Hello, there. I'm running a Pure-FTPd service, with passive FTP, and I encountered what seems to be a defect in the nf_conntrack_ftp module: it seems to not recognize the passive FTP data connection as RELATED to the established control connection.
IPtables rules for passive FTP connections are as follows:
-A INPUT -i ens3 -p tcp -m tcp --dport 50000:50500 -m state --state
RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -o ens3 -p tcp -m tcp --sport 50000:50500 -m state --state
RELATED,ESTABLISHED -j ACCEPT
Pure-FTPd is also configured to use this port range for passive
connections:
root@Ennyn /h/alexandre {⌗0/⬓6}[0]꩜# cat /etc/pure-
ftpd/conf/PassivePortRange
50000 50500
The nf_conntrack_ftp module is also loaded:
root@Ennyn /h/alexandre {⌗0/⬓7}[0]꩜# lsmod | grep conntrack
nf_conntrack_ipv6 20480 3
nf_defrag_ipv6 36864 1 nf_conntrack_ipv6
xt_conntrack 16384 8
nf_conntrack_ipv4 16384 6
nf_defrag_ipv4 16384 1 nf_conntrack_ipv4
nf_conntrack_ftp 20480 0
nf_conntrack 114688 6
nf_conntrack_ipv6,nf_conntrack_ftp,nf_conntrack_ipv4,xt_conntrack,nf_nat_ipv4,nf_nat
x_tables 36864 15
xt_comment,xt_hashlimit,xt_LOG,ipt_REJECT,iptable_mangle,ip_tables,iptable_filter,xt_tcpudp,xt_limit,ip6t_REJECT,ip6table_mangle,xt_recent,ip6table_filter,xt_conntrack,ip6_tables
root@Ennyn /h/alexandre {⌗0/⬓6}[0]꩜# cat /etc/modules
# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
nf_conntrack_ftp
Yet, when I try to connect on FTP, the SYN packets coming from the client
trying to open the data connection never matches the passive FTP IPtables INPUT
rule, though I can see them using tcpdump on the server. If I delete its "-m
state --state RELATED,ESTABLISHED" part, the passive connection establishes
correctly. Besides, the conntrack shows nothing but the established control
connection. All this looks like the nf_conntrack_ftp module no longer
recognizes the data connection attempts from the client as RELATED to the
established control connection. I removed the stateful part of the INPUT rule
to bring the service up, but that is suboptimal. Did I do a mistake? Should I
open a bug ticket?
Awaiting your answers,
Regards.
--
David Guyot
Administrateur système / Sysadmin
Europe Camions Interactive / Stockway
Moulin Collot F-88500 Ambacourt
Tél : +33 (0)3 29 30 47 85
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