Date:	Sun, 28 Feb 2016 21:41:22 -0800
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net, tytso@....edu
Subject: Re: [PATCH 01/10] fs crypto: add basic definitions for per-file
 encryption

On 02/25/16 11:25, Jaegeuk Kim wrote:
> This patch adds definitions for per-file encryption used by ext4 and f2fs.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  include/linux/fs.h       |   8 ++
>  include/linux/fscrypto.h | 239 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/fs.h  |  18 ++++
>  3 files changed, 265 insertions(+)
>  create mode 100644 include/linux/fscrypto.h
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ae68100..d8f57cf 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -53,6 +53,8 @@ struct swap_info_struct;
>  struct seq_file;
>  struct workqueue_struct;
>  struct iov_iter;
> +struct fscrypt_info;
> +struct fscrypt_operations;
>  
>  extern void __init inode_init(void);
>  extern void __init inode_init_early(void);
> @@ -678,6 +680,10 @@ struct inode {
>  	struct hlist_head	i_fsnotify_marks;
>  #endif
>  
> +#ifdef CONFIG_FS_ENCRYPTION
> +	struct fscrypt_info	*i_crypt_info;
> +#endif
> +
>  	void			*i_private; /* fs or device private pointer */
>  };
>  
> @@ -1323,6 +1329,8 @@ struct super_block {
>  #endif
>  	const struct xattr_handler **s_xattr;
>  
> +	const struct fscrypt_operations	*s_cop;
> +
>  	struct hlist_bl_head	s_anon;		/* anonymous dentries for (nfs) exporting */
>  	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
>  	struct block_device	*s_bdev;
> diff --git a/include/linux/fscrypto.h b/include/linux/fscrypto.h
> new file mode 100644
> index 0000000..b0aed92
> --- /dev/null
> +++ b/include/linux/fscrypto.h
> @@ -0,0 +1,239 @@
> +/*
> + * General per-file encryption definition
> + *
> + * Copyright (C) 2015, Google, Inc.
> + *
> + * Written by Michael Halcrow, 2015.
> + * Modified by Jaegeuk Kim, 2015.
> + */
> +
> +#ifndef _LINUX_FSCRYPTO_H
> +#define _LINUX_FSCRYPTO_H
> +
> +#include <linux/key.h>
> +#include <linux/fs.h>
> +#include <linux/mm.h>
> +#include <linux/bio.h>
> +#include <linux/dcache.h>
> +#include <uapi/linux/fs.h>
> +
> +#define FS_KEY_DERIVATION_NONCE_SIZE		16
> +#define FS_ENCRYPTION_CONTEXT_FORMAT_V1		1
> +
> +#define FS_POLICY_FLAGS_PAD_4		0x00
> +#define FS_POLICY_FLAGS_PAD_8		0x01
> +#define FS_POLICY_FLAGS_PAD_16		0x02
> +#define FS_POLICY_FLAGS_PAD_32		0x03
> +#define FS_POLICY_FLAGS_PAD_MASK	0x03
> +#define FS_POLICY_FLAGS_VALID		0x03
> +
> +/* Encryption algorithms */
> +#define FS_ENCRYPTION_MODE_INVALID		0
> +#define FS_ENCRYPTION_MODE_AES_256_XTS		1
> +#define FS_ENCRYPTION_MODE_AES_256_GCM		2
> +#define FS_ENCRYPTION_MODE_AES_256_CBC		3
> +#define FS_ENCRYPTION_MODE_AES_256_CTS		4
> +
> +/**
> + * Encryption context for inode
> + *
> + * Protector format:
> + *  1 byte: Protector format (1 = this version)
> + *  1 byte: File contents encryption mode
> + *  1 byte: File names encryption mode
> + *  1 byte: Flags
> + *  8 bytes: Master Key descriptor
> + *  16 bytes: Encryption Key derivation nonce
> + */
> +struct fscrypt_context {
> +	char format;
> +	char contents_encryption_mode;
> +	char filenames_encryption_mode;
> +	char flags;
> +	char master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
> +	char nonce[FS_KEY_DERIVATION_NONCE_SIZE];

how about u8 instead of char?

