net: fix unneeded replacement of TCP checksum 0

Per RFC768:
If the computed checksum is zero, it is transmitted as all ones.
An all zero transmitted checksum value means that the transmitter
generated no checksum.

RFC793 for TCP has no such special treatment for the checksum of zero.

Fixes: 6006818cfb26 ("net: new checksum functions")
Cc: stable@dpdk.org
Signed-off-by: Hongzhi Guo <guohongzhi1@huawei.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>

diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index 292f63f..a9ffc33 100644 (file)
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -324,8 +324,7 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
  * @param l4_hdr
  *   The pointer to the beginning of the L4 header.
  * @return
- *   The complemented checksum to set in the IP packet
- *   or 0 on error
+ *   The complemented checksum to set in the IP packet.
  */
 static inline uint16_t
 rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
@@ -344,7 +343,12 @@ rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
 
        cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
        cksum = (~cksum) & 0xffff;
-       if (cksum == 0)
+       /*
+        * Per RFC 768:If the computed checksum is zero for UDP,
+        * it is transmitted as all ones
+        * (the equivalent in one's complement arithmetic).
+        */
+       if (cksum == 0 && ipv4_hdr->next_proto_id == IPPROTO_UDP)
                cksum = 0xffff;
 
        return (uint16_t)cksum;
@@ -438,7 +442,12 @@ rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr *ipv6_hdr, const void *l4_hdr)
 
        cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
        cksum = (~cksum) & 0xffff;
-       if (cksum == 0)
+       /*
+        * Per RFC 768: If the computed checksum is zero for UDP,
+        * it is transmitted as all ones
+        * (the equivalent in one's complement arithmetic).
+        */
+       if (cksum == 0 && ipv6_hdr->proto == IPPROTO_UDP)
                cksum = 0xffff;
 
        return (uint16_t)cksum;