*
* Copyright (C) 2015, Google, Inc.
*
- * This contains encryption key functions.
- *
- * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
+ * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
+ * Heavily modified since then.
*/
#ifndef _FSCRYPT_PRIVATE_H
#include <linux/fscrypt.h>
#include <crypto/hash.h>
-/* Encryption parameters */
+#define CONST_STRLEN(str) (sizeof(str) - 1)
+
#define FS_KEY_DERIVATION_NONCE_SIZE 16
-/**
- * Encryption context for inode
- *
- * Protector format:
- * 1 byte: Protector format (1 = this version)
- * 1 byte: File contents encryption mode
- * 1 byte: File names encryption mode
- * 1 byte: Flags
- * 8 bytes: Master Key descriptor
- * 16 bytes: Encryption Key derivation nonce
- */
-struct fscrypt_context {
- u8 format;
+#define FSCRYPT_MIN_KEY_SIZE 16
+
+#define FSCRYPT_CONTEXT_V1 1
+#define FSCRYPT_CONTEXT_V2 2
+
+struct fscrypt_context_v1 {
+ u8 version; /* FSCRYPT_CONTEXT_V1 */
u8 contents_encryption_mode;
u8 filenames_encryption_mode;
u8 flags;
- u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+ u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
-} __packed;
+};
+
+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[FS_KEY_DERIVATION_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;
+}
+
+#undef fscrypt_policy
+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();
+}
-#define FS_ENCRYPTION_CONTEXT_FORMAT_V1 1
+/* 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();
+}
+
+static inline bool
+fscrypt_is_direct_key_policy(const union fscrypt_policy *policy)
+{
+ return fscrypt_policy_flags(policy) & FSCRYPT_POLICY_FLAG_DIRECT_KEY;
+}
/**
* For encrypted symlinks, the ciphertext length is stored at the beginning
struct crypto_cipher *ci_essiv_tfm;
/*
- * Encryption mode used for this inode. It corresponds to either
- * ci_data_mode or ci_filename_mode, depending on the inode type.
+ * 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;
+
/*
- * If non-NULL, then this inode uses a master key directly rather than a
- * derived key, and ci_ctfm will equal ci_master_key->mk_ctfm.
- * Otherwise, this inode uses a derived key.
+ * 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 fscrypt_master_key *ci_master_key;
+ struct key *ci_master_key;
- /* fields from the fscrypt_context */
- u8 ci_data_mode;
- u8 ci_filename_mode;
- u8 ci_flags;
- u8 ci_master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
+ /*
+ * 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_ctfm will equal ci_direct_key->dk_ctfm.
+ */
+ struct fscrypt_direct_key *ci_direct_key;
+
+ /* The encryption policy used by this inode */
+ union fscrypt_policy ci_policy;
+
+ /* This inode's nonce, copied from the fscrypt_context */
u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
};
static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
u32 filenames_mode)
{
- if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC &&
- filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS)
+ if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
+ filenames_mode == FSCRYPT_MODE_AES_128_CTS)
return true;
- if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS &&
- filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)
+ if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
+ filenames_mode == FSCRYPT_MODE_AES_256_CTS)
return true;
- if (contents_mode == FS_ENCRYPTION_MODE_ADIANTUM &&
- filenames_mode == FS_ENCRYPTION_MODE_ADIANTUM)
+ if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
+ filenames_mode == FSCRYPT_MODE_ADIANTUM)
return true;
return false;
u32 orig_len, u32 max_len,
u32 *encrypted_len_ret);
-/* keyinfo.c */
+/* hkdf.c */
+
+struct fscrypt_hkdf {
+ struct crypto_shash *hmac_tfm;
+};
+
+extern 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
+#define HKDF_CONTEXT_PER_FILE_KEY 2
+#define HKDF_CONTEXT_PER_MODE_KEY 3
+
+extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
+ const u8 *info, unsigned int infolen,
+ u8 *okm, unsigned int okmlen);
+
+extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
+
+/* 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. Set even if ->raw isn't set. */
+ 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 key->sem (outer) and mk_secret_sem (inner).
+ * The reason for two locks is that key->sem also protects modifying
+ * mk_users, which ranks it above the semaphore for the keyring key
+ * type, which is in turn above page faults (via keyring_read). But
+ * sometimes filesystems call fscrypt_get_encryption_info() from within
+ * a transaction, which ranks it below page faults. So we need a
+ * separate lock which protects mk_secret but not also mk_users.
+ */
+ struct fscrypt_master_key_secret mk_secret;
+ struct rw_semaphore mk_secret_sem;
+
+ /*
+ * 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 keyrings own semaphore, this is
+ * protected by the 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 tfms for DIRECT_KEY policies, allocated on-demand */
+ struct crypto_skcipher *mk_mode_keys[__FSCRYPT_MODE_MAX + 1];
+
+} __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 ->mk_secret_sem 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;
+}
+
+extern struct key *
+fscrypt_find_master_key(struct super_block *sb,
+ const struct fscrypt_key_specifier *mk_spec);
+
+extern int fscrypt_verify_key_added(struct super_block *sb,
+ const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
+
+extern int __init fscrypt_init_keyring(void);
+
+/* keysetup.c */
struct fscrypt_mode {
const char *friendly_name;
bool needs_essiv;
};
+static inline bool
+fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
+{
+ return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
+}
+
+extern struct crypto_skcipher *
+fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
+ const struct inode *inode);
+
+extern int fscrypt_set_derived_key(struct fscrypt_info *ci,
+ const u8 *derived_key);
+
+/* keysetup_v1.c */
+
+extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
+
+extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
+ const u8 *raw_master_key);
+
+extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
+ struct fscrypt_info *ci);
+/* policy.c */
+
+extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
+ const union fscrypt_policy *policy2);
+extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
+ const struct inode *inode);
+extern int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
+ const union fscrypt_context *ctx_u,
+ int ctx_size);
+
#endif /* _FSCRYPT_PRIVATE_H */
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