ext4 crypto: policies may only be set on directories

Thanks to Chao Yu <chao2.yu@samsung.com> for pointing out we were
missing this check.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/crypto_policy.c

@@ -93,6 +93,8 @@ int ext4_process_policy(const struct ext4_encryption_policy *policy,
 		return -EINVAL;
 
 	if (!ext4_inode_has_encryption_context(inode)) {
+		if (!S_ISDIR(inode->i_mode))
+			return -EINVAL;
 		if (!ext4_empty_dir(inode))
 			return -ENOTEMPTY;
 		return ext4_create_encryption_context_from_policy(inode,