380 lines
8.7 KiB
C
380 lines
8.7 KiB
C
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/* Large capacity key type
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*
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* Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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* Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#define pr_fmt(fmt) "big_key: "fmt
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#include <linux/init.h>
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#include <linux/seq_file.h>
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#include <linux/file.h>
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#include <linux/shmem_fs.h>
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#include <linux/err.h>
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#include <linux/scatterlist.h>
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#include <linux/random.h>
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#include <keys/user-type.h>
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#include <keys/big_key-type.h>
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#include <crypto/aead.h>
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/*
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* Layout of key payload words.
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*/
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enum {
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big_key_data,
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big_key_path,
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big_key_path_2nd_part,
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big_key_len,
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};
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/*
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* Crypto operation with big_key data
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*/
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enum big_key_op {
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BIG_KEY_ENC,
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BIG_KEY_DEC,
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};
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/*
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* If the data is under this limit, there's no point creating a shm file to
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* hold it as the permanently resident metadata for the shmem fs will be at
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* least as large as the data.
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*/
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#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
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/*
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* Key size for big_key data encryption
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*/
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#define ENC_KEY_SIZE 32
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/*
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* Authentication tag length
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*/
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#define ENC_AUTHTAG_SIZE 16
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/*
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* big_key defined keys take an arbitrary string as the description and an
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* arbitrary blob of data as the payload
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*/
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struct key_type key_type_big_key = {
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.name = "big_key",
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.preparse = big_key_preparse,
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.free_preparse = big_key_free_preparse,
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.instantiate = generic_key_instantiate,
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.revoke = big_key_revoke,
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.destroy = big_key_destroy,
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.describe = big_key_describe,
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.read = big_key_read,
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/* no ->update(); don't add it without changing big_key_crypt() nonce */
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};
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/*
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* Crypto names for big_key data authenticated encryption
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*/
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static const char big_key_alg_name[] = "gcm(aes)";
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/*
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* Crypto algorithms for big_key data authenticated encryption
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*/
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static struct crypto_aead *big_key_aead;
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/*
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* Since changing the key affects the entire object, we need a mutex.
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*/
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static DEFINE_MUTEX(big_key_aead_lock);
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/*
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* Encrypt/decrypt big_key data
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*/
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static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
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{
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int ret;
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struct scatterlist sgio;
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struct aead_request *aead_req;
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/* We always use a zero nonce. The reason we can get away with this is
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* because we're using a different randomly generated key for every
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* different encryption. Notably, too, key_type_big_key doesn't define
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* an .update function, so there's no chance we'll wind up reusing the
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* key to encrypt updated data. Simply put: one key, one encryption.
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*/
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u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
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aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
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if (!aead_req)
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return -ENOMEM;
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memset(zero_nonce, 0, sizeof(zero_nonce));
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sg_init_one(&sgio, data, datalen + (op == BIG_KEY_ENC ? ENC_AUTHTAG_SIZE : 0));
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aead_request_set_crypt(aead_req, &sgio, &sgio, datalen, zero_nonce);
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aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
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aead_request_set_ad(aead_req, 0);
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mutex_lock(&big_key_aead_lock);
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if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
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ret = -EAGAIN;
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goto error;
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}
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if (op == BIG_KEY_ENC)
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ret = crypto_aead_encrypt(aead_req);
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else
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ret = crypto_aead_decrypt(aead_req);
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error:
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mutex_unlock(&big_key_aead_lock);
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aead_request_free(aead_req);
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return ret;
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}
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/*
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* Preparse a big key
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*/
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int big_key_preparse(struct key_preparsed_payload *prep)
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{
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struct path *path = (struct path *)&prep->payload.data[big_key_path];
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struct file *file;
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u8 *enckey;
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u8 *data = NULL;
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ssize_t written;
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size_t datalen = prep->datalen;
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int ret;
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ret = -EINVAL;
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if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
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goto error;
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/* Set an arbitrary quota */
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prep->quotalen = 16;
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prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
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if (datalen > BIG_KEY_FILE_THRESHOLD) {
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/* Create a shmem file to store the data in. This will permit the data
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* to be swapped out if needed.
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*
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* File content is stored encrypted with randomly generated key.
