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![Eric Biggers](/assets/img/avatar_default.png)
Improve a few comments. These were extracted from the patch "fscrypt: add support for hardware-wrapped keys" (https://lore.kernel.org/r/20211021181608.54127-4-ebiggers@kernel.org). Link: https://lore.kernel.org/r/20211026021042.6581-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
631 lines
18 KiB
C
631 lines
18 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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#include <linux/blk-crypto.h>
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#define CONST_STRLEN(str) (sizeof(str) - 1)
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#define FSCRYPT_FILE_NONCE_SIZE 16
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/*
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* Minimum size of an fscrypt master key. Note: a longer key will be required
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* if ciphers with a 256-bit security strength are used. This is just the
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* absolute minimum, which applies when only 128-bit encryption is used.
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*/
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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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/* Keep this in sync with include/uapi/linux/fscrypt.h */
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#define FSCRYPT_MODE_MAX FSCRYPT_MODE_ADIANTUM
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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[FSCRYPT_FILE_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[FSCRYPT_FILE_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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/* Check whether an fscrypt_context has a recognized version number and size */
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static inline bool fscrypt_context_is_valid(const union fscrypt_context *ctx,
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int ctx_size)
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{
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return ctx_size >= 1 && ctx_size == fscrypt_context_size(ctx);
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}
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/* Retrieve the context's nonce, assuming the context was already validated */
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static inline const u8 *fscrypt_context_nonce(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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return ctx->v1.nonce;
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case FSCRYPT_CONTEXT_V2:
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return ctx->v2.nonce;
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}
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WARN_ON(1);
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return NULL;
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}
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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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* struct fscrypt_prepared_key - a key prepared for actual encryption/decryption
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* @tfm: crypto API transform object
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* @blk_key: key for blk-crypto
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*
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* Normally only one of the fields will be non-NULL.
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*/
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struct fscrypt_prepared_key {
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struct crypto_skcipher *tfm;
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#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
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struct fscrypt_blk_crypto_key *blk_key;
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#endif
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};
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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 key in a form prepared for actual encryption/decryption */
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struct fscrypt_prepared_key ci_enc_key;
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/* True if ci_enc_key should be freed when this fscrypt_info is freed */
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bool ci_owns_key;
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#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
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/*
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* True if this inode will use inline encryption (blk-crypto) instead of
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* the traditional filesystem-layer encryption.
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*/
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bool ci_inlinecrypt;
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#endif
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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_enc_key will equal ci_direct_key->dk_key.
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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[FSCRYPT_FILE_NONCE_SIZE];
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/* Hashed inode number. Only set for IV_INO_LBLK_32 */
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u32 ci_hashed_ino;
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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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int fscrypt_initialize(unsigned int cop_flags);
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int fscrypt_crypt_block(const struct inode *inode, fscrypt_direction_t rw,
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u64 lblk_num, struct page *src_page,
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struct page *dest_page, unsigned int len,
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unsigned int offs, gfp_t gfp_flags);
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struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
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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[FSCRYPT_FILE_NONCE_SIZE];
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};
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u8 raw[FSCRYPT_MAX_IV_SIZE];
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__le64 dun[FSCRYPT_MAX_IV_SIZE / sizeof(__le64)];
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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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int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
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u8 *out, unsigned int olen);
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bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
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u32 orig_len, u32 max_len,
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u32 *encrypted_len_ret);
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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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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 /* info=<empty> */
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#define HKDF_CONTEXT_PER_FILE_ENC_KEY 2 /* info=file_nonce */
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#define HKDF_CONTEXT_DIRECT_KEY 3 /* info=mode_num */
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#define HKDF_CONTEXT_IV_INO_LBLK_64_KEY 4 /* info=mode_num||fs_uuid */
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#define HKDF_CONTEXT_DIRHASH_KEY 5 /* info=file_nonce */
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#define HKDF_CONTEXT_IV_INO_LBLK_32_KEY 6 /* info=mode_num||fs_uuid */
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#define HKDF_CONTEXT_INODE_HASH_KEY 7 /* info=<empty> */
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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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void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
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/* inline_crypt.c */
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#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
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int fscrypt_select_encryption_impl(struct fscrypt_info *ci);
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static inline bool
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fscrypt_using_inline_encryption(const struct fscrypt_info *ci)
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{
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return ci->ci_inlinecrypt;
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}
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int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
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const u8 *raw_key,
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const struct fscrypt_info *ci);
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void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key);
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/*
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* Check whether the crypto transform or blk-crypto key has been allocated in
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* @prep_key, depending on which encryption implementation the file will use.
