ext4: require encryption feature for EXT4_IOC_SET_ENCRYPTION_POLICY

...otherwise an user can enable encryption for certain files even
when the filesystem is unable to support it.
Such a case would be a filesystem created by mkfs.ext4's default
settings, 1KiB block size. Ext4 supports encyption only when block size
is equal to PAGE_SIZE.
But this constraint is only checked when the encryption feature flag
is set.
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ioctl.c

@@ -769,6 +769,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 		struct fscrypt_policy policy;
 
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+
 		if (copy_from_user(&policy,
 				   (struct fscrypt_policy __user *)arg,
 				   sizeof(policy)))