rtnetlink: Update rtnl_fdb_dump for strict data checking

Update rtnl_fdb_dump for strict data checking. If the flag is set,
the dump request is expected to have an ndmsg 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 NDA_IFINDEX and
NDA_MASTER attributes are supported.
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/core/rtnetlink.c

@@ -3799,6 +3799,60 @@ int ndo_dflt_fdb_dump(struct sk_buff *skb,
 }
 EXPORT_SYMBOL(ndo_dflt_fdb_dump);
 
+static int valid_fdb_dump_strict(const struct nlmsghdr *nlh,
+				 int *br_idx, int *brport_idx,
+				 struct netlink_ext_ack *extack)
+{
+	struct nlattr *tb[NDA_MAX + 1];
+	struct ndmsg *ndm;
+	int err, i;
+
+	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ndm))) {
+		NL_SET_ERR_MSG(extack, "Invalid header for fdb dump request");
+		return -EINVAL;
+	}
+
+	ndm = nlmsg_data(nlh);
+	if (ndm->ndm_pad1  || ndm->ndm_pad2  || ndm->ndm_state ||
+	    ndm->ndm_flags || ndm->ndm_type) {
+		NL_SET_ERR_MSG(extack, "Invalid values in header for fbd dump request");
+		return -EINVAL;
+	}
+
+	err = nlmsg_parse_strict(nlh, sizeof(struct ndmsg), tb, NDA_MAX,
+				 NULL, extack);
+	if (err < 0)
+		return err;
+
+	*brport_idx = ndm->ndm_ifindex;
+	for (i = 0; i <= NDA_MAX; ++i) {
+		if (!tb[i])
+			continue;
+
+		switch (i) {
+		case NDA_IFINDEX:
+			if (nla_len(tb[i]) != sizeof(u32)) {
+				NL_SET_ERR_MSG(extack, "Invalid IFINDEX attribute in fdb dump request");
+				return -EINVAL;
+			}
+			*brport_idx = nla_get_u32(tb[NDA_IFINDEX]);
+			break;
+		case NDA_MASTER:
+			if (nla_len(tb[i]) != sizeof(u32)) {
+				NL_SET_ERR_MSG(extack, "Invalid MASTER attribute in fdb dump request");
+				return -EINVAL;
+			}
+			*br_idx = nla_get_u32(tb[NDA_MASTER]);
+			break;
+		default:
+			NL_SET_ERR_MSG(extack, "Unsupported attribute in fdb dump request");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int valid_fdb_dump_legacy(const struct nlmsghdr *nlh,
 				 int *br_idx, int *brport_idx,
 				 struct netlink_ext_ack *extack)
@@ -3846,6 +3900,10 @@ static int rtnl_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	int err = 0;
 	int fidx = 0;
 
+	if (cb->strict_check)
+		err = valid_fdb_dump_strict(cb->nlh, &br_idx, &brport_idx,
+					    cb->extack);
+	else
 		err = valid_fdb_dump_legacy(cb->nlh, &br_idx, &brport_idx,
 					    cb->extack);
 	if (err < 0)