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*/
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static inline bool
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fscrypt_is_key_prepared(struct fscrypt_prepared_key *prep_key,
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const struct fscrypt_info *ci)
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{
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/*
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* The two smp_load_acquire()'s here pair with the smp_store_release()'s
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* in fscrypt_prepare_inline_crypt_key() and fscrypt_prepare_key().
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* I.e., in some cases (namely, if this prep_key is a per-mode
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* encryption key) another task can publish blk_key or tfm concurrently,
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* executing a RELEASE barrier. We need to use smp_load_acquire() here
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* to safely ACQUIRE the memory the other task published.
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*/
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if (fscrypt_using_inline_encryption(ci))
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return smp_load_acquire(&prep_key->blk_key) != NULL;
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return smp_load_acquire(&prep_key->tfm) != NULL;
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}
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#else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
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static inline int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
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{
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return 0;
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}
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static inline bool
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fscrypt_using_inline_encryption(const struct fscrypt_info *ci)
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{
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return false;
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}
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static inline int
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fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
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const u8 *raw_key,
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const struct fscrypt_info *ci)
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{
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WARN_ON(1);
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return -EOPNOTSUPP;
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}
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static inline void
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fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
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{
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}
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static inline bool
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fscrypt_is_key_prepared(struct fscrypt_prepared_key *prep_key,
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const struct fscrypt_info *ci)
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{
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return smp_load_acquire(&prep_key->tfm) != NULL;
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}
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#endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
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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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/*
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* Size of the raw key in bytes. This remains set even if ->raw was
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* zeroized due to no longer being needed. I.e. we still remember the
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* size of the key even if we don't need to remember the key itself.
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*/
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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 this master key's key->sem.
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*/
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struct fscrypt_master_key_secret mk_secret;
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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 keyring's own semaphore, this is
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* protected by this 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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|
/*
|
|
* List of inodes that were unlocked using this key. This allows the
|
|
* inodes to be evicted efficiently if the key is removed.
|
|
*/
|
|
struct list_head mk_decrypted_inodes;
|
|
spinlock_t mk_decrypted_inodes_lock;
|
|
|
|
/*
|
|
* Per-mode encryption keys for the various types of encryption policies
|
|
* that use them. Allocated and derived on-demand.
|
|
*/
|
|
struct fscrypt_prepared_key mk_direct_keys[FSCRYPT_MODE_MAX + 1];
|
|
struct fscrypt_prepared_key mk_iv_ino_lblk_64_keys[FSCRYPT_MODE_MAX + 1];
|
|
struct fscrypt_prepared_key mk_iv_ino_lblk_32_keys[FSCRYPT_MODE_MAX + 1];
|
|
|
|
/* Hash key for inode numbers. Initialized only when needed. */
|
|
siphash_key_t mk_ino_hash_key;
|
|
bool mk_ino_hash_key_initialized;
|
|
|
|
} __randomize_layout;
|
|
|
|
static inline bool
|
|
is_master_key_secret_present(const struct fscrypt_master_key_secret *secret)
|
|
{
|
|
/*
|
|
* The READ_ONCE() is only necessary for fscrypt_drop_inode() and
|
|
* fscrypt_key_describe(). These run in atomic context, so they can't
|
|
* take the key semaphore and thus 'secret' can change concurrently
|
|
* which would be a data race. But they only need to know whether the
|
|
* secret *was* present at the time of check, so READ_ONCE() suffices.
