b7e7cf7a66
fscrypt provides facilities to use different encryption algorithms which are selectable by userspace when setting the encryption policy. Currently, only AES-256-XTS for file contents and AES-256-CBC-CTS for file names are implemented. This is a clear case of kernel offers the mechanism and userspace selects a policy. Similar to what dm-crypt and ecryptfs have. This patch adds support for using AES-128-CBC for file contents and AES-128-CBC-CTS for file name encryption. To mitigate watermarking attacks, IVs are generated using the ESSIV algorithm. While AES-CBC is actually slightly less secure than AES-XTS from a security point of view, there is more widespread hardware support. Using AES-CBC gives us the acceptable performance while still providing a moderate level of security for persistent storage. Especially low-powered embedded devices with crypto accelerators such as CAAM or CESA often only support AES-CBC. Since using AES-CBC over AES-XTS is basically thought of a last resort, we use AES-128-CBC over AES-256-CBC since it has less encryption rounds and yields noticeable better performance starting from a file size of just a few kB. Signed-off-by: Daniel Walter <dwalter@sigma-star.at> [david@sigma-star.at: addressed review comments] Signed-off-by: David Gstir <david@sigma-star.at> Reviewed-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
138 lines
3 KiB
C
138 lines
3 KiB
C
/*
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* fscrypt_common.h: common declarations for per-file encryption
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* Written by Michael Halcrow, 2015.
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* Modified by Jaegeuk Kim, 2015.
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*/
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#ifndef _LINUX_FSCRYPT_COMMON_H
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#define _LINUX_FSCRYPT_COMMON_H
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#include <linux/key.h>
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#include <linux/fs.h>
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#include <linux/mm.h>
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#include <linux/bio.h>
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#include <linux/dcache.h>
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#include <crypto/skcipher.h>
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#include <uapi/linux/fs.h>
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#define FS_CRYPTO_BLOCK_SIZE 16
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struct fscrypt_info;
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struct fscrypt_ctx {
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union {
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struct {
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struct page *bounce_page; /* Ciphertext page */
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struct page *control_page; /* Original page */
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} w;
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struct {
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struct bio *bio;
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struct work_struct work;
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} r;
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struct list_head free_list; /* Free list */
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};
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u8 flags; /* Flags */
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};
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/**
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* For encrypted symlinks, the ciphertext length is stored at the beginning
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* of the string in little-endian format.
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*/
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struct fscrypt_symlink_data {
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__le16 len;
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char encrypted_path[1];
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} __packed;
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struct fscrypt_str {
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unsigned char *name;
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u32 len;
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};
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struct fscrypt_name {
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const struct qstr *usr_fname;
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struct fscrypt_str disk_name;
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u32 hash;
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u32 minor_hash;
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struct fscrypt_str crypto_buf;
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};
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#define FSTR_INIT(n, l) { .name = n, .len = l }
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#define FSTR_TO_QSTR(f) QSTR_INIT((f)->name, (f)->len)
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#define fname_name(p) ((p)->disk_name.name)
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#define fname_len(p) ((p)->disk_name.len)
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/*
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* fscrypt superblock flags
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*/
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#define FS_CFLG_OWN_PAGES (1U << 1)
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/*
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* crypto opertions for filesystems
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*/
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struct fscrypt_operations {
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unsigned int flags;
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const char *key_prefix;
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int (*get_context)(struct inode *, void *, size_t);
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int (*set_context)(struct inode *, const void *, size_t, void *);
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int (*dummy_context)(struct inode *);
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bool (*is_encrypted)(struct inode *);
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bool (*empty_dir)(struct inode *);
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unsigned (*max_namelen)(struct inode *);
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};
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static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
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{
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if (inode->i_sb->s_cop->dummy_context &&
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inode->i_sb->s_cop->dummy_context(inode))
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return true;
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return false;
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}
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static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
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u32 filenames_mode)
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{
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if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC &&
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filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS)
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return true;
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if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS &&
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filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)
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return true;
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return false;
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}
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static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
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{
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if (str->len == 1 && str->name[0] == '.')
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return true;
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if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
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return true;
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return false;
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}
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static inline struct page *fscrypt_control_page(struct page *page)
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{
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#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
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return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
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#else
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WARN_ON_ONCE(1);
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return ERR_PTR(-EINVAL);
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#endif
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}
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static inline int fscrypt_has_encryption_key(const struct inode *inode)
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{
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#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
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return (inode->i_crypt_info != NULL);
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#else
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return 0;
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#endif
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}
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#endif /* _LINUX_FSCRYPT_COMMON_H */
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