1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 29 #include <string.h> 30 #include <unistd.h> 31 32 #include <sys/types.h> 33 #include <sys/socket.h> 34 35 #include <netinet/in.h> 36 37 #include "findsaddr.h" 38 #include "traceroute.h" 39 40 /* 41 * Return the source address for the given destination address. 42 * 43 * This makes use of proper source address selection in the FreeBSD kernel 44 * even taking jails into account (sys/netinet/in_pcb.c:in_pcbladdr()). 45 * We open a UDP socket, and connect to the destination, letting the kernel 46 * do the bind and then read the source IPv4 address using getsockname(2). 47 * This has multiple advantages: no need to do PF_ROUTE operations possibly 48 * needing special privileges, jails properly taken into account and most 49 * important - getting the result the kernel would give us rather than 50 * best-guessing ourselves. 51 */ 52 const char * 53 findsaddr(register const struct sockaddr_in *to, 54 register struct sockaddr_in *from) 55 { 56 const char *errstr; 57 struct sockaddr_in cto, cfrom; 58 int s; 59 socklen_t len; 60 61 s = socket(AF_INET, SOCK_DGRAM, 0); 62 if (s == -1) 63 return ("failed to open DGRAM socket for src addr selection."); 64 65 errstr = NULL; 66 len = sizeof(struct sockaddr_in); 67 memcpy(&cto, to, len); 68 cto.sin_port = htons(65535); /* Dummy port for connect(2). */ 69 if (connect(s, (struct sockaddr *)&cto, len) == -1) { 70 errstr = "failed to connect to peer for src addr selection."; 71 goto err; 72 } 73 74 if (getsockname(s, (struct sockaddr *)&cfrom, &len) == -1) { 75 errstr = "failed to get socket name for src addr selection."; 76 goto err; 77 } 78 79 if (len != sizeof(struct sockaddr_in) || cfrom.sin_family != AF_INET) { 80 errstr = "unexpected address family in src addr selection."; 81 goto err; 82 } 83 84 /* Update source address for traceroute. */ 85 setsin(from, cfrom.sin_addr.s_addr); 86 87 err: 88 (void) close(s); 89 90 /* No error (string) to return. */ 91 return (errstr); 92 } 93 94 /* end */ 95