1 files changed, 453 insertions, 0 deletions
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
new file mode 100644
index 000000000..630594a5b
--- /dev/null
+++ b/security/keys/big_key.c
@@ -0,0 +1,453 @@
+/* Large capacity key type
+ *
+ * Copyright (C) 2017 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)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#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/scatterlist.h>
+#include <linux/random.h>
+#include <linux/vmalloc.h>
+#include <keys/user-type.h>
+#include <keys/big_key-type.h>
+#include <crypto/aead.h>
+#include <crypto/gcm.h>
+
+struct big_key_buf {
+	unsigned int		nr_pages;
+	void			*virt;
+	struct scatterlist	*sg;
+	struct page		*pages[];
+};
+
+/*
+ * Layout of key payload words.
+ */
+enum {
+	big_key_data,
+	big_key_path,
+	big_key_path_2nd_part,
+	big_key_len,
+};
+
+/*
+ * Crypto operation with big_key data
+ */
+enum big_key_op {
+	BIG_KEY_ENC,
+	BIG_KEY_DEC,
+};
+
+/*
+ * 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))
+
+/*
+ * Key size for big_key data encryption
+ */
+#define ENC_KEY_SIZE 32
+
+/*
+ * Authentication tag length
+ */
+#define ENC_AUTHTAG_SIZE 16
+
+/*
+ * 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,
+	/* no ->update(); don't add it without changing big_key_crypt() nonce */
+};
+
+/*
+ * Crypto names for big_key data authenticated encryption
+ */
+static const char big_key_alg_name[] = "gcm(aes)";
+#define BIG_KEY_IV_SIZE		GCM_AES_IV_SIZE
+
+/*
+ * Crypto algorithms for big_key data authenticated encryption
+ */
+static struct crypto_aead *big_key_aead;
+
+/*
+ * Since changing the key affects the entire object, we need a mutex.
+ */
+static DEFINE_MUTEX(big_key_aead_lock);
+
+/*
+ * Encrypt/decrypt big_key data
+ */
+static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
+{
+	int ret;
+	struct aead_request *aead_req;
+	/* We always use a zero nonce. The reason we can get away with this is
+	 * because we're using a different randomly generated key for every
+	 * different encryption. Notably, too, key_type_big_key doesn't define
+	 * an .update function, so there's no chance we'll wind up reusing the
+	 * key to encrypt updated data. Simply put: one key, one encryption.
+	 */
+	u8 zero_nonce[BIG_KEY_IV_SIZE];
+
+	aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
+	if (!aead_req)
+		return -ENOMEM;
+
+	memset(zero_nonce, 0, sizeof(zero_nonce));
+	aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);
+	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
+	aead_request_set_ad(aead_req, 0);
+
+	mutex_lock(&big_key_aead_lock);
+	if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
+		ret = -EAGAIN;
+		goto error;
+	}
+	if (op == BIG_KEY_ENC)
+		ret = crypto_aead_encrypt(aead_req);
+	else
+		ret = crypto_aead_decrypt(aead_req);
+error:
+	mutex_unlock(&big_key_aead_lock);
+	aead_request_free(aead_req);
+	return ret;
+}
+
+/*
+ * Free up the buffer.
+ */
+static void big_key_free_buffer(struct big_key_buf *buf)
+{
+	unsigned int i;
+
+	if (buf->virt) {
+		memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
+		vunmap(buf->virt);
+	}
+
+	for (i = 0; i < buf->nr_pages; i++)
+		if (buf->pages[i])
+			__free_page(buf->pages[i]);
+
+	kfree(buf);
+}
+
+/*
+ * Allocate a buffer consisting of a set of pages with a virtual mapping
+ * applied over them.
