[net-next v2 3/3] selftests/net: Test PACKET_AUXDATA

Joe Damato
2026-04-03T23:32:50Z

Extend the packet socket selftest, adding a recvmsg path, to test
PACKET_AUXDATA. Check basic attributes of tpacket_auxdata.

Signed-off-by: Joe Damato <joe@dama.to>
---
tools/testing/selftests/net/psock_snd.c | 67 ++++++++++++++++++++++--
tools/testing/selftests/net/psock_snd.sh | 5 ++
2 files changed, 67 insertions(+), 5 deletions(-)

v2:
- Add is_psock bool argument to do_rx.
- Factor out aux data check into its own function for readability.

diff --git a/tools/testing/selftests/net/psock_snd.c b/tools/testing/selftests/net/psock_snd.c
index 81096df5cffc..5464317c1764 100644
--- a/tools/testing/selftests/net/psock_snd.c
+++ b/tools/testing/selftests/net/psock_snd.c
@@ -40,6 +40,7 @@ static bool cfg_use_qdisc_bypass;
static bool cfg_use_vlan;
static bool cfg_use_vnet;
static bool cfg_drop;
+static bool cfg_aux_data;

static char *cfg_ifname = "lo";
static int cfg_mtu = 1500;
@@ -279,11 +280,54 @@ static int setup_rx(void)
return fd;
}

-static void do_rx(int fd, int expected_len, char *expected)
+static void check_aux_data(struct cmsghdr *cmsg, int expected_len)
{
+ struct tpacket_auxdata *adata;
+
+ if (!cmsg)
+ error(1, 0, "auxdata null");
+
+ if (cmsg->cmsg_level != SOL_PACKET)
+ error(1, 0, "cmsg_level != SOL_PACKET");
+
+ if (cmsg->cmsg_type != PACKET_AUXDATA)
+ error(1, 0, "cmsg_type != PACKET_AUXDATA");
+
+ adata = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
+
+ if (adata->tp_net != ETH_HLEN)
+ error(1, 0, "cmsg tp_net != ETH_HLEN");
+
+ if (adata->tp_len != expected_len)
+ error(1, 0, "cmsg tp_len != %u", expected_len);
+
+ if (adata->tp_snaplen != expected_len)
+ error(1, 0, "cmsg tp_snaplen != %u", expected_len);
+}
+
+static void do_rx(int fd, int expected_len, char *expected, bool is_psock)
+{
+ bool aux = is_psock && cfg_aux_data;
+ char cmsg_buf[1024] = {};
+ struct msghdr msg = {};
+ struct iovec iov[1];
int ret;

- ret = recv(fd, rbuf, sizeof(rbuf), 0);
+ if (aux) {
+ iov[0].iov_base = rbuf;
+ iov[0].iov_len = sizeof(rbuf);
+
+ msg.msg_iov = iov;
+ msg.msg_iovlen = 1;
+
+ msg.msg_control = cmsg_buf;
+ msg.msg_controllen = sizeof(cmsg_buf);
+
+ ret = recvmsg(fd, &msg, 0);
+ } else {
+ ret = recv(fd, rbuf, sizeof(rbuf), 0);
+ }
+
if (ret == -1)
error(1, errno, "recv");
if (ret != expected_len)
@@ -292,6 +336,12 @@ static void do_rx(int fd, int expected_len, char *expected)
if (memcmp(rbuf, expected, ret))
error(1, 0, "recv: data mismatch");

+ if (aux) {
+ struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+
+ check_aux_data(cmsg, expected_len);
+ }
+
fprintf(stderr, "rx: %u\n", ret);
}

@@ -312,6 +362,10 @@ static int setup_sniffer(void)
if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &one, sizeof(one)))
error(1, errno, "setsockopt SO_RCVBUF");

+ if (cfg_aux_data)
+ if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA, &one, sizeof(one)))
+ error(1, errno, "setsockopt PACKET_AUXDATA");
+
pair_udp_setfilter(fd);
do_bind(fd);

@@ -322,8 +376,11 @@ static void parse_opts(int argc, char **argv)
{
int c;

- while ((c = getopt(argc, argv, "bcCdDgl:qt:vV")) != -1) {
+ while ((c = getopt(argc, argv, "abcCdDgl:qt:vV")) != -1) {
switch (c) {
+ case 'a':
+ cfg_aux_data = true;
+ break;
case 'b':
cfg_use_bind = true;
break;
@@ -432,11 +489,11 @@ static void run_test(void)
/* BPF filter accepts only this length, vlan changes MAC */
if (cfg_payload_len == DATA_LEN && !cfg_use_vlan) {
do_rx(fds, total_len - sizeof(struct virtio_net_hdr),
- tbuf + sizeof(struct virtio_net_hdr));
+ tbuf + sizeof(struct virtio_net_hdr), true);
check_packet_stats(fds);
}

- do_rx(fdr, cfg_payload_len, tbuf + total_len - cfg_payload_len);
+ do_rx(fdr, cfg_payload_len, tbuf + total_len - cfg_payload_len, false);

out:
if (close(fds))
diff --git a/tools/testing/selftests/net/psock_snd.sh b/tools/testing/selftests/net/psock_snd.sh
index b6ef12fad5d5..111c9e2f0d21 100755
--- a/tools/testing/selftests/net/psock_snd.sh
+++ b/tools/testing/selftests/net/psock_snd.sh
@@ -97,4 +97,9 @@ echo "raw gso max size + 1 (expected to fail)"
echo "test drops statistics"
./in_netns.sh ./psock_snd -D

+# test aux data
+
+echo "test aux data"
+./in_netns.sh ./psock_snd -a
+
echo "OK. All tests passed"
--
2.52.0