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Date:: Wed Nov 16 00:47:26 2016 UTC
Message:: channel: truncate twrite messages based on msize While there are a few problems around handling of msize, the easiest to address and, arguably, the most problematic is that of Twrite. We now truncate Twrite.Data to the correct length if it will overflow the msize limit negotiated on the session. ErrShortWrite is returned by the `Session.Write` method if written data is truncated. In addition, we now reject incoming messages from `ReadFcall` that overflow the msize. Such messages are probably terminal in practice, but can be detected with the `Overflow` function. Tread is also handled accordingly, such that the Count field will be rewritten such that the response doesn't overflow the msize. Signed-off-by: Stephen J Day <stephen.day@docker.com>
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  1 0f5f58bb 2016-11-16 stephen.d package p9p
  2 0f5f58bb 2016-11-16 stephen.d 
  3 0f5f58bb 2016-11-16 stephen.d import (
  4 0f5f58bb 2016-11-16 stephen.d 	"bytes"
  5 0f5f58bb 2016-11-16 stephen.d 	"context"
  6 0f5f58bb 2016-11-16 stephen.d 	"encoding/binary"
  7 0f5f58bb 2016-11-16 stephen.d 	"net"
  8 0f5f58bb 2016-11-16 stephen.d 	"testing"
  9 0f5f58bb 2016-11-16 stephen.d 	"time"
 10 0f5f58bb 2016-11-16 stephen.d )
 11 0f5f58bb 2016-11-16 stephen.d 
 12 0f5f58bb 2016-11-16 stephen.d // TestTwriteOverflow ensures that a Twrite message will have the data field
 13 0f5f58bb 2016-11-16 stephen.d // truncated if the msize would be exceeded.
 14 0f5f58bb 2016-11-16 stephen.d func TestTwriteOverflow(t *testing.T) {
 15 0f5f58bb 2016-11-16 stephen.d 	const (
 16 0f5f58bb 2016-11-16 stephen.d 		msize = 512
 17 0f5f58bb 2016-11-16 stephen.d 
 18 0f5f58bb 2016-11-16 stephen.d 		// size[4] Twrite tag[2] fid[4] offset[8] count[4] data[count] | count = 0
 19 0f5f58bb 2016-11-16 stephen.d 		overhead = 4 + 1 + 2 + 4 + 8 + 4
 20 0f5f58bb 2016-11-16 stephen.d 	)
 21 0f5f58bb 2016-11-16 stephen.d 
 22 0f5f58bb 2016-11-16 stephen.d 	var (
 23 0f5f58bb 2016-11-16 stephen.d 		ctx  = context.Background()
 24 0f5f58bb 2016-11-16 stephen.d 		conn = &mockConn{}
 25 0f5f58bb 2016-11-16 stephen.d 		ch   = NewChannel(conn, msize)
 26 0f5f58bb 2016-11-16 stephen.d 	)
 27 0f5f58bb 2016-11-16 stephen.d 
 28 0f5f58bb 2016-11-16 stephen.d 	for _, testcase := range []struct {
 29 0f5f58bb 2016-11-16 stephen.d 		name     string
 30 0f5f58bb 2016-11-16 stephen.d 		overflow int // amount to overflow the message by.
 31 0f5f58bb 2016-11-16 stephen.d 	}{
 32 0f5f58bb 2016-11-16 stephen.d 		{
 33 0f5f58bb 2016-11-16 stephen.d 			name:     "BoundedOverflow",
 34 0f5f58bb 2016-11-16 stephen.d 			overflow: msize / 2,
 35 0f5f58bb 2016-11-16 stephen.d 		},
 36 0f5f58bb 2016-11-16 stephen.d 		{
