[PATCH bpf-next v3 12/14] selftests/bpf: add network helpers to generate udp checksums

["Alexis Lothoré (eBPF Foundation)" <alexis.lothore@bootlin.com>]

network_helpers.c provides some helpers to generate ip checksums or ip
pseudo-header checksums, but not for upper layers (eg: udp checksums)

Add helpers for udp checksum to allow manually building udp packets.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
---
Changes in v3:
- reuse pseudo-header checksum helper in the new helpers
- reduce parameters list (eg: it does not make sense to passe the l4
  protocol in a udp-specific helper)

Changes in v2:
- new patch
---
 tools/testing/selftests/bpf/network_helpers.h | 42 +++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
index 6ca636643ea2b77fb5cc459b03bf7f8c4f749377..479f678af191e9fa8a7129e050a25bf9ed0cf37e 100644
--- a/tools/testing/selftests/bpf/network_helpers.h
+++ b/tools/testing/selftests/bpf/network_helpers.h
@@ -13,6 +13,7 @@ typedef __u16 __sum16;
 #include <linux/sockios.h>
 #include <linux/err.h>
 #include <netinet/tcp.h>
+#include <netinet/udp.h>
 #include <bpf/bpf_endian.h>
 #include <net/if.h>
 
@@ -192,6 +193,47 @@ static inline __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 	return csum_fold((__u32)s);
 }
 
+/**
+ * build_udp_v4_csum - compute UDP checksum for UDP over IPv4
+ *
+ * Compute the checksum to embed in UDP header, composed of the sum of IP
+ * pseudo-header checksum, UDP header checksum and UDP data checksum
+ * @iph IP header
+ * @udph UDP header, which must be immediately followed by UDP data
+ *
+ * Returns the total checksum
+ */
+
+static inline __sum16 build_udp_v4_csum(const struct iphdr *iph,
+					const struct udphdr *udph)
+{
+	unsigned long sum;
+
+	sum = csum_partial(udph, ntohs(udph->len), 0);
+	return csum_tcpudp_magic(iph->saddr, iph->daddr, ntohs(udph->len),
+				 IPPROTO_UDP, sum);
+}
+
+/**
+ * build_udp_v6_csum - compute UDP checksum for UDP over IPv6
+ *
+ * Compute the checksum to embed in UDP header, composed of the sum of IPv6
+ * pseudo-header checksum, UDP header checksum and UDP data checksum
+ * @ip6h IPv6 header
+ * @udph UDP header, which must be immediately followed by UDP data
+ *
+ * Returns the total checksum
+ */
+static inline __sum16 build_udp_v6_csum(const struct ipv6hdr *ip6h,
+					const struct udphdr *udph)
+{
+	unsigned long sum;
+
+	sum = csum_partial(udph, ntohs(udph->len), 0);
+	return csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr, ntohs(udph->len),
+			       IPPROTO_UDP, sum);
+}
+
 struct tmonitor_ctx;
 
 #ifdef TRAFFIC_MONITOR

-- 
2.47.0