fscrypt: pass super_block to fscrypt_put_master_key_activeref()

As this code confused Linus [1], pass the super_block as an argument to
fscrypt_put_master_key_activeref().  This removes the need to have the
back-pointer ->mk_sb, so remove that.

[1] https://lore.kernel.org/linux-fscrypt/CAHk-=wgud4Bc_um+htgfagYpZAnOoCb3NUoW67hc9LhOKsMtJg@mail.gmail.com

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221110082942.351615-1-ebiggers@kernel.org

fs/crypto/fscrypt_private.h

@@ -439,13 +439,7 @@ struct fscrypt_master_key_secret {
 struct fscrypt_master_key {
 
 	/*
-	 * Back-pointer to the super_block of the filesystem to which this
-	 * master key has been added.  Only valid if ->mk_active_refs > 0.
-	 */
-	struct super_block			*mk_sb;
-
-	/*
-	 * Link in ->mk_sb->s_master_keys->key_hashtable.
+	 * Link in ->s_master_keys->key_hashtable.
 	 * Only valid if ->mk_active_refs > 0.
 	 */
 	struct hlist_node			mk_node;
@@ -456,7 +450,7 @@ 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
-	 * ->mk_sb->s_master_keys, and that any embedded subkeys (e.g.
+	 * ->s_master_keys, and that any embedded subkeys (e.g.
 	 * ->mk_direct_keys) that have been prepared continue to exist.
 	 * A structural ref only guarantees that the struct continues to exist.
 	 *
@@ -569,7 +563,8 @@ static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
 
 void fscrypt_put_master_key(struct fscrypt_master_key *mk);
 
-void fscrypt_put_master_key_activeref(struct fscrypt_master_key *mk);
+void fscrypt_put_master_key_activeref(struct super_block *sb,
+				      struct fscrypt_master_key *mk);
 
 struct fscrypt_master_key *
 fscrypt_find_master_key(struct super_block *sb,

fs/crypto/keyring.c

@@ -79,10 +79,9 @@ void fscrypt_put_master_key(struct fscrypt_master_key *mk)
 	call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
 }
 
-void fscrypt_put_master_key_activeref(struct fscrypt_master_key *mk)
+void fscrypt_put_master_key_activeref(struct super_block *sb,
+				      struct fscrypt_master_key *mk)
 {
-	struct super_block *sb = mk->mk_sb;
-	struct fscrypt_keyring *keyring = sb->s_master_keys;
 	size_t i;
 
 	if (!refcount_dec_and_test(&mk->mk_active_refs))
@@ -93,9 +92,9 @@ void fscrypt_put_master_key_activeref(struct fscrypt_master_key *mk)
 	 * destroying any subkeys embedded in it.
 	 */
 
-	spin_lock(&keyring->lock);
+	spin_lock(&sb->s_master_keys->lock);
 	hlist_del_rcu(&mk->mk_node);
-	spin_unlock(&keyring->lock);
+	spin_unlock(&sb->s_master_keys->lock);
 
 	/*
 	 * ->mk_active_refs == 0 implies that ->mk_secret is not present and
@@ -243,7 +242,7 @@ void fscrypt_destroy_keyring(struct super_block *sb)
 			WARN_ON(refcount_read(&mk->mk_struct_refs) != 1);
 			WARN_ON(!is_master_key_secret_present(&mk->mk_secret));
 			wipe_master_key_secret(&mk->mk_secret);
-			fscrypt_put_master_key_activeref(mk);
+			fscrypt_put_master_key_activeref(sb, mk);
 		}
 	}
 	kfree_sensitive(keyring);
@@ -424,7 +423,6 @@ static int add_new_master_key(struct super_block *sb,
 	if (!mk)
 		return -ENOMEM;
 
-	mk->mk_sb = sb;
 	init_rwsem(&mk->mk_sem);
 	refcount_set(&mk->mk_struct_refs, 1);
 	mk->mk_spec = *mk_spec;
@@ -1068,7 +1066,7 @@ static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
 	err = -ENOKEY;
 	if (is_master_key_secret_present(&mk->mk_secret)) {
 		wipe_master_key_secret(&mk->mk_secret);
-		fscrypt_put_master_key_activeref(mk);
+		fscrypt_put_master_key_activeref(sb, mk);
 		err = 0;
 	}
 	inodes_remain = refcount_read(&mk->mk_active_refs) > 0;

fs/crypto/keysetup.c

@@ -509,7 +509,7 @@ static void put_crypt_info(struct fscrypt_info *ci)
 		spin_lock(&mk->mk_decrypted_inodes_lock);
 		list_del(&ci->ci_master_key_link);
 		spin_unlock(&mk->mk_decrypted_inodes_lock);
-		fscrypt_put_master_key_activeref(mk);
+		fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
 	}
 	memzero_explicit(ci, sizeof(*ci));
 	kmem_cache_free(fscrypt_info_cachep, ci);