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/*-
* Copyright (c) 2010 Bjoern A. Zeeb <bz@FreeBSD.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include "findsaddr.h"
#include "traceroute.h"
/*
* Return the source address for the given destination address.
*
* This makes use of proper source address selection in the FreeBSD kernel
* even taking jails into account (sys/netinet/in_pcb.c:in_pcbladdr()).
* We open a UDP socket, and connect to the destination, letting the kernel
* do the bind and then read the source IPv4 address using getsockname(2).
* This has multiple advantages: no need to do PF_ROUTE operations possibly
* needing special privileges, jails properly taken into account and most
* important - getting the result the kernel would give us rather than
* best-guessing ourselves.
*/
const char *
findsaddr(register const struct sockaddr_in *to,
register struct sockaddr_in *from)
{
const char *errstr;
struct sockaddr_in cto, cfrom;
int s;
socklen_t len;
s = socket(AF_INET, SOCK_DGRAM, 0);
if (s == -1)
return ("failed to open DGRAM socket for src addr selection.");
errstr = NULL;
len = sizeof(struct sockaddr_in);
memcpy(&cto, to, len);
cto.sin_port = htons(65535); /* Dummy port for connect(2). */
if (connect(s, (struct sockaddr *)&cto, len) == -1) {
errstr = "failed to connect to peer for src addr selection.";
goto err;
}
if (getsockname(s, (struct sockaddr *)&cfrom, &len) == -1) {
errstr = "failed to get socket name for src addr selection.";
goto err;
}
if (len != sizeof(struct sockaddr_in) || cfrom.sin_family != AF_INET) {
errstr = "unexpected address family in src addr selection.";
goto err;
}
/* Update source address for traceroute. */
setsin(from, cfrom.sin_addr.s_addr);
err:
(void) close(s);
/* No error (string) to return. */
return (errstr);
}
/* end */
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