Add csum_udp6() helper for calculating UDP over IPv6 checksums

Add a helper for calculating UDP checksums when used over IPv6
For future flexibility, the new helper takes parameters for the fields in
the IPv6 pseudo-header, so an IPv6 header or pseudo-header doesn't need to
be explicitly constructed.  It also allows the UDP header and payload to
be in separate buffers, although we don't use this yet.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/checksum.c b/checksum.c
index f35c948..175381d 100644
--- a/checksum.c
+++ b/checksum.c
@@ -52,6 +52,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <linux/udp.h>
 #include <linux/icmp.h>
 #include <linux/icmpv6.h>
 
@@ -124,6 +125,27 @@ void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t len)
 }
 
 /**
+ * csum_udp6() - Calculate and set checksum for a UDP over IPv6 packet
+ * @udp6hr:	UDP header, initialised apart from checksum
+ * @payload:	UDP packet payload
+ * @len:	Length of @payload (not including UDP header)
+ */
+void csum_udp6(struct udphdr *udp6hr,
+	       const struct in6_addr *saddr, const struct in6_addr *daddr,
+	       const void *payload, size_t len)
+{
+	/* Partial checksum for the pseudo-IPv6 header */
+	uint32_t psum = sum_16b(saddr, sizeof(*saddr)) +
+		        sum_16b(daddr, sizeof(*daddr)) +
+		        htons(len + sizeof(*udp6hr)) + htons(IPPROTO_UDP);
+
+	udp6hr->check = 0;
+	/* Add in partial checksum for the UDP header alone */
+	psum += sum_16b(udp6hr, sizeof(*udp6hr));
+	udp6hr->check = csum_unaligned(payload, len, psum);
+}
+
+/**
  * csum_icmp6() - Calculate and set checksum for an ICMPv6 packet
  * @icmp6hr:	ICMPv6 header, initialised apart from checksum
  * @saddr:	IPv6 source address