net: Implmement RFC 6936 (zero RX csums for UDP/IPv6)

RFC 6936 relaxes the requirement of RFC 2460 that UDP/IPv6 packets which
are received with a zero UDP checksum value must be dropped. RFC 6936
allows zero checksums to support tunnels over UDP.

When sk_no_check is set we allow on a socket we allow a zero IPv6
UDP checksum. This is for both sending zero checksum and accepting
a zero checksum on receive.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 11 deletions

diff --git a/net/ipv6/ip6_checksum.c b/net/ipv6/ip6_checksum.c
index c69fe37b8104..da26224a5993 100644
--- a/net/ipv6/ip6_checksum.c
+++ b/net/ipv6/ip6_checksum.c
@@ -75,16 +75,12 @@ int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
                         return err;
         }
 
-        if (uh->check == 0) {
-                /* RFC 2460 section 8.1 says that we SHOULD log
-                   this error. Well, it is reasonable.
-                 */
-                LIMIT_NETDEBUG(KERN_INFO "IPv6: udp checksum is 0 for [%pI6c]:%u->[%pI6c]:%u\n",
-                               &ipv6_hdr(skb)->saddr, ntohs(uh->source),
-                               &ipv6_hdr(skb)->daddr, ntohs(uh->dest));
-                return 1;
-        }
-
-        return skb_checksum_init(skb, IPPROTO_UDP, ip6_compute_pseudo);
+        /* To support RFC 6936 (allow zero checksum in UDP/IPV6 for tunnels)
+         * we accept a checksum of zero here. When we find the socket
+         * for the UDP packet we'll check if that socket allows zero checksum
+         * for IPv6 (set by socket option).
+         */
+        return skb_checksum_init_zero_check(skb, proto, uh->check,
+                                           ip6_compute_pseudo);
 }
 EXPORT_SYMBOL(udp6_csum_init);