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Date: Thu, 2 Apr 2015 18:10:43 -0400
From: Theodore Ts'o <tytso@....edu>
To: Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc: jaegeuk@...nel.org, mhalcrow@...gle.com,
Theodore Ts'o <tytso@....edu>,
Ildar Muslukhov <muslukhovi@...il.com>
Subject: [PATCH 06/22] ext4 crypto: add encryption policy checking
From: Michael Halcrow <mhalcrow@...gle.com>
The ext4_crypto.h header will get fleshed out as later patches in this
patchset add functionality.
Change-Id: I550d197184af04ed27e4c3abb759ca188a3f0de0
Signed-off-by: Michael Halcrow <mhalcrow@...gle.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Ildar Muslukhov <muslukhovi@...il.com>
---
fs/ext4/Makefile | 1 +
fs/ext4/crypto_policy.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++++
fs/ext4/ext4.h | 2 +
fs/ext4/ext4_crypto.h | 54 +++++++++++++++++
4 files changed, 212 insertions(+)
create mode 100644 fs/ext4/crypto_policy.c
create mode 100644 fs/ext4/ext4_crypto.h
diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index cd6f50f..3886ee4 100644
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -12,3 +12,4 @@ ext4-y := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
ext4-$(CONFIG_EXT4_FS_POSIX_ACL) += acl.o
ext4-$(CONFIG_EXT4_FS_SECURITY) += xattr_security.o
+ext4-$(CONFIG_EXT4_FS_ENCRYPTION) += crypto_policy.o
diff --git a/fs/ext4/crypto_policy.c b/fs/ext4/crypto_policy.c
new file mode 100644
index 0000000..5cb4e74
--- /dev/null
+++ b/fs/ext4/crypto_policy.c
@@ -0,0 +1,155 @@
+/*
+ * linux/fs/ext4/crypto_policy.c
+ *
+ * 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"
+
+/**
+ * ext4_to_hex() - Converts to hexadecimal characters
+ * @dst: Buffer to take hex character representation of contents of
+ * src. Must be at least of size (src_size * 2).
+ * @src: Buffer to be converted to a hex string respresentation.
+ * @src_size: Number of bytes to convert.
+ */
+void ext4_to_hex(char *dst, char *src, size_t src_size)
+{
+ int x;
+
+ for (x = 0; x < src_size; x++)
+ sprintf(&dst[x * 2], "%.2x", (unsigned char)src[x]);
+}
+
+/**
+ *
+ */
+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);
+}
+
+/**
+ * ext4_is_encryption_context_consistent_with_policy() - Checks whether the policy is consistent with the encryption context for the inode
+ * @inode: ...
+ * @policy: ...
+ *
+ * Return ...
+ */
+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_V0;
+ 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)
+{
+ int res = 0;
+
+ if (!ext4_inode_has_encryption_context(inode)) {
+ res = ext4_create_encryption_context_from_policy(inode, policy);
+ goto out;
+ }
+
+ if (!ext4_is_encryption_context_consistent_with_policy(inode, policy)) {
+ printk(KERN_WARNING
+ "%s: Policy inconsistent with encryption context\n",
+ __func__);
+ res = -EINVAL;
+ }
+out:
+ return res;
+}
+
+int ext4_is_child_context_consistent_with_parent(struct inode *parent,
+ struct inode *child)
+{
+ struct ext4_encryption_context parent_ctx, child_ctx;
+ int 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;
+ res = ext4_xattr_get(parent, 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;
+}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 2f3808e..fd2f3dd 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -588,6 +588,8 @@ enum {
#define EXT4_ENCRYPTION_MODE_AES_256_GCM 2
#define EXT4_ENCRYPTION_MODE_AES_256_CBC 3
+#include "ext4_crypto.h"
+
/*
* ioctl commands
*/
diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
new file mode 100644
index 0000000..984ff38
--- /dev/null
+++ b/fs/ext4/ext4_crypto.h
@@ -0,0 +1,54 @@
+/*
+ * linux/fs/ext4/ext4_crypto.h
+ *
+ * This contains encryption header content for ext4
+ *
+ * Written by Michael Halcrow, 2015.
+ */
+
+#ifndef _EXT4_CRYPTO_H
+#define _EXT4_CRYPTO_H
+
+#include <linux/fs.h>
+
+#define EXT4_KEY_DESCRIPTOR_SIZE 8
+
+/* Policy provided via an ioctl on the topmost directory */
+struct ext4_encryption_policy {
+ char version;
+ char contents_encryption_mode;
+ char filenames_encryption_mode;
+ char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
+} __attribute__((__packed__));
+
+#define EXT4_ENCRYPTION_CONTEXT_FORMAT_V0 0
+#define EXT4_KEY_DERIVATION_NONCE_SIZE 16
+
+/**
+ * Encryption context for inode
+ *
+ * Protector format:
+ * 1 byte: Protector format (0 = this version)
+ * 1 byte: File contents encryption mode
+ * 1 byte: File names encryption mode
+ * 1 byte: Reserved
+ * 8 bytes: Master Key descriptor
+ * 16 bytes: Encryption Key derivation nonce
+ */
+struct ext4_encryption_context {
+ char format;
+ char contents_encryption_mode;
+ char filenames_encryption_mode;
+ char reserved;
+ char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
+ char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE];
+} __attribute__((__packed__));
+
+int ext4_is_child_context_consistent_with_parent(struct inode *parent,
+ struct inode *child);
+int ext4_inherit_context(struct inode *parent, struct inode *child);
+void ext4_to_hex(char *dst, char *src, size_t src_size);
+int ext4_process_policy(const struct ext4_encryption_policy *policy,
+ struct inode *inode);
+
+#endif /* _EXT4_CRYPTO_H */
--
2.3.0
--
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