From: Theodore Ts'o Subject: [PATCH 06/22] ext4 crypto: add encryption policy checking Date: Thu, 2 Apr 2015 18:10:43 -0400 Message-ID: <1428012659-12709-7-git-send-email-tytso@mit.edu> References: <1428012659-12709-1-git-send-email-tytso@mit.edu> Cc: jaegeuk@kernel.org, mhalcrow@google.com, Theodore Ts'o , Ildar Muslukhov To: Ext4 Developers List Return-path: Received: from imap.thunk.org ([74.207.234.97]:48032 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752586AbbDBWNF (ORCPT ); Thu, 2 Apr 2015 18:13:05 -0400 In-Reply-To: <1428012659-12709-1-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Michael Halcrow 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 Signed-off-by: Theodore Ts'o Signed-off-by: Ildar Muslukhov --- 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 +#include +#include + +#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 + +#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