> +} __packed;
> +
> +/* Encryption parameters */
> +#define FS_XTS_TWEAK_SIZE		16
> +#define FS_AES_128_ECB_KEY_SIZE		16
> +#define FS_AES_256_GCM_KEY_SIZE		32
> +#define FS_AES_256_CBC_KEY_SIZE		32
> +#define FS_AES_256_CTS_KEY_SIZE		32
> +#define FS_AES_256_XTS_KEY_SIZE		64
> +#define FS_MAX_KEY_SIZE			64
> +
> +#define FS_KEY_DESC_PREFIX		"fscrypt:"
> +#define FS_KEY_DESC_PREFIX_SIZE		8
> +
> +/* This is passed in from userspace into the kernel keyring */
> +struct fscrypt_key {
> +	__u32 mode;
> +	char raw[FS_MAX_KEY_SIZE];
> +	__u32 size;
> +} __packed;
> +
> +struct fscrypt_info {
> +	char ci_data_mode;
> +	char ci_filename_mode;
> +	char ci_flags;

ditto

> +	struct crypto_ablkcipher *ci_ctfm;
> +	struct key *ci_keyring_key;
> +	char ci_master_key[FS_KEY_DESCRIPTOR_SIZE];
> +};
> +
> +#define FS_CTX_REQUIRES_FREE_ENCRYPT_FL		0x00000001
> +#define FS_WRITE_PATH_FL			0x00000002
> +
> +struct fscrypt_ctx {
> +	union {
> +		struct {
> +			struct page *bounce_page;	/* Ciphertext page */
> +			struct page *control_page;	/* Original page  */
> +		} w;
> +		struct {
> +			struct bio *bio;
> +			struct work_struct work;
> +		} r;
> +		struct list_head free_list;	/* Free list */
> +	};
> +	char flags;				/* Flags */
> +	char mode;				/* Encryption mode for tfm */
> +};
> +
> +struct fscrypt_completion_result {
> +	struct completion completion;
> +	int res;
> +};
> +
> +#define DECLARE_FS_COMPLETION_RESULT(ecr) \
> +	struct fscrypt_completion_result ecr = { \
> +		COMPLETION_INITIALIZER((ecr).completion), 0 }
> +
> +static inline int fscrypt_key_size(int mode)
> +{
> +	switch (mode) {
> +	case FS_ENCRYPTION_MODE_AES_256_XTS:
> +		return FS_AES_256_XTS_KEY_SIZE;
> +	case FS_ENCRYPTION_MODE_AES_256_GCM:
> +		return FS_AES_256_GCM_KEY_SIZE;
> +	case FS_ENCRYPTION_MODE_AES_256_CBC:
> +		return FS_AES_256_CBC_KEY_SIZE;
> +	case FS_ENCRYPTION_MODE_AES_256_CTS:
> +		return FS_AES_256_CTS_KEY_SIZE;
> +	default:
> +		BUG();
> +	}
> +	return 0;
> +}
> +
> +#define FS_FNAME_NUM_SCATTER_ENTRIES	4
> +#define FS_CRYPTO_BLOCK_SIZE		16
> +#define FS_FNAME_CRYPTO_DIGEST_SIZE	32
> +
> +/**
> + * For encrypted symlinks, the ciphertext length is stored at the beginning
> + * of the string in little-endian format.
> + */
> +struct fscrypt_symlink_data {
> +	__le16 len;
> +	char encrypted_path[1];
> +} __packed;
> +
> +/**
> + * This function is used to calculate the disk space required to
> + * store a filename of length l in encrypted symlink format.
> + */
> +static inline u32 fscrypt_symlink_data_len(u32 l)
> +{
> +	if (l < FS_CRYPTO_BLOCK_SIZE)
> +		l = FS_CRYPTO_BLOCK_SIZE;
> +	return (l + sizeof(struct fscrypt_symlink_data) - 1);
> +}
> +
> +struct fscrypt_str {
> +	unsigned char *name;
> +	u32 len;
> +};
> +
> +struct fscrypt_name {
> +	const struct qstr *usr_fname;
> +	struct fscrypt_str disk_name;
> +	u32 hash;
> +	u32 minor_hash;
> +	struct fscrypt_str crypto_buf;
> +};
> +
> +#define FSTR_INIT(n, l)		{ .name = n, .len = l }
