![Phil Oester](/assets/img/avatar_default.png)
As reported by Casper Gripenberg, in a bridged setup, using ip[6]t_REJECT with the tcp-reset option sends out reset packets with the src MAC address of the local bridge interface, instead of the MAC address of the intended destination. This causes some routers/firewalls to drop the reset packet as it appears to be spoofed. Fix this by bypassing ip[6]_local_out and setting the MAC of the sender in the tcp reset packet. This closes netfilter bugzilla #531. Signed-off-by: Phil Oester <kernel@linuxace.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
233 lines
5.9 KiB
C
233 lines
5.9 KiB
C
/*
|
|
* This is a module which is used for rejecting packets.
|
|
*/
|
|
|
|
/* (C) 1999-2001 Paul `Rusty' Russell
|
|
* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
|
|
*
|
|
* 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/slab.h>
|
|
#include <linux/ip.h>
|
|
#include <linux/udp.h>
|
|
#include <linux/icmp.h>
|
|
#include <net/icmp.h>
|
|
#include <net/ip.h>
|
|
#include <net/tcp.h>
|
|
#include <net/route.h>
|
|
#include <net/dst.h>
|
|
#include <linux/netfilter/x_tables.h>
|
|
#include <linux/netfilter_ipv4/ip_tables.h>
|
|
#include <linux/netfilter_ipv4/ipt_REJECT.h>
|
|
#ifdef CONFIG_BRIDGE_NETFILTER
|
|
#include <linux/netfilter_bridge.h>
|
|
#endif
|
|
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
|
|
MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4");
|
|
|
|
/* Send RST reply */
|
|
static void send_reset(struct sk_buff *oldskb, int hook)
|
|
{
|
|
struct sk_buff *nskb;
|
|
const struct iphdr *oiph;
|
|
struct iphdr *niph;
|
|
const struct tcphdr *oth;
|
|
struct tcphdr _otcph, *tcph;
|
|
|
|
/* IP header checks: fragment. */
|
|
if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
|
|
return;
|
|
|
|
oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
|
|
sizeof(_otcph), &_otcph);
|
|
if (oth == NULL)
|
|
return;
|
|
|
|
/* No RST for RST. */
|
|
if (oth->rst)
|
|
return;
|
|
|
|
if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
|
|
return;
|
|
|
|
/* Check checksum */
|
|
if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
|
|
return;
|
|
oiph = ip_hdr(oldskb);
|
|
|
|
nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
|
|
LL_MAX_HEADER, GFP_ATOMIC);
|
|
if (!nskb)
|
|
return;
|
|
|
|
skb_reserve(nskb, LL_MAX_HEADER);
|
|
|
|
skb_reset_network_header(nskb);
|
|
niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
|
|
niph->version = 4;
|
|
niph->ihl = sizeof(struct iphdr) / 4;
|
|
niph->tos = 0;
|
|
niph->id = 0;
|
|
niph->frag_off = htons(IP_DF);
|
|
niph->protocol = IPPROTO_TCP;
|
|
niph->check = 0;
|
|
niph->saddr = oiph->daddr;
|
|
niph->daddr = oiph->saddr;
|
|
|
|
skb_reset_transport_header(nskb);
|
|
tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
|
|
memset(tcph, 0, sizeof(*tcph));
|
|
tcph->source = oth->dest;
|
|
tcph->dest = oth->source;
|
|
tcph->doff = sizeof(struct tcphdr) / 4;
|
|
|
|
if (oth->ack)
|
|
tcph->seq = oth->ack_seq;
|
|
else {
|
|
tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
|
|
oldskb->len - ip_hdrlen(oldskb) -
|
|
(oth->doff << 2));
|
|
tcph->ack = 1;
|
|
}
|
|
|
|
tcph->rst = 1;
|
|
tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
|
|
niph->daddr, 0);
|
|
nskb->ip_summed = CHECKSUM_PARTIAL;
|
|
nskb->csum_start = (unsigned char *)tcph - nskb->head;
|
|
nskb->csum_offset = offsetof(struct tcphdr, check);
|
|
|
|
/* ip_route_me_harder expects skb->dst to be set */
|
|
skb_dst_set_noref(nskb, skb_dst(oldskb));
|
|
|
|
nskb->protocol = htons(ETH_P_IP);
|
|
if (ip_route_me_harder(nskb, RTN_UNSPEC))
|
|
goto free_nskb;
|
|
|
|
niph->ttl = ip4_dst_hoplimit(skb_dst(nskb));
|
|
|
|
/* "Never happens" */
|
|
if (nskb->len > dst_mtu(skb_dst(nskb)))
|
|
goto free_nskb;
|
|
|
|
nf_ct_attach(nskb, oldskb);
|
|
|
|
#ifdef CONFIG_BRIDGE_NETFILTER
|
|
/* If we use ip_local_out for bridged traffic, the MAC source on
|
|
* the RST will be ours, instead of the destination's. This confuses
|
|
* some routers/firewalls, and they drop the packet. So we need to
|
|
* build the eth header using the original destination's MAC as the
|
|
* source, and send the RST packet directly.
|
|
*/
|
|
if (oldskb->nf_bridge) {
|
|
struct ethhdr *oeth = eth_hdr(oldskb);
|
|
nskb->dev = oldskb->nf_bridge->physindev;
|
|
niph->tot_len = htons(nskb->len);
|
|
ip_send_check(niph);
|
|
if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
|
|
oeth->h_source, oeth->h_dest, nskb->len) < 0)
|
|
goto free_nskb;
|
|
dev_queue_xmit(nskb);
|
|
} else
|
|
#endif
|
|
ip_local_out(nskb);
|
|
|
|
return;
|
|
|
|
free_nskb:
|
|
kfree_skb(nskb);
|
|
}
|
|
|
|
static inline void send_unreach(struct sk_buff *skb_in, int code)
|
|
{
|
|
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
|
|
}
|
|
|
|
static unsigned int
|
|
reject_tg(struct sk_buff *skb, const struct xt_action_param *par)
|
|
{
|
|
const struct ipt_reject_info *reject = par->targinfo;
|
|
|
|
switch (reject->with) {
|
|
case IPT_ICMP_NET_UNREACHABLE:
|
|
send_unreach(skb, ICMP_NET_UNREACH);
|
|
break;
|
|
case IPT_ICMP_HOST_UNREACHABLE:
|
|
send_unreach(skb, ICMP_HOST_UNREACH);
|
|
break;
|
|
case IPT_ICMP_PROT_UNREACHABLE:
|
|
send_unreach(skb, ICMP_PROT_UNREACH);
|
|
break;
|
|
case IPT_ICMP_PORT_UNREACHABLE:
|
|
send_unreach(skb, ICMP_PORT_UNREACH);
|
|
break;
|
|
case IPT_ICMP_NET_PROHIBITED:
|
|
send_unreach(skb, ICMP_NET_ANO);
|
|
break;
|
|
case IPT_ICMP_HOST_PROHIBITED:
|
|
send_unreach(skb, ICMP_HOST_ANO);
|
|
break;
|
|
case IPT_ICMP_ADMIN_PROHIBITED:
|
|
send_unreach(skb, ICMP_PKT_FILTERED);
|
|
break;
|
|
case IPT_TCP_RESET:
|
|
send_reset(skb, par->hooknum);
|
|
case IPT_ICMP_ECHOREPLY:
|
|
/* Doesn't happen. */
|
|
break;
|
|
}
|
|
|
|
return NF_DROP;
|
|
}
|
|
|
|
static int reject_tg_check(const struct xt_tgchk_param *par)
|
|
{
|
|
const struct ipt_reject_info *rejinfo = par->targinfo;
|
|
const struct ipt_entry *e = par->entryinfo;
|
|
|
|
if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
|
|
pr_info("ECHOREPLY no longer supported.\n");
|
|
return -EINVAL;
|
|
} else if (rejinfo->with == IPT_TCP_RESET) {
|
|
/* Must specify that it's a TCP packet */
|
|
if (e->ip.proto != IPPROTO_TCP ||
|
|
(e->ip.invflags & XT_INV_PROTO)) {
|
|
pr_info("TCP_RESET invalid for non-tcp\n");
|
|
return -EINVAL;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
static struct xt_target reject_tg_reg __read_mostly = {
|
|
.name = "REJECT",
|
|
.family = NFPROTO_IPV4,
|
|
.target = reject_tg,
|
|
.targetsize = sizeof(struct ipt_reject_info),
|
|
.table = "filter",
|
|
.hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
|
|
(1 << NF_INET_LOCAL_OUT),
|
|
.checkentry = reject_tg_check,
|
|
.me = THIS_MODULE,
|
|
};
|
|
|
|
static int __init reject_tg_init(void)
|
|
{
|
|
return xt_register_target(&reject_tg_reg);
|
|
}
|
|
|
|
static void __exit reject_tg_exit(void)
|
|
{
|
|
xt_unregister_target(&reject_tg_reg);
|
|
}
|
|
|
|
module_init(reject_tg_init);
|
|
module_exit(reject_tg_exit);
|