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/*
* Protocol modification target for IP tables
*
* 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.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/checksum.h>
#include <linux/netfilter/x_tables.h>
#include "xt_PROTO.h"
MODULE_AUTHOR("Shanker Wang <i@innull.com>");
MODULE_DESCRIPTION("Xtables: Protocol field modification target");
MODULE_LICENSE("GPL");
static unsigned int
proto_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
struct iphdr *iph;
const struct xt_PROTO_info *info = par->targinfo;
int new_proto;
if (skb_ensure_writable(skb, skb->len))
return NF_DROP;
iph = ip_hdr(skb);
new_proto = iph->protocol;
if (info->mode & (1 << XT_PROTO_SET))
new_proto = info->proto;
if (new_proto != iph->protocol) {
csum_replace2(&iph->check, htons(iph->protocol & 0xff),
htons(new_proto & 0xff));
iph->protocol = new_proto;
}
return XT_CONTINUE;
}
static unsigned int
proto_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
struct ipv6hdr *ip6h;
const struct xt_PROTO_info *info = par->targinfo;
u8 *nexthdr;
unsigned int hdr_offset;
__be16 *fp;
if (skb_ensure_writable(skb, skb->len))
return NF_DROP;
ip6h = ipv6_hdr(skb);
nexthdr = &ip6h->nexthdr;
hdr_offset = sizeof(struct ipv6hdr);
for (;;) {
struct ipv6_opt_hdr _opthdr, *opthp;
unsigned int hdrlen;
unsigned short _frag_off;
if (!ipv6_ext_hdr(*nexthdr) || *nexthdr == NEXTHDR_NONE)
break;
opthp = skb_header_pointer(skb, skb_network_offset(skb) + hdr_offset, sizeof(_opthdr), &_opthdr);
if (!opthp)
return NF_DROP;
if (*nexthdr == NEXTHDR_FRAGMENT) {
if (info->mode & (1 << XT_PROTO_STOP_AT_FRAG))
break;
fp = skb_header_pointer(skb, skb_network_offset(skb) +
hdr_offset + offsetof(struct frag_hdr, frag_off),
sizeof(_frag_off), &_frag_off);
if (!fp)
return NF_DROP;
_frag_off = ntohs(*fp) & ~0x7;
if (_frag_off) { // if the packet is not the first fragment
if (!ipv6_ext_hdr(opthp->nexthdr) || opthp->nexthdr == NEXTHDR_NONE ||
(info->mode & (1 << XT_PROTO_STOP_AT_AUTH) && opthp->nexthdr == NEXTHDR_AUTH)) {
nexthdr = &((struct ipv6_opt_hdr *)(skb_network_header(skb) + hdr_offset))->nexthdr;
break;
} else {
return XT_CONTINUE;
}
}
hdrlen = 8;
} else if(*nexthdr == NEXTHDR_AUTH) {
if (info->mode & (1 << XT_PROTO_STOP_AT_AUTH))
break;
hdrlen = (opthp->hdrlen + 2) << 2;
} else {
hdrlen = ipv6_optlen(opthp);
}
nexthdr = &((struct ipv6_opt_hdr *)(skb_network_header(skb) + hdr_offset))->nexthdr;
hdr_offset += hdrlen;
}
if (info->mode & (1 << XT_PROTO_SET))
*nexthdr = info->proto;
return XT_CONTINUE;
}
static int proto_tg_check(const struct xt_tgchk_param *par)
{
const struct xt_PROTO_info *info = par->targinfo;
if ((info->mode & (1 << XT_PROTO_SET)) == 0) {
pr_info_ratelimited("Did not specify any proto to set\n");
return -EINVAL;
}
if (par->family != NFPROTO_IPV6 && (info->mode & ((1 << XT_PROTO_STOP_AT_FRAG) | (1 << XT_PROTO_STOP_AT_AUTH))) != 0) {
pr_info_ratelimited("Must not specify stop-at-frag and stop-at-auth on non-ipv6 targets\n");
return -EPROTOTYPE;
}
return 0;
}
static struct xt_target proto_tg_reg[] __read_mostly = {
{
.name = "PROTO",
.revision = 0,
.family = NFPROTO_IPV4,
.target = proto_tg,
.targetsize = sizeof(struct xt_PROTO_info),
.table = "mangle",
.checkentry = proto_tg_check,
.me = THIS_MODULE,
},
{
.name = "PROTO",
.revision = 0,
.family = NFPROTO_IPV6,
.target = proto_tg6,
.targetsize = sizeof(struct xt_PROTO_info),
.table = "mangle",
.checkentry = proto_tg_check,
.me = THIS_MODULE,
},
};
static int __init proto_tg_init(void)
{
return xt_register_targets(proto_tg_reg, ARRAY_SIZE(proto_tg_reg));
}
static void __exit proto_tg_exit(void)
{
xt_unregister_targets(proto_tg_reg, ARRAY_SIZE(proto_tg_reg));
}
module_init(proto_tg_init);
module_exit(proto_tg_exit);
MODULE_ALIAS("ipt_PROTO");
MODULE_ALIAS("ip6t_PROTO");
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