Subject: Re: [IPV4] LVS: Allow to send ICMP unreachable responses when real-servers are removed

From: Patrick McHardy <[email-masked]>
Date: Mon, 14 May 2007 19:41:48 +0200

Janusz Krzysztofik wrote:
> Patrick McHardy wrote:
> 
>> Janusz Krzysztofik wrote:
>>
>>> ... ICMP port unreachable messages are not generated inside
>>> IPVS code, they are just sent, with help of the patch in question, from
>>> udp_input() or netfilter REJECT.
>>
>>
>> Both use icmp_send(), which should always pick a local source, so I
>> don't understand why this change was needed. Could you describe
>> the specific case when the packet generated by icmp_send() does
>> not have a local source?
> 
> 
> Yes, it happens when a packet with a non-local destination IP address is
> routed localy in order to reach ip_vs_in(), but is not catched there
> because of no associated connection and no matching service, so it is
> passed through and ends up in udp_input(). Then, inside udp_input(),
> icmp_send() is invoked with original non-local destination IP as source
> address.

So you're adding a local route for non-local destination and the
address selection in icmp_send() uses the original destination
address as source because the route has RTCF_LOCAL set, resulting
in an error in ip_route_output_slow().

If thats correct than this patch should also work, it changes
icmp_send() to check if the original destination address is
non-local when deciding whether to pick a new address (and
reverts the routing changes).

Signed-off-by: Patrick McHardy <[email-masked]>
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index d38cbba..b964863 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -513,7 +513,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 	 */
 
 	saddr = iph->daddr;
-	if (!(rt->rt_flags & RTCF_LOCAL)) {
+	if (inet_addr_type(saddr) != RTN_LOCAL) {
 		if (sysctl_icmp_errors_use_inbound_ifaddr)
 			saddr = inet_select_addr(skb_in->dev, 0, RT_SCOPE_LINK);
 		else
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index cb76e3c..df9fe4f 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2396,7 +2396,7 @@ static int ip_route_output_slow(struct rtable **rp, const struct flowi *oldflp)
 
 		/* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
 		dev_out = ip_dev_find(oldflp->fl4_src);
-		if ((dev_out == NULL) && !(sysctl_ip_nonlocal_bind))
+		if (dev_out == NULL)
 			goto out;
 
 		/* I removed check for oif == dev_out->oif here.
@@ -2407,7 +2407,7 @@ static int ip_route_output_slow(struct rtable **rp, const struct flowi *oldflp)
 		      of another iface. --ANK
 		 */
 
-		if (dev_out && oldflp->oif == 0
+		if (oldflp->oif == 0
 		    && (MULTICAST(oldflp->fl4_dst) || oldflp->fl4_dst == htonl(0xFFFFFFFF))) {
 			/* Special hack: user can direct multicasts
 			   and limited broadcast via necessary interface