[PATCH net-next v2] selftests: net: csum: filter packets by source address and port

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

From: Willem de Bruijn <willemb@google.com>

Add source address and port verification in recv_verify_packet_* and
recv_udp: non-matching packets are skipped.

The receiver reads from PF_PACKET and UDP sockets to verify incoming
packets to test hardware checksum offload. It did not validate the
packet source address or source port.

During tests expecting an invalid checksum (-E), background packets
(with a valid checksum) fail the test.

Also
- add an inter-packet delay to avoid drops from bursts.
- remove a comment that is no longer correct.

Fixes: 91a7de85600d ("selftests/net: add csum offload test")
Signed-off-by: Willem de Bruijn <willemb@google.com>

---

Changes
  v1 -> v2
    - also check udp socket, with recvfrom

v1: https://lore.kernel.org/netdev/20260831210128.1359978-1-willemdebruijn.kernel@gmail.com/
---
 tools/testing/selftests/net/lib/csum.c | 43 ++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/lib/csum.c b/tools/testing/selftests/net/lib/csum.c
index e28884ce3ab3..5c8f9d175dd3 100644
--- a/tools/testing/selftests/net/lib/csum.c
+++ b/tools/testing/selftests/net/lib/csum.c
@@ -2,8 +2,7 @@
 
 /* Test hardware checksum offload: Rx + Tx, IPv4 + IPv6, TCP + UDP.
  *
- * The test runs on two machines to exercise the NIC. For this reason it
- * is not integrated in kselftests.
+ * The test runs on two machines to exercise the NIC.
  *
  *     CMD=$((./csum -[46] -[tu] -S $SADDR -D $DADDR -[RT] -r 1 $EXTRA_ARGS))
  *
@@ -571,15 +570,38 @@ static int recv_prepare_packet(void)
 static int recv_udp(int fd)
 {
 	static char buf[MAX_PAYLOAD_LEN];
+	struct sockaddr_storage addr;
+	socklen_t addrlen;
 	int ret, count = 0;
 
 	while (1) {
-		ret = recv(fd, buf, sizeof(buf), MSG_DONTWAIT);
+		addrlen = sizeof(addr);
+		ret = recvfrom(fd, buf, sizeof(buf), MSG_DONTWAIT,
+			       (struct sockaddr *)&addr, &addrlen);
 		if (ret == -1 && errno == EAGAIN)
 			break;
 		if (ret == -1)
 			error(1, errno, "recv r");
 
+		if (cfg_family == PF_INET) {
+			struct sockaddr_in *sin = (void *)&addr;
+
+			if (sin->sin_addr.s_addr != cfg_saddr4.sin_addr.s_addr)
+				continue;
+			if (!cfg_zero_sum &&
+			    sin->sin_port != htons(cfg_port_src))
+				continue;
+		} else {
+			struct sockaddr_in6 *sin6 = (void *)&addr;
+
+			if (memcmp(&sin6->sin6_addr, &cfg_saddr6.sin6_addr,
+				   sizeof(sin6->sin6_addr)))
+				continue;
+			if (!cfg_zero_sum &&
+			    sin6->sin6_port != htons(cfg_port_src))
+				continue;
+		}
+
 		fprintf(stderr, "rx: udp: len=%u\n", ret);
 		count++;
 	}
@@ -620,6 +642,9 @@ static int recv_verify_packet_tcp(void *th, int len)
 	if (len < sizeof(*tcph) || tcph->dest != htons(cfg_port_dst))
 		return -1;
 
+	if (tcph->source != htons(cfg_port_src))
+		return -1;
+
 	return recv_verify_csum(th, len, ntohs(tcph->source), tcph->check);
 }
 
@@ -647,6 +672,9 @@ static int recv_verify_packet_udp(void *th, int len)
 		return recv_verify_packet_udp_encap(udph + 1,
 						    len - sizeof(*udph));
 
+	if (!cfg_zero_sum && udph->source != htons(cfg_port_src))
+		return -1;
+
 	return recv_verify_csum(th, len, ntohs(udph->source), udph->check);
 }
 
@@ -659,6 +687,9 @@ static int recv_verify_packet_ipv4(void *nh, int len)
 	if (len < sizeof(*iph) || iph->protocol != proto)
 		return -1;
 
+	if (iph->saddr != cfg_saddr4.sin_addr.s_addr)
+		return -1;
+
 	ip_len = ntohs(iph->tot_len);
 	if (ip_len > len || ip_len < sizeof(*iph))
 		return -1;
@@ -680,6 +711,9 @@ static int recv_verify_packet_ipv6(void *nh, int len)
 	if (len < sizeof(*ip6h) || ip6h->nexthdr != proto)
 		return -1;
 
+	if (memcmp(&ip6h->saddr, &cfg_saddr6.sin6_addr, sizeof(ip6h->saddr)))
+		return -1;
+
 	payload_len = ntohs(ip6h->payload_len);
 	if (payload_len > len - sizeof(*ip6h))
 		return -1;
@@ -940,6 +974,9 @@ static void do_tx(void)
 			cfg_payload_len = rand() % MAX_PAYLOAD_LEN;
 			buf = build_packet(_buf, sizeof(_buf), &len);
 		}
+
+		/* avoid bursting */
+		usleep(20);
 	}
 
 	if (close(fd))
-- 
2.55.0.979.g7e5102b832-goog