fscrypt: remove unnecessary calls to fscrypt_require_key()

In an encrypted directory, a regular dentry (one that doesn't have the
no-key name flag) can only be created if the directory's encryption key
is available.

Therefore the calls to fscrypt_require_key() in __fscrypt_prepare_link()
and __fscrypt_prepare_rename() are unnecessary, as these functions
already check that the dentries they're given aren't no-key names.

Remove these unnecessary calls to fscrypt_require_key().

Link: https://lore.kernel.org/r/20201118075609.120337-6-ebiggers@kernel.orgSigned-off-by: NEric Biggers <ebiggers@google.com>

fs/crypto/hooks.c

@@ -54,15 +54,12 @@ EXPORT_SYMBOL_GPL(fscrypt_file_open);
 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
 			   struct dentry *dentry)
 {
-	int err;
-
-	err = fscrypt_require_key(dir);
-	if (err)
-		return err;
-
-	/* ... in case we looked up no-key name before key was added */
 	if (fscrypt_is_nokey_name(dentry))
 		return -ENOKEY;
+	/*
+	 * We don't need to separately check that the directory inode's key is
+	 * available, as it's implied by the dentry not being a no-key name.
+	 */
 
 	if (!fscrypt_has_permitted_context(dir, inode))
 		return -EXDEV;
@@ -75,20 +72,13 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 			     struct inode *new_dir, struct dentry *new_dentry,
 			     unsigned int flags)
 {
-	int err;
-
-	err = fscrypt_require_key(old_dir);
-	if (err)
-		return err;
-
-	err = fscrypt_require_key(new_dir);
-	if (err)
-		return err;
-
-	/* ... in case we looked up no-key name(s) before key was added */
 	if (fscrypt_is_nokey_name(old_dentry) ||
 	    fscrypt_is_nokey_name(new_dentry))
 		return -ENOKEY;
+	/*
+	 * We don't need to separately check that the directory inodes' keys are
+	 * available, as it's implied by the dentries not being no-key names.
+	 */
 
 	if (old_dir != new_dir) {
 		if (IS_ENCRYPTED(new_dir) &&

include/linux/fscrypt.h

@@ -710,8 +710,7 @@ static inline int fscrypt_require_key(struct inode *inode)
  *
  * A new link can only be added to an encrypted directory if the directory's
  * encryption key is available --- since otherwise we'd have no way to encrypt
- * the filename.  Therefore, we first set up the directory's encryption key (if
- * not already done) and return an error if it's unavailable.
+ * the filename.
  *
  * We also verify that the link will not violate the constraint that all files
  * in an encrypted directory tree use the same encryption policy.