// SPDX-License-Identifier: GPL-2.0
/*
- * key management facility for FS encryption support.
+ * Key setup facility for FS encryption support.
*
* Copyright (C) 2015, Google, Inc.
*
- * This contains encryption key functions.
- *
- * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
+ * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
+ * Heavily modified since then.
*/
#include <keys/user-type.h>
static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);
/*
- * Key derivation function. This generates the derived key by encrypting the
- * master key with AES-128-ECB using the inode's nonce as the AES key.
+ * v1 key derivation function. This generates the derived key by encrypting the
+ * master key with AES-128-ECB using the nonce as the AES key. This provides a
+ * unique derived key with sufficient entropy for each inode. However, it's
+ * nonstandard, non-extensible, doesn't evenly distribute the entropy from the
+ * master key, and is trivially reversible: an attacker who compromises a
+ * derived key can "decrypt" it to get back to the master key, then derive any
+ * other key. For all new code, use HKDF instead.
*
* The master key must be at least as long as the derived key. If the master
* key is longer, then only the first 'derived_keysize' bytes are used.
*/
static int derive_key_aes(const u8 *master_key,
- const struct fscrypt_context *ctx,
+ const u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE],
u8 *derived_key, unsigned int derived_keysize)
{
int res = 0;
skcipher_request_set_callback(req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
crypto_req_done, &wait);
- res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
+ res = crypto_skcipher_setkey(tfm, nonce, FS_KEY_DERIVATION_NONCE_SIZE);
if (res < 0)
goto out;
return ERR_PTR(-EINVAL);
}
-/* Find the master key, then derive the inode's actual encryption key */
-static int find_and_derive_key(const struct inode *inode,
- const struct fscrypt_context *ctx,
- u8 *derived_key, const struct fscrypt_mode *mode)
-{
- struct key *key;
- const struct fscrypt_key *payload;
- int err;
-
- key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
- ctx->master_key_descriptor,
- mode->keysize, &payload);
- if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
- key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
- ctx->master_key_descriptor,
- mode->keysize, &payload);
- }
- if (IS_ERR(key))
- return PTR_ERR(key);
-
- if (ctx->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
- if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
- fscrypt_warn(inode,
- "Direct key mode not allowed with %s",
- mode->friendly_name);
- err = -EINVAL;
- } else if (ctx->contents_encryption_mode !=
- ctx->filenames_encryption_mode) {
- fscrypt_warn(inode,
- "Direct key mode not allowed with different contents and filenames modes");
- err = -EINVAL;
- } else {
- memcpy(derived_key, payload->raw, mode->keysize);
- err = 0;
- }
- } else {
- err = derive_key_aes(payload->raw, ctx, derived_key,
- mode->keysize);
- }
- up_read(&key->sem);
- key_put(key);
- return err;
-}
-
-/* Allocate and key a symmetric cipher object for the given encryption mode */
+/* Create a symmetric cipher object for the given encryption mode and key */
static struct crypto_skcipher *
-allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
- const struct inode *inode)
+fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
+ const struct inode *inode)
{
struct crypto_skcipher *tfm;
int err;
*/
static struct fscrypt_direct_key *
find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
- const u8 *raw_key, const struct fscrypt_mode *mode,
- const struct fscrypt_info *ci)
+ const u8 *raw_key, const struct fscrypt_info *ci)
{
unsigned long hash_key;
struct fscrypt_direct_key *dk;
if (memcmp(ci->ci_master_key_descriptor, dk->dk_descriptor,
FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
continue;
- if (mode != dk->dk_mode)
+ if (ci->ci_mode != dk->dk_mode)
continue;
- if (crypto_memneq(raw_key, dk->dk_raw, mode->keysize))
+ if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
continue;
/* using existing tfm with same (descriptor, mode, raw_key) */
refcount_inc(&dk->dk_refcount);
/* Prepare to encrypt directly using the master key in the given mode */
static struct fscrypt_direct_key *
-fscrypt_get_direct_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
- const u8 *raw_key, const struct inode *inode)
+fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key)
{
struct fscrypt_direct_key *dk;
int err;
/* Is there already a tfm for this key? */
- dk = find_or_insert_direct_key(NULL, raw_key, mode, ci);
+ dk = find_or_insert_direct_key(NULL, raw_key, ci);
if (dk)
return dk;
if (!dk)
return ERR_PTR(-ENOMEM);
refcount_set(&dk->dk_refcount, 1);
- dk->dk_mode = mode;
- dk->dk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
+ dk->dk_mode = ci->ci_mode;
+ dk->dk_ctfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key,
+ ci->ci_inode);
if (IS_ERR(dk->dk_ctfm)) {
err = PTR_ERR(dk->dk_ctfm);
dk->dk_ctfm = NULL;
}
memcpy(dk->dk_descriptor, ci->ci_master_key_descriptor,
FSCRYPT_KEY_DESCRIPTOR_SIZE);
- memcpy(dk->dk_raw, raw_key, mode->keysize);
+ memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);
- return find_or_insert_direct_key(dk, raw_key, mode, ci);
+ return find_or_insert_direct_key(dk, raw_key, ci);
err_free_dk:
free_direct_key(dk);
struct crypto_cipher *essiv_tfm;
u8 salt[SHA256_DIGEST_SIZE];
+ if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
+ return -EINVAL;
+
essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
if (IS_ERR(essiv_tfm))
return PTR_ERR(essiv_tfm);
return err;
}
-/*
- * Given the encryption mode and key (normally the derived key, but for
- * DIRECT_KEY mode it's the master key), set up the inode's symmetric cipher
- * transform object(s).