 37 0f5f58bb 2016-11-16 stephen.d 			name:     "LargeOverflow",
 38 0f5f58bb 2016-11-16 stephen.d 			overflow: msize * 3,
 39 0f5f58bb 2016-11-16 stephen.d 		},
 40 0f5f58bb 2016-11-16 stephen.d 		{
 41 0f5f58bb 2016-11-16 stephen.d 			name:     "HeaderOverflow",
 42 0f5f58bb 2016-11-16 stephen.d 			overflow: overhead,
 43 0f5f58bb 2016-11-16 stephen.d 		},
 44 0f5f58bb 2016-11-16 stephen.d 		{
 45 0f5f58bb 2016-11-16 stephen.d 			name:     "HeaderOffsetOverflow",
 46 0f5f58bb 2016-11-16 stephen.d 			overflow: overhead - 1,
 47 0f5f58bb 2016-11-16 stephen.d 		},
 48 0f5f58bb 2016-11-16 stephen.d 		{
 49 0f5f58bb 2016-11-16 stephen.d 			name:     "OverflowByOne",
 50 0f5f58bb 2016-11-16 stephen.d 			overflow: 1,
 51 0f5f58bb 2016-11-16 stephen.d 		},
 52 0f5f58bb 2016-11-16 stephen.d 	} {
 53 0f5f58bb 2016-11-16 stephen.d 
 54 0f5f58bb 2016-11-16 stephen.d 		t.Run(testcase.name, func(t *testing.T) {
 55 0f5f58bb 2016-11-16 stephen.d 			var (
 56 0f5f58bb 2016-11-16 stephen.d 				fcall = overflowMessage(ch.(*channel).codec, msize, testcase.overflow)
 57 0f5f58bb 2016-11-16 stephen.d 				data  = fcall.Message.(MessageTwrite).Data
 58 0f5f58bb 2016-11-16 stephen.d 				size  uint32
 59 0f5f58bb 2016-11-16 stephen.d 			)
 60 0f5f58bb 2016-11-16 stephen.d 
 61 0f5f58bb 2016-11-16 stephen.d 			t.Logf("overflow: %v, len(data): %v, expected overflow: %v", testcase.overflow, len(data), overhead+len(data)-msize)
 62 0f5f58bb 2016-11-16 stephen.d 			conn.buf.Reset()
 63 0f5f58bb 2016-11-16 stephen.d 			if err := ch.WriteFcall(ctx, fcall); err != nil {
 64 0f5f58bb 2016-11-16 stephen.d 				t.Fatal(err)
 65 0f5f58bb 2016-11-16 stephen.d 			}
 66 0f5f58bb 2016-11-16 stephen.d 
 67 0f5f58bb 2016-11-16 stephen.d 			if err := binary.Read(bytes.NewReader(conn.buf.Bytes()), binary.LittleEndian, &size); err != nil {
 68 0f5f58bb 2016-11-16 stephen.d 				t.Fatal(err)
 69 0f5f58bb 2016-11-16 stephen.d 			}
 70 0f5f58bb 2016-11-16 stephen.d 
 71 0f5f58bb 2016-11-16 stephen.d 			if size != msize {
 72 0f5f58bb 2016-11-16 stephen.d 				t.Fatalf("should have truncated size header: %d != %d", size, msize)
 73 0f5f58bb 2016-11-16 stephen.d 			}
 74 0f5f58bb 2016-11-16 stephen.d 
 75 0f5f58bb 2016-11-16 stephen.d 			if conn.buf.Len() != msize {
 76 0f5f58bb 2016-11-16 stephen.d 				t.Fatalf("should have truncated message: conn.buf.Len(%v) != msize(%v)", conn.buf.Len(), msize)
 77 0f5f58bb 2016-11-16 stephen.d 			}
 78 0f5f58bb 2016-11-16 stephen.d 		})
 79 0f5f58bb 2016-11-16 stephen.d 	}
 80 0f5f58bb 2016-11-16 stephen.d 
 81 0f5f58bb 2016-11-16 stephen.d }
 82 0f5f58bb 2016-11-16 stephen.d 
 83 0f5f58bb 2016-11-16 stephen.d // TestWriteOverflowError ensures that we return an error in cases when there
 84 0f5f58bb 2016-11-16 stephen.d // will certainly be an overflow and it cannot be resolved.
