tools/testing: add a selftest for SO_NETNS_COOKIE

Make sure that SO_NETNS_COOKIE returns a non-zero value, and
that sockets from different namespaces have a distinct cookie
value.
Signed-off-by: NLorenz Bauer <lmb@cloudflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/net/.gitignore

@@ -30,3 +30,4 @@ hwtstamp_config
 rxtimestamp
 timestamping
 txtimestamp
+so_netns_cookie

tools/testing/selftests/net/Makefile

@@ -30,7 +30,7 @@ TEST_GEN_FILES =  socket nettest
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy reuseport_addr_any
 TEST_GEN_FILES += tcp_mmap tcp_inq psock_snd txring_overwrite
 TEST_GEN_FILES += udpgso udpgso_bench_tx udpgso_bench_rx ip_defrag
-TEST_GEN_FILES += so_txtime ipv6_flowlabel ipv6_flowlabel_mgr
+TEST_GEN_FILES += so_txtime ipv6_flowlabel ipv6_flowlabel_mgr so_netns_cookie
 TEST_GEN_FILES += tcp_fastopen_backup_key
 TEST_GEN_FILES += fin_ack_lat
 TEST_GEN_FILES += reuseaddr_ports_exhausted

tools/testing/selftests/net/config

 CONFIG_USER_NS=y
+CONFIG_NET_NS=y
 CONFIG_BPF_SYSCALL=y
 CONFIG_TEST_BPF=m
 CONFIG_NUMA=y

tools/testing/selftests/net/so_netns_cookie.c

+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <sched.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#ifndef SO_NETNS_COOKIE
+#define SO_NETNS_COOKIE 71
+#endif
+
+#define pr_err(fmt, ...) \
+	({ \
+		fprintf(stderr, "%s:%d:" fmt ": %m\n", \
+			__func__, __LINE__, ##__VA_ARGS__); \
+		1; \
+	})
+
+int main(int argc, char *argvp[])
+{
+	uint64_t cookie1, cookie2;
+	socklen_t vallen;
+	int sock1, sock2;
+
+	sock1 = socket(AF_INET, SOCK_STREAM, 0);
+	if (sock1 < 0)
+		return pr_err("Unable to create TCP socket");
+
+	vallen = sizeof(cookie1);
+	if (getsockopt(sock1, SOL_SOCKET, SO_NETNS_COOKIE, &cookie1, &vallen) != 0)
+		return pr_err("getsockopt(SOL_SOCKET, SO_NETNS_COOKIE)");
+
+	if (!cookie1)
+		return pr_err("SO_NETNS_COOKIE returned zero cookie");
+
+	if (unshare(CLONE_NEWNET))
+		return pr_err("unshare");
+
+	sock2 = socket(AF_INET, SOCK_STREAM, 0);
+	if (sock2 < 0)
+		return pr_err("Unable to create TCP socket");
+
+	vallen = sizeof(cookie2);
+	if (getsockopt(sock2, SOL_SOCKET, SO_NETNS_COOKIE, &cookie2, &vallen) != 0)
+		return pr_err("getsockopt(SOL_SOCKET, SO_NETNS_COOKIE)");
+
+	if (!cookie2)
+		return pr_err("SO_NETNS_COOKIE returned zero cookie");
+
+	if (cookie1 == cookie2)
+		return pr_err("SO_NETNS_COOKIE returned identical cookies for distinct ns");
+
+	close(sock1);
+	close(sock2);
+	return 0;
+}