net: Enable kernel side filtering of route dumps

Update parsing of route dump request to enable kernel side filtering.
Allow filtering results by protocol (e.g., which routing daemon installed
the route), route type (e.g., unicast), table id and nexthop device. These
amount to the low hanging fruit, yet a huge improvement, for dumping
routes.

ip_valid_fib_dump_req is called with RTNL held, so __dev_get_by_index can
be used to look up the device index without taking a reference. From
there filter->dev is only used during dump loops with the lock still held.

Set NLM_F_DUMP_FILTERED in the answer_flags so the user knows the results
have been filtered should no entries be returned.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 45 insertions, 8 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 37dc8ac366fd..e86ca2255181 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -804,9 +804,14 @@ errout:
 
 int ip_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
 			  struct fib_dump_filter *filter,
-			  struct netlink_ext_ack *extack)
+			  struct netlink_callback *cb)
 {
+	struct netlink_ext_ack *extack = cb->extack;
+	struct nlattr *tb[RTA_MAX + 1];
 	struct rtmsg *rtm;
+	int err, i;
+
+	ASSERT_RTNL();
 
 	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*rtm))) {
 		NL_SET_ERR_MSG(extack, "Invalid header for FIB dump request");
@@ -815,8 +820,7 @@ int ip_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
 
 	rtm = nlmsg_data(nlh);
 	if (rtm->rtm_dst_len || rtm->rtm_src_len  || rtm->rtm_tos   ||
-	    rtm->rtm_table   || rtm->rtm_protocol || rtm->rtm_scope ||
-	    rtm->rtm_type) {
+	    rtm->rtm_scope) {
 		NL_SET_ERR_MSG(extack, "Invalid values in header for FIB dump request");
 		return -EINVAL;
 	}
@@ -825,9 +829,42 @@ int ip_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
 		return -EINVAL;
 	}
 
-	if (nlmsg_attrlen(nlh, sizeof(*rtm))) {
-		NL_SET_ERR_MSG(extack, "Invalid data after header in FIB dump request");
-		return -EINVAL;
+	filter->flags    = rtm->rtm_flags;
+	filter->protocol = rtm->rtm_protocol;
+	filter->rt_type  = rtm->rtm_type;
+	filter->table_id = rtm->rtm_table;
+
+	err = nlmsg_parse_strict(nlh, sizeof(*rtm), tb, RTA_MAX,
+				 rtm_ipv4_policy, extack);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i <= RTA_MAX; ++i) {
+		int ifindex;
+
+		if (!tb[i])
+			continue;
+
+		switch (i) {
+		case RTA_TABLE:
+			filter->table_id = nla_get_u32(tb[i]);
+			break;
+		case RTA_OIF:
+			ifindex = nla_get_u32(tb[i]);
+			filter->dev = __dev_get_by_index(net, ifindex);
+			if (!filter->dev)
+				return -ENODEV;
+			break;
+		default:
+			NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
+			return -EINVAL;
+		}
+	}
+
+	if (filter->flags || filter->protocol || filter->rt_type ||
+	    filter->table_id || filter->dev) {
+		filter->filter_set = 1;
+		cb->answer_flags = NLM_F_DUMP_FILTERED;
 	}
 
 	return 0;
@@ -846,7 +883,7 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 	int dumped = 0, err;
 
 	if (cb->strict_check) {
-		err = ip_valid_fib_dump_req(net, nlh, &filter, cb->extack);
+		err = ip_valid_fib_dump_req(net, nlh, &filter, cb);
 		if (err < 0)
 			return err;
 	}
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 3fa988e6a3df..7a3e2acda94c 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -2532,7 +2532,7 @@ static int ipmr_rtm_dumproute(struct sk_buff *skb, struct netlink_callback *cb)
 
 	if (cb->strict_check) {
 		err = ip_valid_fib_dump_req(sock_net(skb->sk), cb->nlh,
-					    &filter, cb->extack);
+					    &filter, cb);
 		if (err < 0)
 			return err;
 	}