[NETFILTER]: Add address family specific checksum helpers

Add checksum operation which takes care of verifying the checksum and
dealing with HW checksum errors and avoids multiple checksum
operations by setting ip_summed to CHECKSUM_UNNECESSARY after
successful verification.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 33 insertions, 0 deletions

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index b25339c11ea0..6a9e34b794bc 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -161,8 +161,41 @@ static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
         return 0;
 }
 
+unsigned int nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
+                            unsigned int dataoff, u_int8_t protocol)
+{
+        struct iphdr *iph = skb->nh.iph;
+        unsigned int csum = 0;
+
+        switch (skb->ip_summed) {
+        case CHECKSUM_HW:
+                if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
+                        break;
+                if ((protocol == 0 && !(u16)csum_fold(skb->csum)) ||
+                    !csum_tcpudp_magic(iph->saddr, iph->daddr,
+                                       skb->len - dataoff, protocol,
+                                       skb->csum)) {
+                        skb->ip_summed = CHECKSUM_UNNECESSARY;
+                        break;
+                }
+                /* fall through */
+        case CHECKSUM_NONE:
+                if (protocol == 0)
+                        skb->csum = 0;
+                else
+                        skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
+                                                       skb->len - dataoff,
+                                                       protocol, 0);
+                csum = __skb_checksum_complete(skb);
+        }
+        return csum;
+}
+
+EXPORT_SYMBOL(nf_ip_checksum);
+
 static struct nf_afinfo nf_ip_afinfo = {
         .family         = AF_INET,
+        .checksum       = nf_ip_checksum,
         .saveroute      = nf_ip_saveroute,
         .reroute        = nf_ip_reroute,
         .route_key_size = sizeof(struct ip_rt_info),