ip_options.c

Go to the documentation of this file.

/*
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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.
 * 3. 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("$FreeBSD$");
 
#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/route/nhop.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>
 
VNET_DEFINE_STATIC(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)
 
VNET_DEFINE_STATIC(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 nhop_object *nh;
        struct  sockaddr_in ipaddr = { sizeof(ipaddr), AF_INET };
 
        NET_EPOCH_ASSERT();
 
        /* 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 srcbuf[INET_ADDRSTRLEN];
                                        char dstbuf[INET_ADDRSTRLEN];
 
                                        /*
                                         * Acting as a router, so generate
                                         * ICMP
                                         */
nosourcerouting:
                                        log(LOG_WARNING,
                                            "attempted source route from %s "
                                            "to %s\n",
                                            inet_ntoa_r(ip->ip_src, srcbuf),
                                            inet_ntoa_r(ip->ip_dst, dstbuf));
                                        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));
                        } else {
                                /* XXX MRT 0 for routing */
                                nh = fib4_lookup(M_GETFIB(m), ipaddr.sin_addr,
                                     0, NHR_NONE, 0);
                                if (nh == NULL)
                                        goto bad;
 
                                memcpy(cp + off, &(IA_SIN(nh->nh_ifa)->sin_addr),
                                    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));
                        } else if ((nh = fib4_lookup(M_GETFIB(m),
                            ipaddr.sin_addr, 0, NHR_NONE, 0)) != NULL) {
                                memcpy(cp + off, &(IA_SIN(nh->nh_ifa)->sin_addr),
                                    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));
                                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);
}