Go

修复 Go #40569 问题

修复 Go #40569 问题

问题描述

问题 issue： https://github.com/golang/go/issues/40569

在安卓 11 以上版本中，go 调用 net.InterfaceAddrs() 和 net.Interfaces()时会抛出 route ip+net: netlinkrib: permission denied 错误。

出现原因

查找原因发现是由于安卓 11 以上版本对 netlink 套接字的能力进行了限制，详情见：https://developer.android.com/training/articles/user-data-ids#mac-11-plus。

查看 Go 源码，发现在两个地方会存在问题：

（一）在syscall.NetlinkRIB 函数中，进行了 netlink 套接字 bind 操作：

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// NetlinkRIB returns routing information base, as known as RIB, which
// consists of network facility information, states and parameters.
func NetlinkRIB(proto, family int) ([]byte, error) {
	s, err := Socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE)
	if err != nil {
		return nil, err
	}
	defer Close(s)
	sa := &SockaddrNetlink{Family: AF_NETLINK}
    
    //-------------------------------------------------
    // 进行了 bind 操作
	if err := Bind(s, sa); err != nil {
		return nil, err
	}
    //-------------------------------------------------
    
	wb := newNetlinkRouteRequest(proto, 1, family)
	if err := Sendto(s, wb, 0, sa); err != nil {
		return nil, err
	}
	lsa, err := Getsockname(s)
	if err != nil {
		return nil, err
	}
	lsanl, ok := lsa.(*SockaddrNetlink)
	if !ok {
		return nil, EINVAL
	}
	var tab []byte
	rbNew := make([]byte, Getpagesize())
done:
	for {
		rb := rbNew
		nr, _, err := Recvfrom(s, rb, 0)
		if err != nil {
			return nil, err
		}
		if nr < NLMSG_HDRLEN {
			return nil, EINVAL
		}
		rb = rb[:nr]
		tab = append(tab, rb...)
		msgs, err := ParseNetlinkMessage(rb)
		if err != nil {
			return nil, err
		}
		for _, m := range msgs {
			if m.Header.Seq != 1 || m.Header.Pid != lsanl.Pid {
				return nil, EINVAL
			}
			if m.Header.Type == NLMSG_DONE {
				break done
			}
			if m.Header.Type == NLMSG_ERROR {
				return nil, EINVAL
			}
		}
	}
	return tab, nil
}

（二）在 interfaceTable 函数中，调用了 Netlink 套接字的 RTM_GETLINK 能力：

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func interfaceTable(ifindex int) ([]Interface, error) {
    // 调用了 syscall.RTM_GETLINK 套接字
	tab, err := syscall.NetlinkRIB(syscall.RTM_GETLINK, syscall.AF_UNSPEC)
	if err != nil {
		return nil, os.NewSyscallError("netlinkrib", err)
	}
	msgs, err := syscall.ParseNetlinkMessage(tab)
	if err != nil {
		return nil, os.NewSyscallError("parsenetlinkmessage", err)
	}
	var ift []Interface
loop:
	for _, m := range msgs {
		switch m.Header.Type {
		case syscall.NLMSG_DONE:
			break loop
		case syscall.RTM_NEWLINK:
			ifim := (*syscall.IfInfomsg)(unsafe.Pointer(&m.Data[0]))
			if ifindex == 0 || ifindex == int(ifim.Index) {
				attrs, err := syscall.ParseNetlinkRouteAttr(&m)
				if err != nil {
					return nil, os.NewSyscallError("parsenetlinkrouteattr", err)
				}
				ift = append(ift, *newLink(ifim, attrs))
				if ifindex == int(ifim.Index) {
					break loop
				}
			}
		}
	}
	return ift, nil
}

解决方案

经过调研，发现在 Android 中存在一个 NetworkInterface.getNetworkInterfaces() 接口，该接口能够正常返回网卡地址和相关信息（在 Android 11 之后的版本种 HwAddr 为空）。

因此决定参考NetworkInterface.getNetworkInterfaces()接口实现对 Go 的代码进行修复。

相关 Android 代码：

实现代码

完整代码可见：

https://github.com/golang/go/pull/61089

https://github.com/wlynxg/anet

部分代码：

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// src/net/interface_android.go
package net

import (
	"bytes"
	"os"
	"syscall"
	"unsafe"
)

type ifReq [40]byte

// Starting from Android 11, it is no longer possible to retrieve network card information
// using the RTM_GETLINK method.
// As a result, alternative methods need to be employed.
// After considering the Android NetworkInterface.getNetworkInterfaces() method,
// I opted to utilize the RTM_GETADDR + ioctl approach to obtain network card information.
// However, it appears that retrieving the
// HWAddr (hardware address) of the network card is currently not achievable.
func interfaceTableAndroid(ifindex int) ([]Interface, error) {
	tab, err := syscall.NetlinkRIB(syscall.RTM_GETADDR, syscall.AF_UNSPEC)
	if err != nil {
		return nil, os.NewSyscallError("netlinkrib", err)
	}
	msgs, err := syscall.ParseNetlinkMessage(tab)
	if err != nil {
		return nil, os.NewSyscallError("parsenetlinkmessage", err)
	}

