Join Log in
Score:0
itsamemarkus avatar Server

iptables: Only allow one IP address when rules are updated by other tools

fr flag
itsamemarkus

I'm learning about iptables and I want to set up a GNS3 (network emulation) host on a public IP and limit the access to only one IP address.

This one IP address should be able to connect with all protocols and ports.

Now from what I understand I'd usually go with an approach like this on a fresh host:

sudo iptables -P INPUT DROP
sudo iptables -P FORWARD DROP
sudo iptables -A INPUT -i lo -j ACCEPT
sudo iptables -A INPUT -s X.X.X.X -j ACCEPT

But the GNS3 install already comes with rules from docker and I'm not sure if GNS3 itself dynamically sets rules for the QEMU VMs (because it's a network emulation). I think I can't just INPUT and FORWARD DROP here, because it would mess with the existing setup.

Now I want to make sure that my host is not open to the internet. How can I approach this securely? I think I can't use higher level firewalls (on the same host) because it would mess with iptables.

What's a good strategy here?

(This example shows a private IP address 10.11.12.160, the real host would have a public IP address instead)

iptables -L

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
LIBVIRT_INP  all  --  anywhere             anywhere

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
DOCKER-USER  all  --  anywhere             anywhere
DOCKER-ISOLATION-STAGE-1  all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
DOCKER     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
LIBVIRT_FWX  all  --  anywhere             anywhere
LIBVIRT_FWI  all  --  anywhere             anywhere
LIBVIRT_FWO  all  --  anywhere             anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
LIBVIRT_OUT  all  --  anywhere             anywhere

Chain DOCKER (1 references)
target     prot opt source               destination

Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target     prot opt source               destination
DOCKER-ISOLATION-STAGE-2  all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-ISOLATION-STAGE-2 (1 references)
target     prot opt source               destination
DROP       all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-USER (1 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere

Chain LIBVIRT_FWI (1 references)
target     prot opt source               destination
ACCEPT     all  --  anywhere             192.168.122.0/24     ctstate RELATED,ESTABLISHED
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable

Chain LIBVIRT_FWO (1 references)
target     prot opt source               destination
ACCEPT     all  --  192.168.122.0/24     anywhere
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable

Chain LIBVIRT_FWX (1 references)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere

Chain LIBVIRT_INP (1 references)
target     prot opt source               destination
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere             udp dpt:bootps
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:67

Chain LIBVIRT_OUT (1 references)
target     prot opt source               destination
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere             udp dpt:bootpc
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:68

iptables -S

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION-STAGE-1
-N DOCKER-ISOLATION-STAGE-2
-N DOCKER-USER
-N LIBVIRT_FWI
-N LIBVIRT_FWO
-N LIBVIRT_FWX
-N LIBVIRT_INP
-N LIBVIRT_OUT
-A INPUT -j LIBVIRT_INP
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A FORWARD -j LIBVIRT_FWX
-A FORWARD -j LIBVIRT_FWI
-A FORWARD -j LIBVIRT_FWO
-A OUTPUT -j LIBVIRT_OUT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN
-A LIBVIRT_FWI -d 192.168.122.0/24 -o virbr0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A LIBVIRT_FWI -o virbr0 -j REJECT --reject-with icmp-port-unreachable
-A LIBVIRT_FWO -s 192.168.122.0/24 -i virbr0 -j ACCEPT
-A LIBVIRT_FWO -i virbr0 -j REJECT --reject-with icmp-port-unreachable
-A LIBVIRT_FWX -i virbr0 -o virbr0 -j ACCEPT
-A LIBVIRT_INP -i virbr0 -p udp -m udp --dport 53 -j ACCEPT
-A LIBVIRT_INP -i virbr0 -p tcp -m tcp --dport 53 -j ACCEPT
-A LIBVIRT_INP -i virbr0 -p udp -m udp --dport 67 -j ACCEPT
-A LIBVIRT_INP -i virbr0 -p tcp -m tcp --dport 67 -j ACCEPT
-A LIBVIRT_OUT -o virbr0 -p udp -m udp --dport 53 -j ACCEPT
-A LIBVIRT_OUT -o virbr0 -p tcp -m tcp --dport 53 -j ACCEPT
-A LIBVIRT_OUT -o virbr0 -p udp -m udp --dport 68 -j ACCEPT
-A LIBVIRT_OUT -o virbr0 -p tcp -m tcp --dport 68 -j ACCEPT

network config

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether f6:8c:99:ec:54:f4 brd ff:ff:ff:ff:ff:ff
    altname enp0s18
    altname ens18
    inet 10.11.12.160/24 brd 10.11.12.255 scope global eth0
       valid_lft forever preferred_lft forever
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:9d:22:66 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
       valid_lft forever preferred_lft forever
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN group default qlen 1000
    link/ether 52:54:00:9d:22:66 brd ff:ff:ff:ff:ff:ff
5: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:12:b9:bb:c0 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
52
1 + 1
Nikita Kipriyanov avatar
za flag
Nikita Kipriyanov
When rules can be changed by other tools you are out of luck; whatever you do they can disrupt/disengage that. Either configure those other tools to not mess with your firewall or separate them into different containers/VMs/machines.
0
Reply
Score:0
avatar Server
jp flag
AlexD

You can find your answer in the Docker documentation

Restrict connections to the Docker host

By default, all external source IPs are allowed to connect to the Docker host. To allow only a specific IP or network to access the containers, insert a negated rule at the top of the DOCKER-USER filter chain. For example, the following rule restricts external access from all IP addresses except 192.168.1.1:

iptables -I DOCKER-USER -i ext_if ! -s 192.168.1.1 -j DROP

Please note that you will need to change ext_if to correspond with your host’s actual external interface. You could instead allow connections from a source subnet.

+ 0
ธงชาติไทย
Elon Musk
I sit in a Tesla and translated this thread with Ai:

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.