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![Theodore Ts'o](/assets/img/avatar_default.png)
This obscures the length of the filenames, to decrease the amount of information leakage. By default, we pad the filenames to the next 4 byte boundaries. This costs nothing, since the directory entries are aligned to 4 byte boundaries anyway. Filenames can also be padded to 8, 16, or 32 bytes, which will consume more directory space. Change-Id: Ibb7a0fb76d2c48e2061240a709358ff40b14f322 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
166 lines
4.7 KiB
C
166 lines
4.7 KiB
C
/*
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* linux/fs/ext4/crypto_key.c
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* This contains encryption key functions for ext4
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*
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* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
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*/
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#include <keys/encrypted-type.h>
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#include <keys/user-type.h>
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#include <linux/random.h>
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#include <linux/scatterlist.h>
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#include <uapi/linux/keyctl.h>
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#include "ext4.h"
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#include "xattr.h"
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static void derive_crypt_complete(struct crypto_async_request *req, int rc)
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{
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struct ext4_completion_result *ecr = req->data;
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if (rc == -EINPROGRESS)
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return;
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ecr->res = rc;
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complete(&ecr->completion);
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}
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/**
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* ext4_derive_key_aes() - Derive a key using AES-128-ECB
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* @deriving_key: Encryption key used for derivatio.
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* @source_key: Source key to which to apply derivation.
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* @derived_key: Derived key.
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*
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* Return: Zero on success; non-zero otherwise.
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*/
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static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
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char source_key[EXT4_AES_256_XTS_KEY_SIZE],
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char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
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{
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int res = 0;
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struct ablkcipher_request *req = NULL;
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DECLARE_EXT4_COMPLETION_RESULT(ecr);
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struct scatterlist src_sg, dst_sg;
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struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
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0);
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if (IS_ERR(tfm)) {
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res = PTR_ERR(tfm);
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tfm = NULL;
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goto out;
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}
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crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
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req = ablkcipher_request_alloc(tfm, GFP_NOFS);
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if (!req) {
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res = -ENOMEM;
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goto out;
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}
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ablkcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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derive_crypt_complete, &ecr);
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res = crypto_ablkcipher_setkey(tfm, deriving_key,
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EXT4_AES_128_ECB_KEY_SIZE);
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if (res < 0)
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goto out;
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sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
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sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
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ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
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EXT4_AES_256_XTS_KEY_SIZE, NULL);
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res = crypto_ablkcipher_encrypt(req);
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if (res == -EINPROGRESS || res == -EBUSY) {
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BUG_ON(req->base.data != &ecr);
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wait_for_completion(&ecr.completion);
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res = ecr.res;
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}
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out:
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if (req)
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ablkcipher_request_free(req);
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if (tfm)
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crypto_free_ablkcipher(tfm);
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return res;
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}
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/**
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* ext4_generate_encryption_key() - generates an encryption key
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* @inode: The inode to generate the encryption key for.
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*/
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int ext4_generate_encryption_key(struct inode *inode)
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{
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struct ext4_inode_info *ei = EXT4_I(inode);
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struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
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char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
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(EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
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struct key *keyring_key = NULL;
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struct ext4_encryption_key *master_key;
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struct ext4_encryption_context ctx;
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struct user_key_payload *ukp;
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struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
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int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
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&ctx, sizeof(ctx));
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if (res != sizeof(ctx)) {
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if (res > 0)
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res = -EINVAL;
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goto out;
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}
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res = 0;
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ei->i_crypt_policy_flags = ctx.flags;
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if (S_ISREG(inode->i_mode))
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crypt_key->mode = ctx.contents_encryption_mode;
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else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
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crypt_key->mode = ctx.filenames_encryption_mode;
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else {
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printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
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BUG();
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}
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crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
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BUG_ON(!crypt_key->size);
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if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
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memset(crypt_key->raw, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
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goto out;
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}
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memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
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EXT4_KEY_DESC_PREFIX_SIZE);
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sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
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"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
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ctx.master_key_descriptor);
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full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
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(2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
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keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
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if (IS_ERR(keyring_key)) {
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res = PTR_ERR(keyring_key);
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keyring_key = NULL;
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goto out;
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}
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BUG_ON(keyring_key->type != &key_type_logon);
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ukp = ((struct user_key_payload *)keyring_key->payload.data);
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if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
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res = -EINVAL;
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goto out;
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}
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master_key = (struct ext4_encryption_key *)ukp->data;
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BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
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EXT4_KEY_DERIVATION_NONCE_SIZE);
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BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
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res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
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out:
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if (keyring_key)
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key_put(keyring_key);
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if (res < 0)
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crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
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return res;
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}
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int ext4_has_encryption_key(struct inode *inode)
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{
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struct ext4_inode_info *ei = EXT4_I(inode);
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struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
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return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
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}
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