text: /*
   * Copyright (c) 1982, 1986, 1988, 1993
   *      The Regents of the University of California.
   * Copyright (c) 2005 Andre Oppermann, Internet Business Solutions AG.
   * 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.
   * 4. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: releng/11.0/sys/netinet/ip_options.c 298995 2016-05-03 18:05:43Z pfg $");
  
  #include "opt_ipstealth.h"
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/mbuf.h>
  #include <sys/domain.h>
  #include <sys/protosw.h>
  #include <sys/socket.h>
  #include <sys/time.h>
  #include <sys/kernel.h>
  #include <sys/syslog.h>
  #include <sys/sysctl.h>
  
  #include <net/if.h>
  #include <net/if_types.h>
  #include <net/if_var.h>
  #include <net/if_dl.h>
  #include <net/route.h>
  #include <net/netisr.h>
  #include <net/vnet.h>
  
  #include <netinet/in.h>
  #include <netinet/in_fib.h>
  #include <netinet/in_systm.h>
  #include <netinet/in_var.h>
  #include <netinet/ip.h>
  #include <netinet/in_pcb.h>
  #include <netinet/ip_var.h>
  #include <netinet/ip_options.h>
  #include <netinet/ip_icmp.h>
  #include <machine/in_cksum.h>
  
  #include <sys/socketvar.h>
  
  static VNET_DEFINE(int, ip_dosourceroute);
  SYSCTL_INT(_net_inet_ip, IPCTL_SOURCEROUTE, sourceroute,
      CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip_dosourceroute), 0,
      "Enable forwarding source routed IP packets");
  #define	V_ip_dosourceroute	VNET(ip_dosourceroute)
  
  static VNET_DEFINE(int,	ip_acceptsourceroute);
  SYSCTL_INT(_net_inet_ip, IPCTL_ACCEPTSOURCEROUTE, accept_sourceroute, 
      CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip_acceptsourceroute), 0, 
      "Enable accepting source routed IP packets");
  #define	V_ip_acceptsourceroute	VNET(ip_acceptsourceroute)
  
  VNET_DEFINE(int, ip_doopts) = 1; /* 0 = ignore, 1 = process, 2 = reject */
  SYSCTL_INT(_net_inet_ip, OID_AUTO, process_options, CTLFLAG_VNET | CTLFLAG_RW,
      &VNET_NAME(ip_doopts), 0, "Enable IP options processing ([LS]SRR, RR, TS)");
  
  static void	save_rte(struct mbuf *m, u_char *, struct in_addr);
  
  /*
   * Do option processing on a datagram, possibly discarding it if bad options
   * are encountered, or forwarding it if source-routed.
   *
   * The pass argument is used when operating in the IPSTEALTH mode to tell
   * what options to process: [LS]SRR (pass 0) or the others (pass 1).  The
   * reason for as many as two passes is that when doing IPSTEALTH, non-routing
   * options should be processed only if the packet is for us.
   *
   * Returns 1 if packet has been forwarded/freed, 0 if the packet should be
   * processed further.
   */
  int
  ip_dooptions(struct mbuf *m, int pass)
  {
  	struct ip *ip = mtod(m, struct ip *);
  	u_char *cp;
  	struct in_ifaddr *ia;
  	int opt, optlen, cnt, off, code, type = ICMP_PARAMPROB, forward = 0;
  	struct in_addr *sin, dst;
  	uint32_t ntime;
  	struct nhop4_extended nh_ext;
  	struct	sockaddr_in ipaddr = { sizeof(ipaddr), AF_INET };
  
  	/* Ignore or reject packets with IP options. */
  	if (V_ip_doopts == 0)
  		return 0;
  	else if (V_ip_doopts == 2) {
  		type = ICMP_UNREACH;
  		code = ICMP_UNREACH_FILTER_PROHIB;
  		goto bad;
  	}
  
  	dst = ip->ip_dst;
  	cp = (u_char *)(ip + 1);
  	cnt = (ip->ip_hl << 2) - sizeof (struct ip);
  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = cp[IPOPT_OPTVAL];
  		if (opt == IPOPT_EOL)
  			break;
  		if (opt == IPOPT_NOP)
  			optlen = 1;
  		else {
  			if (cnt < IPOPT_OLEN + sizeof(*cp)) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  			optlen = cp[IPOPT_OLEN];
  			if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  		}
  		switch (opt) {
  
  		default:
  			break;
  
