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netfilter: nf_reject_ipv4: split nf_send_reset() in smaller functions

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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: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2014-10-25 18:24:57 +02:00
parent 4d87716cd0
commit 052b9498ee
2 changed files with 72 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/net/netfilter/ipv4/nf_reject.h
View File

@ -1,6 +1,8 @@
#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 */

88
net/ipv4/netfilter/nf_reject_ipv4.c
View File

@ -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;