/
net.go
198 lines (173 loc) · 4.26 KB
/
net.go
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package main
import (
"bytes"
"encoding/hex"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"os/exec"
"strconv"
"strings"
// "syscall"
"github.com/kylelemons/fatchan"
)
// Return true if the other end of `addr` belongs to the same user as the server
// by inspecting the contents of /proc/net/tcp
func CheckUser(addr *net.TCPAddr) (ok bool, err error) {
a := []byte(addr.IP)
// reverse it
for i, j := 0, len(a)-1; i < j; i, j = i+1, j-1 {
a[i], a[j] = a[j], a[i]
}
ADDR := strings.ToUpper(hex.EncodeToString(a))
the_address := ADDR + ":" + fmt.Sprintf("%04X", addr.Port)
f, err := os.Open("/proc/net/tcp")
if err != nil {
return
}
defer f.Close()
data, err := ioutil.ReadAll(f)
if err != nil {
return
}
lines := strings.Split(string(data), "\n")
for _, l := range lines {
fields := strings.Fields(l)
if len(fields) < 3 {
continue
}
remote := fields[1]
// This line represents this connection, check which user it belongs to
if remote == the_address {
user := fields[7]
u, _ := strconv.Atoi(user)
ok = u == os.Geteuid()
return
}
}
return
}
type SSHCloser struct {
stdin, stdout io.Closer
}
func (c *SSHCloser) Close() (err error) {
_ = c.stdin.Close()
_ = c.stdout.Close()
return
}
// Connect to `addr` by sshing through `via`. Assumes that batcher is in $PATH
// on the other end.
func SafeDial(via, addr string) (result io.ReadWriteCloser, err error) {
// TODO(pwaller): Could implement this using go crypto
// https://code.google.com/p/go/source/browse?repo=crypto#hg%2Fssh
netcat := fmt.Sprintf("batcher -forward %v", addr)
cmd := exec.Command("ssh", via, netcat)
// Run in its own process group so that we don't get "Killed by signal" messages
// (NOTE: This is commented out because if we die, the SSH process does not
// - a bad idea, lest we risk spamming everywhere with ssh processes)
// cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
cmd.Stderr = os.Stderr
stdin, err := cmd.StdinPipe()
if err != nil {
return
}
stdout, err := cmd.StdoutPipe()
if err != nil {
return
}
err = cmd.Start()
if err != nil {
return
}
var buf [5]byte
n, err := stdout.Read(buf[:])
if err != nil {
return
}
if n != 5 || !bytes.Equal(buf[:], []byte("CONN\n")) {
err = fmt.Errorf("Failed to connect via SSH: %q", string(buf[:]))
return
}
go func() {
// Note: can't use cmd.Wait here due to data races on the file
// descriptors being closed. Use cmd.Process.Wait() instead.
// err := cmd.Wait()
_, err := cmd.Process.Wait()
if err != nil {
// Crap, ssh bailed on us?
log.Printf("ssh exited: %v", err)
}
}()
return struct {
io.Reader
io.Writer
io.Closer
}{stdout, stdin, &SSHCloser{stdin, stdout}}, nil
}
// Primitive "nc" lookalike which emits "CONN" when there is a successful
// connection
func Forward(addr string) {
// log.Printf("Connecting to %v", addr)
conn, err := net.Dial("tcp", addr)
if err != nil {
log.Printf("batcher -forward: %q", err)
return
}
fmt.Println("CONN")
stdin, stdout := make(chan bool), make(chan bool)
cerr := make(chan error)
go func() {
_, err := io.Copy(conn, os.Stdin)
if err != nil {
cerr <- err
}
// log.Printf("Finished copy (stdin -> conn)")
close(stdin)
}()
go func() {
_, err := io.Copy(os.Stdout, conn)
if err != nil {
cerr <- err
}
// log.Printf("Finished copy (conn -> stdout)")
close(stdout)
}()
// Wait for either side to be closed, then exit
select {
case <-stdin:
case <-stdout:
case err := <-cerr:
log.Fatalf("Forward(%q) errored: %q", addr, err)
}
}
// Connect to `addr` by sshing through `via` (if specified), telling the server
// that we are a `client_type` and passing an approprite Login struct
func Connect(addr, via string, client_type ClientType) (io.ReadWriteCloser, Login) {
var conn io.ReadWriteCloser
var err error
if via != "" {
conn, err = SafeDial(via, addr)
} else {
conn, err = net.Dial("tcp", addr)
}
if err != nil {
log.Fatalf("Connect(%q, %q): %s", addr, via, err)
}
xport := fatchan.New(conn, nil)
login := make(chan Login)
_, err = xport.FromChan(login)
if err != nil {
log.Fatalf("Connect(%q, %q): %s", addr, via, err)
}
defer close(login)
me := Login{
Type: client_type,
Send: make(chan Message),
Recv: make(chan Message),
}
login <- me
return conn, me
}