[PATCH 5/8] selftests/net: add test suite for CLONE_NEWNET_LOOPBACK

["Hallgrimur H. Gunnarsson" <halg@google.com>]

Add tests in tools/testing/selftests/net to validate
CLONE_NEWNET_LOOPBACK and UNSHARE_NEWNET_LOOPBACK behavior.

Signed-off-by: Hallgrimur H. Gunnarsson <halg@google.com>
---
 tools/testing/selftests/net/.gitignore       |   1 +
 tools/testing/selftests/net/Makefile         |   1 +
 tools/testing/selftests/net/loopback_netns.c | 103 +++++++++++++++++++
 3 files changed, 105 insertions(+)
 create mode 100644 tools/testing/selftests/net/loopback_netns.c

diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index c9f46031ac73..54919a8b3682 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -18,6 +18,7 @@ ipv6_flowlabel
 ipv6_flowlabel_mgr
 ipv6_fragmentation
 log.txt
+loopback_netns
 msg_zerocopy
 netlink-dumps
 nettest
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 0f5c178bc224..7d7e88e6676f 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -184,6 +184,7 @@ TEST_GEN_PROGS := \
 	icmp_rfc4884 \
 	ipv6_flowlabel_mgr \
 	ipv6_fragmentation \
+	loopback_netns \
 	proc_net_pktgen \
 	reuseaddr_conflict \
 	reuseport_bpf \
diff --git a/tools/testing/selftests/net/loopback_netns.c b/tools/testing/selftests/net/loopback_netns.c
new file mode 100644
index 000000000000..03cc665fb502
--- /dev/null
+++ b/tools/testing/selftests/net/loopback_netns.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <sched.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <net/if.h>
+
+#include "../clone3/clone3_selftests.h"
+#include "../kselftest_harness.h"
+
+static int get_lo_flags(void)
+{
+	struct ifreq ifr;
+	int fd, ret;
+
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy(ifr.ifr_name, "lo", IFNAMSIZ - 1);
+
+	fd = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd < 0)
+		return -errno;
+
+	ret = ioctl(fd, SIOCGIFFLAGS, &ifr);
+	close(fd);
+
+	if (ret < 0)
+		return -errno;
+
+	return ifr.ifr_flags;
+}
+
+TEST(baseline_lo_down)
+{
+	int flags;
+
+	ASSERT_EQ(0, unshare(CLONE_NEWUSER | CLONE_NEWNET));
+
+	flags = get_lo_flags();
+	ASSERT_GE(flags, 0);
+	EXPECT_EQ(0, flags & IFF_UP);
+}
+
+TEST(unshare_loopback)
+{
+	struct stat st_before, st_after;
+	int flags;
+
+	ASSERT_EQ(0, stat("/proc/self/ns/net", &st_before));
+	ASSERT_EQ(0, unshare(CLONE_NEWUSER | UNSHARE_NEWNET_LOOPBACK));
+	ASSERT_EQ(0, stat("/proc/self/ns/net", &st_after));
+	EXPECT_NE(st_before.st_ino, st_after.st_ino);
+
+	flags = get_lo_flags();
+	ASSERT_GE(flags, 0);
+	EXPECT_NE(0, flags & IFF_UP);
+	EXPECT_NE(0, flags & IFF_RUNNING);
+}
+
+TEST(clone3_loopback)
+{
+	struct __clone_args args = {
+		.flags = CLONE_NEWUSER | CLONE_NEWNET_LOOPBACK,
+		.exit_signal = SIGCHLD,
+	};
+	struct stat st_parent, st_child;
+	int status;
+	pid_t pid;
+
+	ASSERT_EQ(0, stat("/proc/self/ns/net", &st_parent));
+
+	pid = sys_clone3(&args, sizeof(args));
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		int flags;
+
+		if (stat("/proc/self/ns/net", &st_child) != 0 ||
+		    st_parent.st_ino == st_child.st_ino)
+			_exit(1);
+
+		flags = get_lo_flags();
+		if (flags < 0 || !(flags & IFF_UP) || !(flags & IFF_RUNNING))
+			_exit(2);
+
+		_exit(0);
+	}
+
+	ASSERT_EQ(pid, waitpid(pid, &status, 0));
+	ASSERT_TRUE(WIFEXITED(status));
+	EXPECT_EQ(0, WEXITSTATUS(status));
+}
+
+TEST_HARNESS_MAIN
-- 
2.56.0.313.g2479322e68-goog