Date: Wed, 14 Nov 2001 16:05:38 -0800 From: Julian Elischer <julian@vicor-nb.com> To: net@freebsd.org Subject: Re: RFC: ipfirewall_forward patch Message-ID: <3BF306D2.3A50C4AF@vicor-nb.com> References: <3BF30699.E8CC9857@vicor-nb.com>
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Oops forgot the patch.. here it is...
Julian Elischer wrote:
>
> The following patch is expected to
> allow the forwarding of INCOMING packets to an arbitrary next hop
> controlled by the ipfw fwd command..
>
> Ipfw 'fwd' at present has teh following restriction:
>
> only packets already leaving the system can be hijacked and forwarded
> to a 2nd machine. Incoming packets can only be forwarded to local
> addresses/port combinations.
>
> This patch would allow a sequence of mchines to hijack
> a particular conforming packet and pass it allong a chain of
> these machine sot make it fall out somewhere else..
>
> the particular example I have in mind:
>
> [internet]---[A.b.c.d]-------[10.2.3.4]
> \---------[10.2.3.5]
> \---------[10.2.3.6]
> \---------[10.2.3.7]
>
> on A.b.c.d:
> ipfw add 1000 fwd 10.2.3.4 tcp from 0.0.0.0:0.0.3.0 to A.b.c.d 80 in
> recv fxp0
> ipfw add 1000 fwd 10.2.3.5 tcp from 0.0.1.0:0.0.3.0 to A.b.c.d 80 in
> recv fxp0
> ipfw add 1000 fwd 10.2.3.6 tcp from 0.0.2.0:0.0.3.0 to A.b.c.d 80 in
> recv fxp0
> ipfw add 1000 fwd 10.2.3.7 tcp from 0.0.3.0:0.0.3.0 to A.b.c.d 80 in
> recv fxp0
>
> and on each of the four machines:
> ipfw add 1000 fwd localhost tcp from any to A.b.c.d 80 in recv fxp0
>
> this is a 4 -way load sharing setup sharing
> http load across 4 machines (in our case proxies)
>
> implemented in 5 lines of ipfw.
>
> To the external world it would look as if all requests are being
> satisfied
> by A.b.c.d:80.
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diff -u ./ip_input.c /sys/netinet/ip_input.c
--- ./ip_input.c Wed Aug 29 14:41:37 2001
+++ /sys/netinet/ip_input.c Wed Nov 14 15:41:20 2001
@@ -1587,21 +1587,29 @@
int error, type = 0, code = 0;
struct mbuf *mcopy;
n_long dest;
+ struct in_addr pkt_dst;
struct ifnet *destifp;
#ifdef IPSEC
struct ifnet dummyifp;
#endif
dest = 0;
+ /*
+ * Cache the destination address of the packet; this may be
+ * changed by use of 'ipfw fwd'.
+ */
+ pkt_dst = ip_fw_fwd_addr == NULL ?
