net/tap: allow all-zero checksum for UDP over IPv4

Unlike TCP, UDP checksums are optional and may be zero to indicate "not
set" [RFC 768] (except for IPv6, where this prohibited [RFC 8200]). Add
this special case to the checksum offload emulation in net/tap.

Signed-off-by: Michael Pfeiffer <michael.pfeiffer@tu-ilmenau.de>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 2f8abb1..2542de3 100644 (file)
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -303,6 +303,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
        uint16_t cksum = 0;
        void *l3_hdr;
        void *l4_hdr;
+       struct rte_udp_hdr *udp_hdr;
 
        if (l2 == RTE_PTYPE_L2_ETHER_VLAN)
                l2_len += 4;
@@ -349,10 +350,23 @@ tap_verify_csum(struct rte_mbuf *mbuf)
                /* Don't verify checksum for multi-segment packets. */
                if (mbuf->nb_segs > 1)
                        return;
-               if (l3 == RTE_PTYPE_L3_IPV4)
+               if (l3 == RTE_PTYPE_L3_IPV4) {
+                       if (l4 == RTE_PTYPE_L4_UDP) {
+                               udp_hdr = (struct rte_udp_hdr *)l4_hdr;
+                               if (udp_hdr->dgram_cksum == 0) {
+                                       /*
+                                        * For IPv4, a zero UDP checksum
+                                        * indicates that the sender did not
+                                        * generate one [RFC 768].
+                                        */
+                                       mbuf->ol_flags |= PKT_RX_L4_CKSUM_NONE;
+                                       return;
+                               }
+                       }
                        cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
-               else if (l3 == RTE_PTYPE_L3_IPV6)
+               } else if (l3 == RTE_PTYPE_L3_IPV6) {
                        cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
+               }
                mbuf->ol_flags |= cksum ?
                        PKT_RX_L4_CKSUM_BAD :
                        PKT_RX_L4_CKSUM_GOOD;