Re: [PATCH v3 net 3/3] selftests: net: tun: add test for VLAN-tagged GSO without NEEDS_CSUM

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Eric Dumazet wrote:
> Add selftests in tun.c verifying that a VLAN-tagged (802.1Q) TCPv4 GSO
> packet without VIRTIO_NET_HDR_F_NEEDS_CSUM (both flags = 0 and
> flags = VIRTIO_NET_HDR_F_DATA_VALID) is accepted when written to a TAP
> device (/dev/net/tun with IFF_TAP | IFF_NO_PI | IFF_VNET_HDR).
> 
> Also verify that the following are rejected with -EINVAL:
> - a mismatched GSO type (VIRTIO_NET_HDR_GSO_TCPV6 on a VLAN-tagged IPv4
>   packet).
> - a frame whose TCP header is truncated after 10 bytes. Pulling only
>   sizeof(struct iphdr) + sizeof(struct tcphdr) bytes would accept it,
>   so this requires the transport offset found by flow dissection.
> 
> Finally, verify that a 65540-byte frame is accepted. Its skb->len is
> above U16_MAX while it is flow-dissected, before eth_type_trans() pulls
> the Ethernet header.
> 
> Based on a reproducer by Michael S. Tsirkin <mst@redhat.com>.
> 
> Assisted-by: LLM
> Signed-off-by: Eric Dumazet <edumazet@kernel.org>

Reviewed-by: Willem de Bruijn <willemb@google.com>

> ---
>  tools/testing/selftests/net/tun.c | 136 ++++++++++++++++++++++++++++++
>  1 file changed, 136 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/tun.c b/tools/testing/selftests/net/tun.c
> index abe488bac50bb3b05df5c446836c1c3dfa9ea604..afaa81c9bac5311944c9a70a20de05bffb683f26 100644
> --- a/tools/testing/selftests/net/tun.c
> +++ b/tools/testing/selftests/net/tun.c
> @@ -9,6 +9,7 @@
>  #include <string.h>
>  #include <unistd.h>
>  #include <linux/if_tun.h>
> +#include <netinet/tcp.h>
>  #include <sys/ioctl.h>
>  #include <sys/socket.h>
>  
> @@ -542,6 +543,141 @@ TEST_F(tun, reattach_close_delete)
>  	EXPECT_EQ(tun_delete(self->ifname), 0);
>  }
>  
> +FIXTURE(tun_vnet_gso)
> +{
> +	char ifname[IFNAMSIZ];
> +	int fd;
> +};
> +
> +FIXTURE_SETUP(tun_vnet_gso)
> +{
> +	int flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
> +
> +	memset(self->ifname, 0, sizeof(self->ifname));
> +	self->fd = tun_open(self->ifname, flags, 0, 0, NULL);
> +	ASSERT_GE(self->fd, 0);
> +}
> +
> +FIXTURE_TEARDOWN(tun_vnet_gso)
> +{
> +	if (self->fd >= 0)
> +		close(self->fd);
> +}
> +
> +static int build_vlan_tcpv4_gso_packet(uint8_t *buf, int payload_len)
> +{
> +	uint16_t vlan_tag[2] = { htons(100), htons(ETH_P_IP) };
> +	uint8_t *cur = buf + sizeof(struct virtio_net_hdr);
> +	struct virtio_net_hdr vh = { 0 };
> +	struct tcphdr tcph = { 0 };
> +	uint32_t sum;
> +
> +	cur += build_eth(cur, ETH_P_8021Q, param_hwaddr_outer_src,
> +			 param_hwaddr_outer_dst);
> +
> +	/* 802.1Q tag: VID=100, inner protocol=ETH_P_IP */
> +	memcpy(cur, vlan_tag, sizeof(vlan_tag));
> +	cur += sizeof(vlan_tag);
> +
> +	cur += build_ipv4_header(cur, IPPROTO_TCP,
> +				 sizeof(tcph) + payload_len,
> +				 &param_ipaddr4_outer_src,
> +				 &param_ipaddr4_outer_dst);
> +
> +	tcph.source = htons(12345);
> +	tcph.dest = htons(80);
> +	tcph.seq = htonl(1);
> +	tcph.doff = sizeof(tcph) / 4;
> +	tcph.ack = 1;
> +	tcph.window = htons(65535);
> +	memcpy(cur, &tcph, sizeof(tcph));
> +	memset(cur + sizeof(tcph), PKT_DATA, payload_len);
> +
> +	sum = add_csum((const uint8_t *)&param_ipaddr4_outer_src,
> +		       sizeof(param_ipaddr4_outer_src));
> +	sum += add_csum((const uint8_t *)&param_ipaddr4_outer_dst,
> +			sizeof(param_ipaddr4_outer_dst));
> +	sum += htons(IPPROTO_TCP) + htons(sizeof(tcph) + payload_len);
> +	sum += add_csum(cur, sizeof(tcph) + payload_len);
> +	tcph.check = finish_ip_csum(sum);
> +	memcpy(cur, &tcph, sizeof(tcph));
> +	cur += sizeof(tcph) + payload_len;
> +
> +	vh.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
> +	vh.gso_size = 1400;
> +	vh.hdr_len = (cur - buf) - sizeof(vh) - payload_len;
> +	memcpy(buf, &vh, sizeof(vh));
> +
> +	return cur - buf;
> +}
> +
> +TEST_F(tun_vnet_gso, vlan_tcpv4_gso_no_csum)
> +{
> +	struct virtio_net_hdr vh;
> +	uint8_t pkt[4096] = { 0 };
> +	int len, ret;
> +
> +	len = build_vlan_tcpv4_gso_packet(pkt, 2800);
> +	memcpy(&vh, pkt, sizeof(vh));
> +
> +	/* Valid VLAN-tagged TCPv4 GSO with flags = 0 (no NEEDS_CSUM) */

