Date: Fri, 19 May 1995 12:15:18 +0800 (WST) From: Peter Wemm <peter@haywire.dialix.com> To: hackers@FreeBSD.org Subject: More on "Hmm.. Strange..." Message-ID: <Pine.SV4.3.91.950519105053.23362C-100000@haywire.DIALix.COM>
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Well. Something really wierd is going on. I think it's a bug, and
potentially serious, as it makes gated practically useless..
There is some interaction with SO_REUSEADDR.. I have not figured out why
yet, but take the following program (chopped down rwhod.c) which
deterministically demonstrates the problem.
-----------
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/signal.h>
#include <sys/ioctl.h>
#include <sys/sysctl.h>
#include <net/if.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <netinet/in.h>
#include <protocols/rwhod.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <paths.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <utmp.h>
int
main(argc, argv)
int argc;
char *argv[];
{
int on = 1;
char *cp;
struct sockaddr_in sin;
struct servent *sp;
struct hostent *hp;
int s;
sp = getservbyname("router", "udp");
if (sp == NULL) {
fprintf(stderr, "rwhod: man/who: unknown service\n");
exit(1);
}
if ((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
syslog(LOG_ERR, "socket: %m");
exit(1);
}
if (setsockopt(s, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on)) < 0) {
syslog(LOG_ERR, "setsockopt SO_BROADCAST: %m");
exit(1);
}
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_port = sp->s_port;
#if 0
if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
syslog(LOG_ERR, "bind: %m");
exit(1);
}
#endif
hp = gethostbyname(argv[1]);
if (hp == NULL) {
fprintf(stderr, "rwhod: %s unknown host\n", argv[1]);
exit(1);
}
sin.sin_addr.s_addr = *((long *)hp->h_addr);
(void)sendto(s, "hello", 5, 0, (struct sockaddr *)&sin, sizeof(sin));
(void)sendto(s, "hellothere", 10, SO_REUSEADDR, (struct sockaddr *)&sin,
sizeof(sin));
}
The first sendto() always works, and the second sendto() sends the
datagram to the *wrong interface*!
Just a (yet another) reminder of the config:
ed0: flags=8963<UP,BROADCAST,NOTRAILERS,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet 192.203.228.69 netmask 0xfffffff0 broadcast 192.203.228.79
ppp0: flags=151<UP,POINTOPOINT,RUNNING,PROMISC> mtu 1500
inet 192.203.228.69 --> 192.203.228.3 netmask 0xfffffff0
In this case, in the above program, the first sendto() sends a 5 byte
broadcast to 192.203.228.79 on the ethernet (correct!). The second
sendto(), the 10 byte datagram gets sent to 192.203.228.79 on the PPP
interface!!!!! (of which the remote sends it straight back! after a
game of ping-pong, an icmp timer exceeded message is sent).
I recompiled gated to not turn on SO_REUSEADDR at all, but there's some
kernel glue that appears to turn it on inside the kernel if the socket is
implicated in any multicasting (as gated does with OSPF and RIP-II)..
I'm not awake enough to interpret the code to understand what's going
on.. But I thought I'd mention it in case somebody else might recognised
it, or knew what was going wrong.
Any suggestions what to try next?
-Peter
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