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 OSF1

pfconfig

pfconfig(8)						      System Manager's Manual						       pfconfig(8)

NAME

       pfconfig - Configure packet filter parameters

SYNOPSIS

       /usr/sbin/pfconfig [+/-p[romisc]] [+/-c[opyall]] [-b[acklog] nnn] [-a[ll]] [interface-name...]

DESCRIPTION

       The  pfconfig  command  allows  the system manager to configure certain parameters of the packet filter driver (see packetfilter(7)). These
       parameters are configured separately for each interface; the interfaces are specified by name on the command line (for  example,  ln0,  and
       ni1).  If more than one interface is specified, they are all given the same settings.  Alternatively, you can specify -all to configure all
       the packet-filter interfaces on the system.

       You can set the following parameters with pfconfig: Allows packet filter users to set the interface into  promiscuous  mode  (receives  all
       packets).   Whenever there is at least one packet filter descriptor open with the ENPROMISC mode bit set, the interface is put into promis-
       cuous mode.  When no such descriptors are in use, the interface is returned to normal mode.  The interface is no longer put into  promiscu-
       ous  mode  on  behalf  of packet filter users; if the interface is in promiscuous mode when this command is given, it is returned to normal
       mode.  (The superuser may use ifconfig(8) to control promiscuous mode, overriding the mode set by non-superusers.  This is the default set-
       ting.)	Allows packet filter users to set the interface into copy-all mode (receives packets sent/received by the kernel-resident protocol
       software [for example, IP, ARP, DECnet, LAT] on this host). Whenever there is at least one packet filter descriptor open with the ENCOPYALL
       mode bit set, the interface is put into copy-all mode.  When no such descriptors are in use, the interface is returned to normal mode.  The
       interface is no longer put into copy-all mode on behalf of packet filter users; if the interface is in copy-all mode when this  command	is
       given,  it  is  returned to normal mode.  (The superuser may use ifconfig(8) to control copy-all mode, overriding the mode set by non-supe-
       rusers. This is the default setting.)  Sets the maximum backlog (packet filter input queue length) for  non-superuser  descriptors  to  the
       specified number.  When a descriptor is opened, it is given a queue length limit of two. An application can increase this backlog using the
       EIOCSETW ioctl request.	Superusers are allowed to increase their backlog up to	a  system-wide	maximum;  non-superusers  are  allowed	to
       increase  their	backlog  only up to the maximum set by this program.  Note that allowing too large a backlog may result in vast amounts of
       kernel memory being tied up in the packet filter driver queues.

	      If no configuration parameters are specified, the pfconfig command displays the current packet filter configuration for the  network
	      interfaces.

	      Only the superuser may use this command to change the configuration.

DIAGNOSTICS

       PACKETFILTER option is not built into the running kernel

   Explanation:
       Packetfilter support is not built into the kernel. Reconfigure the kernel with the packetfilter option.

       pfopen: xxx: No such device

   Explanation:
       The specified network device does not exist on the system, or no pfilt minor devices exist in the /dev/pf directory.

       pfconfig: your system may not be properly configured; see "man packetfilter"

   Explanation:
       No pfilt minor devices exist in the /dev/pf directory.

       pfconfig: either network interface 'xxx' is down, or your system may not be properly configured; see "man packfilter"

   Explanation:
       The specified network device is not up and running.

       pfconfig: either all of your network interfaces are down, or your system may not be properly configured; see "man packfilter"

   Explanation:
       No network devices are up and running.

SEE ALSO

       Commands: intro(1), netstat(1), pfstat(1), ifconfig(8)

       Files: inet.local(4), bpf(7), packetfilter(7)

																       pfconfig(8)