This is a discussion on X & Gnome crashes the system with iptables within the Linux Security forums, part of the System Security and Security Related category; Hello, My system is : - Debian 3r1, - kernel 2.4.21, - XFree 4.1.0 (on Debian CD 3r1, I'm ...
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Hello,
My system is : - Debian 3r1, - kernel 2.4.21, - XFree 4.1.0 (on Debian CD 3r1, I'm not connected to internet) : i use Gnome. I spent a lot of time to write rules for iptables to obtain a good firewall. I join 2 files : - the iptables rules : /etc/iptables.rules, - the script to run it: /etc/init.d/iptables. If i launch the firewall : - i connect to Gnome ctrl+F7 ( it starts with the boot of the computer), - i write login, password, - gnome deskptop starts, displays task bar, - nothing, i can just move the cursor of the mouse,keybord doesn't answer, - frozen system. If i don't launch the firewall, i havn't any trouble with Gnome. I don't know what i can do ? ideas, advice welcome. Sincerely yours, Jeannot Lelapin ================================================== ========= ================================================== ========= ================================================== ========= /etc/iptables.rules ================================================== ========= ================================================== ========= ================================================== ========= ## ================================================== ========== #!/bin/bash ## ================================================== ========= ## Load modules IPTABLES="/sbin/iptables" DEPMOD="/sbin/depmod" MODPROBE="/sbin/modprobe" # Load all required IPTables modules # Needed to initially load modules $DEPMOD -a # Load appropriate modules. $MODPROBE ip_tables # Support for connection tracking $MODPROBE ip_conntrack $MODPROBE ip_conntrack_ftp # MODIF BEGIN $MODPROBE ip_conntrack_irc # Adds some $IPTABLES targets like LOG, REJECT and MASQUARADE. $MODPROBE ipt_LOG $MODPROBE ipt_REJECT $MODPROBE ipt_MASQUERADE # Support for owner matching $MODPROBE ipt_owner # MODIF END ## ================================================== ========= ## Reset all configurations # # These lines are here in case rules are already in place and the script is ever rerun on the fly. # We want to : # - remove all rules, # - remove pre-exisiting user defined chains, # - zero the counters. # before we implement new rules. $IPTABLES -F $IPTABLES -X $IPTABLES -Z ## ================================================== ========= ## Default Policy # # Set up a default DROP policy for the built-in chains. # If we modify and re-run the script mid-session then (because we have a default DROP # policy), what happens is that there is a small time period when packets are denied until # the new rules are back in place. There is no period, however small, when packets we # don't want are allowed. $IPTABLES -P INPUT DROP $IPTABLES -P FORWARD DROP $IPTABLES -P OUTPUT DROP ## ================================================== ========= ## Some definitions: # Le DNS primaire du fournisseur d'accès Free NAMESERVER_1="212.27.32.5" # Le DNS secondaire du fournisseur d'accès Free NAMESERVER_2="212.27.32.6" # Note : si je mets des FQDN, iptables essaye de les résoudre. Comme le réseau n'est pas encore branché, ca tombe à l'eau. # Il faudra peut etre prévoir le fait rejouer les règles avec des FDQN une fois la connexion ADSL ou PPP établie. # Le serveur de courrier POP du fournisseur d'accès Free # Le FQDN : pop.free.fr : 213.228.0.14, 213.228.0.141, 213.228.0.142, 213.228.0.165 213.228.0.12 INCOMINGMAILSERVER_1="213.228.0.14" # Le serveur de courrier POP du fournisseur d'accès Club-Internet # Le FQDN : mail.club-internet.fr : 195.36.166.10, 195.36.162.10 INCOMINGMAILSERVER_2="195.36.166.10" # Le serveur de courrier SMTP du fournisseur d'accès Free # Le FQDN : smtp.free.fr : 213.228.0.44, 213.228.0.62, 213.228.0.169, 213.228.0.176 OUTGOINGMAILSERVER="213.228.0.44" # Les serveurs de temps # Le FQDN : ntp.uvsq.fr : 193.51.24.1 TIMESERVER_1="193.51.24.1" # Le