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to use the old stack, which will have been replaced by a new stack on the new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

2 files changed, 37 insertions, 0 deletions

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
+}