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![Eric Biggers](/assets/img/avatar_default.png)
Now that there's sometimes a second type of per-file key (the dirhash key), clarify some function names, macros, and documentation that specifically deal with per-file *encryption* keys. Link: https://lore.kernel.org/r/20200120223201.241390-4-ebiggers@kernel.org Reviewed-by: Daniel Rosenberg <drosen@google.com> Signed-off-by: Eric Biggers <ebiggers@google.com>
469 lines
14 KiB
C
469 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* fscrypt_private.h
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
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* Heavily modified since then.
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*/
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#ifndef _FSCRYPT_PRIVATE_H
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#define _FSCRYPT_PRIVATE_H
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#include <linux/fscrypt.h>
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#include <linux/siphash.h>
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#include <crypto/hash.h>
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#define CONST_STRLEN(str) (sizeof(str) - 1)
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#define FS_KEY_DERIVATION_NONCE_SIZE 16
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#define FSCRYPT_MIN_KEY_SIZE 16
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#define FSCRYPT_CONTEXT_V1 1
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#define FSCRYPT_CONTEXT_V2 2
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struct fscrypt_context_v1 {
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u8 version; /* FSCRYPT_CONTEXT_V1 */
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u8 contents_encryption_mode;
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u8 filenames_encryption_mode;
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u8 flags;
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u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
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u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
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};
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struct fscrypt_context_v2 {
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u8 version; /* FSCRYPT_CONTEXT_V2 */
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u8 contents_encryption_mode;
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u8 filenames_encryption_mode;
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u8 flags;
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u8 __reserved[4];
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u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
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u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
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};
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/**
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* fscrypt_context - the encryption context of an inode
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*
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* This is the on-disk equivalent of an fscrypt_policy, stored alongside each
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* encrypted file usually in a hidden extended attribute. It contains the
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* fields from the fscrypt_policy, in order to identify the encryption algorithm
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* and key with which the file is encrypted. It also contains a nonce that was
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* randomly generated by fscrypt itself; this is used as KDF input or as a tweak
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* to cause different files to be encrypted differently.
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*/
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union fscrypt_context {
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u8 version;
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struct fscrypt_context_v1 v1;
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struct fscrypt_context_v2 v2;
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};
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/*
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* Return the size expected for the given fscrypt_context based on its version
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* number, or 0 if the context version is unrecognized.
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*/
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static inline int fscrypt_context_size(const union fscrypt_context *ctx)
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{
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switch (ctx->version) {
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case FSCRYPT_CONTEXT_V1:
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BUILD_BUG_ON(sizeof(ctx->v1) != 28);
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return sizeof(ctx->v1);
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case FSCRYPT_CONTEXT_V2:
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BUILD_BUG_ON(sizeof(ctx->v2) != 40);
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return sizeof(ctx->v2);
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}
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return 0;
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}
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#undef fscrypt_policy
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union fscrypt_policy {
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u8 version;
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struct fscrypt_policy_v1 v1;
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struct fscrypt_policy_v2 v2;
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};
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/*
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* Return the size expected for the given fscrypt_policy based on its version
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* number, or 0 if the policy version is unrecognized.
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*/
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static inline int fscrypt_policy_size(const union fscrypt_policy *policy)
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{
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switch (policy->version) {
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case FSCRYPT_POLICY_V1:
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return sizeof(policy->v1);
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case FSCRYPT_POLICY_V2:
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return sizeof(policy->v2);
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}
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return 0;
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}
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/* Return the contents encryption mode of a valid encryption policy */
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static inline u8
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fscrypt_policy_contents_mode(const union fscrypt_policy *policy)
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{
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switch (policy->version) {
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case FSCRYPT_POLICY_V1:
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return policy->v1.contents_encryption_mode;
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case FSCRYPT_POLICY_V2:
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return policy->v2.contents_encryption_mode;
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}
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BUG();
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}
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/* Return the filenames encryption mode of a valid encryption policy */
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static inline u8
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fscrypt_policy_fnames_mode(const union fscrypt_policy *policy)
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{
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switch (policy->version) {
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case FSCRYPT_POLICY_V1:
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return policy->v1.filenames_encryption_mode;
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case FSCRYPT_POLICY_V2:
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return policy->v2.filenames_encryption_mode;
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}
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BUG();
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}
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/* Return the flags (FSCRYPT_POLICY_FLAG*) of a valid encryption policy */
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static inline u8
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fscrypt_policy_flags(const union fscrypt_policy *policy)
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{
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switch (policy->version) {
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case FSCRYPT_POLICY_V1:
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return policy->v1.flags;
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case FSCRYPT_POLICY_V2:
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return policy->v2.flags;
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}
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BUG();
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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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/*
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* fscrypt_info - the "encryption key" for an inode
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*
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* When an encrypted file's key is made available, an instance of this struct is
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* allocated and stored in ->i_crypt_info. Once created, it remains until the
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* inode is evicted.
