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/user-type.h>
  12 #include <linux/scatterlist.h>
  13 #include "fscrypt_private.h"
  14
  15 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
  16 {
  17         struct fscrypt_completion_result *ecr = req->data;
  18
  19         if (rc == -EINPROGRESS)
  20                 return;
  21
  22         ecr->res = rc;
  23         complete(&ecr->completion);
  24 }
  25
  26 /**
  27  * derive_key_aes() - Derive a key using AES-128-ECB
  28  * @deriving_key: Encryption key used for derivation.
  29  * @source_key:   Source key to which to apply derivation.
  30  * @derived_key:  Derived key.
  31  *
  32  * Return: Zero on success; non-zero otherwise.
  33  */
  34 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
  35                                 u8 source_key[FS_AES_256_XTS_KEY_SIZE],
  36                                 u8 derived_key[FS_AES_256_XTS_KEY_SIZE])
  37 {
  38         int res = 0;
  39         struct skcipher_request *req = NULL;
  40         DECLARE_FS_COMPLETION_RESULT(ecr);
  41         struct scatterlist src_sg, dst_sg;
  42         struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
  43
  44         if (IS_ERR(tfm)) {
  45                 res = PTR_ERR(tfm);
  46                 tfm = NULL;
  47                 goto out;
  48         }
  49         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
  50         req = skcipher_request_alloc(tfm, GFP_NOFS);
  51         if (!req) {
  52                 res = -ENOMEM;
  53                 goto out;
  54         }
  55         skcipher_request_set_callback(req,
  56                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  57                         derive_crypt_complete, &ecr);
  58         res = crypto_skcipher_setkey(tfm, deriving_key,
  59                                         FS_AES_128_ECB_KEY_SIZE);
  60         if (res < 0)
  61                 goto out;
  62
  63         sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE);
  64         sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE);
  65         skcipher_request_set_crypt(req, &src_sg, &dst_sg,
  66                                         FS_AES_256_XTS_KEY_SIZE, NULL);
  67         res = crypto_skcipher_encrypt(req);
  68         if (res == -EINPROGRESS || res == -EBUSY) {
  69                 wait_for_completion(&ecr.completion);
  70                 res = ecr.res;
  71         }
  72 out:
  73         skcipher_request_free(req);
  74         crypto_free_skcipher(tfm);
  75         return res;
  76 }
  77
  78 static int validate_user_key(struct fscrypt_info *crypt_info,
  79                         struct fscrypt_context *ctx, u8 *raw_key,
  80                         const char *prefix)
  81 {
  82         char *description;
  83         struct key *keyring_key;
  84         struct fscrypt_key *master_key;
  85         const struct user_key_payload *ukp;
  86         int res;
  87
  88         description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
  89                                 FS_KEY_DESCRIPTOR_SIZE,
  90                                 ctx->master_key_descriptor);
  91         if (!description)
  92                 return -ENOMEM;
  93
  94         keyring_key = request_key(&key_type_logon, description, NULL);
  95         kfree(description);
  96         if (IS_ERR(keyring_key))
  97                 return PTR_ERR(keyring_key);
  98         down_read(&keyring_key->sem);
  99
 100         if (keyring_key->type != &key_type_logon) {
 101                 printk_once(KERN_WARNING
 102                                 "%s: key type must be logon\n", __func__);
 103                 res = -ENOKEY;
 104                 goto out;
 105         }
 106         ukp = user_key_payload_locked(keyring_key);
 107         if (ukp->datalen != sizeof(struct fscrypt_key)) {
 108                 res = -EINVAL;
 109                 goto out;
 110         }
 111         master_key = (struct fscrypt_key *)ukp->data;
 112         BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 113
 114         if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
 115                 printk_once(KERN_WARNING
 116                                 "%s: key size incorrect: %d\n",
 117                                 __func__, master_key->size);
 118                 res = -ENOKEY;
 119                 goto out;
 120         }
 121         res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
 122 out:
 123         up_read(&keyring_key->sem);
 124         key_put(keyring_key);
 125         return res;
 126 }
 127
 128 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
 129                                  const char **cipher_str_ret, int *keysize_ret)
 130 {
 131         if (S_ISREG(inode->i_mode)) {
 132                 if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) {
 133                         *cipher_str_ret = "xts(aes)";
 134                         *keysize_ret = FS_AES_256_XTS_KEY_SIZE;
 135                         return 0;
 136                 }
 137                 pr_warn_once("fscrypto: unsupported contents encryption mode "
 138                              "%d for inode %lu\n",
 139                              ci->ci_data_mode, inode->i_ino);
 140                 return -ENOKEY;
 141         }
 142
 143         if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
 144                 if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
 145                         *cipher_str_ret = "cts(cbc(aes))";
