/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 2003 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. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
*/
/*
* ip_fastforward gets its speed from processing the forwarded packet to
* completion (if_output on the other side) without any queues or netisr's.
* The receiving interface DMAs the packet into memory, the upper half of
* driver calls ip_fastforward, we do our routing table lookup and directly
* send it off to the outgoing interface, which DMAs the packet to the
* network card. The only part of the packet we touch with the CPU is the
* IP header (unless there are complex firewall rules touching other parts
* of the packet, but that is up to you). We are essentially limited by bus
* bandwidth and how fast the network card/driver can set up receives and
* transmits.
*
* We handle basic errors, IP header errors, checksum errors,
* destination unreachable, fragmentation and fragmentation needed and
* report them via ICMP to the sender.
*
* Else if something is not pure IPv4 unicast forwarding we fall back to
* the normal ip_input processing path. We should only be called from
* interfaces connected to the outside world.
*
* Firewalling is fully supported including divert, ipfw fwd and ipfilter
* ipnat and address rewrite.
*
* IPSEC is not supported if this host is a tunnel broker. IPSEC is
* supported for connections to/from local host.
*
* We try to do the least expensive (in CPU ops) checks and operations
* first to catch junk with as little overhead as possible.
*
* We take full advantage of hardware support for IP checksum and
* fragmentation offloading.
*/
/*
* Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
* is being followed here.
*/
#include <sys/cdefs.h>
#include "opt_ipstealth.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/sdt.h>
#include <sys/socket.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/if_private.h>
#include <net/pfil.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/vnet.h>
#include <netinet/in.h>
#include <netinet/in_fib.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_options.h>
#include <machine/in_cksum.h>
#define V_ipsendredirects VNET(ipsendredirects)
static struct mbuf *
ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len,
struct in_addr *osrc, struct in_addr *newgw)
{
struct in_ifaddr *nh_ia;
struct mbuf *mcopy;
KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m));
/*
* Only send a redirect if:
* - Redirects are not disabled (must be checked by caller),
* - We have not applied NAT (must be checked by caller as possible),
* - Neither a MCAST or BCAST packet (must be checked by caller)
* [RFC1009 Appendix A.2].
* - The packet does not do IP source routing or having any other
* IP options (this case was handled already by ip_input() calling
* ip_dooptions() [RFC792, p13],
* - The packet is being forwarded out the same physical interface
* that it was received from [RFC1812, 5.2.7.2].
*/
/*
* - The forwarding route was not created by a redirect
* [RFC1812, 5.2.7.2], or
* if it was to follow a default route (see below).
* - The next-hop is reachable by us [RFC1009 Appendix A.2].
*/
if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT |
NHF_BLACKHOLE | NHF_REJECT)) != 0)
return (NULL);
/* Get the new gateway. */
if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET)
return (NULL);
newgw->s_addr = nh->gw4_sa.sin_addr.s_addr;
/*
* - The resulting forwarding destination is not "This host on this
* network" [RFC1122, Section 3.2.1.3] (default route check above).
*/
if (newgw->s_addr == 0)
return (NULL);
/*
* - We know how to reach the sender and the source address is
* directly connected to us [RFC792, p13].
* + The new gateway address and the source address are on the same
* subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2].
* NB: if you think multiple logical subnets on the same wire should
* receive redirects read [RFC1812, APPENDIX C (14->15)].
*/
nh_ia = (struct in_ifaddr *)nh->nh_ifa;
if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet)
return (NULL);
/* Prepare for sending the redirect. */
/*
* Make a copy of as much as we need of the packet as the original
* one will be forwarded but we need (a portion) for icmp_error().
*/
mcopy = m_gethdr(M_NOWAIT, m->m_type);
if (mcopy == NULL)
return (NULL);
if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) {
/*
* It's probably ok if the pkthdr dup fails (because
* the deep copy of the tag chain failed), but for now
* be conservative and just discard the copy since
* code below may some day want the tags.
*/
m_free(mcopy);
return (NULL);
}
mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy));
mcopy->m_pkthdr.len = mcopy->m_len;
m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
return (mcopy);
}
static int
ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m)
{
struct nhop_object *nh;
nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE,
m->m_pkthdr.flowid);
if (nh == NULL) {
IPSTAT_INC(ips_noroute);
IPSTAT_INC(ips_cantforward);
icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
return (EHOSTUNREACH);
}
/*
* Drop blackholed traffic and directed broadcasts.
