1201806Sbz/*- 2330449Seadler * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3330449Seadler * 4201806Sbz * Copyright (c) 2010 Bjoern A. Zeeb <bz@FreeBSD.org> 5201806Sbz * All rights reserved. 6201806Sbz * 7201806Sbz * Redistribution and use in source and binary forms, with or without 8201806Sbz * modification, are permitted provided that the following conditions 9201806Sbz * are met: 10201806Sbz * 1. Redistributions of source code must retain the above copyright 11201806Sbz * notice, this list of conditions and the following disclaimer. 12201806Sbz * 2. Redistributions in binary form must reproduce the above copyright 13201806Sbz * notice, this list of conditions and the following disclaimer in the 14201806Sbz * documentation and/or other materials provided with the distribution. 15201806Sbz * 16201806Sbz * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17201806Sbz * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18201806Sbz * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19201806Sbz * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20201806Sbz * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21201806Sbz * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22201806Sbz * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23201806Sbz * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24201806Sbz * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25201806Sbz * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26201806Sbz * SUCH DAMAGE. 27201806Sbz * 28201806Sbz * $FreeBSD: stable/11/usr.sbin/traceroute/findsaddr-udp.c 330449 2018-03-05 07:26:05Z eadler $ 29201806Sbz */ 30201806Sbz 31201806Sbz#include <string.h> 32201806Sbz#include <unistd.h> 33201806Sbz 34201806Sbz#include <sys/types.h> 35201806Sbz#include <sys/socket.h> 36201806Sbz 37201806Sbz#include <netinet/in.h> 38201806Sbz 39201806Sbz#include "findsaddr.h" 40201806Sbz#include "traceroute.h" 41201806Sbz 42201806Sbz/* 43201806Sbz * Return the source address for the given destination address. 44201806Sbz * 45201897Sbz * This makes use of proper source address selection in the FreeBSD kernel 46201806Sbz * even taking jails into account (sys/netinet/in_pcb.c:in_pcbladdr()). 47201806Sbz * We open a UDP socket, and connect to the destination, letting the kernel 48201806Sbz * do the bind and then read the source IPv4 address using getsockname(2). 49201806Sbz * This has multiple advantages: no need to do PF_ROUTE operations possibly 50201806Sbz * needing special privileges, jails properly taken into account and most 51201806Sbz * important - getting the result the kernel would give us rather than 52201806Sbz * best-guessing ourselves. 53201806Sbz */ 54201806Sbzconst char * 55201806Sbzfindsaddr(register const struct sockaddr_in *to, 56201806Sbz register struct sockaddr_in *from) 57201806Sbz{ 58201806Sbz const char *errstr; 59201806Sbz struct sockaddr_in cto, cfrom; 60201806Sbz int s; 61201806Sbz socklen_t len; 62201806Sbz 63201806Sbz s = socket(AF_INET, SOCK_DGRAM, 0); 64201806Sbz if (s == -1) 65201806Sbz return ("failed to open DGRAM socket for src addr selection."); 66201806Sbz 67201806Sbz errstr = NULL; 68201806Sbz len = sizeof(struct sockaddr_in); 69201806Sbz memcpy(&cto, to, len); 70201806Sbz cto.sin_port = htons(65535); /* Dummy port for connect(2). */ 71201806Sbz if (connect(s, (struct sockaddr *)&cto, len) == -1) { 72201806Sbz errstr = "failed to connect to peer for src addr selection."; 73201806Sbz goto err; 74201806Sbz } 75201806Sbz 76201806Sbz if (getsockname(s, (struct sockaddr *)&cfrom, &len) == -1) { 77201806Sbz errstr = "failed to get socket name for src addr selection."; 78201806Sbz goto err; 79201806Sbz } 80201806Sbz 81201806Sbz if (len != sizeof(struct sockaddr_in) || cfrom.sin_family != AF_INET) { 82201806Sbz errstr = "unexpected address family in src addr selection."; 83201806Sbz goto err; 84201806Sbz } 85201806Sbz 86201806Sbz /* Update source address for traceroute. */ 87201806Sbz setsin(from, cfrom.sin_addr.s_addr); 88201806Sbz 89201806Sbzerr: 90201806Sbz (void) close(s); 91201806Sbz 92201806Sbz /* No error (string) to return. */ 93201806Sbz return (errstr); 94201806Sbz} 95201806Sbz 96201806Sbz/* end */ 97