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

From: Daniel Borkmann <[email-masked]>
Date: Fri, 03 Feb 2017 22:56:43 +0100

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?
When making this effort to lookup and hardcode the dev/inode
num into the prog, wouldn't it be easier for these types if
the managing app that loads these progs tailors the progs for
a given netns directly, so also such runtime check can generally
be avoided? Am I missing something wrt 'concerns'? The cgroup
ones are global, so there I can see that it could be used in
some way f.e. to restrict access, account, etc.

Thanks,
Daniel