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Commit 052b9498 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso
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netfilter: nf_reject_ipv4: split nf_send_reset() in smaller functions 



That can be reused by the reject bridge expression to build the reject
packet. The new functions are:

* nf_reject_ip_tcphdr_get(): to sanitize and to obtain the TCP header.
* nf_reject_iphdr_put(): to build the IPv4 header.
* nf_reject_ip_tcphdr_put(): to build the TCP header.

Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 4d87716c

include/net/netfilter/ipv4/nf_reject.h

+10 −0
Original line number Diff line number Diff line 
#ifndef _IPV4_NF_REJECT_H

#define _IPV4_NF_REJECT_H



#include <linux/skbuff.h>

#include <net/ip.h>

#include <net/icmp.h>



static inline void nf_send_unreach(struct sk_buff *skb_in, int code)
@@ -10,4 +12,12 @@ static inline void nf_send_unreach(struct sk_buff *skb_in, int code) 


void nf_send_reset(struct sk_buff *oldskb, int hook);



const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,

					     struct tcphdr *_oth, int hook);

struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,

				  const struct sk_buff *oldskb,

				  __be16 protocol, int ttl);

void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,

			     const struct tcphdr *oth);



#endif /* _IPV4_NF_REJECT_H */

net/ipv4/netfilter/nf_reject_ipv4.c

+62 −26
Original line number Diff line number Diff line
@@ -12,43 +12,39 @@ 
#include <net/route.h>

#include <net/dst.h>

#include <linux/netfilter_ipv4.h>

#include <net/netfilter/ipv4/nf_reject.h>



/* Send RST reply */

void nf_send_reset(struct sk_buff *oldskb, int hook)

const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,

					     struct tcphdr *_oth, 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;

		return NULL;



	oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),

				 sizeof(_otcph), &_otcph);

				 sizeof(struct tcphdr), _oth);

	if (oth == NULL)

		return;

		return NULL;



	/* No RST for RST. */

	if (oth->rst)

		return;



	if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))

		return;

		return NULL;



	/* Check checksum */

	if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))

		return;

	oiph = ip_hdr(oldskb);

		return NULL;



	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +

			 LL_MAX_HEADER, GFP_ATOMIC);

	if (!nskb)

		return;

	return oth;

}

EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);



	skb_reserve(nskb, LL_MAX_HEADER);

struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,

				  const struct sk_buff *oldskb,

				  __be16 protocol, int ttl)

{

	struct iphdr *niph, *oiph = ip_hdr(oldskb);



	skb_reset_network_header(nskb);

	niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
@@ -57,10 +53,23 @@ void nf_send_reset(struct sk_buff *oldskb, int hook) 
	niph->tos	= 0;

	niph->id	= 0;

	niph->frag_off	= htons(IP_DF);

	niph->protocol	= IPPROTO_TCP;

	niph->protocol	= protocol;

	niph->check	= 0;

	niph->saddr	= oiph->daddr;

	niph->daddr	= oiph->saddr;

	niph->ttl	= ttl;



	nskb->protocol = htons(ETH_P_IP);



	return niph;

}

EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);



void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,

			  const struct tcphdr *oth)

{

	struct iphdr *niph = ip_hdr(nskb);

	struct tcphdr *tcph;



	skb_reset_transport_header(nskb);

	tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
@@ -69,9 +78,9 @@ void nf_send_reset(struct sk_buff *oldskb, int hook) 
	tcph->dest	= oth->source;

	tcph->doff	= sizeof(struct tcphdr) / 4;



	if (oth->ack)

	if (oth->ack) {

		tcph->seq = oth->ack_seq;

	else {

	} else {

		tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +

				      oldskb->len - ip_hdrlen(oldskb) -

				      (oth->doff << 2));
@@ -84,16 +93,43 @@ void nf_send_reset(struct sk_buff *oldskb, int hook) 
	nskb->ip_summed = CHECKSUM_PARTIAL;

	nskb->csum_start = (unsigned char *)tcph - nskb->head;

	nskb->csum_offset = offsetof(struct tcphdr, check);

}

EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);



/* Send RST reply */

void nf_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 _oth;



	oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);

	if (!oth)

		return;



	if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))

		return;



	oiph = ip_hdr(oldskb);



	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +

			 LL_MAX_HEADER, GFP_ATOMIC);

	if (!nskb)

		return;



	/* ip_route_me_harder expects skb->dst to be set */

	skb_dst_set_noref(nskb, skb_dst(oldskb));



	nskb->protocol = htons(ETH_P_IP);

	skb_reserve(nskb, LL_MAX_HEADER);

	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,

				   ip4_dst_hoplimit(skb_dst(nskb)));

	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);



	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;