 {
  87         if (!ci)
  88                 return;
  89
  90         if (ci->ci_keyring_key)
  91                 key_put(ci->ci_keyring_key);
  92         crypto_free_ablkcipher(ci->ci_ctfm);
  93         kmem_cache_free(fscrypt_info_cachep, ci);
  94 }
  95
  96 int get_crypt_info(struct inode *inode)
  97 {
  98         struct fscrypt_info *crypt_info;
  99         u8 full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
 100                                 (FS_KEY_DESCRIPTOR_SIZE * 2) + 1];
 101         struct key *keyring_key = NULL;
 102         struct fscrypt_key *master_key;
 103         struct fscrypt_context ctx;
 104         const struct user_key_payload *ukp;
 105         struct crypto_ablkcipher *ctfm;
 106         const char *cipher_str;
 107         u8 raw_key[FS_MAX_KEY_SIZE];
 108         u8 mode;
 109         int res;
 110
 111         res = fscrypt_initialize();
 112         if (res)
 113                 return res;
 114
 115         if (!inode->i_sb->s_cop->get_context)
 116                 return -EOPNOTSUPP;
 117 retry:
 118         crypt_info = ACCESS_ONCE(inode->i_crypt_info);
 119         if (crypt_info) {
 120                 if (!crypt_info->ci_keyring_key ||
 121                                 key_validate(crypt_info->ci_keyring_key) == 0)
 122                         return 0;
 123                 fscrypt_put_encryption_info(inode, crypt_info);
 124                 goto retry;
 125         }
 126
 127         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 128         if (res < 0) {
 129                 if (!fscrypt_dummy_context_enabled(inode))
 130                         return res;
 131                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 132                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 133                 ctx.flags = 0;
 134         } else if (res != sizeof(ctx)) {
 135                 return -EINVAL;
 136         }
 137         res = 0;
 138
 139         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 140         if (!crypt_info)
 141                 return -ENOMEM;
 142
 143         crypt_info->ci_flags = ctx.flags;
 144         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 145         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 146         crypt_info->ci_ctfm = NULL;
 147         crypt_info->ci_keyring_key = NULL;
 148         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 149                                 sizeof(crypt_info->ci_master_key));
 150         if (S_ISREG(inode->i_mode))
 151                 mode = crypt_info->ci_data_mode;
 152         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 153                 mode = crypt_info->ci_filename_mode;
 154         else
 155                 BUG();
 156
 157         switch (mode) {
 158         case FS_ENCRYPTION_MODE_AES_256_XTS:
 159                 cipher_str = "xts(aes)";
 160                 break;
 161         case FS_ENCRYPTION_MODE_AES_256_CTS:
 162                 cipher_str = "cts(cbc(aes))";
 163                 break;
 164         default:
 165                 printk_once(KERN_WARNING
 166                             "%s: unsupported key mode %d (ino %u)\n",
 167                             __func__, mode, (unsigned) inode->i_ino);
 168                 res = -ENOKEY;
 169                 goto out;
 170         }
 171         if (fscrypt_dummy_context_enabled(inode)) {
 172                 memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
 173                 goto got_key;
 174         }
 175         memcpy(full_key_descriptor, FS_KEY_DESC_PREFIX,
 176                                         FS_KEY_DESC_PREFIX_SIZE);
 177         sprintf(full_key_descriptor + FS_KEY_DESC_PREFIX_SIZE,
 178                                         "%*phN", FS_KEY_DESCRIPTOR_SIZE,
 179                                         ctx.master_key_descriptor);
 180         full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
 181                                         (2 * FS_KEY_DESCRIPTOR_SIZE)] = '\0';
 182         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 183         if (IS_ERR(keyring_key)) {
 184                 res = PTR_ERR(keyring_key);
 185                 keyring_key = NULL;
 186                 goto out;
 187         }
 188         crypt_info->ci_keyring_key = keyring_key;
 189         if (keyring_key->type != &key_type_logon) {
 190                 printk_once(KERN_WARNING
 191                                 "%s: key type must be logon\n", __func__);
 192                 res = -ENOKEY;
 193                 goto out;
 194         }
 195         down_read(&keyring_key->sem);
 196         ukp = user_key_payload(keyring_key);
 197         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 198                 res = -EINVAL;
 199                 up_read(&keyring_key->sem);
 200                 goto out;
 201         }
 202         master_key = (struct fscrypt_key *)ukp->data;
 203         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 204
 205         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 206                 printk_once(KERN_WARNING
 207                                 "%s: key size incorrect: %d\n",
 208                                 __func__, master_key->size);
 209                 res = -ENOKEY;
 210                 up_read(&keyring_key->sem);
 211                 goto out;
 212         }
 213         res = derive_key_aes(ctx.nonce, master_key->raw, raw_key);
 214         up_read(&keyring_key->sem);
 215         if (res)
 216                 goto out;
 217 got_key:
 218         ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
 219         if (!ctfm || IS_ERR(ctfm)) {
 220                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 221                 printk(KERN_DEBUG
 222                        "%s: error %d (inode %u) allocating crypto tfm\n",
 223                        __func__, res, (unsigned) inode->i_ino);
 224                 goto out;
 225         }
 226         crypt_info->ci_ctfm = ctfm;
 227         crypto_ablkcipher_clear_flags(ctfm, ~0);
 228         crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
 229                                         CRYPTO_TFM_REQ_WEAK_KEY);
 230         res = crypto_ablkcipher_setkey(ctfm, raw_key, fscrypt_key_size(mode));
 231         if (res)
 232                 goto out;
 233
 234         memzero_explicit(raw_key, sizeof(raw_key));
 235         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
 236                 put_crypt_info(crypt_info);
 237                 goto retry;
 238         }
 239         return 0;
 240
 241 out:
 242         if (res == -ENOKEY)
 243                 res = 0;
 244         put_crypt_info(crypt_info);
 245         memzero_explicit(raw_key, sizeof(raw_key));
 246         return res;
 247 }
 248
 249 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 250 {
 251         struct fscrypt_info *prev;
 252
 253         if (ci == NULL)
 254                 ci = ACCESS_ONCE(inode->i_crypt_info);
 255         if (ci == NULL)
 256                 return;
 257
 258         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 259         if (prev != ci)
 260                 return;
 261
 262         put_crypt_info(ci);
 263 }
 264 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 265
 266 int fscrypt_get_encryption_info(struct inode *inode)
 267 {
 268         struct fscrypt_info *ci = inode->i_crypt_info;
 269
 270         if (!ci ||
 271                 (ci->ci_keyring_key &&
 272                  (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 273                                                (1 << KEY_FLAG_REVOKED) |
 274                                                (1 << KEY_FLAG_DEAD)))))
 275                 return get_crypt_info(inode);
 276         return 0;
 277 }
 278 EXPORT_SYMBOL(fscrypt_get_encryption_info);