Make netstack (//pkg/tcpip) buildable for 32 bit

Doing so involved breaking dependencies between //pkg/tcpip and the rest
of gVisor, which are discouraged anyways.

Tested on the Go branch via:
  gvisor.dev/gvisor/pkg/tcpip/...

Addresses #1446.

PiperOrigin-RevId: 363081778

4 files changed, 67 insertions, 16 deletions

diff --git a/pkg/sentry/devices/tundev/tundev.go b/pkg/sentry/devices/tundev/tundev.go
index d8f4e1d35..c43158aa4 100644
--- a/pkg/sentry/devices/tundev/tundev.go
+++ b/pkg/sentry/devices/tundev/tundev.go
@@ -87,19 +87,18 @@ func (fd *tunFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArg
 		if _, err := req.CopyIn(t, data); err != nil {
 			return 0, err
 		}
-		flags := usermem.ByteOrder.Uint16(req.Data[:])
+
+		// Validate flags.
+		flags, err := netstack.LinuxToTUNFlags(usermem.ByteOrder.Uint16(req.Data[:]))
+		if err != nil {
+			return 0, err
+		}
 		return 0, fd.device.SetIff(stack.Stack, req.Name(), flags)
 
 	case linux.TUNGETIFF:
 		var req linux.IFReq
-
 		copy(req.IFName[:], fd.device.Name())
-
-		// Linux adds IFF_NOFILTER (the same value as IFF_NO_PI unfortunately) when
-		// there is no sk_filter. See __tun_chr_ioctl() in net/drivers/tun.c.
-		flags := fd.device.Flags() | linux.IFF_NOFILTER
-		usermem.ByteOrder.PutUint16(req.Data[:], flags)
-
+		usermem.ByteOrder.PutUint16(req.Data[:], netstack.TUNFlagsToLinux(fd.device.Flags()))
 		_, err := req.CopyOut(t, data)
 		return 0, err
 
diff --git a/pkg/sentry/fs/dev/net_tun.go b/pkg/sentry/fs/dev/net_tun.go
index 5227ef652..11a2984d8 100644
--- a/pkg/sentry/fs/dev/net_tun.go
+++ b/pkg/sentry/fs/dev/net_tun.go
@@ -108,19 +108,18 @@ func (n *netTunFileOperations) Ioctl(ctx context.Context, file *fs.File, io user
 		if _, err := req.CopyIn(t, data); err != nil {
 			return 0, err
 		}
-		flags := usermem.ByteOrder.Uint16(req.Data[:])
+
+		// Validate flags.
+		flags, err := netstack.LinuxToTUNFlags(usermem.ByteOrder.Uint16(req.Data[:]))
+		if err != nil {
+			return 0, err
+		}
 		return 0, n.device.SetIff(stack.Stack, req.Name(), flags)
 
 	case linux.TUNGETIFF:
 		var req linux.IFReq
-
 		copy(req.IFName[:], n.device.Name())
-
-		// Linux adds IFF_NOFILTER (the same value as IFF_NO_PI unfortunately) when
-		// there is no sk_filter. See __tun_chr_ioctl() in net/drivers/tun.c.
-		flags := n.device.Flags() | linux.IFF_NOFILTER
-		usermem.ByteOrder.PutUint16(req.Data[:], flags)
-
+		usermem.ByteOrder.PutUint16(req.Data[:], netstack.TUNFlagsToLinux(n.device.Flags()))
 		_, err := req.CopyOut(t, data)
 		return 0, err
 
diff --git a/pkg/sentry/socket/netstack/BUILD b/pkg/sentry/socket/netstack/BUILD
index 915134b41..244d99436 100644
--- a/pkg/sentry/socket/netstack/BUILD
+++ b/pkg/sentry/socket/netstack/BUILD
@@ -12,6 +12,7 @@ go_library(
         "provider_vfs2.go",
         "save_restore.go",
         "stack.go",
+        "tun.go",
     ],
     visibility = [
         "//pkg/sentry:internal",
@@ -42,6 +43,7 @@ go_library(
         "//pkg/syserror",
         "//pkg/tcpip",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/link/tun",
         "//pkg/tcpip/network/ipv4",
         "//pkg/tcpip/network/ipv6",
         "//pkg/tcpip/stack",
diff --git a/pkg/sentry/socket/netstack/tun.go b/pkg/sentry/socket/netstack/tun.go
new file mode 100644
index 000000000..288dd0c9e
--- /dev/null
+++ b/pkg/sentry/socket/netstack/tun.go
@@ -0,0 +1,51 @@
+// Copyright 2021 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.
+
+package netstack
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/tcpip/link/tun"
+)
+
+// TUNFlagsToLinux converts a tun.Flags to Linux TUN flags.
+func TUNFlagsToLinux(flags tun.Flags) uint16 {
+	ret := uint16(linux.IFF_NOFILTER)
+	if flags.TAP {
+		ret |= linux.IFF_TAP
+	}
+	if flags.TUN {
+		ret |= linux.IFF_TUN
+	}
+	if flags.NoPacketInfo {
+		ret |= linux.IFF_NO_PI
+	}
+	return ret
+}
+
+// LinuxToTUNFlags converts Linux TUN flags to a tun.Flags.
+func LinuxToTUNFlags(flags uint16) (tun.Flags, error) {
+	// Linux adds IFF_NOFILTER (the same value as IFF_NO_PI unfortunately)
+	// when there is no sk_filter. See __tun_chr_ioctl() in
+	// net/drivers/tun.c.
+	if flags&^uint16(linux.IFF_TUN|linux.IFF_TAP|linux.IFF_NO_PI) != 0 {
+		return tun.Flags{}, syserror.EINVAL
+	}
+	return tun.Flags{
+		TUN:          flags&linux.IFF_TUN != 0,
+		TAP:          flags&linux.IFF_TAP != 0,
+		NoPacketInfo: flags&linux.IFF_NO_PI != 0,
+	}, nil
+}