newbie: writing custom target, need help with getting it to work

newbie: writing custom target, need help with getting it to work

[Yossi Weihs]

[-- Attachment #1: Type: text/plain, Size: 1894 bytes --]

Hi List,

I have been working on a custom netfilter target to help with some in-house
testing. I’m running Fedora 13 and building within xtables-addons v 1.2.6 ;
I have gotten both the kernel module and library to build correctly within
the xtables-addons build enviroment, and am inserting the kernel module with
no errors. When trying to create a rule with my target, I get the cryptic
error:

iptables --verbose --table filter --insert INPUT --protocol TCP -m state
--state ESTABLISHED --jump TAP --device TAPPY
TAP  tcp opt -- in * out *  0.0.0.0/0  -> 0.0.0.0/0  state ESTABLISHED TAP
dev:TAPPY 
iptables: No chain/target/match by that name.

I’m seeing dev:TAPPY, which I think means the user space library correctly
parsed the parameters. Since I manually inserted the module, I know it’s
there, although I did not see the module initialization kernel info
message... Any ideas on where to look next? I have attached my target code.

Thanks!


Joseph "Yossi" Weihs, CTO

SeaFire Micros, Inc.
39 Dodge St, #319
Beverly, MA 01915

http://www.seafire.com
yw@seafire.com
http://twitter.com/SeaFireMicros


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[-- Attachment #2: xt_TAP.c --]
[-- Type: application/octet-stream, Size: 4227 bytes --]

/*
 *	"TAP" target extension for Xtables
 *
 */
#include <linux/ip.h>
#include <linux/module.h>
#include <linux/route.h>
#include <linux/skbuff.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/ip6_route.h>
#include <net/route.h>
#include <linux/netfilter/x_tables.h>

#include <linux/version.h>
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 25)
#include <asm/semaphore.h>
#else
#include <linux/semaphore.h>
#endif


#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
#	define WITH_CONNTRACK 1
#	include <net/netfilter/nf_conntrack.h>
#endif
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
#	define WITH_IPV6 1
#endif

#include "compat_xtables.h"
#include "seabatch.h"
#include "xt_TAP.h"

static unsigned int
tap_tg4(struct sk_buff **pskb, const struct xt_target_param *par)
{
	const struct xt_tap_tginfo *info = par->targinfo;
	struct xt_tap_tginfo *private_info = (struct xt_tap_tginfo *)par->targinfo;
	const struct sk_buff *skb = *pskb;
	const struct iphdr *iph;
	const struct tcphdr *tcph;
	int iptcphlen,tcpdlen,idx,fidx;
	void * buf;

	iph = ip_hdr(skb);
	// verify source and dest address match
	fidx = -1;
	for (idx = 0; idx < info->filter_count; ++idx) {
		if ((iph->saddr == info->tap_filter[idx].source) ||
		    (iph->daddr == info->tap_filter[idx].dest)) {
			fidx = idx;
		}
	}
	if (-1 == fidx) {
		return XT_CONTINUE;
	}
	iptcphlen = ip_hdrlen(skb);

	// Time to grab mutex
	if (down_interruptible(private_info->tap_filter[fidx].lock)) {
		printk(KERN_CRIT "TAP down_interruptible %s %d\n",__FILE__,__LINE__);
		return XT_CONTINUE;
	}

	// snip some code removed
	
	// Fall out
	fallout:
	// Release Mutex
	up(private_info->tap_filter[fidx].lock);
	// done
	return XT_CONTINUE;
}

#ifdef WITH_IPV6
static unsigned int
tap_tg6(struct sk_buff **pskb, const struct xt_target_param *par)
{
	printk (KERN_WARNING "TAP IPV6 not supported");
	return XT_CONTINUE;
}
#endif /* WITH_IPV6 */

static int tap_tg_check(const struct xt_tgchk_param *par)
{
	/* Const access to fields set by user space */
	const struct xt_tap_tginfo 	 *info = par->targinfo;
	/* non-const access to private TARGET module fields; TODO: find more elegant
	   way to store TARGET specific private information */
	struct xt_tap_tginfo *private_info = par->targinfo;
	int err;

	private_info->handle = Splinter_Register_TAP(info->dev);

	if (!private_info->handle) {
		/* Failed to register! */
		printk (KERN_ERR "TAP sorry failed to get handle.\n");
		return -EINVAL;
	}