|
|
*/
|
|
return READ_ONCE(secret->size) != 0;
|
|
}
|
|
|
|
static inline const char *master_key_spec_type(
|
|
const struct fscrypt_key_specifier *spec)
|
|
{
|
|
switch (spec->type) {
|
|
case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
|
|
return "descriptor";
|
|
case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
|
|
return "identifier";
|
|
}
|
|
return "[unknown]";
|
|
}
|
|
|
|
static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
|
|
{
|
|
switch (spec->type) {
|
|
case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
|
|
return FSCRYPT_KEY_DESCRIPTOR_SIZE;
|
|
case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
|
|
return FSCRYPT_KEY_IDENTIFIER_SIZE;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
struct key *
|
|
fscrypt_find_master_key(struct super_block *sb,
|
|
const struct fscrypt_key_specifier *mk_spec);
|
|
|
|
int fscrypt_add_test_dummy_key(struct super_block *sb,
|
|
struct fscrypt_key_specifier *key_spec);
|
|
|
|
int fscrypt_verify_key_added(struct super_block *sb,
|
|
const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
|
|
|
|
int __init fscrypt_init_keyring(void);
|
|
|
|
/* keysetup.c */
|
|
|
|
struct fscrypt_mode {
|
|
const char *friendly_name;
|
|
const char *cipher_str;
|
|
int keysize; /* key size in bytes */
|
|
int security_strength; /* security strength in bytes */
|
|
int ivsize; /* IV size in bytes */
|
|
int logged_impl_name;
|
|
enum blk_crypto_mode_num blk_crypto_mode;
|
|
};
|
|
|
|
extern struct fscrypt_mode fscrypt_modes[];
|
|
|
|
int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
|
|
const u8 *raw_key, const struct fscrypt_info *ci);
|
|
|
|
void fscrypt_destroy_prepared_key(struct fscrypt_prepared_key *prep_key);
|
|
|
|
int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci, const u8 *raw_key);
|
|
|
|
int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
|
|
const struct fscrypt_master_key *mk);
|
|
|
|
void fscrypt_hash_inode_number(struct fscrypt_info *ci,
|
|
const struct fscrypt_master_key *mk);
|
|
|
|
int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported);
|
|
|
|
/**
|
|
* fscrypt_require_key() - require an inode's encryption key
|
|
* @inode: the inode we need the key for
|
|
*
|
|
* If the inode is encrypted, set up its encryption key if not already done.
|
|
* Then require that the key be present and return -ENOKEY otherwise.
|
|
*
|
|
* No locks are needed, and the key will live as long as the struct inode --- so
|
|
* it won't go away from under you.
|
|
*
|
|
* Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
|
|
* if a problem occurred while setting up the encryption key.
|
|
*/
|
|
static inline int fscrypt_require_key(struct inode *inode)
|
|
{
|
|
if (IS_ENCRYPTED(inode)) {
|
|
int err = fscrypt_get_encryption_info(inode, false);
|
|
|
|
if (err)
|
|
return err;
|
|
if (!fscrypt_has_encryption_key(inode))
|
|
return -ENOKEY;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* keysetup_v1.c */
|
|
|
|
void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
|
|
|
|
int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
|
|
const u8 *raw_master_key);
|
|
|
|
int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci);
|
|
|
|
/* policy.c */
|
|
|
|
bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
|
|
const union fscrypt_policy *policy2);
|
|
bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
|
|
const struct inode *inode);
|
|
int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
|
|
const union fscrypt_context *ctx_u,
|
|
int ctx_size);
|
|
const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir);
|
|
|
|
#endif /* _FSCRYPT_PRIVATE_H */
|