iff respinning and not relevant for this fix, which targets the
!VIRTIO_NET_HDR_F_NEEDS_CSUM branch.

But would it be worthwhile to also run this test with
VIRTIO_NET_HDR_F_NEEDS_CSUM? Adds coverage of the other branch.

> +	vh.flags = 0;
> +	memcpy(pkt, &vh, sizeof(vh));
> +	ret = write(self->fd, pkt, len);
> +	ASSERT_EQ(ret, len);
> +
> +	/* Valid VLAN-tagged TCPv4 GSO with flags = DATA_VALID */
> +	vh.flags = VIRTIO_NET_HDR_F_DATA_VALID;
> +	memcpy(pkt, &vh, sizeof(vh));
> +	ret = write(self->fd, pkt, len);
> +	ASSERT_EQ(ret, len);
> +
> +	/* Mismatched GSO type (TCPV6 on VLAN-tagged IPv4 packet) */
> +	vh.flags = 0;
> +	vh.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
> +	memcpy(pkt, &vh, sizeof(vh));
> +	ret = write(self->fd, pkt, len);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +
> +	/* TCP header truncated after 10 bytes, without NEEDS_CSUM.
> +	 * Requires the transport header offset found by flow dissection:
> +	 * pulling only sizeof(struct iphdr) + sizeof(struct tcphdr) bytes
> +	 * from the mac header would accept this frame.
> +	 */
> +	vh.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
> +	vh.hdr_len = ETH_HLEN + 4 + sizeof(struct iphdr) + 10;
> +	memcpy(pkt, &vh, sizeof(vh));
> +	ret = write(self->fd, pkt, sizeof(vh) + vh.hdr_len);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +}
> +
> +TEST_F(tun_vnet_gso, vlan_tcpv4_gso_no_csum_64k)
> +{
> +	/* Ethernet frame of 65540 bytes: skb->len is above U16_MAX when the
> +	 * frame is flow-dissected, before eth_type_trans() pulls ETH_HLEN.
> +	 */
> +	const int payload_len = 65540 - ETH_HLEN - 4 -
> +				sizeof(struct iphdr) - sizeof(struct tcphdr);
> +	struct virtio_net_hdr vh;
> +	uint8_t *pkt;
> +	int len, ret;
> +
> +	pkt = calloc(1, sizeof(vh) + 65540);
> +	ASSERT_NE(pkt, NULL);
> +
> +	len = build_vlan_tcpv4_gso_packet(pkt, payload_len);
> +	ASSERT_EQ(len, sizeof(vh) + 65540);
> +	memcpy(&vh, pkt, sizeof(vh));
> +
> +	vh.flags = 0;
> +	memcpy(pkt, &vh, sizeof(vh));
> +	ret = write(self->fd, pkt, len);
> +	free(pkt);
> +	ASSERT_EQ(ret, len);
> +}
> +
>  FIXTURE(tun_vnet_udptnl)
>  {
>  	char ifname[IFNAMSIZ];
> -- 
> 2.56.0.rc1.315.gc6ed9934b7-goog
>