// SPDX-License-Identifier: GPL-2.0-or-later /* Large capacity key type * * Copyright (C) 2017-2020 Jason A. Donenfeld . 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 #include #include #include #include #include #include #include #include /* * Layout of key payload words. */ struct big_key_payload { u8 *data; struct path path; size_t length; }; #define to_big_key_payload(payload) \ (struct big_key_payload *)((payload).data) /* * 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 big_key_payload *payload = to_big_key_payload(prep->payload); struct file *file; u8 *buf, *enckey; ssize_t written; size_t datalen = prep->datalen; size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE; int ret; BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data)); if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data) return -EINVAL; /* Set an arbitrary quota */ prep->quotalen = 16; payload->length = 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 */ payload->data = enckey; payload->path = file->f_path; path_get(&payload->path); fput(file); kvfree_sensitive(buf, enclen); } else { /* Just store the data in a buffer */ void *data = kmalloc(datalen, GFP_KERNEL); if (!data) return -ENOMEM; payload->data = data; memcpy(data, prep->data, prep->datalen); } return 0; err_fput: fput(file); err_enckey: kfree_sensitive(enckey); error: kvfree_sensitive(buf, enclen); return ret; } /* * Clear preparsement. */ void big_key_free_preparse(struct key_preparsed_payload *prep) { struct big_key_payload *payload = to_big_key_payload(prep->payload); if (prep->datalen > BIG_KEY_FILE_THRESHOLD) path_put(&payload->path); kfree_sensitive(payload->data); } /* * dispose of the links from a revoked keyring * - called with the key sem write-locked */ void big_key_revoke(struct key *key) { struct big_key_payload *payload = to_big_key_payload(key->payload); /* clear the quota */ key_payload_reserve(key, 0); if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD) vfs_truncate(&payload->path, 0); } /* * dispose of the data dangling from the corpse of a big_key key */ void big_key_destroy(struct key *key) { struct big_key_payload *payload = to_big_key_payload(key->payload); if (payload->length > BIG_KEY_FILE_THRESHOLD) { path_put(&payload->path); payload->path.mnt = NULL; payload->path.dentry = NULL; } kfree_sensitive(payload->data); payload->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) { struct big_key_payload *payload = to_big_key_payload(key->payload); seq_puts(m, key->description); if (key_is_positive(key)) seq_printf(m, ": %zu [%s]", payload->length, payload->length > 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) { struct big_key_payload *payload = to_big_key_payload(key->payload); size_t datalen = payload->length; long ret; if (!buffer || buflen < datalen) return datalen; if (datalen > BIG_KEY_FILE_THRESHOLD) { struct file *file; u8 *buf, *enckey = payload->data; size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE; loff_t pos = 0; buf = kvmalloc(enclen, GFP_KERNEL); if (!buf) return -ENOMEM; file = dentry_open(&payload->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: kvfree_sensitive(buf, enclen); } else { ret = datalen; memcpy(buffer, payload->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);