[NET]: Make mangling a checksum (0 -> 0xffff on the wire) explicit.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/checksum.h

@@ -92,4 +92,5 @@ static inline __wsum csum_unfold(__sum16 n)
 	return (__force __wsum)n;
 }
 
+#define CSUM_MANGLED_0 ((__force __sum16)0xffff)
 #endif

net/ipv4/ipvs/ip_vs_proto_udp.c

@@ -125,7 +125,7 @@ udp_fast_csum_update(struct udphdr *uhdr, __be32 oldip, __be32 newip,
 				 ip_vs_check_diff(oldport ^ htons(0xFFFF),
 						  newport, uhdr->check));
 	if (!uhdr->check)
-		uhdr->check = -1;
+		uhdr->check = CSUM_MANGLED_0;
 }
 
 static int
@@ -173,7 +173,7 @@ udp_snat_handler(struct sk_buff **pskb,
 						cp->protocol,
 						(*pskb)->csum);
 		if (udph->check == 0)
-			udph->check = -1;
+			udph->check = CSUM_MANGLED_0;
 		IP_VS_DBG(11, "O-pkt: %s O-csum=%d (+%zd)\n",
 			  pp->name, udph->check,
 			  (char*)&(udph->check) - (char*)udph);
@@ -228,7 +228,7 @@ udp_dnat_handler(struct sk_buff **pskb,
 						cp->protocol,
 						(*pskb)->csum);
 		if (udph->check == 0)
-			udph->check = -1;
+			udph->check = CSUM_MANGLED_0;
 		(*pskb)->ip_summed = CHECKSUM_UNNECESSARY;
 	}
 	return 1;

net/ipv4/netfilter/ip_nat_helper.c

@@ -264,7 +264,7 @@ ip_nat_mangle_udp_packet(struct sk_buff **pskb,
 		                                csum_partial((char *)udph,
 		                                             datalen, 0));
 		if (!udph->check)
-			udph->check = -1;
+			udph->check = CSUM_MANGLED_0;
 	} else
 		udph->check = nf_proto_csum_update(*pskb,
 						   htons(oldlen) ^ htons(0xFFFF),

net/ipv4/netfilter/ip_nat_proto_udp.c

@@ -121,7 +121,7 @@ udp_manip_pkt(struct sk_buff **pskb,
 						  *portptr ^ htons(0xFFFF), newport,
 						  hdr->check, 0);
 		if (!hdr->check)
-			hdr->check = -1;
+			hdr->check = CSUM_MANGLED_0;
 	}
 	*portptr = newport;
 	return 1;

net/ipv4/udp.c

@@ -441,7 +441,7 @@ static void udp4_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
 
 		uh->check = csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, csum);
 		if (uh->check == 0)
-			uh->check = -1;
+			uh->check = CSUM_MANGLED_0;
 	}
 }
 
@@ -490,7 +490,7 @@ int udp_push_pending_frames(struct sock *sk, struct udp_sock *up)
 	uh->check = csum_tcpudp_magic(fl->fl4_src, fl->fl4_dst, up->len,
 				      sk->sk_protocol, csum             );
 	if (uh->check == 0)
-		uh->check = -1;
+		uh->check = CSUM_MANGLED_0;
 
 send:
 	err = ip_push_pending_frames(sk);

net/ipv6/raw.c

@@ -536,8 +536,8 @@ static int rawv6_push_pending_frames(struct sock *sk, struct flowi *fl,
 				   &fl->fl6_dst,
 				   total_len, fl->proto, tmp_csum);
 
-	if (tmp_csum == 0 && fl->proto == IPPROTO_UDP)
-		tmp_csum = -1;
+	if (csum == 0 && fl->proto == IPPROTO_UDP)
+		csum = CSUM_MANGLED_0;
 
 	if (skb_store_bits(skb, offset, &csum, 2))
 		BUG();

net/ipv6/udp.c

@@ -536,7 +536,7 @@ static int udp_v6_push_pending_frames(struct sock *sk, struct udp_sock *up)
 	uh->check = csum_ipv6_magic(&fl->fl6_src, &fl->fl6_dst,
 				    up->len, fl->proto, csum   );
 	if (uh->check == 0)
-		uh->check = -1;
+		uh->check = CSUM_MANGLED_0;
 
 	err = ip6_push_pending_frames(sk);
 out: