Hide /dev/net/tun when using hostinet.

/dev/net/tun does not currently work with hostinet. This has caused some
program starts failing because it thinks the feature exists.

PiperOrigin-RevId: 297876196

9 files changed, 78 insertions, 9 deletions

diff --git a/pkg/sentry/fs/dev/BUILD b/pkg/sentry/fs/dev/BUILD
index 9b6bb26d0..9379a4d7b 100644
--- a/pkg/sentry/fs/dev/BUILD
+++ b/pkg/sentry/fs/dev/BUILD
@@ -26,6 +26,7 @@ go_library(
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/ramfs",
         "//pkg/sentry/fs/tmpfs",
+        "//pkg/sentry/inet",
         "//pkg/sentry/kernel",
         "//pkg/sentry/memmap",
         "//pkg/sentry/mm",
diff --git a/pkg/sentry/fs/dev/dev.go b/pkg/sentry/fs/dev/dev.go
index 7e66c29b0..acbd401a0 100644
--- a/pkg/sentry/fs/dev/dev.go
+++ b/pkg/sentry/fs/dev/dev.go
@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/ramfs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/tmpfs"
+	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
@@ -124,10 +125,12 @@ func New(ctx context.Context, msrc *fs.MountSource) *fs.Inode {
 		"ptmx": newSymlink(ctx, "pts/ptmx", msrc),
 
 		"tty": newCharacterDevice(ctx, newTTYDevice(ctx, fs.RootOwner, 0666), msrc, ttyDevMajor, ttyDevMinor),
+	}
 
-		"net": newDirectory(ctx, map[string]*fs.Inode{
+	if isNetTunSupported(inet.StackFromContext(ctx)) {
+		contents["net"] = newDirectory(ctx, map[string]*fs.Inode{
 			"tun": newCharacterDevice(ctx, newNetTunDevice(ctx, fs.RootOwner, 0666), msrc, netTunDevMajor, netTunDevMinor),
-		}, msrc),
+		}, msrc)
 	}
 
 	iops := ramfs.NewDir(ctx, contents, fs.RootOwner, fs.FilePermsFromMode(0555))
diff --git a/pkg/sentry/fs/dev/net_tun.go b/pkg/sentry/fs/dev/net_tun.go
index 755644488..dc7ad075a 100644
--- a/pkg/sentry/fs/dev/net_tun.go
+++ b/pkg/sentry/fs/dev/net_tun.go
@@ -20,6 +20,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/socket/netstack"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -168,3 +169,9 @@ func (fops *netTunFileOperations) EventRegister(e *waiter.Entry, mask waiter.Eve
 func (fops *netTunFileOperations) EventUnregister(e *waiter.Entry) {
 	fops.device.EventUnregister(e)
 }
+
+// isNetTunSupported returns whether /dev/net/tun device is supported for s.
+func isNetTunSupported(s inet.Stack) bool {
+	_, ok := s.(*netstack.Stack)
+	return ok
+}
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 8b76750e9..1d627564f 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -755,6 +755,8 @@ func (ctx *createProcessContext) Value(key interface{}) interface{} {
 		return ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
 	case fs.CtxDirentCacheLimiter:
 		return ctx.k.DirentCacheLimiter
+	case inet.CtxStack:
+		return ctx.k.RootNetworkNamespace().Stack()
 	case ktime.CtxRealtimeClock:
 		return ctx.k.RealtimeClock()
 	case limits.CtxLimits:
@@ -1481,6 +1483,8 @@ func (ctx supervisorContext) Value(key interface{}) interface{} {
 		return ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
 	case fs.CtxDirentCacheLimiter:
 		return ctx.k.DirentCacheLimiter
+	case inet.CtxStack:
+		return ctx.k.RootNetworkNamespace().Stack()
 	case ktime.CtxRealtimeClock:
 		return ctx.k.RealtimeClock()
 	case limits.CtxLimits:
diff --git a/test/syscalls/BUILD b/test/syscalls/BUILD
index 3518e862d..a69b0ce13 100644
--- a/test/syscalls/BUILD
+++ b/test/syscalls/BUILD
@@ -680,6 +680,11 @@ syscall_test(
 
 syscall_test(test = "//test/syscalls/linux:tuntap_test")
 
+syscall_test(
+    add_hostinet = True,
+    test = "//test/syscalls/linux:tuntap_hostinet_test",
+)
+
 syscall_test(test = "//test/syscalls/linux:udp_bind_test")
 
 syscall_test(
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 704bae17b..70c120e42 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -3460,6 +3460,18 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "tuntap_hostinet_test",
+    testonly = 1,
+    srcs = ["tuntap_hostinet.cc"],
+    linkstatic = 1,
+    deps = [
+        gtest,
+        "//test/util:test_main",
+        "//test/util:test_util",
+    ],
+)
+
 cc_library(
     name = "udp_socket_test_cases",
     testonly = 1,
diff --git a/test/syscalls/linux/dev.cc b/test/syscalls/linux/dev.cc
index 4e473268c..4dd302eed 100644
--- a/test/syscalls/linux/dev.cc
+++ b/test/syscalls/linux/dev.cc
@@ -153,13 +153,6 @@ TEST(DevTest, TTYExists) {
   EXPECT_EQ(statbuf.st_mode, S_IFCHR | 0666);
 }
 
-TEST(DevTest, NetTunExists) {
-  struct stat statbuf = {};
-  ASSERT_THAT(stat("/dev/net/tun", &statbuf), SyscallSucceeds());
-  // Check that it's a character device with rw-rw-rw- permissions.
-  EXPECT_EQ(statbuf.st_mode, S_IFCHR | 0666);
-}
-
 }  // namespace
 }  // namespace testing
 
diff --git a/test/syscalls/linux/tuntap.cc b/test/syscalls/linux/tuntap.cc
index f6ac9d7b8..f734511d6 100644
--- a/test/syscalls/linux/tuntap.cc
+++ b/test/syscalls/linux/tuntap.cc
@@ -153,6 +153,13 @@ std::string CreateArpPacket(const uint8_t srcmac[ETH_ALEN], const char* srcip,
 
 }  // namespace
 
+TEST(TuntapStaticTest, NetTunExists) {
+  struct stat statbuf;
+  ASSERT_THAT(stat(kDevNetTun, &statbuf), SyscallSucceeds());
+  // Check that it's a character device with rw-rw-rw- permissions.
+  EXPECT_EQ(statbuf.st_mode, S_IFCHR | 0666);
+}
+
 class TuntapTest : public ::testing::Test {
  protected:
   void TearDown() override {
diff --git a/test/syscalls/linux/tuntap_hostinet.cc b/test/syscalls/linux/tuntap_hostinet.cc
new file mode 100644
index 000000000..0c527419e
--- /dev/null
+++ b/test/syscalls/linux/tuntap_hostinet.cc
@@ -0,0 +1,37 @@
+// 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 <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "gtest/gtest.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+TEST(TuntapHostInetTest, NoNetTun) {
+  SKIP_IF(!IsRunningOnGvisor());
+
+  struct stat statbuf;
+  ASSERT_THAT(stat("/dev/net/tun", &statbuf), SyscallFailsWithErrno(ENOENT));
+}
+
+}  // namespace
+}  // namespace testing
+
+}  // namespace gvisor