[people/ms/linux.git] / fs / crypto / fscrypt_private.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * fscrypt_private.h
 *
 * Copyright (C) 2015, Google, Inc.
 *
 * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
 * Heavily modified since then.
 */

#ifndef _FSCRYPT_PRIVATE_H
#define _FSCRYPT_PRIVATE_H

#include <linux/fscrypt.h>
#include <linux/siphash.h>
#include <crypto/hash.h>
#include <linux/blk-crypto.h>

#define CONST_STRLEN(str)       (sizeof(str) - 1)

#define FSCRYPT_FILE_NONCE_SIZE 16

/*
 * Minimum size of an fscrypt master key.  Note: a longer key will be required
 * if ciphers with a 256-bit security strength are used.  This is just the
 * absolute minimum, which applies when only 128-bit encryption is used.
 */
#define FSCRYPT_MIN_KEY_SIZE    16

#define FSCRYPT_CONTEXT_V1      1
#define FSCRYPT_CONTEXT_V2      2

/* Keep this in sync with include/uapi/linux/fscrypt.h */
#define FSCRYPT_MODE_MAX        FSCRYPT_MODE_ADIANTUM

struct fscrypt_context_v1 {
        u8 version; /* FSCRYPT_CONTEXT_V1 */
        u8 contents_encryption_mode;
        u8 filenames_encryption_mode;
        u8 flags;
        u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
        u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
};

struct fscrypt_context_v2 {
        u8 version; /* FSCRYPT_CONTEXT_V2 */
        u8 contents_encryption_mode;
        u8 filenames_encryption_mode;
        u8 flags;
        u8 __reserved[4];
        u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
        u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
};

/*
 * fscrypt_context - the encryption context of an inode
 *
 * This is the on-disk equivalent of an fscrypt_policy, stored alongside each
 * encrypted file usually in a hidden extended attribute.  It contains the
 * fields from the fscrypt_policy, in order to identify the encryption algorithm
 * and key with which the file is encrypted.  It also contains a nonce that was
 * randomly generated by fscrypt itself; this is used as KDF input or as a tweak
 * to cause different files to be encrypted differently.
 */
union fscrypt_context {
        u8 version;
        struct fscrypt_context_v1 v1;
        struct fscrypt_context_v2 v2;
};

/*
 * Return the size expected for the given fscrypt_context based on its version
 * number, or 0 if the context version is unrecognized.
 */
static inline int fscrypt_context_size(const union fscrypt_context *ctx)
{
        switch (ctx->version) {
        case FSCRYPT_CONTEXT_V1:
                BUILD_BUG_ON(sizeof(ctx->v1) != 28);
                return sizeof(ctx->v1);
        case FSCRYPT_CONTEXT_V2:
                BUILD_BUG_ON(sizeof(ctx->v2) != 40);
                return sizeof(ctx->v2);
        }
        return 0;
}

/* Check whether an fscrypt_context has a recognized version number and size */
static inline bool fscrypt_context_is_valid(const union fscrypt_context *ctx,
                                            int ctx_size)
{
        return ctx_size >= 1 && ctx_size == fscrypt_context_size(ctx);
}

/* Retrieve the context's nonce, assuming the context was already validated */
static inline const u8 *fscrypt_context_nonce(const union fscrypt_context *ctx)
{
        switch (ctx->version) {
        case FSCRYPT_CONTEXT_V1:
                return ctx->v1.nonce;
        case FSCRYPT_CONTEXT_V2:
                return ctx->v2.nonce;
        }
        WARN_ON(1);
        return NULL;
}

union fscrypt_policy {
        u8 version;
        struct fscrypt_policy_v1 v1;
        struct fscrypt_policy_v2 v2;
};

/*
 * Return the size expected for the given fscrypt_policy based on its version
 * number, or 0 if the policy version is unrecognized.
 */
static inline int fscrypt_policy_size(const union fscrypt_policy *policy)
{
        switch (policy->version) {
        case FSCRYPT_POLICY_V1:
                return sizeof(policy->v1);
        case FSCRYPT_POLICY_V2:
                return sizeof(policy->v2);
        }
        return 0;
}

/* Return the contents encryption mode of a valid encryption policy */
static inline u8
fscrypt_policy_contents_mode(const union fscrypt_policy *policy)
{
        switch (policy->version) {
        case FSCRYPT_POLICY_V1:
                return policy->v1.contents_encryption_mode;
        case FSCRYPT_POLICY_V2:
                return policy->v2.contents_encryption_mode;
        }
        BUG();
}

/* Return the filenames encryption mode of a valid encryption policy */
static inline u8
fscrypt_policy_fnames_mode(const union fscrypt_policy *policy)
{
        switch (policy->version) {
        case FSCRYPT_POLICY_V1:
                return policy->v1.filenames_encryption_mode;
        case FSCRYPT_POLICY_V2:
                return policy->v2.filenames_encryption_mode;
        }
        BUG();
}

