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