linux-kernel - Re: [PATCH bpf-next 1/6] bpf: introduce BPF_PROG_TYPE_FILE

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Message-ID: <20181005222752.l5da54rpww6tlyfy@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 5 Oct 2018 15:27:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/6] bpf: introduce BPF_PROG_TYPE_FILE_FILTER

On Fri, Oct 05, 2018 at 03:09:20PM -0700, Andy Lutomirski wrote:
> On Fri, Oct 5, 2018 at 3:05 PM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Fri, Oct 05, 2018 at 05:46:59AM +0100, Al Viro wrote:
> >
> > > Another problem is your direct poking in ->i_ino.  It's not
> > > something directly exposed to userland at the moment and it should
> > > not become such.
> >
> > The patch is not making i_ino directly exposed.
> > Only 'struct bpf_file_info' is exposed to user space / bpf programs.
> 
> I think Al is saying that the valie of i_ino is not something that
> user code is permitted to know regardless of how you format it because
> it may or may not actually match the value returned by stat().
> Another way of saying that is that your patch is digging into an
> internal data structure and is doing it wrong.

several fs implementation I've looked at just do generic_fillattr()
for these fields. Are you saying some FS don't use inode->i_ino at all?
And it's bogus, hence shouldn't be read?