Subject: [PATCH RFC v2 net-next 04/25] net/ipv4: Update inet_dump_ifaddr to support NLM_F_DUMP_PROPER_HDR

From: David Ahern <[email-masked]>
Date: Mon, 1 Oct 2018 17:28:30 -0700

From: David Ahern <[email-masked]>

Update inet_dump_ifaddr to check for NLM_F_DUMP_PROPER_HDR in the netlink
message header. If the flag is set, the dump request is expected to have
an ifaddrmsg struct as the header potentially followed by one or more
attributes. Any data passed in the header or as an attribute is taken as
a request to influence the data returned. Only values suppored by the
dump handler are allowed to be non-0 or set in the request. At the moment
only the IFA_TARGET_NETNSID attribute is supported. Follow on patches
will support for other fields (e.g., honor ifa_index and only return data
for the given device index).

Signed-off-by: David Ahern <[email-masked]>
---
 net/ipv4/devinet.c | 52 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 41 insertions(+), 11 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 44d931a3cd50..c27537f568f0 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1661,15 +1661,15 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
 
 static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 {
+	struct netlink_ext_ack *extack = cb->extack;
+	const struct nlmsghdr *nlh = cb->nlh;
 	struct inet_fill_args fillargs = {
 		.portid = NETLINK_CB(cb->skb).portid,
-		.seq = cb->nlh->nlmsg_seq,
+		.seq = nlh->nlmsg_seq,
 		.event = RTM_NEWADDR,
-		.flags = NLM_F_MULTI,
 		.netnsid = -1,
 	};
 	struct net *net = sock_net(skb->sk);
-	struct nlattr *tb[IFA_MAX+1];
 	struct net *tgt_net = net;
 	int h, s_h;
 	int idx, s_idx;
@@ -1683,15 +1683,45 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 	s_idx = idx = cb->args[1];
 	s_ip_idx = ip_idx = cb->args[2];
 
-	if (nlmsg_parse(cb->nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
-			ifa_ipv4_policy, NULL) >= 0) {
-		if (tb[IFA_TARGET_NETNSID]) {
-			fillargs.netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
+	if (nlh->nlmsg_flags & NLM_F_DUMP_PROPER_HDR) {
+		struct nlattr *tb[IFA_MAX+1];
+		struct ifaddrmsg *ifm;
+		int err, i;
+
+		if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
+			NL_SET_ERR_MSG(extack, "Invalid header");
+			return -EINVAL;
+		}
+
+		ifm = nlmsg_data(nlh);
+		if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
+			NL_SET_ERR_MSG(extack, "Invalid values in header for dump request");
+			return -EINVAL;
+		}
+		if (ifm->ifa_index) {
+			NL_SET_ERR_MSG(extack, "Filter by device index not supported");
+			return -EINVAL;
+		}
 
-			tgt_net = rtnl_get_net_ns_capable(skb->sk,
-							  fillargs.netnsid);
-			if (IS_ERR(tgt_net))
-				return PTR_ERR(tgt_net);
+		err = nlmsg_parse(nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
+				  ifa_ipv4_policy, extack);
+		if (err < 0)
+			return err;
+
+		for (i = 0; i <= IFA_MAX; ++i) {
+			if (i == IFA_TARGET_NETNSID) {
+				fillargs.netnsid = nla_get_s32(tb[i]);
+
+				tgt_net = rtnl_get_net_ns_capable(skb->sk,
+								  fillargs.netnsid);
+				if (IS_ERR(tgt_net))
+					return PTR_ERR(tgt_net);
+
+				fillargs.flags |= NLM_F_DUMP_FILTERED;
+			} else if (tb[i]) {
+				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
+				return -EINVAL;
+			}
 		}
 	}
 
-- 
2.11.0