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Date: Sat, 4 Feb 2017 09:08:38 -0800 From: Andy Lutomirski <luto@...capital.net> To: Daniel Borkmann <daniel@...earbox.net> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Alexei Starovoitov <ast@...com>, "David S . Miller" <davem@...emloft.net>, David Ahern <dsa@...ulusnetworks.com>, Tejun Heo <tj@...nel.org>, "Eric W . Biederman" <ebiederm@...ssion.com>, Thomas Graf <tgraf@...g.ch>, Network Development <netdev@...r.kernel.org> Subject: Re: [PATCH net] bpf: expose netns inode to bpf programs On Fri, Feb 3, 2017 at 3:42 PM, Daniel Borkmann <daniel@...earbox.net> wrote: > On 02/04/2017 12:06 AM, Alexei Starovoitov wrote: >> >> 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. > > > That example for both socket filter and tc progs specifically > wasn't quite clear to me, hence my question wrt why it's right > now a "concern" for these ones. (Again, clear to me for cgroups > progs.) > >> We can have the same cls_bpf attached to all netns-es. >> Same for socket filters and everything else. > > > So use-case would be that someone wants to attach the very same > prog via tc to various netdevs sitting in different netns, and > that prog looks up a map, controlled by initns, with skb->netns_inum > as key and the resulting value could contain allowed feature bits > for that specific netns prog the skbs goes through? That would be > a feature, not "concern", no? At the same time, it's up to the > user or mgmt app what gets loaded so f.e. it might just as well > tailor/optimize the progs individually for the devs sitting in > netns-es to avoid such map lookup. Agreed. I don't see why you would install the exact same program on two sockets in different netnses if the program contains, say, an ifindex. Why not just install a variant with the right ifindex into each socket?
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