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|
package binder
import (
"fmt"
"io"
"net"
"os"
"os/user"
"strconv"
"syscall"
g "euandre.org/gobang/src"
)
type CLIArgs struct {
FromAddr string
ToAddr string
}
const USER = "nobody"
var EmitActiveConnection = g.MakeGauge("active-connections")
func dropPrivileges(username string) {
g.Info("Dropping privileges", "drop-root-init")
user, err := user.Lookup(username)
g.FatalIf(err)
gid, err := strconv.Atoi(user.Gid)
g.FatalIf(err)
uid, err := strconv.Atoi(user.Uid)
g.FatalIf(err)
err = syscall.Setgid(gid)
g.FatalIf(err)
err = syscall.Setgroups([]int{})
g.FatalIf(err)
err = syscall.Setuid(uid)
g.FatalIf(err)
g.Info("Privileges dropped", "drop-root-end")
}
func isRunningAsRoot() bool {
return os.Geteuid() == 0
}
func copyData(closer chan struct{}, from io.Reader, to io.Writer) {
io.Copy(to, from)
closer <- struct{}{}
}
func ParseArgs(args []string) CLIArgs {
if len(args) != 3 {
fmt.Fprintf(
os.Stderr,
"Usage: %s FROM-ADDRESS TO-ADDRESS\n",
args[0],
)
os.Exit(2)
}
return CLIArgs {
FromAddr: args[1],
ToAddr: args[2],
}
}
func Listen(fromAddr string) net.Listener {
listener, err := net.Listen("tcp", fromAddr)
g.FatalIf(err)
g.Info("Started listening", "listen-start", "from-address", fromAddr)
return listener
}
func DropRoot() {
if isRunningAsRoot() {
dropPrivileges(USER)
if isRunningAsRoot() {
panic("Failed to drop privileges")
}
}
}
func Start(toAddr string, listener net.Listener) {
for {
connFrom, err := listener.Accept()
if err != nil {
g.Warning(
"Error accepting connection",
"accept-connection",
"err", err,
)
continue
}
defer connFrom.Close()
EmitActiveConnection.Inc()
connTo, err := net.Dial("unix", toAddr)
if err != nil {
g.Error(
"Error dialing connection",
"dial-connection",
"err", err,
)
return
}
defer connTo.Close()
closer := make(chan struct{}, 2)
go copyData(closer, connFrom, connTo)
go copyData(closer, connTo, connFrom)
go func() {
<-closer
EmitActiveConnection.Dec()
}()
}
}
func Main() {
g.Init()
args := ParseArgs(os.Args)
listener := Listen(args.FromAddr)
DropRoot()
Start(args.ToAddr, listener)
}
|