FQDN : delphi.phys.univ-tours.fr : 193.52.212.3 TIMESERVER_2="193.52.212.3" # Le FQDN : ntp0.oleane.net : 194.2.0.28 TIMESERVER_3="194.2.0.28" # Le FQDN : ntp1.oleane.net : 94.2.0.58 TIMESERVER_4="94.2.0.58" # Le FQDN : ntp.via.ecp.fr : 138.195.130.71 TIMESERVER_5="138.195.130.71" # Le FQDN : ntp.chronos.org : 129.186.121.29 TIMESERVER_6="129.186.121.29" LOOPBACK="127.0.0.0/8" BROADCAST="x.x.x.255" CLASS_A="10.0.0.0/8" CLASS_B="172.16.0.0/12" CLASS_C="192.168.0.0/16" CLASS_D_MULTICAST="224.0.0.0/4" CLASS_E_RESERVED_NET="240.0.0.0/5" P_PORTS="0:1023" UP_PORTS="1024:65535" TR_SRC_PORTS="32769:65535" TR_DEST_PORTS="33434:33523" ## ================================================== ========== ## Kernel flags # # To dynamically change kernel parameters and variables on the fly you need # CONFIG_SYSCTL defined in your kernel. I would advise the following: # If you get your IP address dynamically from SLIP, PPP, or DHCP, enable this # option. This enables dynamic-ip address hacking in IP MASQ, making the connection # with Diald and similar programs much easier. # MODIF BEGIN echo "1" > /proc/sys/net/ipv4/ip_dynaddr # MODIF END # Disable response to ping. /bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all # Disable response to broadcasts. # You don't want yourself becoming a Smurf amplifier. /bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts # Don't accept source routed packets. Attackers can use source routing to generate # traffic pretending to be from inside your network, but which is routed back along # the path from which it came, namely outside, so attackers can compromise your # network. Source routing is rarely used for legitimate purposes. /bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_source_route # Disable ICMP redirect acceptance. ICMP redirects can be used to alter your routing # tables, possibly to a bad end. /bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects # Enable bad error message protection. /bin/echo "1" > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses # Turn on reverse path filtering. This helps make sure that packets use # legitimate source addresses, by automatically rejecting incoming packets # if the routing table entry for their source address doesn't match the network # interface they're arriving on. This has security advantages because it prevents # so-called IP spoofing, however it can pose problems if you use asymmetric routing # (packets from you to a host take a different path than packets from that host to you) # or if you operate a non-routing host which has several IP addresses on different # interfaces. (Note - If you turn on IP forwarding, you will also get this). for interface in /proc/sys/net/ipv4/conf/*/rp_filter; do /bin/echo "1" > ${interface} done # Log spoofed packets, source routed packets, redirect packets. /bin/echo "1" > /proc/sys/net/ipv4/conf/all/log_martians # Make sure that IP forwarding is turned off. We only want this for a multi-homed host. /bin/echo "0" > /proc/sys/net/ipv4/ip_forward # Note: With connection tracking, all fragments are reassembled before being # passed to the packet-filtering code so there is no ip_always_defrag switch as there # was in the 2.2 kernel. ## ================================================== ========== # RULES ## SYN-FLOODING PROTECTION # This rule maximises the rate of incoming connections. In order to do this we divert tcp # packets with the SYN bit set off to a user-defined chain. Up to limit-burst connections # can arrive in 1/limit seconds ..... in this case 4 connections in one second. After this, one # of the burst is regained every second and connections are allowed again. The default limit # is 3/hour. The default limit burst is 5. # $IPTABLES -N syn-flood $IPTABLES -A INPUT -p tcp --syn -j syn-flood $IPTABLES -A syn-flood -m limit --limit 1/s --limit-burst 4 -j RETURN $IPTABLES -A syn-flood -j DROP ## FRAGMENTS # I have to say that fragments scare me more than anything. # Sending lots of non-first fragments was what allowed Jolt2 to effectively "drown" # Firewall-1. Fragments can be overlapped, and the subsequent interpretation of such # fragments is very OS-dependent (see this paper for details). # I am not going to trust any fragments. # Log fragments just to see if we get any, and deny them too. $IPTABLES -A INPUT -f -j LOG --log-prefix "IPTABLES FRAGMENTS: " $IPTABLES -A INPUT -f -j DROP ## SPOOFING # Most of this anti-spoofing stuff is theoretically not really necessary with the flags we # have set in the kernel above ........... but you never know there isn't a bug somewhere in # your IP stack. # # Refuse spoofed packets pretending to be from your IP address. # ( CETTE REGLE SERA MISE EN OEUVRE LORSQUE JE RECUPERERAI L'ADRESSE IP DES INTERFACES CONCERNEES ) #$IPTABLES -A INPUT -s $IPADDR -j DROP # Refuse packets claiming to be from a Class A private network. $IPTABLES -A INPUT -s $CLASS_A -j DROP # Refuse packets claiming to be from a Class B private network. $IPTABLES -A INPUT -s $CLASS_B -j DROP # Refuse packets claiming to be from a Class C private network. $IPTABLES -A INPUT -s $CLASS_C -j DROP # Refuse Class D multicast addresses. Multicast is illegal as a source address. $IPTABLES -A INPUT -s $CLASS_D_MULTICAST -j DROP # Refuse Class E reserved IP addresses. $IPTABLES -A INPUT -s $CLASS_E_RESERVED_NET -j DROP # Refuse packets claiming to be to the loopback interface. # Refusing packets claiming to be to the loopback interface protects against # source quench, whereby a machine can be told to slow itself down by an icmp source # quench to the loopback. $IPTABLES -A INPUT -d $LOOPBACK -j DROP # Refuse broadcast address packets. # ( CETTE REGLE SERA MISE EN OEUVRE LORSQUE JE RECUPERERAI L'ADRESSE DES SOUS RESEAUX DES INTERFACES CONCERNEES ) #$IPTABLES -A INPUT -d $BROADCAST -j DROP ## TELNET # Allow telnet outbound. #$IPTABLES -A INPUT -p tcp --sport 23 -m state --state ESTABLISHED -j ACCEPT #$IPTABLES -A OUTPUT -p tcp --dport 23 -m state --state NEW,ESTABLISHED -j ACCEPT ## FTP # Allow ftp outbound. #$IPTABLES -A INPUT -p tcp --sport 21 -m state --state ESTABLISHED -j ACCEPT #$IPTABLES -A OUTPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j ACCEPT # Now for the connection tracking part of ftp. This is discussed more completely in my section # on connection tracking to be found here. # 1) Active ftp. # This involves a connection INbound from port 20 on the remote machine, to a local port # passed over the ftp channel via a PORT command. The ip_conntrack_ftp module recognizes # the connection as RELATED to the original outgoing connection to port 21 so we don't # need NEW as a state match. #$IPTABLES -A INPUT -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT #$IPTABLES -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j ACCEPT # 2) Passive ftp. # This involves a connection outbound from a port >1023 on the local machine, to a port >1023 # on the remote machine previously passed over the ftp channel via a PORT command. The # ip_conntrack_ftp module recognizes the connection as RELATED to the original outgoing # connection to port 21 so we don't need NEW as a state match. #$IPTABLES -A INPUT -p tcp --sport $UP_PORTS --dport $UP_PORTS -m state --state ESTABLISHED -j ACCEPT #$IPTABLES -A OUTPUT -p tcp --sport $UP_PORTS --dport $UP_PORTS -m state --state ESTABLISHED,RELATED -j ACCEPT ## Make sure NEW tcp connections are SYN packets $IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j DROP ## LOOPBACK # Allow unlimited traffic on the loopback interface. $IPTABLES -A INPUT -i lo -j ACCEPT $IPTABLES -A OUTPUT -o lo -j ACCEPT ## DNS # NOTE: DNS uses tcp for zone transfers, for transfers greater than 512 bytes (possible, but unusual), and on certain # platforms like AIX (I am told), so you might have to add a copy of this rule for tcp if you need it # Allow UDP packets in for DNS client from nameservers. $IPTABLES -A INPUT -p udp -s $NAMESERVER_1 --sport 53 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $NAMESERVER_2 --sport 53 -m state --state ESTABLISHED -j ACCEPT # Allow UDP packets to DNS servers