Subject: Re: [PATCH/RFC 08/10] iptables tproxy table

From: Patrick McHardy <[email-masked]>
Date: Wed, 10 Jan 2007 13:40:49 +0100

KOVACS Krisztian wrote:

> diff --git a/net/ipv4/netfilter/iptable_tproxy.c b/net/ipv4/netfilter/iptable_tproxy.c
> new file mode 100644
> index 0000000..6049c83
> --- /dev/null
> +++ b/net/ipv4/netfilter/iptable_tproxy.c
> @@ -0,0 +1,253 @@
> +/*
> + * Transparent proxy support for Linux/iptables
> + *
> + * Copyright (c) 2006-2007 BalaBit IT Ltd.
> + * Author: Balazs Scheidler, Krisztian Kovacs
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#include <linux/version.h>
> +#include <linux/module.h>
> +
> +#include <linux/sysctl.h>
> +#include <linux/vmalloc.h>
> +#include <linux/net.h>
> +#include <linux/slab.h>
> +#include <linux/if.h>
> +#include <linux/proc_fs.h>
> +#include <linux/seq_file.h>
> +#include <linux/netdevice.h>
> +#include <linux/inetdevice.h>
> +#include <linux/time.h>
> +#include <linux/in.h>
> +#include <net/tcp.h>
> +#include <net/udp.h>
> +#include <net/sock.h>
> +#include <net/inet_sock.h>
> +#include <asm/uaccess.h>

A few of these look unnecessary (like vmalloc, seq_file, proc_fs,
time, uaccess).

> +#include <linux/netfilter.h>
> +#include <linux/netfilter_ipv4.h>
> +#include <linux/netfilter_ipv4/ip_tables.h>
> +
> +#define TPROXY_VALID_HOOKS (1 << NF_IP_PRE_ROUTING)
> +
> +#if 0
> +#define DEBUGP printk
> +#else
> +#define DEBUGP(f, args...)
> +#endif
> +
> +static struct
> +{
> +	struct ipt_replace repl;
> +	struct ipt_standard entries[2];
> +	struct ipt_error term;
> +} initial_table __initdata = {
> +	.repl = {
> +		.name = "tproxy",
> +		.valid_hooks = TPROXY_VALID_HOOKS,
> +		.num_entries = 2,
> +		.size = sizeof(struct ipt_standard) + sizeof(struct ipt_error),
> +		.hook_entry = {
> +			[NF_IP_PRE_ROUTING] = 0 },
> +		.underflow = {
> +			[NF_IP_PRE_ROUTING] = 0 },
> +	},
> +	.entries = {
> +		/* PRE_ROUTING */
> +		{
> +			.entry = {
> +				.target_offset = sizeof(struct ipt_entry),
> +				.next_offset = sizeof(struct ipt_standard),
> +			},
> +			.target = {
> +				.target = {
> +					.u = {
> +						.target_size = IPT_ALIGN(sizeof(struct ipt_standard_target)),
> +					},
> +				},
> +				.verdict = -NF_ACCEPT - 1,
> +			},
> +		},
> +	},
> +	/* ERROR */
> +	.term = {
> +		.entry = {
> +			.target_offset = sizeof(struct ipt_entry),
> +			.next_offset = sizeof(struct ipt_error),
> +		},
> +		.target = {
> +			.target = {
> +				.u = {
> +					.user = {
> +						.target_size = IPT_ALIGN(sizeof(struct ipt_error_target)),
> +						.name = IPT_ERROR_TARGET,
> +					},
> +				},
> +			},
> +			.errorname = "ERROR",
> +		},
> +	}
> +};
> +
> +static struct ipt_table tproxy_table = {
> +	.name		= "tproxy",
> +	.valid_hooks	= TPROXY_VALID_HOOKS,
> +	.lock		= RW_LOCK_UNLOCKED,
> +	.me		= THIS_MODULE,
> +	.af		= AF_INET,
> +};
> +
> +struct sock *
> +ip_tproxy_get_sock(const u8 protocol,
> +		   const __be32 saddr, const __be32 daddr,
> +		   const __be16 sport, const __be16 dport,
> +		   const struct net_device *in)
> +{
> +	struct sock *sk = NULL;
> +
> +	/* look up socket */
> +	switch (protocol) {
> +	case IPPROTO_TCP:
> +		sk = __inet_lookup(&tcp_hashinfo,
> +				   saddr, sport, daddr, sport,
> +				   in->ifindex);
> +		break;
> +	case IPPROTO_UDP:
> +		sk = udp4_lib_lookup(saddr, sport, daddr, dport,
> +				     in->ifindex);
> +		break;
> +	default:
> +		WARN_ON(1);
> +	}
> +
> +	return sk;
> +}
> +EXPORT_SYMBOL_GPL(ip_tproxy_get_sock);
> +
> +int
> +ip_tproxy_do_divert(struct sk_buff *skb, struct sock *sk,
> +		    const int require_freebind,
> +		    const struct net_device *in)
> +{
> +	const struct inet_sock *inet = inet_sk(sk);
> +	struct in_device *indev;
> +
> +	if (unlikely(inet == NULL))
> +		return -EINVAL;
> +
> +	if (!require_freebind || inet->freebind) {
> +		indev = in_dev_get(in);
> +		if (indev == NULL)
> +			return -ENODEV;
> +
> +		skb->ip_tproxy = 1;
> +
> +		ip_divert_local(skb, indev, sk);
> +		in_dev_put(indev);
> +
> +		DEBUGP(KERN_DEBUG "IP_TPROXY: diverted to socket %p\n", sk);
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(ip_tproxy_do_divert);
> +
> +static unsigned int
> +ip_tproxy_prerouting(unsigned int hooknum,
> +		     struct sk_buff **pskb,
> +		     const struct net_device *in,
> +		     const struct net_device *out,
> +		     int (*okfn)(struct sk_buff *))
> +{
> +	int verdict = NF_ACCEPT;
> +	struct sk_buff *skb = *pskb;
> +	u8 protocol = skb->nh.iph->protocol;
> +	struct sock *sk = NULL;
> +	const struct iphdr *iph = (*pskb)->nh.iph;
> +	struct udphdr _hdr, *hp;
> +
> +	/* TCP and UDP only */
> +	if ((protocol != IPPROTO_TCP) && (protocol != IPPROTO_UDP))
> +		return NF_ACCEPT;
> +
> +	if (in == NULL)
> +		return NF_ACCEPT;
> +
> +	if ((skb->dst != NULL) || (skb->ip_tproxy == 1))
> +		return NF_ACCEPT;
> +
> +	hp = skb_header_pointer(skb, skb->nh.iph->ihl * 4, sizeof(_hdr), &_hdr);
> +	if (hp == NULL) {
> +		DEBUGP(KERN_DEBUG "IP_TPROXY: ip_tproxy_fn(): "
> +		       "failed to get protocol header\n");
> +		return NF_DROP;
> +	}
> +
> +	sk = ip_tproxy_get_sock(iph->protocol,
> +				iph->saddr, iph->daddr,
> +				hp->source, hp->dest, in);
> +	if (sk) {
> +		if (ip_tproxy_do_divert(skb, sk, 1, in) < 0) {
> +			DEBUGP(KERN_DEBUG "IP_TPROXY: divert failed, dropping packet\n");
> +			verdict = NF_DROP;
> +		}
> +		sock_put(sk);