  		/*
  		 * Source routing with record.  Find interface with current
  		 * destination address.  If none on this machine then drop if
  		 * strictly routed, or do nothing if loosely routed.  Record
  		 * interface address and bring up next address component.  If
  		 * strictly routed make sure next address is on directly
  		 * accessible net.
  		 */
  		case IPOPT_LSRR:
  		case IPOPT_SSRR:
  #ifdef IPSTEALTH
  			if (V_ipstealth && pass > 0)
  				break;
  #endif
  			if (optlen < IPOPT_OFFSET + sizeof(*cp)) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  			if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
  				code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  				goto bad;
  			}
  			ipaddr.sin_addr = ip->ip_dst;
  			if (ifa_ifwithaddr_check((struct sockaddr *)&ipaddr)
  			    == 0) {
  				if (opt == IPOPT_SSRR) {
  					type = ICMP_UNREACH;
  					code = ICMP_UNREACH_SRCFAIL;
  					goto bad;
  				}
  				if (!V_ip_dosourceroute)
  					goto nosourcerouting;
  				/*
  				 * Loose routing, and not at next destination
  				 * yet; nothing to do except forward.
  				 */
  				break;
  			}
  			off--;			/* 0 origin */
  			if (off > optlen - (int)sizeof(struct in_addr)) {
  				/*
  				 * End of source route.  Should be for us.
  				 */
  				if (!V_ip_acceptsourceroute)
  					goto nosourcerouting;
  				save_rte(m, cp, ip->ip_src);
  				break;
  			}
  #ifdef IPSTEALTH
  			if (V_ipstealth)
  				goto dropit;
  #endif
  			if (!V_ip_dosourceroute) {
  				if (V_ipforwarding) {
  					char buf[16]; /* aaa.bbb.ccc.ddd\0 */
  					/*
  					 * Acting as a router, so generate
  					 * ICMP
  					 */
  nosourcerouting:
  					strcpy(buf, inet_ntoa(ip->ip_dst));
  					log(LOG_WARNING, 
  					    "attempted source route from %s to %s\n",
  					    inet_ntoa(ip->ip_src), buf);
  					type = ICMP_UNREACH;
  					code = ICMP_UNREACH_SRCFAIL;
  					goto bad;
  				} else {
  					/*
  					 * Not acting as a router, so
  					 * silently drop.
  					 */
  #ifdef IPSTEALTH
  dropit:
  #endif
  					IPSTAT_INC(ips_cantforward);
  					m_freem(m);
  					return (1);
  				}
  			}
  
  			/*
  			 * locate outgoing interface
  			 */
  			(void)memcpy(&ipaddr.sin_addr, cp + off,
  			    sizeof(ipaddr.sin_addr));
  
  			type = ICMP_UNREACH;
  			code = ICMP_UNREACH_SRCFAIL;
  
  			if (opt == IPOPT_SSRR) {
  #define	INA	struct in_ifaddr *
  #define	SA	struct sockaddr *
  			    ia = (INA)ifa_ifwithdstaddr((SA)&ipaddr,
  					    RT_ALL_FIBS);
  			    if (ia == NULL)
  				    ia = (INA)ifa_ifwithnet((SA)&ipaddr, 0,
  						    RT_ALL_FIBS);
  				if (ia == NULL)
  					goto bad;
  
  				memcpy(cp + off, &(IA_SIN(ia)->sin_addr),
  				    sizeof(struct in_addr));
  				ifa_free(&ia->ia_ifa);
  			} else {
  				/* XXX MRT 0 for routing */
  				if (fib4_lookup_nh_ext(M_GETFIB(m),
  				    ipaddr.sin_addr, 0, 0, &nh_ext) != 0)
  					goto bad;
  
  				memcpy(cp + off, &nh_ext.nh_src,
  				    sizeof(struct in_addr));
  			}
  
  			ip->ip_dst = ipaddr.sin_addr;
  			cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  			/*
  			 * Let ip_intr's mcast routing check handle mcast pkts
  			 */
  			forward = !IN_MULTICAST(ntohl(ip->ip_dst.s_addr));
  			break;
  
