Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/linux

Pull fscrypt fixes from Eric Biggers: - Fix a bug where in a specific edge case, file contents en/decryption could be done with the wrong data unit size - Fix the data structure used for keeping track of users that have added an fscrypt key to be a simple list instead of a 'struct key' keyring This fixes issues such as a lockdep report found by syzbot and possible unintended interactions with the keyctl() system calls * tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/linux: fscrypt: Replace mk_users keyring with simple list fscrypt: Fix key setup in edge case with multiple data unit sizes
2026-07-21 22:47:51 -04:00 · 2026-06-27 09:20:16 -07:00
parent 5a66900afb 696c030e1e
commit 6ca693ea90
4 changed files with 233 additions and 216 deletions
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -236,7 +236,7 @@ struct fscrypt_symlink_data {
 * @tfm: crypto API transform object
 * @blk_key: key for blk-crypto
 *
- * Normally only one of the fields will be non-NULL.
+ * Only one of the fields is non-NULL.
 */
 struct fscrypt_prepared_key {
 	struct crypto_sync_skcipher *tfm;
@@ -245,6 +245,15 @@ struct fscrypt_prepared_key {
 #endif
 };

+/* An entry in the linked list ->mk_mode_keys */
+struct fscrypt_mode_key {
+	struct fscrypt_prepared_key key;
+	struct list_head link;
+	u8 hkdf_context;
+	u8 mode_num;
+	u8 data_unit_bits;
+};
+
 /*
 * fscrypt_inode_info - the "encryption key" for an inode
 *
@@ -430,20 +439,12 @@ int fscrypt_derive_sw_secret(struct super_block *sb,
 * @prep_key, depending on which encryption implementation the file will use.
 */
 static inline bool
-fscrypt_is_key_prepared(struct fscrypt_prepared_key *prep_key,
+fscrypt_is_key_prepared(const struct fscrypt_prepared_key *prep_key,
 			const struct fscrypt_inode_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;
+		return prep_key->blk_key != NULL;
+	return prep_key->tfm != NULL;
 }

 #else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
@@ -486,15 +487,28 @@ fscrypt_derive_sw_secret(struct super_block *sb,
 }

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

 /* keyring.c */

+/*
+ * fscrypt_master_key_user - a user's claim to a master key
+ */
+struct fscrypt_master_key_user {
+	struct list_head link;
+	kuid_t uid;
+	/*
+	 * This 'struct key' contains no secret.  It exists solely to charge the
+	 * appropriate user's key quota.
+	 */
+	struct key *quota_key;
+};
+
 /*
 * fscrypt_master_key_secret - secret key material of an in-use master key
 */
@@ -577,8 +591,8 @@ struct fscrypt_master_key {
 	/*
 	 * Active and structural reference counts.  An active ref guarantees
 	 * that the struct continues to exist, continues to be in the keyring
-	 * ->s_master_keys, and that any embedded subkeys (e.g.
-	 * ->mk_direct_keys) that have been prepared continue to exist.
+	 * ->s_master_keys, and that any non-file-scoped subkeys (e.g.
+	 * ->mk_mode_keys) that have been prepared continue to exist.
 	 * A structural ref only guarantees that the struct continues to exist.
 	 *
 	 * There is one active ref associated with ->mk_present being true, and
@@ -610,19 +624,18 @@ struct fscrypt_master_key {
 	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.
+	 * List of user claims to this key (struct fscrypt_master_key_user).
+	 * 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.
+	 * Used only for v2 policy keys.  v1 policy keys can be added only by
+	 * root, so user tracking doesn't apply to them.
 	 *
-	 * Locking: protected by ->mk_sem.  (We don't just rely on the keyrings
-	 * subsystem semaphore ->mk_users->sem, as we need support for atomic
-	 * search+insert along with proper synchronization with other fields.)
+	 * Locking: protected by ->mk_sem.
 	 */
-	struct key		*mk_users;
+	struct list_head	mk_users;

