1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2010 Bjoern A. Zeeb <bz@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 * 28 * $FreeBSD$ 29 */ 30 31 #include <string.h> 32 #include <unistd.h> 33 34 #include <sys/types.h> 35 #include <sys/socket.h> 36 37 #include <netinet/in.h> 38 39 #include "findsaddr.h" 40 #include "traceroute.h" 41 42 /* 43 * Return the source address for the given destination address. 44 * 45 * This makes use of proper source address selection in the FreeBSD kernel 46 * even taking jails into account (sys/netinet/in_pcb.c:in_pcbladdr()). 47 * We open a UDP socket, and connect to the destination, letting the kernel 48 * do the bind and then read the source IPv4 address using getsockname(2). 49 * This has multiple advantages: no need to do PF_ROUTE operations possibly 50 * needing special privileges, jails properly taken into account and most 51 * important - getting the result the kernel would give us rather than 52 * best-guessing ourselves. 53 */ 54 const char * 55 findsaddr(register const struct sockaddr_in *to, 56 register struct sockaddr_in *from) 57 { 58 const char *errstr; 59 struct sockaddr_in cto, cfrom; 60 int s; 61 socklen_t len; 62 63 s = socket(AF_INET, SOCK_DGRAM, 0); 64 if (s == -1) 65 return ("failed to open DGRAM socket for src addr selection."); 66 67 errstr = NULL; 68 len = sizeof(struct sockaddr_in); 69 memcpy(&cto, to, len); 70 cto.sin_port = htons(65535); /* Dummy port for connect(2). */ 71 if (connect(s, (struct sockaddr *)&cto, len) == -1) { 72 errstr = "failed to connect to peer for src addr selection."; 73 goto err; 74 } 75 76 if (getsockname(s, (struct sockaddr *)&cfrom, &len) == -1) { 77 errstr = "failed to get socket name for src addr selection."; 78 goto err; 79 } 80 81 if (len != sizeof(struct sockaddr_in) || cfrom.sin_family != AF_INET) { 82 errstr = "unexpected address family in src addr selection."; 83 goto err; 84 } 85 86 /* Update source address for traceroute. */ 87 setsin(from, cfrom.sin_addr.s_addr); 88 89 err: 90 (void) close(s); 91 92 /* No error (string) to return. */ 93 return (errstr); 94 } 95 96 /* end */ 97