ipfw and ssh problem

[krad]

On 26 March 2010 08:02, Peter <fbsdq at peterk.org> wrote:

> > Hi guys,
> >
> > I have searched everywhere and failed to find a solution, hence I write
> > you.
> > I have installed 8.0-RELEASE FreeBSD 8.0-RELEASE #0: Sat Nov 21 15:02:08
> > UTC 2009     root at mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC
> > amd64
> > together with ipfw. The problem I have is this, if I am on the box I can
> > restart my firewall with no problem, but when I log in remotely and
> > restart the firewall for reason I am locked out and can not ssh into it.
> >
> > Below is the messages log:
> > Mar 25 14:51:04 panadine kernel: Trying to mount root from
> ufs:/dev/ad4s1a
> > Mar 25 14:51:04 panadine kernel: ipfw2 (+ipv6) initialized, divert
> > loadable, nat loadable, rule-based forwarding disabled, default to deny,
> > logging disabled
> > Mar 25 14:51:06 panadine kernel: ae0: link state changed to UP
> > Mar 25 14:51:16 panadine ntpd[645]: ntpd 4.2.4p5-a (1)
> > Mar 25 14:51:17 panadine nrpe[698]: Starting up daemon
> > Mar 25 14:51:25 panadine ntpd[646]: kernel time sync status change 2001
> > Mar 25 14:51:32 panadine su: systz to root on /dev/pts/0
> > Mar 25 15:01:46 panadine kernel: ifa_del_loopback_route: deletion failed
> > Mar 25 15:01:46 panadine kernel: ae0: link state changed to DOWN
> > Mar 25 15:01:47 panadine sshd[829]: fatal: Write failed: Permission
> denied
> > Mar 25 15:01:48 panadine kernel: ae0: link state changed to UP
> >
> > Here is a few lines from my /etc/firewall_rules
> >
> > # vim: set syntax=pf :
> >
> > -f flush
> >
> > # Let me talk out
> > add 100 allow all from me to any out keep-state
> > add 101 allow icmp from any to any via any
> > add 102 allow udp from any to any 33434-33523
> >
> > # Deal with loopback
> > #add 1000 allow all from any to any via lo0
> > add 1001 deny ip from any to 127.0.0.0/8
> > add 1002 deny ip from 127.0.0.0/8 to any
> >
> > # Allow established and fragmented sessions
> > add 2000 allow tcp from any to any established
> > add 2001 allow ip from any to any frag
> > add 2002 check-state
> > add 2003 allow icmp from any to any
> >
> >
> > I have enabled net.inet.ip.fw.verbose=1 in /etc/sysctl.conf
> >
> > please help
> >
> >
> > regards
> >
> >
> > Tongai
>
> ipfw -f flush - deletes all rules except the default which is usually
> 'deny from any to any'
>
> As soon as that gets processed, your sshd connection is killed as seen in
> the message up there:
> sshd[829]: fatal: Write failed: Permission denied
> With ssh dead, your shell is terminated and the rest of the script is
> never ran, so you are stuck with a firewall that did not get any rules
> added to it.
>
> Using quiet 'ipfw -q' or doing 'sh /etc/rc.firewall > /dev/null ; sleep 3'
> is what I've usually done.
>
> or my favorite is to do the firewall from 'local console' using 'watch -W
> v4' so even if ssh is killed, the console is up to finish up the script.
> [ this works great for 'buildworld' too where I want to start it, pack my
> laptop and and leave, reconnecting later ]
>
> With quiet mode, ssh is not sending anything back, so the connection is
> not terminated.
>
> ]Peter[
>
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the default deny can be a pain, there are two ways around it i have used in
the past.

1. Compile the kernel module with the the following options

options    IPFIREWALL_DEFAULT_TO_ACCEPT

2. Install screen open a screen session and run "ipfw -f ; ipfw add 1 allow
all from any to any", the screen session is important as it will guarantee
the completion of the command.

Its also worth looking at pf, as its configuration is a lot easier than
ipfw, especially nating. The macros and table functions are also very good
way to right small compact rule sets.