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tailscale/net/interfaces/interfaces_darwin_cgo.go

125 lines
3.3 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build darwin,cgo
package interfaces
/*
#import "route.h"
#import <netinet/in.h>
#import <sys/sysctl.h>
#import <stdlib.h>
#import <stdio.h>
// privateGatewayIPFromRoute returns the private gateway ip address from rtm, if it exists.
// Otherwise, it returns 0.
uint32_t privateGatewayIPFromRoute(struct rt_msghdr2 *rtm)
{
// sockaddrs are after the message header
struct sockaddr* dst_sa = (struct sockaddr *)(rtm + 1);
if((rtm->rtm_addrs & (RTA_DST|RTA_GATEWAY)) != (RTA_DST|RTA_GATEWAY))
return 0; // missing dst or gateway addr
if (dst_sa->sa_family != AF_INET)
return 0; // dst not IPv4
if ((rtm->rtm_flags & RTF_GATEWAY) == 0)
return 0; // gateway flag not set
struct sockaddr_in* dst_si = (struct sockaddr_in *)dst_sa;
if (dst_si->sin_addr.s_addr != INADDR_ANY)
return 0; // not default route
#define ROUNDUP(a) ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
struct sockaddr* gateway_sa = (struct sockaddr *)((char *)dst_sa + ROUNDUP(dst_sa->sa_len));
if (gateway_sa->sa_family != AF_INET)
return 0; // gateway not IPv4
struct sockaddr_in* gateway_si= (struct sockaddr_in *)gateway_sa;
uint32_t ip;
ip = gateway_si->sin_addr.s_addr;
unsigned char a, b;
a = (ip >> 0) & 0xff;
b = (ip >> 8) & 0xff;
// Check whether ip is private, that is, whether it is
// in one of 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16.
if (a == 10)
return ip; // matches 10.0.0.0/8
if (a == 172 && (b >> 4) == 1)
return ip; // matches 172.16.0.0/12
if (a == 192 && b == 168)
return ip; // matches 192.168.0.0/16
// Not a private IP.
return 0;
}
// privateGatewayIP returns the private gateway IP address, if it exists.
// If no private gateway IP address was found, it returns 0.
// On an error, it returns an error code in (0, 255].
// Any private gateway IP address is > 255.
uint32_t privateGatewayIP()
{
size_t needed;
int mib[6];
char *buf;
mib[0] = CTL_NET;
mib[1] = PF_ROUTE;
mib[2] = 0;
mib[3] = 0;
mib[4] = NET_RT_DUMP2;
mib[5] = 0;
if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
return 1; // route dump size estimation failed
if ((buf = malloc(needed)) == 0)
return 2; // malloc failed
if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) {
free(buf);
return 3; // route dump failed
}
// Loop over all routes.
char *next, *lim;
lim = buf + needed;
struct rt_msghdr2 *rtm;
for (next = buf; next < lim; next += rtm->rtm_msglen) {
rtm = (struct rt_msghdr2 *)next;
uint32_t ip;
ip = privateGatewayIPFromRoute(rtm);
if (ip) {
free(buf);
return ip;
}
}
free(buf);
return 0; // no gateway found
}
*/
import "C"
import (
"encoding/binary"
"inet.af/netaddr"
)
func init() {
likelyHomeRouterIP = likelyHomeRouterIPDarwinSyscall
}
func likelyHomeRouterIPDarwinSyscall() (ret netaddr.IP, ok bool) {
ip := C.privateGatewayIP()
if ip < 255 {
return netaddr.IP{}, false
}
var q [4]byte
binary.LittleEndian.PutUint32(q[:], uint32(ip))
return netaddr.IPv4(q[0], q[1], q[2], q[3]), true
}