 	/*
 	 * List of inodes that were unlocked using this key.  This allows the
@@ -632,12 +645,21 @@ struct fscrypt_master_key {
 	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.
+	 * A list of 'struct fscrypt_mode_key' for the (hkdf_context, mode_num,
+	 * data_unit_bits, inlinecrypt) combinations that are in use for this
+	 * master key, for hkdf_context in [HKDF_CONTEXT_DIRECT_KEY,
+	 * HKDF_CONTEXT_IV_INO_LBLK_32_KEY, HKDF_CONTEXT_IV_INO_LBLK_64_KEY].
+	 *
+	 * This is a linked list and not a hash table because in practice
+	 * there's just a single encryption policy per master key, using
+	 * _at most_ 2 nodes in this list.  Per-file keys don't use this at all.
+	 *
+	 * This list is append-only until the master key is fully removed, at
+	 * which time the list is cleared.  Before then,
+	 * fscrypt_mode_key_setup_mutex synchronizes appends, and searches use
+	 * the RCU read lock together with ->mk_sem held for read.
 	 */
-	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];
+	struct list_head	mk_mode_keys;

 	/* Hash key for inode numbers.  Initialized only when needed. */
 	siphash_key_t		mk_ino_hash_key;
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -198,13 +198,7 @@ int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
 		goto fail;
 	}

-	/*
-	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
-	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
-	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
-	 * possible for per-mode keys, not for per-file keys.
-	 */
-	smp_store_release(&prep_key->blk_key, blk_key);
+	prep_key->blk_key = blk_key;
 	return 0;

 fail:
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -65,36 +65,33 @@ static void fscrypt_free_master_key(struct rcu_head *head)
 	kfree_sensitive(mk);
 }

+static void clear_mk_users(struct fscrypt_master_key *mk);
+
 void fscrypt_put_master_key(struct fscrypt_master_key *mk)
 {
 	if (!refcount_dec_and_test(&mk->mk_struct_refs))
 		return;
 	/*
-	 * No structural references left, so free ->mk_users, and also free the
+	 * No structural references left, so clear ->mk_users, and also free the
 	 * fscrypt_master_key struct itself after an RCU grace period ensures
 	 * that concurrent keyring lookups can no longer find it.
 	 */
 	WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0);
-	if (mk->mk_users) {
-		/* Clear the keyring so the quota gets released right away. */
-		keyring_clear(mk->mk_users);
-		key_put(mk->mk_users);
-		mk->mk_users = NULL;
-	}
+	clear_mk_users(mk);
 	call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
 }

 void fscrypt_put_master_key_activeref(struct super_block *sb,
 				      struct fscrypt_master_key *mk)
 {
-	size_t i;
+	struct fscrypt_mode_key *node, *tmp;

 	if (!refcount_dec_and_test(&mk->mk_active_refs))
 		return;
 	/*
 	 * No active references left, so complete the full removal of this
 	 * fscrypt_master_key struct by removing it from the keyring and
-	 * destroying any subkeys embedded in it.
+	 * destroying any non-file-scoped subkeys.
 	 */

 	if (WARN_ON_ONCE(!sb->s_master_keys))
@@ -110,13 +107,16 @@ void fscrypt_put_master_key_activeref(struct super_block *sb,
 	WARN_ON_ONCE(mk->mk_present);
 	WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));

-	for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
-		fscrypt_destroy_prepared_key(
-				sb, &mk->mk_direct_keys[i]);
-		fscrypt_destroy_prepared_key(
-				sb, &mk->mk_iv_ino_lblk_64_keys[i]);
-		fscrypt_destroy_prepared_key(
-				sb, &mk->mk_iv_ino_lblk_32_keys[i]);
+	/*
+	 * Destroy any non-file-scoped subkeys.  Since ->mk_active_refs == 0,
+	 * they're no longer referenced by any inodes.  Nor can key setup run
+	 * and use them again.  So they're no longer needed.  (This implies no
+	 * concurrent readers, so we don't need list_del_rcu() for example.)
+	 */
+	list_for_each_entry_safe(node, tmp, &mk->mk_mode_keys, link) {
+		fscrypt_destroy_prepared_key(sb, &node->key);
+		list_del(&node->link);
+		kfree(node);
 	}
 	memzero_explicit(&mk->mk_ino_hash_key,
 			 sizeof(mk->mk_ino_hash_key));
@@ -162,8 +162,8 @@ static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
 }

 /*
- * Type of key in ->mk_users.  Each key of this type represents a particular
- * user who has added a particular master key.
+ * Type of fscrypt_master_key_user::quota_key.  This contains no secret; it
+ * exists solely to charge a user's key quota.
 *
 * Note that the name of this key type really should be something like
 * ".fscrypt-user" instead of simply ".fscrypt".  But the shorter name is chosen
@@ -177,30 +177,9 @@ static struct key_type key_type_fscrypt_user = {
 	.describe		= fscrypt_user_key_describe,
 };

