Add support to limit network traffic

[sirdarckcat]

Either at the k8s side:
https://github.com/containernetworking/plugins/tree/master/plugins/meta/bandwidth
https://kubernetes.io/docs/concepts/extend-kubernetes/compute-storage-net/#support-traffic-shaping
https://github.com/minrk/tc-init/blob/master/tc-init

or with tc/iptables:
https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html#OWNERMATCH
https://lartc.org/howto/lartc.cookbook.fullnat.intro.html
http://luxik.cdi.cz/~devik/qos/htb/manual/userg.htm

this would limit the risk of DoS

[sirdarckcat]

https://www.linuxtopia.org/Linux_Firewall_iptables/x4368.html

[sirdarckcat]

--pid owner doesnt seem to work anymore, so it doesnt seem to be possible to filter based on that

[sirdarckcat]

here's some other idea on how to do this https://github.com/deitch/ctables/blob/master/ctables

[sirdarckcat]

google/nsjail#140

[sirdarckcat]

after doing some testing with traffic control and network namespaces, I think:

1. you can do network throttling on a per-namespace basis
2. if you clone a new namespace, then you can't get internet unless you clone the interface
3. cloning the interface requires root (well, maybe net_admin)

as such, I think it should be throttled at a per-pod level, rather than at an nsjail level.

[sirdarckcat]

instead of cloning the interface, we could create a veth pair, maybe.. and then add it to nsjail dynamically somehow

[sirdarckcat]

https://josephmuia.ca/2018-05-16-net-namespaces-veth-nat/

[sirdarckcat]

this seems to work

root@ctf-daemon-gcsfuse-b2jfb:/nsjail# ip netns exec 5773 tc qdisc add dev veth-netns0 root tbf rate 1024kbit latency 50ms burst 1540
root@ctf-daemon-gcsfuse-b2jfb:/nsjail# iperf -c ping.online.net

------------------------------------------------------------
Client connecting to ping.online.net, TCP port 5001
TCP window size: 45.0 KByte (default)
------------------------------------------------------------
[  3] local 10.44.3.3 port 56688 connected with 62.210.18.40 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-13.3 sec  1.90 GBytes  1.23 Gbits/sec
root@ctf-daemon-gcsfuse-b2jfb:/nsjail# ip netns exec 5773 iperf -c ping.online.net

------------------------------------------------------------
Client connecting to ping.online.net, TCP port 5001
TCP window size: 45.0 KByte (default)
------------------------------------------------------------
[  3] local 10.0.3.2 port 47546 connected with 62.210.18.40 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-12.2 sec  1005 KBytes   672 Kbits/sec

[sirdarckcat]

So, TL;DR:

1. We could create a DaemonSet that provides a simple service:

echo 1 > /proc/sys/net/ipv4/ip_forward
connect_to_internet() {
vethname=$1
ip link add $vethname-out type veth peer name $vethname-in
ip link set $vethname-in netns $vethname
ip addr add 10.0.$counter.1/24 dev $vethname-out
ip netns exec $vethname ip addr add 10.0.$counter.2/24 dev $vethname-in
ip link set $vethname-out up
ip netns exec $vethname ip link set $vethname-in up
iptables -A FORWARD -o eth0 -i $vethname-out -j ACCEPT
iptables -A FORWARD -i eth0 -o $vethname-out -j ACCEPT
iptables -t nat -A POSTROUTING -s 10.0.$counter.2/24 -o eth0 -j MASQUERADE
ip netns exec $vethname ip route add default via 10.0.$counter.1
ip netns exec $vethname tc qdisc add dev $vethname-in root tbf rate 1024kbit latency 50ms burst 1540
}

2. connect the daemonset somehow with the task (they need to be able to pass the netns)

alternatively, we can just do this at a per-pod level instead. this seems less error-prone, and most likely better anyway..

[sirdarckcat]

this worked (on challenge-name/config/advanced/deployment/containers.yaml), it throttled the speed to 1megabyte per second. more info is available here and an explanation of the burst/rate here.

apiVersion: "apps/v1"
kind: "Deployment"
metadata:
  name: "chal"
spec:
  template:
    spec:
      initContainers:
      - name: tc
        image: ubuntu:19.10
        command: ["sh", "-c", "echo nameserver 1.1.1.1 > /etc/resolv.conf; apt-get update && apt-get install -y iproute2 gawk && tc qdisc add dev `ip route | awk '/default/ {print $5}'` root tbf rate 1mbps latency 50ms burst 2000"]
        securityContext:
          capabilities:
            add:
            - NET_ADMIN

test:

# iperf -c ping.online.net -R
------------------------------------------------------------
Client connecting to ping.online.net, TCP port 5001
TCP window size: 45.0 KByte (default)
------------------------------------------------------------
[  3] local 10.44.3.31 port 41774 connected with 62.210.18.40 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  9.25 MBytes  7.73 Mbits/sec

7.73Mbits/sec = 1MBps

[sirdarckcat]

so yea, it might be worth looking into moving to https://github.com/minrk/tc-init or something similar to that. I don't know how licensing might affect this.

[sirdarckcat]

to use the k8s native one
https://kubernetes.io/docs/concepts/extend-kubernetes/compute-storage-net/#support-traffic-shaping we probably need
projectcalico/calico#2815 to be fixed unless there's some way to enable CNI plugins in GKE