sentry: Replaces saving of inet.Stack with retrieval via context.

Previously, inet.Stack was referenced in 2 structs in sentry/socket that can be
saved/restored.  If an app is saved and restored on another machine, it may try
to use the old stack, which will have been replaced by a new stack on the new
machine.

PiperOrigin-RevId: 196733985
Change-Id: I6a8cfe73b5d7a90749734677dada635ab3389cb9

6 files changed, 66 insertions, 22 deletions

diff --git a/pkg/sentry/fs/context.go b/pkg/sentry/fs/context.go
index b521bce75..da46ad77f 100644
--- a/pkg/sentry/fs/context.go
+++ b/pkg/sentry/fs/context.go
@@ -20,7 +20,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
 )
 
-// contextID is the kernel package's type for context.Context.Value keys.
+// contextID is the fs package's type for context.Context.Value keys.
 type contextID int
 
 const (
diff --git a/pkg/sentry/inet/BUILD b/pkg/sentry/inet/BUILD
index 207cdb692..1150ced57 100644
--- a/pkg/sentry/inet/BUILD
+++ b/pkg/sentry/inet/BUILD
@@ -17,12 +17,14 @@ go_stateify(
 go_library(
     name = "inet",
     srcs = [
+        "context.go",
         "inet.go",
         "inet_state.go",
         "test_stack.go",
     ],
     importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/inet",
     deps = [
+        "//pkg/sentry/context",
         "//pkg/state",
     ],
 )
diff --git a/pkg/sentry/inet/context.go b/pkg/sentry/inet/context.go
new file mode 100644
index 000000000..370381f41
--- /dev/null
+++ b/pkg/sentry/inet/context.go
@@ -0,0 +1,35 @@
+// Copyright 2018 Google Inc.
+//
+// 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 inet
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+)
+
+// contextID is the inet package's type for context.Context.Value keys.
+type contextID int
+
+const (
+	// CtxStack is a Context.Value key for a network stack.
+	CtxStack contextID = iota
+)
+
+// StackFromContext returns the network stack associated with ctx.
+func StackFromContext(ctx context.Context) Stack {
+	if v := ctx.Value(CtxStack); v != nil {
+		return v.(Stack)
+	}
+	return nil
+}
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index 3d2e035e9..490f795c2 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -22,6 +22,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/bpf"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/inet"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/futex"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/sched"
@@ -560,6 +561,8 @@ func (t *Task) Value(key interface{}) interface{} {
 		return t.creds
 	case fs.CtxRoot:
 		return t.FSContext().RootDirectory()
+	case inet.CtxStack:
+		return t.NetworkContext()
 	case ktime.CtxRealtimeClock:
 		return t.k.RealtimeClock()
 	case limits.CtxLimits:
diff --git a/pkg/sentry/socket/epsocket/epsocket.go b/pkg/sentry/socket/epsocket/epsocket.go
index a45dcd551..3e4887e16 100644
--- a/pkg/sentry/socket/epsocket/epsocket.go
+++ b/pkg/sentry/socket/epsocket/epsocket.go
@@ -33,6 +33,7 @@ import (
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/binary"
+	"gvisor.googlesource.com/gvisor/pkg/log"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
@@ -102,7 +103,6 @@ type SocketOperations struct {
 	*waiter.Queue
 
 	family   int
-	stack    inet.Stack
 	Endpoint tcpip.Endpoint
 	skType   unix.SockType
 
@@ -119,7 +119,6 @@ func New(t *kernel.Task, family int, skType unix.SockType, queue *waiter.Queue,
 	return fs.NewFile(t, dirent, fs.FileFlags{Read: true, Write: true}, &SocketOperations{
 		Queue:    queue,
 		family:   family,
-		stack:    t.NetworkContext(),
 		Endpoint: endpoint,
 		skType:   skType,
 	})
@@ -1042,7 +1041,12 @@ func (s *SocketOperations) interfaceIoctl(ctx context.Context, io usermem.IO, ar
 	)
 
