kernel/fs/ext4/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 derivatio.
  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                 BUG_ON(req->base.data != &ecr);
  75                 wait_for_completion(&ecr.completion);
  76                 res = ecr.res;
  77         }
  78
  79 out:
  80         if (req)
  81                 ablkcipher_request_free(req);
  82         if (tfm)
  83                 crypto_free_ablkcipher(tfm);
  84         return res;
  85 }
  86
  87 /**
  88  * ext4_generate_encryption_key() - generates an encryption key
  89  * @inode: The inode to generate the encryption key for.
  90  */
  91 int ext4_generate_encryption_key(struct inode *inode)
  92 {
  93         struct ext4_inode_info *ei = EXT4_I(inode);
  94         struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
  95         char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
  96                                  (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
  97         struct key *keyring_key = NULL;
  98         struct ext4_encryption_key *master_key;
  99         struct ext4_encryption_context ctx;
 100         struct user_key_payload *ukp;
 101         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 102         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 103                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 104                                  &ctx, sizeof(ctx));
 105
 106         if (res != sizeof(ctx)) {
 107                 if (res > 0)
 108                         res = -EINVAL;
 109                 goto out;
 110         }
 111         res = 0;
 112
 113         ei->i_crypt_policy_flags = ctx.flags;
 114         if (S_ISREG(inode->i_mode))
 115                 crypt_key->mode = ctx.contents_encryption_mode;
 116         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 117                 crypt_key->mode = ctx.filenames_encryption_mode;
 118         else {
 119                 printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
 120                 BUG();
 121         }
 122         crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
 123         BUG_ON(!crypt_key->size);
 124         if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
 125                 memset(crypt_key->raw, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
 126                 goto out;
 127         }
 128         memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
 129                EXT4_KEY_DESC_PREFIX_SIZE);
 130         sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
 131                 "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
 132                 ctx.master_key_descriptor);
 133         full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
 134                             (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
 135         keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
 136         if (IS_ERR(keyring_key)) {
 137                 res = PTR_ERR(keyring_key);
 138                 keyring_key = NULL;
 139                 goto out;
 140         }
 141         BUG_ON(keyring_key->type != &key_type_logon);
 142         ukp = ((struct user_key_payload *)keyring_key->payload.data);
 143         if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 144                 res = -EINVAL;
 145                 goto out;
 146         }
 147         master_key = (struct ext4_encryption_key *)ukp->data;
 148         BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
 149                      EXT4_KEY_DERIVATION_NONCE_SIZE);
 150         BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
 151         res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
 152 out:
 153         if (keyring_key)
 154                 key_put(keyring_key);
 155         if (res < 0)
 156                 crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
 157         return res;
 158 }
 159
 160 int ext4_has_encryption_key(struct inode *inode)
 161 {
 162         struct ext4_inode_info *ei = EXT4_I(inode);
 163         struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
 164
 165         return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
 166 }