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*/
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struct fscrypt_info {
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/* The actual crypto transform used for encryption and decryption */
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struct crypto_skcipher *ci_ctfm;
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/* True if the key should be freed when this fscrypt_info is freed */
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bool ci_owns_key;
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/*
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* Encryption mode used for this inode. It corresponds to either the
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* contents or filenames encryption mode, depending on the inode type.
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*/
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struct fscrypt_mode *ci_mode;
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/* Back-pointer to the inode */
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struct inode *ci_inode;
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/*
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* The master key with which this inode was unlocked (decrypted). This
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* will be NULL if the master key was found in a process-subscribed
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* keyring rather than in the filesystem-level keyring.
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*/
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struct key *ci_master_key;
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/*
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* Link in list of inodes that were unlocked with the master key.
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* Only used when ->ci_master_key is set.
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*/
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struct list_head ci_master_key_link;
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/*
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* If non-NULL, then encryption is done using the master key directly
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* and ci_ctfm will equal ci_direct_key->dk_ctfm.
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*/
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struct fscrypt_direct_key *ci_direct_key;
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/*
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* This inode's hash key for filenames. This is a 128-bit SipHash-2-4
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* key. This is only set for directories that use a keyed dirhash over
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* the plaintext filenames -- currently just casefolded directories.
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*/
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siphash_key_t ci_dirhash_key;
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bool ci_dirhash_key_initialized;
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/* The encryption policy used by this inode */
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union fscrypt_policy ci_policy;
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/* This inode's nonce, copied from the fscrypt_context */
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u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
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};
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typedef enum {
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FS_DECRYPT = 0,
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FS_ENCRYPT,
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} fscrypt_direction_t;
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/* crypto.c */
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extern struct kmem_cache *fscrypt_info_cachep;
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extern int fscrypt_initialize(unsigned int cop_flags);
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extern int fscrypt_crypt_block(const struct inode *inode,
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fscrypt_direction_t rw, u64 lblk_num,
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struct page *src_page, struct page *dest_page,
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unsigned int len, unsigned int offs,
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gfp_t gfp_flags);
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extern struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
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extern void __printf(3, 4) __cold
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fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
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#define fscrypt_warn(inode, fmt, ...) \
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fscrypt_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
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#define fscrypt_err(inode, fmt, ...) \
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fscrypt_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
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#define FSCRYPT_MAX_IV_SIZE 32
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union fscrypt_iv {
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struct {
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/* logical block number within the file */
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__le64 lblk_num;
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/* per-file nonce; only set in DIRECT_KEY mode */
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u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
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};
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u8 raw[FSCRYPT_MAX_IV_SIZE];
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};
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void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
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const struct fscrypt_info *ci);
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/* fname.c */
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extern int fscrypt_fname_encrypt(const struct inode *inode,
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const struct qstr *iname,
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u8 *out, unsigned int olen);
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extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
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u32 orig_len, u32 max_len,
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u32 *encrypted_len_ret);
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extern const struct dentry_operations fscrypt_d_ops;
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/* hkdf.c */
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struct fscrypt_hkdf {
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struct crypto_shash *hmac_tfm;
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};
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extern int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
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unsigned int master_key_size);
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/*
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* The list of contexts in which fscrypt uses HKDF. These values are used as
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* the first byte of the HKDF application-specific info string to guarantee that
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* info strings are never repeated between contexts. This ensures that all HKDF
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* outputs are unique and cryptographically isolated, i.e. knowledge of one
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* output doesn't reveal another.
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*/
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#define HKDF_CONTEXT_KEY_IDENTIFIER 1
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#define HKDF_CONTEXT_PER_FILE_ENC_KEY 2
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#define HKDF_CONTEXT_DIRECT_KEY 3
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#define HKDF_CONTEXT_IV_INO_LBLK_64_KEY 4
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#define HKDF_CONTEXT_DIRHASH_KEY 5
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extern int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
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const u8 *info, unsigned int infolen,
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u8 *okm, unsigned int okmlen);
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extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
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/* keyring.c */
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/*
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* fscrypt_master_key_secret - secret key material of an in-use master key
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*/
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struct fscrypt_master_key_secret {
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/*
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* For v2 policy keys: HKDF context keyed by this master key.
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* For v1 policy keys: not set (hkdf.hmac_tfm == NULL).
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*/
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struct fscrypt_hkdf hkdf;
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/* Size of the raw key in bytes. Set even if ->raw isn't set. */
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u32 size;
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/* For v1 policy keys: the raw key. Wiped for v2 policy keys. */
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u8 raw[FSCRYPT_MAX_KEY_SIZE];
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} __randomize_layout;
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/*
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* fscrypt_master_key - an in-use master key
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*
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* This represents a master encryption key which has been added to the
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* filesystem and can be used to "unlock" the encrypted files which were
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* encrypted with it.
