netfilter: xt_TRACE: add explicitly nf_logger_find_get call

Consider such situation, if nf_log_ipv4 kernel module is not installed,
and the user add a following iptables rule:
  # iptables -t raw -I PREROUTING -j TRACE

There will be no trace log generated until the user install nf_log_ipv4
module manully. So we should add request related nf_log module
appropriately here.
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_TRACE.c

@@ -4,12 +4,23 @@
 #include <linux/skbuff.h>
 
 #include <linux/netfilter/x_tables.h>
+#include <net/netfilter/nf_log.h>
 
 MODULE_DESCRIPTION("Xtables: packet flow tracing");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("ipt_TRACE");
 MODULE_ALIAS("ip6t_TRACE");
 
+static int trace_tg_check(const struct xt_tgchk_param *par)
+{
+	return nf_logger_find_get(par->family, NF_LOG_TYPE_LOG);
+}
+
+static void trace_tg_destroy(const struct xt_tgdtor_param *par)
+{
+	nf_logger_put(par->family, NF_LOG_TYPE_LOG);
+}
+
 static unsigned int
 trace_tg(struct sk_buff *skb, const struct xt_action_param *par)
 {
@@ -23,6 +34,8 @@ static struct xt_target trace_tg_reg __read_mostly = {
 	.family		= NFPROTO_UNSPEC,
 	.table		= "raw",
 	.target		= trace_tg,
+	.checkentry	= trace_tg_check,
+	.destroy	= trace_tg_destroy,
 	.me		= THIS_MODULE,
 };