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Message-Id: <041E1EF0-0767-4CC8-B4BF-9C6552C7E11A@dilger.ca>
Date: Wed, 8 Apr 2015 12:07:16 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Theodore Ts'o <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
jaegeuk@...nel.org, mhalcrow@...gle.com,
Ildar Muslukhov <muslukhovi@...il.com>
Subject: Re: [PATCH 06/22] ext4 crypto: add encryption policy checking
On Apr 2, 2015, at 4:10 PM, Theodore Ts'o <tytso@....edu> wrote:
>
> 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__));
It wouldn't be bad to add a padding byte before master_key_descriptor,
even if this is only passed from the ioctl. That allows casting the
key to a numeric value if desired without problems on some arches.
> +
> +#define EXT4_ENCRYPTION_CONTEXT_FORMAT_V0 0
Per comments in the call, it is better not to use "0" as a defined
version, since this is much more likely to be seen accidentally
(e.g. uninitialized buffer, memory corruption, etc). Better to
start with version 1.
> +#define EXT4_KEY_DERIVATION_NONCE_SIZE 16
> +
> +/**
> + * Encryption context for inode
> + *
> + * Protector format:
> + * 1 byte: Protector format (0 = this version)
Same here.
> + * 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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Cheers, Andreas
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