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(a)gibson.dropbear.id.au>
---
checksum.c | 23 +++++++++++++++++++++++
checksum.h | 5 +++++
tap.c | 5 ++---
3 files changed, 30 insertions(+), 3 deletions(-)
diff --git a/checksum.c b/checksum.c
index c8b6b42..0849fb1 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>
@@ -122,6 +123,28 @@ void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t
len)
icmp4hr->checksum = csum_unaligned(payload, len, hrsum);
}
+/**
+ * csum_udp6() - Calculate checksum for a UDP over IPv6 packet
+ * @udp6hr: UDP header, initialized 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 checksum for an ICMPv6 packet
* @icmp6hr: ICMPv6 header, initialized apart from checksum
diff --git a/checksum.h b/checksum.h
index ff95cf9..1b9f48e 100644
--- a/checksum.h
+++ b/checksum.h
@@ -6,6 +6,7 @@
#ifndef CHECKSUM_H
#define CHECKSUM_H
+struct udphdr;
struct icmphdr;
struct icmp6hdr;
@@ -13,6 +14,10 @@ uint32_t sum_16b(const void *buf, size_t len);
uint16_t csum_fold(uint32_t sum);
uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init);
void csum_icmp4(struct icmphdr *ih, const void *payload, size_t len);
+void csum_udp6(struct udphdr *udp6hr,
+ const struct in6_addr *saddr,
+ const struct in6_addr *daddr,
+ const void *payload, size_t len);
void csum_icmp6(struct icmp6hdr *ih,
const struct in6_addr *saddr,
const struct in6_addr *daddr,
diff --git a/tap.c b/tap.c
index f082901..9c197cb 100644
--- a/tap.c
+++ b/tap.c
@@ -183,9 +183,8 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src,
uint8_t proto,
} else if (proto == IPPROTO_UDP) {
struct udphdr *uh = (struct udphdr *)(ip6h + 1);
- uh->check = 0;
- uh->check = csum_unaligned(ip6h, len + sizeof(*ip6h),
- 0);
+ csum_udp6(uh, &ip6h->saddr, &ip6h->daddr,
+ uh + 1, len - sizeof(*uh));
} else if (proto == IPPROTO_ICMPV6) {
struct icmp6hdr *ih = (struct icmp6hdr *)(ip6h + 1);
--
2.37.3