C, LKM, netfilter, PF_PACKET and ARP. Post: 302494683

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Operating Systems Linux C, LKM, netfilter, PF_PACKET and ARP. Post 302494683 by Zykl0n-B on Tuesday 8th of February 2011 04:36:17 AM

02-08-2011

Zykl0n-B

Guest

Hello,
This is what i was afraid of.

Code:

This user-defined filter decides whether a packet
is to be accepted and how many bytes of each packet should
be saved. For each filter that accepts the packet, BPF copies
the requested amount of data to the buffer associated with that
filter. The device driver then regains control. If the packet
was not addressed to the local host, the driver returns from the
interrupt. Otherwise, normal protocol processing proceeds.

LSF and BPF are just a filter for deceiding what packets to show and what packet not to. If the frame doesn't pass the filter, then it's returned to the device driver and it will process it normally (so, in my example, the ARP frame will take effect on the host's cache).

It seems i'll have to keep looking for arp support on netfilter.

By the way, i tried to make a module for blocking all ARP frames with netfilter, and it seems it's not possible. Does anyone know why?

Code:

static unsigned int hook_func(unsigned int hooknum,
                        struct sk_buff *skb,
                                const struct net_device *in,
                                const struct net_device *out,
                                int (*okfn)(struct sk_buff *)){

printk(KERN_INFO "ARP Dropped\n");
return NF_DROP;
}

static int __init init_main(void)
{
nfho.hook = hook_func;
nfho.hooknum = NF_ARP_IN;
nfho.pf = NF_ARP;

nf_register_hook(&nfho);

printk(KERN_INFO "Inserted protocool module!\n");
return(0);
}

This is the normal netfilter_hook_ops structure, i fill it with the funcion name (hook_func), the hook type NF_ARP_IN (0) and the protocol family (NF_ARP) and then register the hook. Since hook_func is "return NF_DROP" it should drop every single ARP frame it receives, but it doesn't. Could some one give me a clue about this?

Zykl0n-B

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LEARN ABOUT REDHAT

pppoe-sniff

PPPOE-SNIFF(8)						      System Manager's Manual						    PPPOE-SNIFF(8)

NAME

       pppoe-sniff - examine network for non-standard PPPoE frames

SYNOPSIS

       pppoe-sniff [options]

DESCRIPTION

       pppoe-sniff listens for likely-looking PPPoE PADR and session frames and deduces extra options required for pppoe(8) to work.

       Some  DSL providers seem to use non-standard frame types for PPPoE frames, and/or require a certain value in the Service-Name field.  It is
       often easier to sniff those values from a machine which can successfully connect rather than try to pry them out of the DSL provider.

       To use pppoe-sniff, you need two computers, a DSL modem and an Ethernet hub (not an Ethernet switch.)

       If the DSL modem normally connects directly to your computer's Ethernet card, connect it to the "uplink" port on the  Ethernet  hub.   Plug
       two  computers into normal ports on the hub.  On one computer, run whatever software the DSL provider gave you on whatever operating system
       the DSL provider supports.  On the other computer, run Linux and log in as root.

       On the Linux machine, put the Ethernet interface into promiscuous mode and start pppoe-sniff.  If the ethernet interface is eth0, for exam-
       ple, type these commands:

	    ifconfig eth0 promisc
	    pppoe-sniff -I eth0

       On  the	other  machine, start your DSL connection as usual.  After a short time, pppoe-sniff should print recommendations for the value of
       PPPOE_EXTRA.  Set this value in /etc/ppp/pppoe.conf.  If pppoe-sniff indicates that something special is required in PPPOE_EXTRA, please e-
       mail this to pppoe@roaringpenguin.com along with the name of your ISP and the manufacturer and model number of your DSL modem.  This infor-
       mation will be collated and provided on the PPPoE web page for users who do not have two computers.

       After pppoe-sniff finishes (or you stop it if it seems hung), remember to turn off promiscuous mode:

	    ifconfig eth0 -promisc

OPTIONS

       -I interface
	      The -I option specifies the Ethernet interface to use.  Under Linux, it is typically eth0 or eth1.  The interface should be "up" and
	      in promiscuous mode before you start pppoe-sniff.

       -V     The -V option causes pppoe-sniff to print its version number and exit.

BUGS

       pppoe-sniff only works on Linux.

AUTHORS

       pppoe-sniff was written by David F. Skoll <dfs@roaringpenguin.com>.

       The pppoe home page is http://www.roaringpenguin.com/pppoe/.

SEE ALSO

       adsl-start(8),  adsl-stop(8),  adsl-connect(8),	pppd(8),  pppoe.conf(5),  pppoe(8), adsl-setup(8), adsl-status(8), pppoe-server(8), pppoe-
       relay(8)

4th Berkeley Distribution					    3 July 2000 						    PPPOE-SNIFF(8)