 85 0f5f58bb 2016-11-16 stephen.d func TestWriteOverflowError(t *testing.T) {
 86 0f5f58bb 2016-11-16 stephen.d 	const (
 87 0f5f58bb 2016-11-16 stephen.d 		msize         = 4
 88 0f5f58bb 2016-11-16 stephen.d 		overflowMSize = msize + 1
 89 0f5f58bb 2016-11-16 stephen.d 	)
 90 0f5f58bb 2016-11-16 stephen.d 
 91 0f5f58bb 2016-11-16 stephen.d 	var (
 92 0f5f58bb 2016-11-16 stephen.d 		ctx   = context.Background()
 93 0f5f58bb 2016-11-16 stephen.d 		conn  = &mockConn{}
 94 0f5f58bb 2016-11-16 stephen.d 		ch    = NewChannel(conn, msize)
 95 0f5f58bb 2016-11-16 stephen.d 		data  = bytes.Repeat([]byte{'A'}, 4)
 96 0f5f58bb 2016-11-16 stephen.d 		fcall = newFcall(1, MessageTwrite{
 97 0f5f58bb 2016-11-16 stephen.d 			Data: data,
 98 0f5f58bb 2016-11-16 stephen.d 		})
 99 0f5f58bb 2016-11-16 stephen.d 		messageSize = 4 + ch.(*channel).codec.Size(fcall)
100 0f5f58bb 2016-11-16 stephen.d 	)
101 0f5f58bb 2016-11-16 stephen.d 
102 0f5f58bb 2016-11-16 stephen.d 	err := ch.WriteFcall(ctx, fcall)
103 0f5f58bb 2016-11-16 stephen.d 	if err == nil {
104 0f5f58bb 2016-11-16 stephen.d 		t.Fatal("error expected when overflowing message")
105 0f5f58bb 2016-11-16 stephen.d 	}
106 0f5f58bb 2016-11-16 stephen.d 
107 0f5f58bb 2016-11-16 stephen.d 	if Overflow(err) != messageSize-msize {
108 0f5f58bb 2016-11-16 stephen.d 		t.Fatalf("overflow should reflect messageSize and msize, %d != %d", Overflow(err), messageSize-msize)
109 0f5f58bb 2016-11-16 stephen.d 	}
110 0f5f58bb 2016-11-16 stephen.d }
111 0f5f58bb 2016-11-16 stephen.d 
112 0f5f58bb 2016-11-16 stephen.d // TestReadOverflow ensures that messages coming over a network connection do
113 0f5f58bb 2016-11-16 stephen.d // not overflow the msize. Invalid messages will cause `ReadFcall` to return an
114 0f5f58bb 2016-11-16 stephen.d // Overflow error.
115 0f5f58bb 2016-11-16 stephen.d func TestReadFcallOverflow(t *testing.T) {
116 0f5f58bb 2016-11-16 stephen.d 	const (
117 0f5f58bb 2016-11-16 stephen.d 		msize = 256
118 0f5f58bb 2016-11-16 stephen.d 	)
119 0f5f58bb 2016-11-16 stephen.d 
120 0f5f58bb 2016-11-16 stephen.d 	var (
121 0f5f58bb 2016-11-16 stephen.d 		ctx   = context.Background()
122 0f5f58bb 2016-11-16 stephen.d 		conn  = &mockConn{}
123 0f5f58bb 2016-11-16 stephen.d 		ch    = NewChannel(conn, msize)
124 0f5f58bb 2016-11-16 stephen.d 		codec = ch.(*channel).codec
125 0f5f58bb 2016-11-16 stephen.d 	)
126 0f5f58bb 2016-11-16 stephen.d 
127 0f5f58bb 2016-11-16 stephen.d 	for _, testcase := range []struct {
128 0f5f58bb 2016-11-16 stephen.d 		name     string
129 0f5f58bb 2016-11-16 stephen.d 		overflow int
130 0f5f58bb 2016-11-16 stephen.d 	}{
131 0f5f58bb 2016-11-16 stephen.d 		{
132 0f5f58bb 2016-11-16 stephen.d 			name:     "OverflowByOne",
133 0f5f58bb 2016-11-16 stephen.d 			overflow: 1,
134 0f5f58bb 2016-11-16 stephen.d 		},
135 0f5f58bb 2016-11-16 stephen.d 		{
136 0f5f58bb 2016-11-16 stephen.d 			name:     "HeaderOverflow",
137 0f5f58bb 2016-11-16 stephen.d 			overflow: overheadMessage(codec, MessageTwrite{}),
138 0f5f58bb 2016-11-16 stephen.d 		},
139 0f5f58bb 2016-11-16 stephen.d 		{
140 0f5f58bb 2016-11-16 stephen.d 			name:     "HeaderOffsetOverflow",
141 0f5f58bb 2016-11-16 stephen.d 			overflow: overheadMessage(codec, MessageTwrite{}) - 1,
142 0f5f58bb 2016-11-16 stephen.d 		},
143 0f5f58bb 2016-11-16 stephen.d 	} {
144 0f5f58bb 2016-11-16 stephen.d 		t.Run(testcase.name, func(t *testing.T) {
145 0f5f58bb 2016-11-16 stephen.d 			fcall := overflowMessage(codec, msize, testcase.overflow)
146 0f5f58bb 2016-11-16 stephen.d 
147 0f5f58bb 2016-11-16 stephen.d 			// prepare the raw message
148 0f5f58bb 2016-11-16 stephen.d 			p, err := ch.(*channel).codec.Marshal(fcall)
149 0f5f58bb 2016-11-16 stephen.d 			if err != nil {
150 0f5f58bb 2016-11-16 stephen.d 				t.Fatal(err)
151 0f5f58bb 2016-11-16 stephen.d 			}
152 0f5f58bb 2016-11-16 stephen.d 
153 0f5f58bb 2016-11-16 stephen.d 			// "send" the message into the buffer
154 0f5f58bb 2016-11-16 stephen.d 			// this message is crafted to overflow the read buffer.