This doesn't handle time wait sockets (need inet_twsk_put).

> +	} else {
> +		verdict = ipt_do_table(pskb, hooknum, in, out, &tproxy_table);
> +	}
> +
> +	return verdict;
> +}
> +
> +static struct nf_hook_ops ip_tproxy_pre_ops = {
> +	.hook		= ip_tproxy_prerouting,
> +	.owner		= THIS_MODULE,
> +	.pf		= PF_INET,
> +	.hooknum	= NF_IP_PRE_ROUTING,
> +	.priority	= -130

This should go in netfilter_ipv4.h

> +};
> +
> +static int __init init(void)
> +{
> +	int ret;
> +
> +	ret = ipt_register_table(&tproxy_table, &initial_table.repl);
> +	if (ret < 0) {
> +		printk("IP_TPROXY: can't register tproxy table.\n");
> +		return ret;
> +	}
> +
> +	ret = nf_register_hook(&ip_tproxy_pre_ops);
> +	if (ret < 0) {
> +		printk("IP_TPROXY: can't register prerouting hook.\n");
> +		goto clean_table;
> +	}
> +
> +	printk("IP_TPROXY: Transparent proxy support initialized, version 4.0.0\n"
> +	       "IP_TPROXY: Copyright (c) 2006-2007 BalaBit IT Ltd.\n");
> +
> +	return ret;
> +
> + clean_table:
> +	ipt_unregister_table(&tproxy_table);
> +	return ret;
> +}
> +
> +static void __exit fini(void)
> +{
> +	nf_unregister_hook(&ip_tproxy_pre_ops);
> +	ipt_unregister_table(&tproxy_table);
> +}
> +
> +module_init(init);
> +module_exit(fini);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Krisztian Kovacs <[email-masked]>");
> +MODULE_DESCRIPTION("iptables transparent proxy table");
>