3 files changed, 140 insertions, 0 deletions
diff --git a/test/syscalls/BUILD b/test/syscalls/BUILD
index d69ac8356..d1977d4de 100644
--- a/test/syscalls/BUILD
+++ b/test/syscalls/BUILD
@@ -258,6 +258,8 @@ syscall_test(
 
 syscall_test(test = "//test/syscalls/linux:munmap_test")
 
+syscall_test(test = "//test/syscalls/linux:network_namespace_test")
+
 syscall_test(
     add_overlay = True,
     test = "//test/syscalls/linux:open_create_test",
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 05a818795..aa303af84 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -3640,6 +3640,23 @@ cc_binary(
 )
 
 cc_binary(
+    name = "network_namespace_test",
+    testonly = 1,
+    srcs = ["network_namespace.cc"],
+    linkstatic = 1,
+    deps = [
+        ":socket_test_util",
+        gtest,
+        "//test/util:capability_util",
+        "//test/util:memory_util",
+        "//test/util:test_main",
+        "//test/util:test_util",
+        "//test/util:thread_util",
+        "@com_google_absl//absl/synchronization",
+    ],
+)
+
+cc_binary(
     name = "semaphore_test",
     testonly = 1,
     srcs = ["semaphore.cc"],
diff --git a/test/syscalls/linux/network_namespace.cc b/test/syscalls/linux/network_namespace.cc
new file mode 100644
index 000000000..6ea48c263
--- /dev/null
+++ b/test/syscalls/linux/network_namespace.cc
@@ -0,0 +1,121 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <net/if.h>
+#include <sched.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/synchronization/notification.h"
+#include "test/syscalls/linux/socket_test_util.h"
+#include "test/util/capability_util.h"
+#include "test/util/memory_util.h"
+#include "test/util/test_util.h"
+#include "test/util/thread_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+using TestFunc = std::function<PosixError()>;
+using RunFunc = std::function<PosixError(TestFunc)>;
+
+struct NamespaceStrategy {
+  RunFunc run;
+
+  static NamespaceStrategy Of(RunFunc run) {
+    NamespaceStrategy s;
+    s.run = run;
+    return s;
+  }
+};
+
+PosixError RunWithUnshare(TestFunc fn) {
+  PosixError err = PosixError(-1, "function did not return a value");
+  ScopedThread t([&] {
+    if (unshare(CLONE_NEWNET) != 0) {
+      err = PosixError(errno);
+      return;
+    }
+    err = fn();
+  });
+  t.Join();
+  return err;
+}
+
+PosixError RunWithClone(TestFunc fn) {
+  struct Args {
+    absl::Notification n;
+    TestFunc fn;
+    PosixError err;
+  };
+  Args args;
+  args.fn = fn;
+  args.err = PosixError(-1, "function did not return a value");
+
+  ASSIGN_OR_RETURN_ERRNO(
+      Mapping child_stack,
+      MmapAnon(kPageSize, PROT_READ | PROT_WRITE, MAP_PRIVATE));
+  pid_t child = clone(
+      +[](void *arg) {
+        Args *args = reinterpret_cast<Args *>(arg);
+        args->err = args->fn();
+        args->n.Notify();
+        syscall(SYS_exit, 0);  // Exit manually. No return address on stack.
+        return 0;
+      },
+      reinterpret_cast<void *>(child_stack.addr() + kPageSize),
+      CLONE_NEWNET | CLONE_THREAD | CLONE_SIGHAND | CLONE_VM, &args);
+  if (child < 0) {
+    return PosixError(errno, "clone() failed");
+  }
+  args.n.WaitForNotification();
+  return args.err;
+}
+
+class NetworkNamespaceTest
+    : public ::testing::TestWithParam<NamespaceStrategy> {};
+
+TEST_P(NetworkNamespaceTest, LoopbackExists) {
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_NET_ADMIN)));
+
+  EXPECT_NO_ERRNO(GetParam().run([]() {
+    // TODO(gvisor.dev/issue/1833): Update this to test that only "lo" exists.
+    // Check loopback device exists.
+    int sock = socket(AF_INET, SOCK_DGRAM, 0);
+    if (sock < 0) {
+      return PosixError(errno, "socket() failed");
+    }
+    struct ifreq ifr;
+    snprintf(ifr.ifr_name, IFNAMSIZ, "lo");
+    if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0) {
+      return PosixError(errno, "ioctl() failed, lo cannot be found");
+    }
+    return NoError();
+  }));
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    AllNetworkNamespaceTest, NetworkNamespaceTest,
+    ::testing::Values(NamespaceStrategy::Of(RunWithUnshare),
+                      NamespaceStrategy::Of(RunWithClone)));
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor