path: root/net/bridge/netfilter/nft_reject_bridge.c

/*
 * Copyright (c) 2014 Pablo Neira Ayuso <pablo@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.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/netlink.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables.h>
#include <net/netfilter/nft_reject.h>
#include <net/netfilter/nf_tables_bridge.h>
#include <net/netfilter/ipv4/nf_reject.h>
#include <net/netfilter/ipv6/nf_reject.h>
#include <linux/ip.h>
#include <net/ip.h>
#include <net/ip6_checksum.h>
#include <linux/netfilter_bridge.h>
#include <linux/netfilter_ipv6.h>
#include "../br_private.h"

static void nft_reject_br_push_etherhdr(struct sk_buff *oldskb,
					struct sk_buff *nskb)
{
	struct ethhdr *eth;

	eth = (struct ethhdr *)skb_push(nskb, ETH_HLEN);
	skb_reset_mac_header(nskb);
	ether_addr_copy(eth->h_source, eth_hdr(oldskb)->h_dest);
	ether_addr_copy(eth->h_dest, eth_hdr(oldskb)->h_source);
	eth->h_proto = eth_hdr(oldskb)->h_proto;
	skb_pull(nskb, ETH_HLEN);
}

/* We cannot use oldskb->dev, it can be either bridge device (NF_BRIDGE INPUT)
 * or the bridge port (NF_BRIDGE PREROUTING).
 */
static void nft_reject_br_send_v4_tcp_reset(struct sk_buff *oldskb,
					    const struct net_device *dev,
					    int hook)
{
	struct sk_buff *nskb;
	struct iphdr *niph;
	const struct tcphdr *oth;
	struct tcphdr _oth;

	if (!nft_bridge_iphdr_validate(oldskb))
		return;

	oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
	if (!oth)
		return;

	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
			 LL_MAX_HEADER, GFP_ATOMIC);
	if (!nskb)
		return;

	skb_reserve(nskb, LL_MAX_HEADER);
	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
				   sysctl_ip_default_ttl);
	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
	niph->ttl	= sysctl_ip_default_ttl;
	niph->tot_len	= htons(nskb->len);
	ip_send_check(niph);

	nft_reject_br_push_etherhdr(oldskb, nskb);

	br_deliver(br_port_get_rcu(dev), nskb);
}

static void nft_reject_br_send_v4_unreach(struct sk_buff *oldskb,
					  const struct net_device *dev,
					  int hook, u8 code)
{
	struct sk_buff *nskb;
	struct iphdr *niph;
	struct icmphdr *icmph;
	unsigned int len;
	void *payload;
	__wsum csum;
	u8 proto;

	if (oldskb->csum_bad || !nft_bridge_iphdr_validate(oldskb))
		return;

	/* IP header checks: fragment. */
	if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
		return;

	/* RFC says return as much as we can without exceeding 576 bytes. */
	len = min_t(unsigned int, 536, oldskb->len);

	if (!pskb_may_pull(oldskb, len))
		return;

	if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
		return;

	if (ip_hdr(oldskb)->protocol == IPPROTO_TCP ||
	    ip_hdr(oldskb)->protocol == IPPROTO_UDP)
		proto = ip_hdr(oldskb)->protocol;
	else
		proto = 0;

	if (!skb_csum_unnecessary(oldskb) &&
	    nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
		return;

	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
			 LL_MAX_HEADER + len, GFP_ATOMIC);
	if (!nskb)
		return;

	skb_reserve(nskb, LL_MAX_HEADER);
	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
				   sysctl_ip_default_ttl);

	skb_reset_transport_header(nskb);
	icmph = (struct icmphdr *)skb_put(nskb, sizeof(struct icmphdr));
	memset(icmph, 0, sizeof(*icmph));
	icmph->type     = ICMP_DEST_UNREACH;
	icmph->code	= code;

	payload = skb_put(nskb, len);
	memcpy(payload, skb_network_header(oldskb), len);

	csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
	icmph->checksum = csum_fold(csum);

	niph->tot_len	= htons(nskb->len);
	ip_send_check(niph);

	nft_reject_br_push_etherhdr(oldskb, nskb);

	br_deliver(br_port_get_rcu(dev), nskb);
}

static void nft_reject_br_send_v6_tcp_reset(struct net *net,
					    struct sk_buff *oldskb,
					    const struct net_device *dev,
					    int hook)
{
	struct sk_buff *nskb;
	const struct tcphdr *oth;
	struct tcphdr _oth;
	unsigned int otcplen;
	struct ipv6hdr *nip6h;

	if (!nft_bridge_ip6hdr_validate(oldskb))
		return;

	oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
	if (!oth)
		return;

	nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
			 LL_MAX_HEADER, GFP_ATOMIC);
	if (!nskb)
		return;

	skb_reserve(nskb, LL_MAX_HEADER);
	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
				     net->ipv6.devconf_all->hop_limit);
	nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
	nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));

	nft_reject_br_push_etherhdr(oldskb, nskb);

	br_deliver(br_port_get_rcu(dev), nskb);
}

static bool reject6_br_csum_ok(struct sk_buff *skb, int hook)
{
	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
	int thoff;
	__be16 fo;
	u8 proto = ip6h->nexthdr;

	if (skb->csum_bad)
		return false;

	if (skb_csum_unnecessary(skb))
		return true;

	if (ip6h->payload_len &&
	    pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
		return false;

	thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
		return false;

	return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
}

static void nft_reject_br_send_v6_unreach(struct net *net,
					  struct sk_buff *oldskb,
					  const struct net_device *dev,
					  int hook, u8 code)
{
	struct sk_buff *nskb;
	struct ipv6hdr *nip6h;
	struct icmp6hdr *icmp6h;
	unsigned int len;
	void *payload;

	if (!nft_bridge_ip6hdr_validate(oldskb))
		return;

	/* Include "As much of invoking packet as possible without the ICMPv6
	 * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
	 */
	len = min_t(unsigned int, 1220, oldskb->len);

	if (!pskb_may_pull(oldskb, len))
		return;

	if (!reject6_br_csum_ok(oldskb, hook))
		return;

	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmp6hdr) +
			 LL_MAX_HEADER + len, GFP_ATOMIC);
	if (!nskb)
		return;

	skb_reserve(nskb, LL_MAX_HEADER);
	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
				     net->ipv6.devconf_all->hop_limit);

	skb_reset_transport_header(nskb);
	icmp6h =