net: Allow ipv6 proxies and arp proxies be shown with iproute2

Add ability to return neighbour proxies list to caller if
it sent full ndmsg structure and has NTF_PROXY flag set.

Before this patch (and before iproute2 patches):
$ ip neigh add proxy 2001::1 dev eth0
$ ip -6 neigh show
$

After it and with applied iproute2 patches:
$ ip neigh add proxy 2001::1 dev eth0
$ ip -6 neigh show
2001::1 dev eth0  proxy
$

Compatibility with old versions of iproute2 is not broken,
kernel checks for incoming structure size and properly
works if old structure is came.

[v2]
* changed comments style.
* removed useless line with continue and curly bracket.
* changed incoming message size check from equal to more or
  equal.

CC: davem@davemloft.net
CC: kuznet@ms2.inr.ac.ru
CC: netdev@vger.kernel.org
CC: xemul@parallels.com
Signed-off-by: Tony Zelenoff <antonz@parallels.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -2165,6 +2165,35 @@ nla_put_failure:
 	return -EMSGSIZE;
 }
 
+static int pneigh_fill_info(struct sk_buff *skb, struct pneigh_entry *pn,
+			    u32 pid, u32 seq, int type, unsigned int flags,
+			    struct neigh_table *tbl)
+{
+	struct nlmsghdr *nlh;
+	struct ndmsg *ndm;
+
+	nlh = nlmsg_put(skb, pid, seq, type, sizeof(*ndm), flags);
+	if (nlh == NULL)
+		return -EMSGSIZE;
+
+	ndm = nlmsg_data(nlh);
+	ndm->ndm_family	 = tbl->family;
+	ndm->ndm_pad1    = 0;
+	ndm->ndm_pad2    = 0;
+	ndm->ndm_flags	 = pn->flags | NTF_PROXY;
+	ndm->ndm_type	 = NDA_DST;
+	ndm->ndm_ifindex = pn->dev->ifindex;
+	ndm->ndm_state	 = NUD_NONE;
+
+	NLA_PUT(skb, NDA_DST, tbl->key_len, pn->key);
+
+	return nlmsg_end(skb, nlh);
+
+nla_put_failure:
+	nlmsg_cancel(skb, nlh);
+	return -EMSGSIZE;
+}
+
 static void neigh_update_notify(struct neighbour *neigh)
 {
 	call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
@@ -2214,23 +2243,78 @@ out:
 	return rc;
 }
 
+static int pneigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
+			     struct netlink_callback *cb)
+{
+	struct pneigh_entry *n;
+	struct net *net = sock_net(skb->sk);
+	int rc, h, s_h = cb->args[3];
+	int idx, s_idx = idx = cb->args[4];
+
+	read_lock_bh(&tbl->lock);
+
+	for (h = 0; h <= PNEIGH_HASHMASK; h++) {
+		if (h < s_h)
+			continue;
+		if (h > s_h)
+			s_idx = 0;
+		for (n = tbl->phash_buckets[h], idx = 0; n; n = n->next) {
+			if (dev_net(n->dev) != net)
+				continue;
+			if (idx < s_idx)
+				goto next;
+			if (pneigh_fill_info(skb, n, NETLINK_CB(cb->skb).pid,
+					    cb->nlh->nlmsg_seq,
+					    RTM_NEWNEIGH,
+					    NLM_F_MULTI, tbl) <= 0) {
+				read_unlock_bh(&tbl->lock);
+				rc = -1;
+				goto out;
+			}
+		next:
+			idx++;
+		}
+	}
+
+	read_unlock_bh(&tbl->lock);
+	rc = skb->len;
+out:
+	cb->args[3] = h;
+	cb->args[4] = idx;
+	return rc;
+
+}
+
 static int neigh_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct neigh_table *tbl;
 	int t, family, s_t;
+	int proxy = 0;
+	int err = 0;
 
 	read_lock(&neigh_tbl_lock);
 	family = ((struct rtgenmsg *) nlmsg_data(cb->nlh))->rtgen_family;
+
+	/* check for full ndmsg structure presence, family member is
+	 * the same for both structures
+	 */
+	if (nlmsg_len(cb->nlh) >= sizeof(struct ndmsg) &&
+	    ((struct ndmsg *) nlmsg_data(cb->nlh))->ndm_flags == NTF_PROXY)
+		proxy = 1;
+
 	s_t = cb->args[0];
 
-	for (tbl = neigh_tables, t = 0; tbl; tbl = tbl->next, t++) {
+	for (tbl = neigh_tables, t = 0; tbl && (err >= 0);
+	     tbl = tbl->next, t++) {
 		if (t < s_t || (family && tbl->family != family))
 			continue;
 		if (t > s_t)
 			memset(&cb->args[1], 0, sizeof(cb->args) -
 						sizeof(cb->args[0]));
-		if (neigh_dump_table(tbl, skb, cb) < 0)
-			break;
+		if (proxy)
+			err = pneigh_dump_table(tbl, skb, cb);
+		else
+			err = neigh_dump_table(tbl, skb, cb);
 	}
 	read_unlock(&neigh_tbl_lock);