fs/ext4/crypto_key.c

/*
 * 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;
	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
	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;

	ei->i_crypt_policy_flags = ctx.flags;
	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);
	if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
		memset(crypt_key->raw, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
		goto out;
	}
	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;
	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);
	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);
}