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![Kees Cook](/assets/img/avatar_default.png)
The randstruct GCC plugin gets upset when it sees struct path (which is randomized) being assigned from a "void *" (which it cannot type-check). There's no need for these casts, as the entire internal payload use is following a normal struct layout. Convert the enum-based void * offset dereferencing to the new big_key_payload struct. No meaningful machine code changes result after this change, and source readability is improved. Drop the randstruct exception now that there is no "confusing" cross-type assignment. Cc: David Howells <dhowells@redhat.com> Cc: Eric Biggers <ebiggers@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Cc: Jarkko Sakkinen <jarkko@kernel.org> Cc: James Morris <jmorris@namei.org> Cc: "Serge E. Hallyn" <serge@hallyn.com> Cc: linux-hardening@vger.kernel.org Cc: keyrings@vger.kernel.org Cc: linux-security-module@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org>
290 lines
6.5 KiB
C
290 lines
6.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Large capacity key type
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*
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* Copyright (C) 2017-2020 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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#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/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/chacha20poly1305.h>
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/*
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* Layout of key payload words.
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*/
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struct big_key_payload {
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u8 *data;
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struct path path;
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size_t length;
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};
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#define to_big_key_payload(payload) \
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(struct big_key_payload *)((payload).data)
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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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* 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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.update = big_key_update,
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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 big_key_payload *payload = to_big_key_payload(prep->payload);
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struct file *file;
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u8 *buf, *enckey;
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ssize_t written;
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size_t datalen = prep->datalen;
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size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
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int ret;
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BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data));
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if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
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return -EINVAL;
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/* Set an arbitrary quota */
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prep->quotalen = 16;
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payload->length = 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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* Since the key is random for each file, we can set the nonce
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* to zero, provided we never define a ->update() call.
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*/
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loff_t pos = 0;
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buf = kvmalloc(enclen, GFP_KERNEL);
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if (!buf)
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return -ENOMEM;
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/* generate random key */
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enckey = kmalloc(CHACHA20POLY1305_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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ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
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if (unlikely(ret))
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goto err_enckey;
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/* encrypt data */
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chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
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0, 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, buf, enclen, &pos);
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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 = -EIO;
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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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payload->data = enckey;
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payload->path = file->f_path;
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path_get(&payload->path);
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fput(file);
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kvfree_sensitive(buf, enclen);
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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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payload->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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kfree_sensitive(enckey);
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error:
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kvfree_sensitive(buf, enclen);
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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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struct big_key_payload *payload = to_big_key_payload(prep->payload);
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if (prep->datalen > BIG_KEY_FILE_THRESHOLD)
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path_put(&payload->path);
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kfree_sensitive(payload->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 big_key_payload *payload = to_big_key_payload(key->payload);
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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) && payload->length > BIG_KEY_FILE_THRESHOLD)
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vfs_truncate(&payload->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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struct big_key_payload *payload = to_big_key_payload(key->payload);
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if (payload->length > BIG_KEY_FILE_THRESHOLD) {
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path_put(&payload->path);
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payload->path.mnt = NULL;
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payload->path.dentry = NULL;
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}
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kfree_sensitive(payload->data);
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payload->data = NULL;
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}
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/*
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* Update a big key
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*/
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int big_key_update(struct key *key, struct key_preparsed_payload *prep)
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{
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int ret;
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ret = key_payload_reserve(key, prep->datalen);
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if (ret < 0)
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return ret;
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if (key_is_positive(key))
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big_key_destroy(key);
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return generic_key_instantiate(key, prep);
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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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struct big_key_payload *payload = to_big_key_payload(key->payload);
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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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payload->length,
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payload->length > 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 *buffer, size_t buflen)
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{
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struct big_key_payload *payload = to_big_key_payload(key->payload);
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size_t datalen = payload->length;
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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 file *file;
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u8 *buf, *enckey = payload->data;
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size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
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loff_t pos = 0;
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buf = kvmalloc(enclen, GFP_KERNEL);
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if (!buf)
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return -ENOMEM;
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file = dentry_open(&payload->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, buf, enclen, &pos);
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if (ret != enclen) {
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if (ret >= 0)
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ret = -EIO;
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goto err_fput;
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}
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ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
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enckey) ? 0 : -EBADMSG;
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if (unlikely(ret))
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goto err_fput;
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ret = datalen;
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/* copy out decrypted data */
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memcpy(buffer, buf, datalen);
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err_fput:
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fput(file);
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error:
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kvfree_sensitive(buf, enclen);
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} else {
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ret = datalen;
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memcpy(buffer, payload->data, datalen);
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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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return register_key_type(&key_type_big_key);
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}
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late_initcall(big_key_init);
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