ext4, f2fs: fscrypt_has_permitted_context() check in file open

Hi!

Both ext4 and f2fs check in the file open code the context of the parent directory too:

ext4:
        if (ext4_encrypted_inode(d_inode(dir)) &&
                        !fscrypt_has_permitted_context(d_inode(dir), inode)) {
                ext4_warning(inode->i_sb,
                             "Inconsistent encryption contexts: %lu/%lu",
                             (unsigned long) d_inode(dir)->i_ino,
                             (unsigned long) inode->i_ino);
                dput(dir);
                return -EPERM;
        }

f2fs:
        if (f2fs_encrypted_inode(d_inode(dir)) &&
                        !fscrypt_has_permitted_context(d_inode(dir), inode)) {
                dput(dir);
                return -EPERM;
        }

Why do we need this check? AFAIK this situation can never happen unless due to
a bug in the filesystem code.

Thanks,
//richard