/* Return the flags (FSCRYPT_POLICY_FLAG*) of a valid encryption policy */
static inline u8
fscrypt_policy_flags(const union fscrypt_policy *policy)
{
        switch (policy->version) {
        case FSCRYPT_POLICY_V1:
                return policy->v1.flags;
        case FSCRYPT_POLICY_V2:
                return policy->v2.flags;
        }
        BUG();
}

/*
 * 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;

/**
 * struct fscrypt_prepared_key - a key prepared for actual encryption/decryption
 * @tfm: crypto API transform object
 * @blk_key: key for blk-crypto
 *
 * Normally only one of the fields will be non-NULL.
 */
struct fscrypt_prepared_key {
        struct crypto_skcipher *tfm;
#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
        struct fscrypt_blk_crypto_key *blk_key;
#endif
};

/*
 * 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 key in a form prepared for actual encryption/decryption */
        struct fscrypt_prepared_key ci_enc_key;

        /* True if ci_enc_key should be freed when this fscrypt_info is freed */
        bool ci_owns_key;

#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
        /*
         * True if this inode will use inline encryption (blk-crypto) instead of
         * the traditional filesystem-layer encryption.
         */
        bool ci_inlinecrypt;
#endif

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

        /* Back-pointer to the inode */
        struct inode *ci_inode;

        /*
         * The master key with which this inode was unlocked (decrypted).  This
         * will be NULL if the master key was found in a process-subscribed
         * keyring rather than in the filesystem-level keyring.
         */
        struct key *ci_master_key;

        /*
         * Link in list of inodes that were unlocked with the master key.
         * Only used when ->ci_master_key is set.
         */
        struct list_head ci_master_key_link;

        /*
         * If non-NULL, then encryption is done using the master key directly
         * and ci_enc_key will equal ci_direct_key->dk_key.
         */
        struct fscrypt_direct_key *ci_direct_key;

        /*
         * This inode's hash key for filenames.  This is a 128-bit SipHash-2-4
         * key.  This is only set for directories that use a keyed dirhash over
         * the plaintext filenames -- currently just casefolded directories.
         */
        siphash_key_t ci_dirhash_key;
        bool ci_dirhash_key_initialized;

        /* The encryption policy used by this inode */
        union fscrypt_policy ci_policy;

        /* This inode's nonce, copied from the fscrypt_context */
        u8 ci_nonce[FSCRYPT_FILE_NONCE_SIZE];

        /* Hashed inode number.  Only set for IV_INO_LBLK_32 */
        u32 ci_hashed_ino;
};

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

/* crypto.c */
extern struct kmem_cache *fscrypt_info_cachep;
int fscrypt_initialize(unsigned int cop_flags);
int fscrypt_crypt_block(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);
struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);

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

#define fscrypt_warn(inode, fmt, ...)           \
        fscrypt_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
#define fscrypt_err(inode, fmt, ...)            \
        fscrypt_msg((inode), 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[FSCRYPT_FILE_NONCE_SIZE];
        };
        u8 raw[FSCRYPT_MAX_IV_SIZE];
        __le64 dun[FSCRYPT_MAX_IV_SIZE / sizeof(__le64)];
};

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

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

/* hkdf.c */

struct fscrypt_hkdf {
        struct crypto_shash *hmac_tfm;
};

int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
                      unsigned int master_key_size);

/*
 * The list of contexts in which fscrypt uses HKDF.  These values are used as
 * the first byte of the HKDF application-specific info string to guarantee that
 * info strings are never repeated between contexts.  This ensures that all HKDF
 * outputs are unique and cryptographically isolated, i.e. knowledge of one
 * output doesn't reveal another.
 */
#define HKDF_CONTEXT_KEY_IDENTIFIER     1 /* info=<empty>               */
#define HKDF_CONTEXT_PER_FILE_ENC_KEY   2 /* info=file_nonce            */
#define HKDF_CONTEXT_DIRECT_KEY         3 /* info=mode_num              */
#define HKDF_CONTEXT_IV_INO_LBLK_64_KEY 4 /* info=mode_num||fs_uuid     */
#define HKDF_CONTEXT_DIRHASH_KEY        5 /* info=file_nonce            */
#define HKDF_CONTEXT_IV_INO_LBLK_32_KEY 6 /* info=mode_num||fs_uuid     */
#define HKDF_CONTEXT_INODE_HASH_KEY     7 /* info=<empty>               */

int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
                        const u8 *info, unsigned int infolen,
                        u8 *okm, unsigned int okmlen);

void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);

