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 *
findsaddr(register const struct sockaddr_in * to,register struct sockaddr_in * from)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