 146                         *keysize_ret = FS_AES_256_CTS_KEY_SIZE;
 147                         return 0;
 148                 }
 149                 pr_warn_once("fscrypto: unsupported filenames encryption mode "
 150                              "%d for inode %lu\n",
 151                              ci->ci_filename_mode, inode->i_ino);
 152                 return -ENOKEY;
 153         }
 154
 155         pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n",
 156                      (inode->i_mode & S_IFMT), inode->i_ino);
 157         return -ENOKEY;
 158 }
 159
 160 static void put_crypt_info(struct fscrypt_info *ci)
 161 {
 162         if (!ci)
 163                 return;
 164
 165         crypto_free_skcipher(ci->ci_ctfm);
 166         kmem_cache_free(fscrypt_info_cachep, ci);
 167 }
 168
 169 int fscrypt_get_encryption_info(struct inode *inode)
 170 {
 171         struct fscrypt_info *crypt_info;
 172         struct fscrypt_context ctx;
 173         struct crypto_skcipher *ctfm;
 174         const char *cipher_str;
 175         int keysize;
 176         u8 *raw_key = NULL;
 177         int res;
 178
 179         if (inode->i_crypt_info)
 180                 return 0;
 181
 182         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 183         if (res)
 184                 return res;
 185
 186         if (!inode->i_sb->s_cop->get_context)
 187                 return -EOPNOTSUPP;
 188
 189         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 190         if (res < 0) {
 191                 if (!fscrypt_dummy_context_enabled(inode) ||
 192                     inode->i_sb->s_cop->is_encrypted(inode))
 193                         return res;
 194                 /* Fake up a context for an unencrypted directory */
 195                 memset(&ctx, 0, sizeof(ctx));
 196                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 197                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 198                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 199                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 200         } else if (res != sizeof(ctx)) {
 201                 return -EINVAL;
 202         }
 203
 204         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 205                 return -EINVAL;
 206
 207         if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
 208                 return -EINVAL;
 209
 210         crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
 211         if (!crypt_info)
 212                 return -ENOMEM;
 213
 214         crypt_info->ci_flags = ctx.flags;
 215         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 216         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 217         crypt_info->ci_ctfm = NULL;
 218         memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
 219                                 sizeof(crypt_info->ci_master_key));
 220
 221         res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
 222         if (res)
 223                 goto out;
 224
 225         /*
 226          * This cannot be a stack buffer because it is passed to the scatterlist
 227          * crypto API as part of key derivation.
 228          */
 229         res = -ENOMEM;
 230         raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
 231         if (!raw_key)
 232                 goto out;
 233
 234         res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX);
 235         if (res && inode->i_sb->s_cop->key_prefix) {
 236                 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
 237                                              inode->i_sb->s_cop->key_prefix);
 238                 if (res2) {
 239                         if (res2 == -ENOKEY)
 240                                 res = -ENOKEY;
 241                         goto out;
 242                 }
 243         } else if (res) {
 244                 goto out;
 245         }
 246         ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
 247         if (!ctfm || IS_ERR(ctfm)) {
 248                 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
 249                 printk(KERN_DEBUG
 250                        "%s: error %d (inode %u) allocating crypto tfm\n",
 251                        __func__, res, (unsigned) inode->i_ino);
 252                 goto out;
 253         }
 254         crypt_info->ci_ctfm = ctfm;
 255         crypto_skcipher_clear_flags(ctfm, ~0);
 256         crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
 257         res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
 258         if (res)
 259                 goto out;
 260
 261         if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
 262                 crypt_info = NULL;
 263 out:
 264         if (res == -ENOKEY)
 265                 res = 0;
 266         put_crypt_info(crypt_info);
 267         kzfree(raw_key);
 268         return res;
 269 }
 270 EXPORT_SYMBOL(fscrypt_get_encryption_info);
 271
 272 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
 273 {
 274         struct fscrypt_info *prev;
 275
 276         if (ci == NULL)
 277                 ci = ACCESS_ONCE(inode->i_crypt_info);
 278         if (ci == NULL)
 279                 return;
 280
 281         prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
 282         if (prev != ci)
 283                 return;
 284
 285         put_crypt_info(ci);
 286 }
 287 EXPORT_SYMBOL(fscrypt_put_encryption_info);