Merge tag 'keys-next-20200602' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull keyring updates from David Howells:

 - Fix a documentation warning.

 - Replace a zero-length array with a flexible one

 - Make the big_key key type use ChaCha20Poly1305 and use the crypto
   algorithm directly rather than going through the crypto layer.

 - Implement the update op for the big_key type.

* tag 'keys-next-20200602' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys: Implement update for the big_key type
  security/keys: rewrite big_key crypto to use library interface
  KEYS: Replace zero-length array with flexible-array
  Documentation: security: core.rst: add missing argument

2 files changed, 52 insertions, 209 deletions

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 47c041563d41..8153ea01d7bb 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -60,9 +60,7 @@ config BIG_KEYS
 	bool "Large payload keys"
 	depends on KEYS
 	depends on TMPFS
-	select CRYPTO
-	select CRYPTO_AES
-	select CRYPTO_GCM
+	depends on CRYPTO_LIB_CHACHA20POLY1305 = y
 	help
 	  This option provides support for holding large keys within the kernel
 	  (for example Kerberos ticket caches).  The data may be stored out to
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index 82008f900930..dd708e8f13c0 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /* Large capacity key type
  *
- * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ * 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)
  */
@@ -12,20 +12,10 @@
 #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[];
-};
+#include <crypto/chacha20poly1305.h>
 
 /*
  * Layout of key payload words.
@@ -38,14 +28,6 @@ enum {
 };
 
 /*
- * 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.
@@ -53,16 +35,6 @@ enum big_key_op {
 #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
  */
@@ -75,136 +47,20 @@ struct key_type key_type_big_key = {
 	.destroy		= big_key_destroy,
 	.describe		= big_key_describe,
 	.read			= big_key_read,
-	/* no ->update(); don't add it without changing big_key_crypt() nonce */
+	.update			= big_key_update,
 };
 
 /*
- * 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;
+	u8 *buf, *enckey;
 	ssize_t written;
-	size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
+	size_t datalen = prep->datalen;
+	size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 	int ret;
 
 	if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
@@ -220,28 +76,28 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 		 * 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 = big_key_alloc_buffer(enclen);
+		buf = kvmalloc(enclen, GFP_KERNEL);
 		if (!buf)
 			return -ENOMEM;
-		memcpy(buf->virt, prep->data, datalen);
 
 		/* generate random key */
-		enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
+		enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
 		if (!enckey) {
 			ret = -ENOMEM;
 			goto error;
 		}
-		ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
+		ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_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;
+		/* encrypt data */
+		chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
+					 0, enckey);
 
 		/* save aligned data to file */
 		file = shmem_kernel_file_setup("", enclen, 0);
@@ -250,11 +106,11 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 			goto err_enckey;
 		}
 
-		written = kernel_write(file, buf->virt, enclen, &pos);
+		written = kernel_write(file, buf, enclen, &pos);
 		if (written != enclen) {
 			ret = written;
 			if (written >= 0)
-				ret = -ENOMEM;
+				ret = -EIO;
 			goto err_fput;
 		}
 
@@ -265,7 +121,8 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 		*path = file->f_path;
 		path_get(path);
 		fput(file);
-		big_key_free_buffer(buf);
+		memzero_explicit(buf, enclen);
+		kvfree(buf);
 	} else {
 		/* Just store the data in a buffer */
 		void *data = kmalloc(datalen, GFP_KERNEL);
@@ -283,7 +140,8 @@ err_fput:
 err_enckey:
 	kzfree(enckey);
 error:
-	big_key_free_buffer(buf);
+	memzero_explicit(buf, enclen);
+	kvfree(buf);
 	return ret;
 }
 
@@ -334,6 +192,23 @@ void big_key_destroy(struct key *key)
 }
 
 /*
+ * 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)
@@ -361,14 +236,13 @@ long big_key_read(const struct key *key, char *buffer, size_t buflen)
 		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;
+		u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
+		size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 		loff_t pos = 0;
 
-		buf = big_key_alloc_buffer(enclen);
+		buf = kvmalloc(enclen, GFP_KERNEL);
 		if (!buf)
 			return -ENOMEM;
 
@@ -379,25 +253,28 @@ long big_key_read(const struct key *key, char *buffer, size_t buflen)
 		}
 
 		/* read file to kernel and decrypt */
-		ret = kernel_read(file, buf->virt, enclen, &pos);
-		if (ret >= 0 && ret != enclen) {
-			ret = -EIO;
+		ret = kernel_read(file, buf, enclen, &pos);
+		if (ret != enclen) {
+			if (ret >= 0)
+				ret = -EIO;
 			goto err_fput;
 		}
 
-		ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
-		if (ret)
+		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->virt, datalen);
+		memcpy(buffer, buf, datalen);
 
 err_fput:
 		fput(file);
 error:
-		big_key_free_buffer(buf);
+		memzero_explicit(buf, enclen);
+		kvfree(buf);
 	} else {
 		ret = datalen;
 		memcpy(buffer, key->payload.data[big_key_data], datalen);
@@ -411,39 +288,7 @@ error:
  */
 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;
+	return register_key_type(&key_type_big_key);
 }
 
 late_initcall(big_key_init);