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*/
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size_t enclen = datalen + ENC_AUTHTAG_SIZE;
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data = kmalloc(enclen, GFP_KERNEL);
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if (!data)
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return -ENOMEM;
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memcpy(data, prep->data, datalen);
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/* generate random key */
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enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
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if (!enckey) {
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ret = -ENOMEM;
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goto error;
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}
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get_random_bytes(enckey, ENC_KEY_SIZE);
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/* encrypt aligned data */
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ret = big_key_crypt(BIG_KEY_ENC, data, datalen, enckey);
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if (ret)
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goto err_enckey;
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/* save aligned data to file */
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file = shmem_kernel_file_setup("", enclen, 0);
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if (IS_ERR(file)) {
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ret = PTR_ERR(file);
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goto err_enckey;
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}
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written = kernel_write(file, data, enclen, 0);
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if (written != enclen) {
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ret = written;
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if (written >= 0)
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ret = -ENOMEM;
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goto err_fput;
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}
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/* Pin the mount and dentry to the key so that we can open it again
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* later
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*/
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prep->payload.data[big_key_data] = enckey;
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*path = file->f_path;
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path_get(path);
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fput(file);
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kzfree(data);
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} else {
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/* Just store the data in a buffer */
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void *data = kmalloc(datalen, GFP_KERNEL);
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if (!data)
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return -ENOMEM;
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prep->payload.data[big_key_data] = data;
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memcpy(data, prep->data, prep->datalen);
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}
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return 0;
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err_fput:
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fput(file);
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err_enckey:
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kzfree(enckey);
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error:
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kzfree(data);
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return ret;
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}
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/*
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* Clear preparsement.
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*/
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void big_key_free_preparse(struct key_preparsed_payload *prep)
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{
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if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
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struct path *path = (struct path *)&prep->payload.data[big_key_path];
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path_put(path);
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}
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kzfree(prep->payload.data[big_key_data]);
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}
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/*
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* dispose of the links from a revoked keyring
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* - called with the key sem write-locked
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*/
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void big_key_revoke(struct key *key)
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{
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struct path *path = (struct path *)&key->payload.data[big_key_path];
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/* clear the quota */
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key_payload_reserve(key, 0);
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if (key_is_positive(key) &&
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(size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
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vfs_truncate(path, 0);
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}
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/*
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* dispose of the data dangling from the corpse of a big_key key
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*/
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void big_key_destroy(struct key *key)
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{
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size_t datalen = (size_t)key->payload.data[big_key_len];
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if (datalen > BIG_KEY_FILE_THRESHOLD) {
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struct path *path = (struct path *)&key->payload.data[big_key_path];
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path_put(path);
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path->mnt = NULL;
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path->dentry = NULL;
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}
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kzfree(key->payload.data[big_key_data]);
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key->payload.data[big_key_data] = NULL;
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}
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/*
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* describe the big_key key
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*/
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void big_key_describe(const struct key *key, struct seq_file *m)
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{
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size_t datalen = (size_t)key->payload.data[big_key_len];
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seq_puts(m, key->description);
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if (key_is_positive(key))
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seq_printf(m, ": %zu [%s]",
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datalen,
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datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
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}
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/*
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* read the key data
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* - the key's semaphore is read-locked
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*/
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long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
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{
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size_t datalen = (size_t)key->payload.data[big_key_len];
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long ret;
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if (!buffer || buflen < datalen)
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return datalen;
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if (datalen > BIG_KEY_FILE_THRESHOLD) {
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struct path *path = (struct path *)&key->payload.data[big_key_path];
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struct file *file;
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u8 *data;
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u8 *enckey = (u8 *)key->payload.data[big_key_data];
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size_t enclen = datalen + ENC_AUTHTAG_SIZE;
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data = kmalloc(enclen, GFP_KERNEL);
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if (!data)
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return -ENOMEM;
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file = dentry_open(path, O_RDONLY, current_cred());
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if (IS_ERR(file)) {
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ret = PTR_ERR(file);
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goto error;
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}
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/* read file to kernel and decrypt */
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ret = kernel_read(file, 0, data, enclen);
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if (ret >= 0 && ret != enclen) {
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ret = -EIO;
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goto err_fput;
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}
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ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
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if (ret)
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goto err_fput;
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ret = datalen;
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/* copy decrypted data to user */
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if (copy_to_user(buffer, data, datalen) != 0)
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ret = -EFAULT;
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err_fput:
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fput(file);
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error:
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kzfree(data);
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} else {
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ret = datalen;
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if (copy_to_user(buffer, key->payload.data[big_key_data],
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datalen) != 0)
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ret = -EFAULT;
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}
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return ret;
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}
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/*
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* Register key type
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*/
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static int __init big_key_init(void)
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{
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int ret;
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/* init block cipher */
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big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
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if (IS_ERR(big_key_aead)) {
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ret = PTR_ERR(big_key_aead);
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pr_err("Can't alloc crypto: %d\n", ret);
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return ret;
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}
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ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
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if (ret < 0) {
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pr_err("Can't set crypto auth tag len: %d\n", ret);
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goto free_aead;
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}
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ret = register_key_type(&key_type_big_key);
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if (ret < 0) {
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pr_err("Can't register type: %d\n", ret);
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goto free_aead;
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}
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return 0;
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free_aead:
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crypto_free_aead(big_key_aead);
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return ret;
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}
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late_initcall(big_key_init);
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