netdev - Re: [PATCH net] bpf: expose netns inode to bpf programs

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Message-ID: <20170203230627.GB26227@ast-mbp.thefacebook.com>
Date:   Fri, 3 Feb 2017 15:06:28 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsa@...ulusnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org
Subject: Re: [PATCH net] bpf: expose netns inode to bpf programs

On Fri, Feb 03, 2017 at 10:56:43PM +0100, Daniel Borkmann wrote:
> On 01/26/2017 04:27 AM, Alexei Starovoitov wrote:
> >in cases where bpf programs are looking at sockets and packets
> >that belong to different netns, it could be useful to read netns inode,
> >so that programs can make intelligent decisions.
> >For example to disallow raw sockets in all non-init netns the program can do:
> >if (sk->type == SOCK_RAW && sk->netns_inum != 0xf0000075)
> >   return 0;
> >where 0xf0000075 inode comes from /proc/pid/ns/net
> >
> >Similarly TC cls_bpf/act_bpf and socket filters can do
> >if (skb->netns_inum == expected_inode)
> >
> >The lack of netns awareness was a concern even for socket filters,
> >since the application can attach the same bpf program to sockets
> >in a different netns. Just like tc cls_bpf program can work in
> >different netns as well, so it has to be addressed uniformly
> >across all types of bpf programs.
> 
> Sorry for jumping in late, but my question is, isn't this helper
> really only relevant for BPF_PROG_TYPE_CGROUP_* typed programs?
> Thus other prog types making use of bpf_convert_ctx_access()
> should probably reject that in .is_valid_access() callback?
> 
> Reason why I'm asking is that for sockets or tc progs, you
> already have a netns context where you're attached to, and f.e.
> skbs leaving that netns context will be orphaned. Thus, why
> would tc or sock filter tailor a program with such a check,
> if it can only match/mismatch its own netns inum eventually?

Please see the example I provided earlier.
We can have the same cls_bpf attached to all netns-es.
Same for socket filters and everything else.
All bpf programs are global.
They can all share info via maps and so on.

> When making this effort to lookup and hardcode the dev/inode
> num into the prog, wouldn't it be easier for these types if

we cannot hardcode dev/inode. They are dynamic and depends
where program runs.
I'll send a patch shortly that exposes both.