Generating 'Fragment Needed but DF was Set' ICMP & Dummynet

[Alexander Motin]

Here are my patches for this problem for FreeBSD 4.8 and 5.2.
Review them please.

Alexander Motin wrote:
> I observe a strange thing. When I create dummynet pipe on output router 
> interface with lower MTU system stops to generate 'Fragment Needed but 
> DF was Set' ICMP in cases when it must. If I create this pipe on 
> incoming interface there is no problem.
> 
> I check this on many routers under 4.8 and 5.2 FreeBSD.
> 
> Is this a bug or feature? :) How pipes can be created leaving ICMP 
> generation working?

-- 
Alexander Motin
-------------- next part --------------
--- ip_dummynet.c.orig	Wed May 28 01:36:02 2003
+++ ip_dummynet.c	Sat Feb 21 12:49:11 2004
@@ -81,6 +81,7 @@
 #include <netinet/ip_fw.h>
 #include <netinet/ip_dummynet.h>
 #include <netinet/ip_var.h>
+#include <netinet/ip_icmp.h>
 
 #include <netinet/if_ether.h> /* for struct arpcom */
 #include <net/bridge.h>
@@ -407,6 +408,9 @@
 transmit_event(struct dn_pipe *pipe)
 {
     struct dn_pkt *pkt ;
+    struct mbuf *mcopy;
+    struct ip *ip;
+    int error, type, code;
 
     while ( (pkt = pipe->head) && DN_KEY_LEQ(pkt->output_time, curr_time) ) {
 	/*
@@ -426,7 +430,39 @@
 	 */
 	switch (pkt->dn_dir) {
 	case DN_TO_IP_OUT:
-	    (void)ip_output((struct mbuf *)pkt, NULL, NULL, 0, NULL, NULL);
+	    MGET(mcopy, M_DONTWAIT, pkt->dn_m->m_type);
+	    if (mcopy != NULL && !m_dup_pkthdr(mcopy, pkt->dn_m, M_DONTWAIT)) {
+		m_free(mcopy);
+		mcopy = NULL;
+	    }
+	    if (mcopy != NULL) {
+		ip = mtod(pkt->dn_m, struct ip *);
+		mcopy->m_len = imin((ip->ip_hl << 2) + 8,
+		    (int)ip->ip_len);
+		m_copydata(pkt->dn_m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
+	    }
+	    
+	    error = ip_output((struct mbuf *)pkt, NULL, NULL, 0, NULL, NULL);
+	    
+	    if (mcopy != NULL) {
+		switch (error) {
+		    case ENETUNREACH:
+		    case EHOSTUNREACH:
+		    case ENETDOWN:
+		    case EHOSTDOWN:
+			type = ICMP_UNREACH;
+		        code = ICMP_UNREACH_HOST;
+			icmp_error(mcopy, type, code, 0, pkt->ifp);
+			break;
+		    case EMSGSIZE:
+			type = ICMP_UNREACH;
+		        code = ICMP_UNREACH_NEEDFRAG;
+			icmp_error(mcopy, type, code, 0, pkt->ifp);
+			break;
+		    default:
+			m_freem(mcopy);
+		};
+	    };
 	    rt_unref (pkt->ro.ro_rt) ;
 	    break ;
 
-------------- next part --------------
--- ip_dummynet.c.orig	Mon Dec  8 11:50:54 2003
+++ ip_dummynet.c	Sat Feb 21 12:17:44 2004
@@ -73,6 +73,7 @@
 #include <netinet/ip_fw.h>
 #include <netinet/ip_dummynet.h>
 #include <netinet/ip_var.h>
+#include <netinet/ip_icmp.h>
 
 #include <netinet/if_ether.h> /* for struct arpcom */
 #include <net/bridge.h>
@@ -426,6 +427,9 @@
 transmit_event(struct dn_pipe *pipe)
 {
     struct dn_pkt *pkt ;
+    struct mbuf *mcopy;
+    struct ip *ip;
+    int error, type, code;
 
     DUMMYNET_LOCK_ASSERT();
 
@@ -449,7 +453,39 @@
 	 */
 	switch (pkt->dn_dir) {
 	case DN_TO_IP_OUT:
-	    (void)ip_output((struct mbuf *)pkt, NULL, NULL, 0, NULL, NULL);
+	    MGET(mcopy, M_DONTWAIT, pkt->dn_m->m_type);
+	    if (mcopy != NULL && !m_dup_pkthdr(mcopy, pkt->dn_m, M_DONTWAIT)) {
+		m_free(mcopy);
+		mcopy = NULL;
+	    }
+	    if (mcopy != NULL) {
+		ip = mtod(pkt->dn_m, struct ip *);
+		mcopy->m_len = imin((ip->ip_hl << 2) + 8,
+		    (int)ip->ip_len);
+		m_copydata(pkt->dn_m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
+	    }
+	    
+	    error = ip_output((struct mbuf *)pkt, NULL, NULL, 0, NULL, NULL);
+	    
+	    if (mcopy != NULL) {
+		switch (error) {
+		    case ENETUNREACH:
+		    case EHOSTUNREACH:
+		    case ENETDOWN:
+		    case EHOSTDOWN:
+			type = ICMP_UNREACH;
+		        code = ICMP_UNREACH_HOST;
+			icmp_error(mcopy, type, code, 0, pkt->ifp);
+			break;
+		    case EMSGSIZE:
+			type = ICMP_UNREACH;
+		        code = ICMP_UNREACH_NEEDFRAG;
+			icmp_error(mcopy, type, code, 0, pkt->ifp);
+			break;
+		    default:
+			m_freem(mcopy);
+		};
+	    };
 	    rt_unref (pkt->ro.ro_rt, __func__) ;
 	    break ;