selftests/net: ignore background traffic in psock_fanout

The packet fanout test generates UDP traffic and reads this with
a pair of packet sockets, testing the various fanout algorithms.

Avoid non-determinism from reading unrelated background traffic.
Fanout decisions are made before unrelated packets can be dropped with
a filter, so that is an insufficient strategy [*]. Run the packet
socket tests in a network namespace, similar to msg_zerocopy.

It it still good practice to install a filter on a packet socket
before accepting traffic. Because this is example code, demonstrate
that pattern. Open the socket initially bound to no protocol, install
a filter, and only then bind to ETH_P_IP.

Another source of non-determinism is hash collisions in FANOUT_HASH.
The hash function used to select a socket in the fanout group includes
the pseudorandom number hashrnd, which is not visible from userspace.
To work around this, the test tries to find a pair of UDP source ports
that do not collide. It gives up too soon (5 times, every 32 runs) and
output is confusing. Increase tries to 20 and revise the error msg.

[*] another approach would be to add a third socket to the fanout
    group and direct all unexpected traffic here. This is possible
    only when reimplementing methods like RR or HASH alongside this
    extra catch-all bucket, using the BPF fanout method.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/in_netns.sh

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Execute a subprocess in a network namespace
+
+set -e
+
+readonly NETNS="ns-$(mktemp -u XXXXXX)"
+
+setup() {
+	ip netns add "${NETNS}"
+	ip -netns "${NETNS}" link set lo up
+}
+
+cleanup() {
+	ip netns del "${NETNS}"
+}
+
+trap cleanup EXIT
+setup
+
+"$@"
+exit "$?"

tools/testing/selftests/net/psock_fanout.c

@@ -50,6 +50,7 @@
 #include <linux/filter.h>
 #include <linux/bpf.h>
 #include <linux/if_packet.h>
+#include <net/if.h>
 #include <net/ethernet.h>
 #include <netinet/ip.h>
 #include <netinet/udp.h>
@@ -73,14 +74,29 @@
  * @return -1 if mode is bad, a valid socket otherwise */
 static int sock_fanout_open(uint16_t typeflags, uint16_t group_id)
 {
+	struct sockaddr_ll addr = {0};
 	int fd, val;
 
-	fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP));
+	fd = socket(PF_PACKET, SOCK_RAW, 0);
 	if (fd < 0) {
 		perror("socket packet");
 		exit(1);
 	}
 
+	pair_udp_setfilter(fd);
+
+	addr.sll_family = AF_PACKET;
+	addr.sll_protocol = htons(ETH_P_IP);
+	addr.sll_ifindex = if_nametoindex("lo");
+	if (addr.sll_ifindex == 0) {
+		perror("if_nametoindex");
+		exit(1);
+	}
+	if (bind(fd, (void *) &addr, sizeof(addr))) {
+		perror("bind packet");
+		exit(1);
+	}
+
 	val = (((int) typeflags) << 16) | group_id;
 	if (setsockopt(fd, SOL_PACKET, PACKET_FANOUT, &val, sizeof(val))) {
 		if (close(fd)) {
@@ -90,7 +106,6 @@ static int sock_fanout_open(uint16_t typeflags, uint16_t group_id)
 		return -1;
 	}
 
-	pair_udp_setfilter(fd);
 	return fd;
 }
 
@@ -229,7 +244,7 @@ static int sock_fanout_read(int fds[], char *rings[], const int expect[])
 
 	if ((!(ret[0] == expect[0] && ret[1] == expect[1])) &&
 	    (!(ret[0] == expect[1] && ret[1] == expect[0]))) {
-		fprintf(stderr, "ERROR: incorrect queue lengths\n");
+		fprintf(stderr, "warning: incorrect queue lengths\n");
 		return 1;
 	}
 
@@ -348,7 +363,8 @@ static int test_datapath(uint16_t typeflags, int port_off,
 	uint8_t type = typeflags & 0xFF;
 	int fds[2], fds_udp[2][2], ret;
 
-	fprintf(stderr, "test: datapath 0x%hx\n", typeflags);
+	fprintf(stderr, "\ntest: datapath 0x%hx ports %hu,%hu\n",
+		typeflags, PORT_BASE, PORT_BASE + port_off);
 
 	fds[0] = sock_fanout_open(typeflags, 0);
 	fds[1] = sock_fanout_open(typeflags, 0);
@@ -419,7 +435,7 @@ int main(int argc, char **argv)
 	const int expect_cpu1[2][2]	= { { 0, 20 },  { 0, 20 } };
 	const int expect_bpf[2][2]	= { { 15, 5 },  { 15, 20 } };
 	const int expect_uniqueid[2][2] = { { 20, 20},  { 20, 20 } };
-	int port_off = 2, tries = 5, ret;
+	int port_off = 2, tries = 20, ret;
 
 	test_control_single();
 	test_control_group();
@@ -428,10 +444,14 @@ int main(int argc, char **argv)
 	/* find a set of ports that do not collide onto the same socket */
 	ret = test_datapath(PACKET_FANOUT_HASH, port_off,
 			    expect_hash[0], expect_hash[1]);
-	while (ret && tries--) {
+	while (ret) {
 		fprintf(stderr, "info: trying alternate ports (%d)\n", tries);
 		ret = test_datapath(PACKET_FANOUT_HASH, ++port_off,
 				    expect_hash[0], expect_hash[1]);
+		if (!--tries) {
+			fprintf(stderr, "too many collisions\n");
+			return 1;
+		}
 	}
 
 	ret |= test_datapath(PACKET_FANOUT_HASH | PACKET_FANOUT_FLAG_ROLLOVER,

tools/testing/selftests/net/run_afpackettests

@@ -9,7 +9,7 @@ fi
 echo "--------------------"
 echo "running psock_fanout test"
 echo "--------------------"
-./psock_fanout
+./in_netns.sh ./psock_fanout
 if [ $? -ne 0 ]; then
 	echo "[FAIL]"
 else
@@ -19,7 +19,7 @@ fi
 echo "--------------------"
 echo "running psock_tpacket test"
 echo "--------------------"
-./psock_tpacket
+./in_netns.sh ./psock_tpacket
 if [ $? -ne 0 ]; then
 	echo "[FAIL]"
 else