github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/test/iptables/iptables_unsafe.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package iptables
    16  
    17  import (
    18  	"fmt"
    19  	"unsafe"
    20  
    21  	"golang.org/x/sys/unix"
    22  )
    23  
    24  type originalDstError struct {
    25  	errno unix.Errno
    26  }
    27  
    28  func (e originalDstError) Error() string {
    29  	return fmt.Sprintf("errno (%d) when calling getsockopt(SO_ORIGINAL_DST): %v", int(e.errno), e.errno.Error())
    30  }
    31  
    32  // SO_ORIGINAL_DST gets the original destination of a redirected packet via
    33  // getsockopt.
    34  const SO_ORIGINAL_DST = 80
    35  
    36  func originalDestination4(connfd int) (unix.RawSockaddrInet4, error) {
    37  	var addr unix.RawSockaddrInet4
    38  	var addrLen uint32 = unix.SizeofSockaddrInet4
    39  	if errno := originalDestination(connfd, unix.SOL_IP, unsafe.Pointer(&addr), &addrLen); errno != 0 {
    40  		return unix.RawSockaddrInet4{}, originalDstError{errno}
    41  	}
    42  	return addr, nil
    43  }
    44  
    45  func originalDestination6(connfd int) (unix.RawSockaddrInet6, error) {
    46  	var addr unix.RawSockaddrInet6
    47  	var addrLen uint32 = unix.SizeofSockaddrInet6
    48  	if errno := originalDestination(connfd, unix.SOL_IPV6, unsafe.Pointer(&addr), &addrLen); errno != 0 {
    49  		return unix.RawSockaddrInet6{}, originalDstError{errno}
    50  	}
    51  	return addr, nil
    52  }
    53  
    54  func originalDestination(connfd int, level uintptr, optval unsafe.Pointer, optlen *uint32) unix.Errno {
    55  	_, _, errno := unix.Syscall6(
    56  		unix.SYS_GETSOCKOPT,
    57  		uintptr(connfd),
    58  		level,
    59  		SO_ORIGINAL_DST,
    60  		uintptr(optval),
    61  		uintptr(unsafe.Pointer(optlen)),
    62  		0)
    63  	return errno
    64  }