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1c238cdce6
The code was using a C "int", which is a signed 32-bit integer.
That means some valid IP addresses were negative numbers.
(In particular, the default router address handed out by AT&T
fiber: 192.168.1.254. No I don't know why they do that.)
A negative number is < 255, and so was treated by the Go code
as an error.
This fixes the unit test failure:
$ go test -v -run=TestLikelyHomeRouterIPSyscallExec ./net/interfaces
=== RUN TestLikelyHomeRouterIPSyscallExec
interfaces_darwin_cgo_test.go:15: syscall() = invalid IP, false, netstat = 192.168.1.254, true
--- FAIL: TestLikelyHomeRouterIPSyscallExec (0.00s)
Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
(cherry picked from commit d139fa9c92)
125 lines
3.3 KiB
Go
125 lines
3.3 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build darwin,cgo
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package interfaces
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/*
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#import "route.h"
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#import <netinet/in.h>
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#import <sys/sysctl.h>
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#import <stdlib.h>
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#import <stdio.h>
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// privateGatewayIPFromRoute returns the private gateway ip address from rtm, if it exists.
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// Otherwise, it returns 0.
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uint32_t privateGatewayIPFromRoute(struct rt_msghdr2 *rtm)
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{
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// sockaddrs are after the message header
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struct sockaddr* dst_sa = (struct sockaddr *)(rtm + 1);
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if((rtm->rtm_addrs & (RTA_DST|RTA_GATEWAY)) != (RTA_DST|RTA_GATEWAY))
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return 0; // missing dst or gateway addr
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if (dst_sa->sa_family != AF_INET)
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return 0; // dst not IPv4
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if ((rtm->rtm_flags & RTF_GATEWAY) == 0)
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return 0; // gateway flag not set
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struct sockaddr_in* dst_si = (struct sockaddr_in *)dst_sa;
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if (dst_si->sin_addr.s_addr != INADDR_ANY)
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return 0; // not default route
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#define ROUNDUP(a) ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
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struct sockaddr* gateway_sa = (struct sockaddr *)((char *)dst_sa + ROUNDUP(dst_sa->sa_len));
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if (gateway_sa->sa_family != AF_INET)
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return 0; // gateway not IPv4
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struct sockaddr_in* gateway_si= (struct sockaddr_in *)gateway_sa;
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uint32_t ip;
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ip = gateway_si->sin_addr.s_addr;
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unsigned char a, b;
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a = (ip >> 0) & 0xff;
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b = (ip >> 8) & 0xff;
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// Check whether ip is private, that is, whether it is
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// in one of 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16.
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if (a == 10)
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return ip; // matches 10.0.0.0/8
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if (a == 172 && (b >> 4) == 1)
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return ip; // matches 172.16.0.0/12
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if (a == 192 && b == 168)
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return ip; // matches 192.168.0.0/16
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// Not a private IP.
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return 0;
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}
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// privateGatewayIP returns the private gateway IP address, if it exists.
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// If no private gateway IP address was found, it returns 0.
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// On an error, it returns an error code in (0, 255].
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// Any private gateway IP address is > 255.
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uint32_t privateGatewayIP()
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{
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size_t needed;
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int mib[6];
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char *buf;
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mib[0] = CTL_NET;
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mib[1] = PF_ROUTE;
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mib[2] = 0;
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mib[3] = 0;
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mib[4] = NET_RT_DUMP2;
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mib[5] = 0;
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if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
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return 1; // route dump size estimation failed
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if ((buf = malloc(needed)) == 0)
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return 2; // malloc failed
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if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) {
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free(buf);
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return 3; // route dump failed
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}
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// Loop over all routes.
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char *next, *lim;
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lim = buf + needed;
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struct rt_msghdr2 *rtm;
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for (next = buf; next < lim; next += rtm->rtm_msglen) {
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rtm = (struct rt_msghdr2 *)next;
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uint32_t ip;
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ip = privateGatewayIPFromRoute(rtm);
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if (ip) {
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free(buf);
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return ip;
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}
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}
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free(buf);
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return 0; // no gateway found
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}
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*/
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import "C"
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import (
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"encoding/binary"
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"inet.af/netaddr"
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)
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func init() {
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likelyHomeRouterIP = likelyHomeRouterIPDarwinSyscall
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}
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func likelyHomeRouterIPDarwinSyscall() (ret netaddr.IP, ok bool) {
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ip := C.privateGatewayIP()
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if ip < 255 {
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return netaddr.IP{}, false
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}
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var q [4]byte
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binary.LittleEndian.PutUint32(q[:], uint32(ip))
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return netaddr.IPv4(q[0], q[1], q[2], q[3]), true
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}
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