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 int validate_user_key(struct fscrypt_info *crypt_info,
  82                         struct fscrypt_context *ctx, u8 *raw_key,
  83                         u8 *prefix, int prefix_size)
  84 {
  85         u8 *full_key_descriptor;
  86         struct key *keyring_key;
  87         struct fscrypt_key *master_key;
  88         const struct user_key_payload *ukp;
  89         int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
  90         int res;
  91
  92         full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
  93         if (!full_key_descriptor)
  94                 return -ENOMEM;
  95
  96         memcpy(full_key_descriptor, prefix, prefix_size);
  97         sprintf(full_key_descriptor + prefix_size,
  98                         "%*phN", FS_KEY_DESCRIPTOR_SIZE,
  99                         ctx->master_key_descriptor);
 100         full_key_descriptor[full_key_len - 1] = '\0';
 101         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 102         kfree(full_key_descriptor);
 103         if (IS_ERR(keyring_key))
 104                 return PTR_ERR(keyring_key);
 105
 106         if (keyring_key->type != &key_type_logon) {
 107                 printk_once(KERN_WARNING
 108                                 "%s: key type must be logon\n", __func__);
 109                 res = -ENOKEY;
 110                 goto out;
 111         }
 112         down_read(&keyring_key->sem);
 113         ukp = user_key_payload(keyring_key);
 114         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 115                 res = -EINVAL;
 116                 up_read(&keyring_key->sem);
 117                 goto out;
 118         }
 119         master_key = (struct fscrypt_key *)ukp->data;
 120         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 121
 122         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 123                 printk_once(KERN_WARNING
 124                                 "%s: key size incorrect: %d\n",
 125                                 __func__, master_key->size);
 126                 res = -ENOKEY;
 127                 up_read(&keyring_key->sem);
 128                 goto out;
 129         }
 130         res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
 131         up_read(&keyring_key->sem);
 132         if (res)
 133                 goto out;
 134
 135         crypt_info->ci_keyring_key = keyring_key;
 136         return 0;
 137 out:
 138         key_put(keyring_key);
 139         return res;
 140 }
 141
 142 static void put_crypt_info(struct fscrypt_info *ci)
 143 {
 144         if (!ci)
 145                 return;
 146
 147         key_put(ci->ci_keyring_key);
 148         crypto_free_skcipher(ci->ci_ctfm);
 149         kmem_cache_free(fscrypt_info_cachep, ci);
 150 }
 151
 152 int get_crypt_info(struct inode *inode)
 153 {
 154         struct fscrypt_info *crypt_info;
 155         struct fscrypt_context ctx;
 156         struct crypto_skcipher *ctfm;
 157         const char *cipher_str;
 158         u8 raw_key[FS_MAX_KEY_SIZE];
 159         u8 mode;
 160         int res;
 161
 162         res = fscrypt_initialize();
 163         if (res)
 164                 return res;
 165
 166         if (!inode->i_sb->s_cop->get_context)
 167                 return -EOPNOTSUPP;
 168 retry:
 169         crypt_info = ACCESS_ONCE(inode->i_crypt_info);
 170         if (crypt_info) {
 171                 if (!crypt_info->ci_keyring_key ||
 172                                 key_validate(crypt_info->ci_keyring_key) == 0)
 173                         return 0;
 174                 fscrypt_put_encryption_info(inode, crypt_info);
 175                 goto retry;
 176         }
 177
 178         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 179         if (res < 0) {
 180                 if (!fscrypt_dummy_context_enabled(inode))
 181                         return res;
 182                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 183                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 184                 ctx.flags = 0;
 185         } else if (res != sizeof(ctx)) {
 186                 return -EINVAL;
 187         }
 188         res = 0;
 189
 190         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 191         if (!crypt_info)
 192                 return -ENOMEM;
 193
 194         crypt_info->ci_flags = ctx.flags;
 195         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 196         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 197         crypt_info->ci_ctfm = NULL;
 198         crypt_info->ci_keyring_key = NULL;
 199         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 200                                 sizeof(crypt_info->ci_master_key));
 201         if (S_ISREG(inode->i_mode))
 202                 mode = crypt_info->ci_data_mode;
 203         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 204                 mode = crypt_info->ci_filename_mode;
 205         else
 206                 BUG();
 207
 208         switch (mode) {
 209         case FS_ENCRYPTION_MODE_AES_256_XTS:
 210                 cipher_str = "xts(aes)";
 211                 break;
 212         case FS_ENCRYPTION_MODE_AES_256_CTS:
 213                 cipher_str = "cts(cbc(aes))";
 214                 break;
 215         default:
 216                 printk_once(KERN_WARNING
 217                             "%s: unsupported key mode %d (ino %u)\n",
 218                             __func__, mode, (unsigned) inode->i_ino);
 219                 res = -ENOKEY;
 220                 goto out;
 221         }
 222         if (fscrypt_dummy_context_enabled(inode)) {
 223                 memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
 224                 goto got_key;
 225         }
 226
 227         res = validate_user_key(crypt_info, &ctx, raw_key,
 228                         FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
 229         if (res && inode->i_sb->s_cop->key_prefix) {
 230                 u8 *prefix = NULL;
 231                 int prefix_size, res2;
 232
 233                 prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
 234                 res2 = validate_user_key(crypt_info, &ctx, raw_key,
 235                                                         prefix, prefix_size);
 236                 if (res2) {
 237                         if (res2 == -ENOKEY)
 238                                 res = -ENOKEY;
 239                         goto out;
 240                 }
 241         } else if (res) {
 242                 goto out;
 243         }
 244 got_key:
 245         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 246         if (!ctfm || IS_ERR(ctfm)) {
 247                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 248                 printk(KERN_DEBUG
 249                        "%s: error %d (inode %u) allocating crypto tfm\n",
 250                        __func__, res, (unsigned) inode->i_ino);
 251                 goto out;
 252         }
 253         crypt_info->ci_ctfm = ctfm;
 254         crypto_skcipher_clear_flags(ctfm, ~0);
 255         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 256         res = crypto_skcipher_setkey(ctfm, raw_key, fscrypt_key_size(mode));
 257         if (res)
 258                 goto out;
 259
 260         memzero_explicit(raw_key, sizeof(raw_key));
 261         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {
 262                 put_crypt_info(crypt_info);
 263                 goto retry;
 264         }
 265         return 0;
 266
 267 out:
 268         if (res == -ENOKEY)
 269                 res = 0;
 270         put_crypt_info(crypt_info);
 271         memzero_explicit(raw_key, sizeof(raw_key));
 272         return res;
 273 }
 274
 275 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 276 {
 277         struct fscrypt_info *prev;
 278
 279         if (ci == NULL)
 280                 ci = ACCESS_ONCE(inode->i_crypt_info);
 281         if (ci == NULL)
 282                 return;
 283
 284         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 285         if (prev != ci)
 286                 return;
 287
 288         put_crypt_info(ci);
 289 }
 290 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 291
 292 int fscrypt_get_encryption_info(struct inode *inode)
 293 {
 294         struct fscrypt_info *ci = inode->i_crypt_info;
 295
 296         if (!ci ||
 297                 (ci->ci_keyring_key &&
 298                  (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 299                                                (1 << KEY_FLAG_REVOKED) |
 300                                                (1 << KEY_FLAG_DEAD)))))
 301                 return get_crypt_info(inode);
 302         return 0;
 303 }
 304 EXPORT_SYMBOL(fscrypt_get_encryption_info);