[dpdk-stable] [PATCH v2 2/4] net/tap: fix Rx cksum flags on TCP packets

[Olivier Matz <olivier.matz@6wind.com>]

Since commit d5df2ae0428a ("net: fix unneeded replacement of TCP
checksum 0"), the functions rte_ipv4_udptcp_cksum() or
rte_ipv6_udptcp_cksum() can return either 0x0000 or 0xffff when used to
verify a packet containing a valid checksum.

This new behavior broke the checksum verification in tap driver for TCP
packets: these packets are marked with PKT_RX_L4_CKSUM_BAD.

Fix this by checking the 2 possible values. A next commit will introduce
a checksum verification helper to simplify this a bit.

Fixes: d5df2ae0428a ("net: fix unneeded replacement of TCP checksum 0")
Cc: stable@dpdk.org

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
---
 drivers/net/tap/rte_eth_tap.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 5513cfd2d7..5429f611c1 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -350,6 +350,8 @@ tap_verify_csum(struct rte_mbuf *mbuf)
 		return;
 	}
 	if (l4 == RTE_PTYPE_L4_UDP || l4 == RTE_PTYPE_L4_TCP) {
+		int cksum_ok;
+
 		l4_hdr = rte_pktmbuf_mtod_offset(mbuf, void *, l2_len + l3_len);
 		/* Don't verify checksum for multi-segment packets. */
 		if (mbuf->nb_segs > 1)
@@ -367,13 +369,13 @@ tap_verify_csum(struct rte_mbuf *mbuf)
 					return;
 				}
 			}
-			cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
+			cksum = rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
 		} else { /* l3 == RTE_PTYPE_L3_IPV6, checked above */
-			cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
+			cksum = rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
 		}
-		mbuf->ol_flags |= cksum ?
-			PKT_RX_L4_CKSUM_BAD :
-			PKT_RX_L4_CKSUM_GOOD;
+		cksum_ok = (cksum == 0) || (cksum == 0xffff);
+		mbuf->ol_flags |= cksum_ok ?
+			PKT_RX_L4_CKSUM_GOOD : PKT_RX_L4_CKSUM_BAD;
 	}
 }
 
-- 
2.29.2