1 files changed, 290 insertions, 0 deletions
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
new file mode 100644
index 000000000..c3367622c
--- /dev/null
+++ b/security/keys/big_key.c
@@ -0,0 +1,290 @@
+// 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.
+ */
+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);