5 files changed, 89 insertions, 2 deletions
diff --git a/pkg/tcpip/stack/BUILD b/pkg/tcpip/stack/BUILD
index 7a43a1d4e..8d80e9cee 100644
--- a/pkg/tcpip/stack/BUILD
+++ b/pkg/tcpip/stack/BUILD
@@ -30,6 +30,7 @@ go_library(
         "nic.go",
         "packet_buffer.go",
         "packet_buffer_state.go",
+        "rand.go",
         "registration.go",
         "route.go",
         "stack.go",
diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index 1850fa8c3..9505a4e92 100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
@@ -10,6 +10,7 @@
 // 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 stack
 
 import "gvisor.dev/gvisor/pkg/tcpip/buffer"
@@ -54,6 +55,10 @@ type PacketBuffer struct {
 	LinkHeader      buffer.View
 	NetworkHeader   buffer.View
 	TransportHeader buffer.View
+
+	// Hash is the transport layer hash of this packet. A value of zero
+	// indicates no valid hash has been set.
+	Hash uint32
 }
 
 // Clone makes a copy of pk. It clones the Data field, which creates a new
diff --git a/pkg/tcpip/stack/packet_buffer_state.go b/pkg/tcpip/stack/packet_buffer_state.go
index 76602549e..0c6b7924c 100644
--- a/pkg/tcpip/stack/packet_buffer_state.go
+++ b/pkg/tcpip/stack/packet_buffer_state.go
@@ -11,6 +11,7 @@
 // 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 stack
 
 import "gvisor.dev/gvisor/pkg/tcpip/buffer"
diff --git a/pkg/tcpip/stack/rand.go b/pkg/tcpip/stack/rand.go
new file mode 100644
index 000000000..421fb5c15
--- /dev/null
+++ b/pkg/tcpip/stack/rand.go
@@ -0,0 +1,40 @@
+// 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.
+
+package stack
+
+import (
+	mathrand "math/rand"
+
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// lockedRandomSource provides a threadsafe rand.Source.
+type lockedRandomSource struct {
+	mu  sync.Mutex
+	src mathrand.Source
+}
+
+func (r *lockedRandomSource) Int63() (n int64) {
+	r.mu.Lock()
+	n = r.src.Int63()
+	r.mu.Unlock()
+	return n
+}
+
+func (r *lockedRandomSource) Seed(seed int64) {
+	r.mu.Lock()
+	r.src.Seed(seed)
+	r.mu.Unlock()
+}
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index a9584d636..41398a1b6 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -20,7 +20,9 @@
 package stack
 
 import (
+	"bytes"
 	"encoding/binary"
+	mathrand "math/rand"
 	"sync/atomic"
 	"time"
 
@@ -465,6 +467,10 @@ type Stack struct {
 	// forwarder holds the packets that wait for their link-address resolutions
 	// to complete, and forwards them when each resolution is done.
 	forwarder *forwardQueue
+
+	// randomGenerator is an injectable pseudo random generator that can be
+	// used when a random number is required.
+	randomGenerator *mathrand.Rand
 }
 
 // UniqueID is an abstract generator of unique identifiers.
@@ -525,9 +531,16 @@ type Options struct {
 	// this is non-nil.
 	RawFactory RawFactory
 
-	// OpaqueIIDOpts hold the options for generating opaque interface identifiers
-	// (IIDs) as outlined by RFC 7217.
+	// OpaqueIIDOpts hold the options for generating opaque interface
+	// identifiers (IIDs) as outlined by RFC 7217.
 	OpaqueIIDOpts OpaqueInterfaceIdentifierOptions
+
+	// RandSource is an optional source to use to generate random
+	// numbers. If omitted it defaults to a Source seeded by the data
+	// returned by rand.Read().
+	//
+	// RandSource must be thread-safe.
+	RandSource mathrand.Source
 }
 
 // TransportEndpointInfo holds useful information about a transport endpoint
@@ -623,6 +636,13 @@ func New(opts Options) *Stack {
 		opts.UniqueID = new(uniqueIDGenerator)
 	}
 
+	randSrc := opts.RandSource
+	if randSrc == nil {
+		// Source provided by mathrand.NewSource is not thread-safe so
+		// we wrap it in a simple thread-safe version.
+		randSrc = &lockedRandomSource{src: mathrand.NewSource(generateRandInt64())}
+	}
+
 	// Make sure opts.NDPConfigs contains valid values only.
 	opts.NDPConfigs.validate()
 
@@ -645,6 +665,7 @@ func New(opts Options) *Stack {
 		ndpDisp:              opts.NDPDisp,
 		opaqueIIDOpts:        opts.OpaqueIIDOpts,
 		forwarder:            newForwardQueue(),
+		randomGenerator:      mathrand.New(randSrc),
 	}
 
 	// Add specified network protocols.
@@ -1818,6 +1839,12 @@ func (s *Stack) Seed() uint32 {
 	return s.seed
 }
 
+// Rand returns a reference to a pseudo random generator that can be used
+// to generate random numbers as required.
+func (s *Stack) Rand() *mathrand.Rand {
+	return s.randomGenerator
+}
+
 func generateRandUint32() uint32 {
 	b := make([]byte, 4)
 	if _, err := rand.Read(b); err != nil {
@@ -1825,3 +1852,16 @@ func generateRandUint32() uint32 {
 	}
 	return binary.LittleEndian.Uint32(b)
 }
+
+func generateRandInt64() int64 {
+	b := make([]byte, 8)
+	if _, err := rand.Read(b); err != nil {
+		panic(err)
+	}
+	buf := bytes.NewReader(b)
+	var v int64
+	if err := binary.Read(buf, binary.LittleEndian, &v); err != nil {
+		panic(err)
+	}
+	return v
+}