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

["Robin Jarry" <rjarry@redhat.com>]

Robin Jarry, Apr 22, 2026 at 12:28:
> 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");

The tests are useless, they don't check that the L2 ptype is correct.
I'll send a v2 with proper ptype tests.