-#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE	\
-	(CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
-	 CONST_STRLEN("-users") + 1)
-
 #define FSCRYPT_MK_USER_DESCRIPTION_SIZE	\
 	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)

-static void format_mk_users_keyring_description(
-			char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
-			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
-{
-	sprintf(description, "fscrypt-%*phN-users",
-		FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
-}
-
-static void format_mk_user_description(
-			char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
-			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
-{
-
-	sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
-		mk_identifier, __kuid_val(current_fsuid()));
-}
-
 /* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
 static int allocate_filesystem_keyring(struct super_block *sb)
 {
@@ -335,91 +314,94 @@ fscrypt_find_master_key(struct super_block *sb,
 	return mk;
 }

-static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
+/* Find the current user's claim in ->mk_users.  ->mk_sem must be held. */
+static struct fscrypt_master_key_user *
+find_master_key_user(struct fscrypt_master_key *mk)
 {
-	char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
-	struct key *keyring;
+	struct fscrypt_master_key_user *mk_user;
+	kuid_t uid = current_fsuid();

-	format_mk_users_keyring_description(description,
-					    mk->mk_spec.u.identifier);
-	keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
-				current_cred(), KEY_POS_SEARCH |
-				  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
-				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
-	if (IS_ERR(keyring))
-		return PTR_ERR(keyring);
-
-	mk->mk_users = keyring;
-	return 0;
-}
-
-/*
- * Find the current user's "key" in the master key's ->mk_users.
- * Returns ERR_PTR(-ENOKEY) if not found.
- */
-static struct key *find_master_key_user(struct fscrypt_master_key *mk)
-{
-	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
-	key_ref_t keyref;
-
-	format_mk_user_description(description, mk->mk_spec.u.identifier);
-
-	/*
-	 * We need to mark the keyring reference as "possessed" so that we
-	 * acquire permission to search it, via the KEY_POS_SEARCH permission.
-	 */
-	keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
-				&key_type_fscrypt_user, description, false);
-	if (IS_ERR(keyref)) {
-		if (PTR_ERR(keyref) == -EAGAIN || /* not found */
-		    PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
-			keyref = ERR_PTR(-ENOKEY);
-		return ERR_CAST(keyref);
+	list_for_each_entry(mk_user, &mk->mk_users, link) {
+		if (uid_eq(mk_user->uid, uid))
+			return mk_user;
 	}
-	return key_ref_to_ptr(keyref);
+	return NULL;
 }

 /*
- * Give the current user a "key" in ->mk_users.  This charges the user's quota
+ * Give the current user a claim in ->mk_users.  This charges the user's quota
 * and marks the master key as added by the current user, so that it cannot be
 * removed by another user with the key.  Either ->mk_sem must be held for
 * write, or the master key must be still undergoing initialization.
 */
 static int add_master_key_user(struct fscrypt_master_key *mk)
 {
+	kuid_t uid = current_fsuid();
 	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
-	struct key *mk_user;
+	struct key *quota_key;
+	struct fscrypt_master_key_user *mk_user;
 	int err;

-	format_mk_user_description(description, mk->mk_spec.u.identifier);
-	mk_user = key_alloc(&key_type_fscrypt_user, description,
-			    current_fsuid(), current_gid(), current_cred(),
-			    KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
-	if (IS_ERR(mk_user))
-		return PTR_ERR(mk_user);
+	snprintf(description, sizeof(description), "%*phN.uid.%u",
+		 FSCRYPT_KEY_IDENTIFIER_SIZE, mk->mk_spec.u.identifier,
+		 __kuid_val(uid));
+	quota_key = key_alloc(&key_type_fscrypt_user, description, uid,
+			      current_gid(), current_cred(),
+			      KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
+	if (IS_ERR(quota_key))
+		return PTR_ERR(quota_key);

-	err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
-	key_put(mk_user);
-	return err;
+	err = key_instantiate_and_link(quota_key, NULL, 0, NULL, NULL);
+	if (err) {
+		key_put(quota_key);
+		return err;
+	}
+
+	mk_user = kzalloc_obj(*mk_user);
+	if (!mk_user) {
+		key_put(quota_key);
+		return -ENOMEM;
+	}
+	mk_user->uid = uid;
+	mk_user->quota_key = quota_key;
+	list_add(&mk_user->link, &mk->mk_users);
+	return 0;
+}
+
+static void unlink_and_free_mk_user(struct fscrypt_master_key_user *mk_user)
+{
+	list_del(&mk_user->link);
+	key_put(mk_user->quota_key);
+	kfree(mk_user);
 }

