github.com/psiphon-labs/psiphon-tunnel-core@v2.0.28+incompatible/psiphon/common/tun/tun_unix.go (about)

     1  //go:build darwin || linux
     2  // +build darwin linux
     3  
     4  /*
     5   * Copyright (c) 2021, Psiphon Inc.
     6   * All rights reserved.
     7   *
     8   * This program is free software: you can redistribute it and/or modify
     9   * it under the terms of the GNU General Public License as published by
    10   * the Free Software Foundation, either version 3 of the License, or
    11   * (at your option) any later version.
    12   *
    13   * This program is distributed in the hope that it will be useful,
    14   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    15   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    16   * GNU General Public License for more details.
    17   *
    18   * You should have received a copy of the GNU General Public License
    19   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    20   *
    21   */
    22  
    23  package tun
    24  
    25  import (
    26  	"os"
    27  	"syscall"
    28  
    29  	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/errors"
    30  	"golang.org/x/sys/unix"
    31  )
    32  
    33  // fileFromFD duplicates the file descriptor; sets O_CLOEXEC to avoid leaking
    34  // to child processes; sets the mode to nonblocking; and creates a os.File
    35  // using os.NewFile.
    36  func fileFromFD(fd int, name string) (*os.File, error) {
    37  
    38  	// Prevent fork between duplicating fd and setting CLOEXEC
    39  	syscall.ForkLock.RLock()
    40  	defer syscall.ForkLock.RUnlock()
    41  
    42  	dupfd, err := unix.Dup(fd)
    43  	if err != nil {
    44  		return nil, errors.Trace(err)
    45  	}
    46  
    47  	// Set CLOEXEC so file descriptor not leaked to network config command
    48  	// subprocesses.
    49  	unix.CloseOnExec(dupfd)
    50  
    51  	err = unix.SetNonblock(dupfd, true)
    52  	if err != nil {
    53  		unix.Close(dupfd)
    54  		return nil, errors.Trace(err)
    55  	}
    56  
    57  	return os.NewFile(uintptr(dupfd), name), nil
    58  }