ext4 crypto: add encryption policy and password salt support

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>

1 files changed, 167 insertions, 0 deletions

diff --git a/fs/ext4/crypto_policy.c b/fs/ext4/crypto_policy.c
new file mode 100644
index 0000000..532b69c
--- /dev/null
+++ b/fs/ext4/crypto_policy.c
@@ -0,0 +1,167 @@
+/*
+ * linux/fs/ext4/crypto_policy.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption policy functions for ext4
+ *
+ * Written by Michael Halcrow, 2015.
+ */
+
+#include <linux/random.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include "ext4.h"
+#include "xattr.h"
+
+static int ext4_inode_has_encryption_context(struct inode *inode)
+{
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
+	return (res > 0);
+}
+
+/*
+ * check whether the policy is consistent with the encryption context
+ * for the inode
+ */
+static int ext4_is_encryption_context_consistent_with_policy(
+	struct inode *inode, const struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+				 sizeof(ctx));
+	if (res != sizeof(ctx))
+		return 0;
+	return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
+			EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
+		(ctx.contents_encryption_mode ==
+		 policy->contents_encryption_mode) &&
+		(ctx.filenames_encryption_mode ==
+		 policy->filenames_encryption_mode));
+}
+
+static int ext4_create_encryption_context_from_policy(
+	struct inode *inode, const struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+	int res = 0;
+
+	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
+	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
+	       EXT4_KEY_DESCRIPTOR_SIZE);
+	ctx.contents_encryption_mode = policy->contents_encryption_mode;
+	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
+	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
+	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
+
+	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+			     sizeof(ctx), 0);
+	if (!res)
+		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
+	return res;
+}
+
+int ext4_process_policy(const struct ext4_encryption_policy *policy,
+			struct inode *inode)
+{
+	if (policy->version != 0)
+		return -EINVAL;
+
+	if (!ext4_inode_has_encryption_context(inode)) {
+		if (!ext4_empty_dir(inode))
+			return -ENOTEMPTY;
+		return ext4_create_encryption_context_from_policy(inode,
+								  policy);
+	}
+
+	if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
+		return 0;
+
+	printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
+	       __func__);
+	return -EINVAL;
+}
+
+int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+				 &ctx, sizeof(ctx));
+	if (res != sizeof(ctx))
+		return -ENOENT;
+	if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
+		return -EINVAL;
+	policy->version = 0;
+	policy->contents_encryption_mode = ctx.contents_encryption_mode;
+	policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
+	memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
+	       EXT4_KEY_DESCRIPTOR_SIZE);
+	return 0;
+}
+
+int ext4_is_child_context_consistent_with_parent(struct inode *parent,
+						 struct inode *child)
+{
+	struct ext4_encryption_context parent_ctx, child_ctx;
+	int res;
+
+	if ((parent == NULL) || (child == NULL)) {
+		pr_err("parent %p child %p\n", parent, child);
+		BUG_ON(1);
+	}
+	/* no restrictions if the parent directory is not encrypted */
+	if (!ext4_encrypted_inode(parent))
+		return 1;
+	res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+			     &parent_ctx, sizeof(parent_ctx));
+	if (res != sizeof(parent_ctx))
+		return 0;
+	/* if the child directory is not encrypted, this is always a problem */
+	if (!ext4_encrypted_inode(child))
+		return 0;
+	res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+			     &child_ctx, sizeof(child_ctx));
+	if (res != sizeof(child_ctx))
+		return 0;
+	return (memcmp(parent_ctx.master_key_descriptor,
+		       child_ctx.master_key_descriptor,
+		       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
+		(parent_ctx.contents_encryption_mode ==
+		 child_ctx.contents_encryption_mode) &&
+		(parent_ctx.filenames_encryption_mode ==
+		 child_ctx.filenames_encryption_mode));
+}
+
+/**
+ * ext4_inherit_context() - Sets a child context from its parent
+ * @parent: Parent inode from which the context is inherited.
+ * @child:  Child inode that inherits the context from @parent.
+ *
+ * Return: Zero on success, non-zero otherwise
+ */
+int ext4_inherit_context(struct inode *parent, struct inode *child)
+{
+	struct ext4_encryption_context ctx;
+	int res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+				 &ctx, sizeof(ctx));
+
+	if (res != sizeof(ctx))
+		return -ENOENT;
+
+	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
+	res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+			     sizeof(ctx), 0);
+	if (!res)
+		ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
+	return res;
+}