  		case IPOPT_RR:
  #ifdef IPSTEALTH
  			if (V_ipstealth && pass == 0)
  				break;
  #endif
  			if (optlen < IPOPT_OFFSET + sizeof(*cp)) {
  				code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  				goto bad;
  			}
  			if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
  				code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  				goto bad;
  			}
  			/*
  			 * If no space remains, ignore.
  			 */
  			off--;			/* 0 origin */
  			if (off > optlen - (int)sizeof(struct in_addr))
  				break;
  			(void)memcpy(&ipaddr.sin_addr, &ip->ip_dst,
  			    sizeof(ipaddr.sin_addr));
  			/*
  			 * Locate outgoing interface; if we're the
  			 * destination, use the incoming interface (should be
  			 * same).
  			 */
  			if ((ia = (INA)ifa_ifwithaddr((SA)&ipaddr)) != NULL) {
  				memcpy(cp + off, &(IA_SIN(ia)->sin_addr),
  				    sizeof(struct in_addr));
  				ifa_free(&ia->ia_ifa);
  			} else if (fib4_lookup_nh_ext(M_GETFIB(m),
  			    ipaddr.sin_addr, 0, 0, &nh_ext) == 0) {
  				memcpy(cp + off, &nh_ext.nh_src,
  				    sizeof(struct in_addr));
  			} else {
  				type = ICMP_UNREACH;
  				code = ICMP_UNREACH_HOST;
  				goto bad;
  			}
  			cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  			break;
  
  		case IPOPT_TS:
  #ifdef IPSTEALTH
  			if (V_ipstealth && pass == 0)
  				break;
  #endif
  			code = cp - (u_char *)ip;
  			if (optlen < 4 || optlen > 40) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  			if ((off = cp[IPOPT_OFFSET]) < 5) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  			if (off > optlen - (int)sizeof(int32_t)) {
  				cp[IPOPT_OFFSET + 1] += (1 << 4);
  				if ((cp[IPOPT_OFFSET + 1] & 0xf0) == 0) {
  					code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  					goto bad;
  				}
  				break;
  			}
  			off--;				/* 0 origin */
  			sin = (struct in_addr *)(cp + off);
  			switch (cp[IPOPT_OFFSET + 1] & 0x0f) {
  
  			case IPOPT_TS_TSONLY:
  				break;
  
  			case IPOPT_TS_TSANDADDR:
  				if (off + sizeof(uint32_t) +
  				    sizeof(struct in_addr) > optlen) {
  					code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  					goto bad;
  				}
  				ipaddr.sin_addr = dst;
  				ia = (INA)ifaof_ifpforaddr((SA)&ipaddr,
  							    m->m_pkthdr.rcvif);
  				if (ia == NULL)
  					continue;
  				(void)memcpy(sin, &IA_SIN(ia)->sin_addr,
  				    sizeof(struct in_addr));
  				ifa_free(&ia->ia_ifa);
  				cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  				off += sizeof(struct in_addr);
  				break;
  
  			case IPOPT_TS_PRESPEC:
  				if (off + sizeof(uint32_t) +
  				    sizeof(struct in_addr) > optlen) {
  					code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  					goto bad;
  				}
  				(void)memcpy(&ipaddr.sin_addr, sin,
  				    sizeof(struct in_addr));
  				if (ifa_ifwithaddr_check((SA)&ipaddr) == 0)
  					continue;
  				cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  				off += sizeof(struct in_addr);
  				break;
  
  			default:
  				code = &cp[IPOPT_OFFSET + 1] - (u_char *)ip;
  				goto bad;
  			}
  			ntime = iptime();
  			(void)memcpy(cp + off, &ntime, sizeof(uint32_t));
  			cp[IPOPT_OFFSET] += sizeof(uint32_t);
  		}
  	}
  	if (forward && V_ipforwarding) {
  		ip_forward(m, 1);
  		return (1);
  	}
  	return (0);
  bad:
  	icmp_error(m, type, code, 0, 0);
  	IPSTAT_INC(ips_badoptions);
  	return (1);
  }
  