+ ip->ip_dst : ip_fw_fwd_addr->sin_addr;
+
#ifdef DIAGNOSTIC
if (ipprintfs)
printf("forward: src %lx dst %lx ttl %x\n",
- (u_long)ip->ip_src.s_addr, (u_long)ip->ip_dst.s_addr,
+ (u_long)ip->ip_src.s_addr, (u_long)pkt_dst.s_addr,
ip->ip_ttl);
#endif
- if (m->m_flags & (M_BCAST|M_MCAST) || in_canforward(ip->ip_dst) == 0) {
+ if (m->m_flags & (M_BCAST|M_MCAST) || in_canforward(pkt_dst) == 0) {
ipstat.ips_cantforward++;
m_freem(m);
return;
@@ -1620,14 +1628,14 @@
sin = (struct sockaddr_in *)&ipforward_rt.ro_dst;
if ((rt = ipforward_rt.ro_rt) == 0 ||
- ip->ip_dst.s_addr != sin->sin_addr.s_addr) {
+ pkt_dst.s_addr != sin->sin_addr.s_addr) {
if (ipforward_rt.ro_rt) {
RTFREE(ipforward_rt.ro_rt);
ipforward_rt.ro_rt = 0;
}
sin->sin_family = AF_INET;
sin->sin_len = sizeof(*sin);
- sin->sin_addr = ip->ip_dst;
+ sin->sin_addr = pkt_dst;
rtalloc_ign(&ipforward_rt, RTF_PRCLONING);
if (ipforward_rt.ro_rt == 0) {
@@ -1674,7 +1682,7 @@
if (rt->rt_ifp == m->m_pkthdr.rcvif &&
(rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0 &&
satosin(rt_key(rt))->sin_addr.s_addr != 0 &&
- ipsendredirects && !srcrt) {
+ ipsendredirects && !srcrt && !ip_fw_fwd_addr) {
#define RTA(rt) ((struct in_ifaddr *)(rt->rt_ifa))
u_long src = ntohl(ip->ip_src.s_addr);
@@ -1683,7 +1691,7 @@
if (rt->rt_flags & RTF_GATEWAY)
dest = satosin(rt->rt_gateway)->sin_addr.s_addr;
else
- dest = ip->ip_dst.s_addr;
+ dest = pkt_dst.s_addr;
/* Router requirements says to only send host redirects */
type = ICMP_REDIRECT;
code = ICMP_REDIRECT_HOST;
diff -u ./ip_output.c /sys/netinet/ip_output.c
--- ./ip_output.c Wed Jul 18 23:37:26 2001
+++ /sys/netinet/ip_output.c Wed Nov 14 15:41:14 2001
@@ -135,6 +135,7 @@
struct sockaddr_in *dst;
struct in_ifaddr *ia = NULL;
int isbroadcast, sw_csum;
+ struct in_addr pkt_dst;
#ifdef IPSEC
struct route iproute;
struct socket *so = NULL;
@@ -154,6 +155,9 @@
divert_cookie = 0;
#endif
+ pkt_dst = ip_fw_fwd_addr == NULL
+ ? ip->ip_dst : ip_fw_fwd_addr->sin_addr;
+
#if defined(IPFIREWALL) && defined(DUMMYNET)
/*
* dummynet packet are prepended a vestigial mbuf with
@@ -227,14 +231,14 @@
* and is still up. If not, free it and try again.
*/
if (ro->ro_rt && ((ro->ro_rt->rt_flags & RTF_UP) == 0 ||
- dst->sin_addr.s_addr != ip->ip_dst.s_addr)) {
+ dst->sin_addr.s_addr != pkt_dst.s_addr)) {
RTFREE(ro->ro_rt);
ro->ro_rt = (struct rtentry *)0;
}
if (ro->ro_rt == 0) {
dst->sin_family = AF_INET;
dst->sin_len = sizeof(*dst);
- dst->sin_addr = ip->ip_dst;
+ dst->sin_addr = pkt_dst;
}
/*
* If routing to interface only,
@@ -279,7 +283,7 @@
else
isbroadcast = in_broadcast(dst->sin_addr, ifp);
}
- if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
+ if (IN_MULTICAST(ntohl(pkt_dst.s_addr))) {
struct in_multi *inm;
m->m_flags |= M_MCAST;
@@ -325,7 +329,7 @@
}
}
- IN_LOOKUP_MULTI(ip->ip_dst, ifp, inm);
+ IN_LOOKUP_MULTI(pkt_dst, ifp, inm);
if (inm != NULL &&
(imo == NULL || imo->imo_multicast_loop)) {
/*
@@ -575,8 +579,9 @@
/*
* Check with the firewall...
+ * but not if we are already being fwd'd from a firewall.
*/
- if (fw_enable && ip_fw_chk_ptr) {
+ if (fw_enable && ip_fw_chk_ptr && !ip_fw_fwd_addr) {
struct sockaddr_in *old = dst;
off = (*ip_fw_chk_ptr)(&ip,
@@ -767,6 +772,7 @@
goto done;
}
+ ip_fw_fwd_addr = NULL;
pass:
m->m_pkthdr.csum_flags |= CSUM_IP;
sw_csum = m->m_pkthdr.csum_flags & ~ifp->if_hwassist;
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