1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
|
// 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 tcp
import (
"sync/atomic"
"time"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/seqnum"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
// segment represents a TCP segment. It holds the payload and parsed TCP segment
// information, and can be added to intrusive lists.
// segment is mostly immutable, the only field allowed to change is viewToDeliver.
//
// +stateify savable
type segment struct {
segmentEntry
refCnt int32
id stack.TransportEndpointID `state:"manual"`
route stack.Route `state:"manual"`
data buffer.VectorisedView `state:".(buffer.VectorisedView)"`
// views is used as buffer for data when its length is large
// enough to store a VectorisedView.
views [8]buffer.View `state:"nosave"`
// viewToDeliver keeps track of the next View that should be
// delivered by the Read endpoint.
viewToDeliver int
sequenceNumber seqnum.Value
ackNumber seqnum.Value
flags uint8
window seqnum.Size
// csum is only populated for received segments.
csum uint16
// csumValid is true if the csum in the received segment is valid.
csumValid bool
// parsedOptions stores the parsed values from the options in the segment.
parsedOptions header.TCPOptions
options []byte `state:".([]byte)"`
hasNewSACKInfo bool
rcvdTime time.Time `state:".(unixTime)"`
// xmitTime is the last transmit time of this segment. A zero value
// indicates that the segment has yet to be transmitted.
xmitTime time.Time `state:".(unixTime)"`
}
func newSegment(r *stack.Route, id stack.TransportEndpointID, pkt tcpip.PacketBuffer) *segment {
s := &segment{
refCnt: 1,
id: id,
route: r.Clone(),
}
s.data = pkt.Data.Clone(s.views[:])
s.rcvdTime = time.Now()
return s
}
func newSegmentFromView(r *stack.Route, id stack.TransportEndpointID, v buffer.View) *segment {
s := &segment{
refCnt: 1,
id: id,
route: r.Clone(),
}
s.views[0] = v
s.data = buffer.NewVectorisedView(len(v), s.views[:1])
s.rcvdTime = time.Now()
return s
}
func (s *segment) clone() *segment {
t := &segment{
refCnt: 1,
id: s.id,
sequenceNumber: s.sequenceNumber,
ackNumber: s.ackNumber,
flags: s.flags,
window: s.window,
route: s.route.Clone(),
viewToDeliver: s.viewToDeliver,
rcvdTime: s.rcvdTime,
}
t.data = s.data.Clone(t.views[:])
return t
}
// flagIsSet checks if at least one flag in flags is set in s.flags.
func (s *segment) flagIsSet(flags uint8) bool {
return s.flags&flags != 0
}
// flagsAreSet checks if all flags in flags are set in s.flags.
func (s *segment) flagsAreSet(flags uint8) bool {
return s.flags&flags == flags
}
func (s *segment) decRef() {
if atomic.AddInt32(&s.refCnt, -1) == 0 {
s.route.Release()
}
}
func (s *segment) incRef() {
atomic.AddInt32(&s.refCnt, 1)
}
// logicalLen is the segment length in the sequence number space. It's defined
// as the data length plus one for each of the SYN and FIN bits set.
func (s *segment) logicalLen() seqnum.Size {
l := seqnum.Size(s.data.Size())
if s.flagIsSet(header.TCPFlagSyn) {
l++
}
if s.flagIsSet(header.TCPFlagFin) {
l++
}
return l
}
// parse populates the sequence & ack numbers, flags, and window fields of the
// segment from the TCP header stored in the data. It then updates the view to
// skip the header.
//
// Returns boolean indicating if the parsing was successful.
//
// If checksum verification is not offloaded then parse also verifies the
// TCP checksum and stores the checksum and result of checksum verification in
// the csum and csumValid fields of the segment.
func (s *segment) parse() bool {
h := header.TCP(s.data.First())
// h is the header followed by the payload. We check that the offset to
// the data respects the following constraints:
// 1. That it's at least the minimum header size; if we don't do this
// then part of the header would be delivered to user.
// 2. That the header fits within the buffer; if we don't do this, we
// would panic when we tried to access data beyond the buffer.
//
// N.B. The segment has already been validated as having at least the
// minimum TCP size before reaching here, so it's safe to read the
// fields.
offset := int(h.DataOffset())
if offset < header.TCPMinimumSize || offset > len(h) {
return false
}
s.options = []byte(h[header.TCPMinimumSize:offset])
s.parsedOptions = header.ParseTCPOptions(s.options)
// Query the link capabilities to decide if checksum validation is
// required.
verifyChecksum := true
if s.route.Capabilities()&stack.CapabilityRXChecksumOffload != 0 {
s.csumValid = true
verifyChecksum = false
s.data.TrimFront(offset)
}
if verifyChecksum {
s.csum = h.Checksum()
xsum := s.route.PseudoHeaderChecksum(ProtocolNumber, uint16(s.data.Size()))
xsum = h.CalculateChecksum(xsum)
s.data.TrimFront(offset)
xsum = header.ChecksumVV(s.data, xsum)
s.csumValid = xsum == 0xffff
}
s.sequenceNumber = seqnum.Value(h.SequenceNumber())
s.ackNumber = seqnum.Value(h.AckNumber())
s.flags = h.Flags()
s.window = seqnum.Size(h.WindowSize())
return true
}
// sackBlock returns a header.SACKBlock that represents this segment.
func (s *segment) sackBlock() header.SACKBlock {
return header.SACKBlock{s.sequenceNumber, s.sequenceNumber.Add(s.logicalLen())}
}
|