/* inline_crypt.c */
#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
int fscrypt_select_encryption_impl(struct fscrypt_info *ci);

static inline bool
fscrypt_using_inline_encryption(const struct fscrypt_info *ci)
{
        return ci->ci_inlinecrypt;
}

int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
                                     const u8 *raw_key,
                                     const struct fscrypt_info *ci);

void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key);

/*
 * Check whether the crypto transform or blk-crypto key has been allocated in
 * @prep_key, depending on which encryption implementation the file will use.
 */
static inline bool
fscrypt_is_key_prepared(struct fscrypt_prepared_key *prep_key,
                        const struct fscrypt_info *ci)
{
        /*
         * The two smp_load_acquire()'s here pair with the smp_store_release()'s
         * in fscrypt_prepare_inline_crypt_key() and fscrypt_prepare_key().
         * I.e., in some cases (namely, if this prep_key is a per-mode
         * encryption key) another task can publish blk_key or tfm concurrently,
         * executing a RELEASE barrier.  We need to use smp_load_acquire() here
         * to safely ACQUIRE the memory the other task published.
         */
        if (fscrypt_using_inline_encryption(ci))
                return smp_load_acquire(&prep_key->blk_key) != NULL;
        return smp_load_acquire(&prep_key->tfm) != NULL;
}

#else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */

static inline int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
{
        return 0;
}

static inline bool
fscrypt_using_inline_encryption(const struct fscrypt_info *ci)
{
        return false;
}

static inline int
fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
                                 const u8 *raw_key,
                                 const struct fscrypt_info *ci)
{
        WARN_ON(1);
        return -EOPNOTSUPP;
}

static inline void
fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
{
}

static inline bool
fscrypt_is_key_prepared(struct fscrypt_prepared_key *prep_key,
                        const struct fscrypt_info *ci)
{
        return smp_load_acquire(&prep_key->tfm) != NULL;
}
#endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */

/* keyring.c */

/*
 * fscrypt_master_key_secret - secret key material of an in-use master key
 */
struct fscrypt_master_key_secret {

        /*
         * For v2 policy keys: HKDF context keyed by this master key.
         * For v1 policy keys: not set (hkdf.hmac_tfm == NULL).
         */
        struct fscrypt_hkdf     hkdf;

        /*
         * Size of the raw key in bytes.  This remains set even if ->raw was
         * zeroized due to no longer being needed.  I.e. we still remember the
         * size of the key even if we don't need to remember the key itself.
         */
        u32                     size;

        /* For v1 policy keys: the raw key.  Wiped for v2 policy keys. */
        u8                      raw[FSCRYPT_MAX_KEY_SIZE];

} __randomize_layout;

/*
 * fscrypt_master_key - an in-use master key
 *
 * This represents a master encryption key which has been added to the
 * filesystem and can be used to "unlock" the encrypted files which were
 * encrypted with it.
 */
struct fscrypt_master_key {

        /*
         * The secret key material.  After FS_IOC_REMOVE_ENCRYPTION_KEY is
         * executed, this is wiped and no new inodes can be unlocked with this
         * key; however, there may still be inodes in ->mk_decrypted_inodes
         * which could not be evicted.  As long as some inodes still remain,
         * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
         * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
         *
         * Locking: protected by this master key's key->sem.
         */
        struct fscrypt_master_key_secret        mk_secret;

        /*
         * For v1 policy keys: an arbitrary key descriptor which was assigned by
         * userspace (->descriptor).
         *
         * For v2 policy keys: a cryptographic hash of this key (->identifier).
         */
        struct fscrypt_key_specifier            mk_spec;

        /*
         * Keyring which contains a key of type 'key_type_fscrypt_user' for each
         * user who has added this key.  Normally each key will be added by just
         * one user, but it's possible that multiple users share a key, and in
         * that case we need to keep track of those users so that one user can't
         * remove the key before the others want it removed too.
         *
         * This is NULL for v1 policy keys; those can only be added by root.
         *
         * Locking: in addition to this keyring's own semaphore, this is
         * protected by this master key's key->sem, so we can do atomic
         * search+insert.  It can also be searched without taking any locks, but
         * in that case the returned key may have already been removed.
         */
        struct key              *mk_users;

        /*
         * Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
         * Once this goes to 0, the master key is removed from ->s_master_keys.
         * The 'struct fscrypt_master_key' will continue to live as long as the
         * 'struct key' whose payload it is, but we won't let this reference
         * count rise again.
         */
        refcount_t              mk_refcount;

        /*
         * 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_get_test_dummy_key_identifier(
                          u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);

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_cryptoapi_impl;
        int logged_blk_crypto_native;
        int logged_blk_crypto_fallback;
        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);
int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
                               struct fscrypt_key_specifier *key_spec);
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 */