155 0f5f58bb 2016-11-16 stephen.d 			if err := sendmsg(&conn.buf, p); err != nil {
156 0f5f58bb 2016-11-16 stephen.d 				t.Fatal(err)
157 0f5f58bb 2016-11-16 stephen.d 			}
158 0f5f58bb 2016-11-16 stephen.d 
159 0f5f58bb 2016-11-16 stephen.d 			var incoming Fcall
160 0f5f58bb 2016-11-16 stephen.d 			err = ch.ReadFcall(ctx, &incoming)
161 0f5f58bb 2016-11-16 stephen.d 			if err == nil {
162 0f5f58bb 2016-11-16 stephen.d 				t.Fatal("expected error on fcall")
163 0f5f58bb 2016-11-16 stephen.d 			}
164 0f5f58bb 2016-11-16 stephen.d 
165 0f5f58bb 2016-11-16 stephen.d 			// sanity check to ensure our test code has the right overflow
166 0f5f58bb 2016-11-16 stephen.d 			if testcase.overflow != ch.(*channel).msgmsize(fcall)-msize {
167 0f5f58bb 2016-11-16 stephen.d 				t.Fatalf("overflow calculation incorrect: %v != %v", testcase.overflow, ch.(*channel).msgmsize(fcall)-msize)
168 0f5f58bb 2016-11-16 stephen.d 			}
169 0f5f58bb 2016-11-16 stephen.d 
170 0f5f58bb 2016-11-16 stephen.d 			if Overflow(err) != testcase.overflow {
171 0f5f58bb 2016-11-16 stephen.d 				t.Fatalf("unexpected overflow on error: %v !=%v", Overflow(err), testcase.overflow)
172 0f5f58bb 2016-11-16 stephen.d 			}
173 0f5f58bb 2016-11-16 stephen.d 		})
174 0f5f58bb 2016-11-16 stephen.d 	}
175 0f5f58bb 2016-11-16 stephen.d }
176 0f5f58bb 2016-11-16 stephen.d 
177 0f5f58bb 2016-11-16 stephen.d // TestTreadRewrite ensures that messages that whose response would overflow
178 0f5f58bb 2016-11-16 stephen.d // the msize will have be adjusted before sending.
179 0f5f58bb 2016-11-16 stephen.d func TestTreadRewrite(t *testing.T) {
180 0f5f58bb 2016-11-16 stephen.d 	const (
181 0f5f58bb 2016-11-16 stephen.d 		msize         = 256
182 0f5f58bb 2016-11-16 stephen.d 		overflowMSize = msize + 1
183 0f5f58bb 2016-11-16 stephen.d 	)
184 0f5f58bb 2016-11-16 stephen.d 
185 0f5f58bb 2016-11-16 stephen.d 	var (
186 0f5f58bb 2016-11-16 stephen.d 		ctx  = context.Background()
187 0f5f58bb 2016-11-16 stephen.d 		conn = &mockConn{}
188 0f5f58bb 2016-11-16 stephen.d 		ch   = NewChannel(conn, msize)
189 0f5f58bb 2016-11-16 stephen.d 		buf  = make([]byte, overflowMSize)
190 0f5f58bb 2016-11-16 stephen.d 		// data  = bytes.Repeat([]byte{'A'}, overflowMSize)
191 0f5f58bb 2016-11-16 stephen.d 		fcall = newFcall(1, MessageTread{
192 0f5f58bb 2016-11-16 stephen.d 			Count: overflowMSize,
193 0f5f58bb 2016-11-16 stephen.d 		})
194 0f5f58bb 2016-11-16 stephen.d 		responseMSize = ch.(*channel).msgmsize(newFcall(1, MessageRread{
195 0f5f58bb 2016-11-16 stephen.d 			Data: buf,
196 0f5f58bb 2016-11-16 stephen.d 		}))
197 0f5f58bb 2016-11-16 stephen.d 	)
198 0f5f58bb 2016-11-16 stephen.d 
199 0f5f58bb 2016-11-16 stephen.d 	if err := ch.WriteFcall(ctx, fcall); err != nil {
200 0f5f58bb 2016-11-16 stephen.d 		t.Fatal(err)
201 0f5f58bb 2016-11-16 stephen.d 	}
202 0f5f58bb 2016-11-16 stephen.d 
203 0f5f58bb 2016-11-16 stephen.d 	// just read the message off the buffer
204 0f5f58bb 2016-11-16 stephen.d 	n, err := readmsg(&conn.buf, buf)