from client. $IPTABLES -A OUTPUT -p udp -d $NAMESERVER_1 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $NAMESERVER_2 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT ## WWW # Allow www outbound to 80. $IPTABLES -A INPUT -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT # Allow www outbound to 443. JE METS LE SERVEUR SSH SUR CE PORT #$IPTABLES -A INPUT -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT #$IPTABLES -A OUTPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT ## SSH # Allow ssh outbound. $IPTABLES -A INPUT -p tcp --sport 443 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT ## SMTP # Allow smtp outbound. $IPTABLES -A INPUT -p tcp -s $OUTGOINGMAILSERVER --sport 25 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $OUTGOINGMAILSERVER --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT ## POP # Allow pop outbound. $IPTABLES -A INPUT -p tcp -s $INCOMINGMAILSERVER_1 --sport 110 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $INCOMINGMAILSERVER_2 --sport 110 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $INCOMINGMAILSERVER_1 --dport 110 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $INCOMINGMAILSERVER_2 --dport 110 -m state --state NEW,ESTABLISHED -j ACCEPT ## AUTH server # Reject ident probes with a tcp reset. # I need to do this for a broken mailhost that won't accept my mail if I just drop its ident probe. $IPTABLES -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset ## TRACEROUTE # Outgoing traceroute anywhere. # The reply to a traceroute is an icmp time-exceeded which is dealt with by the next rule. $IPTABLES -A OUTPUT -p udp --sport $TR_SRC_PORTS --dport $TR_DEST_PORTS -m state --state NEW -j ACCEPT ## NTP # Allow ntp outbound. $IPTABLES -A INPUT -p tcp -s $TIMESERVER_1 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_1 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $TIMESERVER_2 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_2 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $TIMESERVER_3 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_3 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $TIMESERVER_4 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_4 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $TIMESERVER_5 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_5 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p tcp -s $TIMESERVER_6 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A INPUT -p udp -s $TIMESERVER_6 --sport 123 -m state --state ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_1 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_1 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_2 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_2 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_3 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_3 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_4 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_4 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_5 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_5 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_6 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT $IPTABLES -A OUTPUT -p udp -d $TIMESERVER_6 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT # ICMP # We accept icmp in if it is "related" to other connections (e.g a time exceeded (11) # from a traceroute) or it is part of an "established" connection (e.g. an echo reply (0) # from an echo-request (8)). $IPTABLES -A INPUT -p icmp -m state --state ESTABLISHED,RELATED -j ACCEPT # We always allow icmp out. $IPTABLES -A OUTPUT -p icmp -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT ## LOGGING # You don't have to split up your logging like I do below, but I prefer to do it this way # because I can then grep for things in the logs more easily. One thing you probably want # to do is rate-limit the logging. I didn't do that here because it is probably best not too # when you first set things up ................. you actually really want to see everything going