+ */
+static void *big_key_alloc_buffer(size_t len)
+{
+	struct big_key_buf *buf;
+	unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	unsigned int i, l;
+
+	buf = kzalloc(sizeof(struct big_key_buf) +
+		      sizeof(struct page) * npg +
+		      sizeof(struct scatterlist) * npg,
+		      GFP_KERNEL);
+	if (!buf)
+		return NULL;
+
+	buf->nr_pages = npg;
+	buf->sg = (void *)(buf->pages + npg);
+	sg_init_table(buf->sg, npg);
+
+	for (i = 0; i < buf->nr_pages; i++) {
+		buf->pages[i] = alloc_page(GFP_KERNEL);
+		if (!buf->pages[i])
+			goto nomem;
+
+		l = min_t(size_t, len, PAGE_SIZE);
+		sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
+		len -= l;
+	}
+
+	buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
+	if (!buf->virt)
+		goto nomem;
+
+	return buf;
+
+nomem:
+	big_key_free_buffer(buf);
+	return NULL;
+}
+
+/*
+ * Preparse a big key
+ */
+int big_key_preparse(struct key_preparsed_payload *prep)
+{
+	struct big_key_buf *buf;
+	struct path *path = (struct path *)&prep->payload.data[big_key_path];
+	struct file *file;
+	u8 *enckey;
+	ssize_t written;
+	size_t datalen = prep->datalen, enclen = datalen + ENC_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.
+		 */
+		loff_t pos = 0;
+
+		buf = big_key_alloc_buffer(enclen);
+		if (!buf)
+			return -ENOMEM;
+		memcpy(buf->virt, prep->data, datalen);
+
+		/* generate random key */
+		enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
+		if (!enckey) {
+			ret = -ENOMEM;
+			goto error;
+		}
+		ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
+		if (unlikely(ret))
+			goto err_enckey;
+
+		/* encrypt aligned data */
+		ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
+		if (ret)
+			goto err_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->virt, enclen, &pos);
+		if (written != enclen) {
+			ret = written;
+			if (written >= 0)
+				ret = -ENOMEM;
+			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);
+		big_key_free_buffer(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:
+	kzfree(enckey);
+error:
+	big_key_free_buffer(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);
+	}
+	kzfree(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;
+	}
+	kzfree(key->payload.data[big_key_data]);
+	key->payload.data[big_key_data] = NULL;
+}
+
+/*
+ * 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 big_key_buf *buf;
+		struct path *path = (struct path *)&key->payload.data[big_key_path];
+		struct file *file;
+		u8 *enckey = (u8 *)key->payload.data[big_key_data];
+		size_t enclen = datalen + ENC_AUTHTAG_SIZE;
+		loff_t pos = 0;
+
+		buf = big_key_alloc_buffer(enclen);
+		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->virt, enclen, &pos);
+		if (ret >= 0 && ret != enclen) {
+			ret = -EIO;
+			goto err_fput;
+		}
+
+		ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
+		if (ret)
+			goto err_fput;
+
+		ret = datalen;
+
+		/* copy out decrypted data */
+		memcpy(buffer, buf->virt, datalen);
+
+err_fput:
+		fput(file);
+error:
+		big_key_free_buffer(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)
+{
+	int ret;
+
+	/* init block cipher */
+	big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(big_key_aead)) {
+		ret = PTR_ERR(big_key_aead);
+		pr_err("Can't alloc crypto: %d\n", ret);
+		return ret;
+	}
+
+	if (unlikely(crypto_aead_ivsize(big_key_aead) != BIG_KEY_IV_SIZE)) {
+		WARN(1, "big key algorithm changed?");
+		ret = -EINVAL;
+		goto free_aead;
+	}
+
+	ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
+	if (ret < 0) {
+		pr_err("Can't set crypto auth tag len: %d\n", ret);
+		goto free_aead;
+	}
+
+	ret = register_key_type(&key_type_big_key);
+	if (ret < 0) {
+		pr_err("Can't register type: %d\n", ret);
+		goto free_aead;
+	}
+
+	return 0;
+
+free_aead:
+	crypto_free_aead(big_key_aead);
+	return ret;
+}
+
+late_initcall(big_key_init);