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// 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 p9
import (
"errors"
"fmt"
"io"
"io/ioutil"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/fd"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/unet"
)
// ErrSocket is returned in cases of a socket issue.
//
// This may be treated differently than other errors.
type ErrSocket struct {
// error is the socket error.
error
}
// ErrMessageTooLarge indicates the size was larger than reasonable.
type ErrMessageTooLarge struct {
size uint32
msize uint32
}
// Error returns a sensible error.
func (e *ErrMessageTooLarge) Error() string {
return fmt.Sprintf("message too large for fixed buffer: size is %d, limit is %d", e.size, e.msize)
}
// ErrNoValidMessage indicates no valid message could be decoded.
var ErrNoValidMessage = errors.New("buffer contained no valid message")
const (
// headerLength is the number of bytes required for a header.
headerLength uint32 = 7
// maximumLength is the largest possible message.
maximumLength uint32 = 1 << 20
// DefaultMessageSize is a sensible default.
DefaultMessageSize uint32 = 64 << 10
// initialBufferLength is the initial data buffer we allocate.
initialBufferLength uint32 = 64
)
var dataPool = sync.Pool{
New: func() any {
// These buffers are used for decoding without a payload.
// We need to return a pointer to avoid unnecessary allocations
// (see https://staticcheck.io/docs/checks#SA6002).
b := make([]byte, initialBufferLength)
return &b
},
}
// send sends the given message over the socket.
func send(s *unet.Socket, tag Tag, m message) error {
data := dataPool.Get().(*[]byte)
dataBuf := buffer{data: (*data)[:0]}
if log.IsLogging(log.Debug) {
log.Debugf("send [FD %d] [Tag %06d] %s", s.FD(), tag, m.String())
}
// Encode the message. The buffer will grow automatically.
m.encode(&dataBuf)
// Get our vectors to send.
var hdr [headerLength]byte
vecs := make([][]byte, 0, 3)
vecs = append(vecs, hdr[:])
if len(dataBuf.data) > 0 {
vecs = append(vecs, dataBuf.data)
}
totalLength := headerLength + uint32(len(dataBuf.data))
// Is there a payload?
if payloader, ok := m.(payloader); ok {
p := payloader.Payload()
if len(p) > 0 {
vecs = append(vecs, p)
totalLength += uint32(len(p))
}
}
// Construct the header.
headerBuf := buffer{data: hdr[:0]}
headerBuf.Write32(totalLength)
headerBuf.WriteMsgType(m.Type())
headerBuf.WriteTag(tag)
// Pack any files if necessary.
w := s.Writer(true)
if filer, ok := m.(filer); ok {
if f := filer.FilePayload(); f != nil {
defer f.Close()
// Pack the file into the message.
w.PackFDs(f.FD())
}
}
for n := 0; n < int(totalLength); {
cur, err := w.WriteVec(vecs)
if err != nil {
return ErrSocket{err}
}
n += cur
// Consume iovecs.
for consumed := 0; consumed < cur; {
if len(vecs[0]) <= cur-consumed {
consumed += len(vecs[0])
vecs = vecs[1:]
} else {
vecs[0] = vecs[0][cur-consumed:]
break
}
}
if n > 0 && n < int(totalLength) {
// Don't resend any control message.
w.UnpackFDs()
}
}
// All set.
dataPool.Put(&dataBuf.data)
return nil
}
// lookupTagAndType looks up an existing message or creates a new one.
//
// This is called by recv after decoding the header. Any error returned will be
// propagating back to the caller. You may use messageByType directly as a
// lookupTagAndType function (by design).
type lookupTagAndType func(tag Tag, t MsgType) (message, error)
// recv decodes a message from the socket.
//
// This is done in two parts, and is thus not safe for multiple callers.
//
// On a socket error, the special error type ErrSocket is returned.
//
// The tag value NoTag will always be returned if err is non-nil.
func recv(s *unet.Socket, msize uint32, lookup lookupTagAndType) (Tag, message, error) {
// Read a header.