to # the logs to work out what isn't working and why. You cam implement logging with # "-m limit --limit 6/h --limit-burst 5" (or similar) before the -j LOG in each case. # # Any udp not already allowed is logged and then dropped. $IPTABLES -A INPUT -p udp -j LOG --log-prefix "IPTABLES UDP-IN: " $IPTABLES -A INPUT -p udp -j DROP $IPTABLES -A OUTPUT -p udp -j LOG --log-prefix "IPTABLES UDP-OUT: " $IPTABLES -A OUTPUT -p udp -j DROP # Any icmp not already allowed is logged and then dropped. $IPTABLES -A INPUT -p icmp -j LOG --log-prefix "IPTABLES ICMP-IN: " $IPTABLES -A INPUT -p icmp -j DROP $IPTABLES -A OUTPUT -p icmp -j LOG --log-prefix "IPTABLES ICMP-OUT: " $IPTABLES -A OUTPUT -p icmp -j DROP # Any tcp not already allowed is logged and then dropped. $IPTABLES -A INPUT -p tcp -j LOG --log-prefix "IPTABLES TCP-IN: " $IPTABLES -A INPUT -p tcp -j DROP $IPTABLES -A OUTPUT -p tcp -j LOG --log-prefix "IPTABLES TCP-OUT: " $IPTABLES -A OUTPUT -p tcp -j DROP # Anything else not already allowed is logged and then dropped. # It will be dropped by the default policy anyway ........ but let's be paranoid. $IPTABLES -A INPUT -j LOG --log-prefix "IPTABLES PROTOCOL-X-IN: " $IPTABLES -A INPUT -j DROP $IPTABLES -A OUTPUT -j LOG --log-prefix "IPTABLES PROTOCOL-X-OUT: " $IPTABLES -A OUTPUT -j DROP # THE END # ================================================== ================ ================================================== ========= ================================================== ========= ================================================== ========= /etc/init.d/iptables ================================================== ========= ================================================== ========= ================================================== ========= #!/bin/sh # # chkconfig: 2345 08 92 # IPTABLES_CONFIG=/etc/iptables.rules # check we have the iptables executable if [ ! -x /sbin/iptables ]; then exit 0 fi # check we have the right kernel version KERNELMAJ=`uname -r | sed -e 's,\..*,,'` KERNELMIN=`uname -r | sed -e 's,[^\.]*\.,,' -e 's,\..*,,'` if [ "$KERNELMAJ" -lt 2 ] ; then exit 0 fi if [ "$KERNELMAJ" -eq 2 -a "$KERNELMIN" -lt 3 ] ; then exit 0 fi if /sbin/lsmod 2>/dev/null |grep -q ipchains ; then # Don't do both exit 0 fi start() { # don't do squat if we don't have the script if [ -f $IPTABLES_CONFIG ]; then echo "Applying iptables firewall rules:" /etc/iptables.rules touch /var/lock/subsys/iptables fi } stop() { echo "Flushing all chains:" iptables -F echo "Removing user defined chains:" iptables -X echo "Resetting built-in chains to the default ACCEPT policy:" iptables -P INPUT ACCEPT && iptables -P FORWARD ACCEPT && iptables -P OUTPUT ACCEPT && # IL FAUT RECUPERER LE RESULTAT DE L'EXECUTION ET FAIRE LES ECHOS EN CONSEQUENCE # success "Resetting built-in chains to the default ACCEPT policy" || # failure "Resetting built-in chains to the default ACCEPT policy" rm -f /var/lock/subsys/iptables } case "$1" in start) start ;; stop) stop ;; restart) # "restart" is really just "start" as this isn't a daemon, # and "start" clears any pre-defined rules anyway. # This is really only here to make those who expect it happy start ;; status) iptables --list ;; panic) echo "Changing target policies to DROP: " iptables -P INPUT DROP && iptables -P FORWARD DROP && iptables -P OUTPUT DROP # IL FAUT RECUPERER LE RESULTAT DE L'EXECUTION ET FAIRE LES ECHOS EN CONSEQUENCE # success "Changing target policies to DROP" || \ # failure "Changing target policies to DROP" echo echo "Flushing all chains:" iptables -F INPUT && iptables -F FORWARD && iptables -F OUTPUT echo echo "Removing user defined chains:" iptables -X ;; *) echo "Usage: $0 {start|stop|restart|status|panic}" exit 1 esac exit 0 |
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Thanks a lot,
I have a rule which drops all loopback traffic. $IPTABLES -A INPUT -d lo -j DROP I was tired tired when I wrote iptables.rules. I place iptables -A INPUT -i lo -j ACCEPT iptables -A OUTPUT -o lo -j ACCEPT after the policy rules. Then it works fine. Jeannot Lelapin |