net/ipv4: Update inet_dump_ifaddr for strict data checking

Update inet_dump_ifaddr for strict data checking. 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 supported 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 can support for other fields
(e.g., honor ifa_index and only return data for the given device index).
Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Christian Brauner <christian@brauner.io>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -1660,17 +1660,70 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
 	return -EMSGSIZE;
 }
 
+static int inet_valid_dump_ifaddr_req(const struct nlmsghdr *nlh,
+				      struct inet_fill_args *fillargs,
+				      struct net **tgt_net, struct sock *sk,
+				      struct netlink_ext_ack *extack)
+{
+	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, "ipv4: Invalid header for address dump request");
+		return -EINVAL;
+	}
+
+	ifm = nlmsg_data(nlh);
+	if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
+		NL_SET_ERR_MSG(extack, "ipv4: Invalid values in header for address dump request");
+		return -EINVAL;
+	}
+	if (ifm->ifa_index) {
+		NL_SET_ERR_MSG(extack, "ipv4: Filter by device index not supported for address dump");
+		return -EINVAL;
+	}
+
+	err = nlmsg_parse_strict(nlh, sizeof(*ifm), tb, IFA_MAX,
+				 ifa_ipv4_policy, extack);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i <= IFA_MAX; ++i) {
+		if (!tb[i])
+			continue;
+
+		if (i == IFA_TARGET_NETNSID) {
+			struct net *net;
+
+			fillargs->netnsid = nla_get_s32(tb[i]);
+
+			net = rtnl_get_net_ns_capable(sk, fillargs->netnsid);
+			if (IS_ERR(net)) {
+				NL_SET_ERR_MSG(extack, "ipv4: Invalid target network namespace id");
+				return PTR_ERR(net);
+			}
+			*tgt_net = net;
+		} else {
+			NL_SET_ERR_MSG(extack, "ipv4: Unsupported attribute in dump request");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 {
+	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;
@@ -1684,16 +1737,13 @@ 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, cb->extack) >= 0) {
-		if (tb[IFA_TARGET_NETNSID]) {
-			fillargs.netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
+	if (cb->strict_check) {
+		int err;
 
-			tgt_net = rtnl_get_net_ns_capable(skb->sk,
-							  fillargs.netnsid);
-			if (IS_ERR(tgt_net))
-				return PTR_ERR(tgt_net);
-		}
+		err = inet_valid_dump_ifaddr_req(nlh, &fillargs, &tgt_net,
+						 skb->sk, cb->extack);
+		if (err < 0)
+			return err;
 	}
 
 	for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {