net: Add support for filtering neigh dump by master device

Add support for filtering neighbor dumps by master device by adding
the NDA_MASTER attribute to the dump request. A new netlink flag,
NLM_F_DUMP_FILTERED, is added to indicate the kernel supports the
request and output is filtered as requested.
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/netlink.h

@@ -54,6 +54,7 @@ struct nlmsghdr {
 #define NLM_F_ACK		4	/* Reply with ack, with zero or error code */
 #define NLM_F_ECHO		8	/* Echo this request 		*/
 #define NLM_F_DUMP_INTR		16	/* Dump was inconsistent due to sequence change */
+#define NLM_F_DUMP_FILTERED	32	/* Dump was filtered as requested */
 
 /* Modifiers to GET request */
 #define NLM_F_ROOT	0x100	/* specify tree	root	*/

net/core/neighbour.c

@@ -2235,14 +2235,42 @@ static void neigh_update_notify(struct neighbour *neigh)
 	__neigh_notify(neigh, RTM_NEWNEIGH, 0);
 }
 
+static bool neigh_master_filtered(struct net_device *dev, int master_idx)
+{
+	struct net_device *master;
+
+	if (!master_idx)
+		return false;
+
+	master = netdev_master_upper_dev_get(dev);
+	if (!master || master->ifindex != master_idx)
+		return true;
+
+	return false;
+}
+
 static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
 			    struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
+	const struct nlmsghdr *nlh = cb->nlh;
+	struct nlattr *tb[NDA_MAX + 1];
 	struct neighbour *n;
 	int rc, h, s_h = cb->args[1];
 	int idx, s_idx = idx = cb->args[2];
 	struct neigh_hash_table *nht;
+	int filter_master_idx = 0;
+	unsigned int flags = NLM_F_MULTI;
+	int err;
+
+	err = nlmsg_parse(nlh, sizeof(struct ndmsg), tb, NDA_MAX, NULL);
+	if (!err) {
+		if (tb[NDA_MASTER])
+			filter_master_idx = nla_get_u32(tb[NDA_MASTER]);
+
+		if (filter_master_idx)
+			flags |= NLM_F_DUMP_FILTERED;
+	}
 
 	rcu_read_lock_bh();
 	nht = rcu_dereference_bh(tbl->nht);
@@ -2255,12 +2283,14 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
 		     n = rcu_dereference_bh(n->next)) {
 			if (!net_eq(dev_net(n->dev), net))
 				continue;
+			if (neigh_master_filtered(n->dev, filter_master_idx))
+				continue;
 			if (idx < s_idx)
 				goto next;
 			if (neigh_fill_info(skb, n, NETLINK_CB(cb->skb).portid,
 					    cb->nlh->nlmsg_seq,
 					    RTM_NEWNEIGH,
-					    NLM_F_MULTI) < 0) {
+					    flags) < 0) {
 				rc = -1;
 				goto out;
 			}