[PATCH dpdk] net: fix L2 ptype assignment in VLAN loop

[Robin Jarry <rjarry@redhat.com>]

Since commit 1f250674085a ("net: fix packet type for stacked VLAN"),
rte_net_get_ptype() uses |= to set the L2 ptype inside the VLAN
parsing loop. Since pkt_type is already initialized with
RTE_PTYPE_L2_ETHER (0x1), or-ing it with RTE_PTYPE_L2_ETHER_VLAN
(0x6) results in RTE_PTYPE_L2_ETHER_QINQ (0x7). This causes single
VLAN frames to be misidentified as QinQ.

This was detected while testing DPDK 25.11.1 in grout. The net/tap
driver calls rte_net_get_ptype() in tap_verify_csum() to determine
the L2 header length. With the wrong ptype, l2_len is set to 22
(ether + QinQ = 14 + 8) instead of 18 (ether + VLAN = 14 + 4),
shifting the IP header pointer by 4 bytes. The checksum is then
computed on garbage data, causing valid packets to be dropped.

Use a simple assignment to replace the L2 ptype instead. Add VLAN
and QinQ test packets in cksum_autotest to prevent regressions.

Fixes: 1f250674085a ("net: fix packet type for stacked VLAN")
Cc: stable@dpdk.org

Signed-off-by: Robin Jarry <rjarry@redhat.com>
---
 app/test/test_cksum.c | 29 +++++++++++++++++++++++++++++
 lib/net/rte_net.c     |  2 +-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/app/test/test_cksum.c b/app/test/test_cksum.c
index ea443382a128..3cc42eccedd9 100644
--- a/app/test/test_cksum.c
+++ b/app/test/test_cksum.c
@@ -75,6 +75,27 @@ static const char test_cksum_ipv6_udp[] = {
 	0x00, 0x35, 0x00, 0x09, 0x87, 0x70, 0x78,
 };
 
+/* generated in scapy with Ether()/Dot1Q(vlan=42)/IP()/UDP()/Raw('x') */
+static const char test_cksum_vlan_ipv4_udp[] = {
+	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x81, 0x00, 0x00, 0x2a,
+	0x08, 0x00, 0x45, 0x00, 0x00, 0x1d, 0x00, 0x01,
+	0x00, 0x00, 0x40, 0x11, 0x7c, 0xcd, 0x7f, 0x00,
+	0x00, 0x01, 0x7f, 0x00, 0x00, 0x01, 0x00, 0x35,
+	0x00, 0x35, 0x00, 0x09, 0x89, 0x6f, 0x78,
+};
+
+/* generated in scapy with Ether()/Dot1AD(vlan=42)/Dot1Q(vlan=43)/IP()/UDP()/Raw('x') */
+static const char test_cksum_qinq_ipv4_udp[] = {
+	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x88, 0xa8, 0x00, 0x2a,
+	0x81, 0x00, 0x00, 0x2b, 0x08, 0x00, 0x45, 0x00,
+	0x00, 0x1d, 0x00, 0x01, 0x00, 0x00, 0x40, 0x11,
+	0x7c, 0xcd, 0x7f, 0x00, 0x00, 0x01, 0x7f, 0x00,
+	0x00, 0x01, 0x00, 0x35, 0x00, 0x35, 0x00, 0x09,
+	0x89, 0x6f, 0x78,
+};
+
 /* generated in scapy with Ether()/IP(options='\x00')/UDP()/Raw('x')) */
 static const char test_cksum_ipv4_opts_udp[] = {
 	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00,
@@ -252,6 +273,14 @@ test_cksum(void)
 			  sizeof(test_cksum_ipv6_udp)) < 0)
 		GOTO_FAIL("checksum error on ipv6_udp");
 
+	if (test_l4_cksum(pktmbuf_pool, test_cksum_vlan_ipv4_udp,
+			  sizeof(test_cksum_vlan_ipv4_udp)) < 0)
+		GOTO_FAIL("checksum error on vlan_ipv4_udp");
+
+	if (test_l4_cksum(pktmbuf_pool, test_cksum_qinq_ipv4_udp,
+			  sizeof(test_cksum_qinq_ipv4_udp)) < 0)
+		GOTO_FAIL("checksum error on qinq_ipv4_udp");
+
 	if (test_l4_cksum(pktmbuf_pool, test_cksum_ipv4_opts_udp,
 			  sizeof(test_cksum_ipv4_opts_udp)) < 0)
 		GOTO_FAIL("checksum error on ipv4_opts_udp");
diff --git a/lib/net/rte_net.c b/lib/net/rte_net.c
index 458b4814a9c9..ea5ba7019089 100644
--- a/lib/net/rte_net.c
+++ b/lib/net/rte_net.c
@@ -359,7 +359,7 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf *m,
 
 		if (++vlan_depth > RTE_NET_VLAN_MAX_DEPTH)
 			return 0;
-		pkt_type |=
+		pkt_type =
 			proto == rte_cpu_to_be_16(RTE_ETHER_TYPE_VLAN) ?
 				 RTE_PTYPE_L2_ETHER_VLAN :
 				 RTE_PTYPE_L2_ETHER_QINQ;
-- 
2.53.0