1 files changed, 159 insertions, 0 deletions
diff --git a/pkg/sentry/socket/netlink/message.go b/pkg/sentry/socket/netlink/message.go
new file mode 100644
index 000000000..5bd3b49ce
--- /dev/null
+++ b/pkg/sentry/socket/netlink/message.go
@@ -0,0 +1,159 @@
+// Copyright 2018 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 netlink
+
+import (
+	"fmt"
+	"math"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/binary"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+)
+
+// alignUp rounds a length up to an alignment.
+//
+// Preconditions: align is a power of two.
+func alignUp(length int, align uint) int {
+	return (length + int(align) - 1) &^ (int(align) - 1)
+}
+
+// Message contains a complete serialized netlink message.
+type Message struct {
+	buf []byte
+}
+
+// NewMessage creates a new Message containing the passed header.
+//
+// The header length will be updated by Finalize.
+func NewMessage(hdr linux.NetlinkMessageHeader) *Message {
+	return &Message{
+		buf: binary.Marshal(nil, usermem.ByteOrder, hdr),
+	}
+}
+
+// Finalize returns the []byte containing the entire message, with the total
+// length set in the message header. The Message must not be modified after
+// calling Finalize.
+func (m *Message) Finalize() []byte {
+	// Update length, which is the first 4 bytes of the header.
+	usermem.ByteOrder.PutUint32(m.buf, uint32(len(m.buf)))
+
+	// Align the message. Note that the message length in the header (set
+	// above) is the useful length of the message, not the total aligned
+	// length. See net/netlink/af_netlink.c:__nlmsg_put.
+	aligned := alignUp(len(m.buf), linux.NLMSG_ALIGNTO)
+	m.putZeros(aligned - len(m.buf))
+	return m.buf
+}
+
+// putZeros adds n zeros to the message.
+func (m *Message) putZeros(n int) {
+	for n > 0 {
+		m.buf = append(m.buf, 0)
+		n--
+	}
+}
+
+// Put serializes v into the message.
+func (m *Message) Put(v interface{}) {
+	m.buf = binary.Marshal(m.buf, usermem.ByteOrder, v)
+}
+
+// PutAttr adds v to the message as a netlink attribute.
+//
+// Preconditions: The serialized attribute (linux.NetlinkAttrHeaderSize +
+// binary.Size(v) fits in math.MaxUint16 bytes.
+func (m *Message) PutAttr(atype uint16, v interface{}) {
+	l := linux.NetlinkAttrHeaderSize + int(binary.Size(v))
+	if l > math.MaxUint16 {
+		panic(fmt.Sprintf("attribute too large: %d", l))
+	}
+
+	m.Put(linux.NetlinkAttrHeader{
+		Type:   atype,
+		Length: uint16(l),
+	})
+	m.Put(v)
+
+	// Align the attribute.
+	aligned := alignUp(l, linux.NLA_ALIGNTO)
+	m.putZeros(aligned - l)
+}
+
+// PutAttrString adds s to the message as a netlink attribute.
+func (m *Message) PutAttrString(atype uint16, s string) {
+	l := linux.NetlinkAttrHeaderSize + len(s) + 1
+	m.Put(linux.NetlinkAttrHeader{
+		Type:   atype,
+		Length: uint16(l),
+	})
+
+	// String + NUL-termination.
+	m.Put([]byte(s))
+	m.putZeros(1)
+
+	// Align the attribute.
+	aligned := alignUp(l, linux.NLA_ALIGNTO)
+	m.putZeros(aligned - l)
+}
+
+// MessageSet contains a series of netlink messages.
+type MessageSet struct {
+	// Multi indicates that this a multi-part message, to be terminated by
+	// NLMSG_DONE. NLMSG_DONE is sent even if the set contains only one
+	// Message.
+	//
+	// If Multi is set, all added messages will have NLM_F_MULTI set.
+	Multi bool
+
+	// PortID is the destination port for all messages.
+	PortID int32
+
+	// Seq is the sequence counter for all messages in the set.
+	Seq uint32
+
+	// Messages contains the messages in the set.
+	Messages []*Message
+}
+
+// NewMessageSet creates a new MessageSet.
+//
+// portID is the destination port to set as PortID in all messages.
+//
+// seq is the sequence counter to set as seq in all messages in the set.
+func NewMessageSet(portID int32, seq uint32) *MessageSet {
+	return &MessageSet{
+		PortID: portID,
+		Seq:    seq,
+	}
+}
+
+// AddMessage adds a new message to the set and returns it for further
+// additions.
+//
+// The passed header will have Seq, PortID and the multi flag set
+// automatically.
+func (ms *MessageSet) AddMessage(hdr linux.NetlinkMessageHeader) *Message {
+	hdr.Seq = ms.Seq
+	hdr.PortID = uint32(ms.PortID)
+	if ms.Multi {
+		hdr.Flags |= linux.NLM_F_MULTI
+	}
+
+	m := NewMessage(hdr)
+	ms.Messages = append(ms.Messages, m)
+	return m
+}