  /*
   * Save incoming source route for use in replies, to be picked up later by
   * ip_srcroute if the receiver is interested.
   */
  static void
  save_rte(struct mbuf *m, u_char *option, struct in_addr dst)
  {
  	unsigned olen;
  	struct ipopt_tag *opts;
  
  	opts = (struct ipopt_tag *)m_tag_get(PACKET_TAG_IPOPTIONS,
  	    sizeof(struct ipopt_tag), M_NOWAIT);
  	if (opts == NULL)
  		return;
  
  	olen = option[IPOPT_OLEN];
  	if (olen > sizeof(opts->ip_srcrt) - (1 + sizeof(dst))) {
  		m_tag_free((struct m_tag *)opts);
  		return;
  	}
  	bcopy(option, opts->ip_srcrt.srcopt, olen);
  	opts->ip_nhops = (olen - IPOPT_OFFSET - 1) / sizeof(struct in_addr);
  	opts->ip_srcrt.dst = dst;
  	m_tag_prepend(m, (struct m_tag *)opts);
  }
  
  /*
   * Retrieve incoming source route for use in replies, in the same form used
   * by setsockopt.  The first hop is placed before the options, will be
   * removed later.
   */
  struct mbuf *
  ip_srcroute(struct mbuf *m0)
  {
  	struct in_addr *p, *q;
  	struct mbuf *m;
  	struct ipopt_tag *opts;
  
  	opts = (struct ipopt_tag *)m_tag_find(m0, PACKET_TAG_IPOPTIONS, NULL);
  	if (opts == NULL)
  		return (NULL);
  
  	if (opts->ip_nhops == 0)
  		return (NULL);
  	m = m_get(M_NOWAIT, MT_DATA);
  	if (m == NULL)
  		return (NULL);
  
  #define OPTSIZ	(sizeof(opts->ip_srcrt.nop) + sizeof(opts->ip_srcrt.srcopt))
  
  	/* length is (nhops+1)*sizeof(addr) + sizeof(nop + srcrt header) */
  	m->m_len = opts->ip_nhops * sizeof(struct in_addr) +
  	    sizeof(struct in_addr) + OPTSIZ;
  
  	/*
  	 * First, save first hop for return route.
  	 */
  	p = &(opts->ip_srcrt.route[opts->ip_nhops - 1]);
  	*(mtod(m, struct in_addr *)) = *p--;
  
  	/*
  	 * Copy option fields and padding (nop) to mbuf.
  	 */
  	opts->ip_srcrt.nop = IPOPT_NOP;
  	opts->ip_srcrt.srcopt[IPOPT_OFFSET] = IPOPT_MINOFF;
  	(void)memcpy(mtod(m, caddr_t) + sizeof(struct in_addr),
  	    &(opts->ip_srcrt.nop), OPTSIZ);
  	q = (struct in_addr *)(mtod(m, caddr_t) +
  	    sizeof(struct in_addr) + OPTSIZ);
  #undef OPTSIZ
  	/*
  	 * Record return path as an IP source route, reversing the path
  	 * (pointers are now aligned).
  	 */
  	while (p >= opts->ip_srcrt.route) {
  		*q++ = *p--;
  	}
  	/*
  	 * Last hop goes to final destination.
  	 */
  	*q = opts->ip_srcrt.dst;
  	m_tag_delete(m0, (struct m_tag *)opts);
  	return (m);
  }
  
  /*
   * Strip out IP options, at higher level protocol in the kernel.
   */
  void
  ip_stripoptions(struct mbuf *m)
  {
  	struct ip *ip = mtod(m, struct ip *);
  	int olen;
  
  	olen = (ip->ip_hl << 2) - sizeof(struct ip);
  	m->m_len -= olen;
  	if (m->m_flags & M_PKTHDR)
  		m->m_pkthdr.len -= olen;
  	ip->ip_len = htons(ntohs(ip->ip_len) - olen);
  	ip->ip_hl = sizeof(struct ip) >> 2;
  
  	bcopy((char *)ip + sizeof(struct ip) + olen, (ip + 1),
  	    (size_t )(m->m_len - sizeof(struct ip)));
  }
  