 /*
- * Remove the current user's "key" from ->mk_users.
+ * Remove the current user's claim from ->mk_users.
 * ->mk_sem must be held for write.
 *
- * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
+ * Returns 0 if removed or -ENOKEY if not found.
 */
 static int remove_master_key_user(struct fscrypt_master_key *mk)
 {
-	struct key *mk_user;
-	int err;
+	struct fscrypt_master_key_user *mk_user;

 	mk_user = find_master_key_user(mk);
-	if (IS_ERR(mk_user))
-		return PTR_ERR(mk_user);
-	err = key_unlink(mk->mk_users, mk_user);
-	key_put(mk_user);
-	return err;
+	if (!mk_user)
+		return -ENOKEY;
+	unlink_and_free_mk_user(mk_user);
+	return 0;
+}
+
+/*
+ * Clear ->mk_users.  Either ->mk_sem must be held for write, or 'mk' must have
+ * no structural references left.
+ */
+static void clear_mk_users(struct fscrypt_master_key *mk)
+{
+	struct fscrypt_master_key_user *mk_user, *tmp;
+
+	list_for_each_entry_safe(mk_user, tmp, &mk->mk_users, link)
+		unlink_and_free_mk_user(mk_user);
 }

 /*
@@ -442,13 +424,14 @@ static int add_new_master_key(struct super_block *sb,
 	refcount_set(&mk->mk_struct_refs, 1);
 	mk->mk_spec = *mk_spec;

+	INIT_LIST_HEAD(&mk->mk_users);
+
 	INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
 	spin_lock_init(&mk->mk_decrypted_inodes_lock);

+	INIT_LIST_HEAD(&mk->mk_mode_keys);
+
 	if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
-		err = allocate_master_key_users_keyring(mk);
-		if (err)
-			goto out_put;
 		err = add_master_key_user(mk);
 		if (err)
 			goto out_put;
@@ -477,19 +460,13 @@ static int add_existing_master_key(struct fscrypt_master_key *mk,
 	int err;

 	/*
-	 * If the current user is already in ->mk_users, then there's nothing to
-	 * do.  Otherwise, we need to add the user to ->mk_users.  (Neither is
-	 * applicable for v1 policy keys, which have NULL ->mk_users.)
+	 * For v2 policy keys (FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER): If the current
+	 * user is already in ->mk_users, then there's nothing to do.
+	 * Otherwise, add the user to ->mk_users.
 	 */
-	if (mk->mk_users) {
-		struct key *mk_user = find_master_key_user(mk);
-
-		if (mk_user != ERR_PTR(-ENOKEY)) {
-			if (IS_ERR(mk_user))
-				return PTR_ERR(mk_user);
-			key_put(mk_user);
+	if (mk->mk_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
+		if (find_master_key_user(mk) != NULL)
 			return 0;
-		}
 		err = add_master_key_user(mk);
 		if (err)
 			return err;
@@ -888,7 +865,6 @@ int fscrypt_verify_key_added(struct super_block *sb,
 {
 	struct fscrypt_key_specifier mk_spec;
 	struct fscrypt_master_key *mk;
-	struct key *mk_user;
 	int err;

 	mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
@@ -900,13 +876,10 @@ int fscrypt_verify_key_added(struct super_block *sb,
 		goto out;
 	}
 	down_read(&mk->mk_sem);
-	mk_user = find_master_key_user(mk);
-	if (IS_ERR(mk_user)) {
-		err = PTR_ERR(mk_user);
-	} else {
-		key_put(mk_user);
+	if (find_master_key_user(mk) != NULL)
 		err = 0;
-	}
+	else
+		err = -ENOKEY;
 	up_read(&mk->mk_sem);
 	fscrypt_put_master_key(mk);
 out:
@@ -1098,16 +1071,18 @@ static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
 	down_write(&mk->mk_sem);