205 0f5f58bb 2016-11-16 stephen.d 	if err != nil {
206 0f5f58bb 2016-11-16 stephen.d 		t.Fatal(err)
207 0f5f58bb 2016-11-16 stephen.d 	}
208 0f5f58bb 2016-11-16 stephen.d 
209 0f5f58bb 2016-11-16 stephen.d 	*fcall = Fcall{}
210 0f5f58bb 2016-11-16 stephen.d 	if err := ch.(*channel).codec.Unmarshal(buf[:n], fcall); err != nil {
211 0f5f58bb 2016-11-16 stephen.d 		t.Fatal(err)
212 0f5f58bb 2016-11-16 stephen.d 	}
213 0f5f58bb 2016-11-16 stephen.d 
214 0f5f58bb 2016-11-16 stephen.d 	tread, ok := fcall.Message.(MessageTread)
215 0f5f58bb 2016-11-16 stephen.d 	if !ok {
216 0f5f58bb 2016-11-16 stephen.d 		t.Fatalf("unexpected message: %v", fcall)
217 0f5f58bb 2016-11-16 stephen.d 	}
218 0f5f58bb 2016-11-16 stephen.d 
219 0f5f58bb 2016-11-16 stephen.d 	if tread.Count != overflowMSize-(uint32(responseMSize)-msize) {
220 0f5f58bb 2016-11-16 stephen.d 		t.Fatalf("count not rewritten: %v != %v", tread.Count, overflowMSize-(uint32(responseMSize)-msize))
221 0f5f58bb 2016-11-16 stephen.d 	}
222 0f5f58bb 2016-11-16 stephen.d }
223 0f5f58bb 2016-11-16 stephen.d 
224 0f5f58bb 2016-11-16 stephen.d type mockConn struct {
225 0f5f58bb 2016-11-16 stephen.d 	net.Conn
226 0f5f58bb 2016-11-16 stephen.d 	buf bytes.Buffer
227 0f5f58bb 2016-11-16 stephen.d }
228 0f5f58bb 2016-11-16 stephen.d 
229 0f5f58bb 2016-11-16 stephen.d func (m mockConn) SetWriteDeadline(t time.Time) error { return nil }
230 0f5f58bb 2016-11-16 stephen.d func (m mockConn) SetReadDeadline(t time.Time) error  { return nil }
231 0f5f58bb 2016-11-16 stephen.d 
232 0f5f58bb 2016-11-16 stephen.d func (m *mockConn) Write(p []byte) (int, error) {
233 0f5f58bb 2016-11-16 stephen.d 	return m.buf.Write(p)
234 0f5f58bb 2016-11-16 stephen.d }
235 0f5f58bb 2016-11-16 stephen.d 
236 0f5f58bb 2016-11-16 stephen.d func (m *mockConn) Read(p []byte) (int, error) {
237 0f5f58bb 2016-11-16 stephen.d 	return m.buf.Read(p)
238 0f5f58bb 2016-11-16 stephen.d }
239 0f5f58bb 2016-11-16 stephen.d 
240 0f5f58bb 2016-11-16 stephen.d func overheadMessage(codec Codec, msg Message) int {
241 0f5f58bb 2016-11-16 stephen.d 	return 4 + codec.Size(newFcall(1, msg))
242 0f5f58bb 2016-11-16 stephen.d }
243 0f5f58bb 2016-11-16 stephen.d 
244 0f5f58bb 2016-11-16 stephen.d // overflowMessage returns message that overflows the msize by overflow bytes,
245 0f5f58bb 2016-11-16 stephen.d // returning the message size and the fcall.
246 0f5f58bb 2016-11-16 stephen.d func overflowMessage(codec Codec, msize, overflow int) *Fcall {
247 0f5f58bb 2016-11-16 stephen.d 	var (
248 0f5f58bb 2016-11-16 stephen.d 		overhead = overheadMessage(codec, MessageTwrite{})
249 0f5f58bb 2016-11-16 stephen.d 		data     = bytes.Repeat([]byte{'A'}, (msize-overhead)+overflow)
250 0f5f58bb 2016-11-16 stephen.d 		fcall    = newFcall(1, MessageTwrite{
251 0f5f58bb 2016-11-16 stephen.d 			Data: data,
252 0f5f58bb 2016-11-16 stephen.d 		})
253 0f5f58bb 2016-11-16 stephen.d 	)
254 0f5f58bb 2016-11-16 stephen.d 
255 0f5f58bb 2016-11-16 stephen.d 	return fcall
256 0f5f58bb 2016-11-16 stephen.d }