  /*
   * Insert IP options into preformed packet.  Adjust IP destination as
   * required for IP source routing, as indicated by a non-zero in_addr at the
   * start of the options.
   *
   * XXX This routine assumes that the packet has no options in place.
   */
  struct mbuf *
  ip_insertoptions(struct mbuf *m, struct mbuf *opt, int *phlen)
  {
  	struct ipoption *p = mtod(opt, struct ipoption *);
  	struct mbuf *n;
  	struct ip *ip = mtod(m, struct ip *);
  	unsigned optlen;
  
  	optlen = opt->m_len - sizeof(p->ipopt_dst);
  	if (optlen + ntohs(ip->ip_len) > IP_MAXPACKET) {
  		*phlen = 0;
  		return (m);		/* XXX should fail */
  	}
  	if (p->ipopt_dst.s_addr)
  		ip->ip_dst = p->ipopt_dst;
  	if (!M_WRITABLE(m) || M_LEADINGSPACE(m) < optlen) {
  		n = m_gethdr(M_NOWAIT, MT_DATA);
  		if (n == NULL) {
  			*phlen = 0;
  			return (m);
  		}
  		m_move_pkthdr(n, m);
  		n->m_pkthdr.rcvif = NULL;
  		n->m_pkthdr.len += optlen;
  		m->m_len -= sizeof(struct ip);
  		m->m_data += sizeof(struct ip);
  		n->m_next = m;
  		m = n;
  		m->m_len = optlen + sizeof(struct ip);
  		m->m_data += max_linkhdr;
  		bcopy(ip, mtod(m, void *), sizeof(struct ip));
  	} else {
  		m->m_data -= optlen;
  		m->m_len += optlen;
  		m->m_pkthdr.len += optlen;
  		bcopy(ip, mtod(m, void *), sizeof(struct ip));
  	}
  	ip = mtod(m, struct ip *);
  	bcopy(p->ipopt_list, ip + 1, optlen);
  	*phlen = sizeof(struct ip) + optlen;
  	ip->ip_v = IPVERSION;
  	ip->ip_hl = *phlen >> 2;
  	ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
  	return (m);
  }
  
  /*
   * Copy options from ip to jp, omitting those not copied during
   * fragmentation.
   */
  int
  ip_optcopy(struct ip *ip, struct ip *jp)
  {
  	u_char *cp, *dp;
  	int opt, optlen, cnt;
  
  	cp = (u_char *)(ip + 1);
  	dp = (u_char *)(jp + 1);
  	cnt = (ip->ip_hl << 2) - sizeof (struct ip);
  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = cp[0];
  		if (opt == IPOPT_EOL)
  			break;
  		if (opt == IPOPT_NOP) {
  			/* Preserve for IP mcast tunnel's LSRR alignment. */
  			*dp++ = IPOPT_NOP;
  			optlen = 1;
  			continue;
  		}
  
  		KASSERT(cnt >= IPOPT_OLEN + sizeof(*cp),
  		    ("ip_optcopy: malformed ipv4 option"));
  		optlen = cp[IPOPT_OLEN];
  		KASSERT(optlen >= IPOPT_OLEN + sizeof(*cp) && optlen <= cnt,
  		    ("ip_optcopy: malformed ipv4 option"));
  
  		/* Bogus lengths should have been caught by ip_dooptions. */
  		if (optlen > cnt)
  			optlen = cnt;
  		if (IPOPT_COPIED(opt)) {
  			bcopy(cp, dp, optlen);
  			dp += optlen;
  		}
  	}
  	for (optlen = dp - (u_char *)(jp+1); optlen & 0x3; optlen++)
  		*dp++ = IPOPT_EOL;
  	return (optlen);
  }
  
  /*
   * Set up IP options in pcb for insertion in output packets.  Store in mbuf
   * with pointer in pcbopt, adding pseudo-option with destination address if
   * source routed.
   */
  int
  ip_pcbopts(struct inpcb *inp, int optname, struct mbuf *m)
  {
  	int cnt, optlen;
  	u_char *cp;
  	struct mbuf **pcbopt;
  	u_char opt;
  
  	INP_WLOCK_ASSERT(inp);
  
  	pcbopt = &inp->inp_options;
  
  	/* turn off any old options */
  	if (*pcbopt)
  		(void)m_free(*pcbopt);
  	*pcbopt = NULL;
  	if (m == NULL || m->m_len == 0) {
  		/*
  		 * Only turning off any previous options.
  		 */
  		if (m != NULL)
  			(void)m_free(m);
  		return (0);
  	}
  
  	if (m->m_len % sizeof(int32_t))
  		goto bad;
  	/*
  	 * IP first-hop destination address will be stored before actual
  	 * options; move other options back and clear it when none present.
  	 */
  	if (m->m_data + m->m_len + sizeof(struct in_addr) >= &m->m_dat[MLEN])
  		goto bad;
  	cnt = m->m_len;
  	m->m_len += sizeof(struct in_addr);
  	cp = mtod(m, u_char *) + sizeof(struct in_addr);
  	bcopy(mtod(m, void *), cp, (unsigned)cnt);
  	bzero(mtod(m, void *), sizeof(struct in_addr));
  