> +#define FSTR_TO_QSTR(f)		QSTR_INIT((f)->name, (f)->len)
> +#define fname_name(p)		((p)->disk_name.name)
> +#define fname_len(p)		((p)->disk_name.len)
> +
> +/*
> + * crypto opertions for filesystems
> + */
> +struct fscrypt_operations {
> +	int (*get_context)(struct inode *, void *, size_t);
> +	int (*prepare_context)(struct inode *);
> +	int (*set_context)(struct inode *, const void *, size_t, void *);
> +	int (*dummy_context)(struct inode *);
> +	bool (*is_encrypted)(struct inode *);
> +	bool (*empty_dir)(struct inode *);
> +	unsigned (*max_namelen)(struct inode *);
> +};
> +
> +static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
> +{
> +	if (inode->i_sb->s_cop->dummy_context &&
> +				inode->i_sb->s_cop->dummy_context(inode))
> +		return true;
> +	return false;
> +}
> +
> +static inline bool fscrypt_valid_contents_enc_mode(u32 mode)
> +{
> +	return (mode == FS_ENCRYPTION_MODE_AES_256_XTS);
> +}
> +
> +static inline bool fscrypt_valid_filenames_enc_mode(u32 mode)
> +{
> +	return (mode == FS_ENCRYPTION_MODE_AES_256_CTS);
> +}
> +
> +static inline u32 fscrypt_validate_encryption_key_size(u32 mode, u32 size)
> +{
> +	if (size == fscrypt_key_size(mode))
> +		return size;
> +	return 0;
> +}
> +
> +static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
> +{
> +	if (str->len == 1 && str->name[0] == '.')
> +		return true;
> +
> +	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
> +		return true;
> +
> +	return false;
> +}
> +
> +static inline struct page *fscrypt_control_page(struct page *page)
> +{
> +#ifdef CONFIG_FS_ENCRYPTION
> +	return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
> +#else
> +	WARN_ON_ONCE(1);
> +	return ERR_PTR(-EINVAL);
> +#endif
> +}
> +
> +static inline int fscrypt_has_encryption_key(struct inode *inode)
> +{
> +#ifdef CONFIG_FS_ENCRYPTION
> +	return (inode->i_crypt_info != NULL);
> +#else
> +	return 0;
> +#endif
> +}
> +#endif	/* _LINUX_FSCRYPTO_H */
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 149bec8..1d26276 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -247,6 +247,24 @@ struct fsxattr {
>  #define FS_IOC_FSSETXATTR		_IOW ('X', 32, struct fsxattr)
>  
>  /*
> + * File system encryption support
> + */
> +/* Policy provided via an ioctl on the topmost directory */
> +#define FS_KEY_DESCRIPTOR_SIZE	8
> +
> +struct fscrypt_policy {
> +	char version;
> +	char contents_encryption_mode;
> +	char filenames_encryption_mode;
> +	char flags;
> +	char master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];

ditto

> +} __packed;
> +
> +#define FS_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct fscrypt_policy)
> +#define FS_IOC_GET_ENCRYPTION_PWSALT	_IOW('f', 20, __u8[16])
> +#define FS_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct fscrypt_policy)
> +
> +/*
>   * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
>   *
>   * Note: for historical reasons, these flags were originally used and
> 


-- 
~Randy

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