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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Matt Layher <mdlayher@gmail.com>
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There are numerous race conditions. But even this will crash it:
while true; do ifconfig tun0 create; ifconfig tun0 destroy; done
It seems like LLv6 is related, which we're not using anyway, so
explicitly disable it on the interface.
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The new sysconn function of Go 1.12 makes this possible:
package main
import "log"
import "os"
import "unsafe"
import "time"
import "syscall"
import "sync"
import "golang.org/x/sys/unix"
func main() {
fd, err := os.OpenFile("/dev/net/tun", os.O_RDWR, 0)
if err != nil {
log.Fatal(err)
}
var ifr [unix.IFNAMSIZ + 64]byte
copy(ifr[:], []byte("cheese"))
*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = unix.IFF_TUN
var errno syscall.Errno
s, _ := fd.SyscallConn()
s.Control(func(fd uintptr) {
_, _, errno = unix.Syscall(
unix.SYS_IOCTL,
fd,
uintptr(unix.TUNSETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
})
if errno != 0 {
log.Fatal(errno)
}
b := [4]byte{}
wait := sync.WaitGroup{}
wait.Add(1)
go func() {
_, err := fd.Read(b[:])
log.Print("Read errored: ", err)
wait.Done()
}()
time.Sleep(time.Second)
log.Print("Closing")
err = fd.Close()
if err != nil {
log.Print("Close errored: " , err)
}
wait.Wait()
log.Print("Exiting")
}
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Doing so tends to make the tunnel blocking, so we only retrieve it once
before we call SetNonblock, and then cache the result.
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Keeping it on makes IPv6 problematic and confuses routing daemons.
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GOPATH is annoying, but the Go community pushing me to adopt it is even
more annoying.
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