[NETFILTER]: Add partial checksum validation helper

Move the UDP-Lite conntrack checksum validation to a generic helper
similar to nf_checksum() and make it fall back to nf_checksum()
in case the full packet is to be checksummed and hardware checksums
are available. This is to be used by DCCP conntrack, which also
needs to verify partial checksums.

Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 30 insertions, 7 deletions

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index 9a904c6c0dc8..f8edacdf991d 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -182,21 +182,44 @@ __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 	}
 	return csum;
 }
-
 EXPORT_SYMBOL(nf_ip_checksum);
 
+static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
+				      unsigned int dataoff, unsigned int len,
+				      u_int8_t protocol)
+{
+	const struct iphdr *iph = ip_hdr(skb);
+	__sum16 csum = 0;
+
+	switch (skb->ip_summed) {
+	case CHECKSUM_COMPLETE:
+		if (len == skb->len - dataoff)
+			return nf_ip_checksum(skb, hook, dataoff, protocol);
+		/* fall through */
+	case CHECKSUM_NONE:
+		skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
+					       skb->len - dataoff, 0);
+		skb->ip_summed = CHECKSUM_NONE;
+		csum = __skb_checksum_complete_head(skb, dataoff + len);
+		if (!csum)
+			skb->ip_summed = CHECKSUM_UNNECESSARY;
+	}
+	return csum;
+}
+
 static int nf_ip_route(struct dst_entry **dst, struct flowi *fl)
 {
 	return ip_route_output_key(&init_net, (struct rtable **)dst, fl);
 }
 
 static const struct nf_afinfo nf_ip_afinfo = {
-	.family		= AF_INET,
-	.checksum	= nf_ip_checksum,
-	.route		= nf_ip_route,
-	.saveroute	= nf_ip_saveroute,
-	.reroute	= nf_ip_reroute,
-	.route_key_size	= sizeof(struct ip_rt_info),
+	.family			= AF_INET,
+	.checksum		= nf_ip_checksum,
+	.checksum_partial	= nf_ip_checksum_partial,
+	.route			= nf_ip_route,
+	.saveroute		= nf_ip_saveroute,
+	.reroute		= nf_ip_reroute,
+	.route_key_size		= sizeof(struct ip_rt_info),
 };
 
 static int ipv4_netfilter_init(void)