I've stumbled accross one interesting problem with portmapper. I have rules to allow connections to portmapper. The connection goes through three way handshake, however as soon as handshake is over, packets are being dropped by Netfiler.
The relevant rules on host named "client" look something like this (edited a bit for clarity):
/sbin/iptables -A OUTPUT -p udp -s client --sport 0:1023 -d server --dport sunrpc -o eth0 -m rpc --rpcs list_of_services -j ACCEPT
/sbin/iptables -A INPUT -p udp -s server --sport sunrpc -d client --dport 0:1023 -i eth0 -m state --state ESTABLISHED -j ACCEPT
/sbin/iptables -A OUTPUT -p tcp -s client --sport 0:1023 -d server --dport sunrpc -o eth0 -m rpc --rpcs list_of_services -j ACCEPT
/sbin/iptables -A INPUT -p tcp -s server --sport sunrpc -d client --dport 0:1023 -i eth0 -m state --state ESTABLISHED -j ACCEPT
So, this should allow for both TCP and UDP connections to portmapper on host "server". It should also allow me to allow only connections to specified RPC services in subsequent rules. Well, UDP part works. But TCP doesn't work exactly as expected.
I've added some logging rules that will log all portmapper packets with either "RPC UDP" or "RPC TCP" prefix, and placed them before above mentioned rules. Also added logging rules that will log dropped packets with "OUTPUT" or "INPUT" prefix (depending in which chain they were dropped) and placed them at the very end of my rules, just before the unmatched packets are dropped by default policy.
What I can see from log files is that three way handshake goes well. Edited and formated a bit for clarity:
RPC TCP IN= OUT=eth0 SRC=client DST=server
LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=11551 DF
PROTO=TCP SPT=690 DPT=111 WINDOW=5840 RES=0x00 SYN URGP=0RPC TCP IN=eth0 OUT= SRC=server DST=client
LEN=64 TOS=0x00 PREC=0x00 TTL=63 ID=12081 DF
PROTO=TCP SPT=111 DPT=690 WINDOW=33304 RES=0x00 ACK SYN URGP=0RPC TCP IN= OUT=eth0 SRC=client DST=server
LEN=52 TOS=0x00 PREC=0x00 TTL=64 ID=49320 DF
PROTO=TCP SPT=690 DPT=111 WINDOW=5840 RES=0x00 ACK URGP=0However, all subsequent packets are being dropped (this two lines are for the same packet, logged as it entered the chain, and again just before it was dropped by default policy):
RPC TCP IN= OUT=eth0 SRC=client DST=server
LEN=96 TOS=0x00 PREC=0x00 TTL=64 ID=25452 DF
PROTO=TCP SPT=690 DPT=111 WINDOW=5840 RES=0x00 ACK PSH URGP=0OUTPUT IN= OUT=eth0 SRC=client DST=server
LEN=96 TOS=0x00 PREC=0x00 TTL=64 ID=25452 DF
PROTO=TCP SPT=690 DPT=111 WINDOW=5840 RES=0x00 ACK PSH URGP=0The above two lines are repeating several times, until client gives up. After that, client fails over to UDP, and from that point on everything works as expected.
Using tcpdump basically gives same information (I can see three way handshake going on the wire, and after it there's silence).
I've tried adding "-m state --state NEW,ESTABLISHED" to the third line of my rules (the one allowing outgoing TCP portmapper requests). And got same results. For some reason, Netfilter "forgets" that there's established connection between cilent and server, and simply starts to drop packets.
Has anybody else run across this problem? Or am I doing something obviously wrong? I've tried digging around in documentation, Googling, experimenting, always with the same end result.
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
