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- // SPDX-License-Identifier: GPL-2.0-or-later
- /* Large capacity key type
- *
- * Copyright (C) 2017-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
- * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- */
- #define pr_fmt(fmt) "big_key: "fmt
- #include <linux/init.h>
- #include <linux/seq_file.h>
- #include <linux/file.h>
- #include <linux/shmem_fs.h>
- #include <linux/err.h>
- #include <linux/random.h>
- #include <keys/user-type.h>
- #include <keys/big_key-type.h>
- #include <crypto/chacha20poly1305.h>
- /*
- * Layout of key payload words.
- */
- enum {
- big_key_data,
- big_key_path,
- big_key_path_2nd_part,
- big_key_len,
- };
- /*
- * If the data is under this limit, there's no point creating a shm file to
- * hold it as the permanently resident metadata for the shmem fs will be at
- * least as large as the data.
- */
- #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
- /*
- * big_key defined keys take an arbitrary string as the description and an
- * arbitrary blob of data as the payload
- */
- struct key_type key_type_big_key = {
- .name = "big_key",
- .preparse = big_key_preparse,
- .free_preparse = big_key_free_preparse,
- .instantiate = generic_key_instantiate,
- .revoke = big_key_revoke,
- .destroy = big_key_destroy,
- .describe = big_key_describe,
- .read = big_key_read,
- .update = big_key_update,
- };
- /*
- * Preparse a big key
- */
- int big_key_preparse(struct key_preparsed_payload *prep)
- {
- struct path *path = (struct path *)&prep->payload.data[big_key_path];
- struct file *file;
- u8 *buf, *enckey;
- ssize_t written;
- size_t datalen = prep->datalen;
- size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
- int ret;
- if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
- return -EINVAL;
- /* Set an arbitrary quota */
- prep->quotalen = 16;
- prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
- if (datalen > BIG_KEY_FILE_THRESHOLD) {
- /* Create a shmem file to store the data in. This will permit the data
- * to be swapped out if needed.
- *
- * File content is stored encrypted with randomly generated key.
- * Since the key is random for each file, we can set the nonce
- * to zero, provided we never define a ->update() call.
- */
- loff_t pos = 0;
- buf = kvmalloc(enclen, GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
- /* generate random key */
- enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
- if (!enckey) {
- ret = -ENOMEM;
- goto error;
- }
- ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
- if (unlikely(ret))
- goto err_enckey;
- /* encrypt data */
- chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
- 0, enckey);
- /* save aligned data to file */
- file = shmem_kernel_file_setup("", enclen, 0);
- if (IS_ERR(file)) {
- ret = PTR_ERR(file);
- goto err_enckey;
- }
- written = kernel_write(file, buf, enclen, &pos);
- if (written != enclen) {
- ret = written;
- if (written >= 0)
- ret = -EIO;
- goto err_fput;
- }
- /* Pin the mount and dentry to the key so that we can open it again
- * later
- */
- prep->payload.data[big_key_data] = enckey;
- *path = file->f_path;
- path_get(path);
- fput(file);
- memzero_explicit(buf, enclen);
- kvfree(buf);
- } else {
- /* Just store the data in a buffer */
- void *data = kmalloc(datalen, GFP_KERNEL);
- if (!data)
- return -ENOMEM;
- prep->payload.data[big_key_data] = data;
- memcpy(data, prep->data, prep->datalen);
- }
- return 0;
- err_fput:
- fput(file);
- err_enckey:
- kfree_sensitive(enckey);
- error:
- memzero_explicit(buf, enclen);
- kvfree(buf);
- return ret;
- }
- /*
- * Clear preparsement.
- */
- void big_key_free_preparse(struct key_preparsed_payload *prep)
- {
- if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
- struct path *path = (struct path *)&prep->payload.data[big_key_path];
- path_put(path);
- }
- kfree_sensitive(prep->payload.data[big_key_data]);
- }
- /*
- * dispose of the links from a revoked keyring
- * - called with the key sem write-locked
- */
- void big_key_revoke(struct key *key)
- {
- struct path *path = (struct path *)&key->payload.data[big_key_path];
- /* clear the quota */
- key_payload_reserve(key, 0);
- if (key_is_positive(key) &&
- (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
- vfs_truncate(path, 0);
- }
- /*
- * dispose of the data dangling from the corpse of a big_key key
- */
- void big_key_destroy(struct key *key)
- {
- size_t datalen = (size_t)key->payload.data[big_key_len];
- if (datalen > BIG_KEY_FILE_THRESHOLD) {
- struct path *path = (struct path *)&key->payload.data[big_key_path];
- path_put(path);
- path->mnt = NULL;
- path->dentry = NULL;
- }
- kfree_sensitive(key->payload.data[big_key_data]);
- key->payload.data[big_key_data] = NULL;
- }
- /*
- * Update a big key
- */
- int big_key_update(struct key *key, struct key_preparsed_payload *prep)
- {
- int ret;
- ret = key_payload_reserve(key, prep->datalen);
- if (ret < 0)
- return ret;
- if (key_is_positive(key))
- big_key_destroy(key);
- return generic_key_instantiate(key, prep);
- }
- /*
- * describe the big_key key
- */
- void big_key_describe(const struct key *key, struct seq_file *m)
- {
- size_t datalen = (size_t)key->payload.data[big_key_len];
- seq_puts(m, key->description);
- if (key_is_positive(key))
- seq_printf(m, ": %zu [%s]",
- datalen,
- datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
- }
- /*
- * read the key data
- * - the key's semaphore is read-locked
- */
- long big_key_read(const struct key *key, char *buffer, size_t buflen)
- {
- size_t datalen = (size_t)key->payload.data[big_key_len];
- long ret;
- if (!buffer || buflen < datalen)
- return datalen;
- if (datalen > BIG_KEY_FILE_THRESHOLD) {
- struct path *path = (struct path *)&key->payload.data[big_key_path];
- struct file *file;
- u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
- size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
- loff_t pos = 0;
- buf = kvmalloc(enclen, GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
- file = dentry_open(path, O_RDONLY, current_cred());
- if (IS_ERR(file)) {
- ret = PTR_ERR(file);
- goto error;
- }
- /* read file to kernel and decrypt */
- ret = kernel_read(file, buf, enclen, &pos);
- if (ret != enclen) {
- if (ret >= 0)
- ret = -EIO;
- goto err_fput;
- }
- ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
- enckey) ? 0 : -EBADMSG;
- if (unlikely(ret))
- goto err_fput;
- ret = datalen;
- /* copy out decrypted data */
- memcpy(buffer, buf, datalen);
- err_fput:
- fput(file);
- error:
- memzero_explicit(buf, enclen);
- kvfree(buf);
- } else {
- ret = datalen;
- memcpy(buffer, key->payload.data[big_key_data], datalen);
- }
- return ret;
- }
- /*
- * Register key type
- */
- static int __init big_key_init(void)
- {
- return register_key_type(&key_type_big_key);
- }
- late_initcall(big_key_init);
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