platform requirements: Add test for address conflicts with TCP_REPAIR

Simple test program to check the behaviour we need for bind() address
conflicts between listening sockets and repair mode sockets.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

doc/platform-requirements/.gitignore

@@ -1,3 +1,4 @@
+/listen-vs-repair
 /reuseaddr-priority
 /recv-zero
 /udp-close-dup

doc/platform-requirements/Makefile

@@ -3,8 +3,8 @@
 # Copyright Red Hat
 # Author: David Gibson <david@gibson.dropbear.id.au>
 
-TARGETS = reuseaddr-priority recv-zero udp-close-dup
-SRCS = reuseaddr-priority.c recv-zero.c udp-close-dup.c
+TARGETS = reuseaddr-priority recv-zero udp-close-dup listen-vs-repair
+SRCS = reuseaddr-priority.c recv-zero.c udp-close-dup.c listen-vs-repair.c
 CFLAGS = -Wall
 
 all: cppcheck clang-tidy $(TARGETS:%=check-%)

doc/platform-requirements/listen-vs-repair.c

@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* liste-vs-repair.c
+ *
+ * Do listening sockets have address conflicts with sockets under repair
+ * ====================================================================
+ *
+ * When we accept() an incoming connection the accept()ed socket will have the
+ * same local address as the listening socket.  This can be a complication on
+ * migration.  On the migration target we've already set up listening sockets
+ * according to the command line.  However to restore connections that we're
+ * migrating in we need to bind the new sockets to the same address, which would
+ * be an address conflict on the face of it.  This test program verifies that
+ * enabling repair mode before bind() correctly suppresses that conflict.
+ *
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+#define _GNU_SOURCE
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "common.h"
+
+#define PORT	13256U
+#define CPORT	13257U
+
+/* 127.0.0.1:PORT */
+static const struct sockaddr_in addr = SOCKADDR_INIT(INADDR_LOOPBACK, PORT);
+
+/* 127.0.0.1:CPORT */
+static const struct sockaddr_in caddr = SOCKADDR_INIT(INADDR_LOOPBACK, CPORT);
+
+/* Put ourselves into a network sandbox */
+static void net_sandbox(void)
+{
+	/* NOLINTNEXTLINE(altera-struct-pack-align) */
+	const struct req_t {
+		struct nlmsghdr nlh;
+		struct ifinfomsg ifm;
+	} __attribute__((packed)) req = {
+		.nlh.nlmsg_type		= RTM_NEWLINK,
+		.nlh.nlmsg_flags	= NLM_F_REQUEST,
+		.nlh.nlmsg_len		= sizeof(req),
+		.nlh.nlmsg_seq		= 1,
+		.ifm.ifi_family		= AF_UNSPEC,
+                .ifm.ifi_index		= 1,
+                .ifm.ifi_flags		= IFF_UP,
+                .ifm.ifi_change		= IFF_UP,
+	};
+	int nl;
+
+	if (unshare(CLONE_NEWUSER | CLONE_NEWNET))
+		die("unshare(): %s\n", strerror(errno));
+
+	/* Bring up lo in the new netns */
+	nl = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
+	if (nl < 0)
+		die("Can't create netlink socket: %s\n", strerror(errno));
+
+	if (send(nl, &req, sizeof(req), 0) < 0)
+		die("Netlink send(): %s\n", strerror(errno));
+	close(nl);
+}
+
+static void check(void)
+{
+	int s1, s2, op;
+
+	s1 = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+	if (s1 < 0)
+		die("socket() 1: %s\n", strerror(errno));
+
+	if (bind(s1, (struct sockaddr *)&addr, sizeof(addr)))
+		die("bind() 1: %s\n", strerror(errno));
+
+	if (listen(s1, 0))
+		die("listen(): %s\n", strerror(errno));
+
+	s2 = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+	if (s2 < 0)
+		die("socket() 2: %s\n", strerror(errno));
+
+	op = TCP_REPAIR_ON;
+	if (setsockopt(s2, SOL_TCP, TCP_REPAIR, &op, sizeof(op)))
+		die("TCP_REPAIR: %s\n", strerror(errno));
+
+	if (bind(s2, (struct sockaddr *)&addr, sizeof(addr)))
+		die("bind() 2: %s\n", strerror(errno));
+
+	if (connect(s2, (struct sockaddr *)&caddr, sizeof(caddr)))
+		die("connect(): %s\n", strerror(errno));
+
+	op = TCP_REPAIR_OFF_NO_WP;
+	if (setsockopt(s2, SOL_TCP, TCP_REPAIR, &op, sizeof(op)))
+		die("TCP_REPAIR: %s\n", strerror(errno));
+
+	close(s1);
+	close(s2);
+}
+
+int main(int argc, char *argv[])
+{
+	(void)argc;
+	(void)argv;
+
+	net_sandbox();
+
+	check();
+
+	printf("Repair mode appears to properly suppress conflicts with listening sockets\n");
+
+	exit(0);
+}