  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = cp[IPOPT_OPTVAL];
  		if (opt == IPOPT_EOL)
  			break;
  		if (opt == IPOPT_NOP)
  			optlen = 1;
  		else {
  			if (cnt < IPOPT_OLEN + sizeof(*cp))
  				goto bad;
  			optlen = cp[IPOPT_OLEN];
  			if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt)
  				goto bad;
  		}
  		switch (opt) {
  
  		default:
  			break;
  
  		case IPOPT_LSRR:
  		case IPOPT_SSRR:
  			/*
  			 * User process specifies route as:
  			 *
  			 *	->A->B->C->D
  			 *
  			 * D must be our final destination (but we can't
  			 * check that since we may not have connected yet).
  			 * A is first hop destination, which doesn't appear
  			 * in actual IP option, but is stored before the
  			 * options.
  			 */
  			/* XXX-BZ PRIV_NETINET_SETHDROPTS? */
  			if (optlen < IPOPT_MINOFF - 1 + sizeof(struct in_addr))
  				goto bad;
  			m->m_len -= sizeof(struct in_addr);
  			cnt -= sizeof(struct in_addr);
  			optlen -= sizeof(struct in_addr);
  			cp[IPOPT_OLEN] = optlen;
  			/*
  			 * Move first hop before start of options.
  			 */
  			bcopy((caddr_t)&cp[IPOPT_OFFSET+1], mtod(m, caddr_t),
  			    sizeof(struct in_addr));
  			/*
  			 * Then copy rest of options back
  			 * to close up the deleted entry.
  			 */
  			bcopy((&cp[IPOPT_OFFSET+1] + sizeof(struct in_addr)),
  			    &cp[IPOPT_OFFSET+1],
  			    (unsigned)cnt - (IPOPT_MINOFF - 1));
  			break;
  		}
  	}
  	if (m->m_len > MAX_IPOPTLEN + sizeof(struct in_addr))
  		goto bad;
  	*pcbopt = m;
  	return (0);
  
  bad:
  	(void)m_free(m);
  	return (EINVAL);
  }
  
  /*
   * Check for the presence of the IP Router Alert option [RFC2113]
   * in the header of an IPv4 datagram.
   *
   * This call is not intended for use from the forwarding path; it is here
   * so that protocol domains may check for the presence of the option.
   * Given how FreeBSD's IPv4 stack is currently structured, the Router Alert
   * option does not have much relevance to the implementation, though this
   * may change in future.
   * Router alert options SHOULD be passed if running in IPSTEALTH mode and
   * we are not the endpoint.
   * Length checks on individual options should already have been performed
   * by ip_dooptions() therefore they are folded under INVARIANTS here.
   *
   * Return zero if not present or options are invalid, non-zero if present.
   */
  int
  ip_checkrouteralert(struct mbuf *m)
  {
  	struct ip *ip = mtod(m, struct ip *);
  	u_char *cp;
  	int opt, optlen, cnt, found_ra;
  
  	found_ra = 0;
  	cp = (u_char *)(ip + 1);
  	cnt = (ip->ip_hl << 2) - sizeof (struct ip);
  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = cp[IPOPT_OPTVAL];
  		if (opt == IPOPT_EOL)
  			break;
  		if (opt == IPOPT_NOP)
  			optlen = 1;
  		else {
  #ifdef INVARIANTS
  			if (cnt < IPOPT_OLEN + sizeof(*cp))
  				break;
  #endif
  			optlen = cp[IPOPT_OLEN];
  #ifdef INVARIANTS
  			if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt)
  				break;
  #endif
  		}
  		switch (opt) {
  		case IPOPT_RA:
  #ifdef INVARIANTS
  			if (optlen != IPOPT_OFFSET + sizeof(uint16_t) ||
  			    (*((uint16_t *)&cp[IPOPT_OFFSET]) != 0))
  			    break;
  			else
  #endif
  			found_ra = 1;
  			break;
  		default:
  			break;
  		}
  	}
  
  	return (found_ra);
  }
  