*/
if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
IPSTAT_INC(ips_cantforward);
m_freem(m);
return (EHOSTUNREACH);
}
if (nh->nh_flags & NHF_REJECT) {
IPSTAT_INC(ips_cantforward);
icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
return (EHOSTUNREACH);
}
*pnh = nh;
return (0);
}
/*
* Try to forward a packet based on the destination address.
* This is a fast path optimized for the plain forwarding case.
* If the packet is handled (and consumed) here then we return NULL;
* otherwise mbuf is returned and the packet should be delivered
* to ip_input for full processing.
*/
struct mbuf *
ip_tryforward(struct mbuf *m)
{
struct ip *ip;
struct mbuf *m0 = NULL;
struct nhop_object *nh = NULL;
struct route ro;
struct sockaddr_in *dst;
const struct sockaddr *gw;
struct in_addr dest, odest, rtdest, osrc;
uint16_t ip_len, ip_off;
int error = 0;
struct m_tag *fwd_tag = NULL;
struct mbuf *mcopy = NULL;
struct in_addr redest;
/*
* Are we active and forwarding packets?
*/
M_ASSERTVALID(m);
M_ASSERTPKTHDR(m);
/*
* Only IP packets without options
*/
ip = mtod(m, struct ip *);
if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
if (V_ip_doopts == 1)
return m;
else if (V_ip_doopts == 2) {
icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
0, 0);
return NULL; /* mbuf already free'd */
}
/* else ignore IP options and continue */
}
/*
* Only unicast IP, not from loopback, no L2 or IP broadcast,
* no multicast, no INADDR_ANY
*
* XXX: Probably some of these checks could be direct drop
* conditions. However it is not clear whether there are some
* hacks or obscure behaviours which make it necessary to
* let ip_input handle it. We play safe here and let ip_input
* deal with it until it is proven that we can directly drop it.
*/
if ((m->m_flags & (M_BCAST|M_MCAST)) ||
(m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
ip->ip_src.s_addr == INADDR_ANY ||
ip->ip_dst.s_addr == INADDR_ANY )
return m;
/*
* Is it for a local address on this host?
*/
if (in_localip(ip->ip_dst))
return m;
IPSTAT_INC(ips_total);
/*
* Step 3: incoming packet firewall processing
*/
odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
osrc.s_addr = ip->ip_src.s_addr;
/*
* Run through list of ipfilter hooks for input packets
*/
if (!PFIL_HOOKED_IN(V_inet_pfil_head))
goto passin;
if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif,
NULL) != PFIL_PASS)
goto drop;
M_ASSERTVALID(m);
M_ASSERTPKTHDR(m);
ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
dest.s_addr = ip->ip_dst.s_addr;
/*
* Destination address changed?
*/
if (odest.s_addr != dest.s_addr) {
/*
* Is it now for a local address on this host?
*/
if (in_localip(dest))
goto forwardlocal;
/*
* Go on with new destination address
*/
}
if (m->m_flags & M_FASTFWD_OURS) {
/*
* ipfw changed it for a local address on this host.
*/
goto forwardlocal;
}
passin:
/*
* Step 4: decrement TTL and look up route
*/
/*
* Check TTL
*/
#ifdef IPSTEALTH
if (!V_ipstealth) {
#endif
if (ip->ip_ttl <= IPTTLDEC) {
icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
return NULL; /* mbuf already free'd */
}
/*
* Decrement the TTL and incrementally change the IP header checksum.
* Don't bother doing this with hw checksum offloading, it's faster
* doing it right here.
*/
ip->ip_ttl -= IPTTLDEC;
if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
ip->ip_sum -= ~htons(IPTTLDEC << 8);
else
ip->ip_sum += htons(IPTTLDEC << 8);
#ifdef IPSTEALTH
}
#endif
/*
* Next hop forced by pfil(9) hook?
*/
if ((m->m_flags & M_IP_NEXTHOP) &&
((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
/*
* Now we will find route to forced destination.
*/
dest.s_addr = ((struct sockaddr_in *)
(fwd_tag + 1))->sin_addr.s_addr;
m_tag_delete(m, fwd_tag);
m->m_flags &= ~M_IP_NEXTHOP;
}
/*
* Find route to destination.