 	/* If relevant, remove current user's (or all users) claim to the key */
-	if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
-		if (all_users)
-			err = keyring_clear(mk->mk_users);
-		else
+	if (!list_empty(&mk->mk_users)) {
+		if (all_users) {
+			clear_mk_users(mk);
+			err = 0;
+		} else {
 			err = remove_master_key_user(mk);
+		}
 		if (err) {
 			up_write(&mk->mk_sem);
 			goto out_put_key;
 		}
-		if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
+		if (!list_empty(&mk->mk_users)) {
 			/*
 			 * Other users have still added the key too.  We removed
 			 * the current user's claim to the key, but we still
@@ -1193,6 +1168,8 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 	struct super_block *sb = file_inode(filp)->i_sb;
 	struct fscrypt_get_key_status_arg arg;
 	struct fscrypt_master_key *mk;
+	kuid_t uid;
+	const struct fscrypt_master_key_user *mk_user;
 	int err;

 	if (copy_from_user(&arg, uarg, sizeof(arg)))
@@ -1225,19 +1202,13 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 	}

 	arg.status = FSCRYPT_KEY_STATUS_PRESENT;
-	if (mk->mk_users) {
-		struct key *mk_user;

-		arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
-		mk_user = find_master_key_user(mk);
-		if (!IS_ERR(mk_user)) {
+	uid = current_fsuid();
+	list_for_each_entry(mk_user, &mk->mk_users, link) {
+		arg.user_count++;
+		if (uid_eq(mk_user->uid, uid))
 			arg.status_flags |=
 				FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
-			key_put(mk_user);
-		} else if (mk_user != ERR_PTR(-ENOKEY)) {
-			err = PTR_ERR(mk_user);
-			goto out_release_key;
-		}
 	}
 	err = 0;
 out_release_key:
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -163,13 +163,7 @@ int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
 	tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
 	if (IS_ERR(tfm))
 		return PTR_ERR(tfm);
-	/*
-	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
-	 * I.e., here we publish ->tfm with a RELEASE barrier so that
-	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
-	 * possible for per-mode keys, not for per-file keys.
-	 */
-	smp_store_release(&prep_key->tfm, tfm);
+	prep_key->tfm = tfm;
 	return 0;
 }

@@ -190,9 +184,37 @@ int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci,
 	return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
 }

+/*
+ * Find the fscrypt_prepared_key (if any) for a particular (mk, hkdf_context,
+ * mode_num, data_unit_bits, inlinecrypt) combination.
+ *
+ * The caller must hold ->mk_sem for reading and ->mk_present must be true,
+ * ensuring that ->mk_mode_keys is still append-only.
+ */
+static struct fscrypt_prepared_key *
+fscrypt_find_mode_key(struct fscrypt_master_key *mk, u8 hkdf_context,
+		      u8 mode_num, const struct fscrypt_inode_info *ci)
+{
+	struct fscrypt_mode_key *node;
+
+	/*
+	 * The RCU read lock here is used only to synchronize with concurrent
+	 * list_add_tail_rcu().  Concurrent deletions are impossible here, so
+	 * returning a pointer to a node without taking any refcount is safe.
+	 */
+	guard(rcu)();
+	list_for_each_entry_rcu(node, &mk->mk_mode_keys, link) {
+		if (node->hkdf_context == hkdf_context &&
+		    node->mode_num == mode_num &&
+		    node->data_unit_bits == ci->ci_data_unit_bits &&
+		    fscrypt_is_key_prepared(&node->key, ci))
+			return &node->key;
+	}
+	return NULL;
+}
+
 static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
 				  struct fscrypt_master_key *mk,
-				  struct fscrypt_prepared_key *keys,
 				  u8 hkdf_context, bool include_fs_uuid)
 {
 	const struct inode *inode = ci->ci_inode;
@@ -200,7 +222,8 @@ static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
 	struct fscrypt_mode *mode = ci->ci_mode;
 	const u8 mode_num = mode - fscrypt_modes;
 	struct fscrypt_prepared_key *prep_key;
-	u8 mode_key[FSCRYPT_MAX_RAW_KEY_SIZE];
+	struct fscrypt_mode_key *new_node;
+	u8 raw_mode_key[FSCRYPT_MAX_RAW_KEY_SIZE];
 	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
 	unsigned int hkdf_infolen = 0;
 	bool use_hw_wrapped_key = false;
@@ -223,48 +246,56 @@ static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
 		use_hw_wrapped_key = true;
 	}

