[PATCH net-next v2 8/8] selftests: drv-net: gro: add a test for bad IPv4 csum

Jakub Kicinski
2026-04-02T21:00:15Z

We have a test for coalescing with bad TCP checksum, let's also
test bad IPv4 header checksum.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v2:
- add a third packet
v1: https://lore.kernel.org/all/20260401182625.372605-7-kuba@kernel.org/
---
tools/testing/selftests/net/lib/gro.c | 29 ++++++++++++++++++++++
tools/testing/selftests/drivers/net/gro.py | 1 +
2 files changed, 30 insertions(+)

diff --git a/tools/testing/selftests/net/lib/gro.c b/tools/testing/selftests/net/lib/gro.c
index b99c0f00b8fe..11b16ae5f0e8 100644
--- a/tools/testing/selftests/net/lib/gro.c
+++ b/tools/testing/selftests/net/lib/gro.c
@@ -36,6 +36,7 @@
* Packets with different (ECN, TTL, TOS) header, IP options or
* IP fragments shouldn't coalesce.
* - ip_ecn, ip_tos: shared between IPv4/IPv6
+ * - ip_csum: IPv4 only, bad IP header checksum
* - ip_ttl, ip_opt, ip_frag4: IPv4 only
* - ip_id_df*: IPv4 IP ID field coalescing tests
* - ip_frag6, ip_v6ext_*: IPv6 only
@@ -685,6 +686,24 @@ static void send_changed_checksum(int fd, struct sockaddr_ll *daddr)
write_packet(fd, buf, pkt_size, daddr);
}

+/* Packets with incorrect IPv4 header checksum don't coalesce. */
+static void send_changed_ip_checksum(int fd, struct sockaddr_ll *daddr)
+{
+ static char buf[MAX_HDR_LEN + PAYLOAD_LEN];
+ struct iphdr *iph = (struct iphdr *)(buf + ETH_HLEN);
+ int pkt_size = total_hdr_len + PAYLOAD_LEN;
+
+ create_packet(buf, 0, 0, PAYLOAD_LEN, 0);
+ write_packet(fd, buf, pkt_size, daddr);
+
+ create_packet(buf, PAYLOAD_LEN, 0, PAYLOAD_LEN, 0);
+ iph->check = iph->check - 1;
+ write_packet(fd, buf, pkt_size, daddr);
+
+ create_packet(buf, PAYLOAD_LEN * 2, 0, PAYLOAD_LEN, 0);
+ write_packet(fd, buf, pkt_size, daddr);
+}
+
/* Packets with non-consecutive sequence number don't coalesce.*/
static void send_changed_seq(int fd, struct sockaddr_ll *daddr)
{
@@ -1402,6 +1421,10 @@ static void gro_sender(void)
write_packet(txfd, fin_pkt, total_hdr_len, &daddr);

/* ip sub-tests - IPv4 only */
+ } else if (strcmp(testname, "ip_csum") == 0) {
+ send_changed_ip_checksum(txfd, &daddr);
+ usleep(fin_delay_us);
+ write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
} else if (strcmp(testname, "ip_ttl") == 0) {
send_changed_ttl(txfd, &daddr);
write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
@@ -1598,6 +1621,12 @@ static void gro_receiver(void)
check_recv_pkts(rxfd, correct_payload, 2);

/* ip sub-tests - IPv4 only */
+ } else if (strcmp(testname, "ip_csum") == 0) {
+ correct_payload[0] = PAYLOAD_LEN;
+ correct_payload[1] = PAYLOAD_LEN;
+ correct_payload[2] = PAYLOAD_LEN;
+ printf("bad ip checksum doesn't coalesce: ");
+ check_recv_pkts(rxfd, correct_payload, 3);
} else if (strcmp(testname, "ip_ttl") == 0) {
correct_payload[0] = PAYLOAD_LEN;
correct_payload[1] = PAYLOAD_LEN;
diff --git a/tools/testing/selftests/drivers/net/gro.py b/tools/testing/selftests/drivers/net/gro.py
index ee95144b73ac..221f27e57147 100755
--- a/tools/testing/selftests/drivers/net/gro.py
+++ b/tools/testing/selftests/drivers/net/gro.py
@@ -301,6 +301,7 @@ def _run_gro_bin(cfg, test_name, protocol=None, num_flows=None,

# Tests specific to IPv4
ipv4_tests = [
+ "ip_csum",
"ip_ttl", "ip_opt", "ip_frag4",
"ip_id_df1_inc", "ip_id_df1_fixed",
"ip_id_df0_inc", "ip_id_df0_fixed",
--
2.53.0