ext4 crypto: add encryption key management facilities

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 162 insertions, 0 deletions

diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c
new file mode 100644
index 000000000000..572bd97f58dd
--- /dev/null
+++ b/fs/ext4/crypto_key.c
@@ -0,0 +1,162 @@
+/*
+ * linux/fs/ext4/crypto_key.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption key functions for ext4
+ *
+ * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
+ */
+
+#include <keys/encrypted-type.h>
+#include <keys/user-type.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+#include <uapi/linux/keyctl.h>
+
+#include "ext4.h"
+#include "xattr.h"
+
+static void derive_crypt_complete(struct crypto_async_request *req, int rc)
+{
+	struct ext4_completion_result *ecr = req->data;
+
+	if (rc == -EINPROGRESS)
+		return;
+
+	ecr->res = rc;
+	complete(&ecr->completion);
+}
+
+/**
+ * ext4_derive_key_aes() - Derive a key using AES-128-ECB
+ * @deriving_key: Encryption key used for derivatio.
+ * @source_key:   Source key to which to apply derivation.
+ * @derived_key:  Derived key.
+ *
+ * Return: Zero on success; non-zero otherwise.
+ */
+static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
+			       char source_key[EXT4_AES_256_XTS_KEY_SIZE],
+			       char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
+{
+	int res = 0;
+	struct ablkcipher_request *req = NULL;
+	DECLARE_EXT4_COMPLETION_RESULT(ecr);
+	struct scatterlist src_sg, dst_sg;
+	struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
+								0);
+
+	if (IS_ERR(tfm)) {
+		res = PTR_ERR(tfm);
+		tfm = NULL;
+		goto out;
+	}
+	crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
+	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
+	if (!req) {
+		res = -ENOMEM;
+		goto out;
+	}
+	ablkcipher_request_set_callback(req,
+			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+			derive_crypt_complete, &ecr);
+	res = crypto_ablkcipher_setkey(tfm, deriving_key,
+				       EXT4_AES_128_ECB_KEY_SIZE);
+	if (res < 0)
+		goto out;
+	sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
+	sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
+	ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
+				     EXT4_AES_256_XTS_KEY_SIZE, NULL);
+	res = crypto_ablkcipher_encrypt(req);
+	if (res == -EINPROGRESS || res == -EBUSY) {
+		BUG_ON(req->base.data != &ecr);
+		wait_for_completion(&ecr.completion);
+		res = ecr.res;
+	}
+
+out:
+	if (req)
+		ablkcipher_request_free(req);
+	if (tfm)
+		crypto_free_ablkcipher(tfm);
+	return res;
+}
+
+/**
+ * ext4_generate_encryption_key() - generates an encryption key
+ * @inode: The inode to generate the encryption key for.
+ */
+int ext4_generate_encryption_key(struct inode *inode)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
+	char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
+				 (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
+	struct key *keyring_key = NULL;
+	struct ext4_encryption_key *master_key;
+	struct ext4_encryption_context ctx;
+	struct user_key_payload *ukp;
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+				 &ctx, sizeof(ctx));
+
+	if (res != sizeof(ctx)) {
+		if (res > 0)
+			res = -EINVAL;
+		goto out;
+	}
+	res = 0;
+
+	memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
+	       EXT4_KEY_DESC_PREFIX_SIZE);
+	sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
+		"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
+		ctx.master_key_descriptor);
+	full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
+			    (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
+	keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
+	if (IS_ERR(keyring_key)) {
+		res = PTR_ERR(keyring_key);
+		keyring_key = NULL;
+		goto out;
+	}
+	BUG_ON(keyring_key->type != &key_type_logon);
+	ukp = ((struct user_key_payload *)keyring_key->payload.data);
+	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
+		res = -EINVAL;
+		goto out;
+	}
+	master_key = (struct ext4_encryption_key *)ukp->data;
+
+	if (S_ISREG(inode->i_mode))
+		crypt_key->mode = ctx.contents_encryption_mode;
+	else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
+		crypt_key->mode = ctx.filenames_encryption_mode;
+	else {
+		printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
+		BUG();
+	}
+	crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
+	BUG_ON(!crypt_key->size);
+	BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
+		     EXT4_KEY_DERIVATION_NONCE_SIZE);
+	BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
+	BUG_ON(crypt_key->size < EXT4_AES_256_CBC_KEY_SIZE);
+	res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
+out:
+	if (keyring_key)
+		key_put(keyring_key);
+	if (res < 0)
+		crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
+	return res;
+}
+
+int ext4_has_encryption_key(struct inode *inode)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
+
+	return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
+}