 	// Find the relevant device.
-	for index, iface = range s.stack.Interfaces() {
+	stack := inet.StackFromContext(ctx)
+	if stack == nil {
+		log.Warningf("Couldn't find a network stack.")
+		return syserr.ErrInvalidArgument
+	}
+	for index, iface = range stack.Interfaces() {
 		if iface.Name == ifr.Name() {
 			found = true
 			break
@@ -1074,7 +1078,7 @@ func (s *SocketOperations) interfaceIoctl(ctx context.Context, io usermem.IO, ar
 
 	case syscall.SIOCGIFADDR:
 		// Copy the IPv4 address out.
-		for _, addr := range s.stack.InterfaceAddrs()[index] {
+		for _, addr := range stack.InterfaceAddrs()[index] {
 			// This ioctl is only compatible with AF_INET addresses.
 			if addr.Family != linux.AF_INET {
 				continue
@@ -1109,7 +1113,7 @@ func (s *SocketOperations) interfaceIoctl(ctx context.Context, io usermem.IO, ar
 
 	case syscall.SIOCGIFNETMASK:
 		// Gets the network mask of a device.
-		for _, addr := range s.stack.InterfaceAddrs()[index] {
+		for _, addr := range stack.InterfaceAddrs()[index] {
 			// This ioctl is only compatible with AF_INET addresses.
 			if addr.Family != linux.AF_INET {
 				continue
@@ -1189,15 +1193,20 @@ func (s *SocketOperations) ifconfIoctl(ctx context.Context, io usermem.IO, ifc *
 	// If Ptr is NULL, return the necessary buffer size via Len.
 	// Otherwise, write up to Len bytes starting at Ptr containing ifreq
 	// structs.
+	stack := inet.StackFromContext(ctx)
+	if stack == nil {
+		log.Warningf("Couldn't find a network stack.")
+		return syserr.ErrInvalidArgument.ToError()
+	}
 	if ifc.Ptr == 0 {
-		ifc.Len = int32(len(s.stack.Interfaces())) * int32(linux.SizeOfIFReq)
+		ifc.Len = int32(len(stack.Interfaces())) * int32(linux.SizeOfIFReq)
 		return nil
 	}
 
 	max := ifc.Len
 	ifc.Len = 0
-	for key, ifaceAddrs := range s.stack.InterfaceAddrs() {
-		iface := s.stack.Interfaces()[key]
+	for key, ifaceAddrs := range stack.InterfaceAddrs() {
+		iface := stack.Interfaces()[key]
 		for _, ifaceAddr := range ifaceAddrs {
 			// Don't write past the end of the buffer.
 			if ifc.Len+int32(linux.SizeOfIFReq) > max {
diff --git a/pkg/sentry/socket/netlink/route/protocol.go b/pkg/sentry/socket/netlink/route/protocol.go
index d611519d4..e8030c518 100644
--- a/pkg/sentry/socket/netlink/route/protocol.go
+++ b/pkg/sentry/socket/netlink/route/protocol.go
@@ -43,20 +43,13 @@ func typeKind(typ uint16) commandKind {
 }
 
 // Protocol implements netlink.Protocol.
-type Protocol struct {
-	// stack is the network stack that this provider describes.
-	//
-	// May be nil.
-	stack inet.Stack
-}
+type Protocol struct{}
 
 var _ netlink.Protocol = (*Protocol)(nil)
 
 // NewProtocol creates a NETLINK_ROUTE netlink.Protocol.
 func NewProtocol(t *kernel.Task) (netlink.Protocol, *syserr.Error) {
-	return &Protocol{
-		stack: t.NetworkContext(),
-	}, nil
+	return &Protocol{}, nil
 }
 
 // Protocol implements netlink.Protocol.Protocol.
@@ -83,12 +76,13 @@ func (p *Protocol) dumpLinks(ctx context.Context, hdr linux.NetlinkMessageHeader
 	// We always send back an NLMSG_DONE.
 	ms.Multi = true
 
-	if p.stack == nil {
+	stack := inet.StackFromContext(ctx)
+	if stack == nil {
 		// No network devices.
 		return nil
 	}
 
-	for id, i := range p.stack.Interfaces() {
+	for id, i := range stack.Interfaces() {
 		m := ms.AddMessage(linux.NetlinkMessageHeader{
 			Type: linux.RTM_NEWLINK,
 		})
@@ -124,12 +118,13 @@ func (p *Protocol) dumpAddrs(ctx context.Context, hdr linux.NetlinkMessageHeader
 	// We always send back an NLMSG_DONE.
 	ms.Multi = true
 
-	if p.stack == nil {
+	stack := inet.StackFromContext(ctx)
+	if stack == nil {
 		// No network devices.
 		return nil
 	}
 
-	for id, as := range p.stack.InterfaceAddrs() {
+	for id, as := range stack.InterfaceAddrs() {
 		for _, a := range as {
 			m := ms.AddMessage(linux.NetlinkMessageHeader{
 				Type: linux.RTM_NEWADDR,