//
// Since the send above is atomic, we must always receive control
// messages along with the header. This means we need to be careful
// about closing FDs during errors to prevent leaks.
var hdr [headerLength]byte
r := s.Reader(true)
r.EnableFDs(1)
n, err := r.ReadVec([][]byte{hdr[:]})
if err != nil && (n == 0 || err != io.EOF) {
r.CloseFDs()
return NoTag, nil, ErrSocket{err}
}
fds, err := r.ExtractFDs()
if err != nil {
return NoTag, nil, ErrSocket{err}
}
defer func() {
// Close anything left open. The case where
// fds are caught and used is handled below,
// and the fds variable will be set to nil.
for _, fd := range fds {
unix.Close(fd)
}
}()
r.EnableFDs(0)
// Continuing reading for a short header.
for n < int(headerLength) {
cur, err := r.ReadVec([][]byte{hdr[n:]})
if err != nil && (cur == 0 || err != io.EOF) {
return NoTag, nil, ErrSocket{err}
}
n += cur
}
// Decode the header.
headerBuf := buffer{data: hdr[:]}
size := headerBuf.Read32()
t := headerBuf.ReadMsgType()
tag := headerBuf.ReadTag()
if size < headerLength {
// The message is too small.
//
// See above: it's probably screwed.
return NoTag, nil, ErrSocket{ErrNoValidMessage}
}
if size > maximumLength || size > msize {
// The message is too big.
return NoTag, nil, ErrSocket{&ErrMessageTooLarge{size, msize}}
}
remaining := size - headerLength
// Find our message to decode.
m, err := lookup(tag, t)
if err != nil {
// Throw away the contents of this message.
if remaining > 0 {
io.Copy(ioutil.Discard, &io.LimitedReader{R: s, N: int64(remaining)})
}
return tag, nil, err
}
// Not yet initialized.
var dataBuf buffer
var vecs [][]byte
appendBuffer := func(size int) *[]byte {
// Pull a data buffer from the pool.
datap := dataPool.Get().(*[]byte)
data := *datap
if size > len(data) {
// Create a larger data buffer.
data = make([]byte, size)
datap = &data
} else {
// Limit the data buffer.
data = data[:size]
}
dataBuf = buffer{data: data}
vecs = append(vecs, data)
return datap
}
// Read the rest of the payload.
//
// This requires some special care to ensure that the vectors all line
// up the way they should. We do this to minimize copying data around.
if payloader, ok := m.(payloader); ok {
fixedSize := payloader.FixedSize()
// Do we need more than there is?
if fixedSize > remaining {
// This is not a valid message.
if remaining > 0 {
io.Copy(ioutil.Discard, &io.LimitedReader{R: s, N: int64(remaining)})
}
return NoTag, nil, ErrNoValidMessage
}
if fixedSize != 0 {
datap := appendBuffer(int(fixedSize))
defer dataPool.Put(datap)
}
// Include the payload.
p := payloader.Payload()
if p == nil || len(p) != int(remaining-fixedSize) {
p = make([]byte, remaining-fixedSize)
payloader.SetPayload(p)
}
if len(p) > 0 {
vecs = append(vecs, p)
}
} else if remaining != 0 {
datap := appendBuffer(int(remaining))
defer dataPool.Put(datap)
}
if len(vecs) > 0 {
// Read the rest of the message.
//
// No need to handle a control message.
r := s.Reader(true)
for n := 0; n < int(remaining); {
cur, err := r.ReadVec(vecs)
if err != nil && (cur == 0 || err != io.EOF) {
return NoTag, nil, ErrSocket{err}
}
n += cur
// Consume iovecs.
for consumed := 0; consumed < cur; {
if len(vecs[0]) <= cur-consumed {
consumed += len(vecs[0])
vecs = vecs[1:]
} else {
vecs[0] = vecs[0][cur-consumed:]
break
}
}
}
}
// Decode the message data.
m.decode(&dataBuf)
if dataBuf.isOverrun() {
// No need to drain the socket.
return NoTag, nil, ErrNoValidMessage
}
// Save the file, if any came out.
if filer, ok := m.(filer); ok && len(fds) > 0 {
// Set the file object.
filer.SetFilePayload(fd.New(fds[0]))
// Close the rest. We support only one.
for i := 1; i < len(fds); i++ {
unix.Close(fds[i])
}
// Don't close in the defer.
fds = nil
}
if log.IsLogging(log.Debug) {
log.Debugf("recv [FD %d] [Tag %06d] %s", s.FD(), tag, m.String())
}
// All set.
return tag, m, nil
}
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