*/
if (ip_findroute(&nh, dest, m) != 0)
return (NULL); /* icmp unreach already sent */
/*
* Avoid second route lookup by caching destination.
*/
rtdest.s_addr = dest.s_addr;
/*
* Step 5: outgoing firewall packet processing
*/
if (!PFIL_HOOKED_OUT(V_inet_pfil_head))
goto passout;
if (pfil_mbuf_out(V_inet_pfil_head, &m, nh->nh_ifp,
NULL) != PFIL_PASS)
goto drop;
M_ASSERTVALID(m);
M_ASSERTPKTHDR(m);
ip = mtod(m, struct ip *);
dest.s_addr = ip->ip_dst.s_addr;
/*
* Destination address changed?
*/
if (m->m_flags & M_IP_NEXTHOP)
fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
else
fwd_tag = NULL;
if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
/*
* Is it now for a local address on this host?
*/
if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
forwardlocal:
/*
* Return packet for processing by ip_input().
*/
m->m_flags |= M_FASTFWD_OURS;
return (m);
}
/*
* Redo route lookup with new destination address
*/
if (fwd_tag) {
dest.s_addr = ((struct sockaddr_in *)
(fwd_tag + 1))->sin_addr.s_addr;
m_tag_delete(m, fwd_tag);
m->m_flags &= ~M_IP_NEXTHOP;
}
if (dest.s_addr != rtdest.s_addr &&
ip_findroute(&nh, dest, m) != 0)
return (NULL); /* icmp unreach already sent */
}
passout:
/*
* Step 6: send off the packet
*/
ip_len = ntohs(ip->ip_len);
ip_off = ntohs(ip->ip_off);
bzero(&ro, sizeof(ro));
dst = (struct sockaddr_in *)&ro.ro_dst;
dst->sin_family = AF_INET;
dst->sin_len = sizeof(*dst);
dst->sin_addr = dest;
if (nh->nh_flags & NHF_GATEWAY) {
gw = &nh->gw_sa;
ro.ro_flags |= RT_HAS_GW;
} else
gw = (const struct sockaddr *)dst;
/* Handle redirect case. */
redest.s_addr = 0;
if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr &&
nh->nh_ifp == m->m_pkthdr.rcvif)
mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest);
/*
* Check if packet fits MTU or if hardware will fragment for us
*/
if (ip_len <= nh->nh_mtu) {
/*
* Avoid confusing lower layers.
*/
m_clrprotoflags(m);
/*
* Send off the packet via outgoing interface
*/
IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL);
error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro);
} else {
/*
* Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
*/
if (ip_off & IP_DF) {
IPSTAT_INC(ips_cantfrag);
icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
0, nh->nh_mtu);
goto consumed;
} else {
/*
* We have to fragment the packet
*/
m->m_pkthdr.csum_flags |= CSUM_IP;
if (ip_fragment(ip, &m, nh->nh_mtu,
nh->nh_ifp->if_hwassist) != 0)
goto drop;
KASSERT(m != NULL, ("null mbuf and no error"));
/*
* Send off the fragments via outgoing interface
*/
error = 0;
do {
m0 = m->m_nextpkt;
m->m_nextpkt = NULL;
/*
* Avoid confusing lower layers.
*/
m_clrprotoflags(m);
IP_PROBE(send, NULL, NULL,
mtod(m, struct ip *), nh->nh_ifp,
mtod(m, struct ip *), NULL);
error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
gw, &ro);
if (error)
break;
} while ((m = m0) != NULL);
if (error) {
/* Reclaim remaining fragments */
for (m = m0; m; m = m0) {
m0 = m->m_nextpkt;
m_freem(m);
}
} else
IPSTAT_INC(ips_fragmented);
}
}
if (error != 0)
IPSTAT_INC(ips_odropped);
else {
IPSTAT_INC(ips_forward);
IPSTAT_INC(ips_fastforward);
}
/* Send required redirect */
if (mcopy != NULL) {
icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0);
mcopy = NULL; /* Was consumed by callee. */
}
consumed:
if (mcopy != NULL)
m_freem(mcopy);
return NULL;
drop:
if (m)
m_freem(m);
return NULL;
}