-	prep_key = &keys[mode_num];
-	if (fscrypt_is_key_prepared(prep_key, ci)) {
+	prep_key = fscrypt_find_mode_key(mk, hkdf_context, mode_num, ci);
+	if (prep_key) {
 		ci->ci_enc_key = *prep_key;
 		return 0;
 	}

-	mutex_lock(&fscrypt_mode_key_setup_mutex);
+	guard(mutex)(&fscrypt_mode_key_setup_mutex);

-	if (fscrypt_is_key_prepared(prep_key, ci))
-		goto done_unlock;
+	prep_key = fscrypt_find_mode_key(mk, hkdf_context, mode_num, ci);
+	if (prep_key) {
+		ci->ci_enc_key = *prep_key;
+		return 0;
+	}
+
+	new_node = kzalloc_obj(*new_node);
+	if (!new_node)
+		return -ENOMEM;
+	new_node->hkdf_context = hkdf_context;
+	new_node->mode_num = mode_num;
+	new_node->data_unit_bits = ci->ci_data_unit_bits;
+	prep_key = &new_node->key;

 	if (use_hw_wrapped_key) {
 		err = fscrypt_prepare_inline_crypt_key(prep_key,
 						       mk->mk_secret.bytes,
 						       mk->mk_secret.size, true,
 						       ci);
-		if (err)
-			goto out_unlock;
-		goto done_unlock;
+	} else {
+		static_assert(sizeof(mode_num) == 1);
+		static_assert(sizeof(sb->s_uuid) == 16);
+		static_assert(sizeof(hkdf_info) == 17);
+		hkdf_info[hkdf_infolen++] = mode_num;
+		if (include_fs_uuid) {
+			memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
+			       sizeof(sb->s_uuid));
+			hkdf_infolen += sizeof(sb->s_uuid);
+		}
+		fscrypt_hkdf_expand(&mk->mk_secret.hkdf, hkdf_context,
+				    hkdf_info, hkdf_infolen, raw_mode_key,
+				    mode->keysize);
+		err = fscrypt_prepare_key(prep_key, raw_mode_key, ci);
+		memzero_explicit(raw_mode_key, mode->keysize);
 	}
-
-	BUILD_BUG_ON(sizeof(mode_num) != 1);
-	BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
-	BUILD_BUG_ON(sizeof(hkdf_info) != 17);
-	hkdf_info[hkdf_infolen++] = mode_num;
-	if (include_fs_uuid) {
-		memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
-		       sizeof(sb->s_uuid));
-		hkdf_infolen += sizeof(sb->s_uuid);
+	if (err) {
+		kfree(new_node);
+		return err;
 	}
-	fscrypt_hkdf_expand(&mk->mk_secret.hkdf, hkdf_context, hkdf_info,
-			    hkdf_infolen, mode_key, mode->keysize);
-	err = fscrypt_prepare_key(prep_key, mode_key, ci);
-	memzero_explicit(mode_key, mode->keysize);
-	if (err)
-		goto out_unlock;
-done_unlock:
+	list_add_tail_rcu(&new_node->link, &mk->mk_mode_keys);
 	ci->ci_enc_key = *prep_key;
-	err = 0;
-out_unlock:
-	mutex_unlock(&fscrypt_mode_key_setup_mutex);
-	return err;
+	return 0;
 }

 /*
@@ -311,8 +342,8 @@ static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
 {
 	int err;

-	err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
-				     HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
+	err = setup_per_mode_enc_key(ci, mk, HKDF_CONTEXT_IV_INO_LBLK_32_KEY,
+				     true);
 	if (err)
 		return err;

@@ -364,8 +395,8 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
 		 * encryption key.  This ensures that the master key is
 		 * consistently used only for HKDF, avoiding key reuse issues.
 		 */
-		err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
-					     HKDF_CONTEXT_DIRECT_KEY, false);
+		err = setup_per_mode_enc_key(ci, mk, HKDF_CONTEXT_DIRECT_KEY,
+					     false);
 	} else if (ci->ci_policy.v2.flags &
 		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
 		/*
@@ -374,9 +405,8 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
 		 * the IVs.  This format is optimized for use with inline
 		 * encryption hardware compliant with the UFS standard.
 		 */
-		err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
-					     HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
-					     true);
+		err = setup_per_mode_enc_key(
+			ci, mk, HKDF_CONTEXT_IV_INO_LBLK_64_KEY, true);
 	} else if (ci->ci_policy.v2.flags &
 		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
 		err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);