neighbour: add support for NUD_PERMANENT proxy entries

As discussesd before in [0] proxy entries (which are more configuration
than runtime data) should stay when the link (carrier) goes does down.
This is what happens for regular neighbour entries.

So lets fix this by:
  - storing in proxy entries the fact that it was added as NUD_PERMANENT
  - not removing NUD_PERMANENT proxy entries when the carrier goes down
    (same as how it's done in neigh_flush_dev() for regular neigh entries)

[0]: https://lore.kernel.org/netdev/[email protected]/

Signed-off-by: Nicolas Escande <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: nscnd

include/net/neighbour.h

@@ -182,6 +182,7 @@ struct pneigh_entry {
 	netdevice_tracker	dev_tracker;
 	u32			flags;
 	u8			protocol;
+	bool			permanent;
 	u32			key[];
 };
 

net/core/neighbour.c

@@ -54,7 +54,8 @@ static void __neigh_notify(struct neighbour *n, int type, int flags,
 			   u32 pid);
 static void neigh_update_notify(struct neighbour *neigh, u32 nlmsg_pid);
 static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
-				    struct net_device *dev);
+				    struct net_device *dev,
+				    bool skip_perm);
 
 #ifdef CONFIG_PROC_FS
 static const struct seq_operations neigh_stat_seq_ops;
@@ -423,7 +424,7 @@ static int __neigh_ifdown(struct neigh_table *tbl, struct net_device *dev,
 {
 	write_lock_bh(&tbl->lock);
 	neigh_flush_dev(tbl, dev, skip_perm);
-	pneigh_ifdown_and_unlock(tbl, dev);
+	pneigh_ifdown_and_unlock(tbl, dev, skip_perm);
 	pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL,
 			   tbl->family);
 	if (skb_queue_empty_lockless(&tbl->proxy_queue))
@@ -803,20 +804,24 @@ int pneigh_delete(struct neigh_table *tbl, struct net *net, const void *pkey,
 }
 
 static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
-				    struct net_device *dev)
+				    struct net_device *dev,
+				    bool skip_perm)
 {
 	struct pneigh_entry *n, **np, *freelist = NULL;
 	u32 h;
 
 	for (h = 0; h <= PNEIGH_HASHMASK; h++) {
 		np = &tbl->phash_buckets[h];
 		while ((n = *np) != NULL) {
+			if (skip_perm && n->permanent)
+				goto skip;
 			if (!dev || n->dev == dev) {
 				*np = n->next;
 				n->next = freelist;
 				freelist = n;
 				continue;
 			}
+skip:
 			np = &n->next;
 		}
 	}
@@ -1983,6 +1988,7 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 		pn = pneigh_lookup(tbl, net, dst, dev, 1);
 		if (pn) {
 			pn->flags = ndm_flags;
+			pn->permanent = !!(ndm->ndm_state & NUD_PERMANENT);
 			if (protocol)
 				pn->protocol = protocol;
 			err = 0;