Re: Verify rules

[Mart Frauenlob <mart.frauenlob@chello.at>]

netfilter-owner@vger.kernel.org wrote:
> I was wondering if I could get someone to verify my rules.  What I am trying
> to do to start with, is make only certain ports available on my outgoing
> mail server - essentially blocking all other ports not listed.  I have the
> below on my server in an inactive state because when I activate it, it locks
> it completely down.
>
> Could someone please take a look at my rules and share with me what I did
> wrong?  Here is my entire config file:
>
>
> -----------------------------
>
> *mangle
> :PREROUTING ACCEPT [6:948]
> :INPUT ACCEPT [6:948]
> :FORWARD ACCEPT [0:0]
> :OUTPUT ACCEPT [7:3269]
> :POSTROUTING ACCEPT [7:3269]
> COMMIT
> *nat
> :OUTPUT ACCEPT [0:0]
> :PREROUTING ACCEPT [0:0]
> :POSTROUTING ACCEPT [0:0]
> COMMIT
> *filter
> :FORWARD ACCEPT [0:0]
> :INPUT ACCEPT [0:0]
> :OUTPUT ACCEPT [0:0]
> # HTTP
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 80 --state NEW -j
> ACCEPT
> # SSH
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 22 --state NEW -j
> ACCEPT
> # DNS
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 53 --state NEW -j
> ACCEPT
> # TIME
> -A INPUT -p udp -m udp -m state NEW,ESTABLISHED --dport 123 --state NEW -j
> ACCEPT
> # WEBMIN
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 10000 --state NEW -j
> ACCEPT
> # SMTP
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 25 --state NEW -j
> ACCEPT
> # POP3
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 110 --state NEW -j
> ACCEPT
> # IMAP
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 993 --state NEW -j
> ACCEPT
> # RSYNC-TCP
> -A INPUT -p tcp -m tcp -m state NEW,ESTABLISHED --dport 873 --state NEW -j
> ACCEPT
> # RSYNC-UDP
> -A INPUT -p udp -m udp -m state NEW,ESTABLISHED --dport 873 --state NEW -j
> ACCEPT
> # DENY ALL OTHERS
> -A INPUT -i eth0 -j REJECT --reject-with icmp-net-unreachable
> COMMIT
>
> --------------------------
>   

The state match syntax is wrong.

correct: -m state --state NEW,ESTABLISHED

you can write all your input allow rules in one line by using multiport 
match:
-A INPUT -p tcp -m multiport --dports 22,25,110,873,993,10000 -m state 
--state NEW,ESTABLISHED -j ACCEPT
same for udp...

Also I suggest setting INPUT policy to DROP.
Personally I'm not a friend of 'reject all unmatched'.
I prefer plain DROP, as I don't really like to send a packet for each 
not accepted connection attempt.

Read the iptables tutorial at frozentux, if you want to continue writing 
your own ruleset.
Otherwise I suggest to use a firewalling program to manage iptables. 
There's lots of them out there.

greets

Mart