	err = Copy_Splinter_Table(private_info->handle, 
	                          &private_info->tap_filter[0],
	                          MAX_FILTERS_PER_TARGET * 
	                            sizeof(struct SeaFire_Connection_Filter));

	if (-1 == err) {
		private_info->handle = 0;
		return -EINVAL;
	}

	private_info->filter_count = err;

	printk(KERN_INFO "SeaFire TAP Check Passed\n");
	
	return 0;
}

/* dunno why - this does not exist in current rev of library
static int tap_tg_dtor(const struct xt_tgchk_param *par)
{
	const struct xt_tap_tginfo *info = par->targinfo;

	return 0;
}
*/

static struct xt_target tap_tg_reg[] __read_mostly = {
	{
		.name       = "TAP",
		.revision   = 0,
		.family     = NFPROTO_IPV4,
		.target     = tap_tg4,
		.targetsize = sizeof(struct xt_tap_tginfo),
		.checkentry = tap_tg_check,
//		.destroy    = tap_tg_dtor,
		.me         = THIS_MODULE,
	},
#ifdef WITH_IPV6
	{
		.name       = "TAP",
		.revision   = 0,
		.family     = NFPROTO_IPV6,
		.target     = tap_tg6,
		.targetsize = sizeof(struct xt_tap_tginfo),
		.checkentry = tap_tg_check,
//		.destroy    = tap_tg_dtor,
		.me         = THIS_MODULE,
	},
#endif
};

static int __init tap_tg_init(void)
{
	printk(KERN_INFO "SeaFire TAP Installed\n");
	return xt_register_targets(tap_tg_reg, ARRAY_SIZE(tap_tg_reg));
}

static void __exit tap_tg_exit(void)
{
	printk(KERN_INFO "SeaFire TAP Removed\n");
	xt_unregister_targets(tap_tg_reg, ARRAY_SIZE(tap_tg_reg));
	/* Free up any allocated memory */
}

module_init(tap_tg_init);
module_exit(tap_tg_exit);

Re: newbie: writing custom target, need help with getting it to work

[Jan Engelhardt]

On Sunday 2010-08-08 22:20, Yossi Weihs wrote:

>Hi List,
>
>I have been working on a custom netfilter target to help with some in-house
>testing. I?m running Fedora 13 and building within xtables-addons v 1.2.6 ;
>I have gotten both the kernel module and library to build correctly within
>the xtables-addons build enviroment, and am inserting the kernel module with
>no errors. When trying to create a rule with my target, I get the cryptic
>error:
>
>iptables --verbose --table filter --insert INPUT --protocol TCP -m state
>--state ESTABLISHED --jump TAP --device TAPPY
>TAP  tcp opt -- in * out *  0.0.0.0/0  -> 0.0.0.0/0  state ESTABLISHED TAP
>dev:TAPPY 
>iptables: No chain/target/match by that name.

When you want iptables to recognize (the user portion) of Xt-a's extra 
modules, you need to point to it via the XTABLES_LIBDIR environment 
variable.

XTABLES_LIBDIR=$HOME/xta/extensions:/usr/lib(64)/xtables iptables -S

Don't forget usr/lib/xtables otherwise it won't find the tcp match and 
all the ones that already ship with iptables.

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Re: newbie: writing custom target, need help with getting it to work

[Jan Engelhardt]

On Sunday 2010-08-08 22:20, Yossi Weihs wrote:

>I?m seeing dev:TAPPY, which I think means the user space library correctly
>parsed the parameters. Since I manually inserted the module, I know it?s
>there, although I did not see the module initialization kernel info
>message... Any ideas on where to look next? I have attached my target code.

>#include "compat_xtables.h"
>#include "seabatch.h"
>#include "xt_TAP.h"
>
>static unsigned int
>tap_tg4(struct sk_buff **pskb, const struct xt_target_param *par)
>{
...
>	// Time to grab mutex
>	if (down_interruptible(private_info->tap_filter[fidx].lock)) {

Your tap makes for water damage. You must not sleep in Xtables kernel
code, that is, anythiing higher of a class than a spinlock_bh
is a no-no.