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*/
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struct fscrypt_master_key {
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/*
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* The secret key material. After FS_IOC_REMOVE_ENCRYPTION_KEY is
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* executed, this is wiped and no new inodes can be unlocked with this
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* key; however, there may still be inodes in ->mk_decrypted_inodes
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* which could not be evicted. As long as some inodes still remain,
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* FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
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* FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
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*
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* Locking: protected by key->sem (outer) and mk_secret_sem (inner).
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* The reason for two locks is that key->sem also protects modifying
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* mk_users, which ranks it above the semaphore for the keyring key
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* type, which is in turn above page faults (via keyring_read). But
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* sometimes filesystems call fscrypt_get_encryption_info() from within
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* a transaction, which ranks it below page faults. So we need a
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* separate lock which protects mk_secret but not also mk_users.
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*/
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struct fscrypt_master_key_secret mk_secret;
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struct rw_semaphore mk_secret_sem;
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/*
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* For v1 policy keys: an arbitrary key descriptor which was assigned by
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* userspace (->descriptor).
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*
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* For v2 policy keys: a cryptographic hash of this key (->identifier).
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*/
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struct fscrypt_key_specifier mk_spec;
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/*
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* Keyring which contains a key of type 'key_type_fscrypt_user' for each
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* user who has added this key. Normally each key will be added by just
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* one user, but it's possible that multiple users share a key, and in
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* that case we need to keep track of those users so that one user can't
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* remove the key before the others want it removed too.
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*
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* This is NULL for v1 policy keys; those can only be added by root.
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*
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* Locking: in addition to this keyrings own semaphore, this is
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* protected by the master key's key->sem, so we can do atomic
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* search+insert. It can also be searched without taking any locks, but
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* in that case the returned key may have already been removed.
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*/
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struct key *mk_users;
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/*
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* Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
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* Once this goes to 0, the master key is removed from ->s_master_keys.
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* The 'struct fscrypt_master_key' will continue to live as long as the
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* 'struct key' whose payload it is, but we won't let this reference
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* count rise again.
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*/
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refcount_t mk_refcount;
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/*
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* List of inodes that were unlocked using this key. This allows the
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* inodes to be evicted efficiently if the key is removed.
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*/
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struct list_head mk_decrypted_inodes;
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spinlock_t mk_decrypted_inodes_lock;
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/* Crypto API transforms for DIRECT_KEY policies, allocated on-demand */
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struct crypto_skcipher *mk_direct_tfms[__FSCRYPT_MODE_MAX + 1];
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/*
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* Crypto API transforms for filesystem-layer implementation of
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* IV_INO_LBLK_64 policies, allocated on-demand.
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*/
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struct crypto_skcipher *mk_iv_ino_lblk_64_tfms[__FSCRYPT_MODE_MAX + 1];
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} __randomize_layout;
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static inline bool
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is_master_key_secret_present(const struct fscrypt_master_key_secret *secret)
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{
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/*
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* The READ_ONCE() is only necessary for fscrypt_drop_inode() and
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* fscrypt_key_describe(). These run in atomic context, so they can't
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* take ->mk_secret_sem and thus 'secret' can change concurrently which
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* would be a data race. But they only need to know whether the secret
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* *was* present at the time of check, so READ_ONCE() suffices.
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*/
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return READ_ONCE(secret->size) != 0;
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}
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static inline const char *master_key_spec_type(
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const struct fscrypt_key_specifier *spec)
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{
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switch (spec->type) {
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case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
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return "descriptor";
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case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
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return "identifier";
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}
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return "[unknown]";
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}
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static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
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{
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switch (spec->type) {
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case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
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return FSCRYPT_KEY_DESCRIPTOR_SIZE;
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case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
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return FSCRYPT_KEY_IDENTIFIER_SIZE;
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}
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return 0;
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}
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extern struct key *
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fscrypt_find_master_key(struct super_block *sb,
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const struct fscrypt_key_specifier *mk_spec);
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extern int fscrypt_verify_key_added(struct super_block *sb,
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const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
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extern int __init fscrypt_init_keyring(void);
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/* keysetup.c */
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struct fscrypt_mode {
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const char *friendly_name;
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const char *cipher_str;
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int keysize;
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int ivsize;
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int logged_impl_name;
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};
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extern struct fscrypt_mode fscrypt_modes[];
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extern struct crypto_skcipher *
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fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
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const struct inode *inode);
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extern int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci,
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const u8 *raw_key);
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extern int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
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const struct fscrypt_master_key *mk);
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/* keysetup_v1.c */
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extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
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extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
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const u8 *raw_master_key);
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extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
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struct fscrypt_info *ci);
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/* policy.c */
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extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
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const union fscrypt_policy *policy2);
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extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
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const struct inode *inode);
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extern int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
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const union fscrypt_context *ctx_u,
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int ctx_size);
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#endif /* _FSCRYPT_PRIVATE_H */
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