On Fri, Mar 16, 2001 at 08:19:16PM +0200, Ruslan Ermilov wrote:
> Hi!
>
> First of all, I would like to commit the attached patch; it removes
> duplicate code. Please review.
>
This got already committed as part of another bugfix.
See ip_input.c, revision 1.164.
> Also, I found a nasty bug in IP routing. The new route added may not
> take immediate effect for routing decisions, because ip_forward() may
> use the cached route (rt_forwarding).
>
The attached patch fixes this.
> DEMO (only relevant routes are shown).
>
> Step 1. On a router, add a route to the network (192.168.1).
>
> : # route add -net 192.168.1 gateway
> : add net 192.168.1: gateway gateway
> :
> : # netstat -rn
> : Routing tables
> :
> : Internet:
> : Destination Gateway Flags Refs Use Netif Expire
> : 192.168.1 gateway UGSc 0 0 rl0
>
> Step 2. From some other host for which this machine is the default router,
> run ``traceroute -m 2 -n 192.168.1.1''. Observe, on the router,
> that the reference count grown on the 192.168.1 route.
>
> : # netstat -rn
> : Routing tables
> :
> : Internet:
> : Destination Gateway Flags Refs Use Netif Expire
> : 192.168.1 gateway UGSc 1 3 rl0
>
> Step 3. Add RTF_REJECT host route to the destination:
>
> : # route add 192.168.1.1 -iface lo0 -reject
> : add host 192.168.1.1: gateway lo0
> : # netstat -rn
> : Routing tables
> :
> : Internet:
> : Destination Gateway Flags Refs Use Netif Expire
> : 192.168.1 gateway UGSc 1 3 rl0
> : 192.168.1.1 lo0 UHRS 0 0 lo0
>
> Step 4. The fun begins. What you would expect if you run traceroute to
> 192.168.1.1 again? Obviously host route should take precedence
> over network route, and I expected ICMP Destination Unreachable.
> But... what's a hell? the new route did not take immediate effect,
> traceroute succeeded (192.168.1.1 still has zero refcound and use):
>
> : # netstat -rn
> : Routing tables
> :
> : Internet:
> : Destination Gateway Flags Refs Use Netif Expire
> : 192.168.1 gateway UGSc 1 6 rl0
> : 192.168.1.1 lo0 UHRS 0 0 lo0
>
> Step 5. The fun continues. From another host, run traceroute to another
> destination (to help router change rt_forward.ro_dst).
> traceroute -m 2 -n 192.168.1.2:
>
> : # netstat -rn
> : Routing tables
> :
> : Internet:
> : Destination Gateway Flags Refs Use Netif Expire
> : 192.168.1 gateway UGSc 1 9 rl0
> : 192.168.1.1 lo0 UHRS 0 0 lo0
>
> Step 6. Run traceroute again to 192.168.1.1. The fun ends.
>
>
> The solution I found so far is to unstaticize the ``rt_forward'', and
> invalidate the rt_forward.ro_rt in in_addroute() (in_rmx.c). Any better
> ideas?
--
Ruslan Ermilov Oracle Developer/DBA,
[EMAIL PROTECTED] Sunbay Software AG,
[EMAIL PROTECTED] FreeBSD committer,
+380.652.512.251 Simferopol, Ukraine
http://www.FreeBSD.org The Power To Serve
http://www.oracle.com Enabling The Information Age
Index: in_rmx.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/in_rmx.c,v
retrieving revision 1.38
diff -u -p -r1.38 in_rmx.c
--- in_rmx.c 2001/03/15 14:52:12 1.38
+++ in_rmx.c 2001/03/18 15:08:25
@@ -54,6 +54,7 @@
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_var.h>
+#include <netinet/ip_var.h>
extern int in_inithead __P((void **head, int off));
@@ -137,6 +138,16 @@ in_addroute(void *v_arg, void *n_arg, st
RTFREE(rt2);
}
}
+
+ /*
+ * If the new route successfully added, and we are forwarding,
+ * and there is a cached route, free it.
+ */
+ if (ret != NULL && ipforwarding && ipforward_rt.ro_rt) {
+ RTFREE(ipforward_rt.ro_rt);
+ ipforward_rt.ro_rt = 0;
+ }
+
return ret;
}
Index: ip_input.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/ip_input.c,v
retrieving revision 1.164
diff -u -p -r1.164 ip_input.c
--- ip_input.c 2001/03/18 13:04:07 1.164
+++ ip_input.c 2001/03/18 15:08:26
@@ -257,7 +257,7 @@ ip_init()
}
static struct sockaddr_in ipaddr = { sizeof(ipaddr), AF_INET };
-static struct route ipforward_rt;
+struct route ipforward_rt;
/*
* Ip input routine. Checksum and byte swap header. If fragmented
Index: ip_var.h
===================================================================
RCS file: /home/ncvs/src/sys/netinet/ip_var.h,v
retrieving revision 1.53
diff -u -p -r1.53 ip_var.h
--- ip_var.h 2001/03/16 20:00:53 1.53
+++ ip_var.h 2001/03/18 15:08:26
@@ -141,6 +141,7 @@ extern struct ipstat ipstat;
extern u_short ip_id; /* ip packet ctr, for ids */
extern int ip_defttl; /* default IP ttl */
extern int ipforwarding; /* ip forwarding */
+extern struct route ipforward_rt; /* ip forwarding cached route */
extern u_char ip_protox[];
extern struct socket *ip_rsvpd; /* reservation protocol daemon */
extern struct socket *ip_mrouter; /* multicast routing daemon */
