Introduction

In response to the modifications made to the permissions for accessing system MAC addresses in Android 11, ordinary applications encounter several main issues when using NETLINK sockets:

• Not allowing bind operations on NETLINK sockets.
• Not permitting the use of the RTM_GETLINK functionality.

For detailed information, please refer to: https://developer.android.com/training/articles/user-data-ids#mac-11-plus

As a result of the aforementioned reasons, using net.Interfaces() and net.InterfaceAddrs() from the Go net package in the Android environment leads to the route ip+net: netlinkrib: permission denied error.

You can find specific issue details here: https://github.com/golang/go/issues/40569

To address the issue of using the Go net package in the Android environment, we have made partial modifications to its source code to ensure proper functionality on Android.

I have fully resolved the issues with net.InterfaceAddrs().

However, for net.Interfaces(), we have only addressed some problems, as the following issues still remain:

• It can only return interfaces with IP addresses.
• It cannot return hardware MAC addresses.

Nevertheless, the fixed net.Interfaces() function now aligns with the Android API's NetworkInterface.getNetworkInterfaces() and can be used normally in most scenarios.

The specific fix logic includes:

Removing the Bind() operation on Netlink sockets in the NetlinkRIB() function. Using ioctl based on the Index number returned by RTM_GETADDR to retrieve the network card's name, MTU, and flags.

There are two implementations of the net package: one from the Go standard library and another from the golang.org/x/net module. Both of these implementations have the same issues in the Android environment. The anet package should be compatible with both of them.

How to build with Go 1.23.0 or later

Since https://github.com/golang/go/issues/68082 and https://github.com/golang/go/issues/40569 have the same problem, anet chose to solve https://github.com/golang/go/issues/68082 together.

In order to solve https://github.com/golang/go/issues/68082 anet introduced the //golinkname mechanism.

But unfortunately, since the usage of //go:linkname has been restricted since Go 1.23.0 (Go 1.23 Release Notes), it is necessary to specify the -ldflags "-checklinkname=0" linker flag when building the anet package with Go 1.23.0 or later.

Without this flag, the following linker error will occur:

link: github.com/wlynxg/anet: invalid reference to net.zoneCache

Test Code

net.Interface()

use net.Interface():

func RawInterface() {
	interfaces, err := net.Interfaces()
	if err != nil {
		panic(err)
	}

	for _, i := range interfaces {
		log.Println(i)
	}
}

result:

panic: route ip+net: netlinkrib: permission denied

use anet.Interface():

func AnetInterface() {
	interfaces, err := anet.Interfaces()
	if err != nil {
		panic(err)
	}

	for _, i := range interfaces {
		log.Println(i)
	}
}

result:

{1 65536 lo  up|loopback|running}
{15 1400 rmnet_data1  up|running}
{24 1500 wlan0  up|broadcast|multicast|running}
{3 1500 dummy0  up|broadcast|running}
{4 1500 ifb0  up|broadcast|running}
{5 1500 ifb1  up|broadcast|running}
{12 1500 ifb2  up|broadcast|running}
{14 1500 rmnet_data0  up|running}
{16 1400 rmnet_data2  up|running}
{17 1400 rmnet_data3  up|running}

net.InterfaceAddrs()

use net.InterfaceAddrs():

func NetInterfaceAddrs() {
	addrs, err := net.InterfaceAddrs()
	if err != nil {
		panic(err)
	}

	for _, addr := range addrs {
		log.Println(addr)
	}
}

result:

panic: route ip+net: netlinkrib: permission denied

use anet.InterfaceAddrs():

func AnetInterfaceAddrs() {
	addrs, err := anet.InterfaceAddrs()
	if err != nil {
		panic(err)
	}

	for _, addr := range addrs {
		log.Println(addr)
	}
}

result:

127.0.0.1/8
::1/128
...
192.168.6.143/24
fe80::7e4f:4446:eb3:1eb8/64

Other issues due to #40569

• https://github.com/golang/go/issues/68082