Alternative fix for the crash on conntrack unload. Simply flush all
fragment queues when unloading conntrack_standalone so that there are
no partially assembled fragments left with skb->dst == NULL.

Index: v2.6.8/include/net/ip.h
===================================================================
--- v2.6.8.orig/include/net/ip.h
+++ v2.6.8/include/net/ip.h
@@ -255,6 +255,7 @@ extern int	ip_call_ra_chain(struct sk_bu
  */
  
 struct sk_buff *ip_defrag(struct sk_buff *skb);
+extern void ipfrag_flush(void);
 extern int ip_frag_nqueues;
 extern atomic_t ip_frag_mem;
 
Index: v2.6.8/net/ipv4/ip_fragment.c
===================================================================
--- v2.6.8.orig/net/ipv4/ip_fragment.c
+++ v2.6.8/net/ipv4/ip_fragment.c
@@ -239,13 +239,13 @@ static void ipq_kill(struct ipq *ipq)
 /* Memory limiting on fragments.  Evictor trashes the oldest 
  * fragment queue until we are back under the low threshold.
  */
-static void ip_evictor(void)
+static void __ip_evictor(int threshold)
 {
 	struct ipq *qp;
 	struct list_head *tmp;
 
 	for(;;) {
-		if (atomic_read(&ip_frag_mem) <= sysctl_ipfrag_low_thresh)
+		if (atomic_read(&ip_frag_mem) <= threshold)
 			return;
 		read_lock(&ipfrag_lock);
 		if (list_empty(&ipq_lru_list)) {
@@ -267,6 +267,11 @@ static void ip_evictor(void)
 	}
 }
 
+static inline void ip_evictor(void)
+{
+	__ip_evictor(sysctl_ipfrag_low_thresh);
+}
+
 /*
  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
  */
@@ -677,4 +682,10 @@ void ipfrag_init(void)
 	add_timer(&ipfrag_secret_timer);
 }
 
+void ipfrag_flush(void)
+{
+	__ip_evictor(0);
+}
+
 EXPORT_SYMBOL(ip_defrag);
+EXPORT_SYMBOL(ipfrag_flush);
Index: v2.6.8/net/ipv4/netfilter/ip_conntrack_standalone.c
===================================================================
--- v2.6.8.orig/net/ipv4/netfilter/ip_conntrack_standalone.c
+++ v2.6.8/net/ipv4/netfilter/ip_conntrack_standalone.c
@@ -562,6 +562,8 @@ static int init_or_cleanup(int init)
 	nf_unregister_hook(&ip_conntrack_defrag_local_out_ops);
  cleanup_defragops:
 	nf_unregister_hook(&ip_conntrack_defrag_ops);
+	/* Frag queues may hold fragments with skb->dst == NULL */
+	ipfrag_flush();
  cleanup_proc:
 	proc_net_remove("ip_conntrack");
  cleanup_init: