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: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/net/netfilter/ipv4/nf_reject.h b/include/net/netfilter/ipv4/nf_reject.h
index e842719..03e928a 100644 (file)
--- a/include/net/netfilter/ipv4/nf_reject.h
+++ b/include/net/netfilter/ipv4/nf_reject.h
@@ -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 */

diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 92b303d..1baaa83 100644 (file)
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -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;