	var ift []Interface
	im := make(map[uint32]struct{})
loop:
	for _, m := range msgs {
		switch m.Header.Type {
		case syscall.NLMSG_DONE:
			break loop
		case syscall.RTM_NEWADDR:
			ifam := (*syscall.IfAddrmsg)(unsafe.Pointer(&m.Data[0]))
			if _, ok := im[ifam.Index]; ok {
				continue
			} else {
				im[ifam.Index] = struct{}{}
			}

			if ifindex == 0 || ifindex == int(ifam.Index) {
				ifi := newLinkAndroid(ifam)
				if ifi != nil {
					ift = append(ift, *ifi)
				}
				if ifindex == int(ifam.Index) {
					break loop
				}
			}
		}
	}

	return ift, nil
}

// According to the network card Index, get the Name, MTU and Flags of the network card through ioctl
func newLinkAndroid(ifam *syscall.IfAddrmsg) *Interface {
	ift := &Interface{Index: int(ifam.Index)}

	name, err := indexToName(ifam.Index)
	if err != nil {
		return nil
	}
	ift.Name = name

	mtu, err := nameToMTU(name)
	if err != nil {
		return nil
	}
	ift.MTU = mtu

	flags, err := nameToFlags(name)
	if err != nil {
		return nil
	}
	ift.Flags = flags
	return ift
}

func ioctl(fd int, req uint, arg unsafe.Pointer) error {
	_, _, e1 := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), uintptr(req), uintptr(arg))
	if e1 != 0 {
		return e1
	}
	return nil
}

func indexToName(index uint32) (string, error) {
	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM|syscall.SOCK_CLOEXEC, 0)
	if err != nil {
		return "", err
	}
	defer syscall.Close(fd)

	var ifr ifReq
	*(*uint32)(unsafe.Pointer(&ifr[syscall.IFNAMSIZ])) = index
	err = ioctl(fd, syscall.SIOCGIFNAME, unsafe.Pointer(&ifr[0]))
	if err != nil {
		return "", err
	}

	return string(bytes.Trim(ifr[:syscall.IFNAMSIZ], "\x00")), nil
}

func nameToMTU(name string) (int, error) {
	// Leave room for terminating NULL byte.
	if len(name) >= syscall.IFNAMSIZ {
		return 0, syscall.EINVAL
	}

	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM|syscall.SOCK_CLOEXEC, 0)
	if err != nil {
		return 0, err
	}
	defer syscall.Close(fd)

	var ifr ifReq
	copy(ifr[:], name)
	err = ioctl(fd, syscall.SIOCGIFMTU, unsafe.Pointer(&ifr[0]))
	if err != nil {
		return 0, err
	}

	return int(*(*int32)(unsafe.Pointer(&ifr[syscall.IFNAMSIZ]))), nil
}

func nameToFlags(name string) (Flags, error) {
	// Leave room for terminating NULL byte.
	if len(name) >= syscall.IFNAMSIZ {
		return 0, syscall.EINVAL
	}

	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM|syscall.SOCK_CLOEXEC, 0)
	if err != nil {
		return 0, err
	}
	defer syscall.Close(fd)

	var ifr ifReq
	copy(ifr[:], name)
	err = ioctl(fd, syscall.SIOCGIFFLAGS, unsafe.Pointer(&ifr[0]))
	if err != nil {
		return 0, err
	}

	return linkFlags(*(*uint32)(unsafe.Pointer(&ifr[syscall.IFNAMSIZ]))), nil
}

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// src/syscall/netlink_linux.go

// NetlinkRIB returns routing information base, as known as RIB, which
// consists of network facility information, states and parameters.
func NetlinkRIB(proto, family int) ([]byte, error) {
	s, err := Socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE)
	if err != nil {
		return nil, err
	}
	defer Close(s)
	sa := &SockaddrNetlink{Family: AF_NETLINK}
	if err := Bind(s, sa); err != nil {
		// Bind operation of Netlink socket is prohibited in Android11 and later versions
		if !(runtime.GOOS == "android" && os.IsPermission(err)) {
			return nil, err
		}
	}
	wb := newNetlinkRouteRequest(proto, 1, family)
	if err := Sendto(s, wb, 0, sa); err != nil {
		return nil, err
	}
	lsa, err := Getsockname(s)
	if err != nil {
		return nil, err
	}
	lsanl, ok := lsa.(*SockaddrNetlink)
	if !ok {
		return nil, EINVAL
	}
	var tab []byte

	rbNew := pageBufPool.Get().(*[]byte)
	defer pageBufPool.Put(rbNew)
done:
	for {
		rb := *rbNew
		nr, _, err := Recvfrom(s, rb, 0)
		if err != nil {
			return nil, err
		}
		if nr < NLMSG_HDRLEN {
			return nil, EINVAL
		}
		rb = rb[:nr]
		tab = append(tab, rb...)
		msgs, err := ParseNetlinkMessage(rb)
		if err != nil {
			return nil, err
		}
		for _, m := range msgs {
			if m.Header.Seq != 1 || m.Header.Pid != lsanl.Pid {
				return nil, EINVAL
			}
			if m.Header.Type == NLMSG_DONE {
				break done
			}
			if m.Header.Type == NLMSG_ERROR {
				return nil, EINVAL
			}
		}
	}
	return tab, nil
}
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