- */
-static int setup_crypto_transform(struct fscrypt_info *ci,
- struct fscrypt_mode *mode,
- const u8 *raw_key, const struct inode *inode)
+/* Given the per-file key, set up the file's crypto transform object(s) */
+static int fscrypt_set_derived_key(struct fscrypt_info *ci,
+ const u8 *derived_key)
{
- struct fscrypt_direct_key *dk;
+ struct fscrypt_mode *mode = ci->ci_mode;
struct crypto_skcipher *ctfm;
int err;
- if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
- dk = fscrypt_get_direct_key(ci, mode, raw_key, inode);
- if (IS_ERR(dk))
- return PTR_ERR(dk);
- ctfm = dk->dk_ctfm;
- } else {
- dk = NULL;
- ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
- if (IS_ERR(ctfm))
- return PTR_ERR(ctfm);
- }
- ci->ci_direct_key = dk;
+ ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
+ if (IS_ERR(ctfm))
+ return PTR_ERR(ctfm);
+
ci->ci_ctfm = ctfm;
if (mode->needs_essiv) {
- /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
- WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
- WARN_ON(ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
-
- err = init_essiv_generator(ci, raw_key, mode->keysize);
+ err = init_essiv_generator(ci, derived_key, mode->keysize);
if (err) {
- fscrypt_warn(inode,
+ fscrypt_warn(ci->ci_inode,
"Error initializing ESSIV generator: %d",
err);
return err;
return 0;
}
+/* v1 policy, DIRECT_KEY: use the master key directly */
+static int setup_v1_file_key_direct(struct fscrypt_info *ci,
+ const u8 *raw_master_key)
+{
+ const struct fscrypt_mode *mode = ci->ci_mode;
+ struct fscrypt_direct_key *dk;
+
+ if (!fscrypt_mode_supports_direct_key(mode)) {
+ fscrypt_warn(ci->ci_inode,
+ "Direct key mode not allowed with %s",
+ mode->friendly_name);
+ return -EINVAL;
+ }
+
+ if (ci->ci_data_mode != ci->ci_filename_mode) {
+ fscrypt_warn(ci->ci_inode,
+ "Direct key mode not allowed with different contents and filenames modes");
+ return -EINVAL;
+ }
+
+ /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
+ if (WARN_ON(mode->needs_essiv))
+ return -EINVAL;
+
+ dk = fscrypt_get_direct_key(ci, raw_master_key);
+ if (IS_ERR(dk))
+ return PTR_ERR(dk);
+ ci->ci_direct_key = dk;
+ ci->ci_ctfm = dk->dk_ctfm;
+ return 0;
+}
+
+/* v1 policy, !DIRECT_KEY: derive the file's encryption key */
+static int setup_v1_file_key_derived(struct fscrypt_info *ci,
+ const u8 *raw_master_key)
+{
+ u8 *derived_key;
+ int err;
+
+ /*
+ * This cannot be a stack buffer because it will be passed to the
+ * scatterlist crypto API during derive_key_aes().
+ */
+ derived_key = kmalloc(ci->ci_mode->keysize, GFP_NOFS);
+ if (!derived_key)
+ return -ENOMEM;
+
+ err = derive_key_aes(raw_master_key, ci->ci_nonce,
+ derived_key, ci->ci_mode->keysize);
+ if (err)
+ goto out;
+
+ err = fscrypt_set_derived_key(ci, derived_key);
+out:
+ kzfree(derived_key);
+ return err;
+}
+
+static int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
+ const u8 *raw_master_key)
+{
+ if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
+ return setup_v1_file_key_direct(ci, raw_master_key);
+ else
+ return setup_v1_file_key_derived(ci, raw_master_key);
+}
+
+static int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
+ struct fscrypt_info *ci)
+{
+ struct key *key;
+ const struct fscrypt_key *payload;
+ int err;
+
+ key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
+ ci->ci_master_key_descriptor,
+ ci->ci_mode->keysize, &payload);
+ if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
+ key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
+ ci->ci_master_key_descriptor,
+ ci->ci_mode->keysize, &payload);
+ }
+ if (IS_ERR(key))
+ return PTR_ERR(key);
+
+ err = fscrypt_setup_v1_file_key(ci, payload->raw);
+ up_read(&key->sem);
+ key_put(key);
+ return err;
+}
+
+/*
+ * Find the master key, then set up the inode's actual encryption key.
+ */
+static int setup_file_encryption_key(struct fscrypt_info *ci)
+{
+ return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
+}
+
static void put_crypt_info(struct fscrypt_info *ci)
{
if (!ci)
struct fscrypt_info *crypt_info;
struct fscrypt_context ctx;
struct fscrypt_mode *mode;
- u8 *raw_key = NULL;
int res;
if (fscrypt_has_encryption_key(inode))
WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
crypt_info->ci_mode = mode;
- /*
- * This cannot be a stack buffer because it may be passed to the
- * scatterlist crypto API as part of key derivation.
- */
- res = -ENOMEM;
- raw_key = kmalloc(mode->keysize, GFP_NOFS);
- if (!raw_key)
- goto out;
-
- res = find_and_derive_key(inode, &ctx, raw_key, mode);
- if (res)
- goto out;
-
- res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
+ res = setup_file_encryption_key(crypt_info);
if (res)
goto out;
if (res == -ENOKEY)
res = 0;
put_crypt_info(crypt_info);
- kzfree(raw_key);
return res;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);
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