Re: [PATCH net-next v2 4/4] cgroup: bpf: Add an example to do cgroup checking in BPF

From: Daniel Borkmann
Date: Thu Jun 23 2016 - 05:58:26 EST


On 06/22/2016 11:17 PM, Martin KaFai Lau wrote:
test_cgrp2_array_pin.c:
A userland program that creates a bpf_map (BPF_MAP_TYPE_GROUP_ARRAY),
pouplates/updates it with a cgroup2's backed fd and pins it to a
bpf-fs's file. The pinned file can be loaded by tc and then used
by the bpf prog later. This program can also update an existing pinned
array and it could be useful for debugging/testing purpose.

test_cgrp2_tc_kern.c:
A bpf prog which should be loaded by tc. It is to demonstrate
the usage of bpf_skb_in_cgroup.

test_cgrp2_tc.sh:
A script that glues the test_cgrp2_array_pin.c and
test_cgrp2_tc_kern.c together. The idea is like:
1. Use test_cgrp2_array_pin.c to populate a BPF_MAP_TYPE_CGROUP_ARRAY
with a cgroup fd
2. Load the test_cgrp2_tc_kern.o by tc
3. Do a 'ping -6 ff02::1%ve' to ensure the packet has been
dropped because of a match on the cgroup

Most of the lines in test_cgrp2_tc.sh is the boilerplate
to setup the cgroup/bpf-fs/net-devices/netns...etc. It is
not bulletproof on errors but should work well enough and
give enough debug info if things did not go well.

Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>

Btw, when no bpf fs is mounted, tc will already auto-mount it. I noticed in
your script, you do mount the fs manually. I guess it's okay to leave it like
this, but I hope users won't wrongly copy it assuming they /have/ to mount it
themselves.