110 lines
3.3 KiB
C
110 lines
3.3 KiB
C
/*
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* Routine to disable IP-level socket options. This code was taken from 4.4BSD
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* rlogind and kernel source, but all mistakes in it are my fault.
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*
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* Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
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*/
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#ifndef lint
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static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
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#endif
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#include <sys/types.h>
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#include <sys/param.h>
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#include <netinet/in.h>
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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#include <netdb.h>
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#include <stdio.h>
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#include <syslog.h>
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#ifndef IPOPT_OPTVAL
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#define IPOPT_OPTVAL 0
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#define IPOPT_OLEN 1
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#endif
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#include "tcpd.h"
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#define BUFFER_SIZE 512 /* Was: BUFSIZ */
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/* fix_options - get rid of IP-level socket options */
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fix_options(request)
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struct request_info *request;
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{
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#ifdef IP_OPTIONS
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unsigned char optbuf[BUFFER_SIZE / 3], *cp;
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char lbuf[BUFFER_SIZE], *lp;
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int optsize = sizeof(optbuf), ipproto;
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struct protoent *ip;
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int fd = request->fd;
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unsigned int opt;
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int optlen;
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struct in_addr dummy;
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if ((ip = getprotobyname("ip")) != 0)
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ipproto = ip->p_proto;
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else
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ipproto = IPPROTO_IP;
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if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
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&& optsize != 0) {
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/*
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* Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
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* address to the result IP options list when source routing options
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* are present (see <netinet/ip_var.h>), but produces no output for
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* other IP options. Solaris 2.x getsockopt() does produce output for
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* non-routing IP options, and uses the same format as BSD even when
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* the space for the destination address is unused. The code below
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* does the right thing with 4.[34]BSD derivatives and Solaris 2, but
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* may occasionally miss source routing options on incompatible
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* systems such as Linux. Their choice.
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*
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* Look for source routing options. Drop the connection when one is
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* found. Just wiping the IP options is insufficient: we would still
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* help the attacker by providing a real TCP sequence number, and the
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* attacker would still be able to send packets (blind spoofing). I
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* discussed this attack with Niels Provos, half a year before the
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* attack was described in open mailing lists.
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*
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* It would be cleaner to just return a yes/no reply and let the caller
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* decide how to deal with it. Resident servers should not terminate.
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* However I am not prepared to make changes to internal interfaces
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* on short notice.
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*/
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#define ADDR_LEN sizeof(dummy.s_addr)
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for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
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opt = cp[IPOPT_OPTVAL];
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if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
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syslog(LOG_WARNING,
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"refused connect from %s with IP source routing options",
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eval_client(request));
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shutdown(fd, 2);
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return;
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}
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if (opt == IPOPT_EOL)
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break;
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if (opt == IPOPT_NOP) {
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optlen = 1;
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} else {
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optlen = cp[IPOPT_OLEN];
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if (optlen <= 0) /* Do not loop! */
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break;
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}
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}
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lp = lbuf;
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for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
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sprintf(lp, " %2.2x", *cp);
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syslog(LOG_NOTICE,
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"connect from %s with IP options (ignored):%s",
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eval_client(request), lbuf);
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if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
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syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
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shutdown(fd, 2);
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}
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}
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#endif
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}
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