>		printk(KERN_CRIT "TAP down_interruptible %s %d\n",__FILE__,__LINE__);
>		return XT_CONTINUE;
>	}
>
>	// snip some code removed
>	
>	// Fall out
>	fallout:
>	// Release Mutex
>	up(private_info->tap_filter[fidx].lock);
>	// done
>	return XT_CONTINUE;
>}
>

RE: newbie: writing custom target, need help with getting it to work

[Yossi Weihs]

Thanks Jan!

I have added the env variable, but saw no change. My libxt_TAP.so is getting found as it is checking my parameter. I have tried a different xtables_addons target such as TEE, and the rule gets inserted fine. I had SELinux block my libxt_TAP.so and had added it to the SELinux rules, so that shouldn't be a problem. Any other idea what might be going on? I know my module is calling xt_register_targets(), is there a way for me to check the contents of its tables?

Thanks for looking at my code! I'll switch my mutex to a spinlock - I'd be wasting a lot of time once I get running with this without your help.

Yossi Weihs

-----Original Message-----
From: Jan Engelhardt [mailto:jengelh@medozas.de] 
Sent: Sunday, August 08, 2010 4:29 PM
To: Yossi Weihs
Cc: netfilter-devel@vger.kernel.org
Subject: Re: newbie: writing custom target, need help with getting it to work

On Sunday 2010-08-08 22:20, Yossi Weihs wrote:

>Hi List,
>
>I have been working on a custom netfilter target to help with some in-house
>testing. I?m running Fedora 13 and building within xtables-addons v 1.2.6 ;
>I have gotten both the kernel module and library to build correctly within
>the xtables-addons build enviroment, and am inserting the kernel module with
>no errors. When trying to create a rule with my target, I get the cryptic
>error:
>
>iptables --verbose --table filter --insert INPUT --protocol TCP -m state
>--state ESTABLISHED --jump TAP --device TAPPY
>TAP  tcp opt -- in * out *  0.0.0.0/0  -> 0.0.0.0/0  state ESTABLISHED TAP
>dev:TAPPY 
>iptables: No chain/target/match by that name.

When you want iptables to recognize (the user portion) of Xt-a's extra 
modules, you need to point to it via the XTABLES_LIBDIR environment 
variable.

XTABLES_LIBDIR=$HOME/xta/extensions:/usr/lib(64)/xtables iptables -S

Don't forget usr/lib/xtables otherwise it won't find the tcp match and 
all the ones that already ship with iptables.

RE: newbie: writing custom target, need help with getting it to work

[Jan Engelhardt]

On Sunday 2010-08-08 23:09, Yossi Weihs wrote:

>I have added the env variable, but saw no change.

Make sure that xt_TAP.ko is then actually loaded.

>going on? I know my module is calling xt_register_targets(), is there a 
>way for me to check the contents of its tables?

iptables -vvL

should print the semi-raw dump of the table before trying to resolve 
targets.

RE: newbie: writing custom target, need help with getting it to work

[Yossi Weihs]

OK - xt_TAP.ko is not getting loaded by iptables. I can modprobe it
manually, but iptables won't load it. Trying telling iptables which modprobe
to use, but no luck. xt_TEE.ko is getting loaded fine, and I cloned my
module off it ... I feel we're getting close.

-YW

-----Original Message-----
From: netfilter-devel-owner@vger.kernel.org
[mailto:netfilter-devel-owner@vger.kernel.org] On Behalf Of Jan Engelhardt
Sent: Sunday, August 08, 2010 5:13 PM
To: Yossi Weihs
Cc: netfilter-devel@vger.kernel.org
Subject: RE: newbie: writing custom target, need help with getting it to
work

On Sunday 2010-08-08 23:09, Yossi Weihs wrote:

>I have added the env variable, but saw no change.

Make sure that xt_TAP.ko is then actually loaded.

>going on? I know my module is calling xt_register_targets(), is there a 
>way for me to check the contents of its tables?

iptables -vvL

should print the semi-raw dump of the table before trying to resolve 
targets.
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RE: newbie: writing custom target, need help with getting it to work

[Jan Engelhardt]

On Monday 2010-08-09 06:23, Yossi Weihs wrote:

>OK - xt_TAP.ko is not getting loaded by iptables. I can modprobe it
>manually, but iptables won't load it. Trying telling iptables which modprobe
>to use, but no luck. xt_TEE.ko is getting loaded fine, and I cloned my
>module off it ... I feel we're getting close.

iptables just calls modprobe. And modprobe only looks in /lib/modules.