fs/crypto/fscrypt_private.h

/*
 * fscrypt_private.h
 *
 * Copyright (C) 2015, Google, Inc.
 *
 * This contains encryption key functions.
 *
 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
 */

#ifndef _FSCRYPT_PRIVATE_H
#define _FSCRYPT_PRIVATE_H

#include <linux/fscrypt.h>
#include <crypto/hash.h>

/* Encryption parameters */
#define FS_KEY_DERIVATION_NONCE_SIZE	16

/**
 * 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 {
	u8 format;
	u8 contents_encryption_mode;
	u8 filenames_encryption_mode;
	u8 flags;
	u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
	u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
} __packed;

#define FS_ENCRYPTION_CONTEXT_FORMAT_V1		1

/**
 * 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;

/*
 * fscrypt_info - the "encryption key" for an inode
 *
 * When an encrypted file's key is made available, an instance of this struct is
 * allocated and stored in ->i_crypt_info.  Once created, it remains until the
 * inode is evicted.
 */
struct fscrypt_info {

	/* The actual crypto transform used for encryption and decryption */
	struct crypto_skcipher *ci_ctfm;

	/*
	 * Cipher for ESSIV IV generation.  Only set for CBC contents
	 * encryption, otherwise is NULL.
	 */
	struct crypto_cipher *ci_essiv_tfm;

	/*
	 * Encryption mode used for this inode.  It corresponds to either
	 * ci_data_mode or ci_filename_mode, depending on the inode type.
	 */
	struct fscrypt_mode *ci_mode;

	/*
	 * If non-NULL, then this inode uses a master key directly rather than a
	 * derived key, and ci_ctfm will equal ci_master_key->mk_ctfm.
	 * Otherwise, this inode uses a derived key.
	 */
	struct fscrypt_master_key *ci_master_key;

	/* fields from the fscrypt_context */
	u8 ci_data_mode;
	u8 ci_filename_mode;
	u8 ci_flags;
	u8 ci_master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
	u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
};

typedef enum {
	FS_DECRYPT = 0,
	FS_ENCRYPT,
} fscrypt_direction_t;

#define FS_CTX_REQUIRES_FREE_ENCRYPT_FL		0x00000001
#define FS_CTX_HAS_BOUNCE_BUFFER_FL		0x00000002

static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
					   u32 filenames_mode)
{
	if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC &&
	    filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS)
		return true;

	if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS &&
	    filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)
		return true;

	if (contents_mode == FS_ENCRYPTION_MODE_ADIANTUM &&
	    filenames_mode == FS_ENCRYPTION_MODE_ADIANTUM)
		return true;

	return false;
}

/* crypto.c */
extern struct kmem_cache *fscrypt_info_cachep;
extern int fscrypt_initialize(unsigned int cop_flags);
extern int fscrypt_do_page_crypto(const struct inode *inode,
				  fscrypt_direction_t rw, u64 lblk_num,
				  struct page *src_page,
				  struct page *dest_page,
				  unsigned int len, unsigned int offs,
				  gfp_t gfp_flags);
extern struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
					      gfp_t gfp_flags);
extern const struct dentry_operations fscrypt_d_ops;

extern void __printf(3, 4) __cold
fscrypt_msg(struct super_block *sb, const char *level, const char *fmt, ...);

#define fscrypt_warn(sb, fmt, ...)		\
	fscrypt_msg(sb, KERN_WARNING, fmt, ##__VA_ARGS__)
#define fscrypt_err(sb, fmt, ...)		\
	fscrypt_msg(sb, KERN_ERR, fmt, ##__VA_ARGS__)

#define FSCRYPT_MAX_IV_SIZE	32

union fscrypt_iv {
	struct {
		/* logical block number within the file */
		__le64 lblk_num;

		/* per-file nonce; only set in DIRECT_KEY mode */
		u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
	};
	u8 raw[FSCRYPT_MAX_IV_SIZE];
};

void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
			 const struct fscrypt_info *ci);

/* fname.c */
extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
			 u8 *out, unsigned int olen);
extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
					 u32 orig_len, u32 max_len,
					 u32 *encrypted_len_ret);

/* keyinfo.c */

struct fscrypt_mode {
	const char *friendly_name;
	const char *cipher_str;
	int keysize;
	int ivsize;
	bool logged_impl_name;
	bool needs_essiv;
};

extern void __exit fscrypt_essiv_cleanup(void);

#endif /* _FSCRYPT_PRIVATE_H */